WorldWideScience

Sample records for collimation assistee par

  1. Developpement d'algorithmes de reconstruction statistique appliques en tomographie rayons-X assistee par ordinateur

    Science.gov (United States)

    Thibaudeau, Christian

    La tomodensitometrie (TDM) permet d'obtenir, et ce de facon non invasive, une image tridimensionnelle de l'anatomie interne d'un sujet. Elle constitue l'evolution logique de la radiographie et permet l'observation d'un volume sous differents plans (sagittal, coronal, axial ou n'importe quel autre plan). La TDM peut avantageusement completer la tomographie d'emission par positrons (TEP), un outil de predilection utilise en recherche biomedicale et pour le diagnostic du cancer. La TEP fournit une information fonctionnelle, physiologique et metabolique, permettant la localisation et la quantification de radiotraceurs a l'interieur du corps humain. Cette derniere possede une sensibilite inegalee, mais peut neanmoins souffrir d'une faible resolution spatiale et d'un manque de repere anatomique selon le radiotraceur utilise. La combinaison, ou fusion, des images TEP et TDM permet d'obtenir cette localisation anatomique de la distribution du radiotraceur. L'image TDM represente une carte de l'attenuation subie par les rayons-X lors de leur passage a travers les tissus. Elle permet donc aussi d'ameliorer la quantification de l'image TEP en offrant la possibilite de corriger pour l'attenuation. L'image TDM s'obtient par la transformation de profils d'attenuation en une image cartesienne pouvant etre interpretee par l'humain. Si la qualite de cette image est fortement influencee par les performances de l'appareil, elle depend aussi grandement de la capacite de l'algorithme de reconstruction a obtenir une representation fidele du milieu image. Les techniques de reconstruction standards, basees sur la retroprojection filtree (FBP, filtered back-projection), reposent sur un modele mathematiquement parfait de la geometrie d'acquisition. Une alternative a cette methode etalon est appelee reconstruction statistique, ou iterative. Elle permet d'obtenir de meilleurs resultats en presence de bruit ou d'une quantite limitee d'information et peut virtuellement s'adapter a toutes formes

  2. Beam collimator

    CERN Multimedia

    1977-01-01

    A four-block collimator installed on a control table for positioning the alignment reference marks. Designed for use with SPS secondary beams, the collimator operates under vacuum conditions. See Annual Report 1976 p. 121 and photo 7701014.

  3. Conception et mises a l'essai d'un environnement d'apprentissage integrant l'experimentation assistee par ordinateur et la simulation assistee par ordinateur

    Science.gov (United States)

    Riopel, Martin

    To make science laboratory sessions more instructive, we have developed a learning environment that will allow students enrolled in a mechanics course at college or university level to engage in a scientific modelization process by combining computer-simulated experimentation and microcomputer-based laboratories. The main goal is to assist and facilitate both inductive and deductive reasoning. Within this computer application, each action can also be automatically recorded and identified while the student is using the software. The most original part of the environment is to let the student compare the simulated animation with the real video by superposing the images. We used the software with students and observed that they effectively engaged in a modelization process that included both inductive and deductive reasoning. We also observed that the students were able to use the software to produce adequate answers to questions concerning both previously taught and new theoretical concepts in physics. The students completed the experiment about twice as fast as usual and considered that using the software resulted in a better understanding of the phenomenon. We conclude that this use of the computer in science education can broaden the range of possibilities for learning and for teaching and can provide new avenues for researchers who can use it to record and study students' path of reasoning. We also believe that it would be interesting to investigate more some of the benefits associated with this environment, particularly the acceleration effect, the improvement of students' reasoning and the equilibrium between induction and deduction that we observed within this research.

  4. Pan-encephalic irradiation of brain metastases: dosimetric impact of the technique with a rotating collimator without mask in comparison with a multi-blade collimator; Irradiation pan encephalique des metastases cerebrales: impact dosimetrique de la technique avec rotation du collimateur sans cache par comparaison a celle avec collimateur mutilame

    Energy Technology Data Exchange (ETDEWEB)

    Loos, G.; Paulon, R.; Achard, J.L.; Belliere, A.; Biau, J.; Bourry, N.; Chilles, A.; Toledano, I.; Verrelle, O.; Lapeyre, M. [Centre Jean-Perrin, 63 - Clermont-Ferrand (France)

    2010-10-15

    The authors report the dosimetric impacts of two techniques (collimator without mask and multi-blade collimator) on organs at risk as well as the influence of meningeal dead ends when using the technique of conventional pan-encephalic irradiation of brain metastases. Data have been acquired for 10 patients. The use of a multi-blade collimator is better for a pan-encephalic irradiation by two lateral beams in order to reduce the average dose received by the parotids, and particularly if meningeal dead ends are to be treated. The dose received by other organs at risk is equivalent, whichever method is used. Short communication

  5. The ARCS radial collimator

    OpenAIRE

    Stone M.B.; Niedziela J.L.; Overbay M.A.; Abernathy D.L.

    2015-01-01

    We have designed, installed, and commissioned a scattered beam radial collimator for use at the ARCS Wide Angular Range Chopper Spectrometer at the Spallation Neutron Source. The collimator has been designed to work effectively for thermal and epithermal neutrons and with a range of sample environments. Other design considerations include the accommodation of working within a high vacuum environment and having the ability to quickly install and remove the collimator from the scattered beam. W...

  6. The ARCS radial collimator

    Directory of Open Access Journals (Sweden)

    Stone M.B.

    2015-01-01

    Full Text Available We have designed, installed, and commissioned a scattered beam radial collimator for use at the ARCS Wide Angular Range Chopper Spectrometer at the Spallation Neutron Source. The collimator has been designed to work effectively for thermal and epithermal neutrons and with a range of sample environments. Other design considerations include the accommodation of working within a high vacuum environment and having the ability to quickly install and remove the collimator from the scattered beam. We present here characterization of the collimator's performance and methodologies for its effective use.

  7. The ARCS radial collimator

    Science.gov (United States)

    Stone, M. B.; Niedziela, J. L.; Overbay, M. A.; Abernathy, D. L.

    2015-01-01

    We have designed, installed, and commissioned a scattered beam radial collimator for use at the ARCS Wide Angular Range Chopper Spectrometer at the Spallation Neutron Source. The collimator has been designed to work effectively for thermal and epithermal neutrons and with a range of sample environments. Other design considerations include the accommodation of working within a high vacuum environment and having the ability to quickly install and remove the collimator from the scattered beam. We present here characterization of the collimator's performance and methodologies for its effective use.

  8. Characterization of Embedded BPM Collimators

    CERN Document Server

    VALENTINO, Gianluca

    2015-01-01

    During LS1, 16 tertiary collimators (TCTs) and 2 secondary collimators (TCSGs) in IR6 were replaced by new embedded BPM collimators. The BPM functionality allows the possibility to align the collimators more quickly and therefore be able to respond faster to machine configuration changes, as well as a direct monitoring of the beam orbit at the collimators. Following an initial commissioning phase, an MD was carried out to test the new collimators and acquisition electronics with beam in the LHC.

  9. Collimation study for LCLS

    Science.gov (United States)

    Marin, E.; Raubenhaimer, T.; Welch, J.; White, G.

    2017-09-01

    In this paper we investigate the power deposition along the undulator section of the SLAC Linac Coherent Light Source (LCLS) due to the primary e--beam but also due to potential secondary particles. The expected beam distribution after the LCLS injector is deliberately broadened as an approximated representation of the beam halo. Secondary particles, as e+, e- and photons, are generated as a result of tracking the intercepted beam through a dense material. This process is carried out by means of GEANT-4, which has been convoluted into our main tracking engine, LUCRETIA. Simulations show no losses along the undulator section when assuming the nominal primary beam and collimator gaps. However when opening the gaps of collimators located at the first collimator section, by 25%, the fattened beam is partially intercepted by the second collimator section, which is aligned to the undulators. Secondary particles, mostly photons generated at the second collimator section, deposit their energy along the undulator section, at a rate of the order of a milliwatt.

  10. Les apports de l'experimentation assistee par ordinateur (ExAO) en pedagogie par projet en Sciences de la nature au collegial

    Science.gov (United States)

    Marcotte, Alice

    The goals of this research were to conceptualize and to produce a test synthesis model for the Sciences program, where the student had to demonstrate his or her competency using the approach Considering New Situations from Acquired Knowledge. The test took the form of a student-structured project utilizing the experimental process: the student's scientific investigation was supported and facilitated by computer-assisted experimentation (CAEx). The model of action was elaborated in developmental research within the school setting, tested in biology, and continued in an interdisciplinary context. Our study focused on the advantages and the constraints of this new learning environment, which modify laboratories using traditional instrumentation. The final research was not to evaluate a type of test synthesis, but to propose and to improve this model of test synthesis based on experimental process and supported by CAEx. In order to implement the competency approach within an integration activity, we chose a cooperative learning environment contained within the pedagogical project. This didactic environment was inspired by socio-constructivism which involves students in open scientific problem-solving. Computer-assisted experimentation turned out to be a valuable tool for this environment, facilitating the implementation of the scientific process by increased induction. Resistance to confronted and uncircumvented reality changes students' perception of scientific knowledge. They learn to integrate the building of this knowledge, and then to realize the extent of their learning and their training. Students' opinions, which were gathered from questionnaires, reveal that they favorably perceive this type of environment in interaction with their peers and the experimentation. While this new knowledge contributes to CAEx within the pedagogical project, the products of this research included a teaching guide for the test synthesis, a booklet featuring the projects carried out by the students with CAEx, and the proposals to renew the didactic approach in the laboratory.

  11. Actinides(3)/lanthanides(3) separation by nano-filtration assisted by complexation; Separation actinides(3)lanthanides(3) par nanofiltration assistee par complexation

    Energy Technology Data Exchange (ETDEWEB)

    Sorin, A

    2006-07-01

    In France, one of the research trend concerning the reprocessing of spent nuclear fuel consists to separate selectively the very radio-toxic elements with a long life to be recycled (Pu) or transmuted (Am, Cm, Np). The aim of this thesis concerns the last theme about actinides(III)/lanthanides(III) separation by a process of nano-filtration assisted by complexation. Thus, a pilot of tangential membrane filtration was designed and established in a glove box at the ATALANTE place of CEA-Marcoule. Physico-chemical characterisation of the Desal GH membrane (OSMONICS), selected to carry out actinides(III)/lanthanides(III) separation, was realized to determine the zeta potential of the active layer and its resistance to ionizing radiations. Moreover, a parametric study was also carried out to optimize the selectivity of complexation, and the operating conditions of complex retention (influences of the transmembrane pressure, solute concentration, tangential velocity and temperature). Finally, the separation of traces of Am(III) contained in a mixture of lanthanides(III), simulating the real load coming from a reprocessing cycle, was evaluated with several chelating agents such as poly-amino-carboxylic acids according to the solution acidity and the [Ligand]/[Cation(III)] ratio. (author)

  12. Cleaning insertions and collimation challenges

    CERN Document Server

    Redaelli, S; Bertarelli, A; Bruce, R; Jowett, J M; Lechner, A; Losito, R

    2015-01-01

    High-performance collimation systems are essential for operating efficiently modern hadron machine with large beam intensities. In particular, at the LHC the collimation system ensures a clean disposal of beam halos in the superconducting environment. The challenges of the HL-LHC study pose various demanding requests for beam collimation. In this paper we review the present collimation system and its performance during the LHC Run 1 in 2010–2013. Various collimation solutions under study to address the HL-LHC requirements are then reviewed, identifying the main upgrade baseline and pointing out advanced collimation concept for further enhancement of the performance.

  13. Process for manufacturing slit collimators

    Science.gov (United States)

    Romanenko, V. P.; Yemelyanov, A. A.; Churbakov, K. I.

    1974-01-01

    Peculiarities are described of the manufacturing process and the control of elements of slit collimators, the structural design of the required equipment and the process or assembling the collimators.

  14. VIRUS instrument collimator assembly

    Science.gov (United States)

    Marshall, Jennifer L.; DePoy, Darren L.; Prochaska, Travis; Allen, Richard D.; Williams, Patrick; Rheault, Jean-Philippe; Li, Ting; Nagasawa, Daniel Q.; Akers, Christopher; Baker, David; Boster, Emily; Campbell, Caitlin; Cook, Erika; Elder, Alison; Gary, Alex; Glover, Joseph; James, Michael; Martin, Emily; Meador, Will; Mondrik, Nicholas; Rodriguez-Patino, Marisela; Villanueva, Steven; Hill, Gary J.; Tuttle, Sarah; Vattiat, Brian; Lee, Hanshin; Chonis, Taylor S.; Dalton, Gavin B.; Tacon, Mike

    2014-07-01

    The Visual Integral-Field Replicable Unit Spectrograph (VIRUS) instrument is a baseline array 150 identical fiber fed optical spectrographs designed to support observations for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). The collimator subassemblies of the instrument have been assembled in a production line and are now complete. Here we review the design choices and assembly practices used to produce a suite of identical low-cost spectrographs in a timely fashion using primarily unskilled labor.

  15. Collimation Cleaning at the LHC with Advanced Secondary Collimator Materials

    CERN Document Server

    AUTHOR|(CDS)2085459; Bruce, Roderik; Mereghetti, Alessio; Redaelli, Stefano; Rossi, A

    2015-01-01

    The LHC collimation system must ensure efficient beam halo cleaning in all machine conditions. The first run in 2010-2013 showed that the LHC performance may be limited by collimator material-related concerns, such as the contribution from the present carbon-based secondary collimators to the machine impedance and, consequently, to the beam instability. Novel materials based on composites are currently under development for the next generation of LHC collimators to address these limitations. Particle tracking simulations of collimation efficiency were performed using the Sixtrack code and a material database updated to model these composites. In this paper, the simulation results will be presented with the aim of studying the effect of the advanced collimators on the LHC beam cleaning.

  16. Beam Cleaning and Collimation Systems

    CERN Document Server

    Redaelli, S

    2016-01-01

    Collimation systems in particle accelerators are designed to dispose of unavoidable losses safely and efficiently during beam operation. Different roles are required for different types of accelerator. The present state of the art in beam collimation is exemplified in high-intensity, high-energy superconducting hadron colliders, like the CERN Large Hadron Collider (LHC), where stored beam energies reach levels up to several orders of magnitude higher than the tiny energies required to quench cold magnets. Collimation systems are essential systems for the daily operation of these modern machines. In this document, the design of a multistage collimation system is reviewed, taking the LHC as an example case study. In this case, unprecedented cleaning performance has been achieved, together with a system complexity comparable to no other accelerator. Aspects related to collimator design and operational challenges of large collimation systems are also addressed.

  17. Four-block beam collimator

    CERN Multimedia

    1977-01-01

    The photo shows a four-block collimator installed on a control table for positioning the alignment reference marks. Designed for use with the secondary beams, the collimators operated in vacuum conditions. The blocks were made of steel and had a standard length of 1 m. The maximum aperture had a square coss-section of 144 cm2. (See Annual Report 1976.)

  18. Collimation: a silicon solution

    CERN Multimedia

    2007-01-01

    Silicon crystals could be used very efficiently to deflect high-energy beams. Testing at CERN has produced conclusive results, which could pave the way for a new generation of collimators. The set of five crystals used to test the reflection of the beams. The crystals are 0.75 mm wide and their alignment is adjusted with extreme precision. This figure shows the deflection of a beam by channelling and by reflection in the block of five crystals. Depending on the orientation of the crystals: 1) The beam passes without "seeing" the crystals and is not deflected 2) The beam is deflected by channelling (with an angle of around 100 μrad) 3) The beam is reflected (with an angle of around 50 μrad). The intensity of the deflected beam is illustrated by the intensity of the spot. The spot of the reflected beam is clearly more intense than that one of the channelled beam, demonstrating the efficiency of t...

  19. Fermilab Recycler Collimation System Design

    Energy Technology Data Exchange (ETDEWEB)

    Brown, B. C. [Fermilab; Adamson, P. [Fermilab; Ainsworth, R. [Fermilab; Capista, D. [Fermilab; Hazelwood, K. [Fermilab; Kourbanis, I. [Fermilab; Mokhov, N. V. [Fermilab; Morris, D. K. [Fermilab; Murphy, M. [Fermilab; Sidorov, V. [Fermilab; Stern, E. [Fermilab; Tropin, I. [Fermilab; Yang, M-J. [Fermilab

    2016-10-04

    To provide 700 kW proton beams for neutrino production in the NuMI facility, we employ slip stacking in the Recycler with transfer to the Main Injector for recapture and acceleration. Slip stacking with 12 Booster batches per 1.33 sec cycle of the Main Injector has been implemented and briefly tested while extensive operation with 8 batches and 10 batches per MI cycle has been demonstrated. Operation in this mode since 2013 shows that loss localization is an essential component for long term operation. Beam loss in the Recycler will be localized in a collimation region with design capability for absorbing up to 2 kW of lost protons in a pair of 20-Ton collimators (absorbers). This system will employ a two stage collimation with a thin molybdenum scattering foil to define the bottom edge of both the injected and decelerated-for-slipping beams. Optimization and engineering design of the collimator components and radiation shielding are based on comprehensive MARS15 simulations predicting high collimation efficiency as well as tolerable levels of prompt and residual radiation. The system installation during the Fermilab 2016 facility shutdown will permit commissioning in the subsequent operating period.

  20. First cleaning with LHC collimators

    CERN Document Server

    Wollmann, D; Arnau-Izquiedo, G; Assmann, R; Bacher, J P; Baglin, V; Bellodi, G; Bertarelli, A; Bouzoud, A; Bracco, C; Bruce, R; Brugger, M; Calatroni, S; Cerruti, F; Chamizo, R; Cherif, A; Chiaveri, E; Chiggiato, P; Dallochio, A; Dehning, B; Donze, M; Ferrari, A; Folch, R; Francon, P; Gander, P; Geisser, J M; Grudiev, A; Holzer, EB; Jacquet, D; Jeanneret, J B; Jimenez, J M; Jonker, M; Jowett, J; Kershaw, K; Lari, L; Lendaro, J; Loprete, F; Losito, R; Magistris, M; Malabaila, M; Mayer, M; Marsili, A; Masi, A; Mathot, S; Métral, E; Mitifiot, C; Mounet, N; de Morais Amaral, R; Nordt, A; Perret, R; Perrollaz, S; Rathjen, C; Redaelli, S; Robert-Demolaize, G; Roesler, S; Rossi, A; Salvant, B; Santana, M; Sexton, I; Sievers, P; Tardy, T; Timmins, M; Tsoulou, K; Veyrunes, E; Vincke, H; Vlachoudis, V; Vuillemin, V; Weiler, T; Zimmermann, F; Baishev, I; Kurochkin, I; Kaltchev, D; Caspers, F; Kadi, Y

    2010-01-01

    The LHC has two dedicated cleaning insertions: IR3 for momentum cleaning and IR7 for betatron cleaning. The collimation system has been specified and built with tight mechanical tolerances (e.g. jaw flatness ~ 40 μm ) and is designed to achieve a high accuracy and reproducibility of the jaw positions (~ 20 μm). The practically achievable cleaning efficiency of the present Phase-I system depends on the precision of the jaw centering around the beam, the accuracy of the gap size and the jaw parallelism against the beam. The reproducibility and stability of the collimation system is important to avoid the frequent repetition of beam based alignment which is currently a lengthy procedure. Within this paper we describe the method used for the beam based alignment of the LHC collimation system, its achieved accuracy and stability and its performance at 450GeV.

  1. Transverse Impedance of LHC Collimators

    CERN Document Server

    Métral, E; Assmann, Ralph Wolfgang; Boccardi, A; Bracco, C; Bohl, T; Caspers, Friedhelm; Gasior, M; Jones, O R; Kasinski, K; Kroyer, T; Redaelli, S; Robert-Demolaize, R; Roncarolo, F; Rumolo, G; Salvant, B; Steinhagen, R; Weiler, T; Zimmermann, F

    2007-01-01

    The transverse impedance in the LHC is expected to be dominated by the numerous collimators, most of which are made of Fibre-Reinforced-Carbon to withstand the impacts of high intensity proton beams in case of failures, and which will be moved very close to the beam, with full gaps of few millimetres, in order to protect surrounding super-conducting equipments. We present an estimate of the transverse resistive-wall impedance of the LHC collimators, the total impedance in the LHC at injection and top energy, the induced coupled-bunch growth rates and tune shifts, and finally the result of the comparison of the theoretical predictions with measurements performed in 2004 and 2006 on a prototype collimator installed in the SPS.

  2. Crystal collimator systems for high energy frontier

    CERN Document Server

    AUTHOR|(CDS)2100516; Tikhomirov, Viktor; Lobko, Alexander

    2017-01-01

    Crystalline collimators can potentially considerably improve the cleaning performance of the presently used collimator systems using amorphous collimators. A crystal-based collimation scheme which relies on the channeling particle deflection in bent crystals has been proposed and extensively studied both theoretically and experimentally. However, since the efficiency of particle capture into the channeling regime does not exceed ninety percent, this collimation scheme partly suffers from the same leakage problems as the schemes using amorphous collimators. To improve further the cleaning efficiency of the crystal-based collimation system to meet the requirements of the FCC, we suggest here a double crystal-based collimation scheme, to which the second crystal is introduced to enhance the deflection of the particles escaping the capture to the channeling regime in its first crystal. The application of the effect of multiple volume reflection in one bent crystal and of the same in a sequence of crystals is simu...

  3. Carbon nanotube collimator fabrication and application

    Science.gov (United States)

    Chow, Lee; Chai, Guangyu; Schenkel, Thomas

    2010-07-06

    Apparatus, methods, systems and devices for fabricating individual CNT collimators. Micron size fiber coated CNT samples are synthesized with chemical vapor deposition method and then the individual CNT collimators are fabricated with focused ion beam technique. Unfocused electron beams are successfully propagated through the CNT collimators. The CNT nano-collimators are used for applications including single ion implantation and in high-energy physics, and allow rapid, reliable testing of the transmission of CNT arrays for transport of molecules.

  4. Collimator with attachment mechanism and system

    Science.gov (United States)

    Kross, Brian J.; McKisson, John; Stolin, Aleksandr; Weisenberger, Andrew G.; Zorn, Carl

    2012-07-10

    A self-aligning collimator for a radiation imaging device that is secured and aligned through the use of a plurality of small magnets. The collimator allows for the rapid exchange, removal, or addition of collimators for the radiation imaging device without the need for tools. The accompanying method discloses the use of magnets and accompanying magnetic fields to align and secure collimators in a radiation imaging assembly.

  5. Optimization of the CLIC Baseline Collimation System

    Energy Technology Data Exchange (ETDEWEB)

    Resta-Lopez, Javier; /Oxford U., JAI; Angal-Kalinin, Deepa; /Daresbury; Fernandez-Hernando, Juan; /Daresbury; Jackson, Frank; /Daresbury; Dalena, Barbara; /CERN; Schulte, Daniel; /CERN; Tomas, Rogelio; /CERN; Seryi, Andrei; /SLAC

    2012-07-06

    Important efforts have recently been dedicated to the improvement of the design of the baseline collimation system of the Compact Linear Collider (CLIC). Different aspects of the design have been optimized: the transverse collimation depths have been recalculated in order to reduce the collimator wakefield effects while maintaining a good efficiency in cleaning the undesired beam halo; the geometric design of the spoilers have also been reviewed to minimize wakefields; in addition, the optics design have been polished to improve the collimation efficiency. This paper describes the current status of the CLIC collimation system after this optimization.

  6. Jet quenching via jet collimation

    CERN Document Server

    Casalderrey-Solana, J; Wiedemann, U

    2011-01-01

    The strong modifications of dijet properties in heavy ion collisions measured by ATLAS and CMS provide important constraints on the dynamical mechanisms underlying jet quenching. In this work, we show that the transport of soft gluons away from the jet cone - jet collimation - can account for the observed dijet asymmetry with values of $\\hat{q}\\, L$ that lie in the expected order of magnitude. Further, we show that the energy loss attained through this mechanism results in a very mild distortion of the azimuthal angle dijet distribution.

  7. Jet Quenching via Jet Collimation

    CERN Document Server

    Casalderrey-Solana, Jorge; Wiedemann, Urs Achim

    2011-01-01

    The ATLAS Collaboration recently reported strong modifications of dijet properties in heavy ion collisions. In this work, we discuss to what extent these first data constrain already the microscopic mechanism underlying jet quenching. Simple kinematic arguments lead us to identify a frequency collimation mechanism via which the medium efficiently trims away the soft components of the jet parton shower. Through this mechanism, the observed dijet asymmetry can be accomodated with values of $\\hat{q}\\, L$ that lie in the expected order of magnitude.

  8. Beam halo collimation in heavy ion synchrotrons

    Science.gov (United States)

    Strašík, I.; Prokhorov, I.; Boine-Frankenheim, O.

    2015-08-01

    This paper presents a systematic study of the halo collimation of ion beams from proton up to uranium in synchrotrons. The projected Facility for Antiproton and Ion Research synchrotron SIS100 is used as a reference case. The concepts are separated into fully stripped (e.g., 238U92+ ) and partially stripped (e.g., 238U28+ ) ion collimation. An application of the two-stage betatron collimation system, well established for proton accelerators, is intended also for fully stripped ions. The two-stage system consists of a primary collimator (a scattering foil) and secondary collimators (bulky absorbers). Interaction of the particles with the primary collimator (scattering, momentum losses, and nuclear interactions) was simulated by using fluka. Particle-tracking simulations were performed by using mad-x. Finally, the dependence of the collimation efficiency on the primary ion species was determined. The influence of the collimation system adjustment, lattice imperfections, and beam parameters was estimated. The concept for the collimation of partially stripped ions employs a thin stripping foil in order to change their charge state. These ions are subsequently deflected towards a dump location using a beam optical element. The charge state distribution after the stripping foil was obtained from global. The ions were tracked by using mad-x.

  9. Digital chest radiography: collimation and dose reduction

    DEFF Research Database (Denmark)

    Debess, Jeanne; Johnsen, Karen Kirstine; Vejle-Sørensen, Jens Kristian

    Purpose: Quality improvement of basic radiography focusing on collimation and dose reduction in digital chest radiography Methods and Materials:A retrospective study of digital chest radiography is performed to evaluate the primary x-ray tube collimation of the PA and lateral radiographs. Data from...... of clinical supervisors. Optimal collimation is determined by European and Regional Danish guidelines. The areal between current and optimal collimation is calculated. The experimental research is performed in September - October 2014 Siemens Axiom Aristos digital radiography system DR using 150 kV, 1,25 -3...

  10. Calibrating the HXMT collimators using diffuse illumination

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    We propose a new method to calibrate the HXMT collimators by measuring the optical point spread function(PSF) of the hard X-ray modulation telescope(HXMT).The light transmission of the collimator at different viewing angles with a camera and a diffuse backlight placed behind the collimator is measured.This method is much easier to accomplish than measuring the PSF with a parallel optical beam.The experimental results are very consistent with the simulations.The PSF of the collimator of the high energy X-ray telescope on HXMT is found to be in good agreement with the design,with accuracy better than 1 arcmin.

  11. Modeling of a multileaf collimator

    Science.gov (United States)

    Kim, Siyong

    A comprehensive physics model of a multileaf collimator (MLC) field for treatment planning was developed. Specifically, an MLC user interface module that includes a geometric optimization tool and a general method of in- air output factor calculation were developed. An automatic tool for optimization of MLC conformation is needed to realize the potential benefits of MLC. It is also necessary that a radiation therapy treatment planning (RTTP) system is capable of modeling MLC completely. An MLC geometric optimization and user interface module was developed. The planning time has been reduced significantly by incorporating the MLC module into the main RTTP system, Radiation Oncology Computer System (ROCS). The dosimetric parameter that has the most profound effect on the accuracy of the dose delivered with an MLC is the change in the in-air output factor that occurs with field shaping. It has been reported that the conventional method of calculating an in-air output factor cannot be used for MLC shaped fields accurately. Therefore, it is necessary to develop algorithms that allow accurate calculation of the in-air output factor. A generalized solution for an in-air output factor calculation was developed. Three major contributors of scatter to the in-air output-flattening filter, wedge, and tertiary collimator-were considered separately. By virtue of a field mapping method, in which a source plane field determined by detector's eye view is mapped into a detector plane field, no additional dosimetric data acquisition other than the standard data set for a range of square fields is required for the calculation of head scatter. Comparisons of in-air output factors between calculated and measured values show a good agreement for both open and wedge fields. For rectangular fields, a simple equivalent square formula was derived based on the configuration of a linear accelerator treatment head. This method predicts in-air output to within 1% accuracy. A two

  12. Measuring Collimator Infrared (IR) Spectral Transmission

    Science.gov (United States)

    2016-05-01

    TECHNICAL REPORT RDMR-WD-16-15 MEASURING COLLIMATOR INFRARED (IR) SPECTRAL TRANSMISSION Christopher L. Dobbins Weapons...Distribution Statement A: Approved for public release; distribution unlimited. DESTRUCTION NOTICE FOR CLASSIFIED DOCUMENTS...AND DATES COVERED Final 4. TITLE AND SUBTITLE Measuring Collimator Infrared (IR) Spectral Transmission 5. FUNDING NUMBERS 6. AUTHOR(S) Christopher L

  13. Nonlinear Energy Collimation System for Linear Colliders

    CERN Document Server

    Resta-Lopez, Javier

    2011-01-01

    The post-linac energy collimation system of multi-TeV linear colliders is designed to fulfil an important function of protection of the Beam Delivery System (BDS) against miss-steered beams likely generated by failure modes in the main linac. For the case of the Compact Linear Collider (CLIC), the energy collimators are required to withstand the impact of a full bunch train in case of failure. This is a very challenging task, assuming the nominal CLIC beam parameters at 1.5 TeV beam energy. The increase of the transverse spot size at the collimators using nonlinear magnets is a potential solution to guarantee the survival of the collimators. In this paper we present an alternative nonlinear optics based on a skew sextupole pair for energy collimation. Performance simulation results are also presented.

  14. Characterisation of fan-beam collimators.

    Science.gov (United States)

    Pareto, D; Pavía, J; Falcón, C; Juvells, I; Cot, A; Ros, D

    2001-02-01

    Fan-beam collimators offer a good balance between resolution and noise. The collimator response may be included in iterative reconstruction algorithms in order to improve single-photon emission tomography (SPET) resolution. To this end, accurate determination of the focal region and characterisation of the collimator response as a function of the source co-ordinates must be performed. In this paper, a method to characterise fanbeam collimators is evaluated. First, we calculated the real focal region and the accuracy of the collimator convergence. Then, we confirmed the hypothesis that Gaussian distributions adequately fit the collimator responses, although no individualised treatment was performed for the tails of detector response which are associated with scattering and septal penetration. Finally, analytical functions were used to model the resolution and sensitivity. The parameter values in these functions were obtained from experimental measures by non-linear regression fitting. Our findings show differences of 1.43% between nominal and real focal length and standard deviations of 2.5 mm in the x-direction and 7.1 mm in the y-direction for the focal convergence. The correlation coefficients between experimental and predicted values were 0.994 for resolution and 0.991 for sensitivity. As a consequence, the proposed method can be used to characterise the collimator response.

  15. Scrapping and Collimation Tests in the SPS

    CERN Document Server

    Fischer, C; Jung, R; CERN. Geneva. AB Department

    2004-01-01

    Scraping of the SPS beam will be required prior to extraction towards the LHC in order to remove the beam tails and ensure clean injection conditions. Scraper mechanisms recuperated from the ISR and collimators coming from LEP are installed since a few years in the SPS to test this concept. The purpose of these tests was to show that with the help of the associated two stage collimation system, it is possible to make the scraping process very clean by confining the losses at the collimator locations, hence without irradiating any other part of the machine.

  16. Crystal Collimation with protons at injection energy

    CERN Document Server

    Rossi, Roberto; Masi, Alessandro; Mirarchi, Daniele; Montesano, Simone; Redaelli, Stefano; Valentino, Gianluca; Scandale, Walter; CERN. Geneva. ATS Department

    2015-01-01

    During this MD, performed on August 30th, 2015, bent silicon crystals were tested with protons beams for a possible usage of crystal-assisted collimation. Tests were performed at injection energy, using both horizontal and vertical crystals, providing a crucial test of the hardware for precise crystal angle adjustments (goniometers). Proton channeling was observed for the first time with LHC beams and the channeled beams were probed with scans performed with secondary collimators. Measurements of cleaning efficiency of a crystal-based collimation system were also performed.

  17. CODEX sounding rocket wire grid collimator design

    Science.gov (United States)

    Shipley, Ann; Zeiger, Ben; Rogers, Thomas

    2011-05-01

    CODEX is a sounding rocket payload designed to operate in the soft x-ray (0.1-1.0 kV) regime. The instrument has a 3.25 degree square field of view that uses a one meter long wire grid collimator to create a beam that converges to a line in the focal plane. Wire grid collimator performance is directly correlated to the geometric accuracy of actual grid features and their relative locations. Utilizing a strategic combination of manufacturing and assembly techniques, this design is engineered for precision within the confines of a typical rocket budget. Expected resilience of the collimator under flight conditions is predicted by mechanical analysis.

  18. Collimator for the SPS extracted beam

    CERN Multimedia

    1976-01-01

    This is a water cooled copper collimator (TCSA) which has exactly the shape of the cross section of the downstream magnetic beam splitter. Parts of the blown up primary proton beam pass above/below and left through this collimator. A small part of the protons is absorbed in the thin copper wedges. In this way the downstream magnetic splitter of the same cross section receives already a beam where its magnetic wedges are no longer hit by protons. The upstream, water cooled collimator, more resistant to protons, has cast a 'shadow' onto the downstream magnetic splitter, less resistant to protons. Gualtero Del Torre stands on the left.

  19. Semiautomatic beam-based LHC collimator alignment

    CERN Document Server

    Valentino, Gianluca; Bruce, Roderik; Wollmann, Daniel; Sammut, Nicholas; Rossi, Adriana; Redaelli, Stefano

    2012-01-01

    Full beam-based alignment of the LHC collimation system was a time-consuming procedure (up to 28 hours) as the collimators were set up manually. A yearly alignment campaign has been sufficient for now, although in the future due to tighter tolerances this may lead to a decrease in the cleaning efficiency if machine parameters such as the beam orbit drift over time. Automating the collimator setup procedure can reduce the beam time for collimator setup and allow for more frequent alignments, therefore reducing the risk of performance degradation. This article describes the design and testing of a semiautomatic algorithm as a first step towards a fully automatic setup procedure. The parameters used to measure the accuracy and performance of the alignment are defined and determined from experimental data. A comparison of these measured parameters at 450 GeV and 3.5 TeV with manual and semiautomatic alignment is provided.

  20. New methods of particle collimation in colliders

    CERN Document Server

    Stancari, Giulio

    2011-01-01

    The collimation system is an essential part of the design of any high-power accelerator. Its functions include protection of components from accidental and intentional energy deposition, reduction of backgrounds, and beam diagnostics. Conventional multi-stage systems based on scatterers and absorbers offer robust shielding and efficient collection of losses. Two complementary concepts have been proposed to address some of the limitations of conventional systems: channeling and volume reflection in bent crystals and collimation with hollow electron beams. The main focus of this paper is the hollow electron beam collimator, a novel concept based on the interaction of the circulating beam with a 5-keV, magnetically confined, pulsed hollow electron beam in a 2-m-long section of the ring. The electrons enclose the circulating beam, kicking halo particles transversely and leaving the beam core unperturbed. By acting as tunable diffusion enhancer and not as a hard aperture limitation, the hollow electron beam collim...

  1. Crystal collimator systems for high energy frontier

    Science.gov (United States)

    Sytov, A. I.; Tikhomirov, V. V.; Lobko, A. S.

    2017-07-01

    Crystalline collimators can potentially considerably improve the cleaning performance of the presently used collimator systems using amorphous collimators. A crystal-based collimation scheme which relies on the channeling particle deflection in bent crystals has been proposed and extensively studied both theoretically and experimentally. However, since the efficiency of particle capture into the channeling regime does not exceed ninety percent, this collimation scheme partly suffers from the same leakage problems as the schemes using amorphous collimators. To improve further the cleaning efficiency of the crystal-based collimation system to meet the requirements of the FCC, we suggest here a double crystal-based collimation scheme, to which the second crystal is introduced to enhance the deflection of the particles escaping the capture to the channeling regime in its first crystal. The application of the effect of multiple volume reflection in one bent crystal and of the same in a sequence of crystals is simulated and compared for different crystal numbers and materials at the energy of 50 TeV. To enhance also the efficiency of use of the first crystal of the suggested double crystal-based scheme, we propose: the method of increase of the probability of particle capture into the channeling regime at the first crystal passage by means of fabrication of a crystal cut and the method of the amplification of nonchanneled particle deflection through the multiple volume reflection in one bent crystal, accompanying the particle channeling by a skew plane. We simulate both of these methods for the 50 TeV FCC energy.

  2. Comparison of carbon and HI-Z primary collimators for the LHC phase II collimation system

    CERN Document Server

    Keller, L; Smith, J; Assmann, R; Bracco, C; Weiler, T

    2010-01-01

    A current issue with the LHC collimation system is single-diffractive, off-energy protons from the primary collimators that pass completely through the secondary collimation system and are absorbed immediately downbeam in the cold magnets of the dispersion suppressor section. Simulations suggest that the high impact rate could result in quenching of these magnets. We have studied replacing the 60 cm primary graphite collimators, which remove halo mainly by inelastic strong interactions, with 5.25 mm tungsten, which remove halo mainly by multiple coulomb scattering and thereby reduce the rate of single-diffractive interactions that cause losses in the dispersion suppressor.

  3. Comparison of the current LHC Collimators and the SLAC Phase 2 Collimator Impedances

    CERN Document Server

    Day, Hugo; Metral, Elias; Salvant, Benoit; Jones, Roger

    2011-01-01

    One of the key sources of transverse impedance in the LHC has been the secondary graphite collimators that sit close to the beam at all energies. This limits the stable bunch intensity due to transverse coupled-bunch instabilities and transverse mode coupling instability. To counteract this, new secondary collimators have been proposed for the phase II upgrade of the LHC collimation system. A number of designs based on different jaw materials and mechanical designs have been proposed. A comparison of the beam coupling impedance of these different designs derived from simulations are presented, with reference to the existing phase I secondary collimator design.

  4. Comparison of the current LHC Collimators and the SLAC phase 2 Collimator impedances

    CERN Document Server

    Day, H A; Metral, E; Salvant, B; Jones, R M

    2011-01-01

    One of the key sources of transverse impedance in the LHC has been the secondary graphite collimators that sit close to the beam at all energies. This limits the stable bunch intensity due to transverse coupled-bunch instabilities and transverse mode coupling instability. To counteract this, new secondary collimators have been proposed for the phase II upgrade of the LHC collimation system. A number of designs based on different jaw materials and mechanical designs have been proposed. A comparison of the beam coupling impedance of these different designs derived from simulations are presented, with reference to the existing phase I secondary collimator design.

  5. Comparison of the current LHC Collimators and the SLAC Phase 2 Collimator Impedances

    CERN Document Server

    Day, Hugo; Metral, Elias; Salvant, Benoit; Jones, Roger

    2011-01-01

    One of the key sources of transverse impedance in the LHC has been the secondary graphite collimators that sit close to the beam at all energies. This limits the stable bunch intensity due to transverse coupled-bunch instabilities and transverse mode coupling instability. To counteract this, new secondary collimators have been proposed for the phase II upgrade of the LHC collimation system. A number of designs based on different jaw materials and mechanical designs have been proposed. A comparison of the beam coupling impedance of these different designs derived from simulations are presented, with reference to the existing phase I secondary collimator design.

  6. A Simple and Inexpensive Collimator for Neutron Radiography

    DEFF Research Database (Denmark)

    Olsen, J.; Mortensen, L.

    1974-01-01

    A neutron beam collimator was constructed by means of plastic drinking “straws”. The properties of the collimator were investigated, and especially the distribution of the neutrons at different distances.......A neutron beam collimator was constructed by means of plastic drinking “straws”. The properties of the collimator were investigated, and especially the distribution of the neutrons at different distances....

  7. A study of RHIC crystal collimation

    CERN Document Server

    Trbojevic, D; Harrison, M; Parker, B; Thompson, P; Stevens, A; Mokhov, N V; Drozhdin, A I

    1998-01-01

    The Relativistic Heavy Ion Collider (RHIC) will experience increasing longitudinal and transverse heavy ion emittances, mostly due to intra-beam scattering (IBS). The experiments in RHIC are expected to not only have reduced luminosities due to IBS but also an unwanted beam halo. Primary betatron collimators will be used to remove the large amplitude particles. The efficiency of the primary collimator in RHIC depends very much on the alignment of the jaws which needs to be within few micro-radians for the best conditions. As proposed by V. Biryukov bent crystals could be used to improve the efficiency of an existing collimation system by installing them upstream of the collimator jaws. Bent crystals have been successfully used in SPS, Protvino and Fermilab for extraction of the beam particles channeled through them. This study examines possible improvements of the primary collimator system for heavy ions at RHIC by use of bent crystals. Bent crystals will reduce the collimator jaws alignment requirement and w...

  8. Wake fields in SLAC Linac Collimators

    Energy Technology Data Exchange (ETDEWEB)

    Novokhatski, Alexander [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Stanford Univ., Stanford, CA (United States); Decker, F. -J. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Stanford Univ., Stanford, CA (United States); Smith, H. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Stanford Univ., Stanford, CA (United States); Sullivan, M. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Stanford Univ., Stanford, CA (United States)

    2014-12-02

    When a beam travels near collimator jaws, it gets an energy loss and a transverse kick due to the backreaction of the beam field diffracted from the jaws. The effect becomes very important for an intense short bunch when a tight collimation of the background beam halo is required. In the Linac Coherent Light Source at SLAC a collimation system is used to protect the undulators from radiation due to particles in the beam halo. The halo is most likely formed from gun dark current or dark current in some of the accelerating sections. However, collimators are also responsible for the generation of wake fields. The wake field effect from the collimators not only brings an additional energy jitter and change in the trajectory of the beam, but it also rotates the beam on the phase plane, which consequently leads to a degradation of the performance of the Free Electron Laser at the Linac Coherent Light Source. In this paper, we describe a model of the wake field radiation in the SLAC linac collimators. We use the results of a numerical simulation to illustrate the model. Based on the model, we derive simple formulas for the bunch energy loss and the average kick. In addition, we also present results from experimental measurements that confirm our model.

  9. Collimating Slicer for Optical Integral Field Spectroscopy

    CERN Document Server

    Laurent, Florence

    2016-01-01

    Integral Field Spectroscopy (IFS) is a technique that gives simultaneously the spectrum of each spatial sampling element in a given object field. It is a powerful tool which rearranges the data cube (x, y, lambda) represented by two spatial dimensions defining the field and the spectral decomposition in a detector plane. In IFS, the spatial unit reorganizes the field and the spectral unit is being composed of a classical spectrograph.The development of a Collimating Slicer aims at proposing a new type of integral field spectrograph which should be more compact. The main idea is to combine the image slicer with the collimator of the spectrograph, thus mixing the spatial and spectral units. The traditional combination of slicer, pupil and slit elements and the spectrograph collimator is replaced by a new one composed of a slicer and collimator only. In this paper, the state of the art of integral field spectroscopy using image slicers is described. The new system based onto the development of a Collimating Slic...

  10. Collimating slicer for optical integral field spectroscopy

    Science.gov (United States)

    Laurent, Florence; Hénault, François

    2016-07-01

    Integral Field Spectroscopy (IFS) is a technique that gives simultaneously the spectrum of each spatial sampling element of a given field. It is a powerful tool which rearranges the data cube represented by two spatial dimensions defining the field and the spectral decomposition (x, y, λ) in a detector plane. In IFS, the "spatial" unit reorganizes the field, the "spectral" unit is being composed of a classical spectrograph. For the spatial unit, three main techniques - microlens array, microlens array associated with fibres and image slicer - are used in astronomical instrumentations. The development of a Collimating Slicer is to propose a new type of optical integral field spectroscopy which should be more compact. The main idea is to combine the image slicer with the collimator of the spectrograph mixing the "spatial" and "spectral" units. The traditional combination of slicer, pupil and slit elements and spectrograph collimator is replaced by a new one composed of a slicer and spectrograph collimator only. After testing few configurations, this new system looks very promising for low resolution spectrographs. In this paper, the state of art of integral field spectroscopy using image slicers will be described. The new system based onto the development of a Collimating Slicer for optical integral field spectroscopy will be depicted. First system analysis results and future improvements will be discussed.

  11. Upgrade scenario for the RHIC collimation system

    Energy Technology Data Exchange (ETDEWEB)

    Robert-Demolaize, G.; Drees, A.

    2012-01-19

    The RHIC collimation system is used to reduce background levels in both STAR and PHENIX detectors. With a push for higher luminosity in the near future, it becomes critical to check if and how the level of performance of the collimators can be improved. The following reviews a proposal for additional collimators placed further downstream of the current system and designed to intercept the tertiary halo coming out of the IR8 insertion before it can reach the triplet quadrupoles in either STAR or PHENIX. Simulations have been peformed to quantify the efficiency of additional collimator jaws in RHIC. Each figure presented in this article clearly shows that the additional mask collimators provide the expected reduction in losses around the machine, and especially to the incoming triplet to the STAR experiment (IP6), for the Yellow beam as much as for the Blue beam. Looking at compiled statistics for all three working point cases studied, proton losses around the machine are reduced by roughly one order of magnitude: at most a factor 30 for magnet losses, and at most a factor 40 for losses in spaces between magnets.

  12. Vol. 31 - Crystal Collimation for LHC

    CERN Document Server

    Mirarchi, Daniele; Scandale, Walter; Hall, Geoffrey

    2015-01-01

    Future upgrades of the CERN Large Hadron Collider (LHC) may demand improved cleaning performance of its collimation system. Very efficient collimation is required during regular operations at high intensities, because even a small amount of energy deposited on superconducting magnets can cause an abrupt loss of superconducting conditions (quench). The present collimation system has accomplished its tasks during the LHC Run I very well, where no quench with circulating beam took place with up to 150 MJ of stored energy at 4 TeV. On the other hand, uncertainty remains on the performance at the design energy of 7 TeV and with 360 MJ of stored energy. In particular, a further increase up to about 700 MJ is expected for the high luminosity upgrade (HL-LHC), where improved cleaning performance may be needed together with a reduction of collimator impedance. The possibility to use a crystal-based collimation system represents an option for improving both cleaning performance and impedance compared to the present s...

  13. Upgrade scenario for the RHIC collimation system

    Energy Technology Data Exchange (ETDEWEB)

    Robert-Demolaize, G.; Drees, A.

    2012-01-19

    The RHIC collimation system is used to reduce background levels in both STAR and PHENIX detectors. With a push for higher luminosity in the near future, it becomes critical to check if and how the level of performance of the collimators can be improved. The following reviews a proposal for additional collimators placed further downstream of the current system and designed to intercept the tertiary halo coming out of the IR8 insertion before it can reach the triplet quadrupoles in either STAR or PHENIX. Simulations have been peformed to quantify the efficiency of additional collimator jaws in RHIC. Each figure presented in this article clearly shows that the additional mask collimators provide the expected reduction in losses around the machine, and especially to the incoming triplet to the STAR experiment (IP6), for the Yellow beam as much as for the Blue beam. Looking at compiled statistics for all three working point cases studied, proton losses around the machine are reduced by roughly one order of magnitude: at most a factor 30 for magnet losses, and at most a factor 40 for losses in spaces between magnets.

  14. A SPECT imager with synthetic collimation

    Science.gov (United States)

    Havelin, Ronan J.; Miller, Brian W.; Barrett, Harrison H.; Furenlid, Lars R.; Murphy, J. M.; Foley, Mark J.

    2013-09-01

    This work outlines the development of a multi-pinhole SPECT system designed to produce a synthetic-collimator image of a small field of view. The focused multi-pinhole collimator was constructed using rapid-prototyping and casting techniques. The collimator projects the field of view through forty-six pinholes when the detector is adjacent to the collimator. The detector is then moved further from the collimator to increase the magnification of the system. The amount of pinhole-projection overlap increases with the system magnification. There is no rotation in the system; a single tomographic angle is used in each system configuration. The maximum-likelihood expectation-maximization (MLEM) algorithm is implemented on graphics processing units to reconstruct the object in the field of view. Iterative reconstruction algorithms, such as MLEM, require an accurate model of the system response. For each system magnification, a sparsely-sampled system response is measured by translating a point source through a grid encompassing the field of view. The pinhole projections are individually identified and associated with their respective apertures. A 2D elliptical Gaussian model is applied to the pinhole projections on the detector. These coefficients are associated with the object-space location of the point source, and a finely-sampled system matrix is interpolated. Simulations with a hot-rod phantom demonstrate the efficacy of combining low-resolution non-multiplexed data with high-resolution multiplexed data to produce high-resolution reconstructions.

  15. De Par en Par (Wide Open), 1993.

    Science.gov (United States)

    De Par en Par, 1993

    1993-01-01

    This document consists of the four issues of the serial "De Par en Par" published during 1993. This serial provides lessons in Spanish for elementary school children. It is written by bilingual education teachers for use in the bilingual classroom. The magazine bases itself on the K-6 curriculum and offers a variety of activities for classroom…

  16. High power collimated diode laser stack

    Institute of Scientific and Technical Information of China (English)

    LIU Yuan-yuan; FANG Gao-zhan; MA Xiao-yu; LIU Su-ping; FENG Xiao-ming

    2006-01-01

    A high power collimated diode laser stack is carried out based on fast-axis collimation and stack packaging techniques.The module includes ten typical continuous wave (cw) bars and the total output power can be up to 368W at 48.6A.Using a cylindrical lens as the collimation elements,we can make the fast-axis divergence and the slow-axis divergence are 0.926 40 and 8.2060 respectively.The light emitting area is limited in a square area of 18.3 mm×11 mm.The module has the advantage of high power density and offers a wide potential applications in pumping and material processing.

  17. Macrostrain measurement using radial collimators at LANSCE

    Energy Technology Data Exchange (ETDEWEB)

    Bourke, M.A.M.; Roberts, J.A.; Davis, D.

    1996-06-01

    A series of `short` radial collimators have been implemented in the 90{degrees} scattering geometries on the neutron powder diffractometer at Los Alamos. The capability to perform macrostrain measurements has been improved by the commensurate ability to rapidly select a sampling volume appropriate to the specimen. The compact design of the collimators was dictated by the need to fit them in a cylindrical vacuum chamber as well as providing space in which to manipulate a specimen in three dimensions. Collimators of different vane lengths were fabricated to give 4 different resolutions for which 2/3 of the diffracted intensity comes form distances of 0.75, 1. 25, 2.5, and 4.0 mm along the incident beam. Qualifying scans and a demonstration of a cracked ring, containing a steep stress gradient, are included.

  18. Dielectric Collimators for Linear Collider Beam Delivery System

    CERN Document Server

    Kanareykin, A; Baturin, S; Tomás, R

    2011-01-01

    The current status of ILC and CLIC concepts require additional research on wakefield reduction in the collimator sections. New materials and new geometries have been considered recently*. Dielectric collimators for the CLIC Beam Delivery System have been discussed with a view to minimize the BDS collimation wakefields**. Dielectric collimator concepts for the linear collider are presented in this paper; cylindrical and planar collimators for the CLIC parameters have been considered, and simulations to minimize the beam impedance have been performed. The prototype collimator system is planned to be fabricated and experimentally tested at Facilities for Accelerator Science and Experimental Test Beams (FACET) at SLAC.

  19. Channeling collimation studies at the Fermilab Tevatron

    Energy Technology Data Exchange (ETDEWEB)

    Carrigan, Richard A.; Drozhdin, Alexandr I.; Fliller, Raymond P., III; Mokhov, Nikolai V.; Shiltsev, Vladimir D.; Still, Dean A.; /Fermilab

    2006-08-01

    Bent crystal channeling has promising advantages for accelerator beam collimation at high energy hadron facilities such as the LHC. This significance has been amplified by several surprising developments including multi-pass channeling and the observation of enhanced deflections over the entire arc of a bent crystal. The second effect has been observed both at RHIC and recently at the Tevatron. Results are reported showing channeling collimation of the circulating proton beam halo at the Tevatron. Parenthetically, this study is the highest energy proton channeling experiment ever carried out. The study is continuing.

  20. Photonic crystal self-collimation sensor.

    Science.gov (United States)

    Wang, Yufei; Wang, Hailing; Xue, Qikun; Zheng, Wanhua

    2012-05-21

    A novel refractive index sensor based on the two dimensional photonic crystal folded Michelson interferometer employing the self-collimation effect is proposed and its performances are theoretically investigated. Two sensing areas are included in the sensor. Simulation results indicate the branch area is suitable for the small index variety range and fine detection, whereas the reflector area prone to the large index change range and coarse detection. Because of no defect waveguides and no crosstalk of signal, the sensor is desirable to perform monolithic integrated, low-cost, label-free real-time parallel sensing. In addition, a flexible design of self-collimation sensors array is demonstrated.

  1. Par-tjek Manualen

    DEFF Research Database (Denmark)

    Trillingsgaard, Tea; Due, Mattias Stølen; Nørr Fentz, Hanne;

    Par-tjek er et tilbud til par, der ønsker at styrke forholdet og forebygge vanskeligheder. Et Par-tjek består af et indledende online spørgeskema efterfulgt at to samtaler med en psykolog eller lignende vejleder. Ved den sidste samtale modtager parret en personlig feedback-rapport, som de kan...

  2. Online Status and Settings Monitoring for the LHC Collimators

    CERN Document Server

    Valentino, G; Jacquet, D; Redaelli, S; Veyrunes, E

    2014-01-01

    The Large Hadron Collider is equipped with 100 movable collimators. The LHC collimator control system is responsible for the accurate synchronization of around 400 axes of motion at the microsecond level, and with the precision of a few micrometers.

  3. ENERGY DEPOSITION STUDIES FOR POSSIBLE INNOVATIVE PHASE II COLLIMATOR DESIGNS

    CERN Document Server

    Lari, L; Brugger, M; Cerutti, F; Ferrari, A; Vlachoudis, V; Weiler, T

    2009-01-01

    Due to the known limitations of Phase I LHC collimators in stable physics conditions, the LHC collimation system will be complemented by additional 30 Phase II collimators. The Phase II collimation system is designed to improve cleaning efficiency and to minimize the collimator-induced impedance with the main function of protecting the Super Conducting (SC) magnets from quenching due to beam particle losses. To fulfil these requirements, different possible innovative collimation designs were taken in consideration. Advanced jaw materials, including new composite materials (e.g. Cu–Diamond), jaw SiC insertions, coating foil, in-jaw instrumentation (e.g. BPM) and improved mechanical robustness of the jaw are the main features of these new promising Phase II collimator designs developed at CERN. The FLUKA Monte Carlo code is extensively used to evaluate the behavior of these collimators in the most radioactive areas of LHC, supporting the mechanical integration. These studies aim to identify the possible criti...

  4. Energy Deposition Studies for Possible Innovative Phase II Collimator Designs

    CERN Document Server

    Lari, L; Brugger, M; Cerutti, F; Ferrari, A; Vlachoudis, V; Weiler, T

    2010-01-01

    Due to the known limitations of Phase I LHC collimators in stable physics conditions, the LHC collimation system will be complemented by additional 30 Phase II collimators. The Phase II collimation system is designed to improve cleaning efficiency and to minimize the collimator-induced impedance with the main function of protecting the Super Conducting (SC) magnets from quenching due to beam particle losses. To fulfil these requirements, different possible innovative collimation designs were taken in consideration. Advanced jaw materials, including new composite materials (e.g. Cu–Diamond), jaw SiC insertions, coating foil, in-jaw instrumentation (e.g. BPM) and improved mechanical robustness of the jaw are the main features of these new promising Phase II collimator designs developed at CERN. The FLUKA Monte Carlo code is extensively used to evaluate the behavior of these collimators in the most radioactive areas of LHC, supporting the mechanical integration. These studies aim to identify the possible criti...

  5. Robust Collimation Control of Laser-Generated Ion Beam

    CERN Document Server

    Kawata, S; Kamiyama, D; Nagashima, T; Barada, D; Gu, Y J; Li, X; Yu, Q; Kong, Q; Wang, P X

    2015-01-01

    The robustness of a structured collimation device is discussed for an intense-laser-produced ion beam. In this paper the ion beam collimation is realized by the solid structured collimation device, which produces the transverse electric field; the electric field contributes to reduce the ion beam transverse velocity and collimate the ion beam. Our 2.5 dimensional particle-in cell simulations demonstrate that the collimation device is rather robust against the changes in the laser parameters and the collimation target sizes. The intense short-pulse lasers are now available, and are used to generate an ion beam. The issues in the laser ion acceleration include an ion beam collimation, ion energy spectrum control, ion production efficiency, ion energy control, ion beam bunching, etc. The laser-produced ion beam tends to expand in the transverse and longitudinal directions during the ion beam propagation. The ion beam collimation is focused in this paper.

  6. BPM Design and Impedance Considerations for a Rotatable Collimator for the LHC Collimation Upgrade

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Jeffrey Claiborne; /SLAC; Keller, Lewis; /SLAC; Lundgren, Steven; /SLAC; Markiewicz, Thomas; /SLAC; Young, Andrew; /SLAC

    2010-08-26

    The Phase II upgrade to the LHC collimation system calls for complementing the 30 high robust Phase I graphite secondary collimators with 30 high Z Phase II collimators. This paper reports on BPM and impedance considerations and measurements of the integrated BPMs in the prototype rotatable collimator to be installed in the Super Proton Synchrotron (SPS) at CERN. The BPMs are necessary to align the jaws with the beam. Without careful design the beam impedance can result in unacceptable heating of the chamber wall or beam instabilities. The impedance measurements involve utilizing both a single displaced wire and two wires excited in opposite phase to disentangle the driving and detuning transverse impedances. Trapped mode resonances and longitudinal impedance are to also be measured and compared with simulations. These measurements, when completed, will demonstrate the device is fully operational and has the impedance characteristics and BPM performance acceptable for installation in the SPS.

  7. Grazing function g and collimation angular acceptance

    Directory of Open Access Journals (Sweden)

    Stephen G. Peggs

    2009-11-01

    Full Text Available The grazing function g is introduced—a synchrobetatron optical quantity that is analogous (and closely connected to the Twiss and dispersion functions β, α, η, and η^{′}. It parametrizes the rate of change of total angle with respect to synchrotron amplitude for grazing particles, which just touch the surface of an aperture when their synchrotron and betatron oscillations are simultaneously (in time at their extreme displacements. The grazing function can be important at collimators with limited acceptance angles. For example, it is important in both modes of crystal collimation operation—in channeling and in volume reflection. The grazing function is independent of the collimator type—crystal or amorphous—but can depend strongly on its azimuthal location. The rigorous synchrobetatron condition g=0 is solved, by invoking the close connection between the grazing function and the slope of the normalized dispersion. Propagation of the grazing function is described, through drifts, dipoles, and quadrupoles. Analytic expressions are developed for g in perfectly matched periodic FODO cells, and in the presence of β or η error waves. These analytic approximations are shown to be, in general, in good agreement with realistic numerical examples. The grazing function is shown to scale linearly with FODO cell bend angle, but to be independent of FODO cell length. The ideal value is g=0 at the collimator, but finite nonzero values are acceptable. Practically achievable grazing functions are described and evaluated, for both amorphous and crystal primary collimators, at RHIC, the SPS (UA9, the Tevatron (T-980, and the LHC.

  8. Collimator scatter and 2D dosimetry in small proton beams

    NARCIS (Netherlands)

    van Luijk, P.; van 't Veld, A.A.; Zelle, H.D.; Schippers, J.M.

    2001-01-01

    Monte Carlo simulations have been performed to determine the influence of collimator-scattered protons from a 150 MeV proton beam on the dose distribution behind a collimator. Slit-shaped collimators with apertures between 2 and 20 mm have been simulated. The Monte Carlo code GEANT 3.21 has been val

  9. PERFORMANCE OF AND UPGRADES TO THE SNS COLLIMATOR SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Plum, Michael A [ORNL; Abdou, Ashraf A [ORNL; Jacobs, Lorelei L [ORNL; Janney, Jim G [ORNL; Geoghegan, Patrick J [ORNL; McTeer, Stephen Mark [ORNL; Popova, Irina [ORNL; Ferguson, Phillip D [ORNL; Zhukov, Alexander P [ORNL

    2009-01-01

    As the Spallation Neutron Source (SNS) beam power is increased, the collimator systems are becoming correspondingly more important. The High Energy Beam Transport (HEBT) transverse collimators are now routinely used during neutron production. We are in the process of redesigning the HEBT momentum collimation system due to problems with gas production from radiolysis. The Ring collimators are designed for two-stage operation but to date they are mainly used in one-stage mode. In this paper we will discuss the status, the operational performance, and upgrades to the collimation systems.

  10. Collimated Magnetron Sputter Deposition for Mirror Coatings

    DEFF Research Database (Denmark)

    Vickery, A.; Cooper-Jensen, Carsten P.; Christensen, Finn Erland

    2008-01-01

    At the Danish National Space Center (DNSC), a planar magnetron sputtering chamber has been established as a research and production coating facility for curved X-ray mirrors for hard X-ray optics for astronomical X-ray telescopes. In the following, we present experimental evidence that a collimat......At the Danish National Space Center (DNSC), a planar magnetron sputtering chamber has been established as a research and production coating facility for curved X-ray mirrors for hard X-ray optics for astronomical X-ray telescopes. In the following, we present experimental evidence...... that a collimation of the sputtered particles is an efficient way to suppress the interfacial roughness of the produced multilayer. We present two different types of collimation optimized for the production of low roughness curved mirrors and flat mirrors, respectively....

  11. Can Collimated Extraterrestrial Signals be Intercepted?

    CERN Document Server

    Forgan, Duncan H

    2014-01-01

    The Optical Search for Extraterrestrial Intelligence (OSETI) attempts to detect collimated, narrowband pulses of electromagnetic radiation. These pulses may either consist of signals intentionally directed at the Earth, or signals between two star systems with a vector that unintentionally intersects the Solar System, allowing Earth to intercept the communication. But should we expect to be able to intercept these unintentional signals? And what constraints can we place upon the frequency of intelligent civilisations if we do? We carry out Monte Carlo Realisation simulations of interstellar communications between civilisations in the Galactic Habitable Zone (GHZ) using collimated beams. We measure the frequency with which beams between two stars are intercepted by a third. The interception rate increases linearly with the fraction of communicating civilisations, and as the cube of the beam opening angle, which is somewhat stronger than theoretical expectations, which we argue is due to the geometry of the GHZ...

  12. A Novel Collimation Method for Large Hadron Colliders

    CERN Document Server

    Zou, Ye; Tang, Jingyu

    2016-01-01

    This paper proposes a novel collimation method for large hadron colliders by arranging betatron and momentum collimation systems in the same insertion to improve the overall cleaning efficiency. The method has the potential of avoiding beam losses at the downstream dispersion suppression section following the conventional betatron collimation section, which is caused by those particles with single diffractive scattering at the collimators. Evident beam loss in arc sections should be avoided to protect the superconducting magnets from quenching, especially when the stored beam energy is up to hundreds of MJ level or even higher in modern proton-proton collider. Our studies show that it is beneficial to arrange the momentum collimation system just after the betatron collimation system so that it can clean the particles with lower momentum due to the single diffractive scattering in the betatron collimators. This method is being applied to the future proton-proton collider SPPC. Preliminary multi-particle simula...

  13. Gamma Imaging using Rotational Modulation Collimation

    Science.gov (United States)

    2014-01-01

    in detection probabilities over traditional gamma detection, especially when the radiation source was shielded . Within DSTO the gamma imaging program...container Figure A2: Experimental setup used to measure radiation source stored in its lead and steel shielding transport container 16 UNCLASSIFIED...characterise the performance of two rotating modulation collimator (RMC) gamma imagers built by DSTO. The ability of these devices to image shielded and

  14. Electron Lenses for particle collimation in LHC

    CERN Document Server

    Shiltsev, V

    2008-01-01

    Electron Lenses built and installed in Tevatron have proven themselves as safe and very reliable instruments which can be effectively used in hadron collider operation for a number of applications, including compensation of beam-beam effects , DC beam removal from abort gaps , as a diagnostic tool. In this presentation we – following original proposal – consider in more detail a possibility of using electron lenses with hollow electron beam for ion and proton collimation in LHC.

  15. Coronal Jet Collimation by Nonlinear Induced Flows

    Science.gov (United States)

    Vasheghani Farahani, S.; Hejazi, S. M.

    2017-08-01

    Our objective is to study the collimation of solar jets by nonlinear forces corresponding to torsional Alfvén waves together with external forces. We consider a straight, initially non-rotating, untwisted magnetic cylinder embedded in a plasma with a straight magnetic field, where a shear between the internal and external flows exists. By implementing magnetohydrodynamic theory and taking into account the second-order thin flux tube approximation, the balance between the internal nonlinear forces is visualized. The nonlinear differential equation containing the ponderomotive, magnetic tension, and centrifugal forces in the presence of the shear flow is obtained. The solution presents the scale of influence of the propagating torsional Alfvén wave on compressive perturbations. Explicit expressions for the compressive perturbations caused by the forces connected to the torsional Alfvén wave show that, in the presence of a shear flow, the magnetic tension and centrifugal forces do not cancel each other’s effects as they did in its absence. This shear flow plays in favor of the magnetic tension force, resulting in a more efficient collimation. Regarding the ponderomotive force, the shear flow has no effect. The phase relations highlight the interplay of the shear flow and the plasma-β. As the shear flow and plasma-β increase, compressive perturbation amplitudes emerge. We conclude that the jet collimation due to the torsional Alfvén wave highly depends on the location of the jet. The shear flow tightens the collimation as the jet elevates up to the solar corona.

  16. Ion beam assisted synthesis of nano-crystals in glasses (silver and lead chalcogenides); Synthese assistee par faisceau d'ions d'agregats dans les verres (argent et chalcogenures de plomb)

    Energy Technology Data Exchange (ETDEWEB)

    Espiau de Lamaestre, R

    2005-04-15

    This work deals with the interest in ion beams for controlling nano-crystals synthesis in glasses. We show two different ways to reach this aim, insisting on importance of redox phenomena induced by the penetration and implantation of ions in glasses. We first show that we can use the great energy density deposited by the ions to tailor reducing conditions, favorable to metallic nano-crystal precipitation. In particular, we show that microscopic mechanism of radiation induced silver precipitation in glasses are analogous to the ones of classical photography. Ion beams can also be used to overcome supersaturation of elements in a given matrix. In this work, we synthesized lead chalcogenide nano-crystals (PbS, PbSe, PbTe) whose optical properties are interesting for telecommunication applications. We demonstrate the influence of complex chalcogenide chemistry in oxide glasses, and its relationship with the observed loss of growth control when nano-crystals are synthesized by sequential implantation of Pb and S in pure silica. As a consequence of this understanding, we demonstrate a novel and controlled synthesis of PbS nano-crystals, consisting in implanting sulfur into a Pb-containing glass, before annealing. Choice of glass composition provides a better control of precipitation physico-chemistry, whereas the use of implantation allows high nano-crystal volume fractions to be reached. Our study of IR emission properties of these nano-crystals shows a very high excitation cross section, and evidence for a 'dark exciton' emitting level. (author)

  17. Benefits of Computer Assisted Translation to Information Managers and End-Users (L’Interet de la Traduction Assistee par Ordinateur Pour les Responsables de Centres d’Information et Pour Les Utilisateurs Finaux)

    Science.gov (United States)

    1990-06-01

    diverses-prov, enances. creneaux associes au develfpement de Ia synthese de Ia parole, et og) iL V a place En matiere de recherche, Ic Japon a prevu...at Pnicollies *a vuo 08 l� EN 90lx’u 0 at514 Ca is 14 rtir on 080 texes... pre’ilers risaltats FR Do 0440 1080 tI IOrC lesl. 489041s 81 japonals

  18. Characterization and modelling of microwave multi dipole plasmas. Application to multi dipolar plasma assisted sputtering; Caracterization et modelisation des plasmas micro-onde multi-dipolaires. Application a la pulverisation assistee par plasma multi-dipolaire

    Energy Technology Data Exchange (ETDEWEB)

    Tran, Tan Vinh [Universite Joseph Fourier/CNRS-IN2P3, 53 Avenue des Martyrs, F-38026 Grenoble (France)

    2006-07-01

    The scaling up of plasma processes in the low pressure range remains a question to be solved for their rise at the industrial level. One solution is the uniform distribution of elementary plasma sources where the plasma is produced via electron cyclotron resonance (ECR) coupling. These elementary plasma sources are made up of a cylindrical permanent magnet (magnetic dipole) set at the end of a coaxial microwave line. Although of simple concept, the optimisation of these dipolar plasma sources is in fact a complex problem. It requires the knowledge, on one hand, of the configurations of static magnetic fields and microwave electric fields, and, on the other hand, of the mechanisms of plasma production in the region of high intensity magnetic field (ECR condition), and of plasma diffusion. Therefore, the experimental characterisation of the operating ranges and plasma parameters has been performed by Langmuir probes and optical emission spectroscopy on different configurations of dipolar sources. At the same time, in a first analytical approach, calculations have been made on simple magnetic field configurations, motion and trajectory of electrons in these magnetic fields, and the acceleration of electrons by ECR coupling. Then, the results have been used for the validation of the numerical modelling of the electron trajectories by using a hybrid PIC (particle-in-cell) / MC (Monte Carlo) method. The experimental study has evidenced large operating domains, between 15 and 200 W of microwave power, and from 0.5 to 15 mTorr argon pressure. The analysis of plasma parameters has shown that the region of ECR coupling is localised near the equatorial plane of the magnet and dependent on magnet geometry. These characterizations, applied to a cylindrical reactor using 48 sources, have shown that densities between 10{sup 11} and 10{sup 12} cm{sup -3} could be achieved in the central part of the volume at a few mTorr argon pressures. The modelling of electron trajectories near the magnet has also shown a better radial confinement with magnets exhibiting high length over diameter ratios. In addition, the numerical study corroborates the results of the experimental study, i.e. an ECR coupling region close to the equatorial plane of the magnet and not near the end of the coaxial microwave line. Finally, these results have been successfully applied to plasma assisted sputtering of targets allowing, in particular, their uniform erosion. (author)

  19. Characterization and modeling of multi-dipolar microwave plasmas: application to multi-dipolar plasma assisted sputtering; Caracterisation et modelisation des plasmas micro-onde multi-dipolaires: application a la pulverisation assistee par plasma multi-dipolaire

    Energy Technology Data Exchange (ETDEWEB)

    Tran, T.V

    2006-12-15

    The scaling up of plasma processes in the low pressure range remains a question to be solved for their rise at the industrial level. One solution is the uniform distribution of elementary plasma sources where the plasma is produced via electron cyclotron resonance (ECR) coupling. These elementary plasma sources are made up of a cylindrical permanent magnet (magnetic dipole) set at the end of a coaxial microwave line. Although of simple concept, the optimisation of these dipolar plasma sources is in fact a complex problem. It requires the knowledge, on one hand, of the configurations of static magnetic fields and microwave electric fields, and, on the other hand, of the mechanisms of plasma production in the region of high intensity magnetic field (ECR condition), and of plasma diffusion. Therefore, the experimental characterisation of the operating ranges and plasma parameters has been performed by Langmuir probes and optical emission spectroscopy on different configurations of dipolar sources. At the same time, in a first analytical approach, calculations have been made on simple magnetic field configurations, motion and trajectory of electrons in these magnetic fields, and the acceleration of electrons by ECR coupling. Then, the results have been used for the validation of the numerical modelling of the electron trajectories by using a hybrid PIC (particle-in-cell) / MC (Monte Carlo) method. The experimental study has evidenced large operating domains, between 15 and 200 W of microwave power, and from 0.5 to 15 mtorr argon pressure. The analysis of plasma parameters has shown that the region of ECR coupling is localised near the equatorial plane of the magnet and dependent on magnet geometry. These characterizations, applied to a cylindrical reactor using 48 sources, have shown that densities between 10{sup 11} and 10{sup 12} cm{sup -3} could be achieved in the central part of the volume at a few mtorr argon pressures. The modelling of electron trajectories near the magnet has also shown a better radial confinement with magnets exhibiting high length over diameter ratios. (author)

  20. FooPar

    DEFF Research Database (Denmark)

    Hargreaves, F. P.; Merkle, D.

    2013-01-01

    We present FooPar, an extension for highly efficient Parallel Computing in the multi-paradigm programming language Scala. Scala offers concise and clean syntax and integrates functional programming features. Our framework FooPar combines these features with parallel computing techniques. Foo...

  1. Source holder collimator for encapsulating radioactive material and collimating the emanations from the material

    Science.gov (United States)

    Laurer, G.R.

    1974-01-22

    This invention provides a transportable device capable of detecting normal levels of a trace element, such as lead in a doughnutshaped blood sample by x-ray fluorescence with a minimum of sample preparation in a relatively short analyzing time. In one embodiment, the blood is molded into a doughnut-shaped sample around an annular array of low-energy radioactive material that is at the center of the doughnut-shaped sample but encapsulated in a collimator, the latter shielding a detector that is close to the sample and facing the same so that the detector receives secondary emissions from the sample while the collimator collimates ths primary emissions from the radioactive material to direct these emissions toward the sample around 360 deg and away from the detector. (Official Gazette)

  2. Preliminary assessment of beam impact consequences on LHC Collimators

    CERN Document Server

    Cauchi, M; Bertarelli, A; Bruce, R; Carra, F; Dallocchio, A; Deboy, D; Mariani, N; Rossi, A; Lari, L; Mollicone, P; Sammut, N

    2011-01-01

    The correct functioning of the LHC collimation system is crucial to attain the desired LHC luminosity performance. However, the requirements to handle high intensity beams can be demanding. In this respect, the robustness of the collimators plays an important role. An accident, which causes the proton beam to hit a collimator, might result in severe beam-induced damage and, in some cases, replacement of the collimator, with consequent downtime for the machine. In this paper, several case studies representing different realistic beam impact scenarios are shown. A preliminary analysis of the thermal response of tertiary collimators to beam impact is presented, from which the most critical cases can be identified. Such work will also help to give an initial insight on the operational constraints of the LHC by taking into account all relevant collimator damage limits.

  3. Beam Delivery WG Summary: Optics, Collimation & Background

    Energy Technology Data Exchange (ETDEWEB)

    Angal-Kalinin, D.; Jackson, F.; /Daresbury; Mokhov, N.V.; /Fermilab; Kuroda, S.; /KEK, Tsukuba; Seryi, A.A.; /SLAC

    2006-01-20

    The presented paper partially summarizes the work of the Beam Delivery working group (WG4) at Snowmass, concentrating on status of optics, layout, collimation, and background. The strawman layout with 2 interaction regions was recommended at the first ILC workshop at KEK in November 2004. Two crossing-angle designs were included in this layout. The design of the ILC BDS has evolved since the first ILC workshop. The progress on the BDS design and extraction line design has been reviewed and the design issues were discussed during the optics and layout session at the Snowmass.

  4. Design of optimal collimation for dedicated molecular breast imaging systems

    Energy Technology Data Exchange (ETDEWEB)

    Weinmann, Amanda L.; Hruska, Carrie B.; O' Connor, Michael K. [Department of Radiology, Division of Nuclear Medicine, Mayo Clinic, Rochester, Minnesota 55905 (United States)

    2009-03-15

    Molecular breast imaging (MBI) is a functional imaging technique that uses specialized small field-of-view gamma cameras to detect the preferential uptake of a radiotracer in breast lesions. MBI has potential to be a useful adjunct method to screening mammography for the detection of occult breast cancer. However, a current limitation of MBI is the high radiation dose (a factor of 7-10 times that of screening mammography) associated with current technology. The purpose of this study was to optimize the gamma camera collimation with the aim of improving sensitivity while retaining adequate resolution for the detection of sub-10-mm lesions. Square-hole collimators with holes matched to the pixilated cadmium zinc telluride detector elements of the MBI system were designed. Data from MBI patient studies and parameters of existing dual-head MBI systems were used to guide the range of desired collimator resolutions, source-to-collimator distances, pixel sizes, and collimator materials that were examined. General equations describing collimator performance for a conventional gamma camera were used in the design process along with several important adjustments to account for the specialized imaging geometry of the MBI system. Both theoretical calculations and a Monte Carlo model were used to measure the geometric efficiency (or sensitivity) and resolution of each designed collimator. Results showed that through optimal collimation, collimator sensitivity could be improved by factors of 1.5-3.2, while maintaining a collimator resolution of either {<=}5 or {<=}7.5 mm at a distance of 3 cm from the collimator face. These gains in collimator sensitivity permit an inversely proportional drop in the required dose to perform MBI.

  5. Optimization of convergent collimators for pixelated SPECT systems

    Energy Technology Data Exchange (ETDEWEB)

    Capote, Ricardo M.; Matela, Nuno; Conceicao, Raquel C.; Almeida, Pedro [Universidade de Lisboa, Faculdade de Ciencias, Instituto de Biofisica e Engenharia Biomedica, Campo Grande, 1749-016 Lisboa (Portugal)

    2013-06-15

    Purpose: The optimization of the collimator design is essential to obtain the best possible sensitivity in single photon emission computed tomography imaging. The aim of this work is to present a methodology for maximizing the sensitivity of convergent collimators, specifically designed to match the pitch of pixelated detectors, for a fixed spatial resolution value and to present some initial results using this approach. Methods: Given the matched constraint, the optimal collimator design cannot be simply found by allowing the highest level of septal penetration and spatial resolution consistent with the imposed restrictions, as it is done for the optimization of conventional collimators. Therefore, an algorithm that interactively calculates the collimator dimensions, with the maximum sensitivity, which respect the imposed restrictions was developed and used to optimize cone and fan beam collimators with tapered square-shaped holes for low (60-300 keV) and high energy radiation (300-511 keV). The optimal collimator dimensions were locally calculated based on the premise that each hole and septa of the convergent collimator should locally resemble an appropriate optimal matched parallel collimator. Results: The optimal collimator dimensions, calculated for subcentimeter resolutions (3 and 7.5 mm), common pixel sizes (1.6, 2.1, and 2.5 mm), and acceptable septal penetration at 140 keV, were approximately constant throughout the collimator, despite their different hole incidence angles. By using these input parameters and a less strict septal penetration value of 5%, the optimal collimator dimensions and the corresponding mass per detector area were calculated for 511 keV. It is shown that a low value of focal distance leads to improvements in the average sensitivity at a fixed source-collimator distance and resolution. The optimal cone beam performance outperformed that of other optimal collimation geometries (fan and parallel beam) in imaging objects close to the

  6. suPAR

    DEFF Research Database (Denmark)

    Hodges, Gethin W; Bang, Casper N; Wachtell, Kristian;

    2015-01-01

    The fundamental role of inflammation in cardiovascular disease (CVD) has prompted interest in numerous biomarkers that detect subclinical levels of inflammation. Soluble urokinase plasminogen activator receptor (suPAR) is a novel biomarker that correlates significantly with cardiovascular events ...

  7. Leaky wave lenses for spoof plasmon collimation.

    Science.gov (United States)

    Panaretos, Anastasios H; Werner, Douglas H

    2016-06-27

    We theoretically demonstrate the feasibility of collimating radiating spoof plasmons using a leaky wave lens approach. Spoof plasmons are surface waves excited along reactance surfaces realized through metallic corrugations. By employing a periodic perturbation to the geometric profile of this type of reactance surface, it becomes feasible to convert the excited spoof plasmons into free-space radiating leaky wave modes. It is demonstrated that by structurally modifying such a corrugated surface through the introduction of a non-uniform sinusoidally modulated reactance profile, then a tapered wavenumber, with a real part less than that of free space, can be established along the surface. In this way the radiating properties of the structure (amplitude and phase) can be locally controlled thereby creating a radiating effect similar to that of a non-uniform current distribution. By properly engineering the space dependent wavenumber along the corrugated surface, different regions of the structure will emit spoof plasmon energy at different angles with varying intensity. The combined effect is the emission of an electromagnetic wave exhibiting a converging wave-front that eventually collimates spoof plasmon energy at some desired focal point.

  8. Self-collimation in photonic crystals with anisotropic constituents

    Institute of Scientific and Technical Information of China (English)

    J. W. Haus; M. Siraj; P. Prasad; P. Markowicz

    2007-01-01

    @@ In a photonic crystal composed of anisotropic constituents we quantify the range of input angles and the degree of collimation of the beam inside the crystal. The optical properties of a photobleached 4-dimethylamino-N-methyl-4-stilbazolium-tosylate (DAST) crystal are used in our model to demonstrate the efficacy of the self-collimation features.

  9. Towards Optimum Material Choices for HL-LHC Collimator Upgrade

    CERN Document Server

    Quaranta, E.; Biancacci, N.; Bruce, R.; Carra, F.; Métral, E.; Redaelli, S.; Rossi, A.; Salvant, B.

    2016-01-01

    properties that address different limitations of the present collimation system, solutions have been found to fulfil various upgrade challenges. This paper describes the proposed staged approach to deploy new materials in the upgraded HL-LHC collimation system. Beam tests at the CERN HiRadMat facility were also performed to benchmark simulation methods and constitutive material models.

  10. Magnetic collimation of the relativistic jet in M 87

    NARCIS (Netherlands)

    Gracia, JG; Tsinganos, KT; Bogovalov, SV

    2005-01-01

    We apply a two-zone MHD model to the jet of M87. The model consists of an inner relativistic outflow, which is surrounded by a non-nonrelativistic outer disk-wind. The relativistic outer disk-wind collimates very well through magnetic self-collimation and confines the inner relativistic jet into a n

  11. Radiation collimation in a thick crystalline undulator

    Science.gov (United States)

    Wistisen, Tobias Nyholm; Uggerhøj, Ulrik Ingerslev; Hansen, John Lundsgaard; Lauth, Werner; Klag, Pascal

    2017-05-01

    With the recent experimental confirmation of the existence of energetic radiation from a Small Amplitude, Small Period (SASP) crystalline undulator [T.N. Wistisen, K.K. Andersen, S. Yilmaz, R. Mikkelsen, J. Lundsgaard Hansen, U.I. Uggerhøj, W. Lauth, H. Backe, Phys. Rev. Lett. 112, 254801 (2014)], the field of specially manufactured crystals, from which specific radiation characteristics can be obtained, has evolved substantially. In this paper we confirm the existence of the crystalline undulator radiation, using electrons of energies of 855 GeV from the MAinzer MIcrotron (MAMI) in a crystal that is approximately 10 times thicker than the previous one. Furthermore, we have measured a significant increase in enhancement, in good agreement with calculations, of the undulator peak by collimation to angles smaller than the natural opening angle of the radiation emission process, 1 /γ. Contribution to the Topical Issue: "Dynamics of Systems at the Nanoscale", edited by Andrey Solov'yov and Andrei Korol.

  12. Preliminary Exploratory Study of Different Phase II Collimators

    CERN Document Server

    Lari, L; Bertarelli, A; Bracco, C; Brugger, M; Cerutti, F; Dallocchio, Alessandro; Doyle, E; Ferrari, A; Keller, L; Lundgren, S; Markiewicz, T; Mauri, M; Roesler, S; Sarchiapone, L; Smith, J; Vlachoudis, V

    2008-01-01

    The LHC collimation system is installed and commissioned in different phases, following the natural evolution of the LHC performance. To improve cleaning efficiency towards the end of the low beta squeeze at 7TeV, and in stable physics conditions, it is foreseen to complement the 30 highly robust Phase I secondary collimators with low impedance Phase II collimators. At this stage, their design is not yet finalized. Possible options include metallic collimators, graphite jaws with a movable metallic foil, or collimators with metallic rotating jaws. As part of the evaluation of the different designs, the FLUKA Monte Carlo code is extensively used for calculating energy deposition and studying material damage and activation. This report outlines the simulation approach and defines the critical quantities involved.

  13. Photonic crystals for broadband, omnidirectional self-collimation

    Science.gov (United States)

    Chuang, Y.-C.; Suleski, T. J.

    2011-03-01

    In this paper, multiple photonic crystal (PC) structures are proposed to improve three-dimensional (3D) self-collimation performance, including two 3D PCs (tetragonal lattice structures and a complex hexagonal lattice structure) and two two-dimensional (2D) PCs (triangular lattice structures and kagome lattice structures) with out-of-plane orientation. Different design strategies are investigated and compared in terms of the resulting self-collimation performance. Several desired 3D properties are numerically realized for the first time, including broadband 3D self-collimation, omnidirectional beam confinement and broadband omnidirectional self-collimation. These developments can enable future self-collimation applications, such as multiplexers, PC core fibers and solar light collection.

  14. [Influence of collimation system on static Fourier transform spectrometer].

    Science.gov (United States)

    Jiang, Cheng-Zhi; Liang, Jing-Qiu; Liang, Zhong-Zhu; Sun, Qiang; Wang, Wei-Biao

    2014-01-01

    Collimation system provides collimated light for the static Fourier-transform spectroscopy (SFTS). Its quality is crucial to the signal to noise ratio (SNR) of SFTS. In the present paper, the physical model of SFTS was established based on the Fresnel diffraction theory by means of numerical software. The influence of collimation system on the SFTS was discussed in detail focusing on the aberrations of collimation lens and the quality of extended source. The results of simulation show that the influences of different kinds of aberrations on SNR take on obvious regularity, and in particular, the influences of off-axis aberrations on SNR are closely related to the location of off-axis point source. Finally the extended source's maximum radius allowed was obtained by simulation, which equals to 0.65 mm. The discussion results will be used for the design of collimation system.

  15. Beam diffusion measurements using collimator scans in the LHC

    CERN Document Server

    Valentino, Gianluca; Bruce, Roderik; Burkart, Florian; Previtali, Valentina; Redaelli, Stefano; Salvachua, Belen; Stancari, Giuliov; Valishev, Alexander

    2013-01-01

    The time evolution of beam losses during a collimator scan provides information on halo diffusion and population. This is an essential input for machine performance characterization and for the design of collimation systems. Beam halo measurements in the CERN Large Hadron Collider were conducted through collimator scrapings in a dedicated beam study for the first time at 4 TeV. Four scans were performed with two collimators, in the vertical plane for beam 1 and horizontally for beam 2, before and after bringing the beams into collisions. Inward and outward steps were performed. A diffusion model was used to interpret the observed loss rate evolution in response to the collimator steps. With this technique, diffusion coefficients were estimated as a function of betatron oscillation amplitude from approximately 3 to 7 standard deviations of the transverse beam distribution. A comparison of halo diffusion and core emittance growth rates is also presented.

  16. Modeling and simulation of LHC beam-based collimator setup

    CERN Document Server

    Valentino, G; Assmann, R W; Burkart, F; Redaelli, S; Rossi, A; Lari, L

    2012-01-01

    In the 2011 Large Hadron Collider run, collimators were aligned for proton and heavy ion beams using a semiautomatic setup algorithm. The algorithm provided a reduction in the beam time required for setup, an elimination of beam dumps during setup and better reproducibility with respect to manual alignment. A collimator setup simulator was developed based on a Gaussian model of the beam distribution as well as a parametric model of the beam losses. A time-varying beam loss signal can be simulated for a given collimator movement into the beam. The simulation results and comparison to measurement data obtained during collimator setups and dedicated fills for beam halo scraping are presented. The simulator will then be used to develop a fully automatic collimator alignment algorithm.

  17. Determination of optimal collimation parameters for a rotating slat collimator system: a system matrix method using ML-EM

    Science.gov (United States)

    Boisson, F.; Bekaert, V.; Brasse, D.

    2016-03-01

    Nowadays, Single Photon imaging has become an essential part of molecular imaging and nuclear medicine. Whether to establish a diagnosis or in the therapeutic monitoring, this modality presents performance that continues to improve. For over 50 years, several collimators have been proposed. Mainly governed by collimation parameters, the resolution-sensitivity trade-off is the factor determining the collimator the most suitable for an intended study. One alternative to the common approaches is the rotating slat collimator (RSC). In the present study, we are aiming at developing a preclinical system equipped with a RSC dedicated to mice and rats imaging, which requires both high sensitivity and spatial resolution. We investigated the resolution-sensitivity trade-offs obtained by varying different collimation parameters: (i) the slats height (H), and (ii) the gap between two consecutive slats (g), considering different intrinsic spatial resolutions. One system matrix was generated for each set of collimation parameters (H,g). Spatial resolutions, Signal-to-Noise Ratio (SNR) and sensitivity obtained for all the set of collimation parameters (H,g) were measured in the 2D projections reconstructed with ML-EM. According to our results, 20 mm high slats and a 1 mm gap were chosen as a good RSC candidate for a preclinical detection module. This collimator will ensure a sensitivity greater than 0.2% and a system spatial resolution below 1 mm, considering an intrinsic spatial resolution below 0.8 mm.

  18. It's quicker "Par Avignon"!

    CERN Multimedia

    2005-01-01

    For a few years, the CERN Library has been receiving books from the University of Hanover sent via Avignon, at least that's what it says on the envelope. Such a detour would mean that parcels were travelling 720 km more than the distance separating Geneva and Hanover, which would be a very strange state of affairs. The explanation lies in a spelling mistake. The sender has been stamping parcels with a stamp that says "Par Avignon prioritaire" (first-class via Avignon) instead of "Par Avion prioritaire" (First Class Air Mail), a source of much amusement to the librarians!

  19. Multipinhole collimator with 20 apertures for a brain SPECT application

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Tzu-Cheng; Ellin, Justin R.; Shrestha, Uttam; Seo, Youngho, E-mail: youngho.seo@ucsf.edu [Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, California 94107 (United States); Huang, Qiu [School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200030 (China); Gullberg, Grant T. [Department of Radiotracer Development and Imaging Technology, Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94702 (United States)

    2014-11-01

    Purpose: Several new technologies for single photon emission computed tomography (SPECT) instrumentation with parallel-hole collimation have been proposed to improve detector sensitivity and signal collection efficiency. Benefits from improved signal efficiency include shorter acquisition times and lower dose requirements. In this paper, the authors show a possibility of over an order of magnitude enhancement in photon detection efficiency (from 7.6 × 10{sup −5} to 1.6 × 10{sup −3}) for dopamine transporter (DaT) imaging of the striatum over the conventional SPECT parallel-hole collimators by use of custom-designed 20 multipinhole (20-MPH) collimators with apertures of 0.75 cm diameter. Methods: Quantifying specific binding ratio (SBR) of {sup 123}I-ioflupane or {sup 123}I-iometopane’s signal at the striatal region is a common brain imaging method to confirm the diagnosis of the Parkinson’s disease. The authors performed imaging of a striatal phantom filled with aqueous solution of I-123 and compared camera recovery ratios of SBR acquired between low-energy high-resolution (LEHR) parallel-hole collimators and 20-MPH collimators. Results: With only two-thirds of total acquisition time (20 min against 30 min), a comparable camera recovery ratio of SBR was achieved using 20-MPH collimators in comparison to that from the LEHR collimator study. Conclusions: Their systematic analyses showed that the 20-MPH collimator could be a promising alternative for the DaT SPECT imaging for brain over the traditional LEHR collimator, which could give both shorter scan time and improved diagnostic accuracy.

  20. The HEAO-1 Scanning Modulation Collimator

    Science.gov (United States)

    Schwartz, Daniel A.

    2013-01-01

    My niche on this panel seems to be the High Energy Astronomy Observatory-1 Scanning Modulation Collimator experiment. Our chair, Hale Bradt, and the late Herb Gursky each proposed a different version modulation collimator, which was condensed by NASA via "forced marriage," to the SMC. I worked as Project Scientist under Herb, later inheriting the PI role. The MIT Project Scientist, the late Rodger Doxsey, and I were told "this is your experiment," and "we are a seamless team regardless of institution." Rodger and I were young enough to believe this, and we made it happen (and not always with the best results vis a vis higher internal management). I was never interested in astronomy, and allegedly am still not. Why do an astro-metrical job of measuring and reporting the coordinates of X-ray sources? In fact we participated widely in the identification of the sources with astronomical object, and making each paper a discussion of the physics of the emission. An enjoyable way to learn some astronomy. The stated purpose of the Gursky/Bradt experiment was to enable optical identifications so that more detailed study could be done. I remember meeting with John Whelan to discuss his collaboration in making the optical identifications. He said he only wanted to study sources after they were identified. For many milliseconds I became very angry - "who is going to to the work to MAKE those identifications," but luckily before speaking I realized how satisfying it was that astronomers indeed wanted to study X-ray sources in other wavebands. The second biggest excitement in the HEAO-1 program was the "glitches" that appeared in the gyro data during final functional testing. This took some high-powered politics by all the PI's to convince MSFC to delay for 4 months, replacing the "funny" unit with one from HEAO-2 (Einstein) and later refurbishing that unit. Third biggest excitement was when a computer failed and final checkout during countdown at the Cape was done by looking at

  1. Momentum slits, collimators and masks in the SLC

    Energy Technology Data Exchange (ETDEWEB)

    Walz, D.R.; McFarlane, A.; Lewandowski, E.; Zabdyr, J.

    1989-04-01

    The high specific power densities in the SLC give rise to a multitude of challenging problems in collimation and momentum analysis, beam containment, machine protection and background control. The results of an extensive program to develop most of the devices deemed necessary for operation of the arcs matching sections and the final focus region are presented. Emphasis is placed on materials selection and on unique features of remotely adjustable slits and halo clipper collimators which have to operate with great precision in a high-radiation, ultra-high vacuum environment. Also covered are solutions for a few fixed aperture machine protection collimators. 7 refs., 5 figs.

  2. Tracking studies of the Compact Linear Collider collimation system

    Energy Technology Data Exchange (ETDEWEB)

    Agapov, I.; Burkhardt, H.; Schulte, D.; /CERN; Latina, A.; /Fermilab; Blair, G.A.; Malton, S.; /Royal Holloway, U. of London; Resta-Lopez, J.; /Oxford U., JAI

    2009-08-01

    A collimation system performance study includes several types of computations performed by different codes. Optics calculations are performed with codes such as MADX, tracking studies including additional effects such as wakefields, halo and tail generation, and dynamical machine alignment are done with codes such as PLACET, and energy deposition can be studied with BDSIM. More detailed studies of hadron production in the beam halo interaction with collimators are better performed with GEANT4 and FLUKA. A procedure has been developed that allows one to perform a single tracking study using several codes simultaneously. In this paper we study the performance of the Compact Linear Collider collimation system using such a procedure.

  3. Studies for an alternative LHC non-linear collimation system

    CERN Document Server

    Lari, L; Boccone, V; Cerutti, F; Versaci, R; Vlachoudis, V; Mereghetti, A; Faus-Golfe, A; Resta-Lopez, J

    2012-01-01

    A LHC non-linear betatron cleaning collimation system would allow larger gap for the mechanical jaws, reducing as a consequence the collimator-induced impedance, which may limit the LHC beam intensity. In this paper, the performance of the proposed system is analyzed in terms of beam losses distribution around the LHC ring and cleaning efficiency in stable physics condition at 7TeV for Beam1. Moreover, the energy deposition distribution on the machine elements is compared to the present LHC Betatron cleaning collimation system in the Point 7 Insertion Region (IR).

  4. A Fresnel zone plate collimator: potential and aberrations

    Science.gov (United States)

    Menz, Benedikt; Bräuninger, Heinrich; Burwitz, Vadim; Hartner, Gisela; Predehl, Peter

    2015-09-01

    A collimator, that parallelizes an X-ray beam, provides a significant improvement of the metrology to characterize X-ray optics for space instruments at MPE's PANTER X-ray test facility. A Fresnel zone plate was selected as a collimating optic, as it meets a good angular resolution 10 cm2. Such an optic is ideally suited to illuminate Silicon Pore Optic (SPO) modules as proposed for ATHENA. This paper provides the theoretic description of such a Fresnel zone plate especially considering resolution and efficiency. Based on the theoretic results the collimator setup performance is analyzed and requirements for fabrication and alignment are calculated.

  5. Development of hollow electron beams for proton and ion collimation

    CERN Document Server

    Stancari, G.; Kuznetsov, G.; Shiltsev, V.; Still, D.A.; Valishev, A.; Vorobiev, L.G.; Assmann, R.; Kabantsev, A.

    2010-01-01

    Magnetically confined hollow electron beams for controlled halo removal in high-energy colliders such as the Tevatron or the LHC may extend traditional collimation systems beyond the intensity limits imposed by tolerable material damage. They may also improve collimation performance by suppressing loss spikes due to beam jitter and by increasing capture efficiency. A hollow electron gun was designed and built. Its performance and stability were measured at the Fermilab test stand. The gun will be installed in one of the existing Tevatron electron lenses for preliminary tests of the hollow-beam collimator concept, addressing critical issues such as alignment and instabilities of the overlapping proton and electron beams

  6. Hollow Electron Beam Collimator: R&D Status Report

    CERN Document Server

    Stancari, G; Kuznetsov, G; Shiltsev, V; Valishev, A; Kabantsev, A; Vorobiev, L

    2012-01-01

    Magnetically confined hollow electron beams for controlled halo removal in high-energy colliders such as the Tevatron or the LHC may extend traditional collimation systems beyond the intensity limits imposed by tolerable material damage. They may also improve collimation performance by suppressing loss spikes due to beam jitter and by increasing capture efficiency. A hollow electron gun was designed and built. Its performance and stability were measured at the Fermilab test stand. The gun will be installed in one of the existing Tevatron electron lenses for preliminary tests of the hollow-beam collimator concept, addressing critical issues such as alignment and instabilities of the overlapping proton and electron beams.

  7. Development of hollow electron beams for proton and ion collimation

    CERN Document Server

    Stancari, G; Kuznetsov, G; Shiltsev, V; Still, D A; Valishev, A; Vorobiev, L G; Assmann, R; Kabantsev, A

    2012-01-01

    Magnetically confined hollow electron beams for controlled halo removal in high-energy colliders such as the Tevatron or the LHC may extend traditional collimation systems beyond the intensity limits imposed by tolerable material damage. They may also improve collimation performance by suppressing loss spikes due to beam jitter and by increasing capture efficiency. A hollow electron gun was designed and built. Its performance and stability were measured at the Fermilab test stand. The gun will be installed in one of the existing Tevatron electron lenses for preliminary tests of the hollow-beam collimator concept, addressing critical issues such as alignment and instabilities of the overlapping proton and electron beams.

  8. The final collimator has been installed ready for the LHC restart (phase 1 of the LHC collimator project)

    CERN Multimedia

    CERN audiovisual service

    2009-01-01

    The collimators are installed around the LHC ring and the transfer lines to absorb ‘stray’ particles that have spread out, forming a halo around the beam. It is important to absorb this halo to protect the rest of the machine from damage, in particular the superconducting magnets, where any slight heating by the ‘stray particles’ could cause a magnet quench. The one-meter long collimators absorb the particles in the halo by closing a set of ‘jaws’ of various materials around the beam; the most robust collimators use fiber-reinforced graphite. Before the start-up last year, 88 collimators were installed. The unforeseen shutdown caused by the incident in Sector 3-4, allowed the collimator team to continue with the final 20 collimators necessary to maximize the LHC intensity and luminosity reach with the phase 1 collimation system. This marks the end of 6.5 years of hard work since the project began

  9. Euclid mirrors and test collimator: AMOS developments

    Science.gov (United States)

    Gloesener, Pierre; Wolfs, Fabrice; Cola, Marcel; Pirnay, Olivier; Flebus, Carlo

    2016-07-01

    EUCLID is an optical/near-infrared survey mission to be launched in 2020 towards the L2 Lagrange point. It will aim at studying the dark universe and providing a better understanding of the origin of the accelerating expansion of the universe. Through the use of cosmological sounding, it will investigate the nature of dark energy, dark matter and gravity by tracking their observational signatures on the geometry of the universe and on the cosmic history of large structures formation. The EUCLID payload module (PLM) consists of a 1.2 m-class telescope and will accommodate two instruments. As a subcontractor of AIRBUS Defence and Space, AMOS is responsible for the manufacturing of the secondary and the third mirrors of the telescope as well as for the flat folding mirror set within the focal plane arrangement of EUCLID telescope, which incorporates dedicated filtering functions. AMOS produces in addition the 1.3 m-class test collimator for the on-ground validation of the EUCLID instrument.

  10. Simulation of MHD collimation from differential rotation

    Science.gov (United States)

    Carey, Christopher

    2005-10-01

    Recent observations indicate that astrophysical outflows from active galactic nuclei are permeated with helical magnetic fields[1]. The most promising theory for the formation of the magnetic configurations in these magnetically driven jets is the coiling of an initial seed field by the differential rotation of the accretion disk surrounding the central object. We have begun simulations that are relevant to these Poynting jets using the NIMROD code[2]. To simulate dynamics on length scales that are significantly larger than the accretion disk, the non-relativistic MHD equations are evolved on a hemispherical logarithmic mesh. The accretion disk is treated as a condition on the lower boundary by applying a Keplerian velocity to the azimuthal component of the fluid velocity and a prescribed flux of mass through the boundary. The magnetic field configuration is initialized to a dipole like field. Formation of a jet outflow is observed later in time. The initial field is coiled up and collimated, driving a large current density on the axis of symmetry. Slipping of magnetic field lines due to non-ideal effects has been investigated. 1. Asada K. et. al., Pub. of the Astr. Soc. of Japan, 54, L39-L43, 2002 2. Sovinec C. et. al., J. Comp. Phys., 195, 355-386, 2004

  11. Radionuclide annular single crystal scintillator camera with rotating collimator

    Energy Technology Data Exchange (ETDEWEB)

    Genna, S.; Pang, S.-C.

    1986-04-22

    A radionuclide emission tomography camera is described for sensing gamma ray emissions from a source within the field of view consisting of: a fixed, position-sensitive detector means, responsive to the gamma ray emissions and surrounding the field of view for detecting the contact position and the trajectory from which a gamma ray emission originates, the fixed, position-sensitive detector including a single continuous stationary scintillation crystal; rotatable collimator means, disposed between the fixed, position-sensitive detecto means and the field of view, and including at least one array of collimator elements, for restricting and collimating the gamma ray emissions; and means for rotating the collimator means relative to the fixed, position-sensitive detector, for exposing different sections of the position-sensitive detector to the gamma ray emissions in order to view the source from different angles.

  12. Mechanical Design for Robustness of the LHC Collimators

    CERN Document Server

    Bertarelli, Alessandro; Assmann, R W; Calatroni, Sergio; Dallocchio, Alessandro; Kurtyka, Tadeusz; Mayer, Manfred; Perret, Roger; Redaelli, Stefano; Robert-Demolaize, Guillaume

    2005-01-01

    The functional specification of the LHC Collimators requires, for the start-up of the machine and the initial luminosity runs (Phase 1), a collimation system with maximum robustness against abnormal beam operating conditions. The most severe cases to be considered in the mechanical design are the asynchronous beam dump at 7 TeV and the 450 GeV injection error. To ensure that the collimator jaws survive such accident scenarios, low-Z materials were chosen, driving the design towards Graphite or Carbon/Carbon composites. Furthermore, in-depth thermo-mechanical simulations, both static and dynamic, were necessary.This paper presents the results of the numerical analyses performed for the 450 GeV accident case, along with the experimental results of the tests conducted on a collimator prototype in Cern TT40 transfer line, impacted by a 450 GeV beam of 3.1·1013

  13. COLLIMATORS AND MATERIALS FOR HIGH INTENSITY HEAVY ION SYNCHROTRONS

    CERN Document Server

    Stadlmann, J; Kollmus, H; Spiller, P; Strasik, I; Tahir, N A; Tomut, M; Trautmann, C

    2012-01-01

    The operation of high power high brightness accelerators requires huge efforts for beam cleaning and machine protection. Within the WP 8 (ColMat) of the EU research framework EuCARD[1] we investigate new materials and methods for beam collimation and machine protection. We present an overview of these activities at the GSI Helmholtzzentrum f¨ur Schwerionenforschung, Darmstadt. Simulations of accidental beam losses in LHC and SIS100 have been performed. Scenarios for halo collimation of heavy ions and protons in SIS100 routine operation have been investigated. A prototype of a cryogenic collimator for charge exchange losses during intermediate charge state heavy ion operation in SIS100 has been build and tested with beam. Several candidates of advanced composite materials for collimation system upgrades of present and future high power accelerators have been irradiated and their properties are being characterized. Most deliverables and milestones of the R&D programme were already reached before the end of...

  14. Beam Loss and Beam Shape at the LHC Collimators

    CERN Document Server

    Burkart, Florian

    In this master thesis the beam loss and the beam shape at the LHC collimators was measured, analysed, presented and discussed. Beginning with a short introduction of the LHC, the experiments, the supercon- ducting magnet system, the basics on linear beam dynamics and a describtion of the LHC collimation system are given. This is followed by the presentation of the performance of the LHC collimation sys- tem during 2011. A method to convert the Beam Loss Monitor signal in Gy/s to a proton beam loss rate will be introduced. Also the beam lifetime during the proton physics runs in 2011 will be presented and discussed. Finally, the shape of the LHC beams is analysed by using data obtained by scraping the beam at the LHC primary collimators.

  15. Beam Loss Patterns at the LHC Collimators Measurements & Simulations

    CERN Document Server

    Böhlen, Till Tobias

    2008-01-01

    The Beam Loss Monitoring (BLM) system of the Large Hadron Collider (LHC) detects particle losses of circulating beams and initiates an emergency extraction of the beam in case that the BLM thresholds are exceeded. This protection is required as energy deposition in the accelerator equipment due to secondary shower particles can reach critical levels; causing damage to the beam-line components and quenches of superconducting magnets. Robust and movable beam line elements, so-called collimators, are the aperture limitations of the LHC. Consequently, they are exposed to the excess of lost beam particles and their showers. Proton loss patterns at LHC collimators have to be determined to interpret the signal of the BLM detectors and to set adequate BLM thresholds for the protection of collimators and other equipment in case of unacceptably increased loss rates. The first part of this work investigates the agreement of BLM detector measurements with simulations for an LHC-like collimation setup. The setup consists ...

  16. Magnetized and collimated millimeter scale plasma jets with astrophysical relevance

    Energy Technology Data Exchange (ETDEWEB)

    Brady, Parrish C.; Quevedo, Hernan J. [Texas Center for High Intensity Laser Science, University of Texas at Austin, Austin, Texas 78712 (United States); Valanju, Prashant M. [Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712-1060 (United States); Bengtson, Roger D.; Ditmire, Todd [Department of Physics, University of Texas at Austin, Austin, Texas 78712 (United States)

    2012-01-15

    Magnetized collimated plasma jets are created in the laboratory to extend our understanding of plasma jet acceleration and collimation mechanisms with particular connection to astrophysical jets. In this study, plasma collimated jets are formed from supersonic unmagnetized flows, mimicking a stellar wind, subject to currents and magnetohydrodynamic forces. It is found that an external poloidal magnetic field, like the ones found anchored to accretion disks, is essential to stabilize the jets against current-driven instabilities. The maximum jet length before instabilities develop is proportional to the field strength and the length threshold agrees well with Kruskal-Shafranov theory. The plasma evolution is modeled qualitatively using MHD theory of current-carrying flux tubes showing that jet acceleration and collimation arise as a result of electromagnetic forces.

  17. Dynamic multileaf collimation without `tongue-and-groove' underdosage effects

    Science.gov (United States)

    van Santvoort, J. P. C.; Heijmen, B. J. M.

    1996-10-01

    In all commercially available multileaf collimators, a `tongue-and-groove' - or similar - construction is used for reduction of leakage radiation between adjacent leaves. These constructions can cause serious underdosages in intensity-modulated photon beams. A method for leaf trajectory calculation for dynamic multileaf collimation, which fully avoids these underdosage effects, is presented. The method is based on pairwise synchronizations of trajectories of adjacent leaf pairs, such that the delivered beam intensity in each `tongue-and-groove' region is always equal to the smallest of the two prescribed intensities for the two corresponding leaf pairs. The effectiveness of the method has been proven for a large number of intensity-modulated fields, using the dynamic multileaf collimation mode of our MM50 Racetrack Microtron. Compared to dynamic multileaf collimation without synchronization, beam-on times are always equal or longer. For the cases that we studied, the beam-on time was typically increased by 5 to 15%.

  18. Dynamic multileaf collimation without 'tongue-and-groove' underdosage effects.

    Science.gov (United States)

    van Santvoort, J P; Heijmen, B J

    1996-10-01

    In all commercially available multileaf collimators, a 'tongue-and-groove'--or similar--construction is used for reduction of leakage radiation between adjacent leaves. These constructions can cause serious underdosages in intensity-modulated photon beams. A method for leaf trajectory calculation for dynamic multileaf collimation, which fully avoids these underdosage effects, is presented. The method is based on pairwise synchronizations of trajectories of adjacent leaf pairs, such that the delivered beam intensity in each 'tongue-and-groove' region is always equal to the smallest of the two prescribed intensities for the two corresponding leaf pairs. The effectiveness of the method has been proven for a large number of intensity-modulated fields, using the dynamic multileaf collimation mode of our MM50 Racetrack Microtron. Compared to dynamic multileaf collimation without synchronization, beam-on times are always equal or longer. For the cases that we studied, the beam-on time was typically increased by 5 to 15%.

  19. Errors generated with the use of rectangular collimation

    Energy Technology Data Exchange (ETDEWEB)

    Parks, E.T. (Department of Allied Health, Western Kentucky University, Bowling Green (USA))

    1991-04-01

    This study was designed to determine whether various techniques for achieving rectangular collimation generate different numbers and types of errors and remakes and to determine whether operator skill level influences errors and remakes. Eighteen students exposed full-mouth series of radiographs on manikins with the use of six techniques. The students were grouped according to skill level. The radiographs were evaluated for errors and remakes resulting from errors in the following categories: cone cutting, vertical angulation, and film placement. Significant differences were found among the techniques in cone cutting errors and remakes, vertical angulation errors and remakes, and total errors and remakes. Operator skill did not appear to influence the number or types of errors or remakes generated. Rectangular collimation techniques produced more errors than did the round collimation techniques. However, only one rectangular collimation technique generated significantly more remakes than the other techniques.

  20. PAR Loop Schedule Review

    Energy Technology Data Exchange (ETDEWEB)

    Schaffer, Jr.; W.F.

    1958-04-30

    The schedule for the installation of the PAR slurry loop experiment in the South Facility of the ORR has been reviewed and revised. The design, fabrications and Installation is approximately two weeks behind schedule at this time due to many factors; however, indications are that this time can be made up. Design is estimated to be 75% complete, fabrication 32% complete and installation 12% complete.

  1. Electron Beam Collimation for the Next Generation Light Source

    Energy Technology Data Exchange (ETDEWEB)

    Steier, C.; Emma, P.; Nishimura, H.; Papadopoulos, C.; Sannibale, F.

    2013-05-20

    The Next Generation Light Source will deliver high (MHz) repetition rate electron beams to an array of free electron lasers. Because of the significant average current in such a facility, effective beam collimation is extremely important to minimize radiation damage to undulators, prevent quenches of superconducting cavities, limit dose rates outside of the accelerator tunnel and prevent equipment damage. This paper describes the early conceptual design of a collimation system, as well as initial results of simulations to test its effectiveness.

  2. Collimation of fast electrons in critical density plasma channel

    OpenAIRE

    2015-01-01

    Significantly collimated fast electron beam with a divergence angle 10° (FWHM) is generated through the interaction of ultra-intense laser light with a uniform critical density plasma in experiments and 2D PIC simulations. In the experiment, the uniform critical density plasma is created by ionizing an ultra-low density foam target. The spacial distribution of the fast electron is observed by Imaging Plate. 2D PIC simulation and post process analysis reveal magnetic collimation of energetic e...

  3. Benchmarking of collimation tracking using RHIC beam loss data.

    Energy Technology Data Exchange (ETDEWEB)

    Robert-Demolaize,G.; Drees, A.

    2008-06-23

    State-of-the-art tracking tools were recently developed at CERN to study the cleaning efficiency of the Large Hadron Collider (LHC) collimation system. In order to estimate the prediction accuracy of these tools, benchmarking studies can be performed using actual beam loss measurements from a machine that already uses a similar multistage collimation system. This paper reviews the main results from benchmarking studies performed with specific data collected from operations at the Relativistic Heavy Ion Collider (RHIC).

  4. Mini-beam collimator applications at the Advanced Photon Source

    Energy Technology Data Exchange (ETDEWEB)

    Xu Shenglan, E-mail: sxu@anl.gov [GM/CA CAT, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Keefe, Lisa J.; Mulichak, Anne [IMCA CAT, Argonne National Laboratory, Argonne, IL 60439 (United States); Yan Lifen; Alp, Ercan E.; Zhao Jiyong [X-ray Sciences Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Fischetti, Robert F. [GM/CA CAT, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439 (United States)

    2011-09-01

    In 2007, the General Medicine and Cancer Institutes Collaborative Access Team (GM/CA CAT, Sector 23, Advanced Photon Source) began providing mini-beam collimators to its users. These collimators contained individual, 5- or 10-{mu}m pinholes and were rapidly exchangeable, thereby allowing users to tailor the beam size to their experimental needs. The use of these collimators provided a reduction in background noise, and thus improved the signal-to-noise ratio . Recent improvements in the collimator design include construction of the device from a monolithic piece of molybdenum with multiple pinholes mounted inside . This allows users to select from various size options from within the beamline control software without the realignment that was previously necessary. In addition, a new, 20-{mu}m pinhole has been added to create a 'quad-collimator', resulting in greater flexibility for the users. The mini-beam collimator is now available at multiple crystallographic beamlines and also is a part of the first Moessbauer Microscopic system at sector 3-ID.

  5. Parallel-hole collimator concept for stationary SPECT imaging.

    Science.gov (United States)

    Pato, Lara R V; Vandenberghe, Stefaan; Zedda, Tiziana; Van Holen, Roel

    2015-11-21

    Parallel-hole SPECT collimators have traditionally been manufactured by stacking sheets of lead foil or by casting. These techniques significantly restrict our options in terms of collimator geometry. However, recent developments in metal additive manufacturing are making novel collimator designs possible, giving rise to new opportunities in SPECT imaging. In this paper we propose an innovative type of collimator for stationary SPECT, using parallel-holes whose collimation direction depends on their axial position. Its main advantage compared to current stationary SPECT systems (which are based on pinholes) is that, using only axial bed translations, we can achieve complete angular sampling of an increased portion of the transaxial area of the collimator bore. This allows the system to be much more compact than current stationary SPECT systems that image objects of the same size. We describe three possible designs, for full-body, brain and small-animal imaging, respectively, and test their feasibility using simulations. The system modeling method is validated against realistic Monte Carlo simulations, and then used in the evaluation of the systems' performances and reconstructions. The simulations show that the system is able to reconstruct objects occupying the predicted field of view ([Formula: see text] of the transaxial area of the bore) without sampling artifacts. In particular, we perform reconstructions from noisy projection data obtained for an activity and scanning time similar to standard protocols for the three applications, and the resulting images indicate the possibility of using the proposed systems in practice.

  6. Dual self-image technique for beam collimation

    Science.gov (United States)

    Herrera-Fernandez, Jose Maria; Sanchez-Brea, Luis Miguel; Torcal-Milla, Francisco Jose; Morlanes, Tomas; Bernabeu, Eusebio

    2016-07-01

    We propose an accurate technique for obtaining highly collimated beams, which also allows testing the collimation degree of a beam. It is based on comparing the period of two different self-images produced by a single diffraction grating. In this way, variations in the period of the diffraction grating do not affect to the measuring procedure. Self-images are acquired by two CMOS cameras and their periods are determined by fitting the variogram function of the self-images to a cosine function with polynomial envelopes. This way, loss of accuracy caused by imperfections of the measured self-images is avoided. As usual, collimation is obtained by displacing the collimation element with respect to the source along the optical axis. When the period of both self-images coincides, collimation is achieved. With this method neither a strict control of the period of the diffraction grating nor a transverse displacement, required in other techniques, are necessary. As an example, a LED considering paraxial approximation and point source illumination is collimated resulting a resolution in the divergence of the beam of δ φ =+/- 1.57 μ {rad}.

  7. End-of-fill study on collimator tight settings

    CERN Document Server

    Assmann, R; Burkart, F; Cauchi, M; Deboy, D; Redaelli, S; Rossi, A; Schmidt, R; Valentino, G; Wollmann, D

    2012-01-01

    In 2010 and 2011 the collimation system has been operated with relaxed settings, i.e. with retractions between different collimator families larger than the nominal settings that provide optimum cleaning. This configuration ensured a sufficient cleaning performance at 3.5 TeV while allowing larger tolerances on orbit control. Tighter collimator settings were proposed to push the cleaning performance and to allow larger orbit margins between TCDQ dump protection and tertiary collimators, which opens the possibility to push further the LHC β* reach. After having verified with beam that the cleaning is improved as expected, the feasibility of tighter collimator settings must be addressed with high stored intensity. For this purpose, an end-of-fill study was proposed after a standard physics fill with 1380 bunches nominal bunches at 3.5 TeV, for a total stored energy of 95 MJ. During this test, primary and secondary collimators were moved to that tight settings after about 8 hours of stable physics conditions in...

  8. La pelade par plaques

    Science.gov (United States)

    Spano, Frank; Donovan, Jeff C.

    2015-01-01

    Résumé Objectif Présenter aux médecins de famille des renseignements de base pour faire comprendre les schémas thérapeutiques et les résultats des traitements pour la pelade par plaques, de même que les aider à identifier les patients pour qui une demande de consultation en dermatologie pourrait s’imposer. Sources des données Une recension a été effectuée dans PubMed pour trouver des articles pertinents concernant le traitement de la pelade par plaques. Message principal La pelade par plaques est une forme auto-immune de perte pileuse qui touche à la fois les enfants et les adultes. Même s’il n’y a pas de mortalité associée à la maladie, la morbidité découlant des effets psychologiques de la perte des cheveux peut être dévastatrice. Lorsque la pelade par plaques et le sous-type de la maladie sont identifiés, un schéma thérapeutique approprié peut être amorcé pour aider à arrêter la chute des cheveux et possiblement faire commencer la repousse. Les traitements de première intention sont la triamcinolone intralésionnelle avec des corticostéroïdes topiques ou du minoxidil ou les 2. Les médecins de famille peuvent prescrire ces traitements en toute sécurité et amorcer ces thérapies. Les cas plus avancés ou réfractaires pourraient avoir besoin de diphénylcyclopropénone topique ou d’anthraline topique. On peut traiter la perte de cils avec des analogues de la prostaglandine. Les personnes ayant subi une perte de cheveux abondante peuvent recourir à des options de camouflage ou à des prothèses capillaires. Il est important de surveiller les troubles psychiatriques en raison des effets psychologiques profonds de la perte de cheveux. Conclusion Les médecins de famille verront de nombreux patients qui perdent leurs cheveux. La reconnaissance de la pelade par plaques et la compréhension du processus pathologique sous-jacent permettent d’amorcer un schéma thérapeutique approprié. Les cas plus graves ou r

  9. Evaluation of calculation methods of collimator scatter factors in a linear accelerator equipped with MLC instead of lower collimators.

    Science.gov (United States)

    Kojima, Tomo; Sasaki, Koji

    2009-09-20

    In the monitor unit verification for high-energy radiation therapy, we evaluated methods of calculation of collimator scatter factors (S(c)) in a linear accelerator equipped with MLC instead of lower collimators. Routinely,S(c) is calculated from rectangular fields shaped by upper and lower jaws in the linear accelerator. However, this calculation method should not be used for the linear accelerator equipped with MLC instead of lower collimators. Consequently, we used a backprojected field at the flattening filter plane projected by calculation point's eye view on each MLC. We then attempted to deviseS(c) by using Clarkson's integration for these backprojected irregular fields. This method makes it possible to calculate collimator scatter factors in error of less than +/-0.3% in all of sixteen measured irregular fields.

  10. Scattered electron beams shaped by a multileaf collimator

    Science.gov (United States)

    Moran, Jean Marie

    Recent developments in conformal radiation therapy have focused primarily on applying computer-controlled equipment and techniques to photon beams. Despite favorable characteristics of the dose fall-off with depth for electron beams, their application to conformal therapy has been limited. Factors such as geometrically limiting applicator systems, lack of automatic field shaping, and dose calculation model limitations must be addressed before routine clinical use of electron beams for conformal radiotherapy becomes common. This work evaluates dose characteristics and modeling of dose distributions and output factors for a system specifically designed for computer-controlled collimation of dual-foil scattered and scanned electron beams. Dose characteristics determined from measured depth dose curves and profiles were evaluated for multileaf- collimated and applicator-collimated beams produced by the dual-foil scattered gantry of a two-gantry racetrack microtron system. The resulting dose distributions and characteristics were used to evaluate and modify the existing 3-D electron pencil beam algorithm in UMPlan, the University of Michigan treatment planning system, to predict relative dose distributions for MLC-shaped fields. Output factors (dose of a field relative to that of a reference field) were measured, analyzed, and modeled for MLC-collimated rectangular and shaped fields. For output factor calculations, two models were evaluated: a pencil beam-derived model and an empirical edge model originally developed for photon dose calculations. The current work shows that the dosimetric characteristics of MLC and applicator-collimated beams of the racetrack microtron are similar once the collimation geometry is accounted for. The dosimetric characteristics are also consistent with those for other dual-foil scattered machines with applicator systems and earlier generation scanned beams collimated with trimmer bars. By accounting for collimation geometry, electron

  11. Characteristics of scattered electron beams shaped with a multileaf collimator.

    Science.gov (United States)

    Moran, J M; Martel, M K; Bruinvis, I A; Fraass, B A

    1997-09-01

    Characteristics of dual-foil scattered electron beams shaped with a multileaf collimator (MLC) (instead of an applicator system) were studied. The electron beams, with energies between 10 and 25 MeV, were produced by a racetrack microtron using a dual-foil scattering system. For a range of field sizes, depth dose curves, profiles, penumbra width, angular spread in air, and effective and virtual source positions were compared. Measurements were made when the MLC alone provided collimation and when an applicator provided collimation. Identical penumbra widths were obtained at a source-to-surface distance of 85 cm for the MLC and 110 cm for the applicator. The MLC-shaped beams had characteristics similar to other machines which use trimmers or applicators to collimate scanned or scattered electron beams. Values of the effective source position and the angular spread parameter for the MLC beams were similar to those of the dual-foil scattered beams of the Varian Clinac 2100 CD and the scanned beams of the Sagittaire linear accelerators. A model, based on Fermi-Eyges multiple scattering theory, was adapted and applied successfully to predict penumbra width as a function of collimator-surface distance.

  12. An improved scattering routine for collimation tracking studies at LHC

    CERN Document Server

    Tambasco, Claudia; Salvachua Ferrando, Maria Belen; Cavoto, Gianluca

    The present Master thesis work has been carried out at CERN in the framework of the LHC (Large Hadron Collider) Collimation project. The LHC accelerates proton beams up to 7 TeV colliding in the experiment detectors installed in four points of the accelerator ring. The LHC is built to store a energy of 360MJ for each beam. The energy deposition induced by local beam losses could quench the superconducting magnets located around the accelerator beam pipes. To prevent and keep under control dangerous beam losses, an efficient collimation system is required. In addition, the achievable LHC beam intensity is related to the beam loss rate and, consequently, to the cleaning efficiency of the collimation system. Collimation studies at LHC are carried out also by means of simulations by using SixTrack, a dedicated simulation tool that tracks a large numbers of particles for many turns around the ring. The SixTrack code includes a scattering routine to model proton interactions with the material of the collimators j...

  13. Radiation shielding for the Main Injector collimation system

    Energy Technology Data Exchange (ETDEWEB)

    Rakhno, Igor; /Fermilab

    2007-12-01

    The results of Monte Carlo radiation shielding studies performed with the MARS15 code for the Main Injector collimation system are presented and discussed. A Proton Plan was developed recently at Fermilab for the benefit of the existing neutrino programs as well as to increase anti-proton production for the Tevatron programs [1]. As a part of the plan, the intensity of proton beams in the Main Injector (MI) should be increased by means of slip-stacking injection. In order to localize beam loss associated with the injection, a collimation system was designed [2] that satisfies all the radiation and engineering constraints. The system itself comprises a primary collimator and four secondary ones to which various masks are added. It is assumed that beam loss at the slip-stacking injection is equal to 5% of total intensity which is 5.5 x 10{sup 13} protons per pulse [2]. As far as pulse separation is 2.2 seconds, one has (5.5 x 10{sup 13}/2.2) x 0.05 = 1.25 x 10{sup 12} protons interacting per second with the primary collimator. In the paper the geometry model of the corresponding MI region and beam loss model are described. The model of the region was built by means of the MAD-MARS Beam Line Builder (MMBLB) [3] using results of the collimation studies [2]. The results of radiation shielding calculations performed with the MARS15 code [4] are presented.

  14. Parálisis cerebral :

    OpenAIRE

    Giral Lamenca, Mónica

    2015-01-01

    Se aborda el tema de la parálisis cerebral definiendo qué es, clasificando los tipos de parálisis dependiendo de la afectación y las características principales. Se explican algunos de sus tratamientos, se dan sistemas alternativos y/o aumentativos de comunicación para un alumno con PC (parálisis cerebral).

  15. Observing the onset of outflow collimation in a massive protostar

    CERN Document Server

    Carrasco-González, C; Cantó, J; Curiel, S; Surcis, G; Vlemmings, W H T; van Langevelde, H J; Goddi, C; Anglada, G; Kim, S -W; Kim, J -S; Gómez, J F

    2015-01-01

    The current paradigm of star formation through accretion disks, and magnetohydrodynamically driven gas ejections, predicts the development of collimated outflows, rather than expansion without any preferential direction. We present radio continuum observations of the massive protostar W75N(B)-VLA 2, showing that it is a thermal, collimated ionized wind and that it has evolved in 18 years from a compact source into an elongated one. This is consistent with the evolution of the associated expanding water-vapor maser shell, which changed from a nearly circular morphology, tracing an almost isotropic outflow, to an elliptical one outlining collimated motions. We model this behavior in terms of an episodic, short-lived, originally isotropic, ionized wind whose morphology evolves as it moves within a toroidal density stratification.

  16. Broadband super-collimation with low-symmetric photonic crystal

    Science.gov (United States)

    Giden, Ibrahim H.; Turduev, Mirbek; Kurt, Hamza

    2013-05-01

    We investigate dispersive properties of two dimensional photonic crystal (PC) called star-shaped PC (STAR-PC) in order to succeed super-collimation over a broad bandwidth. Both time- and frequency-domain numerical methods are conducted. Due to introduced low-symmetry in the primitive cell, flat contours are observed at the fifth band for transverse magnetic mode. The proposed structure supports a super-collimation effect over a broad wavelength range between 1443 nm and 1701 nm with a bandwidth of Δω = 16.42%. The intrinsic characteristic of STAR-PC provides in-plane beam propagation with a limited diffraction length of 120a, where a is the lattice constant. By means of STAR-PC, one may realize super-collimation based single-mode optical devices with a low insertion loss, reduced dispersion and wide bandwidth.

  17. Novel Materials for Collimators at LHC and its Upgrades

    CERN Document Server

    AUTHOR|(CDS)2108536; Dallocchio, Alessandro; Garlasche, Marco; Gentini, Luca; Gradassi, Paolo; Guinchard, Michael; Redaelli, Stefano; Rossi, Adriana; Sacristan De Frutos, Oscar; Carra, Federico; Quaranta, Elena

    2015-01-01

    Collimators for last-generation particle accelerators like the LHC, must be designed to withstand the close interaction with intense and energetic particle beams, safely operating over an extended range of temperatures in harsh environments, while minimizing the perturbing effects, such as instabilities induced by RF impedance, on the circulating beam. The choice of materials for collimator active components is of paramount importance to meet these requirements, which are to become even more demanding with the increase of machine performances expected in future upgrades, such as the High Luminosity LHC (HL-LHC). Consequently, a farreaching R&D program has been launched to develop novel materials with excellent thermal shock resistance and high thermal and electrical conductivity, replacing or complementing materials used for present collimators. Molybdenum Carbide - Graphite and Copper-Diamond composites have been so far identified as the most promising materials. The manufacturing methods, properties and...

  18. Scraping for LHC and collimation tests in the CERN SPS

    CERN Document Server

    Facchini, M; Gras, J J; Hutchins, S; Jung, R

    2005-01-01

    Scraping of the SPS beam prior to extraction towards the LHC will be important in order to remove the beam tails and ensure clean injection conditions. Scrapers recuperated from the ISR were installed in the SPS for this purpose. The scrapers are associated with a two stage collimation system using collimators previously installed in LEP to reduce the irradiated area in the SPS. Tests have been performed to demonstrate that with the help of these collimators, it is possible to scrape with very little contamination outside the scraping area. Another issue was whether enough time is left for ejection towards the LHC after scraping, before repopulation of the removed tails. This was investigated with the SPS rest gas profile monitor and synchrotron radiation telescope. The system is described and the results of these tests are presented and discussed.

  19. Updated Simulation Studies of Damage Limit of LHC Tertiary Collimators

    CERN Document Server

    AUTHOR|(CDS)2085459; Bertarelli, Alessandro; Bruce, Roderik; Carra, Federico; Cerutti, Francesco; Gradassi, Paolo; Lechner, Anton; Redaelli, Stefano; Skordis, Eleftherios

    2015-01-01

    The tertiary collimators (TCTs) in the LHC, installed in front of the experiments, in standard operation intercept fractions of 10−3 halo particles. However, they risk to be hit by high-intensity primary beams in case of asynchronous beam dump. TCT damage thresholds were initially inferred from results of destructive tests on a TCT jaw, supported by numerical simulations, assuming simplified impact scenarios with one single bunch hitting the jaw with a given impact parameter. In this paper, more realistic failure conditions, including a train of bunches and taking into account the full collimation hierarchy, are used to derive updated damage limits. The results are used to update the margins in the collimation hierarchy and could thus potentially have an influence on the LHC performance.

  20. Photon collimator system for the ILC Positron Source

    CERN Document Server

    Riemann, S; Moortgat-Pick, G; Ushakov, A

    2014-01-01

    High energy e+e- linear colliders are the next large scale project in particle physics. They need intense sources to achieve the required luminosity. In particular, the positron source must provide about 10E+14 positrons per second. The positron source for the International Linear Collider (ILC) is based on a helical undulator passed by the electron beam to create an intense circularly polarized photon beam. With these photons a longitudinally polarized positron beam is generated; the degree of polarization can be enhanced by collimating the photon beam. However, the high photon beam intensity causes huge thermal load in the collimator material. In this paper the thermal load in the photon collimator is discussed and a flexible design solution is presented.

  1. Betatron Cleaning for Heavy Ion Beams with IR7 Dispersion Suppressor Collimators

    CERN Document Server

    AUTHOR|(CDS)2083002; Bruce, Roderik; Jowett, John; Redaelli, Stefano

    2015-01-01

    The betatron collimators in IR7 constitute the backbone of the collimation system of the LHC. A fraction of the secondary halo protons or heavy-ion fragments, scattered out of the primary collimator, is not captured by the secondary collimators but hits cold magnets in the IR7 dispersion suppressor (DS) where the dispersion starts to increase. A possible approach to reduce these losses is based on the installation of additional collimators in the DS region. In this paper, simulations of the cleaning efficiency for Pb82+ ions are used to evaluate the effect of the additional collimators. The results indicate a significant improvement of the heavyion cleaning efficiency.

  2. Simulation of the low-frequency collimator impedance

    CERN Document Server

    Kroyer, T

    2008-01-01

    The low-frequency transverse collimator impedance constitutes a major part of the LHC impedance budget. In this paper numerical simulations for frequencies below 1 MHz using a commercial package are presented. From the 3D field solution of the two-wire simulations the transverse impedance is directly calculated. After a cross-check with theory for rotationally symmetric structures a geometry with two jaws and an LHC graphite collimator is examined. Furthermore, a simple physics picture that explains the principal characteristics of the impedance at high and low frequencies is given.

  3. ILC Beam delivery WG summary: Optics, collimation and background

    Energy Technology Data Exchange (ETDEWEB)

    Angal-Kalinin, D.; Jackson, F.; /Daresbury; Mokhov, N.V.; /Fermilab; Kuroda, S.; /KEK, Tsukuba; Seryi, A.A.; /SLAC

    2006-07-01

    The paper summarizes the work of the Beam Delivery working group (WG4) at Snowmass 2005 workshop, focusing on status of optics, layout, collimation and detector background. The strawman layout with two interaction regions was recommended at the first ILC workshop at KEK in November 2004. Two crossing-angle designs were included in this layout. The design of the ILC BDS has evolved since the first ILC workshop. The progress on the BDS design including the collimation system, and extraction line design have been reviewed and the design issues were discussed during the WG4 sessions at the Snowmass, and are described in this paper.

  4. Measurements of Collimator Wakefields at End Station A

    Energy Technology Data Exchange (ETDEWEB)

    Fernandez-Hernando, J.L.; /Daresbury; Molloy, S.; /SLAC; Smith, J.D.A.; /Cockcroft Inst. Accel. Sci. Tech.; Watson, Nigel Keith; /Birmingham U.

    2011-11-01

    The angular deflection of a 28.5 GeV electron beam passing off-axis between the jaws of a collimator, generating a transverse wakefield, were measured in End Station A (ESA) at SLAC. In total, fifteen different configurations of collimator geometry and material were tested: some were chosen for compatibility with previous measurements while others served to study the effect of geometry and taper angles (geometrical contribution to the wakefield) and the effect of the material resistivity (resistive contribution) to the imparted kick. This paper summarises the last update of preliminary experimental results before they are finalised. The reconstructed kick factor is compared to analytical calculations and simulations.

  5. Impedance Studies for the Phase 2 LHC Collimators

    CERN Document Server

    Métral, E; Grudiev, A; Kroyer, T; Zotter, B; Roncarolo, F; Salvant, B

    2010-01-01

    The LHC phase 2 collimation project aims at gaining a factor ten in cleaning efficiency, robustness and impedance reduction. From the impedance point of view, several ideas emerged during the last year, such as using dielectric collimators, slots or rods in copper plates, or Litz wires. The purpose of this paper is to discuss the possible choices, showing analytical estimates, electromagnetic simulations performed using Maxwell, HFSS and GdFidL, and preliminary bench measurements. The corresponding complex tune shifts are computed for the different cases and compared on the stability diagram defined by the settings of the Landau octupoles available in the LHC at 7 TeV.

  6. ParB spreading requires DNA bridging

    NARCIS (Netherlands)

    Graham, Thomas G. W.; Wang, Xindan; Song, Dan; Etson, Candice M.; van Oijen, Antoine M.; Rudner, David Z.; Loparo, Joseph J.

    2014-01-01

    The parABS system is a widely employed mechanism for plasmid partitioning and chromosome segregation in bacteria. ParB binds to parS sites on plasmids and chromosomes and associates with broad regions of adjacent DNA, a phenomenon known as spreading. Although essential for ParB function, the mechani

  7. Advances in pinhole and multi-pinhole collimators for single photon emission computed tomography imaging.

    Science.gov (United States)

    Islamian, Jalil Pirayesh; Azazrm, AhmadReza; Mahmoudian, Babak; Gharapapagh, Esmail

    2015-01-01

    The collimator in single photon emission computed tomography (SPECT), is an important part of the imaging chain. One of the most important collimators that used in research, preclinical study, small animal, and organ imaging is the pinhole collimator. Pinhole collimator can improve the tradeoff between sensitivity and resolution in comparison with conventional parallel-hole collimator and facilities diagnosis. However, a major problem with pinhole collimator is a small field of view (FOV). Multi-pinhole collimator has been investigated in order to increase the sensitivity and FOV with a preserved spatial resolution. The geometry of pinhole and multi-pinhole collimators is a critical factor in the image quality and plays a key role in SPECT imaging. The issue of the material and geometry for pinhole and multi-pinhole collimators have been a controversial and much disputed subject within the field of SPECT imaging. On the other hand, recent developments in collimator optimization have heightened the need for appropriate reconstruction algorithms for pinhole SPECT imaging. Therefore, iterative reconstruction algorithms were introduced to minimize the undesirable effect on image quality. Current researches have focused on geometry and configuration of pinhole and multi-pinhole collimation rather than reconstruction algorithm. The lofthole and multi-lofthole collimator are samples of novel designs. The purpose of this paper is to provide a review on recent researches in the pinhole and multi-pinhole collimators for SPECT imaging.

  8. Collimation of energetic neutrinos and muons inside EAS cores

    Directory of Open Access Journals (Sweden)

    Cherif Talai Mohammed

    2013-06-01

    Full Text Available High-energy muon and neutrino components are simulated inside cores of EAS generated by primary protons and heavy nuclei of energies 1014-1020 eV. The collimation of muons and neutrinos inside the core is compared with present penetrating beams generated by accelerators.

  9. Geometric Beam Coupling Impedance of LHC Secondary Collimators

    CERN Document Server

    Frasciello, O; Zobov, M; Grudiev, A; Mounet, N; Salvant, B

    2014-01-01

    The High Luminosity LHC project is aimed at increasing the LHC luminosity by an order of magnitude. One of the key ingredients to achieve the luminosity goal is the beam intensity increase. In order to keep under control beam instabilities and to avoid excessive power losses a careful design of new vacuum chamber components and an improvement of the present LHC impedance model are required. Collimators are the main impedance contributors. Measurements with beam have revealed that the betatron coherent tune shifts were by about a factor of 2 higher with respect to the theoretical predictions based on the current model. Up to now the resistive wall impedance has been considered as the major impedance contribution for collimators. By carefully simulating their geometric impedance we show that for the graphite collimators with half-gaps higher than 10 mm the geometric impedance exceeds the resistive wall one. In turn, for the tungsten collimators the geometric impedance dominates for all used gap values. Hence, i...

  10. Geometric beam coupling impedance of LHC secondary collimators

    Energy Technology Data Exchange (ETDEWEB)

    Frasciello, Oscar, E-mail: oscar.frasciello@lnf.infn.it [Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali di Frascati, Via Enrico Fermi 40, 00044 Frascati (Italy); Tomassini, Sandro; Zobov, Mikhail [Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali di Frascati, Via Enrico Fermi 40, 00044 Frascati (Italy); Salvant, Benoit; Grudiev, Alexej; Mounet, Nicolas [CERN, CH-1211 Geneva 23 (Switzerland)

    2016-02-21

    The High Luminosity LHC project is aimed at increasing the LHC luminosity by an order of magnitude. One of the key ingredients to achieve the luminosity goal is the beam intensity increase. In order to keep beam instabilities under control and to avoid excessive power losses a careful design of new vacuum chamber components and an improvement of the present LHC impedance model are required. Collimators are among the major impedance contributors. Measurements with beam have revealed that the betatron coherent tune shifts were higher by about a factor of 2 with respect to the theoretical predictions based on the LHC impedance model up to 2012. In that model the resistive wall impedance has been considered as the dominating impedance contribution for collimators. By carefully simulating also their geometric impedance we have contributed to the update of the LHC impedance model, reaching also a better agreement between the measured and simulated betatron tune shifts. During the just ended LHC Long Shutdown I (LSI), TCS/TCT collimators were replaced by new devices embedding BPMs and TT2-111R ferrite blocks. We present here preliminary estimations of their broad-band impedance, showing that an increase of about 20% is expected in the kick factors with respect to previous collimators without BPMs.

  11. The practical Pomeron for high energy proton collimation

    Energy Technology Data Exchange (ETDEWEB)

    Appleby, R.B. [University of Manchester, The Cockcroft Institute, Manchester (United Kingdom); Barlow, R.J.; Toader, A. [The University of Huddersfield, Huddersfield (United Kingdom); Molson, J.G. [Univ. Paris-Sud, CNRS/IN2P3, Universite Paris-Saclay, LAL, Orsay (France); Serluca, M. [CERN, Geneva (Switzerland)

    2016-10-15

    We present a model which describes proton scattering data from ISR to Tevatron energies, and which can be applied to collimation in high energy accelerators, such as the LHC and FCC. Collimators remove beam halo particles, so that they do not impinge on vulnerable regions of the machine, such as the superconducting magnets and the experimental areas. In simulating the effect of the collimator jaws it is crucial to model the scattering of protons at small momentum transfer t, as these protons can subsequently survive several turns of the ring before being lost. At high energies these soft processes are well described by Pomeron exchange models. We study the behaviour of elastic and single-diffractive dissociation cross sections over a wide range of energy, and show that the model can be used as a global description of the wide variety of high energy elastic and diffractive data presently available. In particular it models low mass diffraction dissociation, where a rich resonance structure is present, and thus predicts the differential and integrated cross sections in the kinematical range appropriate to the LHC. We incorporate the physics of this model into the beam tracking code MERLIN and use it to simulate the resulting loss maps of the beam halo lost in the collimators in the LHC. (orig.)

  12. The practical Pomeron for high energy proton collimation

    Science.gov (United States)

    Appleby, R. B.; Barlow, R. J.; Molson, J. G.; Serluca, M.; Toader, A.

    2016-10-01

    We present a model which describes proton scattering data from ISR to Tevatron energies, and which can be applied to collimation in high energy accelerators, such as the LHC and FCC. Collimators remove beam halo particles, so that they do not impinge on vulnerable regions of the machine, such as the superconducting magnets and the experimental areas. In simulating the effect of the collimator jaws it is crucial to model the scattering of protons at small momentum transfer t, as these protons can subsequently survive several turns of the ring before being lost. At high energies these soft processes are well described by Pomeron exchange models. We study the behaviour of elastic and single-diffractive dissociation cross sections over a wide range of energy, and show that the model can be used as a global description of the wide variety of high energy elastic and diffractive data presently available. In particular it models low mass diffraction dissociation, where a rich resonance structure is present, and thus predicts the differential and integrated cross sections in the kinematical range appropriate to the LHC. We incorporate the physics of this model into the beam tracking code MERLIN and use it to simulate the resulting loss maps of the beam halo lost in the collimators in the LHC.

  13. Crystal Collimation with protons at flat top energy

    CERN Document Server

    Rossi, Roberto; Galluccio, Francesca; Masi, Alessandro; Mirarchi, Daniele; Montesano, Simone; Valentino, Gianluca; Scandale, Walter; CERN. Geneva. ATS Department

    2017-01-01

    During this MD, performed on November 6th, 2015, bent silicon crystals were tested with proton beams for a possible usage of crystal-assisted collimation. Tests were performed at both injection and at top energy using horizontal crystal. Proton channeling was observed for the first time at 6.5 TeV.

  14. MD1878: Operation with primary collimators at tighter settings

    CERN Document Server

    Mirarchi, Daniele; Biancacci, Nicolo; Bruce, Roderik; Buffat, Xavier; Carver, Lee Robert; Fiascaris, Maria; Mereghetti, Alessio; Redaelli, Stefano; Rossi, Roberto; Salvachua Ferrando, Belen Maria; Soderen, Martin; Trad, Georges

    2017-01-01

    Primary (TCP) collimators of the betatron cleaning insertion determine the betatron cut of the LHC beam. During the 2016 they were set at 5.5 nominal beam sigmas at 6.5 TeV (i.e. by using a normalized emittance " = 3:5 m is used). Reducing their settings is a possible way to push the at the LHC, which depends on the collimation hierarchy. This study aims at understanding possible limitations of operating the LHC with tighter settings of the primary collimators. This is a crucial input to the choice of operational conguration in terms of at the LHC as well as at the HL-LHC. This study follows a successful MD done in block 3 to understand limitations from TCP impedance [1]. The outcome of this MD can also have an impact for the design of the FCC collimation system, which is currently based on the present TCP gaps. Studies of beam stability as a function of octupole current, transverse feedback gain (ADT) and transverse separation at the IPs were also carried out.

  15. Implementation of intensity modulation with dynamic multileaf collimation

    Energy Technology Data Exchange (ETDEWEB)

    Wong, J.W.; Yu, C.; Jaffray, D. [William Beaumont Hospital, Royal Oak, MI (United States)

    1995-12-01

    The computer-controlled multileaf collimator (MLC) marks one of the most important advances in radiation therapy. The device efficiently replaces manual blocking to shape fields and can be used to modulate beam intensity. The results of a research programme at William Beaumont Hospital, aimed at bringing dynamic intensity modulation into clinical use, are discussed.

  16. EPICS Controlled Collimator for Controlling Beam Sizes in HIPPO

    Energy Technology Data Exchange (ETDEWEB)

    Napolitano, Arthur Soriano [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Vogel, Sven C. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-08-03

    Controlling the beam spot size and shape in a diffraction experiment determines the probed sample volume. The HIPPO - High-Pressure-Preferred Orientation– neutron time-offlight diffractometer is located at the Lujan Neutron Scattering Center in Los Alamos National Laboratories. HIPPO characterizes microstructural parameters, such as phase composition, strains, grain size, or texture, of bulk (cm-sized) samples. In the current setup, the beam spot has a 10 mm diameter. Using a collimator, consisting of two pairs of neutron absorbing boron-nitride slabs, horizontal and vertical dimensions of a rectangular beam spot can be defined. Using the HIPPO robotic sample changer for sample motion, the collimator would enable scanning of e.g. cylindrical samples along the cylinder axis by probing slices of such samples. The project presented here describes implementation of such a collimator, in particular the motion control software. We utilized the EPICS (Experimental Physics Interface and Control System) software interface to integrate the collimator control into the HIPPO instrument control system. Using EPICS, commands are sent to commercial stepper motors that move the beam windows.

  17. Inverse-collimated proton radiography for imaging thin materials

    Science.gov (United States)

    Freeman, Matthew S.; Allison, Jason; Andrews, Malcolm; Ferm, Eric; Goett, John J.; Kwiatkowski, Kris; Lopez, Julian; Mariam, Fesseha; Marr-Lyon, Mark; Martinez, Michael; Medina, Jason; Medina, Patrick; Merrill, Frank E.; Morris, Chris L.; Murray, Matthew M.; Nedrow, Paul; Neukirch, Levi P.; Prestridge, Katherine; Rigg, Paolo; Saunders, Alexander; Schurman, Tamsen; Tainter, Amy; Trouw, Frans; Tupa, Dale; Tybo, Josh; Vogan-McNeil, Wendy; Wilde, Carl

    2017-01-01

    Relativistic, magnetically focused proton radiography was invented at Los Alamos National Laboratory using the 800 MeV LANSCE beam and is inherently well-suited to imaging dense objects, at areal densities >20 g cm-2. However, if the unscattered portion of the transmitted beam is removed at the Fourier plane through inverse-collimation, this system becomes highly sensitive to very thin media, of areal densities <100 mg cm-2. Here, this inverse-collimation scheme is described in detail and demonstrated by imaging Xe gas with a shockwave generated by an aluminum plate compressing the gas at Mach 8.8. With a 5-mrad inverse collimator, an areal density change of just 49 mg cm-2 across the shock front is discernible with a contrast-to-noise ratio of 3. Geant4 modeling of idealized and realistic proton transports can guide the design of inverse-collimators optimized for specific experimental conditions and show that this technique performs better for thin targets with reduced incident proton beam emittance. This work increases the range of areal densities to which the system is sensitive to span from ˜25 mg cm-2 to 100 g cm-2, exceeding three orders of magnitude. This enables the simultaneous imaging of a dense system as well as thin jets and ejecta material that are otherwise difficult to characterize with high-energy proton radiography.

  18. The collimation of magnetic jets by disk winds

    CERN Document Server

    Globus, Noemie

    2016-01-01

    The collimation of a Poynting-flux dominated jet by a wind emanating from the surface of an accretion flow is computed using a semi-analytic model. The injection of the disk wind is treated as a boundary condition in the equatorial plane, and its evolution is followed by invoking a prescribed geometry of streamlines. Solutions are obtained for a wide range of disk wind parameters. It is found that jet collimation generally occurs when the total wind power exceeds about ten percents of the jet power. For moderate wind powers we find gradual collimation. For strong winds we find rapid collimation followed by focusing of the jet, after which it remains narrow over many Alfv\\'en crossing times before becoming conical. We estimate that in the later case the jet's magnetic field may be dissipated by the current-driven kink instability over a distance of a few hundreds gravitational radii. We apply the model to M87 and show that the observed parabolic shape of the radio jet within the Bondi radius can be reproduced ...

  19. Inverse-collimated proton radiography for imaging thin materials.

    Science.gov (United States)

    Freeman, Matthew S; Allison, Jason; Andrews, Malcolm; Ferm, Eric; Goett, John J; Kwiatkowski, Kris; Lopez, Julian; Mariam, Fesseha; Marr-Lyon, Mark; Martinez, Michael; Medina, Jason; Medina, Patrick; Merrill, Frank E; Morris, Chris L; Murray, Matthew M; Nedrow, Paul; Neukirch, Levi P; Prestridge, Katherine; Rigg, Paolo; Saunders, Alexander; Schurman, Tamsen; Tainter, Amy; Trouw, Frans; Tupa, Dale; Tybo, Josh; Vogan-McNeil, Wendy; Wilde, Carl

    2017-01-01

    Relativistic, magnetically focused proton radiography was invented at Los Alamos National Laboratory using the 800 MeV LANSCE beam and is inherently well-suited to imaging dense objects, at areal densities >20 g cm(-2). However, if the unscattered portion of the transmitted beam is removed at the Fourier plane through inverse-collimation, this system becomes highly sensitive to very thin media, of areal densities <100 mg cm(-2). Here, this inverse-collimation scheme is described in detail and demonstrated by imaging Xe gas with a shockwave generated by an aluminum plate compressing the gas at Mach 8.8. With a 5-mrad inverse collimator, an areal density change of just 49 mg cm(-2) across the shock front is discernible with a contrast-to-noise ratio of 3. Geant4 modeling of idealized and realistic proton transports can guide the design of inverse-collimators optimized for specific experimental conditions and show that this technique performs better for thin targets with reduced incident proton beam emittance. This work increases the range of areal densities to which the system is sensitive to span from ∼25 mg cm(-2) to 100 g cm(-2), exceeding three orders of magnitude. This enables the simultaneous imaging of a dense system as well as thin jets and ejecta material that are otherwise difficult to characterize with high-energy proton radiography.

  20. Creating a collimated ultrasound beam in highly attenuating fluids.

    Science.gov (United States)

    Raeymaekers, Bart; Pantea, Cristian; Sinha, Dipen N

    2012-04-01

    We have devised a method, based on a parametric array concept, to create a low-frequency (300-500 kHz) collimated ultrasound beam in fluids highly attenuating to sound. This collimated beam serves as the basis for designing an ultrasound visualization system that can be used in the oil exploration industry for down-hole imaging in drilling fluids. We present the results of two different approaches to generating a collimated beam in three types of highly attenuating drilling mud. In the first approach, the drilling mud itself was used as a nonlinear mixing medium to create a parametric array. However, the short absorption length in mud limits the mixing length and, consequently, the resulting beam is weak and broad. In the second improved approach, the beam generation process was confined to a separate "frequency mixing tube" that contained an acoustically non-linear, low attenuation medium (e.g., water) that allowed establishing a usable parametric array in the mixing tube. A low-frequency collimated beam was thus created prior to its propagation into the drilling fluid. Using the latter technique, the penetration depth of the low frequency ultrasound beam in the drilling fluid was significantly extended. We also present measurements of acoustic nonlinearity in various types of drilling mud.

  1. The collimation of magnetic jets by disc winds

    Science.gov (United States)

    Globus, N.; Levinson, A.

    2016-09-01

    The collimation of a Poynting-flux dominated jet by a wind emanating from the surface of an accretion flow is computed using a semi-analytic model. The injection of the disc wind is treated as a boundary condition in the equatorial plane, and its evolution is followed by invoking a prescribed geometry of streamlines. Solutions are obtained for a wide range of disc wind parameters. It is found that jet collimation generally occurs when the total wind power exceeds about 10 percents of the jet power. For moderate wind powers, we find gradual collimation. For strong winds, we find rapid collimation followed by focusing of the jet, after which it remains narrow over many Alfvén crossing times before becoming conical. We estimate that in the later case, the jet's magnetic field may be dissipated by the current-driven kink instability over a distance of a few hundreds gravitational radii. We apply the model to M87 and show that the observed parabolic shape of the radio jet within the Bondi radius can be reproduced provided that the wind injection zone extends to several hundreds gravitational radii, and that its total power is about one-third of the jet power. The radio spectrum can be produced by synchrotron radiation of relativistically hot, thermal electrons in the sheath flow surrounding the inner jet.

  2. MD1878: Operation with primary collimators at tighter settings

    CERN Document Server

    Mirarchi, Daniele; Biancacci, Nicolo; Bruce, Roderik; Buffat, Xavier; Carver, Lee Robert; Fiascaris, Maria; Mereghetti, Alessio; Redaelli, Stefano; Rossi, Roberto; Salvachua Ferrando, Belen Maria; Soderen, Martin; Trad, Georges; CERN. Geneva. ATS Department

    2017-01-01

    Primary (TCP) collimators of the betatron cleaning insertion determine the betatron cut of the LHC beam. During the 2016 they were set at 5.5 nominal beam sigmas at 6.5 TeV (i.e. by using a normalized emittance ε* = 3:5 μm is used). Reducing their settings is a possible way to push the ß* at the LHC, which depends on the collimation hierarchy. This study aims at understanding possible limitations of operating the LHC with tighter settings of the primary collimators. This is a crucial input to the choice of operational configuration in terms of ß* at the LHC as well as at the HL-LHC. This study follows a successful MD done in block 3 to understand limitations from TCP impedance [1]. The outcome of this MD can also have an impact for the design of the FCC collimation system, which is currently based on the present TCP gaps. Studies of beam stability as a function of octupole current, transverse feedback gain (ADT) and transverse separation at the IPs were also carried out.

  3. Slow axis collimation lens with variable curvature radius for semiconductor laser bars

    Science.gov (United States)

    Xiong, Ling-Ling; Cai, Lei; Zheng, Yan-Fang; Liu, Hui; Zhang, Pu; Nie, Zhi-Qiang; Liu, Xing-Sheng

    2016-03-01

    Based on Snell's law and the constant phase in the front of optical field, a design method of the slow axis collimation lens with variable curvature radius is proposed for semiconductor laser bars. Variable radius of the collimator is designed by the transmission angle, and it is demonstrated that the collimator has good beam collimation ability by material with low refractive index. Resorting to the design thought of finite element method, the surface of the collimator has been divided, and it is feasible to be fabricated. This method is applied as an example in collimation of a 976 nm semiconductor laser bar. 6 mrad divergence angle of collimated beam at slow axis is realized by the designed collimation lens with refraction index of 1.51.

  4. Automatic Computer Algorithms for Beam-based Setup of the LHC Collimators

    CERN Document Server

    Valentino, G; Assmann, R W; Bruce, R; Redaelli, S; Salvachua, B; Wollmann, D

    2012-01-01

    Beam-based setup of the LHC collimators is necessary to establish the beam centers and beam sizes at the collimator locations and determine the operational settings during various stages of the LHC machine cycle.

  5. Observation of strong leakage reduction in crystal assisted collimation of the SPS beam

    Science.gov (United States)

    Scandale, W.; Arduini, G.; Butcher, M.; Cerutti, F.; Garattini, M.; Gilardoni, S.; Lechner, A.; Losito, R.; Masi, A.; Mereghetti, A.; Metral, E.; Mirarchi, D.; Montesano, S.; Redaelli, S.; Rossi, R.; Schoofs, P.; Smirnov, G.; Bagli, E.; Bandiera, L.; Baricordi, S.; Dalpiaz, P.; Germogli, G.; Guidi, V.; Mazzolari, A.; Vincenzi, D.; Claps, G.; Dabagov, S.; Hampai, D.; Murtas, F.; Cavoto, G.; Iacoangeli, F.; Ludovici, L.; Santacesaria, R.; Valente, P.; Galluccio, F.; Afonin, A. G.; Chesnokov, Yu. A.; Durum, A. A.; Maisheev, V. A.; Sandomirskiy, Yu. E.; Yanovich, A. A.; Kovalenko, A. D.; Taratin, A. M.; Gavrikov, Yu. A.; Ivanov, Yu. M.; Lapina, L. P.; Fulcher, J.; Hall, G.; Pesaresi, M.; Raymond, M.

    2015-09-01

    In ideal two-stage collimation systems, the secondary collimator-absorber should have its length sufficient to exclude practically the exit of halo particles with large impact parameters. In the UA9 experiments on the crystal assisted collimation of the SPS beam a 60 cm long tungsten bar is used as a secondary collimator-absorber which is insufficient for the full absorption of the halo protons. Multi-turn simulation studies of the collimation allowed to select the position for the beam loss monitor downstream the collimation area where the contribution of particles deflected by the crystal in channeling regime but emerging from the secondary collimator-absorber is considerably reduced. This allowed observation of a strong leakage reduction of halo protons from the SPS beam collimation area, thereby approaching the case with an ideal absorber.

  6. Halo collimation of light and heavy ions in the FAIR synchrotron SIS100

    Energy Technology Data Exchange (ETDEWEB)

    Prokhorov, Ivan [TU Darmstadt (Germany); Strasik, Ivan [GSI, Darmstadt (Germany); Boine-Frankenheim, Oliver [TU Darmstadt (Germany); GSI, Darmstadt (Germany)

    2013-07-01

    The halo collimation system in the FAIR synchrotron SIS100 is needed to prevent an interception of the beam halo particles by the accelerator structure. The two-stage betatron collimation system is considered for operation with protons and fully-stripped ions. An adequate numerical simulation of the collimation system performance taking into account a precise description of the following processes: 1) particle scattering by the primary collimator; 2) inelastic nuclear interaction of the ions with the collimator foil; 3) momentum losses during the interaction with the collimator foil; 4) multi-turn tracking of the particles with the collimation optics included. The concept of the halo collimation, the current status of research and future plans are presented. Scattering processes and momentum losses were analytically estimated for various ion species and energies; analytical results were compared with the numerical simulations by the ATIMA code. Preliminary results of particle tracking using MAD-X code were obtained.

  7. Execution of mantle field with multileaf collimator: A simple approach

    Directory of Open Access Journals (Sweden)

    Prabhakar Ramachandran

    2008-01-01

    Full Text Available Background: Until very recently mantle field radiotherapy remained the gold standard for the treatment of favorable early-stage Hodgkin′s lymphoma. The classic mantle includes all the major lymph nodes above the diaphragm and extends from the inferior portion of the mandible to the level of the insertion of the diaphragm. Aims: To describe a simple technique that has been devised to treat the mantle field with the help of multileaf collimator and using computed tomography (CT-based treatment planning. Materials and Methods: CT scan was performed with the patient in the supine position and the datasets were transferred to the Eclipse™ treatment planning system. Elekta Precise™ linear accelerator equipped with 40 pairs of multileaf collimator (MLC was used for the execution of the mantle field. The MLC′s shapes were designed to take the shape of the conventional customized blocks used for treatment of mantle field. The anterior mantle field was divided into three separate MLC segments with the collimator kept at 0°. The first MLC segment was shaped to cover the neck, clavicular regions, and mediastinum. The second and the third MLC segments covered the right and left axilla, respectively. The posterior fields were opposed to the anterior subfields in a similar fashion. The dose was prescribed at the midplane, using reference points. Results and Conclusion: The technique described in this study is very simple, easy to implement, and avoids unnecessary delay in the execution of the mantle field. The mantle field can be easily shaped with the multileaf collimators, without any collimator rotation.

  8. Variable Circular Collimator in Robotic Radiosurgery: A Time-Efficient Alternative to a Mini-Multileaf Collimator?

    NARCIS (Netherlands)

    Van de Water, S.; Hoogeman, M.S.; Breedveld, S.; Nuyttens, J.J.M.E.; Schaart, D.R.; Heijmen, B.J.M.

    2011-01-01

    urpose Compared with many small circular beams used in CyberKnife treatments, beam’s eye view-shaped fields are generally more time-efficient for dose delivery. However, beam’s eye view-shaping devices, such as a mini-multileaf collimator (mMLC), are not presently available for CyberKnife, although

  9. Improved robustness of the LHC collimation system by operating with a jaw-beam angle

    CERN Document Server

    Lari, L; Rossi, A; Cauchi, M; Faus-Golfe, A

    2012-01-01

    The robustness of the Phase I collimation system could be improved playing with the angular orientation of each single jaw. A preliminary study on the asymmetric misalignment of the collimator jaws, scanning through different jaw angles and varying beam sizes and energy, have been carried out, aiming at minimizing the energy deposited on metallic collimators, following an asynchronous dump.

  10. Development of the ICOSIM Program and Application to Magnetised Collimators in the LHC

    CERN Document Server

    Holden, N

    2008-01-01

    This note has two parts. The first part provides documentation for the ICOSIM program used to simulate collimation of Ion beams. The second part contains results of a preliminary study of the effectiveness of magnetised collimators as a means to increase collimation efficiency for lead ion beams in the LHC.

  11. Elusloom lennukiga puhkusele / Inge Parring

    Index Scriptorium Estoniae

    Parring, Inge

    2003-01-01

    Ilmunud ka: Delovõje Vedomosti 1. okt. lk. 13. Air Cargo Estonia/ACE Logisticsi müügijuht Inge Parring tutvustab elusloomade transpordivõimalusi. Vt. samas: Loomade transportimiseks vajalikud dokumendid

  12. Pars planitis in a family.

    Science.gov (United States)

    Tejada, P; Sanz, A; Criado, D

    1994-01-01

    The familial occurrence of pars planitis is rare. We have found ten cases reported previously. We describe a new case of pars planitis in a family. The affected members included a mother and two of her four children. The family was tested for HLA antigens in order to establish a comparison with others HLA types by different authors. We have not identified any cause for the familial occurrence of this disease. We discuss the role of genetic and ambiental factors.

  13. Prokaryotic ParA-ParB-parS system links bacterial chromosome segregation with the cell cycle.

    Science.gov (United States)

    Mierzejewska, Jolanta; Jagura-Burdzy, Grażyna

    2012-01-01

    While the essential role of episomal par loci in plasmid DNA partitioning has long been appreciated, the function of chromosomally encoded par loci is less clear. The chromosomal parA-parB genes are conserved throughout the bacterial kingdom and encode proteins homologous to those of the plasmidic Type I active partitioning systems. The third conserved element, the centromere-like sequence called parS, occurs in several copies in the chromosome. Recent studies show that the ParA-ParB-parS system is a key player of a mitosis-like process ensuring proper intracellular localization of certain chromosomal regions such as oriC domain and their active and directed segregation. Moreover, the chromosomal par systems link chromosome segregation with initiation of DNA replication and the cell cycle.

  14. A radial collimator for a time-of-flight neutron spectrometer

    Energy Technology Data Exchange (ETDEWEB)

    Stone, M. B.; Abernathy, D. L. [Quantum Condensed Matter Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Niedziela, J. L.; Loguillo, M. J.; Overbay, M. A. [Instrument and Source Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

    2014-08-15

    We have engineered and installed a radial collimator for use in the scattered beam of a neutron time-of-flight spectrometer at a spallation neutron source. The radial collimator may be used with both thermal and epithermal neutrons, reducing the detected scattering intensity due to material outside of the sample region substantially. The collimator is located inside of the sample chamber of the instrument, which routinely cycles between atmospheric conditions and cryogenic vacuum. The oscillation and support mechanism of the collimator allow it to be removed from use without breaking vacuum. We describe here the design and characterization of this radial collimator.

  15. A radial collimator for a time-of-flight neutron spectrometer

    Science.gov (United States)

    Stone, M. B.; Niedziela, J. L.; Loguillo, M. J.; Overbay, M. A.; Abernathy, D. L.

    2014-08-01

    We have engineered and installed a radial collimator for use in the scattered beam of a neutron time-of-flight spectrometer at a spallation neutron source. The radial collimator may be used with both thermal and epithermal neutrons, reducing the detected scattering intensity due to material outside of the sample region substantially. The collimator is located inside of the sample chamber of the instrument, which routinely cycles between atmospheric conditions and cryogenic vacuum. The oscillation and support mechanism of the collimator allow it to be removed from use without breaking vacuum. We describe here the design and characterization of this radial collimator.

  16. Impedance simulations and measurements on the LHC collimators with embedded beam position monitors

    CERN Document Server

    Biancacci, N; Kuczerowski, J; Métral,; Mounet, N; Salvant, B; Mostacci, A; Frasciello, O; Zobov, M

    2017-01-01

    The LHC collimation system is a critical element for the safe operation of the LHC machine. The necessity of fast accurate positioning of the collimator’s jaws, recently introduced the need to have button beam position monitors directly embedded in the jaws extremities of the LHC tertiary collimators and some secondary collimators. This addition led to a new design of these collimators including ferrites to damp higher order modes instead of rf fingers. In this work we will present the impedance bench measurements and simulations on a TCT (Transverse Tertiary Collimator) prototype including estimations for beam stability for the LHC.

  17. Impedance simulations and measurements on the LHC collimators with embedded beam position monitors

    Directory of Open Access Journals (Sweden)

    N. Biancacci

    2017-01-01

    Full Text Available The LHC collimation system is a critical element for the safe operation of the LHC machine. The necessity of fast accurate positioning of the collimator’s jaws, recently introduced the need to have button beam position monitors directly embedded in the jaws extremities of the LHC tertiary collimators and some secondary collimators. This addition led to a new design of these collimators including ferrites to damp higher order modes instead of rf fingers. In this work we will present the impedance bench measurements and simulations on a TCT (Transverse Tertiary Collimator prototype including estimations for beam stability for the LHC.

  18. Experimental demonstration of an inertial collimation mechanism in nested outflows

    CERN Document Server

    Yurchak, R; Pelka, A; Pikuz, S; Falize, E; Vinci, T; Koenig, M; Loupias, B; Benuzzi-Mounaix, A; Fatenejad, M; Tzeferacos, P; Lamb, D Q; Blackman, E G

    2014-01-01

    Interaction between a central outflow and a surrounding wind is common in astrophysical sources powered by accretion. Understanding how the interaction might help to collimate the inner central outflow is of interest for assessing astrophysical jet formation paradigms. In this context, we studied the interaction between two nested supersonic plasma flows generated by focusing a long pulse high-energy laser beam onto a solid target. A nested geometry was created by shaping the energy distribution at the focal spot with a dedicated phase plate. Optical and X-ray diagnostics were used to study the interacting flows. Experimental results and numerical hydrodynamic simulations indeed show the formation of strongly collimated jets. Our work experimentally confirms the "shock-focused inertial confinement" mechanism proposed in previous theoretical astrophysics investigations.

  19. Ocular vergence measurement in projected and collimated simulator displays.

    Science.gov (United States)

    Morahan, P; Meehan, J W; Patterson, J; Hughes, P K

    1998-09-01

    The purpose of this study was to investigate electrooculography (EOG) as a measurement of ocular vergence in both collimated and projected simulator environments. The task required participants to shift their gaze between a central fixation point and a target appearing at one of three eccentricities. EOG was effective in recording ocular vergence. The EOG results were similar between collimated and projected displays, except for differences in vergence changes during lateral movement of the eyes, and ocular excursions downward elicited a greater EOG response than the reverse upward movement. The computer-based technique of recording vergence was found to produce measurable traces from a majority of participants. The technique has potential for further development as a tool for measuring ocular vergence in virtual environments where methods that require the wearing of head-mounted apparatus to track ocular structures (e.g., the pupil), which cannot be worn at the same time as a flight or flight-simulator helmet, are unsuitable.

  20. On Magnetic Self-Collimation of Relativistic Jets

    Science.gov (United States)

    Globus, N.; Cayatte, V.; Sauty, C.

    We present a semi-analytical model using the equations of general relativistic magnetohydrodynamics (GRMHD) for jets emitted by a rotating black hole. We assume steady axisymmetric outflows of a relativistic ideal fluid in Kerr metrics. We express the conservation equations in the frame of the FIDucial Observer (FIDO or ZAMO) using a 3+1 space-time splitting. Calculating the total energy variation between a non-polar field line and the polar axis, we extend to the Kerr metric the simple criterion for the magnetic collimation of jets obtained for a nonrotating black hole by Meliani et al.10 We show that the black role rotation induced a more efficient magnetic collimation of the jet.

  1. Synchrotron radiation of self-collimating relativistic MHD jets

    CERN Document Server

    Porth, Oliver; Meliani, Zakaria; Vaidya, Bhargav

    2011-01-01

    The goal of this paper is to derive signatures of synchrotron radiation from state-of-the-art simulation models of collimating relativistic magnetohydrodynamic (MHD) jets featuring a large-scale helical magnetic field. We perform axisymmetric special relativistic MHD simulations of the jet acceleration region using the PLUTO code. The computational domain extends from the slow magnetosonic launching surface of the disk up to 6000^2 Schwarzschild radii allowing to reach highly relativistic Lorentz factors. The Poynting dominated disk wind develops into a jet with Lorentz factors of 8 and is collimated to 1 degree. In addition to the disk jet, we evolve a thermally driven spine jet, emanating from a hypothetical black hole corona. Solving the linearly polarized synchrotron radiation transport within the jet, we derive VLBI radio and (sub-) mm diagnostics such as core shift, polarization structure, intensity maps, spectra and Faraday rotation measure (RM), directly from the Stokes parameters. We also investigate...

  2. Advanced Bent Crystal Collimation Studies at the Tevatron (T-980)

    CERN Document Server

    Zvoda, V; Carrigan, R; Drozhdin, A; Johnson, T; Kwan, S; Mokhov, N; Prosser, A; Reilly, R; Uplegger, R Rivera L; Shiltsev, V; Still, D; Zagel, J; Guidi, V; Bagli, E; Mazzolari, A; Ivanov, Yu; Chesnokov, Yu; Yazynin, I

    2011-01-01

    The T-980 bent crystal collimation experiment at the Tevatron has recently acquired substantial enhancements. First, two new crystals - a 16-strip one manufactured and characterized by the INFN Ferrara group and a quasi-mosaic crystal manufactured and characterized by the PNPI group. Second, a two plane telescope with 3 high-resolution pixel detectors per plane along with corresponding mechanics, electronics, control and software has been manufactured, tested and installed in the E0 crystal region. The purpose of the pixel telescope is to measure and image channeled (CH), volume-reflected (VR) and multiple volume-reflected (MVR) beam profiles produced by bent crystals. Third, an ORIGIN-based system has been developed for thorough analysis of experimental and simulation data. Results of analysis are presented for different types of crystals used from 2005 to present for channeling and volume reflection including pioneering tests of two-plane crystal collimation at the collider, all in comparison with detailed ...

  3. Fabricating High-Resolution X-Ray Collimators

    Science.gov (United States)

    Appleby, Michael; Atkinson, James E.; Fraser, Iain; Klinger, Jill

    2008-01-01

    A process and method for fabricating multi-grid, high-resolution rotating modulation collimators for arcsecond and sub-arcsecond x-ray and gamma-ray imaging involves photochemical machining and precision stack lamination. The special fixturing and etching techniques that have been developed are used for the fabrication of multiple high-resolution grids on a single array substrate. This technology has application in solar and astrophysics and in a number of medical imaging applications including mammography, computed tomography (CT), single photon emission computed tomography (SPECT), and gamma cameras used in nuclear medicine. This collimator improvement can also be used in non-destructive testing, hydrodynamic weapons testing, and microbeam radiation therapy.

  4. Collimation and splitting of valley electron diffraction in graphene

    Science.gov (United States)

    Yang, Mou; Bai, Yan-Kui; Zhang, Wen-Lian; Wang, Rui-Qiang

    2016-08-01

    We reported the collimation and splitting effects of the diffraction of valley electrons in graphene. When the incident energy increases from the neutral point, the diffraction tends to be collimated for one valley and split for the other valley. The difference in the diffraction between valleys results in valley-dependent transport. We investigated the left-right conductance of a four-terminal graphene device. The conductance ratio between the two valleys was derived to be 1 -(8 /3 )E , where E is the incident energy in units of the atom-atom hopping. The ratio is independent of the device dimensions and reflects the intrinsic properties of the electronic structure of graphene.

  5. Simulator for beam-based LHC collimator alignment

    Science.gov (United States)

    Valentino, Gianluca; Aßmann, Ralph; Redaelli, Stefano; Sammut, Nicholas

    2014-02-01

    In the CERN Large Hadron Collider, collimators need to be set up to form a multistage hierarchy to ensure efficient multiturn cleaning of halo particles. Automatic algorithms were introduced during the first run to reduce the beam time required for beam-based setup, improve the alignment accuracy, and reduce the risk of human errors. Simulating the alignment procedure would allow for off-line tests of alignment policies and algorithms. A simulator was developed based on a diffusion beam model to generate the characteristic beam loss signal spike and decay produced when a collimator jaw touches the beam, which is observed in a beam loss monitor (BLM). Empirical models derived from the available measurement data are used to simulate the steady-state beam loss and crosstalk between multiple BLMs. The simulator design is presented, together with simulation results and comparison to measurement data.

  6. Collimation in the Transfer Lines to the LHC

    CERN Document Server

    Burkhardt, Helmut; Kadi, Yacine; Kain, Verena; Risselada, Thys; Weterings, Wim

    2005-01-01

    Injection intensities for the LHC are over an order of magnitude above damage level. The TI 2 and TI 8 transfer lines between the SPS and LHC are each about 2.5 km long and comprise many active elements running in pulsed mode. The collimation system in the transfer lines is designed to dilute the beam energy sufficiently in case of accidental beam loss or mis-steered beam. A system using three collimator families spaced by 60 degrees in phase advance, both in the horizontal and the vertical plane has been chosen. We discuss the reasons for this choice, the layout and, the expected performance of the system in terms of maximum amplitudes and energy deposition.

  7. Collimator Improvements 2011 and Upgrade 2012: What Do We Plan?

    CERN Document Server

    Redaelli, S

    2011-01-01

    The LHC collimation system has provided an outstanding performance during the first year of high-intensity beam operation. The complete Phase I system was commissioned and delivered routinely a cleaning performance close to the nominal exceptions with relaxed collimator settings. On the other hand, the first commissioning experience has also provided first indications of system limitations alongside of hints for possible improvements. In particular, the expected performance limitations from losses in the cold dispersion suppressors (DSs) at either side of the warm cleaning insertions have been confirmed. While improvements of the system will already be implemented during the 2010 shutdown, the major performance limitation from the DS require a change of the machine layout that will be addresses in the 2012 long shutdown. In this papers, the proposed improvements of the system are presented. The expected gains and the implication of the proposed changes on the system re-commissioning are discussed.

  8. Transmission characteristics of x-ray in MCP collimator in parallel structure

    Science.gov (United States)

    Qin, Xulei; Li, Ye; Chen, Weijun

    2016-11-01

    In order to improve the imaging quality of X-ray and reduce the effects of X-ray and scatter line on image, the adoption of X-ray collimator is the most effective method. MCP collimator in parallel structure can effectively reduce the ratio of X-ray and scatter line to reach on image plane, and reduce the atomization degree of images, so as to improve the image contrast. Through the establishment first-order radiation transmittance model of MCP collimator, test the performance of MCP collimator, it is prove that the MCP collimator can be used in the imaging system that consists of proximity of X-ray image intensifier, first-order radiation transmittance calculation formula of MCP absorption type collimator in parallel structure is reduced, obtain the transmittance distribution non cosine curve distribution of MCP collimator through calculating.

  9. Neutron collimator design of neutron radiography based on the BNCT facility

    Science.gov (United States)

    Yang, Xiao-Peng; Yu, Bo-Xiang; Li, Yi-Guo; Peng, Dan; Lu, Jin; Zhang, Gao-Long; Zhao, Hang; Zhang, Ai-Wu; Li, Chun-Yang; Liu, Wan-Jin; Hu, Tao; Lü, Jun-Guang

    2014-02-01

    For the research of CCD neutron radiography, a neutron collimator was designed based on the exit of thermal neutron of the Boron Neutron Capture Therapy (BNCT) reactor. Based on the Geant4 simulations, the preliminary choice of the size of the collimator was determined. The materials were selected according to the literature data. Then, a collimator was constructed and tested on site. The results of experiment and simulation show that the thermal neutron flux at the end of the neutron collimator is greater than 1.0×106 n/cm2/s, the maximum collimation ratio (L/D) is 58, the Cd-ratio(Mn) is 160 and the diameter of collimator end is 10 cm. This neutron collimator is considered to be applicable for neutron radiography.

  10. Neutron collimator design of neutron radiography based on the BNCT facility

    CERN Document Server

    Yang, XP; Li, YG; Peng, D; Lu, J; Zhang, GL; Zhao, H; Zhang, AW; Li, CY; Liu, WJ; Hu, T; Lv, JG

    2013-01-01

    For the research of CCD neutron radiography, a neutron collimator was designed based on the exit of thermal neutron of the Boron Neutron Capture Therapy (BNCT) reactor. Based on the Geant4 simulations, the preliminary choice of the size of the collimator was determined. The materials were selected according to the literature data. Then, a collimator was constructed and tested on site. The results of experiment and simulation show that the thermal neutron flux at the end of theneutron collimator is greater than 10^6 n/cm^2/s, the maximum collimation ratio (L/D) is 58, the Cd-ratio(Mn) is 160 and the diameter of collimator end is 10 cm. This neutron collimator is considered to be applicable for neutron radiography.

  11. Mechanical Engineering and Design of Novel Collimators for HL-LHC

    CERN Document Server

    Carra, F; Dallocchio, A; Gentini, L; Gradassi, P; Maitrejean, G; Manousos, A; Mariani, N; Mounet, N; Quaranta, E; Redaelli, S; Vlachoudis, V

    2014-01-01

    In view of High Luminosity LHC (HL-LHC) upgrades, collimator materials may become a limit to the machine performance: the high RF impedance of Carbon-Carbon composites used for primary and secondary collimators can lead to beam instabilities, while the Tungsten alloy adopted in tertiary collimators exhibits low robustness in case of beam-induced accidents. An R&D program has been pursued to develop new materials overcoming such limitations. Molybdenum-Graphite, in addition to its outstanding thermal conductivity, can be coated with pure molybdenum, reducing collimator impedance by a factor of 10. A new secondary collimator is being designed around this novel composite. New high-melting materials are also proposed to improve the robustness of tertiary collimators. New collimators will also be equipped with BPMs, significantly enhancing the alignment speed and the beta-star reach. This implies additional constraints of space, as well as detailed static and fatigue calculations on cables and connectors. This...

  12. Changes to the Transfer Line Collimation System for the High-Luminosity LHC Beams

    Energy Technology Data Exchange (ETDEWEB)

    Kain, V. [CERN; Aberle, O. [CERN; Bracco, C. [CERN; Fraser, M. [CERN; Galleazzi, F. [CERN; Gianfelice-Wendt, E. [Fermilab; Kosmicki, A. [CERN; Maciariello, F. [CERN; Meddahi, M. [CERN; Nuiry, F. X. [CERN; Steele, G. [CERN; Velotti, F. [CERN

    2015-06-01

    The current LHC transfer line collimation system will not be able to provide enough protection for the high brightness beams in the high-luminosity LHC era. The new collimation system will have to attenuate more and be more robust than its predecessor. The active jaw length of the new transfer line collimators will therefore be 2.1 m instead of currently 1.2 m. The transfer line optics will have to be adjusted for the new collimator locations and larger beta functions at the collimators for absorber robustness reasons. In this paper the new design of the transfer line collimation system will be presented with its implications on transfer line optics and powering, maintainability, protection of transfer line magnets in case of beam loss on a collimator and protection of the LHC aperture.

  13. Changes to the Transfer Line Collimation System for the High-Luminosity LHC Beams

    CERN Document Server

    Kain, V; Bracco, C; Fraser, M; Galleazzi, F; Gianfelice-Wendt, E; Kosmicki, A; Maciariello, F; Meddahi, M; Nuiry, F X; Steele, G; Velotti, F

    2015-01-01

    The current LHC transfer line collimation system will not be able to provide enough protection for the high brightness beams in the high-luminosity LHC era. The new collimation system will have to attenuate more and be more robust than its predecessor. The active jaw length of the new transfer line collimators will therefore be 2.1 m instead of currently 1.2 m. The transfer line optics will have to be adjusted for the new collimator locations and larger beta functions at the collimators for absorber robustness reasons. In this paper the new design of the transfer line collimation system will be presented with its implications on transfer line optics and powering, maintainability, protection of transfer line magnets in case of beam loss on a collimator and protection of the LHC aperture.

  14. New Post-Linac Collimation System for the Next Linear Collider(LCC-0052)

    Energy Technology Data Exchange (ETDEWEB)

    Tenenbaum, P.

    2003-12-03

    We present a new design for the NLC post-linac collimation system. The new design separates the collimation of off-energy particles and particles with large betatron amplitudes. The energy collimation system achieves passive protection against damage by an errant bunch train via large horizontal dispersion and vertical betatron functions, and makes use of optical symmetries to reduce jitter amplification. The betatron collimation system permits infrequent damage to the thin ''spoiler'' collimators, while the thick ''absorber'' collimators have a much larger aperture and are thus more difficult to hit. The physical phenomena which are relevant to the design and operation of the collimation system are reviewed, and the associated properties of the new system are discussed.

  15. suPAR: the molecular crystal ball

    DEFF Research Database (Denmark)

    Thunø, Maria; Macho, Betina; Eugen-Olsen, Jesper

    2009-01-01

    soluble urokinase Plasminogen Activator Receptor (suPAR) levels reflect inflammation and elevated suPAR levels are found in several infectious diseases and cancer. suPAR exists in three forms; suPAR(I-III), suPAR(II-III) and suPAR(I) which show different properties due to structural differences....... Studies suggest that full-length suPAR is a regulator of uPAR/uPA by actingas uPA-scavenger, whereas the cleaved suPAR(II-III) act as a chemotactic agent promoting the immune response via the SRSRY sequence in the linker-region. This review focus on the various suPAR fragments and their involvement...

  16. The Practical Pomeron for High Energy Proton Collimation

    CERN Document Server

    AUTHOR|(CDS)2108501; Molson, J. G; Serluca, M.; Toader, A.

    2016-01-01

    We present a model which describes proton scattering data from ISR to Tevatron energies, and which can be applied to collimation n high energy accelerators, such as the LHC and FCC. Collimators remove beam halo particles, so that they do not impinge on vulnerable regions of the machine, such as the superconducting magnets and the experimental areas. In simulating the effect of the collimator jaws it is crucial to model the scattering of protons at small momentum transfer~$t$,as these protons can subsequently survive several turns of the ring before being lost. At high energies these soft processes are well described by Pomeron exchange models. We study the behaviour of elastic and single-diffractive dissociation cross sections over a wide range of energy, and show that the model can be used as a global description of the wide variety of high energy elastic and diffractive data presently available. In particular it models low mass diffraction dissociation, where a rich resonance structure is present, and thus ...

  17. Evaluation of the penumbras of a Philips multileaf collimator

    Energy Technology Data Exchange (ETDEWEB)

    Lafay, F.; Malet, C.; Mombard, C.; Ginestet, C. [Centre de Lutte Contre le Cancer Leon-Berard, 69 - Lyon (France); Blondel, E. [Isotec, Saint-Quentin (France); Desfarges, Y.; Dupin, G. [Philips Medical System, Lyon (France)

    1995-12-01

    Since January 1995, a Philips SL20 linear accelerator which is connected to a multileaf collimator has been used. Computer-controlled multileaf collimators open up the opportunity to practice conformal radiotherapy. Its aim is to adjust as well as possible the Planning Target Volume (PTV) to the effective treated volume with an homogeneous dose distribution in the PTV, and to protect healthy tissues and delicate organs. This is possible by means of a multileaf collimator by increasing the number of complex fields with different incidences during a same session. Moreover, the Beam`s Eye View function of the three-dimensional treatment planning system allows to define the shape of complex fields. For rectangular fields, the penumbra is defined by the distance between the 80% and 20% isodoses relative to the beam axis. In addition, the distances between, respectively, the 95% and 50% isodoses, the 90% and 50% isodoses, the 50% and 20% isodoses relative to the beam axis have been analysed. Different penumbras were evaluated. The result of this work will enable to adjust the reference isodose to the PTV either by integrating this result into dosimetry software, or by taking it into account for drawing the PTV.

  18. Negative particle planar and axial channeling and channeling collimation

    Energy Technology Data Exchange (ETDEWEB)

    Carrigan, Richard A., Jr.; /Fermilab

    2009-12-01

    While information exists on high energy negative particle channeling there has been little study of the challenges of negative particle bending and channeling collimation. Partly this is because negative dechanneling lengths are relatively much shorter. Electrons are not particularly useful for investigating negative particle channeling effects because their material interactions are dominated by channeling radiation. Another important factor is that the current central challenge in channeling collimation is the proton-proton Large Hadron Collider (LHC) where both beams are positive. On the other hand in the future the collimation question might reemerge for electon-positron or muon colliders. Dechanneling lengths increase at higher energies so that part of the negative particle experimental challenge diminishes. In the article different approaches to determining negative dechanneling lengths are reviewed. The more complicated case for axial channeling is also discussed. Muon channeling as a tool to investigate dechanneling is also discussed. While it is now possible to study muon channeling it will probably not illuminate the study of negative dechanneling.

  19. First Sub-arcsecond Collimation of Monochromatic Neutrons

    Energy Technology Data Exchange (ETDEWEB)

    Wagh, Apoorva G; Abbas, Sohrab; Treimer, Wolfgang, E-mail: nintsspd@barc.gov.in

    2010-11-01

    We have achieved the tightest collimation to date of a monochromatic neutron beam by diffracting neutrons from a Bragg prism, viz. a single crystal prism operating in the vicinity of Bragg incidence. An optimised silicon {l_brace}111{r_brace} Bragg prism has collimated 5.26A neutrons down to 0.58 arcsecond. In conjunction with a similarly optimised Bragg prism analyser of opposite asymmetry, this ultra-parallel beam yielded a 0.62 arcsecond wide rocking curve. This beam has produced the first SUSANS spectrum in Q {approx} 10{sup -6} A{sup -1} range with a hydroxyapatite casein protein sample and demonstrated the instrument capability of characterising agglomerates upto 150 {mu}m in size. The super-collimation has also enabled recording of the first neutron diffraction pattern from a macroscopic grating of 200 {mu}m period. An analysis of this pattern yielded the beam transverse coherence length of 175 {mu}m (FWHM), the greatest achieved to date for A wavelength neutrons.

  20. Precessing collimated outflows in the planetary nebula IC 4846

    CERN Document Server

    Miranda, L F; Torrelles, J M; Miranda, Luis F; Guerrero, Martin A; Torrelles, Jose M

    2000-01-01

    We present [N II] and H-alpha images and high resolution long-slit spectra of the planetary nebula IC 4846, which reveal, for the first time, its complex structure and the existence of collimated outflows. The object consists of a moderately elongated shell, two (and probably three) pairs of collimated bipolar outflows at different orientations, and an attached circular shell. One of the collimated pairs is constituted by two curved, extended filaments whose properties indicate a high velocity, bipolar precessing jet. A difference of \\~10 km/s is found between the systemic velocity of the precessing jets and the centroid velocity of the nebula, as recently report for Hu 2-1. We propose that this difference is due to orbital motion of the ejection source in a binary central star. The orbital separation and period estimates for the binary star are less than or equal to 30 AU and 100 yr, respectively. These are similar to those previously estimated for Hu 2-1, linking the central stars of both planetary nebulae ...

  1. LOR-interleaving image reconstruction for PET imaging with fractional-crystal collimation

    Science.gov (United States)

    Li, Yusheng; Matej, Samuel; Karp, Joel S.; Metzler, Scott D.

    2015-01-01

    Positron emission tomography (PET) has become an important modality in medical and molecular imaging. However, in most PET applications, the resolution is still mainly limited by the physical crystal sizes or the detector’s intrinsic spatial resolution. To achieve images with better spatial resolution in a central region of interest (ROI), we have previously proposed using collimation in PET scanners. The collimator is designed to partially mask detector crystals to detect lines of response (LORs) within fractional crystals. A sequence of collimator-encoded LORs is measured with different collimation configurations. This novel collimated scanner geometry makes the reconstruction problem challenging, as both detector and collimator effects need to be modeled to reconstruct high-resolution images from collimated LORs. In this paper, we present a LOR-interleaving (LORI) algorithm, which incorporates these effects and has the advantage of reusing existing reconstruction software, to reconstruct high-resolution images for PET with fractional-crystal collimation. We also develop a 3D ray-tracing model incorporating both the collimator and crystal penetration for simulations and reconstructions of the collimated PET. By registering the collimator-encoded LORs with the collimator configurations, high-resolution LORs are restored based on the modeled transfer matrices using the non-negative least-squares method and EM algorithm. The resolution-enhanced images are then reconstructed from the high-resolution LORs using the MLEM or OSEM algorithm. For validation, we applied the LORI method to a small-animal PET scanner, A-PET, with a specially designed collimator. We demonstrate through simulated reconstructions with a hot-rod phantom and MOBY phantom that the LORI reconstructions can substantially improve spatial resolution and quantification compared to the uncollimated reconstructions. The LORI algorithm is crucial to improve overall image quality of collimated PET, which

  2. The ParB-parS Chromosome Segregation System Modulates Competence Development in Streptococcus pneumoniae

    NARCIS (Netherlands)

    Attaiech, Laetitia; Minnen, Anita; Kjos, Morten; Gruber, Stephan; Veening, Jan-Willem

    2015-01-01

    UNLABELLED: ParB proteins bind centromere-like DNA sequences called parS sites and are involved in plasmid and chromosome segregation in bacteria. We previously showed that the opportunistic human pathogen Streptococcus pneumoniae contains four parS sequences located close to the origin of replicati

  3. Optic capture pars plana lensectomy

    Directory of Open Access Journals (Sweden)

    Lee JE

    2012-10-01

    Full Text Available Joo Eun LeeDepartment of Ophthalmology, Inje University College of Medicine, Busan, South KoreaObjective: To describe an optic capture pars plana lensectomy technique.Methods: After core vitrectomy, pars plana lensectomy is performed with preservation of the anterior capsule. Capsulorhexis is performed on the preserved anterior capsule through a 2.8 mm clear corneal incision. An intraocular lens (IOL is placed in the ciliary sulcus, and then the optic of the IOL is pushed back to the vitreous cavity so that the optic is captured by the surrounding capsulorhexis margin.Results: The captured IOL-capsule diaphragm remained stable during air–fluid exchange and prevented air prolapse to the anterior chamber. IOL stability and a clear visual axis were preserved during the follow-up period.Conclusion: With this modified pars plana lensectomy technique, stable IOL position and clear visual axis can be maintained when a pars plana approach is needed during combined cataract and vitreoretinal surgery.Keywords: lensectomy, optic capture, pars plana lensectomy, vitrectomy

  4. Designing Tone Reservation PAR Reduction

    Directory of Open Access Journals (Sweden)

    Johansson Albin

    2006-01-01

    Full Text Available Tone reservation peak-to-average (PAR ratio reduction is an established area when it comes to bringing down signal peaks in multicarrier (DMT or OFDM systems. When designing such a system, some questions often arise about PAR reduction. Is it worth the effort? How much can it give? How much does it give depending on the parameter choices? With this paper, we attempt to answer these questions without resolving to extensive simulations for every system and every parameter choice. From a specification of the allowed spectrum, for instance prescribed by a standard, including a PSD-mask and a number of tones, we analytically predict achievable PAR levels, and thus implicitly suggest parameter choices. We use the ADSL2 and ADSL2+ systems as design examples.

  5. Tomographic image quality of rotating slat versus parallel hole-collimated SPECT

    Science.gov (United States)

    Van Holen, Roel; Staelens, Steven; Vandenberghe, Stefaan

    2011-11-01

    Parallel and converging hole collimators are most frequently used in nuclear medicine. Less common is the use of rotating slat collimators for single photon emission computed tomography (SPECT). The higher photon collection efficiency, inherent to the geometry of rotating slat collimators, results in much lower noise in the data. However, plane integrals contain spatial information in only one direction, whereas line integrals provide two-dimensional information. It is not a trivial question whether the initial gain in efficiency will compensate for the lower information content in the plane integrals. Therefore, a comparison of the performance of parallel hole and rotating slat collimation is needed. This study compares SPECT with rotating slat and parallel hole collimation in combination with MLEM reconstruction with accurate system modeling and correction for scatter and attenuation. A contrast-to-noise study revealed an improvement of a factor 2-3 for hot lesions and more than a factor of 4 for cold lesion. Furthermore, a clinically relevant case of heart lesion detection is simulated for rotating slat and parallel hole collimators. In this case, rotating slat collimators outperform the traditional parallel hole collimators. We conclude that rotating slat collimators are a valuable alternative for parallel hole collimators.

  6. Simultaneous reduction of radiation dose and scatter for CBCT by using collimators

    Energy Technology Data Exchange (ETDEWEB)

    Li, Tianfang; Li, Xiang; Yang, Yong; Zhang, Yongqian; Heron, Dwight E.; Huq, M. Saiful [Department of Radiation Oncology, University of Pittsburgh Cancer Institute, Pittsburgh, Pennsylvania 15232 (United States)

    2013-12-15

    Purpose: On-board cone-beam CT (CBCT) imaging has been widely available in radiotherapy clinic for target localization. However, the extra radiation dose from CBCT is always a concern for its frequent use. Additionally, the relatively large scatter in CBCT often degrades the image quality. By using collimators, some of the X-rays can be stopped from reaching the patient and the detectors, hence both the scatter and the patient doses are simultaneously reduced. The authors show in this work that the collimated CBCT data can be reconstructed without any noticeable artifacts for certain collimator blocking ratios and blocking patterns, and the focus of this work is to study the relationship between the image quality and these two collimator factors.Methods: A CBCT system with collimators was simulated following the typical geometry used in clinic. Different collimator designs were tested by varying the size and the number of the collimator slits, and at the same time, the ratio of transmitted beams to total beams was varied from 100% to 10%, resulting in hundreds of different simulation scenarios. Lung and pelvis phantoms created from patients CT images were used in the simulations, and an iterative reconstruction algorithm using the compressed sensing technique was adopted. The image quality was examined by root mean square errors (RMSEs) and compared with the conventional CBCT images.Results: The CBCT image quality increases as the amount of beams passing through the collimators increases, and decreases as the size of the collimator slits increases. With ultra-high resolution collimators, the RMSEs were comparable to the conventional CBCT image quality until the beam transmission rate is reduced below 25%.Conclusions: Collimators can reduce the scatters and radiation dose, however, the collimated CBCT image quality is strongly dependent on both the collimator blocking ratio and the blocking pattern. To achieve image quality comparable to the conventional CBCT, the

  7. Vision par ordinateur: outils fondamentaux

    OpenAIRE

    Horaud, Radu; Monga, Olivier

    1995-01-01

    National audience; Cet ouvrage présente les outils fondamentaux de la vision par ordinateur dans un langage mathématique accessible aux étudiants de niveau DEUG en mathématiques ou informatique. Il donne également de nombreux exemples d'utilisation de la vision par ordinateur dans deux domaines de technologie de pointe : la robotique et l'imagerie médicale. Cette deuxième édition largement augmentée est un manuel de référence. Les outils fondamentaux sont présentés dans un langage mathématiqu...

  8. A dosimetric characterization of a novel linear accelerator collimator

    Energy Technology Data Exchange (ETDEWEB)

    Thompson, C. M.; Weston, S. J., E-mail: steve.weston@leedsth.nhs.uk; Cosgrove, V. C. [Leeds Cancer Centre, Bexley Wing, St. James’ University Hospital, Leeds LS9 7TF (United Kingdom); Thwaites, D. I. [Institute of Medical Physics, School of Physics, University of Sydney, Sydney NSW 2006, Australia and Division of Medical Physics, Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds LS2 9JT (United Kingdom)

    2014-03-15

    Purpose: The aim of this work is to characterize a new linear accelerator collimator which contains a single pair of sculpted diaphragms mounted orthogonally to a 160 leaf multileaf collimator (MLC). The diaphragms have “thick” regions providing full attenuation and “thin” regions where attenuation is provided by both the leaves and the diaphragm. The leaves are mounted on a dynamic leaf guide allowing rapid leaf motion and leaf travel over 350 mm. Methods: Dosimetric characterization, including assessment of leaf transmission, leaf tip transmission, penumbral width, was performed in a plotting tank. Head scatter factor was measured using a mini-phantom and the effect of leaf guide position on output was assessed using a water phantom. The tongue and groove effect was assessed using multiple exposures on radiochromic film. Leaf reproducibility was assessed from portal images of multiple abutting fields. Results: The maximum transmission through the multileaf collimator is 0.44% at 6 MV and 0.52% at 10 MV. This reduced to 0.22% and 0.27%, respectively, when the beam passes through the dynamic leaf guide in addition to the MLC. The maximum transmission through the thick part of the diaphragm is 0.32% and 0.36% at 6 and 10 MV. The combination of leaf and diaphragm transmission ranges from 0.08% to 0.010% at 6 MV and 0.10% to 0.14% depending on whether the shielding is through the thick or thin part of the diaphragm. The off-axis intertip transmission for a zero leaf gap is 2.2% at 6 and 10 MV. The leaf tip penumbra for a 100 × 100 mm field ranges from 5.4 to 4.3 mm at 6 and 10 MV across the full range of leaf motion when measured in the AB direction, which reduces to 4.0–3.4 mm at 6 MV and 4.5–3.8 mm at 10 MV when measured in the GT direction. For a 50 × 50 mm field, the diaphragm penumbra ranges from 4.3 to 3.7 mm at 6 MV and 4.5 to 4.1 mm at 10 MV in the AB direction and 3.7 to 3.2 mm at 6 MV and 4.2 to 3.7 mm when measured in the GT direction. The

  9. ParSplice, Version 1

    Energy Technology Data Exchange (ETDEWEB)

    2017-01-05

    The ParSplice code implements the Parallel Trajectory Splicing algorithm described in [1]. This method is part of the Accelerated Molecular Dynamics family of techniques developed in Los Alamos National Laboratory over the last 16 years. These methods aim at generating high-quality trajectories of ensembles of atoms in materials. ParSplice uses multiple independent replicas of the system in order to parallelize the generation of such trajectories in the time domain, enabling simulations of systems of modest size over very long timescales. ParSplice includes capabilities to store configurations of the system, to generate and distribute tasks across a large number of processors, and to harvest the results of these tasks to generate long trajectories. ParSplice is a management layer that orchestrate large number of calculations, but it does not perform the actual molecular dynamics itself; this is done by external molecular dynamics engines. [1] Danny Perez, Ekin D Cubuk, Amos Waterland, Efthimios Kaxiras, Arthur F Voter, Long-time dynamics through parallel trajectory splicing, Journal of chemical theory and computation 12, 18 (2015)

  10. Cerrobend collimation effect on electron beams; Efeito de colimacoes de cerrobend em feixes de eletrons

    Energy Technology Data Exchange (ETDEWEB)

    Furnari, Laura; Albino, Lucas D.; Ribeiro, Victor A.B.; Santos, Gabriela R., E-mail: laurafurnari@hotmail.com [Universidade de Sao Paulo (InRad/FM/USP), SP (Brazil). Faculdade de Medicina. Hospital das Clinicas. Instituto de Radiologia

    2012-12-15

    The aim of this work was to discuss about the cerrobend collimation effect on clinical electron beams. When a cerrobend collimation is used, both the percentage depth dose (PDD) and the absolute dose that is delivered to the patient changes. It was analyzed how those parameters change and it was evaluated in which cases a correction factor should be applied due to this collimation. It was founded that, when the smallest dimension of the collimation is smaller than the minimum radius to lateral scatter equilibrium, the collimation will change the PDD in such a way that it should take into account in the treatment planning. For one specific collimation usually applied in head and neck treatments, it was found that no correction factor is necessary. (author)

  11. First Design of a Proton Collimation System for 50 TeV FCC-hh

    CERN Document Server

    Fiascaris, Maria; Mirarchi, Daniele; Redaelli, Stefano

    2016-01-01

    We present studies aimed at defining a first conceptual solution for a collimation system for the hadron-hadron option for the Future Circular Collider (FCC-hh). The baseline collimation layout is based on the scaling of the present LHC collimation system to the FCC-hh energy. It currently includes a dedicated betatron cleaning insertion as well as collimators in the experimental insertions to protect the inner triplets. An aperture model for the FCC-hh is defined and the geometrical acceptance is calculated at top energy taking into account mechanical and optics imperfections. Based on these studies the collimator settings needed to protect the machine are defined. The performance of the collimation system is then assessed with particle tracking simulation tools assuming a perfect machine.

  12. Efficient Dielectric Metasurface Collimating Lenses for Mid-Infrared Quantum Cascade Lasers

    CERN Document Server

    Arbabi, Amir; Horie, Yu; Bagheri, Mahmood; Faraon, Andrei

    2015-01-01

    Light emitted from single-mode semiconductor lasers generally has large divergence angles, and high numerical aperture lenses are required for beam collimation. Visible and near infrared lasers are collimated using aspheric glass or plastic lenses, yet collimation of mid-infrared quantum cascade lasers typically requires more costly aspheric lenses made of germanium, chalcogenide compounds, or other infrared-transparent materials. Here we report mid-infrared dielectric metasurface flat lenses that efficiently collimate the output beam of single-mode quantum cascade lasers. The metasurface lenses are composed of amorphous silicon posts on a flat sapphire substrate and can be fabricated at low cost using a single step conventional UV binary lithography. Mid-infrared radiation from a 4.8 $\\mu$m distributed-feedback quantum cascade laser is collimated using a polarization insensitive metasurface lens with 0.86 numerical aperture and 79% transmission efficiency. The collimated beam has a half divergence angle of 0...

  13. A combined radial collimator and cooled beryllium filter for neutron scattering

    Energy Technology Data Exchange (ETDEWEB)

    Groitl, Felix, E-mail: felix.groitl@psi.ch [Laboratory for Quantum Magnetism, École Polytechnique Fédérale de Lausanne, 1015 Lausanne (Switzerland); Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen (Switzerland); Rantsiou, Emmanouela; Bartkowiak, Marek; Filges, Uwe; Graf, Dieter [Laboratory for Scientific Developments and Novel Materials, Paul Scherrer Institut, 5232 Villigen (Switzerland); Niedermayer, Christof [Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen (Switzerland); Rüegg, Christian [Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen (Switzerland); Department of Quantum Matter Physics, University of Geneva, 1211 Geneva (Switzerland); Rønnow, Henrik M. [Laboratory for Quantum Magnetism, École Polytechnique Fédérale de Lausanne, 1015 Lausanne (Switzerland); Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen (Denmark)

    2016-05-21

    A flexible, combined, radial collimator and beryllium (Be) filter have been designed and manufactured at the Paul Scherrer Institut (PSI), Switzerland. The Be is integrated in the radial collimator by placing thin Be slices between the collimator lamellas. The filter/collimator is mounted within a vacuum vessel and dry cooled. The flexible design allows for different degrees of collimation and for different Be lengths. Results of measurements carried out at the BOA beamline at PSI are presented. These experiments include rotation scans determining the focal full width half maximum (FWHM), transmission measurements, test of different collimator lamellas and performance tests of the cooling of the filter. This new combined device will be a crucial part of the CAMEA spectrometer at SINQ, PSI.

  14. Proposal for Single-Bunch Collimator Wakefield Measurements at SLAC ESTB

    CERN Document Server

    Resta-Lopez, J; Faus-Golfe, A; Fuster-Martinez, N; Hast, C; Jones, R M; Latina, A; Pivi, M; Rumolo, G; Schulte, D; Smith, J; Tomas, R

    2012-01-01

    Collimator wakefields in the Beam Delivery System (BDS) of future linear colliders, such as the International Linear Collider (ILC) and the Compact Linear Collider (CLIC), can be an important source of emittance growth and beam jitter amplification, consequently degrading the luminosity. Therefore, a better understanding of collimator wakefield effects is essential to optimise the collimation systems of future linear colliders in order to minimise wakefield effects. In the past, measurements of single-bunch collimator wakefields have been carried out at SLAC with the aim of benchmarking theory, numerical calculations and experiments. Those studies revealed some discrepancies between the measurements and the theoretical models. New experimental tests using available beam test facilities, such as the End Station A Test Beam (ESTB) at SLAC, would help to improve our understanding on collimator wakefields. ESTB will provide the perfect test bed to investigate collimator wakefields for different bunch length condi...

  15. Remote Estimation of Collimator Jaw Damages With Sounds Measurements During Beam Impacts

    CERN Document Server

    Deboy, D; Aberle, O; Carra, F; Cauchi, M; Lendaro, J; Masi, A; Redaelli, S

    2013-01-01

    Irregular hits of high-intensity LHC beams on collimators can lead to severe damage of the collimator jaws. The identification of damaged collimator jaws by observation of beam measurements is challenging: online loss measurements at the moment of the impacts can be tricky and degradation of the overall performance from single collimator damage can be difficult to measure. Visual inspections are excluded because collimator jaws are enclosed in vacuum tanks without windows. However, the sound generated during the beam impact can be used to give an estimate of the damage level. In 2012, high-intensity beam comparable to a full nominal LHC bunch at 7 TeV was shot on a tertiary type LHC collimator at the HiRadMat test facility at CERN. The paper presents results from sound recordings of this experiment.

  16. Off-momentum collimation and cleaning in the energy ramp in the LHC

    CERN Document Server

    Quaranta, Elena; Giulini Castiglioni Agosteo, Stefano Luigi Maria

    This Master thesis work has been carried out at CERN in the framework of the LHC (Large Hadron Collider) Collimation project. The LHC is a two-beam proton collider, built to handle a stored energy of 360MJ for each beam. Since the energy deposition from particle losses could quench the superconducting magnets, a system of collimators has been installed in two cleaning insertions in the ring and in the experimental areas. The achievable LHC beam intensity is directly coupled to the beam loss rate and, consequently, to the cleaning eciency of the collimation system. This study analyses the collimation cleaning performance in dierent scenarios inside the accelerator. First, simulations are performed of the transverse losses in the LHC collimation system during the acceleration process. The results are compared with data taken during a dedicated session at the LHC machine. Simulations are also performed to predict the collimation eciency during future operation at higher energy. Furthermore, an investigation of t...

  17. A combined radial collimator and cooled beryllium filter for neutron scattering

    Science.gov (United States)

    Groitl, Felix; Rantsiou, Emmanouela; Bartkowiak, Marek; Filges, Uwe; Graf, Dieter; Niedermayer, Christof; Rüegg, Christian; Rønnow, Henrik M.

    2016-05-01

    A flexible, combined, radial collimator and beryllium (Be) filter have been designed and manufactured at the Paul Scherrer Institut (PSI), Switzerland. The Be is integrated in the radial collimator by placing thin Be slices between the collimator lamellas. The filter/collimator is mounted within a vacuum vessel and dry cooled. The flexible design allows for different degrees of collimation and for different Be lengths. Results of measurements carried out at the BOA beamline at PSI are presented. These experiments include rotation scans determining the focal full width half maximum (FWHM), transmission measurements, test of different collimator lamellas and performance tests of the cooling of the filter. This new combined device will be a crucial part of the CAMEA spectrometer at SINQ, PSI.

  18. Self-collimated axial jets from thin accretion disks

    CERN Document Server

    Tirabassi, Giulio; Carlevaro, Nakia; Benini, Riccardo

    2012-01-01

    We show how an appropriate stationary crystalline structure of the magnetic field can induce a partial fragmentation of the accretion disk, generating an axial jet composed of hot rising plasma twisted in a funnel-like structure by the rotation of the system. The most important feature of the obtained jet is its high degree of collimation, naturally arising from the condition for its existence. The presence of non-zero dissipative effects allows the plasma ejection throughout the axial jet and the predicted values of the accretion rate are in agreement with observations.

  19. Compact collimated fiber optic array diagnostic for railgun plasma experiments

    Energy Technology Data Exchange (ETDEWEB)

    Tang, V; Solberg, J; Ferriera, T; Tully, L; Stephan, P

    2008-10-02

    We have developed and tested a compact collimated sixteen channel fiber optic array diagnostic for studying the light emission of railgun armature plasmas with {approx}mm spatial and sub-{micro}s temporal resolution. The design and operational details of the diagnostic are described. Plasma velocities, oscillation, and dimension data from the diagnostic for the Livermore Fixed Hybrid Armature experiment are presented and compared with 1-D simulations. The techniques and principles discussed allow the extension of the diagnostic to other railgun and related dense plasma experiments.

  20. Compact collimated fiber optic array diagnostic for railgun plasmas.

    Science.gov (United States)

    Tang, V; Solberg, J M; Ferriera, T J; Tully, L K; Stephan, P L

    2009-01-01

    We developed and tested a compact collimated 16 channel fiber optic array diagnostic for studying the light emission of railgun armature plasmas with approximately millimeter spatial and submicrosecond temporal resolution. The design and operational details of the diagnostic are described. Plasma velocities, oscillation, and dimension data from the diagnostic for the Livermore fixed hybrid armature experiment are presented and compared with one-dimensional simulations. The techniques and principles discussed allow the extension of the diagnostic to other railgun and related dense plasma experiments.

  1. Acceleration and Collimation of Relativistic Magnetohydrodynamic Disk Winds

    Science.gov (United States)

    Porth, Oliver; Fendt, Christian

    2010-02-01

    We perform axisymmetric relativistic magnetohydrodynamic simulations to investigate the acceleration and collimation of jets and outflows from disks around compact objects. Newtonian gravity is added to the relativistic treatment in order to establish the physical boundary condition of an underlying accretion disk in centrifugal and pressure equilibrium. The fiducial disk surface (respectively a slow disk wind) is prescribed as boundary condition for the outflow. We apply this technique for the first time in the context of relativistic jets. The strength of this approach is that it allows us to run a parameter study in order to investigate how the accretion disk conditions govern the outflow formation. Substantial effort has been made to implement a current-free, numerical outflow boundary condition in order to avoid artificial collimation present in the standard outflow conditions. Our simulations using the PLUTO code run for 500 inner disk rotations and on a physical grid size of 100 × 200 inner disk radii. The simulations evolve from an initial state in hydrostatic equilibrium and an initially force-free magnetic field configuration. Two options for the initial field geometries are applied—an hourglass-shaped potential magnetic field and a split monopole field. Most of our parameter runs evolve into a steady state solution which can be further analyzed concerning the physical mechanism at work. In general, we obtain collimated beams of mildly relativistic speed with Lorentz factors up to 6 and mass-weighted half-opening angles of 3-7 deg. The split-monopole initial setup usually results in less collimated outflows. The light surface of the outflow magnetosphere tends to align vertically—implying three relativistically distinct regimes in the flow—an inner subrelativistic domain close to the jet axis, a (rather narrow) relativistic jet and a surrounding subrelativistic outflow launched from the outer disk surface—similar to the spine-sheath structure

  2. Plume collimation for laser ablation electrospray ionization mass spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Vertes, Akos; Stolee, Jessica A.

    2016-06-07

    In various embodiments, a device may generally comprise a capillary having a first end and a second end; a laser to emit energy at a sample in the capillary to ablate the sample and generate an ablation plume in the capillary; an electrospray apparatus to generate an electrospray plume to intercept the ablation plume to produce ions; and a mass spectrometer having an ion transfer inlet to capture the ions. The ablation plume may comprise a collimated ablation plume. The device may comprise a flow cytometer. Methods of making and using the same are also described.

  3. Plume collimation for laser ablation electrospray ionization mass spectrometry

    Science.gov (United States)

    Vertes, Akos; Stolee, Jessica A.

    2016-06-07

    In various embodiments, a device may generally comprise a capillary having a first end and a second end; a laser to emit energy at a sample in the capillary to ablate the sample and generate an ablation plume in the capillary; an electrospray apparatus to generate an electrospray plume to intercept the ablation plume to produce ions; and a mass spectrometer having an ion transfer inlet to capture the ions. The ablation plume may comprise a collimated ablation plume. The device may comprise a flow cytometer. Methods of making and using the same are also described.

  4. Characteristic of laser diode beam propagation through a collimating lens.

    Science.gov (United States)

    Xu, Qiang; Han, Yiping; Cui, Zhiwei

    2010-01-20

    A mathematical model of a laser diode beam propagating through a collimating lens is presented. Wave propagation beyond the paraxial approximation is studied. The phase delay of the laser diode wave in passing through the lens is analyzed in detail. The propagation optical field after the lens is obtained from the diffraction integral by the stationary phase method. The model is employed to predict the light intensity at various beam cross sections, and the computed intensity distributions are in a good agreement with the corresponding measurements.

  5. Plume collimation for laser ablation electrospray ionization mass spectrometry

    Science.gov (United States)

    Vertes, Akos; Stolee, Jessica A.

    2014-09-09

    In various embodiments, a device may generally comprise a capillary having a first end and a second end; a laser to emit energy at a sample in the capillary to ablate the sample and generate an ablation plume in the capillary; an electrospray apparatus to generate an electrospray plume to intercept the ablation plume to produce ions; and a mass spectrometer having an ion transfer inlet to capture the ions. The ablation plume may comprise a collimated ablation plume. The device may comprise a flow cytometer. Methods of making and using the same are also described.

  6. Preliminary Comparison of the Response of LHC Tertiary Collimators to Proton and Ion Beam Impacts

    CERN Document Server

    Cauchi, M; Bertarelli, A; Carra, F; Cerutti, F; Lari, L; Mollicone, P; Sammut, N

    2013-01-01

    The CERN Large Hadron Collider is designed to bring into collision protons as well as heavy ions. Accidents involving impacts on collimators can happen for both species. The interaction of lead ions with matter differs to that of protons, thus making this scenario a new interesting case to study as it can result in different damage aspects on the collimator. This paper will present a preliminary comparison of the response of collimators to proton and ion beam impacts.

  7. Dosimetric dependence on the collimator angle in prostate volumetric modulated arc therapy

    Directory of Open Access Journals (Sweden)

    Muhammad Isa

    2014-12-01

    Full Text Available Purpose: The purpose of this study is to investigate the dose-volume variations of planning target volume (PTV and organs-at-risk (OARs in prostate volumetric modulated arc therapy (VMAT when varying collimator angle. The collimator angle has the largest impact and is worth considering, so, its awareness is essential for a planner to produce an optimal prostate VMAT plan in a reasonable time frame. Methods: Single-arc VMAT plans at different collimator angles (0o, 15o, 30o, 45o, 60o, 75o and 90o were created systematically using a Harold heterogeneous pelvis phantom. The conformity index (CI, homogeneity index (HI, gradient index (GI, machine monitor units (MUs, dose-volume histogram and mean and maximum dose of the PTV were calculated and analyzed. On the other hand, the dose-volume histogram and mean and maximum doses of the OARs such as the bladder, rectum and femoral heads for different collimator angles were determined from the plans.Results: There was no significant difference, based on the planned dose-volume evaluation criteria, found in the VMAT optimizations for all studied collimator angles. A higher CI (0.53 and lower HI (0.064 were found in the 45o collimator angle. In addition, the 15o collimator angle provided a lower value of HI similar to the 45o collimator angle. Collimator angles of 75o and 90o were found to be good for rectum sparing, and collimator angles of 75o and 30o were found to be good for sparing of right and left femur, respectively. The PTV dose coverage for each plan was comparatively independent of the collimator angle. Conclusion: Our study indicates that the dosimetric results provide support and guidance to allow the clinical radiation physicists to make careful decisions in implementing suitable collimator angles to improve the PTV coverage and OARs sparing in prostate VMAT.

  8. A phased rotating collimator for a pulsed-neutron fixed scattering angle spectrometer

    Energy Technology Data Exchange (ETDEWEB)

    Wahba, M. (Ain Shams Univ., Cairo (Egypt). Dept. of Engineering Physics and Mathematics)

    1991-06-01

    The design principle of a phased rotating collimator for a pulsed-neutron fixed scattering angle spectrometer is given. The collimator's dimensions were selected to match the curved slot rotor of the spectrometer which is in operation at the ET-RR-1 reactor. The collimator has one slot, whose shape was determined to satisfy a 100% transmission of the polyenergetic neutron bursts produced by the curved slot rotor. (orig.).

  9. Influence of atomic screening on fragmentation of ultrarelativistic lead ions in LHC collimators

    DEFF Research Database (Denmark)

    Baggesen, Jan C.; Sørensen, Allan H.

    2009-01-01

    When a lead beam is collimated in the CERN LHC some of the ions fragment in the collimators causing problems downstream. For design purposes the fragmentation probability needs to be assessed. At LHC energies ( γ 3000 ; the Lorentz-factor γ is the total energy of an ion in units of its rest energ...... case for various collimator materials and find a significant effect for tungsten, the heaviest candidate planned for use....

  10. Anatomically shaped cranial collimation (ACC) for lateral cephalometric radiography: a technical report.

    Science.gov (United States)

    Hoogeveen, R C; van der Stelt, P F; Berkhout, W E R

    2014-01-01

    Lateral cephalograms in orthodontic practice display an area cranial of the base of the skull that is not required for diagnostic evaluation. Attempts have been made to reduce the radiation dose to the patient using collimators combining the shielding of the areas above the base of the skull and below the mandible. These so-called "wedge-shaped" collimators have not become standard equipment in orthodontic offices, possibly because these collimators were not designed for today's combination panoramic-cephalometric imaging systems. It also may be that the anatomical variability of the area below the mandible makes this area unsuitable for standardized collimation. In addition, a wedge-shaped collimator shields the cervical vertebrae; therefore, assessment of skeletal maturation, which is based on the stage of development of the cervical vertebrae, cannot be performed. In this report, we describe our investigations into constructing a collimator to be attached to the cephalostat and shield the cranial area of the skull, while allowing the visualization of diagnostically relevant structures and markedly reducing the size of the irradiated area. The shape of the area shielded by this "anatomically shaped cranial collimator" (ACC) was based on mean measurements of cephalometric landmarks of 100 orthodontic patients. It appeared that this collimator reduced the area of irradiation by almost one-third without interfering with the imaging system or affecting the quality of the image. Further research is needed to validate the clinical efficacy of the collimator.

  11. MERLIN Cleaning Studies with Advanced Collimator Materials for HL-LHC

    CERN Document Server

    Valloni, A.; Mereghetti, A.; Molson, J. G.; Appleby, R.; Bruce, R.; Quaranta, E.; Redaelli, S.

    2016-01-01

    The challenges of the High-Luminosity upgrade of the Large Hadron Collider require improving the beam collimation system. An intense R&D program has started at CERN to explore novel materials for new collimator jaws to improve robustness and reduce impedance. Particle tracking simulations of collimation efficiency are performed using the code MERLIN which has been extended to include new materials based on composites. After presenting two different implementations of composite materials tested in MERLIN, we present simulation studies with the aim of studying the effect of the advanced collimators on the LHC beam cleaning.

  12. Optimization of the collimation system for CSNS/RCS with the robust conjugate direction search algorithm

    CERN Document Server

    Ji, H F; Huang, M Y; Xu, S Y; Wang, N; Wang, S

    2016-01-01

    The Robust Conjugate Direction Search (RCDS) method is used to optimize the collimation system for Rapid Cycling Synchrotron (RCS) of the Chinese Spallation Neutron Source (CSNS). The parameters of secondary collimators are optimized for a better performance of the collimation system. To improve the efficiency of the optimization, the Objective Ring Beam Injection and Tracking (ORBIT) parallel module combined with MATLAB parallel computing is used, which can run multiple ORBIT instances simultaneously. This study presents a way to figure out an optimal parameter combination of the secondary collimators for a machine model in preparation for CSNS/RCS commissioning.

  13. Collimator equipment of the Large Optical Test Facility Vertical for testing space telescopes

    Science.gov (United States)

    Sergeev, Pavel A.; Gogolev, Yuri A.; Zvonkova, V. V.; Kobozev, I. R.; Ostapenko, S. V.; Malamed, Evgeny R.; Demidov, V. V.

    1995-06-01

    This paper is concerned with the collimator equipment of the large optical test facility (LOTF) 'vertical' designed for testing space telescopes. It is being created in the Research Center 'S.I. Vavilov State Optical Institute' in Russia. The optical scheme and special structural features of the vacuum vertical-type double-mirror collimator will be covered here. This paper deals with technical data and potentials of collimator focal equipment. Estimations of the collimator thermal aberrations caused by temperature fields coming from thermal simulators are put forward.

  14. SU-E-T-11: A Dosimetric Comparison of Robotic Prostatic Radiosugery Using Multi- Leaf Collimation Vs Circular Collimators

    Energy Technology Data Exchange (ETDEWEB)

    Feng, J; Yang, J; Lamond, J; Lavere, N; Laciano, R; Ding, W; Arrigo, S; Brady, L [Philadelphia Cyberknife, Philadelphia, PA (United States)

    2014-06-01

    Purpose: The study compared the dosimetry plans of Stereotatic Body Radiotherapy (SBRT) prostate cancer patients using the M6 Cyberknife with Multi-leaf Collimation (MLC) compared with the plans using G4 Cyberknife with circular collimators. Methods: Eight previously treated prostate cancer patients' SBRT plans using circular collimators, designed with Multiplan v3.5.3, were used as a benchmark. The CT, contours and the optimization scripts were imported into Multiplan v5.0 system and replanned with MLC. The same planning objectives were used: more than 95% of PTV received 36.25Gy, 90% of prostate received 40Gy and maximum dose <45Gy, in five fractions. For organs at risk, less than 1cc of rectum received 36Gy and less than 10cc of bladder received 37Gy. Plans were evaluated on parameters derived from dose volume. The beam number, MU and delivery time were recorded to compare the treatment efficiency. Results: The mean CTV volume was 41.3cc (27.5∼57.6cc) and mean PTV volume was 76.77cc (59.1∼99.7cc). The mean PTV coverage was comparable between MLC (98.87%) and cone (98.74%). MLC plans had a slightly more favorable homogeneity index (1.22) and conformity index (1.17), than the cone (1.24 and 1.15). The mean rectum volume of 36 Gy (0.52cc) of MLC plans was slightly larger than cone (0.38cc) and the mean bladder volume of 37 Gy was smaller in MLC (1.82cc) than in cone plans (3.09cc). The mean number of nodes and beams were 65.9 and 80.5 in MLC vs 65.9 and 203.6 in cone. The mean MUs were significantly less for MLC plans (24,228MUs) than cone (32,347MUs). The total delivery time (which included 5 minutes for setup) was less, 29.6min (26∼32min) for MLC vs 45min (35∼55min) for cone. Conclusion: While the differences in the dosimetry between the MLC and circular collimator plans were rather minor, the MLC plans were much more efficient and required significantly less treatment time.

  15. Design and Performance Optimization of the LHC Collimation System

    CERN Document Server

    Robert-Démolaize, G

    2006-01-01

    The Large Hadron Collider (LHC) is presently under construction at CERN. The LHC is a circular accelerator that stores proton beams and accelerates them to a 7 TeV beam energy. The required bending fields are achieved with super-conducting magnets. The stored proton beams are collided in experimental detectors and produce a design luminosity of 1E+34 cm-2.s-1. Every storage ring encounters unavoidable proton losses. The protons that diffuse into the so-called beam halo can touch accelerator components. In order to avoid quenches of the superconducting magnets, the halo protons must be removed before reaching the magnets. This is achieved with a multi-stage cleaning system, built out of two-sided collimators that are located at adequate positions in the machine. Due to the high stored beam intensity (required for high luminosity), the efficiency of the LHC beam cleaning must be much better than in any other exisiting machine: not more than 0.00002% of protons hitting the collimators may escape and impact on an...

  16. Calculating and measuring thermal neutrons exiting from neutron diffractometers collimators

    CERN Document Server

    Tafazolee, K

    2000-01-01

    process, effectiveness of them are studied for the enhancement of the available system. Final conclusion from the simulation process, indicates that the heavy water with the thickness of 50 to 60 cm. is the best moderator for gaining the better thermal neutrons flux for enhancement of P.N.D. in the T.R.R. Powder Neutron Diffractometer y (P.N.D.) is relatively good and practical way for identification of the 3 dimensional construction of materials. In order to exploit the capabilities of this method, in one of the neutron beam of the Tehran Research Reactor (T.R.R.), a collimator embedded inside the concrete wall, direct the neutrons produced in the core reactor towards a monochromator e. Neutrons having been monochromated by 2 nd collimator are then directed towards the sample. Then the pattern of diffracted neutrons from the sample are studied. In order to make the best out of it, neutrons coming to sit on the sample must be of the thermal type. That means the number/amount of thermal neutrons flux in compar...

  17. Acceleration and collimation of relativistic MHD disk winds

    CERN Document Server

    Porth, O

    2009-01-01

    We perform axisymmetric relativistic magnetohydrodynamic (MHD) simulations to investigate the acceleration and collimation of jets and outflows from disks around compact objects. The fiducial disk surface (respectively a slow disk wind) is prescribed as boundary condition for the outflow. We apply this technique for the first time in the context of relativistic jets. The strength of this approach is that it allows us to run a parameter study in order to investigate how the accretion disk conditions govern the outflow formation. Our simulations using the PLUTO code run for 500 inner disk rotations and on a physical grid size of 100x200 inner disk radii. In general, we obtain collimated beams of mildly relativistic speed and mass-weighted half-opening angles of 3-7 degrees. When we increase the outflow Poynting flux by injecting an additional disk toroidal field into the inlet, Lorentz factors up to 6 are reached. These flows gain super-magnetosonic speed and remain Poynting flux dominated. The light surface of...

  18. Application of multileaf collimator in breast cancer radiation techniques

    Science.gov (United States)

    Janiszewska, Marzena; Dupla, Dorota; Nowakowski, Grzegorz

    2004-07-01

    Modern radiation therapy tools allow a precise delivery of a high dose to a target area (so-called planning target volume -- PTV) and spare, at the same time, critical organs in the vicinity of cancerous lesions. One of the tools of conformal therapy is a multi-leaf collimator, which provides the opportunity to optimally adjust the therapeutic field to the tumor area. More difficult areas for radiation therapy include: mamma, after BCT, and chest after mammectomy with regional lymph nodes. The objective of the study is to present technical and physical aspects of breast carcinoma irradiation when applying a multi-leaf collimator. The following techniques were applied: (a) the isocentric technique of tangent fields (from two to four) for the mamma after BCT; (b) the method of a common isocenter, for the areas of mamma and for regional lymph nodes; (c) the technique of complementary photon + electron fields, for the area of chest after mammectomy and lymph nodes. The presented techniques were implemented as standard procedures in the preparation of breast carcinoma radiation treatment in the Lower Silesian Oncology Center.

  19. Collimation with tighter TCTs at β*=40 cm

    CERN Document Server

    Bruce, Roderik; Kwee-Hinzmann, Regina; Mereghetti, Alessio; Mirarchi, Daniele; Quaranta, Elena; Redaelli, Stefano; Salvachua Ferrando, Belen Maria; Valentino, Gianluca; Valloni, Alessandra; Garcia Morales, Hector; CERN. Geneva. ATS Department

    2015-01-01

    MD 310 was carried out on August 28 2015, in order to investigate the collimation performance using nominal optics with β* =40 cm, 2 σ retraction collimator settings in IR7, and the very tight TCT settings which are necessary to protect the small normalized aperture. With these tight settings, we expect higher losses on the TCTs which should cause also higher beam-halo background at the experiments. During the MD, a total of 70 betatron loss maps were performed over a range of TCT settings and for dierent settings of the TCLAs in IR7. ATLAS and CMS were exceptionally taking data outside stable beams, in order to monitor the background. Furthermore, betatron loss maps were performed with a small momentum oset of the whole beam, induced by a shift of the RF frequency. The MD results can therefore also be used to assess the cleaning eciency in IR7 with the β* =40 cm optics, as well as the eects of energy osets on the cleaning. At the end of the MD, an asynchronous dump test was performed, in order to monitor ...

  20. Par Pond Fish, Water, and Sediment Chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Paller, M.H. [Westinghouse Savannah River Company, AIKEN, SC (United States); Wike, L.D.

    1996-06-01

    The objectives of this report are to describe the Par Pond fish community and the impact of the drawdown and refill on the community, describe contaminant levels in Par Pond fish, sediments, and water and indicate how contaminant concentrations and distributions were affected by the drawdown and refill, and predict possible effects of future water level fluctuations in Par Pond.

  1. An energy-optimized collimator design for a CZT-based SPECT camera

    Energy Technology Data Exchange (ETDEWEB)

    Weng, Fenghua [School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200030 (China); Department of Nuclear Medicine, Ruijin Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030 (China); Bagchi, Srijeeta [Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA (United States); Zan, Yunlong [School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200030 (China); Department of Nuclear Medicine, Ruijin Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030 (China); Huang, Qiu, E-mail: qiuhuang@sjtu.edu.cn [School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200030 (China); Department of Nuclear Medicine, Ruijin Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030 (China); Seo, Youngho, E-mail: youngho.seo@ucsf.edu [Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA (United States); Department of Radiation Oncology, University of California, San Francisco, CA (United States)

    2016-01-11

    In single photon emission computed tomography, it is a challenging task to maintain reasonable performance using only one specific collimator for radiotracers over a broad spectrum of diagnostic photon energies, since photon scatter and penetration in a collimator differ with the photon energy. Frequent collimator exchanges are inevitable in daily clinical SPECT imaging, which hinders throughput while subjecting the camera to operational errors and damage. Our objective is to design a collimator, which is independent of the photon energy, performs reasonably well for commonly used radiotracers with low- to medium-energy levels of gamma emissions. Using the Geant4 simulation toolkit, we simulated and evaluated a parallel-hole collimator mounted to a CZT detector. With the pixel-geometry-matching collimation, the pitch of the collimator hole was fixed to match the pixel size of the CZT detector throughout this work. Four variables, hole shape, hole length, hole radius/width and the source-to-collimator distance were carefully studied. Scatter and penetration of the collimator, sensitivity and spatial resolution of the system were assessed for four radionuclides including {sup 57}Co, {sup 99m}Tc, {sup 123}I and {sup 111}In, with respect to the aforementioned four variables. An optimal collimator was then decided upon such that it maximized the total relative sensitivity (TRS) for the four considered radionuclides while other performance parameters, such as scatter, penetration and spatial resolution, were benchmarked to prevalent commercial scanners and collimators. Digital phantom studies were also performed to validate the system with the optimal square-hole collimator (23 mm hole length, 1.28 mm hole width, and 0.32 mm septal thickness) in terms of contrast, contrast-to-noise ratio and recovery ratio. This study demonstrates promise of our proposed energy-optimized collimator to be used in a CZT-based gamma camera, with comparable or even better imaging performance

  2. High-resolution field shaping utilizing a masked multileaf collimator.

    Science.gov (United States)

    Williams, P C; Cooper, P

    2000-08-01

    Multileaf collimators (MLCs) have become an important tool in the modern radiotherapy department. However, the current limit of resolution (1 cm at isocentre) can be too coarse for acceptable shielding of all fields. A number of mini- and micro-MLCs have been developed, with thinner leaves to achieve approved resolution. Currently however, such devices are limited to modest field sizes and stereotactic applications. This paper proposes a new method of high-resolution beam collimation by use of a tertiary grid collimator situated below the conventional MLC. The width of each slit in the grid is a submultiple of the MLC width. A composite shaped field is thus built up from a series of subfields, with the main MLC defining the length of each strip within each subfield. Presented here are initial findings using a prototype device. The beam uniformity achievable with such a device was examined by measuring transmission profiles through the grid using a diode. Profiles thus measured were then copied and superposed to generate composite beams, from which the uniformity achievable could be assessed. With the average dose across the profile normalized to 100%, hot spots up to 5.0% and troughs of 3% were identified for a composite beam of 2 x 5.0 mm grids, as measured at Dmax for a 6 MV beam. For a beam composed from 4 x 2.5 mm grids, the maximum across the profile was 3.0% above the average, and the minimum 2.5% below. Actual composite profiles were also formed using the integrating properties of film, with the subfield indexing performed using an engineering positioning stage. The beam uniformity for these fields compared well with that achieved in theory using the diode measurements. Finally sine wave patterns were generated to demonstrate the potential improvements in field shaping and conformity using this device as opposed to the conventional MLC alone. The scalloping effect on the field edge commonly seen on MLC fields was appreciably reduced by use of 2 x 5.0 mm

  3. suPAR: The Molecular Crystal Ball

    Directory of Open Access Journals (Sweden)

    Maria Thunø

    2009-01-01

    Full Text Available soluble urokinase Plasminogen Activator Receptor (suPAR levels reflect inflammation and elevated suPAR levels are found in several infectious diseases and cancer. suPAR exists in three forms; suPARI-III, suPARII-III and suPARI which show different properties due to structural differences. Studies suggest that full-length suPAR is a regulator of uPAR/uPA by acting as uPA-scavenger, whereas the cleaved suPARII-III act as a chemotactic agent promoting the immune response via the SRSRY sequence in the linker-region. This review focus on the various suPAR fragments and their involvement in inflammation and pathogenic processes. We focus on the molecular mechanisms of the suPAR fragments and the link to the inflammatory process, as this could lead to medical applications in infectious and pathological conditions.

  4. Lumbar spine radiography — poor collimation practices after implementation of digital technology

    DEFF Research Database (Denmark)

    Zetterberg, Lars Gøran; Espeland, Ansgar

    2011-01-01

    Objectives: The transition from analogue to digital radiography may have reduced the motivation to perform proper collimation, as digital techniques have made it possible to mask areas irradiated outside the area of diagnostic interest (ADI). We examined the hypothesis that collimation practices ...

  5. Design and experimental validation of a compact collimated Knudsen source

    CERN Document Server

    Wouters, Steinar H W; Mutsaers, Peter H A; Vredenbregt, Edgar J D

    2015-01-01

    In this paper we discuss the design and performance of a collimated Knudsen source which has the benefit of a simple design over recirculating sources. Measurements of the flux, transverse velocity distribution and brightness at different temperatures were conducted to evaluate the performance. The scaling of the flux and brightness with the source temperature follow the theoretical predictions. The transverse velocity distribution in the transparent operation regime also agrees with the simulated data. The source was found able to produce a flux of $10^{14}$ s$^{-1}$ at a temperature of 433 K. Furthermore the transverse reduced brightness of an ion beam with equal properties as the atomic beam reads $1.7 \\times 10^2$ A/(m${}^2$ sr eV) which is sufficient for our goal: the creation of an ultra-cold ion beam by ionization of a laser-cooled and compressed atomic rubidium beam.

  6. Adaptive fiber optics collimator based on flexible hinges.

    Science.gov (United States)

    Zhi, Dong; Ma, Yanxing; Ma, Pengfei; Si, Lei; Wang, Xiaolin; Zhou, Pu

    2014-08-20

    In this manuscript, we present a new design for an adaptive fiber optics collimator (AFOC) based on flexible hinges by using piezoelectric stacks actuators for X-Y displacement. Different from traditional AFOC, the new structure is based on flexible hinges to drive the fiber end cap instead of naked fiber. We fabricated a real AFOC based on flexible hinges, and the end cap's deviation and resonance frequency of the device were measured. Experimental results show that this new AFOC can provide fast control of tip-tilt deviation of the laser beam emitting from the end cap. As a result, the fiber end cap can support much higher power than naked fiber, which makes the new structure ideal for tip-tilt controlling in a high-power fiber laser system.

  7. IMRT delivery performance with a varian multileaf collimator.

    Science.gov (United States)

    Losasso, Thomas

    2008-01-01

    The use of a multileaf collimator (MLC) for intensity-modulated radiotherapy poses unique dosimetric issues. The nature of intensity-modulated radiotherapy dosimetry, centered on leaf position accuracy, is common to all MLCs. However, the mechanical and software designs of MLCs from the different manufacturers distinguish them. This report focused on the Varian Millennium 120, although the concepts are applicable to the earlier Varian Mark series as well. The factors that affect dose delivery in clinical fields (i.e., mechanical tolerances, motor fatigue, and latency effects) have been quantified. Moreover, inadequate modeling of the MLC in the planning system can be perceived as erratic performance. Individually, some problems have been shown to be insignificant; others are correctable using software. If these problems are rectified or at least understood by the physicist, quality assurance can be simplified.

  8. Performance evaluation of advanced industrial SPECT system with diverging collimator.

    Science.gov (United States)

    Park, Jang Guen; Jung, Sung-Hee; Kim, Jong Bum; Moon, Jinho; Yeom, Yeon Soo; Kim, Chan Hyeong

    2014-12-01

    An advanced industrial SPECT system with 12-fold-array diverging collimator was developed for flow visualization in industrial reactors and was discussed in the previous study. The present paper describes performance evaluation of the SPECT system under both static- and dynamic- flow conditions. Under static conditions, the movement of radiotracer inside the test reactor was compared with that of color tracer (blue ink) captured with a high-speed camera. The comparison of the reconstructed images obtained with the radiotracer and the SPECT system showed fairly good agreement with video-frames of the color tracer obtained with the camera. Based on the results of the performance evaluation, it is concluded that the SPECT system is suitable for investigation and visualization of flows in industrial flow reactors.

  9. Solar Divergence Collimators for Optical Characterisation of Solar Components

    Directory of Open Access Journals (Sweden)

    D. Fontani

    2013-01-01

    Full Text Available Experimentation and laboratory optical tests on solar components are central aspects of the research on renewable energies. The key element of the proposed testing systems is a solar divergence collimator, which exactly reproduces in laboratory the sunlight divergence, while commercial solar simulators are mainly aimed to replicate intensity and spectrum of the sun. Precise solar divergence reproduction is essential to correctly assess the optical properties and to simulate the operative conditions of a solar collecting device. Optical characterisation and experimentation can give information about production quality and homogeneity; moreover, specific tests can address the serial production of solar components detecting defects type and location. For Concentrating Photovoltaic systems, appropriate tests can analyze solar concentrators of various shapes, dimensions, and collection features. Typically, to characterise a solar component the most important and commonly examined quantities are collection efficiency, image plane analysis, and angle dependence.

  10. Solar wind collimation of the Jupiter high velocity dust streams

    Science.gov (United States)

    Flandes, A.; Krueger, H.

    2006-12-01

    The dust bursts discovered by the Ulysses dust sensor when approaching Jupiter in 1992 were later confirmed as collimated streams of high velocity (~200 km/s) charged (~5V) dust grains escaping from Jupiter and dominated by the interplanetary Magnetic field (IMF). With Cassini, a similar phenomenon was observed in Saturn. It was demonstrated that the Jovian dust streams are closely related to the solar wind compressed regions, either Corotating interaction regions (CIRs) or Coronal mass ejections (CMEs) ¨Cto a minor extent-. Actually the dust streams seem ultimately to be generated by such events. This can be explained considering that dust grains are accelerated as they gain substantial energy while compressed at the forward and reverse shocks that bound or precede these solar wind regions.

  11. Augmented reality aiding collimator exchange at the LHC

    Energy Technology Data Exchange (ETDEWEB)

    Martínez, Héctor, E-mail: hector.martinez@sensetrix.com [SenseTrix, PL 20 FI-00101 Helsinki (Finland); Fabry, Thomas [European Organization for Nuclear Research, CERN, CH-1211 Genève 23 (Switzerland); Laukkanen, Seppo [SenseTrix, PL 20 FI-00101 Helsinki (Finland); Mattila, Jouni [Tampere University of Technology, PO Box 527, FI-33101 Tampere (Finland); Tabourot, Laurent [SYMME, Université de Savoie, Polytech Annecy-Chambéry, 5 chemin de Bellevue, 74944 Annecy le Vieux (France)

    2014-11-01

    Novel Augmented Reality techniques have the potential to have a large positive impact on the way remote maintenance operations are carried out in hazardous areas, e.g. areas where radiation doses that imply careful planning and optimization of maintenance operations are present. This paper describes an Augmented Reality strategy, system and implementation for aiding the remote collimator exchange in the LHC, currently the world's largest and highest-energy particle accelerator. The proposed system relies on marker detection and multi-modal augmentation in real-time. A database system has been used to ensure flexibility. The system has been tested in a mock-up facility, showing real time performance and great potential for future use in the LHC. The technical-scientific difficulties identified during the development of the system and the proposed solutions described in this paper may help the development of future Augmented Reality systems for remote handling in scientific facilities.

  12. Preliminary thermo-mechanical analysis of angular beam impact on LHC collimators

    CERN Document Server

    Cauchi, M; Bertarelli, A; Carra, F; Dallocchio, A; Deboy, D; Mariani, N; Rossi, A; Lari, L; Mollicone, P; Sammut, N

    2012-01-01

    The correct functioning of the LHC Collimation System is crucial to attain the desired LHC luminosity performance. However, the requirements to handle high intensity beams can be demanding. In this respect, accident scenarios must be well studied in order to assess their effect on the robustness of the collimators. One of the most probable accident scenarios identified is an asynchronous beam dump coupled with slight angular misalignment errors of the collimator installation at the beam-line. Previous work presented a preliminary thermal evaluation of the extent of beam-induced damage for such scenarios, where it was shown that in some cases, a tilt of the jaw could actually serve to mitigate the effect of an asynchronous dump on the collimators. This paper will further analyze the response of tertiary collimators in presence of such angular jaw alignments. Such work will also help to start identifying optimal operational conditions.

  13. Observation of strong leakage reduction in crystal assisted collimation of the SPS beam

    Energy Technology Data Exchange (ETDEWEB)

    Scandale, W. [CERN, European Organization for Nuclear Research, CH-1211 Geneva 23 (Switzerland); Laboratoire de l' Accelerateur Lineaire (LAL), Universite Paris Sud Orsay, Orsay (France); INFN Sezione di Roma, Piazzale Aldo Moro 2, 00185 Rome (Italy); Arduini, G.; Butcher, M.; Cerutti, F.; Garattini, M.; Gilardoni, S.; Lechner, A.; Losito, R.; Masi, A.; Mereghetti, A.; Metral, E. [CERN, European Organization for Nuclear Research, CH-1211 Geneva 23 (Switzerland); Mirarchi, D. [CERN, European Organization for Nuclear Research, CH-1211 Geneva 23 (Switzerland); Imperial College, London (United Kingdom); Montesano, S.; Redaelli, S. [CERN, European Organization for Nuclear Research, CH-1211 Geneva 23 (Switzerland); Rossi, R. [CERN, European Organization for Nuclear Research, CH-1211 Geneva 23 (Switzerland); INFN Sezione di Roma, Piazzale Aldo Moro 2, 00185 Rome (Italy); Schoofs, P.; Smirnov, G. [CERN, European Organization for Nuclear Research, CH-1211 Geneva 23 (Switzerland); Bagli, E.; Bandiera, L.; Baricordi, S. [INFN Sezione di Ferrara, Dipartimento di Fisica, Università di Ferrara, Ferrara (Italy); and others

    2015-09-02

    In ideal two-stage collimation systems, the secondary collimator–absorber should have its length sufficient to exclude practically the exit of halo particles with large impact parameters. In the UA9 experiments on the crystal assisted collimation of the SPS beam a 60 cm long tungsten bar is used as a secondary collimator–absorber which is insufficient for the full absorption of the halo protons. Multi-turn simulation studies of the collimation allowed to select the position for the beam loss monitor downstream the collimation area where the contribution of particles deflected by the crystal in channeling regime but emerging from the secondary collimator–absorber is considerably reduced. This allowed observation of a strong leakage reduction of halo protons from the SPS beam collimation area, thereby approaching the case with an ideal absorber.

  14. Calculation of effective dose in whole body in dependence of angle of collimator for photon fields

    Energy Technology Data Exchange (ETDEWEB)

    Fuenzalida, M. [Universidad de la Frontera, Temuco (Chile). Programa de Magister en Fisica Medica; Varon, C.; Piriz, G.; Banguero, Y.; Lozano, E.; Mancilla, C., E-mail: fisicamedica@incancer.c [Instituto Nacional del Cancer, Santiago (Chile). Unidad de Fisica Medica

    2011-07-01

    The objective of this work is to obtain quantifiable data of whole body effective dose for photons fields of 6 MV and 18 MV in function of the collimator angle of a Varian Clinac 21EX lineal accelerator. It has been made a variety of studies which investigate the form to reduce the dose in whole body with photons fields, specially over the potential risks and the influence of the collimator angle, as performed Stanthakis et al. [1] with the Monte Carlo method. As a result of this work, the values of whole body effective doses are higher with a 0 deg collimator than with a 90 deg collimator, and as the field size increases, the effective doses difference in whole body, between 0 deg and 90 deg collimator angle, for both energies, becomes smaller. (author)

  15. Studying ATHENA optics with divergent and collimated x-ray beams

    Science.gov (United States)

    Menz, Benedikt; Bräuninger, Heinrich; Burwitz, Vadim; Hartner, Gisela; Predehl, Peter

    2014-07-01

    An open question in the measurement of X-ray optics for satellite experiments is what the PSF (point spread function) looks like in orbit and what the focal length for a source at infinite distance is. In order to measure segmented optics as proposed for ATHENA a collimated X-ray beam with a size of several square centimeters is necessary. We showed that by using a zone plate such a collimated beam can be achieved. We discuss here the requirements such a zone plate collimator has to comply in order to characterize with this collimator an ATHENA type optic. Additional we can present results obtained with a first version of such a collimator and can show so the proof of principle.

  16. Observation of strong leakage reduction in crystal assisted collimation of the SPS beam

    Directory of Open Access Journals (Sweden)

    W. Scandale

    2015-09-01

    Full Text Available In ideal two-stage collimation systems, the secondary collimator–absorber should have its length sufficient to exclude practically the exit of halo particles with large impact parameters. In the UA9 experiments on the crystal assisted collimation of the SPS beam a 60 cm long tungsten bar is used as a secondary collimator–absorber which is insufficient for the full absorption of the halo protons. Multi-turn simulation studies of the collimation allowed to select the position for the beam loss monitor downstream the collimation area where the contribution of particles deflected by the crystal in channeling regime but emerging from the secondary collimator–absorber is considerably reduced. This allowed observation of a strong leakage reduction of halo protons from the SPS beam collimation area, thereby approaching the case with an ideal absorber.

  17. Note: Detector collimators for the nanoscale ordered materials diffractometer instrument at the Spallation Neutron Source

    Energy Technology Data Exchange (ETDEWEB)

    Tamalonis, A. [Materials Development, Inc., Arlington Heights, Illinois 60004, USA; Weber, J. K. R. [Materials Development, Inc., Arlington Heights, Illinois 60004, USA; Argonne National Laboratory, Argonne, Illinois 60439, USA; Neuefeind, J. C. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA; Carruth, J. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA; Skinner, L. B. [Materials Development, Inc., Arlington Heights, Illinois 60004, USA; Argonne National Laboratory, Argonne, Illinois 60439, USA; Stony Brook University, Stony Brook, New York 11794, USA; Alderman, O. L. G. [Materials Development, Inc., Arlington Heights, Illinois 60004, USA; Argonne National Laboratory, Argonne, Illinois 60439, USA; Benmore, C. J. [Argonne National Laboratory, Argonne, Illinois 60439, USA

    2015-09-01

    Five neutron collimator designs were constructed and tested at the nanoscale ordered materials diffractometer (NOMAD) instrument. Collimators were made from High Density PolyEthylene (HDPE) or 5% borated HDPE. In all cases, collimators improved the signal to background ratio and reduced detection of secondary scattering. In the Q-range 10-20 (angstrom)-1, signal to background ratio improved by factors of approximately 1.6 and 2.0 for 50 and 100 mm deep collimators, respectively. In the Q-range 40-50 angstrom-1, the improvement factors were 1.8 and 2.7. Secondary scattering as measured at Q similar to 9.5 angstrom-1 was significantly decreased when the collimators were installed.

  18. Note: Detector collimators for the nanoscale ordered materials diffractometer instrument at the Spallation Neutron Source

    Energy Technology Data Exchange (ETDEWEB)

    Tamalonis, A. [Materials Development, Inc., Arlington Heights, Illinois 60004 (United States); Weber, J. K. R., E-mail: rweber@anl.gov; Alderman, O. L. G. [Materials Development, Inc., Arlington Heights, Illinois 60004 (United States); Argonne National Laboratory, Argonne, Illinois 60439 (United States); Neuefeind, J. C.; Carruth, J. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 (United States); Skinner, L. B. [Materials Development, Inc., Arlington Heights, Illinois 60004 (United States); Argonne National Laboratory, Argonne, Illinois 60439 (United States); Stony Brook University, Stony Brook, New York 11794 (United States); Benmore, C. J. [Argonne National Laboratory, Argonne, Illinois 60439 (United States)

    2015-09-15

    Five neutron collimator designs were constructed and tested at the nanoscale ordered materials diffractometer (NOMAD) instrument. Collimators were made from High Density PolyEthylene (HDPE) or 5% borated HDPE. In all cases, collimators improved the signal to background ratio and reduced detection of secondary scattering. In the Q-range 10-20 Å{sup −1}, signal to background ratio improved by factors of approximately 1.6 and 2.0 for 50 and 100 mm deep collimators, respectively. In the Q-range 40-50 Å{sup −1}, the improvement factors were 1.8 and 2.7. Secondary scattering as measured at Q ∼ 9.5 Å{sup −1} was significantly decreased when the collimators were installed.

  19. Collimation Down to 2 Sigma in Special Physics Runs in the LHC

    CERN Document Server

    Burkhardt, H; Salvachua, B; Valentino, G

    2013-01-01

    We report on observations with collimation very close to the beam. Primary collimators were moved in small steps down to 2 σ from the beam axis to allow for measurements of very forward proton scattering in special highbeta runs in the LHC. We studied the reduction in intensity as a function of collimator position which provides information about the halo shape. After scraping at 2σ, collimators were retracted to 2:5 σ. This allowed for measurements of very forward proton-proton scattering with roman pot detectors at 3 σ from the beam axis at acceptable background levels for about an hour. Good background conditions were restored by another scraping with primary collimators at 2 σ. Beam lifetimes and halo repopulation times were found to be sufficiently long to allow for several hours of data taking between scraping in a single LHC fill.

  20. Collimator optimization and collimator-detector response compensation in myocardial perfusion SPECT using the ideal observer with and without model mismatch and an anthropomorphic model observer

    Science.gov (United States)

    Ghaly, Michael; Links, Jonathan M.; Frey, Eric C.

    2016-03-01

    The collimator is the primary factor that determines the spatial resolution and noise tradeoff in myocardial perfusion SPECT images. In this paper, the goal was to find the collimator that optimizes the image quality in terms of a perfusion defect detection task. Since the optimal collimator could depend on the level of approximation of the collimator-detector response (CDR) compensation modeled in reconstruction, we performed this optimization for the cases of modeling the full CDR (including geometric, septal penetration and septal scatter responses), the geometric CDR, or no model of the CDR. We evaluated the performance on the detection task using three model observers. Two observers operated on data in the projection domain: the Ideal Observer (IO) and IO with Model-Mismatch (IO-MM). The third observer was an anthropomorphic Channelized Hotelling Observer (CHO), which operated on reconstructed images. The projection-domain observers have the advantage that they are computationally less intensive. The IO has perfect knowledge of the image formation process, i.e. it has a perfect model of the CDR. The IO-MM takes into account the mismatch between the true (complete and accurate) model and an approximate model, e.g. one that might be used in reconstruction. We evaluated the utility of these projection domain observers in optimizing instrumentation parameters. We investigated a family of 8 parallel-hole collimators, spanning a wide range of resolution and sensitivity tradeoffs, using a population of simulated projection (for the IO and IO-MM) and reconstructed (for the CHO) images that included background variability. We simulated anterolateral and inferior perfusion defects with variable extents and severities. The area under the ROC curve was estimated from the IO, IO-MM, and CHO test statistics and served as the figure-of-merit. The optimal collimator for the IO had a resolution of 9-11 mm FWHM at 10 cm, which is poorer resolution than typical collimators

  1. Efficacy of a dynamic collimator for overranging dose reduction in a second- and third-generation dual source CT scanner

    OpenAIRE

    Booij, Ronald; Dijkshoorn, Marcel; Straten, Marcel

    2017-01-01

    textabstractObjectives: The purpose of this study was to assess the efficacy of the renewed dynamic collimator in a third-generation dual source CT (DSCT) scanner and to determine the improvements over the second-generation scanner. Methods: Collimator efficacy is defined as the percentage overranging dose in terms of dose–length product (DLP) that is blocked by the dynamic collimator relative to the total overranging dose in case of a static collimator. Efficacy was assessed at various pitch...

  2. An investigation of the dose distribution effect related with collimator angle for VMAT method

    Science.gov (United States)

    Tas, B.; Bilge, H.; Ozturk, S. Tokdemir

    2016-03-01

    Aim of this study is to investigate the efficacy of dose distribution in eleven prostate cancer patients with single VMAT and double VMAT when varying collimator angle. We generated optimum single and double VMAT treatment plans when collimator angle was 0°. We recalculated single VMAT plans at different collimator angles(0°,15°,30°,45°,60°,75°,90°) for double VMAT plans(0°-0°,15°-345°,30°-330°,45°-315°,60°-300°,75°-285°,90°-270°) without changing any optimization parameters. HI, DVH and %95 dose coverage of PTV calculated and analyzed. We determined better dose distribution with some collimator angles. Plans were verified using the 2 dimensional ion chamber array Matrixx® and 3 dimensional Compass® software program. A higher %95 dose coverage of PTV was found for single VMAT in the 15° collimator angle, for double VMAT in the 60°-300° and 75°-285° collimator angles. Because of lower rectum doses, we suggested 75°-285°. When we compared single and double VMAT's dose distribution, we had better % 95 dose coverage of PTV and lower HI with double VMAT. Our result was significant statistically. These finds are informative for choosing 75°-285° collimator angles in double VMAT plans for prostate cancer.

  3. Beam feasibility study of a collimator with in-jaw beam position monitors

    Science.gov (United States)

    Wollmann, Daniel; Nosych, Andriy A.; Valentino, Gianluca; Aberle, Oliver; Aßmann, Ralph W.; Bertarelli, Alessandro; Boccard, Christian; Bruce, Roderik; Burkart, Florian; Calvo, Eva; Cauchi, Marija; Dallocchio, Alessandro; Deboy, Daniel; Gasior, Marek; Jones, Rhodri; Kain, Verena; Lari, Luisella; Redaelli, Stefano; Rossi, Adriana

    2014-12-01

    At present, the beam-based alignment of the LHC collimators is performed by touching the beam halo with both jaws of each collimator. This method requires dedicated fills at low intensities that are done infrequently and makes this procedure time consuming. This limits the operational flexibility, in particular in the case of changes of optics and orbit configuration in the experimental regions. The performance of the LHC collimation system relies on the machine reproducibility and regular loss maps to validate the settings of the collimator jaws. To overcome these limitations and to allow a continuous monitoring of the beam position at the collimators, a design with jaw-integrated Beam Position Monitors (BPMs) was proposed and successfully tested with a prototype (mock-up) collimator in the CERN SPS. Extensive beam experiments allowed to determine the achievable accuracy of the jaw alignment for single and multi-turn operation. In this paper, the results of these experiments are discussed. The non-linear response of the BPMs is compared to the predictions from electromagnetic simulations. Finally, the measured alignment accuracy is compared to the one achieved with the present collimators in the LHC.

  4. Thermal analysis and cooling structure design of the primary collimator in CSNS/RCS

    CERN Document Server

    Zou, Yi-Qing; Kang, Ling; Qu, Hua-Min; He, Zhe-Xi; Yu, Jie-Bing; 10.1088/1674-1137/37/5/057004

    2013-01-01

    The rapid cycling synchrotron (RCS) of the China Spallation Neutron Source (CSNS) is a high intensity proton ring with beam power of 100 kW. In order to control the residual activation to meet the requirements of hands-on maintenance, a two-stage collimation system has been designed for the RCS. The collimation system consists of one primary collimator made of thin metal to scatter the beam and four secondary collimators as absorbers. Thermal analysis is an important aspect in evaluating the reliability of the collimation system. The calculation of the temperature distribution and thermal stress of the primary collimator with different materials is carried out by using ANSYS code. In order to control the temperature rise and thermal stress of the primary collimator to a reasonable level, an air cooling structure is intended to be used. The mechanical design of the cooling structure is presented, and the cooling effciency with different chin numbers and wind velocity is also analyzed. Finally, the fatigue life...

  5. Collimator design for a multipinhole brain SPECT insert for MRI

    Energy Technology Data Exchange (ETDEWEB)

    Van Audenhaege, Karen; Van Holen, Roel; Vanhove, Christian; Vandenberghe, Stefaan [Department of Electronics and Information Systems, Ghent University-iMinds Medical IT, MEDISIP-IBiTech, De Pintelaan 185 block B/5, Ghent B-9000 (Belgium)

    2015-11-15

    Purpose: Brain single photon emission computed tomography (SPECT) imaging is an important clinical tool, with unique tracers for studying neurological diseases. Nowadays, most commercial SPECT systems are combined with x-ray computed tomography (CT) in so-called SPECT/CT systems to obtain an anatomical background for the functional information. However, while CT images have a high spatial resolution, they have a low soft-tissue contrast, which is an important disadvantage for brain imaging. Magnetic resonance imaging (MRI), on the other hand, has a very high soft-tissue contrast and does not involve extra ionizing radiation. Therefore, the authors designed a brain SPECT insert that can operate inside a clinical MRI. Methods: The authors designed and simulated a compact stationary multipinhole SPECT insert based on digital silicon photomultiplier detector modules, which have shown to be MR-compatible and have an excellent intrinsic resolution (0.5 mm) when combined with a monolithic 2 mm thick LYSO crystal. First, the authors optimized the different parameters of the SPECT system to maximize sensitivity for a given target resolution of 7.2 mm in the center of the field-of-view, given the spatial constraints of the MR system. Second, the authors performed noiseless simulations of two multipinhole configurations to evaluate sampling and reconstructed resolution. Finally, the authors performed Monte Carlo simulations and compared the SPECT insert with a clinical system with ultrahigh-resolution (UHR) fan beam collimators, based on contrast-to-noise ratio and a visual comparison of a Hoffman phantom with a 9 mm cold lesion. Results: The optimization resulted in a stationary multipinhole system with a collimator radius of 150.2 mm and a detector radius of 172.67 mm, which corresponds to four rings of 34 diSPM detector modules. This allows the authors to include eight rings of 24 pinholes, which results in a system volume sensitivity of 395 cps/MBq. Noiseless simulations

  6. Collimator design for a multipinhole brain SPECT insert for MRI.

    Science.gov (United States)

    Van Audenhaege, Karen; Van Holen, Roel; Vanhove, Christian; Vandenberghe, Stefaan

    2015-11-01

    Brain single photon emission computed tomography (SPECT) imaging is an important clinical tool, with unique tracers for studying neurological diseases. Nowadays, most commercial SPECT systems are combined with x-ray computed tomography (CT) in so-called SPECT/CT systems to obtain an anatomical background for the functional information. However, while CT images have a high spatial resolution, they have a low soft-tissue contrast, which is an important disadvantage for brain imaging. Magnetic resonance imaging (MRI), on the other hand, has a very high soft-tissue contrast and does not involve extra ionizing radiation. Therefore, the authors designed a brain SPECT insert that can operate inside a clinical MRI. The authors designed and simulated a compact stationary multipinhole SPECT insert based on digital silicon photomultiplier detector modules, which have shown to be MR-compatible and have an excellent intrinsic resolution (0.5 mm) when combined with a monolithic 2 mm thick LYSO crystal. First, the authors optimized the different parameters of the SPECT system to maximize sensitivity for a given target resolution of 7.2 mm in the center of the field-of-view, given the spatial constraints of the MR system. Second, the authors performed noiseless simulations of two multipinhole configurations to evaluate sampling and reconstructed resolution. Finally, the authors performed Monte Carlo simulations and compared the SPECT insert with a clinical system with ultrahigh-resolution (UHR) fan beam collimators, based on contrast-to-noise ratio and a visual comparison of a Hoffman phantom with a 9 mm cold lesion. The optimization resulted in a stationary multipinhole system with a collimator radius of 150.2 mm and a detector radius of 172.67 mm, which corresponds to four rings of 34 diSPM detector modules. This allows the authors to include eight rings of 24 pinholes, which results in a system volume sensitivity of 395 cps/MBq. Noiseless simulations show sufficient axial

  7. Bending self-collimated one-way light by using gyromagnetic photonic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Li, Qing-Bo [School of Electronic Sciences and Engineering, Nanjing University, Nanjing 210093 (China); Jiangsu Key Construction Laboratory of Modern Measurement Technology and Intelligent System, Huaiyin Normal University, Huaian 223300 (China); Li, Zhen; Wu, Rui-xin, E-mail: rxwu@nju.edu.cn [School of Electronic Sciences and Engineering, Nanjing University, Nanjing 210093 (China)

    2015-12-14

    We theoretically demonstrate that electromagnetic waves can self-collimate and propagate unidirectionally in photonic crystals fabricated using semicylindrical ferrite rods in magnetized states. The parity and time-reversal symmetries of such photonic crystals are broken, resulting in a self-collimated one-way body wave within the photonic crystals. By applying the bias magnetic field in a complex configuration, the self-collimated one-way wave beam can be bent into arbitrary trajectories within the photonic crystal, providing an avenue for controlling wave beams.

  8. Single photon image from position emission tomography with insertable collimator for boron neutron capture therapy

    Energy Technology Data Exchange (ETDEWEB)

    Jung, Joo Young; Yoo, Do Kun; Suh, Tae Suk [Dept. of Biomedical Engineering and Research Institute of Biomedical Engineering, College of Medicine, Catholic University of Korea, Seoul (Korea, Republic of); Hong, Key Jo [Molecular Imaging Program at Stanford (MIPS), Dept. of Radiology, Stanford University, Stanford (United States)

    2014-04-15

    The aim of our proposed system is to confirm the feasibility of extraction of two types of images from one positron emission tomography (PET) module with an insertable collimator for brain tumor treatment during the boron neutron capture therapy (BNCT). The BNCT theory and conceptual diagram of our proposed system are shown fig.1. Data from the PET module, neutron source, and collimator was entered in the Monte Carlon-particle extende source code. We attempted to acquire the PET and SPECT images simultaneously using only PET without an additional isotope. Single photon images were acquired using an insertable collimator on a PET detector.

  9. Polarization Beam Splitter Based on Self-Collimation of a Hybrid Photonic Crystal

    Directory of Open Access Journals (Sweden)

    F. Bagci

    2014-12-01

    Full Text Available A photonic crystal polarization beam splitter based on photonic band gap and self-collimation effects is designed for optical communication wavelengths. The photonic crystal structure consists of a polarization-insensitive self-collimation region and a splitting region. TM- and TE-polarized waves propagate without diffraction in the self-collimation region, whereas they split by 90 degrees in the splitting region. Efficiency of more than 75% for TM- and TE-polarized light is obtained for a polarization beam splitter size of only 17 μm x 17 μm in a wavelength interval of 60 nm including 1.55 μm.

  10. Optimum angle-cut of collimator for dense objects in high-energy proton radiography

    Science.gov (United States)

    Xu, Hai-Bo; Zheng, Na

    2016-02-01

    The use of minus identity lenses with an angle-cut collimator can achieve high contrast images in high-energy proton radiography. This article presents the principles of choosing the angle-cut aperture of the collimator for different energies and objects. Numerical simulation using the Monte Carlo code Geant4 has been implemented to investigate the entire radiography for the French test object. The optimum angle-cut apertures of the collimators are also obtained for different energies. Supported by NSAF (11176001) and Science and Technology Developing Foundation of China Academy of Engineering Physics (2012A0202006)

  11. Low-loss fiber optic rotary joint using C-lens collimators

    Institute of Scientific and Technical Information of China (English)

    JIA Da-gong; JING Wen-cai; ZHANG Yi-mo; ZHOU Ge; ZHANG Jin; TANG Feng

    2005-01-01

    A low-loss fiber optic rotary joint (FORJ) has been designed by using two kinds of C-lens collimators. Its insertion loss and insertion loss variation due to rotation with single-mode fiber collimator is less than 1.76 dB and 0.43 dB respectively.The maximum insertion loss and coupling variation due to rotation with multi-mode fiber collimator is 1.71 dB and 0.29 dB, respectively. This kind of FORJ features low insertion loss, small coupling variation due to rotation and low cost.

  12. Simulation and Measurements of Beam Losses on LHC Collimators During Beam Abort Failures

    CERN Document Server

    Lari, L; Bruce, R; Goddard, B; Redaelli, S; Salvachua, B; Valentino, G; Faus-Golfe, A

    2013-01-01

    One of the main purposes of tracking simulations for collimation studies is to produce loss maps along the LHC ring, in order to identify the level of local beam losses during nominal and abnormal operation scenarios. The SixTrack program is the standard tracking tool used at CERN to perform these studies. Recently, it was expanded in order to evaluate the proton load on different collimators in case of fast beam failures. Simulations are compared with beam measurements at 4 TeV. Combined failures are assumed which provide worst-case scenarios of the load on tungsten tertiary collimators.

  13. Deposition of thin layers of boron nitrides and hydrogenated microcrystalline silicon assisted by high current direct current arc plasma; Deposition assistee par un plasma a arc a haut courant continu de couches minces de Nitrure de Bore et de Silicium microcristallin hydrogene

    Energy Technology Data Exchange (ETDEWEB)

    Franz, D. [Ecole Polytechnique Federale de Lausanne, Centre de Recherches en Physique des Plasmas (CRPP), CH-1015 Lausanne (Switzerland)

    1999-09-01

    In the frame of this thesis, a high current direct current arc (HCDCA) used for the industrial deposition of diamond, has been adapted to study the deposition of two types of coatings: a) boron nitride, whose cubic phase is similar to diamond, for tribological applications, b) hydrogenated microcrystalline silicon, for applications in the semiconductor fields (flat panel displays, solar cells,...). For the deposition of these coatings, the substrates were placed in the diffusion region of the arc. The substrate heating is mainly due to atomic species recombining on its surface. The deposition temperature, varying from 300 to 900 {sup o}C according to the films deposited, is determined by the substrate position, the arc power and the injected gas fluxes, without the use of any external heating or cooling system. Measurements performed on the arc plasma show that the electronic temperature is around 2 eV (23'000 K) while the gas temperature is lower than 5500 K. Typical electronic densities are in the range of 10{sup 12}-10{sup 1'}3 cm{sup -3}. For the deposition of boron nitride films, different boron precursors were used and a wide parameter range was investigated. The extreme difficulty of synthesising cubic boron nitride films by chemical vapour deposition (CVD) did not allow to stabilize the cubic phase of boron nitride in HCDCA. Coatings resulted in hexagonal or amorphous boron nitride with a chemical composition close to stoichiometric. The presence of hydrogen leads to the deposition of rough and porous films. Negative biasing of the samples, for positive ion bombardment, is commonly used to stabilize the cubic phase. In HCDCA and in our biasing range, only a densification of the films could be observed. A boron nitride deposition plasma study by infrared absorption spectroscopy in a capacitive radio frequency reactor has demonstrated the usefulness of this diagnostic for the understanding of the various chemical reactions which occur in this kind of plasma. Diborane dissociation, the different reactions and new species created in the gas phase, such as aminoborane, containing boron-nitrogen bonds, reveals a rich chemistry in the plasma phase. A large amount of atomic hydrogen is necessary to deposit hydrogenated microcrystalline silicon coatings. The study of HCDCA regarding the deposition of diamond has shown that this arc efficiently dissociates molecular hydrogen by way of intermediate vibrationally excited states. This efficient dissociation has allowed the fast deposition (up to 0.6 microns per minute) of highly crystalline silicon films, even without any addition of molecular hydrogen, where the atomic hydrogen was created by the molecular dissociation of silane (SiH{sub 4}). The nature of the deposition precursors is highly dependent on the magnetic field used to confine the arc. At low field, the deposition of hydrogenated silicon radicals created in the plasma leads to columnar growth, whereas with an increase of the magnetic field, the film growth is probably dominated by the deposition of crystallites created in the plasma phase, whose size increases with the field. Moreover, a strong dependence of the film morphology on the deposition parameters has been observed, in particular, regarding the substrate temperature, the hydrogen dilution and the magnetic field. This new deposition technique of hydrogenated microcrystalline silicon is promising for industrial applications. (author)

  14. Improvement of personalized Monte Carlo-aided direct internal contamination monitoring: optimization of calculation times and measurement methodology for the establishment of activity distribution; Amelioration des mesures anthroporadiametriques personnalisees assistees par calcul Monte Carlo: optimisation des temps de calculs et methodologie de mesure pour l'etablissement de la repartition d'activite

    Energy Technology Data Exchange (ETDEWEB)

    Farah, Jad

    2011-10-06

    To optimize the monitoring of female workers using in vivo spectrometry measurements, it is necessary to correct the typical calibration coefficients obtained with the Livermore male physical phantom. To do so, numerical calibrations based on the use of Monte Carlo simulations combined with anthropomorphic 3D phantoms were used. Such computational calibrations require on the one hand the development of representative female phantoms of different size and morphologies and on the other hand rapid and reliable Monte Carlo calculations. A library of female torso models was hence developed by fitting the weight of internal organs and breasts according to the body height and to relevant plastic surgery recommendations. This library was next used to realize a numerical calibration of the AREVA NC La Hague in vivo counting installation. Moreover, the morphology-induced counting efficiency variations with energy were put into equation and recommendations were given to correct the typical calibration coefficients for any monitored female worker as a function of body height and breast size. Meanwhile, variance reduction techniques and geometry simplification operations were considered to accelerate simulations. Furthermore, to determine the activity mapping in the case of complex contaminations, a method that combines Monte Carlo simulations with in vivo measurements was developed. This method consists of realizing several spectrometry measurements with different detector positioning. Next, the contribution of each contaminated organ to the count is assessed from Monte Carlo calculations. The in vivo measurements realized at LEDI, CIEMAT and KIT have demonstrated the effectiveness of the method and highlighted the valuable contribution of Monte Carlo simulations for a more detailed analysis of spectrometry measurements. Thus, a more precise estimate of the activity distribution is given in the case of an internal contamination. (author)

  15. Performance testing of passive autocatalytic recombiners (PARs)

    Energy Technology Data Exchange (ETDEWEB)

    Blanchat, T. [Sandia National Laboratories, Albuquerque, NM (United States); Malliakos, A. [U.S. Nuclear Regulatory Commission, Washington, DC (United States)

    1997-03-01

    Passive autocatalytic recombiners (PARs) have been under consideration in the U.S. as a combustible gas control system in advanced light water reactor (ALWR) containments for design basis and severe accidents. PARs do not require a source of power. Instead they use palladium or platinum as a catalyst to recombine hydrogen and oxygen gases into water vapor upon contact with the catalyst. Energy from the recombination of hydrogen with oxygen is released at a relatively slow but continuous rate into the containment which prevents the pressure from becoming too high. The heat produced creates strong buoyancy effects which increases the influx of the surrounding gases to the recombiner. These natural convective flow currents promote mixing of combustible gases in the containment. PARs are self-starting and self-feeding under a very wide range of conditions. The recombination rate of the PAR system needs to be great enough to keep the concentration of hydrogen (or oxygen) below acceptable limits. There are several catalytic recombiner concepts under development worldwide. The USNRC is evaluating a specific design of a PAR which is in an advanced stage of engineering development and has been proposed for ALWR designs. Sandia National laboratories (SNL), under the sponsorship and the direction of the USNRC, is conducting an experimental program to evaluate the performance of PARs. The PAR will be tested at the SURTSEY facility at SNL. The test plan currently includes the following experiments: experiments will be conducted to define the startup characteristics of PARs (i.e., to define what is the lowest hydrogen concentration that the PAR starts recombining the hydrogen with oxygen); experiments will be used to define the hydrogen depletion rate of PARs as a function of hydrogen concentration; and experiments will be used to define the PAR performance in the presence of high concentrations of steam. (author)

  16. Collimation and material science studies (ColMat) at GSI.

    CERN Document Server

    Stadlmann, J; Kollmus, H; Krause, M; Mustafin, E; Petzenhauser, I; Spiller, P; Strasik, I; Tahir, N; Tomut, M; Trautmann, C

    2010-01-01

    Within the frame of the EuCARD program, the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt is performing accelerator R&D in workpackage 8: ColMat. The coordinated effort is focussed on materials aspects important for building the FAIR accelerator facility at GSI and the LHC upgrade at CERN. Accelerator components and especially protection devices have to be operated in high dose environments. The radiation hazard occurs either by the primary proton and ion beams or the secondary radiation after initial beam loss. Detailed numerical simulations have been carried out to study the damage caused to solid targets by the full impact of the LHC beam as well as the SPS beam. Tungsten, copper and graphite as possible collimator materials have been studied. Experimental an theoretical studies on radiation damage on materials used for the LHC upgrade and the FAIR accelerators are performed at the present GSI experimental facilities. Technical decisions based on these results will have an impact on the F...

  17. DSP-Based Stepping Motor Drivers for the LHC Collimators

    CERN Document Server

    Masi, A; Losito, R; Martino, M

    2008-01-01

    The control electronics of the LHC collimators stepping motors will be located in radiation safe zones up to 800 meters far from the motors. With such cable lengths the standard chopping drivers do not work properly because of the voltage losses on the cable and even more because of the high cable capacitance. The capacitance in fact produces a ringing phenomenon on the driver feedback current that limits the control chopping frequency to the point of being incompatible with the tight EM emissions requirements of the LHC tunnel. In some cases the feedback loop may even become unstable and the driver would fail. The problem was solved by accurately modeling the overall motor-cable system taking into account non-linearities due to hysteresis and eddy currents and by designing an adaptive digital controller, self-tuning to the real cable length. The controller will aim at increasing the chopping frequency to reduce the spectral density of the emissions and at damping the oscillations of the feedback current to a...

  18. Novel adaptive fiber-optics collimator for coherent beam combination.

    Science.gov (United States)

    Zhi, Dong; Ma, Pengfei; Ma, Yanxing; Wang, Xiaolin; Zhou, Pu; Si, Lei

    2014-12-15

    In this manuscript, we experimentally validate a novel design of adaptive fiber-optics collimator (AFOC), which utilizes two levers to enlarge the movable range of the fiber end cap. The enlargement of the range makes the new AFOC possible to compensate the end-cap/tilt aberration in fiber laser beam combining system. The new AFOC based on flexible hinges and levers was fabricated and the performance of the new AFOC was tested carefully, including its control range, frequency response and control accuracy. Coherent beam combination (CBC) of two 5-W fiber amplifiers array with simultaneously end-cap/tilt control and phase-locking control was implemented successfully with the novel AFOC. Experimental results show that the average normalized power in the bucket (PIB) value increases from 0.311 to 0.934 with active phasing and tilt aberration compensation simultaneously, and with both controls on, the fringe contrast improves to more than 82% from 0% for the case with both control off. This work presents a promising structure for tilt aberration control in high power CBC system.

  19. Review of BLM thresholds at tertiary LHC collimators

    CERN Document Server

    D'Andrea, Marco; Zanetti, Marco

    The Large Hadron Collider is designed to accelerate protons at the unprecedented energy of 7 TeV. With a total stored energy of 360 MJ, even tiny losses can cause machine downtime or induce damage to sensitive accelerator components. The Beam Loss Monitors (BLMs) are an important component of the complex LHC protection system. They consist of a series of ionisation chambers located all around the ring to detect secondary particle showers induced by beam losses. The monitors are assigned thresholds such that if the radiation generated by the loss is too high, the BLM triggers a beam dump, preventing the loss to grow excessively. BLM signals are recorded for different integration windows, in order to detect losses on very different time scales, ranging from the extremely short ones (taking place over half a turn) to those very close to steady state (i.e. lasting for more than a minute). The LHC is equipped with a complex collimation system, to provide the machine with passive protection in case of transient los...

  20. RADBALLTECHNOLOGY TESTING AND MCNP MODELING OF THE TUNGSTEN COLLIMATOR

    Energy Technology Data Exchange (ETDEWEB)

    Farfan, E.

    2010-07-08

    The United Kingdom's National Nuclear Laboratory (NNL) has developed a remote, non-electrical, radiation-mapping device known as RadBall{trademark}, which can locate and quantify radioactive hazards within contaminated areas of the nuclear industry. RadBall{trademark} consists of a colander-like outer shell that houses a radiation-sensitive polymer sphere. The outer shell works to collimate radiation sources and those areas of the polymer sphere that are exposed react, becoming increasingly more opaque, in proportion to the absorbed dose. The polymer sphere is imaged in an optical-CT scanner, which produces a high resolution 3D map of optical attenuation coefficients. Subsequent analysis of the optical attenuation matrix provides information on the spatial distribution of sources in a given area forming a 3D characterization of the area of interest. RadBall{trademark} has no power requirements and can be positioned in tight or hard-to reach locations. The RadBall{trademark} technology has been deployed in a number of technology trials in nuclear waste reprocessing plants at Sellafield in the United Kingdom and facilities of the Savannah River National Laboratory (SRNL). This study focuses on the RadBall{trademark} testing and modeling accomplished at SRNL.

  1. A collimated neutron detector for RFP plasmas in MST

    Science.gov (United States)

    Capecchi, W. J.; Anderson, J. K.; Bonofiglo, P. J.; Kim, J.; Sears, S.

    2016-11-01

    The neutron emissivity profile in the Madison Symmetric Torus is being reconstructed through the use of a collimated neutron detector. A scintillator-photomultiplier tube (PMT) system is employed to detect the fusion neutrons with the plasma viewing volume defined by a 55 cm deep, 5 cm diameter aperture. Effective detection of neutrons from the viewing volume is achieved through neutron moderation using 1300 lbs of high density polyethylene shielding, which modeling predicts attenuates the penetrating flux by a factor of 104 or more. A broad spectrum of gamma radiation is also present due to the unconfined fusion proton bombardment of the thick aluminum vacuum vessel. A 15 cm cylindrical liquid scintillator of 3.8 cm diameter is used to further increase directional sensitivity. A fast (5 ns rise time) preamplifier and digitization at 500 MHz prevent pulse pile-up even at high count rates (˜104/s). The entire neutron camera system is situated on an adjustable inclining base which provides the differing plasma viewing volumes necessary for reconstruction of the neutron emissivity profile. This profile, directly related to the fast-ion population, allows for an investigation of the critical fast-ion pressure gradient required to destabilize a neutral beam driven Alfvénic mode which has been shown to transport fast ions.

  2. Magnetically collimated pair jets at the LLNL Titan laser

    Science.gov (United States)

    Williams, Jackson; Chen, Hui; Barnak, Daniel; Betti, Riccardo; Fiksel, Gennady; Hazi, Andrew; Kerr, Shaun; Krauland, Christine; Link, Anthony; Manuel, Mario; Meyerhofer, David; Nagel, Sabrina; Park, Jaebum; Peebles, Jonathan; Pollock, Bradley; Tommasini, Riccardo

    2015-11-01

    Positron-electron pair production experiments were performed at the Titan laser at the Jupiter Laser Facility to investigate the dependence of target thickness and atomic number on pair yield. Externally applied axial magnetic fields, generated by a Helmholtz coil, were used to collimate positrons where the signal observed at the detector increased by a factor of 20 over reference shots without a field. This enabled the detection of positrons from a range of target materials. The emitted positron yield was found to be proportional to the square of the atomic number. This scaling is reduced from the Bethe-Heitler cross section of Z4 by Compton scattering and the stopping power of the target. Monte Carlo simulations support these conclusions, providing a power-law scaling of emitted positrons for all materials and a range of mm-thick targets. This work was performed under the auspices of the U.S. Department of Energy (DOE) by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the LLNL LDRD program under tracking code 12-ERD-062 and the LLNL LGSP.

  3. The tele-robotics system MT200-TAO replaces mechanical tele-manipulators in COGEMA/AREVA-La Hague hot cells

    Energy Technology Data Exchange (ETDEWEB)

    Garrec, Philippe; Lamy-Perbal, Sylvie; Friconneau, Jean-Pierre [CEA France (France); Piolain, Gerard [COGEMA/AREVA-Hague (France)

    2006-07-01

    We present here for the first time the tele-robotics system for hot-cells MT200-TAO (TAO stands for Teleoperation Assistee par Ordinateur or Computer Assisted Tele-robotics), able to replace a conventional telescopic medium tele-manipulator (extension 4 m; capacity 20 kg). The system is currently under evaluation in COGEMA/AREVA- La Hague hot-cells. (authors)

  4. Optimisation of the design of round-hole parallel collimators for ultra-compact nuclear medicine imaging

    CERN Document Server

    Lowe, D; Kwok, H; Bergman, A

    2002-01-01

    Hexagonal-hole parallel collimators are generally desirable over round-hole parallel collimators for most all medical imaging applications due to the optimum sensitivity offered by such a close-packed arrangement of apertures. However, such a sophisticated close-packed collimator arrangement is unlikely to adapt itself well to newly emerging, ultra-compact nuclear medicine gamma cameras. This is principally due to difficulties in machining and fabrication. In searching for alternative collimator designs, one must attempt, as far as possible, to preserve sensitivity, while optimising the spatial resolution achievable with the gamma camera. This work presents a general analysis of round-hole parallel collimator design for nuclear medicine imaging of 140 keV incident gamma-rays. Optimised designs are considered for a variety of source-collimator distances (z=10, 20, 30, 40 mm) which represent typical sentinel node to collimator distances for our particular medical imaging application. Resolution and sensitivity ...

  5. Comparison of LHC collimator beam-based alignment to BPM-Interpolated centers

    CERN Document Server

    Valentino, G; Assmann, R W; Bruce, R; Muller, G J; Redaelli, S; Rossi, A; Lari, L

    2012-01-01

    The beam centers at the Large Hadron Collider collimators are determined by beam-based alignment, where both jaws of a collimator are moved in separately until a loss spike is detected on a Beam LossMonitor downstream. Orbit drifts of more than a few hundred micrometers cannot be tolerated, as they would compromise the performance of the collimation system. Beam Position Monitors (BPMs) are installed at various locations around the LHC ring, and a linear interpolation of the orbit can be obtained at the collimator positions. In this paper, the results obtained from beam-based alignment are compared with the orbit interpolated from the BPM data throughout the 2011 and 2012 LHC proton runs.

  6. Astrophysics of magnetically collimated jets generated from laser-produced plasmas

    CERN Document Server

    Ciardi, A; Fuchs, J; Albertazzi, B; Riconda, C; Pépin, H; Portugall, O

    2012-01-01

    The generation of astrophysically relevant jets, from magnetically collimated, laser-produced plasmas, is investigated through three-dimensional, magneto-hydrodynamic simulations. We show that for laser intensities I ~ 10^12 - 10^14 W/cm^2, a magnetic field in excess of ~ 0.1 MG, can collimate the plasma plume into a prolate cavity bounded by a shock envelope with a standing conical shock at its tip, which re-collimates the flow into a super magneto-sonic jet beam. This mechanism is equivalent to astrophysical models of hydrodynamic inertial collimation, where an isotropic wind is focused into a jet by a confining circumstellar torus-like envelope. The results suggest an alternative mechanism for a large-scale magnetic field to produce jets from wide-angle winds. (abridged version)

  7. Micro-Slit Collimators for X-ray/Gamma-ray Imaging Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Mikro Systems, Inc. (MSI) will advance the state-of-the-art in high resolution, high-aspect-ratio x-ray/gamma-ray collimator fabrication into the micro-slit regime...

  8. A numerical model of a coated capillary-plate thermal neutron collimator

    Institute of Scientific and Technical Information of China (English)

    TIAN Yang; YANG Yi-Gang; LI Yu-Lan; LI Yuan-Jing

    2012-01-01

    A novel thermal neutron collimator was successfully fabricated by coating the inner surface of the capillary plate (CP) with gadolinium oxide using atomic layer deposition (ALD) technology.This CP-based collimator is efficient and compact.A numerical model is presented in the paper to estimate the main performance characteristics of the collimator and to optimize the design for specific applications.According to the results of the calculation based on currently available CPs,the FWHM of the collimator's rocking curve can be smaller than 0.15° while suppressing more than 99.9% of the incident thermal neutrons on the double wings of the curve.Such a coated CP is as thin as 1.25 mm or even thinner,providing high angular resolution with good transmission in a very limited space.

  9. Thermo-mechanical Analysis of the CLIC Post-Linac Energy Collimators

    CERN Document Server

    Resta-Lopez, J; Latina, A

    2012-01-01

    The post-linac energy collimation system of the Compact Linear Collider (CLIC) has been designed for passive protection of the Beam Delivery System (BDS) against miss-steered beams due to failure modes in the main linac. In this paper, a thermo-mechanical analysis of the CLIC energy collimators is presented. This study is based on simulations using the codes FLUKA and ANSYS when an entire bunch train hits the collimators. Different failure mode scenarios in the main linac are considered. The aim is to improve the collimator in order to make a reliable and robust design so that survives without damage the impact of a full bunch train in case of likely events generating energy errors.

  10. Successive approximation algorithm for beam-position-monitor-based LHC collimator alignment

    Science.gov (United States)

    Valentino, Gianluca; Nosych, Andriy A.; Bruce, Roderik; Gasior, Marek; Mirarchi, Daniele; Redaelli, Stefano; Salvachua, Belen; Wollmann, Daniel

    2014-02-01

    Collimators with embedded beam position monitor (BPM) button electrodes will be installed in the Large Hadron Collider (LHC) during the current long shutdown period. For the subsequent operation, BPMs will allow the collimator jaws to be kept centered around the beam orbit. In this manner, a better beam cleaning efficiency and machine protection can be provided at unprecedented higher beam energies and intensities. A collimator alignment algorithm is proposed to center the jaws automatically around the beam. The algorithm is based on successive approximation and takes into account a correction of the nonlinear BPM sensitivity to beam displacement and an asymmetry of the electronic channels processing the BPM electrode signals. A software implementation was tested with a prototype collimator in the Super Proton Synchrotron. This paper presents results of the tests along with some considerations for eventual operation in the LHC.

  11. Optimization of the collimation system for CSNS/RCS with the robust conjugate direction search algorithm

    Science.gov (United States)

    Ji, Hong-Fei; Jiao, Yi; Huang, Ming-Yang; Xu, Shou-Yan; Wang, Na; Wang, Sheng

    2016-09-01

    The Robust Conjugate Direction Search (RCDS) method is used to optimize the collimation system for the Rapid Cycling Synchrotron (RCS) of the China Spallation Neutron Source (CSNS). The parameters of secondary collimators are optimized for a better performance of the collimation system. To improve the efficiency of the optimization, the Objective Ring Beam Injection and Tracking (ORBIT) parallel module combined with MATLAB parallel computing is used, which can run multiple ORBIT instances simultaneously. This study presents a way to find an optimal parameter combination of the secondary collimators for a machine model in preparation for CSNS/RCS commissioning. Supported by National Natural Science Foundation of China (11475202, 11405187, 11205185) and Youth Innovation Promotion Association of Chinese Academy of Sciences (2015009)

  12. Collimation quench test with 6.5 TeV proton beams

    CERN Document Server

    Salvachua Ferrando, Belen Maria; Bruce, Roderik; Hermes, Pascal Dominik; Holzer, Eva Barbara; Jacquet, Delphine; Kalliokoski, Matti; Mereghetti, Alessio; Mirarchi, Daniele; Redaelli, Stefano; Skordis, Eleftherios; Valentino, Gianluca; Valloni, Alessandra; Wollmann, Daniel; Zerlauth, Markus; CERN. Geneva. ATS Department

    2016-01-01

    We show here the analysis of the MD test that aimed to quench the superconducting magnets in the dispersion suppressor region downstream of the main betatron collimation system. In Run I there were several attempts to quench the magnets in the same region. This was done by exciting the Beam 2 in a controlled way using the transverse damper and generating losses leaking from the collimation cleaning. No quench was achieved in 2013 with a maximum of 1 MW of beam power loss absorbed by the collimation system at 4 TeV beam energy. In 2015 a new collimation quench test was done at 6.5 TeV aiming at similar power loss over longer period, 5-10 s. The main outcome of this test is reviewed.

  13. Significance of self magnetic field in long-distance collimation of laser-generated electron beams

    CERN Document Server

    Chen, Shi; Niu, Yifei; Dan, Jiakun; Chen, Ziyu; Li, Jianfeng

    2014-01-01

    Long-distance collimation of fast electron beams generated by laser-metallic-wire targets has been observed in recent experiments, while the mechanism behind this phenomenon remains unclear. In this work, we investigate in detail the laser-wire interaction processes with a simplified model and Classical Trajectory Monte Carlo simulations, and demonstrate the significance of the self magnetic fields of the beams in the long-distance collimation. Good agreements of simulated image plate patterns with various experiments and detailed analysis of electron trajectories show that the self magnetic fields provide restoring force that is critical for the beam collimation. By studying the wire-length dependence of beam divergence in certain experiments, we clarify that the role of the metallic wire is to balance the space-charge effect and thus maintain the collimation.

  14. The Performance of Reflecting Multichannel Collimators as a Neutron Beam Filter and Polarizer

    DEFF Research Database (Denmark)

    Bjerrum Møller, Hans; Passell, L.; Stecher-Rasmussen, F.

    1963-01-01

    Summarizes the results obtained to date from a study of the properties of reflecting multi-channel collimators. The measurements have not yet been completed but enough information is available to give an indication of the capabilities of the system....

  15. VLBI collimation tower technique for time-delay studies of a large ground station communications antenna

    Science.gov (United States)

    Otoshi, T. Y.; Young, L. E.; Rusch, W. V. T.

    1983-01-01

    A need for an accurate but inexpensive method for measuring and evaluating time delays of large ground antennas for VLBI applications motivated the development of the collimation tower technique. Supporting analytical work which was performed primarily to verify time delay measurement results obtained for a large antenna when the transmitter was at a collimation distance of 1/25 of the usual far field criterion is discussed. Comparisons of theoretical and experimental results are also given.

  16. Mesoscopic self-collimation and slow light in all-positive index layered photonic crystals

    CERN Document Server

    Arlandis, Julien; Pollès, Rémi; Moreau, Antoine; Campos, Julien; Gauthier-Lafaye, Olivier; Monmayrant, Antoine

    2011-01-01

    We demonstrate a mesoscopic self-collimation effect in photonic crystal superlattices consisting of a periodic set of all-positive index 2D photonic crystal and homogeneous layers. We develop an electromagnetic theory showing that diffraction-free beams are observed when the curvature of the optical dispersion relation is properly compensated for. This approach allows to combine slow light regime together with self-collimation in photonic crystal superlattices presenting an extremely low filling ratio in air.

  17. Evaluating Red Reflex and Surgeon Preference Between Nearly-Collimated and Focused Beam Microscope Illumination Systems.

    Science.gov (United States)

    Cionni, Robert J; Pei, Ron; Dimalanta, Ramon; Lubeck, David

    2015-08-01

    To evaluate the intensity and stability of the red reflex produced by ophthalmic surgical microscopes with nearly-collimated versus focused illumination systems and to assess surgeon preference in a simulated surgical setting. This two-part evaluation consisted of postproduction surgical video analysis of red reflex intensity and a microscope use and preference survey completed by 13 experienced cataract surgeons. Survey responses were based on bench testing and experience in a simulated surgical setting. A microscope with nearly-collimated beam illumination and two focused beam microscopes were assessed. Red reflex intensity and stability were greater with the nearly-collimated microscope illumination system. In the bench testing survey, surgeons reported that the red reflex was maintained over significantly greater distances away from pupillary center, and depth of focus was numerically greater with nearly-collimated illumination relative to focused illumination. Most participating surgeons (≥64%) reported a preference for the microscope with nearly-collimated illumination with regard to red reflex stability, depth of focus, visualization, surgical working distance, and perceived patient comfort. The microscope with nearly-collimated illumination produced a more intense and significantly more stable red reflex and was preferred overall by more surgeons. This is the first report of an attempt to quantify red reflex intensity and stability and to evaluate surgically-relevant parameters between microscope systems. The data and methods presented here may provide a basis for future studies attempting to quantify differences between surgical microscopes that may affect surgeon preference and microscope use in ophthalmic surgery.

  18. Study on the optical properties of the off-axis parabolic collimator with eccentric pupil

    Science.gov (United States)

    Li, Gang; Gao, Xin; Duan, Jing; Zhang, Henjin

    2017-02-01

    The off-axis parabolic collimator with eccentric pupil has the advantages of wide spectrum, simple structure, easy assembly and adjustment, high performance price ratio. So, it is widely used for parameters testing and image quality calibration of ground-based and space-based cameras. In addition to the Strehl ratio, resolution, wavefront aberration, modulation transfer function, the general evaluation criteria on the imaging quality of the optical system, the beam parallelism characterize the collimator angle resolving capability and collimation condition of the collimator with the target board, can be measured easily ,quickly and operation process is simple, but the study mainly focus on how to measure it so far. In order to solve Quantitative calculation of this problem, firstly, the discussion of aberration condition of the off- axis parabolic is carried out based on the primary aberration theory. Secondly, analysis on the influencing factor on collimator optical properties is given, including the geometrical aberrations of spherical aberration, coma, astigmatism , the relation between the position of the eccentric pupil and the aberration and optical element surface wavefront aberration, after that, according to the basis of diffraction and wavefront aberration theory, the paper deduced calculation method of the beam parallelism, at last, an example of a 400mm diameter off-axis parabolic collimator with eccentric pupil is given to calculate, the practical results shows that calculation data is well in accordance with actual measurement data and results can meet the demand and has a guiding significance to the actual project manufacture and the theory analysis.

  19. Final implementation, commissioning, and performance of embedded collimator beam position monitors in the Large Hadron Collider

    Directory of Open Access Journals (Sweden)

    Gianluca Valentino

    2017-08-01

    Full Text Available During Long Shutdown 1, 18 Large Hadron Collider (LHC collimators were replaced with a new design, in which beam position monitor (BPM pick-up buttons are embedded in the collimator jaws. The BPMs provide a direct measurement of the beam orbit at the collimators, and therefore can be used to align the collimators more quickly than using the standard technique which relies on feedback from beam losses. Online orbit measurements also allow for reducing operational margins in the collimation hierarchy placed specifically to cater for unknown orbit drifts, therefore decreasing the β^{*} and increasing the luminosity reach of the LHC. In this paper, the results from the commissioning of the embedded BPMs in the LHC are presented. The data acquisition and control software architectures are reviewed. A comparison with the standard alignment technique is provided, together with a fill-to-fill analysis of the measured orbit in different machine modes, which will also be used to determine suitable beam interlocks for a tighter collimation hierarchy.

  20. Final implementation, commissioning, and performance of embedded collimator beam position monitors in the Large Hadron Collider

    Science.gov (United States)

    Valentino, Gianluca; Baud, Guillaume; Bruce, Roderik; Gasior, Marek; Mereghetti, Alessio; Mirarchi, Daniele; Olexa, Jakub; Redaelli, Stefano; Salvachua, Belen; Valloni, Alessandra; Wenninger, Jorg

    2017-08-01

    During Long Shutdown 1, 18 Large Hadron Collider (LHC) collimators were replaced with a new design, in which beam position monitor (BPM) pick-up buttons are embedded in the collimator jaws. The BPMs provide a direct measurement of the beam orbit at the collimators, and therefore can be used to align the collimators more quickly than using the standard technique which relies on feedback from beam losses. Online orbit measurements also allow for reducing operational margins in the collimation hierarchy placed specifically to cater for unknown orbit drifts, therefore decreasing the β* and increasing the luminosity reach of the LHC. In this paper, the results from the commissioning of the embedded BPMs in the LHC are presented. The data acquisition and control software architectures are reviewed. A comparison with the standard alignment technique is provided, together with a fill-to-fill analysis of the measured orbit in different machine modes, which will also be used to determine suitable beam interlocks for a tighter collimation hierarchy.

  1. Development of the Collimator System for the 3GEV Rapid Cycling Synchrotron

    CERN Document Server

    Yamamoto, Kazami

    2005-01-01

    In order to localize the beam loss in the restricted area, the beam collimation system is prepared in the 3GeV Rapid Cycling Synchrotron (RCS) of the Japan Proton Accelerator Complex (J-PARC) Project. The amount of the localized beam loss on the one collimator is estimated about 1.2kW, and that loss generates a large quantity of the secondary radiations. So the beam collimator must be designed that it is covered with enough shielding. We calculated the radiation level of the collimator and decided necessary shielding thickness. This result indicated that the residual dose rate at the outside surface of the shielding is mostly under 1mSv/h. We developed the remote cramp system and rad-hard components in order to reduce the radiation exposure during maintenance of the collimator. And also we coated Titanium Nitride (TiN) film on the inside surface of the vacuum chamber in order to reduce the secondary electron emission from the collimator and chamber surface. Now we investigate the possibility of another coatin...

  2. Single- and double-slit collimating effects on fast-atom diffraction spectra

    Science.gov (United States)

    Gravielle, M. S.; Miraglia, J. E.

    2016-09-01

    Diffraction patterns produced by fast He atoms grazingly impinging on a LiF(0 0 1) surface are investigated focusing on the influence of the beam collimation. Single- and double-slit collimating devices situated in front of the beam source are considered. To describe the scattering process we use the Surface Initial Value Representation (SIVR) approximation, which is a semi-quantum approach that incorporates a realistic description of the initial wave packet in terms of the collimating parameters. Our initial wave-packet model is based on the Van Cittert-Zernike theorem. For a single-slit collimation the width of the collimating aperture controls the shape of the azimuthal angle distribution, making different interference mechanisms visible, while the length of the slit affects the polar angle distribution. Additionally, we found that by means of a double-slit collimation it might be possible to obtain a wide polar angle distribution, which is associated with a large spread of the initial momentum perpendicular to the surface, derived from the uncertainty principle. It might be used as a simple way to probe the surface potential for different normal energies.

  3. Effect of the Collimator Angle on Dosimetric Verification of the Volumetric Modulated Arc Therapy

    CERN Document Server

    Kim, Yong Ho; Kim, Won Taek; Kim, Dong Won; Ki, Yongkan; Lee, Juhye; Bae, Jinsuk; Park, Dahl

    2015-01-01

    Collimator angle is usually rotated when planning volumetric modulated arc therapy (VMAT) due to the leakage of radiation between multi-leaf collimator (MLC) leaves. We studied the effect of the collimator angles on the results of dosimetric verification of the VMAT plans for head and neck patients. We studied VMAT plans for 10 head and neck patients. We made 2 sets of VMAT plans for each patient. Each set was composed of 10 plans with collimator angles of 0, 5, 10, 15, 20, 25, 30, 35, 40, 45 degrees. Plans in the first set were optimized individually and plans in the second set shared the 30 degree collimator angle optimization. Two sets of plans were verified using the 2-dimensional ion chamber array MatriXX (IBA Dosimetry, Germany). The comparison between the calculation and measurements were made by the $\\gamma$-index analysis. The $\\gamma$-index (2\\%/2 mm) and (3\\%/3 mm) passing rates had negative correlations with the collimator angle. Maximum difference between $\\gamma$-index (3\\%/3 mm) passing rates o...

  4. The design of the radial collimator for residual stress analysis diffractometer of J-PARC

    Energy Technology Data Exchange (ETDEWEB)

    Torii, Shuki [Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195 (Japan)]. E-mail: torii@post.kek.jp; Moriai, Atsushi [Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195 (Japan)

    2006-11-15

    Radial collimators are devices needed to define gauge sizes in neutron diffraction experiments. A design work of collimators needed for an engineering diffractometer that will be built at J-PARC is being progressed. Several collimators for different gauge sizes (1, 3, 5mm, etc ...) are going to be designed to define a gauge size range from 1 to 10mm. An equation was established to express a relation between the gauge size and geometrical design parameters of the collimator, by applying a normal distribution curve to the error distribution of measured gauge size. Currently, the geometric calculations for several collimators have been finished. A prototype collimator for a gauge size of 1mm was made and an FWHM (full width at half maximum) of the normal distribution of 1mm was obtained from performance tests conducted at the neutron diffractometer for residual stress analysis RESA in JRR-3 (Japan Research Reactor-3) of Japan Atomic Energy Agency (JAEA). In addition, the performance test results are in a good agreement with results from a Monte Carlo simulation with the McStas using the design parameters.

  5. The design of the radial collimator for residual stress analysis diffractometer of J-PARC

    Science.gov (United States)

    Torii, Shuki; Moriai, Atsushi

    2006-11-01

    Radial collimators are devices needed to define gauge sizes in neutron diffraction experiments. A design work of collimators needed for an engineering diffractometer that will be built at J-PARC is being progressed. Several collimators for different gauge sizes (1, 3, 5 mm, etc …) are going to be designed to define a gauge size range from 1 to 10 mm. An equation was established to express a relation between the gauge size and geometrical design parameters of the collimator, by applying a normal distribution curve to the error distribution of measured gauge size. Currently, the geometric calculations for several collimators have been finished. A prototype collimator for a gauge size of 1 mm was made and an FWHM (full width at half maximum) of the normal distribution of 1 mm was obtained from performance tests conducted at the neutron diffractometer for residual stress analysis RESA in JRR-3 (Japan Research Reactor-3) of Japan Atomic Energy Agency (JAEA). In addition, the performance test results are in a good agreement with results from a Monte Carlo simulation with the McStas using the design parameters.

  6. ParAB Partition Dynamics in Firmicutes: Nucleoid Bound ParA Captures and Tethers ParB-Plasmid Complexes.

    Directory of Open Access Journals (Sweden)

    Virginia S Lioy

    Full Text Available In Firmicutes, small homodimeric ParA-like (δ2 and ParB-like (ω2 proteins, in concert with cis-acting plasmid-borne parS and the host chromosome, secure stable plasmid inheritance in a growing bacterial population. This study shows that (ω:YFP2 binding to parS facilitates plasmid clustering in the cytosol. (δ:GFP2 requires ATP binding but not hydrolysis to localize onto the cell's nucleoid as a fluorescent cloud. The interaction of (δ:CFP2 or δ2 bound to the nucleoid with (ω:YFP2 foci facilitates plasmid capture, from a very broad distribution, towards the nucleoid and plasmid pairing. parS-bound ω2 promotes redistribution of (δ:GFP2, leading to the dynamic release of (δ:GFP2 from the nucleoid, in a process favored by ATP hydrolysis and protein-protein interaction. (δD60A:GFP2, which binds but cannot hydrolyze ATP, also forms unstable complexes on the nucleoid. In the presence of ω2, (δD60A:GFP2 accumulates foci or patched structures on the nucleoid. We propose that (δ:GFP2 binding to different nucleoid regions and to ω2-parS might generate (δ:GFP2 gradients that could direct plasmid movement. The iterative pairing and unpairing cycles may tether plasmids equidistantly on the nucleoid to ensure faithful plasmid segregation by a mechanism compatible with the diffusion-ratchet mechanism as proposed from in vitro reconstituted systems.

  7. Pitfalls of tungsten multileaf collimator in proton beam therapy

    Energy Technology Data Exchange (ETDEWEB)

    Moskvin, Vadim; Cheng, Chee-Wai; Das, Indra J. [Department of Radiation Oncology, Indiana University School of Medicine, Indianapolis, Indiana 46202 (United States) and Indiana University Health Proton Therapy Center (Formerly Midwest Proton Radiotherapy Institute), Bloomington, Indiana 47408 (United States)

    2011-12-15

    Purpose: Particle beam therapy is associated with significant startup and operational cost. Multileaf collimator (MLC) provides an attractive option to improve the efficiency and reduce the treatment cost. A direct transfer of the MLC technology from external beam radiation therapy is intuitively straightforward to proton therapy. However, activation, neutron production, and the associated secondary cancer risk in proton beam should be an important consideration which is evaluated. Methods: Monte Carlo simulation with FLUKA particle transport code was applied in this study for a number of treatment models. The authors have performed a detailed study of the neutron generation, ambient dose equivalent [H*(10)], and activation of a typical tungsten MLC and compared with those obtained from a brass aperture used in a typical proton therapy system. Brass aperture and tungsten MLC were modeled by absorber blocks in this study, representing worst-case scenario of a fully closed collimator. Results: With a tungsten MLC, the secondary neutron dose to the patient is at least 1.5 times higher than that from a brass aperture. The H*(10) from a tungsten MLC at 10 cm downstream is about 22.3 mSv/Gy delivered to water phantom by noncollimated 200 MeV beam of 20 cm diameter compared to 14 mSv/Gy for the brass aperture. For a 30-fraction treatment course, the activity per unit volume in brass aperture reaches 5.3 x 10{sup 4} Bq cm{sup -3} at the end of the last treatment. The activity in brass decreases by a factor of 380 after 24 h, additional 6.2 times after 40 days of cooling, and is reduced to background level after 1 yr. Initial activity in tungsten after 30 days of treating 30 patients per day is about 3.4 times higher than in brass that decreases only by a factor of 2 after 40 days and accumulates to 1.2 x 10{sup 6} Bq cm{sup -3} after a full year of operation. The daily utilization of the MLC leads to buildup of activity with time. The overall activity continues to increase

  8. Collimator design for a dedicated molecular breast imaging-guided biopsy system: Proof-of-concept

    Energy Technology Data Exchange (ETDEWEB)

    Weinmann, Amanda L.; Hruska, Carrie B.; Conners, Amy L.; O' Connor, Michael K. [Department of Radiology, Mayo Clinic, 200 First Street SW, Rochester, Minnesota 55905 (United States)

    2013-01-15

    Purpose: Molecular breast imaging (MBI) is a dedicated nuclear medicine breast imaging modality that employs dual-head cadmium zinc telluride (CZT) gamma cameras to functionally detect breast cancer. MBI has been shown to detect breast cancers otherwise occult on mammography and ultrasound. Currently, a MBI-guided biopsy system does not exist to biopsy such lesions. Our objective was to consider the utility of a novel conical slant-hole (CSH) collimator for rapid (<1 min) and accurate monitoring of lesion position to serve as part of a MBI-guided biopsy system. Methods: An initial CSH collimator design was derived from the dimensions of a parallel-hole collimator optimized for MBI performed with dual-head CZT gamma cameras. The parameters of the CSH collimator included the collimator height, cone slant angle, thickness of septa and cones of the collimator, and the annular areas exposed at the base of the cones. These parameters were varied within the geometric constraints of the MBI system to create several potential CSH collimator designs. The CSH collimator designs were evaluated using Monte Carlo simulations. The model included a breast compressed to a thickness of 6 cm with a 1-cm diameter lesion located 3 cm from the collimator face. The number of particles simulated was chosen to represent the count density of a low-dose, screening MBI study acquired with the parallel-hole collimator for 10 min after a {approx}150 MBq (4 mCi) injection of Tc-99m sestamibi. The same number of particles was used for the CSH collimator simulations. In the resulting simulated images, the count sensitivity, spatial resolution, and accuracy of the lesion depth determined from the lesion profile width were evaluated. Results: The CSH collimator design with default parameters derived from the optimal parallel-hole collimator provided 1-min images with error in the lesion depth estimation of 1.1 {+-} 0.7 mm and over 21 times the lesion count sensitivity relative to 1-min images

  9. ¡París!

    Directory of Open Access Journals (Sweden)

    Beatriz Caballero

    2003-01-01

    Full Text Available El día no le alcanzaba para caminarlo. Conocía cada puente, cada calle,plaza, museo, rincón, iglesia, café, y la mesa con el mejor ángulo para mirar siempre una iglesia, ojalá Saint-Germain-des-Pres, o Notre-Dame. Siempre contaba la impresión que le había causado a Bolívar ver allí cuando el papa coronó a Napoleón. Él se iba para la oficina todos los días, Luis a un taller a pintar, Antonio a estudiar ciencias políticas, yo al colegio y mamá hacía las cosas prácticas. Aprendíamos francés todos al tiempo y por la noche nos contábamos lo nuevo que cada uno había aprendido. Mamá después, cuando ya se quería volver, decía que París nos había maleado a todos. Estaba en pleno furor el cine francés de la "nueva ola", pero ella sólo me llevaba a ver películas de vaqueros pues no se fiaba de la clasificación de los periódicos.

  10. Donovanose no Pará

    Directory of Open Access Journals (Sweden)

    Domingos Silva

    1991-12-01

    Full Text Available Foram estudados 259 casos de donovanose registrados no Serviço de Dermatologia do Departamento de Medicina Tropical/UFPA entre 1954-1990. Observa-se que no período 1954-1974 existiam nos arquivos apenas 56 prontuários da doença, enquanto que no último quinquénio estudado (1986-1990 foram identificados 133 casos. Para os autores esse crescimento está ligado a excessiva liberalidade sexual, ao homossexualismo e as precárias condições sócio-econômicas, acentuada nos últimos tempos.From 1954 to 1990 granuloma inguinale was diagnosed in 259 patients al the dermatology service of the Universidade Federal do Pará in Belém, Brazil. Among them, 56 cases had ocurred in the twenty-year period 1954-1974 and as many as 133 cases were seen during the last five years only. Greater sexual liberty, poor social and economic conditions, and especially increasing homosexual behavior were implicated by the authors as chief determinants for this augmented incidence of the disease.

  11. SU-E-T-604: Dosimetric Dependence On the Collimator Angle in Prostate Volumetric Modulated Arc Therapy

    Energy Technology Data Exchange (ETDEWEB)

    Khan, M; Rehman, J; Khan, M [The Islaimia University of Bahawalpur, Bahawalpur, Punjab (Pakistan); Chow, J [Princess Margaret Cancer Center, Toronto, ON (Canada)

    2014-06-01

    Purpose: The purpose of this study is to investigate the dose-volume variations of planning target volume (PTV) and organs-at-risk (OARs) in prostate volumetric modulated arc therapy (VMAT) when using different collimator angles. It is because collimator angle awareness is essential for planner to produce an optimal prostate VMAT plan in a rational time. Methods: Single-arc VMAT plans at different collimator angles (0o, 15o, 30o, 45o, 60o, 75o and 90o) were created systematically using a Harold heterogeneous pelvis phantom. For each change of collimator angle, a new plan was re-optimized for that angle. The prescription dose was 78 Gy per 39 fractions. Conformity index (CI), homogeneity index (HI), gradient index, machine monitor unit, dose-volume histogram, the mean and maximum doses of the PTV were calculated and analyzed. On the other hand, dose-volume histogram, the mean and maximum doses of the OARs such as bladder, rectum and femoral heads for different collimator angles were determined from the plans. Results: There was no significance difference, based on the plan dose-volume evaluation criteria, found in the VMAT optimizations for all studied collimator angles. Higher CI and lower HI were found for the 45o collimator angle. In addition, the 15o collimator angle provided lower HI similar to the 45o collimator angle. The 75o and 90o collimator angle were found good for the rectum sparing, and the 75o and 30o collimator angle were found good for the right and left femur sparing, respectively. The PTV dose coverage for each plan was comparatively independent of the collimator angle. Conclusion: The dosimetric results in this study are useful to the planner to select different collimator angles to improve the PTV coverage and OAR sparing in prostate VMAT.

  12. Influence of collimator rotation on dose distribution and delivery in intensity modulated radiation therapy for parotid cancer

    Directory of Open Access Journals (Sweden)

    Seema Sharma

    2015-01-01

    Full Text Available Purpose: To evaluate the influence of collimator rotation in IMRT planning with respect to the target coverage and dose to critical structures. In addition, the delivery efficiency of desired fluence with collimator rotation is assessed.Methods: The computed tomography (CT datasets of 5 patients with parotid cancer were employed for this study. Dynamic IMRT plans were generated with a dose prescription of 60 Gy in 30 fractions. IMRT plans were generated with five unilateral fields using 6MV X-rays. Four different plans were generated for each patient by keeping the collimator angle at 0, 30, 60, and 90 degree. All plans were analyzed using dose volume histogram. Conformity index (CI and heterogeneity index (HI were calculated. The total monitor units (MU required to deliver one fraction were noted and compared. To verify the delivery efficiency; the measured fluence on IBA I’mRT MatriXX ionization chamber array detector was compared with the TPS dose plan with 2D gamma evaluation.Results: There is not much difference in the PTV Dmax and Dmean with respect to the different collimator angles. The PTV coverage is best at collimator angle of 0 degree. A slight reduction in CI was observed with plans at other collimator angles as compared to 0 degree. The HI values were almost similar for plans with collimator angle 0, 30, and 60 degree. The plan with 90 degree collimator showed a slightly higher heterogeneity for the PTV. A slight reduction in the average Dmax to spinal cord was observed for the plan with collimator angle 30 degree as compared to other angles whereas maximum value of Dmax to spinal cord was at collimator angle 60 degree. No clinically relevant difference was observed among the plans with respect to brainstem and mandible Dmax. An increase in average of oral cavity Dmax and Dmean was observed for collimator angle 60 and 90 degree as compared to collimator angle 0 and 30 degree. Not much difference was observed with respect to Dmax

  13. Evaluation of collimators' response: round and hexagonal holes in parallel and fan beam.

    Science.gov (United States)

    Khorshidi, Abdollah; Ashoor, Mansour; Hosseini, S Hamed; Rajaee, Azimeh

    2012-08-01

    With regard to the different requirements, various collimators are widely employed within nuclear medicine systems in order to evaluate the metabolism of organs as well as improve the contrast of images and better diagnosis. In this study, Fan Beam (FB) and Parallel Beam (PB) collimators in the shapes of round and hexagonal holes have been investigated and compared based on the Geometric Efficiency (G), Geometric Resolution (R(c)), Total Resolution (R(t)), FWHM and Scatter and Penetration (S + P) components using the Monte Carlo simulation. Calculations demonstrated that the G was improved with the increase in the distance between point source and collimator face (z). In contrast, the G was reduced with an increase in the angle of slant hole. In the FB collimator, the R(c) and R(t) were increased when the increase in the hole angle and/or the distance. The simulated results indicated in both collimators with the increase in z, a) the FWHM was increased as well as the peak of the PSF curve was decreased, and b) the S + P amounts decreased, but in the distinct z, the FWHM of the FB collimator is better than that of the PB collimator. It is shown that the results were in agreement with the ADAC company data. Also, Benchmark for measuring ADAC company demonstrated the calculated and simulated amounts of the R(c) and R(t) with round and hexagonal holes shapes had maximum and minimum average relative differences equal to -7.6% for PB and 1% for FB, respectively.

  14. The Mechanical Design of a Collimator and Cryogenic Bypass for Installation in the Dispersion Suppressors of the LHC

    CERN Document Server

    Ramos, D; Bertarelli, A; Cherif, A; Chritin, N; Claret, R; Gentini, L; Lombard, D; Minginette, P; Moyret, P; Redondas, M; Renaglia, T; Timmins, M

    2012-01-01

    A project to install collimators in the dispersion suppressor regions of the LHC was launched early 2010, aiming to reduce the power deposition in superconducting magnets by a factor of 10. To be placed in the continuous arc cryostat, the design of such collimators had to comply with challenging integration, functional and time constraints. A pre-study for a cold collimator solution was launched in parallel with an alternative design consisting of a room temperature collimator and a cryogenic bypass. The second was eventually preferred, as it was based on proven LHC technologies for cryogenic, vacuum, electrical and collimator material solutions, despite the increased difficulty on the mechanical integration and assembly. This paper presents the mechanical design of a cryogenic bypass for the LHC continuous cryostat andrespective collimator unit, both made to comply with the functionality of existing LHC systems. The approach taken to achieve a reliable design within schedule will be explained alongside the m...

  15. Pars Plana Vitrectomy in Advanced Coats’ Disease

    OpenAIRE

    Gulipek Muftuoglu; Gokhan Gulkilik

    2011-01-01

    Purpose: To report 5 cases of advanced Coats’ disease managed with pars plana vitrectomy and silicone oil tamponade. Methods: Five patients with advanced Coats’ disease and serous or tractional retinal detachment underwent pars plana vitrectomy with internal drainage, endolaser photocoagulation and silicone oil tamponade. One patient had combined phacoemulsification-vitrectomy surgery. Of the 5 patients, 1 had intravitreal hemorrhage and a retinal macrocyst and 1 had a retinal cyst. Follow-up...

  16. MD 755: Instability threshold and tune shift study with reduced retraction between primary and secondary collimators in IR7

    CERN Document Server

    Carver, Lee Robert; Mereghetti, Alessio; Bruce, Roderik; Metral, Elias; Salvant, Benoit; Nisbet, David; Redaelli, Stefano; Salvachua Ferrando, Belen Maria; CERN. Geneva. ATS Department

    2016-01-01

    The purpose of this MD is to quantify in terms of stabilising octupole current threshold the impedance change when reducing the retraction between the primary and secondary collimators in IR7. This will be performed by first measuring the octupole current threshold required for stability with the tighter secondary collimator settings at 6.5 (w.r.t. to the nominal settings at 8 ), and then measuring the tune shift that occurs when the collimators are moved to the new settings.

  17. The design, physical properties and clinical utility of an iris collimator for robotic radiosurgery

    Energy Technology Data Exchange (ETDEWEB)

    Echner, G G; Kilby, W; Rhein, B; Lang, C; Schlegel, W [Department of Medical Physics, DKFZ, Im Neuenheimer Feld 280, D-69120 Heidelberg (Germany); Lee, M; Earnst, E; Sayeh, S; Dooley, J R; Lessard, E; Maurer, C R Jr [Accuray Incorporated, 1310 Chesapeake Terrace, Sunnyvale, CA 94089 (United States); Schlaefer, A; Blanck, O [Institute for Robotics and Cognitive Systems, University of Luebeck, Gebaeude 64, Ratzeburger Allee 160, D-23538 Luebeck (Germany)], E-mail: wkilby@accuray.com

    2009-09-21

    Robotic radiosurgery using more than one circular collimator can improve treatment plan quality and reduce total monitor units (MU). The rationale for an iris collimator that allows the field size to be varied during treatment delivery is to enable the benefits of multiple-field-size treatments to be realized with no increase in treatment time due to collimator exchange or multiple traversals of the robotic manipulator by allowing each beam to be delivered with any desired field size during a single traversal. This paper describes the Iris(TM) variable aperture collimator (Accuray Incorporated, Sunnyvale, CA, USA), which incorporates 12 tungsten-copper alloy segments in two banks of six. The banks are rotated by 30 deg. with respect to each other, which limits the radiation leakage between the collimator segments and produces a 12-sided polygonal treatment beam. The beam is approximately circular, with a root-mean-square (rms) deviation in the 50% dose radius of <0.8% (corresponding to <0.25 mm at the 60 mm field size) and an rms variation in the 20-80% penumbra width of about 0.1 mm at the 5 mm field size increasing to about 0.5 mm at 60 mm. The maximum measured collimator leakage dose rate was 0.07%. A commissioning method is described by which the average dose profile can be obtained from four profile measurements at each depth based on the periodicity of the isodose line variations with azimuthal angle. The penumbra of averaged profiles increased with field size and was typically 0.2-0.6 mm larger than that of an equivalent fixed circular collimator. The aperture reproducibility is {<=}0.1 mm at the lower bank, diverging to {<=}0.2 mm at a nominal treatment distance of 800 mm from the beam focus. Output factors (OFs) and tissue-phantom-ratio data are identical to those used for fixed collimators, except the OFs for the two smallest field sizes (5 and 7.5 mm) are considerably lower for the Iris Collimator. If average collimator profiles are used, the assumption

  18. Performance of a novel collimator for high-sensitivity brain SPECT.

    Science.gov (United States)

    El Fakhri, Georges; Ouyang, Jinsong; Zimmerman, Robert E; Fischman, Alan J; Kijewski, Marie Foley

    2006-01-01

    We assessed improvements in performance in detection and estimation tasks due to a novel brain single photon computed tomography collimator. Data were acquired on the CeraSPECT scanner using both new and standard collimators. The new variable focusing collimator SensOgrade samples the projections unequally, with central regions more heavily represented, to compensate for attenuation of counts from central brain structures. Furthermore, it utilizes more of the cylindrical crystal surface. Two phantom studies were performed. The first phantom was a 21-cm-diameter cylindrical background containing nine spheres ranging from 0.5 to 5 cm3 in volume. 99mTc sphere to background activity ratio was 10:1. Twenty-nine 10-min datasets were acquired with each collimator. The second phantom was the Radiology Support Devices (Long Beach, CA) striatal phantom with striatal-background ratios of 10:1 on the left and 5:1 on the right. Twenty-nine 4-min datasets were acquired with each collimator. Perfusion imaging using 99mTc-HMPAO was also performed in three healthy volunteers using both collimators under identical simulations. Projections were reconstructed by filtered backprojection with an unwindowed ramp filter. The nonprewhitening matched filter signal-to-noise ratio (NPW-SNR) was computed as a surrogate for human performance in detecting spherical lesions. Sphere activity concentration, radius, and location coordinates were simultaneously estimated by fitting images to an assumed model using an iterative nonlinear algorithm. Resolution recovery was implicit in the estimation procedure, as the point spread function was incorporated into the model. NPW-SNR for sphere detection was 1.5 to 2 times greater with the new collimator; for the striatal phantom the improvement in SNR was 54%. The SNR for estimating sphere activity concentration improved by 46 to 89% for spheres located more than 5 cm from the phantom center. Images acquired with the standard collimator were too noisy in

  19. C9.A/14 steelwork joints de poutres par plaque frontale : assemblages par gousset

    CERN Document Server

    2015-01-01

    Les Tables de résistances ultimes des assemblages boulonnés par plaque frontale et par gousset, complétées par une description des modèles de calcul et des exemples d’application, ont pour but de faciliter la tâche de l'ingénieur et du constructeur. Cette première partie C9.A/14 contient les chapitres suivants: - Joints de poutres par plaque frontale en acier S235 et S355 - Assemblages par gousset en acier S235 et S355 Les Tables contiennent des données relatives à la géométrie ainsi que les valeurs de calcul correspondantes des résistances ultimes des assemblages ; elles remplacent le chapitre « Assemblages par plaques frontales et boulons HR » des anciennes Tables C9.1 de 1983 / 2002. Le calcul de ces assemblages par plaque frontale est basé sur les hypothèses du modèle de la méthode des composants décrite dans la norme SN EN 1993-1-8. Les vérifications sont effectuées selon la norme SIA 263:2013. Les assemblages par gousset remplacent les assemblages par double cornière, (telle...

  20. Collimator angle influence on dose distribution optimization for vertebral metastases using volumetric modulated arc therapy

    Energy Technology Data Exchange (ETDEWEB)

    Mancosu, Pietro; Cozzi, Luca; Fogliata, Antonella; Lattuada, Paola; Reggiori, Giacomo; Cantone, Marie Claire; Navarria, Pierina; Scorsetti, Marta [Department of Radiation Oncology, IRCCS Istituto Clinico Humanitas, Milano (Rozzano) 20089 (Italy); Medical Physics Unit, Oncology Institute of Southern Switzerland, Bellinzona 6504 (Switzerland); Department of Radiation Oncology, IRCCS Istituto Clinico Humanitas, Milano (Rozzano) 20089 (Italy); Department of Physics, Universita Degli Studi di Milano, Milano 20133 (Italy); Department of Radiation Oncology, IRCCS Istituto Clinico Humanitas, Milano (Rozzano) 20089 (Italy)

    2010-08-15

    Purpose: The cylindrical symmetry of vertebrae favors the use of volumetric modulated arc therapy in generating a dose ''hole'' on the center of the vertebrae limiting the dose to the spinal cord. The authors have evaluated if collimator angle is a significant parameter for dose distribution optimization in vertebral metastases. Methods: Three patients with one-three vertebrae involved were considered. Twenty-one differently optimized plans (nine single-arc and 12 double-arc plans) were performed, testing various collimator angle positions. Clinical target volume was defined as the whole vertebrae, excluding the spinal cord canal. The planning target volume (PTV) was defined as CTV+5 mm. Dose prescription was 5x4 Gy{sup 2} with normalization to PTV mean dose. The dose at 1 cm{sup 3} of spinal cord was limited to 11.5Gy. Results: The best plans in terms of target coverage and spinal cord sparing were achieved by two arcs and Arc1-80 deg. and Arc2-280 deg. collimator angles for all the cases considered (i.e., leaf travel parallel to the spinal cord primary orientation). If one arc is used, only 80 deg. reached the objectives. Conclusions: This study demonstrated the role of collimation rotation for the vertebrae metastasis irradiation, with the leaf travel parallel to the spinal cord primary orientation to be better than other solutions. Thus, optimal choice of collimator angle increases the optimization freedom to shape a desired dose distribution.

  1. Design and development of new collimator cones for fractionated stereotactic radiation therapy in Samsung Medical Center.

    Science.gov (United States)

    Ahn, Y C; Ju, S G; Kim, D Y; Choi, D R; Huh, S J; Park, Y H; Lim, D H; Kim, M K

    1999-05-01

    In stereotactic radiotherapy using X-Knife system, the commercially supplied collimator cone system had a few mechanical limitations. The authors have developed new collimator cones to overcome these limitations and named them "SMC type" collimator cones. We made use of cadmium-free cerrobend alloy within the stainless steel cylinder housing. We made nine cones of relatively larger sizes (3.0 cm to 7.0 cm in diameter) and of shorter length with bigger clearance from the isocenter than the commercial cones. The cone housing and the collimator cones were designed to insert into the wedge mount of the gantry head to enable double-exposure linac-gram taking. The mechanical accuracy of pointing to the isocenter was tested by ball test and cone rotation test, and the dosimetric measurements were performed, all of which were with satisfactory results. A new innovative quality assurance procedure using linac-grams on the patients at the actual treatment setup was attempted after taking 10 sets of AP and lateral linac-grams and the overall mechanical isocenter accuracy was excellent (average error = 0.4 +/- 0.2 mm). We have developed the SMC type collimator cone system mainly for fractionated stereotactic radiation therapy use with our innovative ideas. The new cones' mechanical accuracy and physical properties were satisfactory for clinical use, and the verification of the isocenter accuracy on the actual treatment setup has become possible.

  2. Evaluation of Beam Losses and Energy Depositions for a Possible Phase II Design for LHC Collimation

    CERN Document Server

    Lari, L; Bracco, C; Brugger, M; Cerutti, F; Doyle, E; Ferrari, A; Keller, L; Lundgren, S; Keller, L; Mauri, M; Redaelli, S; Sarchiapone, L; Smith, J; Vlachoudis, V; Weiler, T

    2008-01-01

    The LHC beams are designed to have high stability and to be stored for many hours. The nominal beam intensity lifetime is expected to be of the order of 20h. The Phase II collimation system has to be able to handle particle losses in stable physics conditions at 7 TeV in order to avoid beam aborts and to allow correction of parameters and restoration to nominal conditions. Monte Carlo simulations are needed in order to evaluate the behavior of metallic high-Z collimators during operation scenarios using a realistic distribution of losses, which is a mix of the three limiting halo cases. Moreover, the consequences in the IR7 insertion of the worst (case) abnormal beam loss are evaluated. The case refers to a spontaneous trigger of the horizontal extraction kicker at top energy, when Phase II collimators are used. These studies are an important input for engineering design of the collimation Phase II system and for the evaluation of their effect on adjacent components. The goal is to build collimators that can ...

  3. Impact of the A48 collimator on the Tevatron B0 dipoles

    CERN Document Server

    Nicolas, L Y

    2003-01-01

    To protect the CDF detector components in an event of an abort kicker prefire (AKP) in the Tevatron, a new collimator is to be installed at the A48 location during the summer 2003 shutdown. Detailed calculations have shown that this 0.5-m long ''single L-shape'' steel collimator will intercept a bunch of protons when such an incident occurs, providing reliable protection of the CDF main detector at an AKP. It will also mitigate the backgrounds induced by elastic beam-gas interactions upstream of B0. Although the Roman Pot detectors downstream of the A48 collimator will see an increased background, the amount of radiation they will receive either resulting from beam halo interactions in the collimator or during an AKP will not damage their sensitive parts. Secondaries resulting from beam halo interactions with the A48 collimator do not noticeably affect the downstream dipoles. The case of an AKP is quite different. As opposed to halo hits in the ''single-L shape'' unit (around 10 sup 5 p/s), a bunch lost on A4...

  4. Design of the pre-collimator for the NeXT x-ray telescopes

    Science.gov (United States)

    Mori, Hideyuki; Ogasaka, Yasushi; Ishida, Manabu; Maeda, Yoshitomo; Tamura, Keisuke; Kunieda, Hideyo; Furuzawa, Akihiro; Haba, Yoshito; Miyazawa, Takuya; Yamashita, Koujun; Awaki, Hisamitsu; Serlemitsos, Peter J.; Soong, Yang; Chan, Kai-Wing; Okajima, Takashi

    2008-07-01

    We present the design of the pre-collimator for the X-ray telescopes (XRTs) onboard New X-ray Telescope (NeXT). The optical design adopted for the NeXT XRTs is conically-approximated Wolter-I type optics. The tightly-nested reflectors with thin substrates (150-300 μm) enable us to achieve the large effective area and extremely light weight simultaneously. However, due to the packed reflector shells, X-rays from the outside of the XRT field of view occasionally arrive at the focal plane without the normal double reflection (stray lights), and then produce a ghost image on the detector. Thus, the stray-lights contamination degrades sensitivity of the source detection In order to reduce the stray lights efficiently, we plan to mount a collimator onto each telescope (referred to as pre-collimator), which is similar to that equipped with the Suzaku XRTs. The pre-collimator consists of coaxially-nested cylindrical blades, each of which is aligned radially with the corresponding primary refector. We found the height of the pre-collimator blade to be ~100 mm that is required to block the X-rays with off-axis angles of 30'-50', which are the main ligth pass of the stray lights for the NeXT XRTs.

  5. Two-dimensional dielectric collimator design and its experimental verification for microwave beam focusing

    Science.gov (United States)

    Kim, H.; Park, J.; Seo, I.; Yoo, J.

    2016-10-01

    A collimator is an electromagnetic device that focuses or aligns the direction of wave propagation to achieve a narrow, intense beam. In this study, we propose a two-dimensional dielectric collimator for microwave beam focusing. This is something that is difficult to achieve using theoretical- or intuition-based approaches. We therefore used a systematic design process, which is referred to as the phase field design method, to obtain an optimal topological configuration for the collimator. The phase field parameter determines the optimal configuration of the dielectric material and, as a consequence, it determines the relative permittivity of the component. To verify the design results, we fabricated a prototype via three-dimensional printing and performed an experimental verification using an electric field scanner to measure the near field distributions of the designed collimator positioned parallel to an incident wave. We also performed angle dependent experiments for which the collimator position was offset at various angles. We confirmed that the experimental results are consistent with the simulation results.

  6. Aperture correction with an asymmetrically trimmed Gaussian weight in SPECT with a fan-beam collimator.

    Science.gov (United States)

    Kamiya, Ryo; Ogawa, Koichi

    2013-08-01

    The aim of the study is to improve the spatial resolution of SPECT images acquired with a fan-beam collimator. The aperture angle of a hole in the fan-beam collimator depends on the position of the collimator. To correct the aperture effect in an iterative image reconstruction, an asymmetrically trimmed Gaussian weight was used for a model. To confirm the validity of our method, point source phantoms and brain phantom were used in the simulation, and we applied the method to the clinical data. The results of the simulation showed that the spatial resolution of point sources improved from about 6 to 2 pixels full width at half maximum, and the corrected point sources were isotropic. The results of the simulation with the brain phantom showed that our proposed method could improve the spatial resolution of the phantom, and our method was effective for different fan-beam collimators with different focal lengths. The results of clinical data showed that the quality of the reconstructed image was improved with our proposed method. Our proposed aperture correction method with the asymmetrically trimmed Gaussian weighting function was effective in improving the spatial resolution of SPECT images acquired with the fan-beam collimator.

  7. Measurements and analysis of a high-brightness electron beam collimated in a magnetic bunch compressor

    Directory of Open Access Journals (Sweden)

    F. Zhou

    2015-05-01

    Full Text Available A collimator located in a magnetic bunch compressor of a linear accelerator driven x-ray free electron laser has many potential applications, such as the removal of horns in the current distribution, the generation of ultrashort beams, and as a diagnostic of the beam slice emittance. Collective effects, however, are a major concern in applying the technique. Systematic measurements of emittance and analysis were performed using a collimator in the first bunch compressor of the Linac Coherent Light Source (LCLS. In the nominal, undercompressed configuration using the collimator we find that the y emittance (nonbending plane is not increased, and the x emittance (in the bending plane is increased by about 25%, in comparison to the injector emittance. From the analysis we conclude that the parasitic effects associated with this method are dominated by coherent synchrotron radiation (CSR, which causes a “systematic error” for measuring slice emittance at the bending plane using the collimation method. In general, we find good agreement between the measurements and simulations including CSR. However, for overcompressed beams at smaller collimator gaps, an extra emittance increase is found that does not agree with 1D simulations and is not understood.

  8. Development of a 0.5m clear aperture Cassegrain type collimator telescope

    Science.gov (United States)

    Ekinci, Mustafa; Selimoǧlu, Özgür

    2016-07-01

    Collimator is an optical instrument used to evaluate performance of high precision instruments, especially space-born high resolution telescopes. Optical quality of the collimator telescope needs to be better than the instrument to be measured. This requirement leads collimator telescope to be a very precise instrument with high quality mirrors and a stable structure to keep it operational under specified conditions. In order to achieve precision requirements and to ensure repeatability of the mounts for polishing and metrology, opto-mechanical principles are applied to mirror mounts. Finite Element Method is utilized to simulate gravity effects, integration errors and temperature variations. Finite element analyses results of deformed optical surfaces are imported to optical domain by using Zernike polynomials to evaluate the design against specified WFE requirements. Both mirrors are aspheric and made from Zerodur for its stability and near zero CTE, M1 is further light-weighted. Optical quality measurements of the mirrors are achieved by using custom made CGHs on an interferometric test setup. Spider of the Cassegrain collimator telescope has a flexural adjustment mechanism driven by precise micrometers to overcome tilt errors originating from finite stiffness of the structure and integration errors. Collimator telescope is assembled and alignment methods are proposed.

  9. β*-Reach – IR7 Collimation Hierarchy Limit and Impedance

    CERN Document Server

    Mereghetti, Alessio; Bruce, Roderik; Carver, Lee Robert; Kwee-Hinzmann, Regina; Metral, Elias; Mirarchi, Daniele; Quaranta, Elena; Redaelli, Stefano; Rossi, Adriana; Rossi, Roberto; Salvachua Ferrando, Belen Maria; Salvant, Benoit; Valentino, Gianluca; Valloni, Alessandra; CERN. Geneva. ATS Department

    2016-01-01

    This report summarises the results of the MD314 about the hierarchy limit of the IR7 collimation system and its impedance. While the activity, the procedures and the results concerning the collimator hierarchy limit are detailed here, the main outcomes from the impedance studies are only briefly reported, as a detailed MD report has been prepared. The MD was carried out during MD block II of 2015, on 29th August, at 6.5 TeV. Different retractions of the IR7 secondary collimators (TCSGs) from the primary collimators (TCPs) were qualified in terms of cleaning inefficiency and impedance. For each retraction, settings of the IR7 movable shower absorbers (TCLAs) tighter than those operationally deployed were qualified as well. Afterwards, the alignment of all IR7 collimators was performed and the beam-based centers compared to those from the alignment done in May 2015, to verify stability. Selected configurations were qualified with loss maps, to spot possible improvements in the cleaning inefficiency due to the ...

  10. QUALITY OF RADIOGRAPHIC IMAGES: LABORATORY EVALUATION OF INTRAORAL FILMS, FILTERS, COLLIMATORS, AND RADIATION EXPOSURE

    Directory of Open Access Journals (Sweden)

    TAMBURUS José Roberto

    1997-01-01

    Full Text Available In order to evaluate density, radiographic contrast and dose of radiation exposure, the author analyzed 80 radiographs containing 640 optical density data of the images of a penetrometer, exposed to the radiation beam with combinations between D and E periapical films, aluminum and copper/aluminum filters, and circular or rectangular collimators. The data obtained were analyzed by ANOVA and allowed the following conclusions: 1 aluminum filtration resulted in improved image contrast; 2 the use of group D film and an aluminum filter produced improved image contrast quality; 3 the rectangular collimator contributed to the production of improved contrast and to the reduction of radiation exposure, but did not affect density; 4 the combination of copper/aluminum filter, E group film and rectangular collimation significantly reduced radiation exposure.

  11. Development and Beam Tests of an Automatic Algorithm for Alignment of LHC Collimators with Embedded BPMs

    CERN Document Server

    Valentino, G; Gasior, M; Mirarchi, D; Nosych, A A; Redaelli, S; Salvachua, B; Assmann, R W; Sammut, N

    2013-01-01

    Collimators with embedded Beam Position Monitor (BPM) buttons will be installed in the LHC during the upcoming long shutdown period. During the subsequent operation, the BPMs will allow the collimator jaws to be kept centered around the beam trajectory. In this manner, the best possible beam cleaning efficiency and machine protection can be provided at unprecedented higher beam energies and intensities. A collimator alignment algorithm is proposed to center the jaws automatically around the beam. The algorithm is based on successive approximation, as the BPM measurements are affected by non-linearities, which vary with the distance between opposite buttons, as well as the difference between the beam and the jaw centers. The successful test results, as well as some considerations for eventual operation in the LHC are also presented.

  12. Acoustic logic gates and Boolean operation based on self-collimating acoustic beams

    Science.gov (United States)

    Zhang, Ting; Cheng, Ying; Guo, Jian-zhong; Xu, Jian-yi; Liu, Xiao-jun

    2015-03-01

    The reveal of self-collimation effect in two-dimensional (2D) photonic or acoustic crystals has opened up possibilities for signal manipulation. In this paper, we have proposed acoustic logic gates based on the linear interference of self-collimated beams in 2D sonic crystals (SCs) with line-defects. The line defects on the diagonal of the 2D square SCs are actually functioning as a 3 dB splitter. By adjusting the phase difference between two input signals, the basic Boolean logic functions such as XOR, OR, AND, and NOT are achieved both theoretically and experimentally. Due to the non-diffracting property of self-collimation beams, more complex Boolean logic and algorithms such as NAND, NOR, and XNOR can be realized by cascading the basic logic gates. The achievement of acoustic logic gates and Boolean operation provides a promising approach for acoustic signal computing and manipulations.

  13. Acoustic logic gates and Boolean operation based on self-collimating acoustic beams

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Ting; Xu, Jian-yi [Key Laboratory of Modern Acoustics, Department of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093 (China); Cheng, Ying, E-mail: chengying@nju.edu.cn; Liu, Xiao-jun, E-mail: liuxiaojun@nju.edu.cn [Key Laboratory of Modern Acoustics, Department of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093 (China); State Key Laboratory of Acoustics, Chinese Academy of Sciences, Beijing 100190 (China); Guo, Jian-zhong [School of Physics and Information Technology, Shaanxi Normal University, Xian 710119 (China)

    2015-03-16

    The reveal of self-collimation effect in two-dimensional (2D) photonic or acoustic crystals has opened up possibilities for signal manipulation. In this paper, we have proposed acoustic logic gates based on the linear interference of self-collimated beams in 2D sonic crystals (SCs) with line-defects. The line defects on the diagonal of the 2D square SCs are actually functioning as a 3 dB splitter. By adjusting the phase difference between two input signals, the basic Boolean logic functions such as XOR, OR, AND, and NOT are achieved both theoretically and experimentally. Due to the non-diffracting property of self-collimation beams, more complex Boolean logic and algorithms such as NAND, NOR, and XNOR can be realized by cascading the basic logic gates. The achievement of acoustic logic gates and Boolean operation provides a promising approach for acoustic signal computing and manipulations.

  14. Long-range visible light communication system based on LED collimating lens

    Science.gov (United States)

    Chen, Yingcong; Wen, Shangsheng; Wu, Yuxiang; Ren, Yuanyuan; Guan, Weipeng; Zhou, Yunlin

    2016-10-01

    An advanced visible light communication (VLC) system is proposed for long-range VLC, such as marine communication. The design of the system is conducted into two parts. Firstly, we design and optimize a collimating lens for the optical antenna by using Taguchi method. The lighting effects and optical power of the receiving end in different distances are simulated by TracePro software. Then, the long-range VLC channel is reconstructed by integrating the influence of the atmospheric attenuation and frequency response. The performance of the OOK coding VLC system is tested by Matlab software. The results show that: the emitting angle of the optimized collimating lens is 1.7°. By using 1 W LED and collimating lens as an optical antenna, the system can achieve a data rate of 210 Mbit/s at a bit error rate of 10-3 in 90 m.

  15. Numerical Calculations of Wake Fields and Impedances of LHC Collimators' Real Structures

    CERN Document Server

    Frasciello, Oscar; Zobov, Mikhail

    2015-01-01

    The LHC collimators have very complicated mechanical designs including movable jaws made of higly resistive materials, ferrite materials, tiny RF contacts. Since the jaws are moved very close to the circulating beams their contribution in the overall LHC coupling impedance is dominant, with respect to other machine components. For these reasons accurate simulation of collimators' impedance becomes very important and challenging. Besides, several dedicated tests have been performed to verify correct simulations of lossy dispersive material properties, such as resistive wall and ferrites, benchmarking code results with analytical, semi-analytical and other numerical codes outcomes. Here we describe all the performed numerical tests and discuss the results of LHC collimators' impedances and wake fields calculations.

  16. The effect of pitch and collimation on radiation dose in spiral CT

    Institute of Scientific and Technical Information of China (English)

    CHENG Qi-Jun; TSANG Cheung; FENG Ding-Hua

    2005-01-01

    Measurements of radiation dose to patients in spiral computed tomography (CT) were completed for various collimations, table speeds and pitch. A standard CT head dosimetry phantom and thermoluminescent dosimeters (TLD) were used for the measurement. The.effect of collimation and pitch on radiation dose was studied. The results indicated that the radiation dose at the given tube current, voltage and rotation speed was inversely proportional to pitch. And the increasing times of dose were as decreasing times of pitch. This regular pattern was tenable for radiation dose at both central holes and peripheral holes of the phantom at pitch = 1, >1 and <1. The collimation had no impact on the radiation dose. The results also indicated that radiation dose at central holes was nearly equal to that at peripheral holes. There was no significant difference between them statistically. The study demonstrates that the pitch in spiral CT scans is the primary parameter and has significant impact on radiation dose.

  17. Systematic study on visible light collimation by nanostructured slits in the metal surface

    Institute of Scientific and Technical Information of China (English)

    Fu Jin-Xin; Hua Yi-Lei; Chen Yu-Hui; Liu Rong-Juan; Li Jia-Fang; Li Zhi-Yuan

    2011-01-01

    We present a systematic experimental investigation on visible light collimation by a nanostructured slit flanked with a pair of periodic array of grooves in gold thin film. A wide variety of aspects are considered, such as the polarization state, the transport path of incident light, the groove-groove spacing, the groove width and depth. Our results clearly show that the relationship between the collimation wavelength and the periodicity of the slit-groove structure accords well with the surface plasmon dispersion model proposed by previous researchers. Furthermore, the surface plasmon wave phase retardation effect induced by the surface structure is also verified via the measurement for samples with different groove widths and depths. These results indicate that the detailed geometry of the groove structure has obvious impacts on the collimation effect and the angular distribution of the diffraction light in the subwavelength plasmonic system.

  18. Diffusion and Halo Population Measurements with Collimator Scans at 6.5 TeV

    CERN Document Server

    Valentino, Gianluca; Redaelli, Stefano; Rossi, Roberto; Salvachua Ferrando, Belen Maria; Stancari, Giulio; Valloni, Alessandra; Wagner, Joschka; CERN. Geneva. ATS Department

    2016-01-01

    Beam halo measurements at 6.5 TeV in the LHC were conducted via collimator scrapings in an MD carried out on the 4th November 2015. From the time evolution of the beam losses in a collimator scan, it is possible to extract information on the halo diffusion and population. Six scans were performed with two collimators in the vertical and horizontal planes in B1 and B2 respectively. The scans were done with squeezed, separated beams, with colliding beams and once again with separated beams but with a gentle continuous transverse blow-up with the ADT. The results obtained were compared with those from similar scrapings performed in a MD in 2012 at 4 TeV.

  19. Self-collimated waveguide bends and partial bandgap reflection of photonic crystals with parallelogram lattice.

    Science.gov (United States)

    Gao, Dingshan; Zhou, Zhiping; Citrin, David S

    2008-03-01

    The photonic crystal structure with parallelogram lattice, capable of bending a self-collimated wave with free angles and partial bandgap reflection, is presented. The equifrequency contours show that the direction of the collimation wave can be turned by tuning the angle between the two basic vectors of the lattice. Acute, right, and obtuse angles of collimating waveguide bends have been realized by arc lattices of parallelogram photonic crystals. Moreover, partial bandgap reflection of the parallelogram lattice photonic crystals is validated from the equifrequency contours and the projected band structures. A waveguide taper based on this partial bandgap reflection is also designed and proved to have above 85% transmittance over a very wide operating bandwidth of 180 nm.

  20. Crab dispersion and its impact on the CERN Large Hadron Collider collimation

    CERN Document Server

    Sun, P; Tomàs, R; Zimmermann, F

    2010-01-01

    Crab cavities are proposed to be used for a luminosity upgrade of the Large Hadron Collider (LHC). Crab cavities are rf cavities operated in a transverse dipole mode, which imparts on the beam particles a transverse kick that varies with the longitudinal position along the bunch. The crab cavity introduces another kind of dispersion to the particles which is z dependent, and thus could complicate the beam dynamics and have an impact on the LHC collimation system. As for LHC, the off-momentum beta-beat and dispersion-beat already compromise the performance of the collimation system; the crab dispersion introduced by global crab cavities might do the same, and should be carefully evaluated. In this paper, we present a definition for the crab dispersion, and study its impact on the LHC collimation system.

  1. Handling High Activity Components on the SNS (Collimators and Linac Passive Dump Window)

    Science.gov (United States)

    Murdoch, G.; Decarlo, A.; Potter, K.; Roseberry, T.; Schubert, J.; Brodowski, J.; Ludewig, H.; Tuozzolo, J.; Simos, N.; Hirst, J.

    2003-12-01

    The Spallation Neutron Source accelerator will provide a 1 GeV, 1.44 MW proton beam to a liquid mercury target for neutron production. The expected highest doses to components are in the collimation regions. This paper presents the mechanical engineering design of a typical collimator highlighting the features incorporated to assist with collimator removal once it is activated. These features include modular shielding, integrated crane mounting, remote water fittings and vacuum clamps. Also presented is the design work in progress at present to validate the remote vacuum clamp design. This includes a test rig that mimics an active handling scenario where vacuum bellows can be compressed and clamps removed/replaced from a safe distance.

  2. Beam Collimation and Machine-Detector Interface at the International Linear Collider

    CERN Document Server

    Mokhov, Nikolai V; Kostin, Mikhail A

    2005-01-01

    Synchrotron radiation, spray from the dumps and extraction lines, beam-gas and beam halo interactions with collimators and other components in the ILC beam delivery system create fluxes of muons and other secondaries which can exceed the tolerable levels at a detector by a few orders of magnitude. It is shown that with a multi-stage collimation system, magnetized iron spoilers which fill the tunnel and a set of masks in the detector, one can hopefully meet the design goals. Results of modeling with the STRUCT and MARS15 codes of beam loss and energy deposition effects are presented in this paper. We concentrate on collimation system and mask design and optimization, short- and long-term survivability of the critical components (spoilers, absorbers, magnets, separators, dumps), dynamic heat loads and radiation levels in magnets and other components, machine-related backgrounds and damage in collider detectors, and environmental aspects (prompt dose, ground-water and air activation).

  3. Structured mirror array for two-dimensional collimation of a chromium beam in atom lithography

    Institute of Scientific and Technical Information of China (English)

    Zhang Wan-Jing; Ma Yan; Li Tong-Bao; Zhang Ping-Ping; Deng Xiao; Chen Sheng; Xiao Sheng-Wei

    2013-01-01

    Direct-write atom lithography,one of the potential nanofabrication techniques,is restricted by some difficulties in producing optical masks for the deposition of complex structures.In order to make further progress,a structured mirror array is developed to transversely collimate the chromium atomic beam in two dimensions.The best collimation is obtained when the laser red detunes by natural line-width of transition 7S3 → 7P40 of the chromium atom.The collimation ratio is 0.45 vertically (in x axis),and it is 0.55 horizontally (in y axis).The theoretical model is also simulated,and success of our structured mirror array is achieved.

  4. Heavy-Ion Collimation at the Large Hadron Collider Simulations and Measurements

    CERN Document Server

    AUTHOR|(CDS)2083002; Wessels, Johannes Peter; Bruce, Roderik; Wessels, Johannes Peter; Bruce, Roderik

    The CERN Large Hadron Collider (LHC) stores and collides proton and $^{208}$Pb$^{82+}$ beams of unprecedented energy and intensity. Thousands of superconducting magnets, operated at 1.9 K, guide the very intense and energetic particle beams, which have a large potential for destruction. This implies the demand for a multi-stage collimation system to provide protection from beam-induced quenches or even hardware damage. In heavy-ion operation, ion fragments with significant rigidity offsets can still scatter out of the collimation system. When they irradiate the superconducting LHC magnets, the latter risk to quench (lose their superconducting property). These secondary collimation losses can potentially impose a limitation for the stored heavy-ion beam energy. Therefore, their distribution in the LHC needs to be understood by sophisticated simulations. Such simulation tools must accurately simulate the particle motion of many different nuclides in the magnetic LHC lattice and simulate their interaction with t...

  5. Beam Collimation Using an Anisotropic Metamaterial Slab without Any Nanometer-sized Aperture

    CERN Document Server

    Zhang, Shou; Cui, Yanxia; Zhang, Feng; He, Sailing; Hao, Yuying; Zhu, Furong

    2015-01-01

    Plasmonic beam collimation effect has been thoroughly investigated based on the well-known nanometer-scale bull's eye structure formed by complex and high-cost fabrication processes. In this work, we report our effort for attaining beam collimation using an anisotropic metamaterial (AMM) slab that consists of a stack of alternating metal/dielectric layers and an integrated top metal grating. The results show that AMM slab allows creating the beam collimation effect similar to that of the bull's eye structure, an enabling technology for practical application due to its simple architecture and cost benefits. The excitation of surface plasmons at the AMM/air interface is derived. The structure of the AMM slab and its impact on beaming performance were analyzed using the effective medium theory and Finite Element Method.

  6. All-angle collimation of incident light in μ-near-zero metamaterials

    Science.gov (United States)

    Fedorov, Vladimir Yu.; Nakajima, Takashi

    2013-11-01

    We use the theory of inhomogeneous waves to study the transmission of light in $\\mu$-near-zero metamaterials. We find the effect of all-angle collimation of incident light, which means that the vector of energy flow in a wave transmitted to a $\\mu$-near-zero metamaterial is perpendicular to the interface for any incident angles if an incident wave is s-polarized. This effect is similar to the all-angle collimation of incident light recently found through a different theoretical framework in $\\varepsilon$-near-zero metamaterials for a p-polarized incident wave [S. Feng, Phys. Rev. Lett. 108, 193904 (2012)]. To provide a specific example, we consider the transmission of light in a negative-index metamaterial in the spectral region with a permeability resonance, and show that all-angle collimation indeed takes place at the wavelength for which the real part of permeability is vanishingly small.

  7. Study on collimation and shielding of the back-streaming neutrons at the CSNS target

    CERN Document Server

    Han-Tao, Jing; Zheng, Yang

    2013-01-01

    The back-streaming neutrons from the spallation target at CSNS are very intense, and can pose serious damage problems for the devices in the accelerator-target interface region. To tackle the problems, a possible scheme for this region was studied, namely a specially designed optics for the proton beam line produces two beam waists, and two collimators are placed at the two waist positions to maximize the collimation effect of the back-streaming neutrons. Detailed Monte Carlo simulations with the beams in the two different CSNS phases show the effectiveness of the collimation system, and the radiation dose rate decreases largely in the interface section. This can ensure the use of epoxy coils for the last magnets and other devices in the beam transport line with reasonable lifetimes, e.g. thirty years. The design philosophy for such an accelerator-target interface region can also be applicable to other high-power proton beam applications.

  8. Astrophysics of magnetically collimated jets generated from laser-produced plasmas.

    Science.gov (United States)

    Ciardi, A; Vinci, T; Fuchs, J; Albertazzi, B; Riconda, C; Pépin, H; Portugall, O

    2013-01-11

    The generation of astrophysically relevant jets, from magnetically collimated, laser-produced plasmas, is investigated through three-dimensional, magnetohydrodynamic simulations. We show that for laser intensities I∼10(12)-10(14) W cm(-2), a magnetic field in excess of ∼0.1  MG, can collimate the plasma plume into a prolate cavity bounded by a shock envelope with a standing conical shock at its tip, which recollimates the flow into a supermagnetosonic jet beam. This mechanism is equivalent to astrophysical models of hydrodynamic inertial collimation, where an isotropic wind is focused into a jet by a confining circumstellar toruslike envelope. The results suggest an alternative mechanism for a large-scale magnetic field to produce jets from wide-angle winds.

  9. Rapid additive manufacturing of MR compatible multipinhole collimators with selective laser melting of tungsten powder.

    Science.gov (United States)

    Deprez, Karel; Vandenberghe, Stefaan; Van Audenhaege, Karen; Van Vaerenbergh, Jonas; Van Holen, Roel

    2013-01-01

    The construction of complex collimators with a high number of oblique pinholes is very labor intensive, expensive or is sometimes impossible with the current available techniques (drilling, milling or electric discharge machining). All these techniques are subtractive: one starts from solid plates and the material at the position of the pinholes is removed. The authors used a novel technique for collimator construction, called metal additive manufacturing. This process starts with a solid piece of tungsten on which a first layer of tungsten powder is melted. Each subsequent layer is then melted on the previous layer. This melting is done by selective laser melting at the locations where the CAD design file defines solid material. A complex collimator with 20 loftholes with 500 μm diameter pinhole opening was designed and produced (16 mm thick and 70 × 52 mm(2) transverse size). The density was determined, the production accuracy was measured (GOM ATOS II Triple Scan, Nikon AZ100M microscope, Olympus IMT200 microscope). Point source measurements were done by mounting the collimator on a SPECT detector. Because there is increasing interest in dual-modality SPECT-MR imaging, the collimator was also positioned in a 7T MRI scanner (Bruker Pharmascan). A uniform phantom was acquired using T1, T2, and T2* sequences to check for artifacts or distortion of the phantom images due to the collimator presence. Additionally, three tungsten sample pieces (250, 500, and 750 μm thick) were produced. The density, attenuation (140 keV beam), and uniformity (GE eXplore Locus SP micro-CT) of these samples were measured. The density of the collimator was equal to 17.31 ± 0.10 g∕cm(3) (89.92% of pure tungsten). The production accuracy ranges from -260 to +650 μm. The aperture positions have a mean deviation of 5 μm, the maximum deviation was 174 μm and the minimum deviation was -122 μm. The mean aperture diameter is 464 ± 19 μm. The calculated and measured sensitivity and

  10. Tuning negative refractive collimation beam by square lattice sonic crystal with concave incident surface

    Directory of Open Access Journals (Sweden)

    F. Shen

    2016-02-01

    Full Text Available Negative refractive collimation beam at the low frequency region is achieved in a square lattice sonic crystal with the small magnitude of effective refractive index. A simple tuning approach for such acoustic beam is also proposed by attaching an additional concave surface of incidence to the crystal slab. This can increase the propagation distance of collimation beam, enhance or suppress the beam intensity. The proposed approach is rather general and applicable to other acoustic materials as long as their effective index can be retrieved. Moreover, the results can be applied to wavefront manipulation and transmission enhancement.

  11. Collimating lamp with well color mixing of red/green/blue LEDs.

    Science.gov (United States)

    Sun, Ching-Cherng; Moreno, Ivan; Lo, Yi-Chien; Chiu, Bo-Chun; Chien, Wei-Ting

    2012-01-02

    A novel light luminaire is proposed and experimentally analyzed, which efficiently mixes and projects the tunable light from red, green and blue (RGB) light-emitting diodes (LEDs). Simultaneous light collimation and color mixing is a challenging task because most collimators separate colors, and most color mixers spread the light beam. Our method is simple and compact; it only uses a short light pipe, a thin diffuser, and a total internal reflection lens. We performed an experimental study to find a balance between optical efficiency and color uniformity by changing light recycling and color mixing.

  12. An adjustable in-pile fan collimator for focusing at a neutron diffractometer

    CERN Document Server

    Stüsser, N

    2002-01-01

    An adjustable in-pile fan collimator was built and tested in a neutron diffraction set-up with a large horizontally curved monochromator for focusing in real and reciprocal space. For small samples, enhancements of intensity up to a factor of five without losing 2 theta-resolution are possible in comparison to a conventional diffractometer equipped with Soller-type collimators. Our geometry will be discussed and compared to both the conventional diffractometer and a focusing arrangement using an in-pile diaphragm.

  13. Geometric wakefield regimes study of a rectangular tapered collimator for ATF2

    CERN Document Server

    Fuster-Martinez, Nuria; Latina, Andrea; Snuverink, Jochem

    2016-01-01

    In this paper we study the discrepancy found between the wakefield impact effect induced by a rectangular tapered collimator prototype for ATF2 calculated using analytical models, calculated from CST PS numerical simulations and implemented in the tracking code PLACET v1.0.0. In order to get consistent results between the analytical calculations, CST PS simulations and the tracking code PLACET v1.0.0 the collimator wakefield module in PLACET v1.0.0 has to be modified. The changes have been implemented in the tracking code PLACET v1.0.1.

  14. Collimator optimization for small animal radiation therapy at a micro-CT

    Energy Technology Data Exchange (ETDEWEB)

    Felix, Manuela C. [Heidelberg Univ., Mannheim (Germany). Medical Radiation Physics/Radiation Protection; Heidelberg Univ., Mannheim (Germany). Dept. of Radiation Oncology; Glatting, Gerhard [Heidelberg Univ., Mannheim (Germany). Medical Radiation Physics/Radiation Protection; Giordano, Frank A.; Wenz, Frederik; Fleckenstein, Jens [Heidelberg Univ., Mannheim (Germany). Dept. of Radiation Oncology; Brockmann, Marc A. [Heidelberg Univ., Mannheim (Germany). Dept. of Neuroradiology; University Medical Center Mainz (Germany). Dept. of Neuroradiology

    2017-05-01

    In radiation therapy of small animals treatment depths range from a few millimetres to several centimetres. In order to spare surrounding organs at risk steep dose gradients are necessary. To minimize the treatment time, and therefore the strain to the animals, a high dose rate is required. A description how these parameters can be optimized through an appropriate choice of collimators with different source surface distances (SSD) as well as different materials and geometries is presented. An industrial micro-CT unit (Y.Fox, YXLON GmbH, Hamburg, Germany) was converted into a precision irradiator for small animals. Different collimators of either stainless steel (Fe) with cylindrical bores (SSD = 42 mm) or tungsten (W) with conical bores (SSD = 14 mm) were evaluated. The dosimetry of very small radiation fields presents a challenge and was performed with GafChromic EBT3 films (Ashland, Vayne, KY, USA) in a water phantom. The films were calibrated with an ionization chamber in the uncollimated field. Treatments were performed via a rotation of the objects with a fixed radiation source. As expected, the shorter SSD of the W-collimators resulted in a (4.5 ± 1.6)-fold increase of the dose rates compared to the corresponding Fe-collimators. The ratios of the dose rates at 1 mm and 10 mm depth in the water phantom was (2.6 ± 0.2) for the Fe- and (4.5 ± 0.1) for the W-collimators. For rotational treatments in a cylindrical plastic phantom maximum dose rates of up to 1.2 Gy/min for Fe- and 5.1 Gy/min for W-collimators were measured. Choosing the smallest possible SSD leads to a high dose rate and a high surface dose, which is of advantage for the treatment of superficial target volumes. For larger SSD the dose rate is lower and the depth dose curve is shallower. This leads to a reduction of the surface dose and is best suited for treatments of deeper seated target volumes. Divergent collimator bores have, due to the reduced scatter within the collimators, a steeper

  15. External-cavity diode lasers with different devices and collimating optics.

    Science.gov (United States)

    Kane, D M; Willis, A P

    1995-07-20

    Comparative operating characteristics of external-cavity diode lasers (ECDL's) with either a channel substrate planar device or a multi-quantum-well (MQW) device are presented. These include the output beam profile, which is significantly altered depending on the collimating lens used (either multielement or graded index), power versus injection-current characteristics, and the optical frequency and the rf spectra. The coherence lengths of the different laser diode-collimating-lens combinations in the ECDL are measured, and a new method for calculating the coupling coefficient and the coupled values of the internal quantum efficiency and the internal lumped loss is demonstrated for the MQW device.

  16. Metal micro-arrays for collimating neutrons and X-rays

    Energy Technology Data Exchange (ETDEWEB)

    Allman, B.E.; Cimmino, A.; Klein, A.G. [Univ. of Melbourne, Parkville (Australia). School of Physics; Hamilton, W.A. [Oak Ridge National Lab., TN (United States). Neutron Scattering Group

    1998-08-01

    The authors describe the theory, fabrication and experimental results of novel, compact optical elements for collimating and/or focusing beams of X-rays or thermal neutrons. These optical elements are solid composites consisting of regular stacks of alternating micro-foils, analogous in action to Soller slits. They are made out of pairs of metals with suitable refractive indices for reflection and/or absorption of the radiation. The performance of these proof-in-principle collimating elements is limited only by the choice of micro-foil materials and the uniformity of their interfaces.

  17. Hollow Electron Beam Collimation for HL-LHC - Effects on the Beam Core

    Energy Technology Data Exchange (ETDEWEB)

    Fitterer, M. [Fermilab; Stancari, G. [Fermilab; Valishev, A. [Fermilab; Bruce, R. [CERN; Papotti, G [CERN; Redaelli, S. [CERN; Valentino, G. [Malta U.; Valentino, G. [CERN; Valuch, D. [CERN; Xu, C. [CERN

    2017-06-13

    Collimation with hollow electron beams is currently one of the most promising concepts for active halo control in the High Luminosity Large Hadron Collider (HL-LHC). To ensure the successful operation of the hollow beam collimator the unwanted effects on the beam core, which might arise from the operation with a pulsed electron beam, must be minimized. This paper gives a summary of the effect of hollow electron lenses on the beam core in terms of sources, provides estimates for HL-LHC and discusses the possible mitigation methods.

  18. High-frequency impedance of small-angle tapers and collimators

    Directory of Open Access Journals (Sweden)

    G. Stupakov

    2010-10-01

    Full Text Available Collimators and transitions in accelerator vacuum chambers often include small-angle tapering to lower the wakefields generated by the beam. While the low-frequency impedance is well described by Yokoya’s formula (for axisymmetric geometry, much less is known about the behavior of the impedance in the high-frequency limit. In this paper we develop an analytical approach to the high-frequency regime for round collimators and tapers. Our analytical results are compared with computer simulations using the code ECHO.

  19. A dynamic dispersion insert in the Fermilab Main Injector for momentum collimation

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, D.E.; /Fermilab

    2007-06-01

    The Fermilab Main Injector (MI) accelerator is designed as a FODO lattice with zero dispersion straight sections. A scheme will be presented that can dynamically alter the dispersion of one of the long straight sections to create a non-zero dispersion straight section suitable for momentum collimation. During the process of slip stacking DC beam is generated which is lost during the first few milliseconds of the ramp. A stationary massive primary collimator/absorber with optional secondary masks could be utilized to isolate beam loss due to uncaptured beam.

  20. Final layout and expected cleaning for the first crystal-assisted collimation test at the LHC

    CERN Document Server

    Mirarchi, D; Redaelli, S; Scandale, W; Taratin, A M; Galluccio, F

    2014-01-01

    The installation in the CERN Large Hadron Collider (LHC) of two crystals in the horizontal and vertical planes was accomplished during the present LHC long shutdown (LS1) for crystal collimation studies. An appropriate layout was designed to demonstrate the principle feasibility of crystal collimation at the LHC. Extensive simulation campaigns were made to evaluate different crystal positions and parameters, in order to ensure that the main goals of these first feasibility tests in the LHC are within reach. In this paper, the final layout is presented. An overview of the considerations behind the design choices and the crystal parameters is given, and the expected performance of the system is discussed.

  1. Hollow Electron Beam Collimation for HL-LHC - Effects on the Beam Core

    CERN Document Server

    Fitterer, M; Valishev, A; Bruce, R; Papotti, G; Redaelli, S; Valentino, G; Valentino, G; Valuch, D; Xu, C

    2017-01-01

    Collimation with hollow electron beams is currently one of the most promising concepts for active halo control in the High Luminosity Large Hadron Collider (HL-LHC). To ensure the successful operation of the hollow beam collimator the unwanted effects on the beam core, which might arise from the operation with a pulsed electron beam, must be minimized. This paper gives a summary of the effect of hollow electron lenses on the beam core in terms of sources, provides estimates for HL-LHC and discusses the possible mitigation methods.

  2. Comparison between vertical parallel hole collimator and 30/sup 0/ rotating slant hole collimator for assessing global and regional left ventricular function by radionuclide angiography

    Energy Technology Data Exchange (ETDEWEB)

    Berthout, P.; Faivre, R.; Bernard, Y.; Bassand, J.P.; Maurat, J.P.; Cardot, J.C.; Baud, M.; Jouan, A.; Verdenet, J.; Bidet, R.

    1988-06-01

    Left ventricular ejection fraction (LVEF) and regional wall motion abnormalities were determined in 40 patients using equilibrium radionuclide angiography. Scintigraphic acquisitions were collected in random order with 2 different collimators. Results were compared to contrast ventriculography (CV) performed in the 30/sup 0/ right anterior view and in a 60/sup 0/ left anterior oblique view. Radionuclide LVEF in both series was closely correlated with contrast ventriculographic LVEF. Regional wall motion analysis was only performed among the 30 patients suffering from coronary heart disease. Eight contrast angiographic studies were normal and 22 abnormal. Global sensitivity and specificity were 100% and 63% with the VTC and 91% and 87% with the 30/sup 0/ RSHC. Agreement for the localisation of the regional wall motion abnormalities between CV and radionuclide angiography was 70.6% with the VTC and 71.2% with the RSHC (P=ns). Intensity of the regional wall motion abnormalities was assessed with the 30/sup 0/ RSHC as well as with the VTC. We conclude that the use of a rotating slant hole collimator associated with radionuclide ventriculography allows improved determination of left ventricular ejection fraction and more accurate assessment of regional wall motion abnormalities with only two projections while the vertical collimator requires three.

  3. ParCAT: Parallel Climate Analysis Toolkit

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Brian E. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Steed, Chad A. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Shipman, Galen M. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Ricciuto, Daniel M. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Thornton, Peter E. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Wehner, Michael [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Williams, Dean N. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2013-01-01

    Climate science is employing increasingly complex models and simulations to analyze the past and predict the future of Earth s climate. This growth in complexity is creating a widening gap between the data being produced and the ability to analyze the datasets. Parallel computing tools are necessary to analyze, compare, and interpret the simulation data. The Parallel Climate Analysis Toolkit (ParCAT) provides basic tools to efficiently use parallel computing techniques to make analysis of these datasets manageable. The toolkit provides the ability to compute spatio-temporal means, differences between runs or differences between averages of runs, and histograms of the values in a data set. ParCAT is implemented as a command-line utility written in C. This allows for easy integration in other tools and allows for use in scripts. This also makes it possible to run ParCAT on many platforms from laptops to supercomputers. ParCAT outputs NetCDF files so it is compatible with existing utilities such as Panoply and UV-CDAT. This paper describes ParCAT and presents results from some example runs on the Titan system at ORNL.

  4. Efficacy of a dynamic collimator for overranging dose reduction in a second- and third-generation dual source CT scanner

    NARCIS (Netherlands)

    R. Booij (Ronald); M.L. Dijkshoorn (Marcel); M. van Straten (Marcel)

    2017-01-01

    textabstractObjectives: The purpose of this study was to assess the efficacy of the renewed dynamic collimator in a third-generation dual source CT (DSCT) scanner and to determine the improvements over the second-generation scanner. Methods: Collimator efficacy is defined as the percentage overrangi

  5. Development of unmatched system model for iterative image reconstruction for pinhole collimator of imaging systems in nuclear medicine

    Energy Technology Data Exchange (ETDEWEB)

    Bae, Jae Keon; Bae, Seung Bin; Lee, Ki Sung; Kim, Yong Kwon; Joung, Jin Hun [Korea Univ., Seoul (Korea, Republic of)

    2012-12-15

    Diverse designs of collimator have been applied to Single Photon Emission Computed Tomography (SPECT) according to the purpose of acquisition; thus, it is necessary to reflect geometric characteristic of each collimator for successive image reconstruction. This study carry out reconstruction algorithm for imaging system in nuclear medicine with pinhole collimator. Especially, we study to solve sampling problem which caused in the system model of pinhole collimator. System model for a maximum likelihood expectation maximization (MLEM) was developed based on the geometry of the collimator. The projector and back-projector were separately implemented based on the ray-driven and voxel-driven methods, respectively, to overcome sparse sampling problem. We perform phantom study for pinhole collimator by using geant4 application for tomographic emission(GATE) simulation tool. The reconstructed images show promising results. Designed iterative reconstruction algorithm with unmatched system model effective to remove sampling problem artefact. Proposed algorithm can be used not only for pinhole collimator but also for various collimator system of imaging system in nuclear medicine.

  6. SU-E-T-600: Utilizing Collimator Rotation to Increase Maximum Treatable Target Dimensions Using an Elekta Synergy-S with Beam Modulator Multileaf Collimator.

    Science.gov (United States)

    Rhodes, C; Campbell, S; Shields, W; Fabien, J; Colussi, V; Wessels, B

    2012-06-01

    To determine if a rotated collimator on an Elekta Synergy-S with Beam Modulator MLC (BMx) allows for dosimetrically acceptable treatment of targets exceeding the length of the maximum field size (21×16cm). The BMx is a high-resolution MLC with 4mm leaves but is of limited clinical use on patient target volumes exceeding 20cm in length. Rotation of the collimator utilizes the Pythagorean geometry to extend treatment length. This potentially increases the length of the PTV that be conformally treated. Rods of 21-23cm length were contoured in water with the Pinnacle treatment planning system. The width of the rods varies from 1 -5cm. Four isocentric treatment plans were generated for each target: four-field conformal, 7-field IMRT, single-arc VMAT, and a modified double-arc VMAT (MDAV), with the collimator angled at 55°. The MDAV method consists of two opposing 180° arcs with the collimator turned 55° in opposite directions. A successful plan is defined as 99% of the target volume being covered by a minimum of 95% of the prescribed dose. Conformality is determined as a ratio of the volume exposed to prescribed isodose and target volume. Targets of length 21cm, 22cm, and 23 cm are able to be treated with widths of 4cm, 5 cm, and 4cm respectively. The MDAV method achieves these results on all trials. The VMAT method achieves these results for the 21cm and 23cm long target. The IMRT Method achieves these results for the 21cm long target. With the exception of the 1cm wide targets, the average conformality is approximately 2.5. Changing the collimator angle of the BMx Elekta-S machine allows for a 3cm length increase of targets up to 5cm. Further work will assess clinical suitability of these findings for treatment of head and neck tumors and spinal masses. © 2012 American Association of Physicists in Medicine.

  7. Outgassing measurement of an LHC collimator and estimation for the NEG performances

    CERN Document Server

    Kamiya, Junichiro; Jimenez, J M; Bregliozzi, G

    2011-01-01

    The outgassing rate of the collimators in the Large Hadron Collider (LHC) at CERN has an important role for the life-time of the Non-Evaporable Getter (NEC), and an accurate analysis allows the definition of future activities, like NEC vacuum activation. For these reasons, both, total outgassing rate and gas composition of a secondary collimator have been measured in the laboratory. The outgassing rate decreases by about two orders of magnitude by after bake-out and moreover, repeated bake-out further reduced the outgassing rate. The gas transmission through the NEC coated beam pipes and the resulting pressure distributions near the collimator were also measured in a dedicated setup. It is found that the main gas component after just 2 m of NEC coated beam pipe is CH(4) due to the extreme pumping speed of NEC for the other gases. Large amount of outgassing for H(2) and carbon related molecules are released when moving the collimator jaws. It is found that the NEC is very effective even in such case with large...

  8. Verification of passive cooling techniques in the Super-FRS beam collimators

    Science.gov (United States)

    Douma, C. A.; Gellanki, J.; Najafi, M. A.; Moeini, H.; Kalantar-Nayestanaki, N.; Rigollet, C.; Kuiken, O. J.; Lindemulder, M. F.; Smit, H. A. J.; Timersma, H. J.

    2016-08-01

    The Super FRagment Separator (Super-FRS) at the FAIR facility will be the largest in-flight separator of heavy ions in the world. One of the essential steps in the separation procedure is to stop the unwanted ions with beam collimators. In one of the most common situations, the heavy ions are produced by a fission reaction of a primary 238U-beam (1.5 GeV/u) hitting a 12C target (2.5 g/cm2). In this situation, some of the produced ions are highly charged states of 238U. These ions can reach the collimators with energies of up to 1.3 GeV/u and a power of up to 500 W. Under these conditions, a cooling system is required to prevent damage to the collimators and to the corresponding electronics. Due to the highly radioactive environment, both the collimators and the cooling system must be suitable for robot handling. Therefore, an active cooling system is undesirable because of the increased possibility of malfunctioning and other complications. By using thermal simulations (performed with NX9 of Siemens PLM), the possibility of passive cooling is explored. The validity of these simulations is tested by independent comparison with other simulation programs and by experimental verification. The experimental verification is still under analysis, but preliminary results indicate that the explored passive cooling option provides sufficient temperature reduction.

  9. Gaussian Schell Source as Model for Slit-Collimated Atomic and Molecular Beams

    CERN Document Server

    McMorran, Ben

    2008-01-01

    We show how to make a Gaussian Schell-model (GSM) beam. Then we compare the intensity profile, the transverse coherence width and the divergence angle of a GSM beam with those same properties of a beam that is collimated with two hard-edged slits. This work offers an intuitive way to understand various interferometer designs, and we compare our results with data.

  10. Fast Automatic Beam-Based Alignment of the LHC Collimator Jaws

    CERN Document Server

    AUTHOR|(CDS)2080813; Assmann, R W

    2014-01-01

    The CERN Large Hadron Collider (LHC) in Geneva, Switzerland is the largest and most powerful particle accelerator ever built. With a circumference of 27 km, it is designed to collide particles in two counter-rotating beams at a centre-of-mass energy of 14 TeV to explore the fundamental forces and constituents of matter. Due to its potentially destructive high energy particle beams, the LHC is equipped with several machine protection systems. The LHC collimation system is tasked with scattering and absorbing beam halo particles before they can quench the superconducting magnets. The 108 collimators also protect the machine from damage in the event of very fast beam losses, and shields sensitive devices in the tunnel from radiation over years of operation. Each collimator is made up of two blocks or ‘jaws’ of carbon, tungsten or copper material. The collimator jaws need be placed symmetrically on either side of the beam trajectory, to clean halo particles with maximum efficiency. The beam orbit and beam siz...

  11. Investigation of collimator materials for the High Luminosity Large Hadron Collider

    CERN Document Server

    Quaranta, Elena; Bertarelli, Alessandro; Redaelli, Stefano

    This PhD thesis work has been carried out at the European Organisation for Nuclear Research (CERN), Geneva, Switzerland), in the framework of the High Luminosity (HL) upgrade of the Large Hadron Collider (LHC). The HL-LHC upgrade will bring the accelerator beyond the nominal performance: it is planning to reach higher stored beam energy up to 700 MJ, through more intense proton beams. The present multi-stage LHC collimation system was designed to handle 360 MJ stored beam energy and withstand realistic losses only for this nominal beam. Therefore, the challenging HL-LHC beam parameters pose strong concerns for beam collimation, which call for important upgrades of the present system. The objective of this thesis is to provide solid basis for optimum choices of materials for the different collimators that will be upgraded for the baseline layout of the HL-LHC collimation system. To achieve this goal, material-related limitations of the present system are identified and novel advanced composite materials are se...

  12. Anatomically shaped cranial collimation (ACC) for lateral cephalometric radiography: a technical report

    NARCIS (Netherlands)

    Hoogeveen, R.C.; van der Stelt, P.F.; Berkhout, W.E.R.

    2013-01-01

    Lateral cephalograms in orthodontic practice display an area cranial of the base of the skull that is not required for diagnostic evaluation. Attempts have been made to reduce the radiation dose to the patient using collimators combining the shielding of the areas above the base of the skull and bel

  13. Penumbra characteristics of square photon beams delimited by a GEMS multi-leaf collimator

    Energy Technology Data Exchange (ETDEWEB)

    Briot, E.; Julia, F. [Centre de Lutte Contre le Cancer Gustave-Roussy, 94 - Villejuif (France)

    1995-12-01

    A multi-leaf collimator (MLC) has been designed to replace directly the standard collimator of a SATURNE IV Series linac. It consists of 2 x 32 tungsten leaves and one set of upper block jaws. Isodose curves and dose profiles were measured for symmetric fields at the depth of the maximum and the reference depths for 6 MV, 10 MV, 18 MV photon beams. The penumbra (80%-20%) corresponding to the face and the side of the leaves have been compared with the standard collimators. Along with the X direction, the field delimitation is performed primarily with the leaves which are continuously variable in position. Along the Y direction, the field is initially approximated by the closure of opposite leaf pairs; then the Y upper jaws produce the exact size of the required field. As the leaves move linearly the penumbra (80%-20%) corresponding to the leaf ends is minimized and held constant at all positions by curvature of their faces. Penumbra obtained with the superposition of leaves and Y jaws depend on their relative position. The penumbra is minimum when the leaf side and the Y jaw edge coincide and the comparison of the measurement values with the conventional collimator shows that the differences are within 1 mm. When the leaves delineating the field are not entirely covered by the Y block upper jaws, the penumbra increases, and the junction of the opposing leaves, a width increase up to 3.5 mm has been measured.

  14. Thermal behavior of TAXN and TCDXM D2 collimator mask, Finite element studies

    CERN Document Server

    Sklariks, Stepans

    2015-01-01

    The objective of this project was to perform thermal loading simulations of TCDXM (D2 collimator mask) and TAXN so as to allow the preliminary evaluation of the suitability of the given parts for the upcoming high luminosity upgrade that is to be performed in LHC in the nearest future.

  15. Summary of the CERN Workshop on Materials for Collimators and Beam Absorbers

    CERN Document Server

    Schmidt, R; Bertarelli, A; Ferrari, A; Weterings, W; Mokhov, N V

    2008-01-01

    The main focus of the workshop was on collimators and beam absorbers for (mainly) High Energy Hadron Accelerators, with the energy stored in the beams far above damage limit. The objective was to better understand the technological limits imposed by mechanisms related to beam impact on materials. The idea to organise this workshop came up during the High Intensity High Brightness Hadron Beams, ICFA-HB2006 in Japan [1]. The workshop was organised 3-5 September 2007 at CERN, with about 60 participants, including 20 from outside CERN. About 30 presentations were given [2]. The event was driven by the LHC challenge, with more than 360 MJoule stored in each proton beam. The entire beam or its fraction will interact with LHC collimators and beam absorbers, and with the LHC beam dump blocks. Collimators and beam absorbers are also of the interest for other labs and accelerators: - CERN: for the CNGS target, for SPS beam absorbers (extraction protection) and collimators for protecting the transfer line between SPS an...

  16. A collimation system for ELI-NP Gamma Beam System - design and simulation of performance

    Science.gov (United States)

    Paternò, G.; Cardarelli, P.; Marziani, M.; Bagli, E.; Evangelisti, F.; Andreotti, M.; Gambaccini, M.; Petrillo, V.; Drebot, I.; Bacci, A.; Vaccarezza, C.; Palumbo, L.; Variola, A.

    2017-07-01

    The purpose of this study was to evaluate the performance and refine the design of the collimation system for the gamma radiation source (GBS) currently being realised at ELI-NP facility. The gamma beam, produced by inverse Compton scattering, will provide a tunable average energy in the range between 0.2 and 20 MeV, an energy bandwidth 0.5% and a flux of about 108 photons/s. As a result of the inverse Compton interaction, the energy of the emitted radiation is related to the emission angle, it is maximum in the backscattering direction and decreases as the angle increase [1,2]. Therefore, the required energy bandwidth can be obtained only by developing a specific collimation system of the gamma beam, i.e. filtering out the radiation emitted at larger angles. The angular acceptance of the collimation for ELI-NP-GBS must be continuously adjustable in a range from about 700 to 60 μrad, to obtain the required parameters in the entire energy range. The solution identified is a stack of adjustable slits, arranged with a relative rotation around the beam axis to obtain an hole with an approximately circular shape. In this contribution, the final collimation design and its performance evaluated by carrying out a series of detailed Geant4 simulations both of the high-energy and the low-energy beamline are presented.

  17. LHC Heavy-Ion Collimation Quench Test at 6.37Z TeV

    CERN Document Server

    Hermes, Pascal Dominik; Bruce, Roderik; Hofle, Wolfgang; Holzer, Eva Barbara; Kalliokoski, Matti; Kotzian, Gerd; Mereghetti, Alessio; Mirarchi, Daniele; Quaranta, Elena; Redaelli, Stefano; Valentino, Gianluca; Valuch, Daniel; Wollmann, Daniel; Zerlauth, Markus; CERN. Geneva. ATS Department

    2016-01-01

    This note summarizes the collimation quench test MD with 208Pb82+ beams at 6.37Z TeV in which a quench of a dipole magnet in the dispersion suppressor (DS) downstream of the betatron collimation region (IR7) was achieved. The aim of the test was to experimentally validate the quench limit in this region by means of inducing high losses at the LHC collimation system and quench the magnet with the collimation debris mainly lost at the IR7 DS. It was the first test with heavy-ions in which the transverse damper (ADT) could be used to induce these losses over extended periods of time (approximately 10-15s) while previous tests used tune resonance crossing methods in which the beam loss is less controllable and faster. The quench was achieved at a beam loss rate of 15 kW. The note summarizes the measurement strategy, technical realization, the test results and implications for future heavy-ion operation.

  18. Studies on heavy ion losses from collimation cleaning at the LHC

    CERN Document Server

    Hermes, P D; Jowett, J M; Redaelli, S; Salvachua, B M; Valentino, G; Wollmann, D

    2015-01-01

    The LHC collimation system protects superconducting magnets from beam losses. By design, it was optimized for the high-intensity proton challenges but so far provided adequate protection also during the LHC heavy-ion runs with 208Pb82+ ions up to a beam energy of 4 Z TeV. Ion beam cleaning brings specific challenges due to different physical interactions with the collimator materials and might require further improvements for operation at 7 Z TeV. In this article, we study heavy-ion beam losses leaking out of the LHC collimation system, both in measurement and simulations. The simulations are carried out using both ICOSIM, with a simplified ion physics model implemented, and SixTrack, including more detailed starting conditions from FLUKA but without including online scattering in subsequent collimator hits. The results agree well with measurements overall, although some discrepancies are present. The reasons for the discrepancies are investigated and, on this basis, the requirements for an improved simulatio...

  19. Comparative results on collimation of the SPS beam of protons and Pb ions with bent crystals

    CERN Document Server

    Scandale, W.; Assmann, R.; Bracco, C.; Cerutti, F.; Christiansen, J.; Gilardoni, S.; Laface, E.; Losito, R.; Masi, A.; Metral, E.; Mirarchi, D.; Montesano, S.; Previtali, V.; Redaelli, S.; Valentino, G.; Schoofs, P.; Smirnov, G.; Tlustos, L.; Bagli, E.; Baricordi, S.; Dalpiaz, P.; Guidi, V.; Mazzolari, A.; Vincenzi, D.; Dabagov, S.; Murtas, F.; Carnera, A.; Della Mea, G.; De Salvador, D.; Lombardi, A.; Lytovchenko, O.; Tonezzer, M.; Cavoto, G.; Ludovici, L.; Santacesaria, R.; Valente, P.; Galluccio, F.; Afonin, A.G.; Bulgakov, M.K.; Chesnokov, Yu.A.; Maisheev, V.A.; Yazynin, I.A.; Kovalenko, A.D.; Taratin, A.M.; Uzhinskiy, V.V.; Gavrikov, Yu.A.; Ivanov, Yu.M.; Lapina, L.P.; Skorobogatov, V.V.; Ferguson, W.; Fulcher, J.; Hall, G.; Pesaresi, M.; Raymond, M.; Rose, A.; Ryan, M.; Zorba, O.; Robert-Demolaize, G.; Markiewicz, T.; Oriunno, M.; Wienands, U.

    2011-01-01

    New experiments on crystal assisted collimation have been carried out at the CERN SPS with stored beams of 120 Gev/c protons and Pb ions. Bent silicon crystals of 2 mm long with about 170 mu rad bend angle and a small residual torsion were used as primary collimators. In channeling conditions, the beam loss rate induced by inelastic interactions of particles with the crystal nuclei is minimal. The loss reduction was about 6 for protons and about 3 for Pb ions. Lower reduction value for Pb ions can be explained by their considerably larger ionization losses in the crystal. In one of the crystals, the measured fraction of the Pb ion beam halo deflected in channeling conditions was 74\\%, a value very close to that for protons. The intensity of the off-momentum halo leaking out from the collimation station was measured in the first high dispersion area downstream. The particle population in the shadow of the secondary collimator-absorber was considerably smaller in channeling conditions than for amorphous orienta...

  20. Low-frequency ultrasonic Bessel-like collimated beam generation from radial modes of piezoelectric transducers

    Science.gov (United States)

    Chillara, Vamshi Krishna; Pantea, Cristian; Sinha, Dipen N.

    2017-02-01

    We present a very simple approach to generate a collimated ultrasonic beam that exploits the natural Bessel-like vibration pattern of the radial modes of a piezoelectric disc with lateral clamping. This eliminates the need for the conventional annular Bessel pattern of the electrodes with individual electrode excitation on the piezo-disc, thus simplifying the transducer design. Numerical and experimental studies are carried out to investigate the Bessel-like vibration patterns of these radial modes showing an excellent agreement between these two studies. Measured ultrasonic beam-profiles in water from the radial modes confirm the profile to be a Bessel beam. Collimated beam generation from radial modes is investigated using a coupled electromechanical finite-element model. It is found that clamping the lateral edges of piezoelectric transducers results in a high-degree of collimation with practically no side-lobes similar to a parametric array beam. Ultrasonic beam-profile measurements in water with both free and clamped piezoelectric transducer are presented. The collimated beam generation using the present technique of using the laterally clamped radial modes finds significant applications in low-frequency imaging through highly attenuating materials.

  1. Bent silicon crystals for the LHC collimation Studies with an ultrarelativistic proton beam

    CERN Document Server

    Hasan, Said; Scandale, Walter; Vallazza, Erik

    2007-01-01

    LHC is a source of new challenges in every HEP field; among these, the beam collimation requires an innovative approach. The H8RD22 collaboration is undertaking an intense study of bent crystal properties with the goal of using crystals as primary collimators. The thesis gives an introduction to the theory of channeling and its related phenomena in bent crystals explaining how these can be used to perform an efficient beam collimation. The pre-thesis experiments are described to introduce the scientific context in which the H8RD22 collaboration is working. The thesis core is the description of two beam tests held in Sept. 2006 and May 2007 on the CERN SPS H8 beamline with 400 GeV/c protons: the experimental setups and procedures are shown together with the analysis of the collected data. With the observation of the volume reflection for the first time at these energies and the use of multi crystal systems, these experiments are a clear indication that crystal collimation is a real possibility for the second p...

  2. Technical Note: Modeling a complex micro-multileaf collimator using the standard BEAMnrc distribution

    Energy Technology Data Exchange (ETDEWEB)

    Kairn, T.; Kenny, J.; Crowe, S. B.; Fielding, A. L.; Franich, R. D.; Johnston, P. N.; Knight, R. T.; Langton, C. M.; Schlect, D.; Trapp, J. V. [School of Physical and Chemical Sciences, Queensland University of Technology, G.P.O. Box 2434, Brisbane, Queensland 4001 (Australia); Premion, Wesley Medical Centre, Suite 1, 40 Chasely St., Auchenflower, Queensland 4066 (Australia); School of Physical and Chemical Sciences, Queensland University of Technology, G.P.O. Box 2434, Brisbane, Queensland 4001 (Australia); School of Applied Sciences, RMIT University, G.P.O. Box 2476, Melbourne, Victoria 3001 (Australia); Australian Radiation Protection and Nuclear Safety Agency, 619 Lower Plenty Road, Yallambie, Victoria 3085 (Australia); Premion, Wesley Medical Centre, Suite 1, 40 Chasely St., Auchenflower, Queensland 4066 (Australia); School of Physical and Chemical Sciences, Queensland University of Technology, G.P.O. Box 2434, Brisbane, Queensland 4001 (Australia); Premion, Wesley Medical Centre, Suite 1, 40 Chasely St., Auchenflower, Queensland 4066 (Australia); School of Physical and Chemical Sciences, Queensland University of Technology, G.P.O. Box 2434, Brisbane, Queensland 4001 (Australia)

    2010-04-15

    Purpose: The component modules in the standard BEAMnrc distribution may appear to be insufficient to model micro-multileaf collimators that have trifaceted leaf ends and complex leaf profiles. This note indicates, however, that accurate Monte Carlo simulations of radiotherapy beams defined by a complex collimation device can be completed using BEAMnrc's standard VARMLC component module. Methods: That this simple collimator model can produce spatially and dosimetrically accurate microcollimated fields is illustrated using comparisons with ion chamber and film measurements of the dose deposited by square and irregular fields incident on planar, homogeneous water phantoms. Results: Monte Carlo dose calculations for on-axis and off-axis fields are shown to produce good agreement with experimental values, even on close examination of the penumbrae. Conclusions: The use of a VARMLC model of the micro-multileaf collimator, along with a commissioned model of the associated linear accelerator, is therefore recommended as an alternative to the development or use of in-house or third-party component modules for simulating stereotactic radiotherapy and radiosurgery treatments. Simulation parameters for the VARMLC model are provided which should allow other researchers to adapt and use this model to study clinical stereotactic radiotherapy treatments.

  3. Design of a Tri-PET collimator for high-resolution whole-body mouse imaging.

    Science.gov (United States)

    DiFilippo, Frank P

    2017-08-01

    Tri-PET refers to high-resolution 511-keV emission tomography using a multipinhole collimator in conjunction with lower resolution PET detectors operating in coincidence mode. Tri-PET is unique in that three spatial locations are associated with each event (two detector coordinates and one pinhole location). Spatial resolution and sensitivity are similar to that of 511-keV SPECT and are governed mainly by the collimator design. However because of a third spatial location in Tri-PET, the line-of-response is overdetermined. This feature permits new opportunities in data processing which impact collimator design. In particular, multiplexing can be avoided since the coincidence data identify the pinhole through which the photon passed. In this paper, the principles of Tri-PET collimator design are reviewed and then applied to the case of high-resolution imaging of a small animal in a clinical PET scanner. The design of a 148-pinhole collimator for whole-body imaging of a mouse is presented. Two pinhole designs were investigated: knife-edge pinholes with 1.1 mm aperture and novel hyperboloidal pinholes with 1.2 mm aperture, both having 18° cone angle. The pinhole configuration is unfocused, covering a whole-body mouse field of view with nearly uniform sensitivity. Computer simulations were performed of a micro hot rods phantom imaged with this collimator in a clinical PET scanner. Sensitivity was estimated by simulating a point source centered on-axis at locations spanning a 70-mm axial range, similar to the NEMA NU-4 standard for whole-body mouse imaging. Reconstructed images of the hot rods phantom demonstrated the ability to resolve 1.1 mm structures with the knife-edge pinholes and 1.0 mm structures with the hyperboloidal pinholes. Sensitivity was found to be 0.093% and 0.054% for the knife-edge and hyperboloidal pinholes, respectively. With a properly designed multipinhole collimator, high-resolution and acceptable sensitivity are achievable with Tri-PET using

  4. Structural analysis of the ParR/parC plasmid partition complex

    DEFF Research Database (Denmark)

    Møller-Jensen, Jakob; Ringgaard, Simon; Mercogliano, Christopher P

    2007-01-01

    Accurate DNA partition at cell division is vital to all living organisms. In bacteria, this process can involve partition loci, which are found on both chromosomes and plasmids. The initial step in Escherichia coli plasmid R1 partition involves the formation of a partition complex between the DNA...... and biochemical experiments support a structural arrangement in which the centromere-like parC DNA is wrapped around a ParR protein scaffold. This structure holds implications for how ParM polymerization drives active DNA transport during plasmid partition....

  5. Prostatektomie radicale robot assistee (Da Vinci(R: abord transperitoneal

    Directory of Open Access Journals (Sweden)

    Rochat CH

    2006-01-01

    Full Text Available La prostatectomie robotisée à l’aide d’un micro-manipulateur (DaVinci(R Intuitive Surgical est le prolongement logique de la prostatectomie laparoscopique. Une meilleure vision et plus de précision permettent des prostatectomies de haute qualité pour des laparoscopeurs déjà expérimentés. Après avoir pratiqué toutes les voies d’abord en laparoscopie traditionnelle et en privilégiant à la fin de notre expérience la voie extra-péritonéale rétrograde, nous avons opté pour un retour à la voie trans-péritonéale lors de la prostatectomie robotisée. Cette voie offre plus d’espace de travail, l’installation des bras du robot est facilitée et il y a un gain de temps dans la préparation du retzius. Nous décrivons ici step-by-step le protocole opératoire de la prostatectomie laparoscopique transpéritonéale robot assistée.

  6. A novel compact three-dimensional laser-sintered collimator for neutron scattering

    Energy Technology Data Exchange (ETDEWEB)

    Ridley, Christopher J., E-mail: c.ridley@ed.ac.uk [The School of Engineering and the Centre for Science at Extreme Conditions, The University of Edinburgh, Peter Guthrie Tait Road, Edinburgh EH9 3FD (United Kingdom); ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX (United Kingdom); Manuel, Pascal; Khalyavin, Dmitry; Kirichek, Oleg [ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX (United Kingdom); Kamenev, Konstantin V. [The School of Engineering and the Centre for Science at Extreme Conditions, The University of Edinburgh, Peter Guthrie Tait Road, Edinburgh EH9 3FD (United Kingdom)

    2015-09-15

    Improvements in the available flux at neutron sources are making it increasingly feasible to obtain refineable neutron diffraction data from samples smaller than 1 mm{sup 3}. The signal is typically too weak to introduce any further sample environment in the 30–50 mm diameter surrounding the sample (such as the walls of a pressure cell) due to the high ratio of background to sample signal, such that even longer count times fail to reveal reflections from the sample. Many neutron instruments incorporate collimators to reduce parasitic scattering from the instrument and from any surrounding material and larger pieces of sample environment, such as cryostats. However, conventional collimation is limited in the volume it can focus on due to difficulties in producing tightly spaced neutron-absorbing foils close to the sample and in integrating this into neutron instruments. Here we present the design of a novel compact 3D rapid-prototyped (or “printed”) collimator which reduces these limitations and is shown to improve the ratio of signal to background, opening up the feasibility of using additional sample environment for neutron diffraction from small sample volumes. The compactness and ease of customisation of the design allows this concept to be integrated with existing sample environment and with designs that can be tailored to individual detector geometries without the need to alter the setup of the instrument. Results from online testing of a prototype collimator are presented. The proof of concept shows that there are many additional collimator designs which may be manufactured relatively inexpensively, with a broad range of customisation, and geometries otherwise impossible to manufacture by conventional techniques.

  7. Pars plana Baerveldt tube insertion with pars plana vitrectomy for refractory glaucoma

    Directory of Open Access Journals (Sweden)

    Anton M Kolomeyer

    2012-01-01

    Conclusions: Pars plana Baerveldt tube implantation with PPV can preserve vision, reduce IOP, and decrease the number of glaucoma medications necessary to achieve target IOP in patients with recalcitrant glaucoma.

  8. PAR Corneal Topography System (PAR CTS): the clinical application of close-range photogrammetry.

    Science.gov (United States)

    Belin, M W; Cambier, J L; Nabors, J R; Ratliff, C D

    1995-11-01

    The PAR Corneal Topography System (CTS) is a computer-driven corneal imaging system which uses close-range photogrammetry (rasterphotogrammetry) to measure and produce a topographic map of the corneal surface. The PAR CTS makes direct point-by-point measurements of surface elevation using a stereo-triangulation technique. The CTS uses a grid pattern composed of horizontal and vertical lines spaced about 0.2 mm (200 microns) apart. Each grid intersection comprises a surface feature which can be located in multiple images and used to generate an (x,y,z) coordinate. Unlike placido disc-based videokeratoscopes, the PAR CTS requires neither a smooth reflective surface nor precise spatial alignment for accurate imaging. In addition to surface elevation, the PAR CTS computes axial and tangential curvatures and refractive power. Difference maps are available in all curvatures, refractive power, and in absolute elevation.

  9. Dosimetric and radiobiological comparison of CyberKnife M6TM InCise multileaf collimator over IRISTM variable collimator in prostate stereotactic body radiation therapy

    Directory of Open Access Journals (Sweden)

    Vindu Kathriarachchi

    2016-01-01

    Full Text Available The impetus behind our study was to establish a quantitative comparison between the IRIS collimator and the InCise multileaf collimator (MLC (Accuray Inc. Synnyvale, CA for prostate stereotactic body radiation therapy (SBRT. Treatment plans for ten prostate cancer patients were performed on MultiPlan™ 5.1.2 treatment planning system utilizing MLC and IRIS for 36.25 Gy in five fractions. To reduce the magnitude of variations between cases, the planning tumor volume (PTV was defined and outlined for treating prostate gland only, assuming no seminal vesicle or ex-capsule involvement. Evaluation indices of each plan include PTV coverage, conformity index (CI, Paddick's new CI, homogeneity index, and gradient index. Organ at risk (OAR dose sparing was analyzed by the bladder wall Dmaxand V37Gy, rectum Dmaxand V36Gy. The radiobiological response was evaluated by tumor control probability and normal tissue complication probability based on equivalent uniform dose. The dose delivery efficiency was evaluated on the basis of planned monitor units (MUs and the reported treatment time per fraction. Statistical significance was tested using the Wilcoxon signed rank test. The studies indicated that CyberKnife M6™ IRIS and InCise™ MLC produce equivalent SBRT prostate treatment plans in terms of dosimetry, radiobiology, and OAR sparing, except that the MLC plans offer improvement of the dose fall-off gradient by 29% over IRIS. The main advantage of replacing the IRIS collimator with MLC is the improved efficiency, determined from the reduction of MUs by 42%, and a 36% faster delivery time.

  10. Assessment of a fast generated analytical matrix for rotating slat collimation iterative reconstruction: a possible method to optimize the collimation profile

    Science.gov (United States)

    Boisson, F.; Bekaert, V.; Reilhac, A.; Wurtz, J.; Brasse, D.

    2015-03-01

    In SPECT imaging, improvement or deterioration of performance is mostly due to collimator design. Classical SPECT systems mainly use parallel hole or pinhole collimators. Rotating slat collimators (RSC) can be an interesting alternative to optimize the tradeoff between detection efficiency and spatial resolution. The present study was conducted using a RSC system for small animal imaging called CLiR. The CLiR system was used in planar mode only. In a previous study, planar 2D projections were reconstructed using the well-known filtered backprojection algorithm (FBP). In this paper, we investigated the use of the statistical reconstruction algorithm maximum likelihood expectation maximization (MLEM) to reconstruct 2D images with the CLiR system using a probability matrix calculated using an analytic approach. The primary objective was to propose a method to quickly generate a light system matrix, which facilitates its handling and storage, while providing accurate and reliable performance. Two other matrices were calculated using GATE Monte Carlo simulations to investigate the performance obtained using the matrix calculated analytically. The first matrix calculated using GATE took all the physics processes into account, where the second did not consider for the scattering, as the analytical matrix did not take this physics process into account either. 2D images were reconstructed using FBP and MLEM with the three different probability matrices. Both simulated and experimental data were used. A comparative study of these images was conducted using different metrics: the modulation transfert function, the signal-to-noise ratio and quantification measurement. All the results demonstrated the suitability of using a probability matrix calculated analytically. It provided similar results in terms of spatial resolution (about 0.6 mm with differences image.

  11. Monte-Carlo simulation of pinhole collimator of a small field of view gamma camera for small animal imaging

    Institute of Scientific and Technical Information of China (English)

    ZHU Jie; MA Wenyan; ZHU Yufeng; MA Hongguang; WU Yuelei; HU Huasi; ZHANG Boping; HUO Yonggang; LIU Silu; JIAN Bin; WANG Zhaomin

    2009-01-01

    Needs in scintimammography applications,especially for small animal cardiac imaging,lead to develop a small field of view,high spatial resolution gamma camera with a pinhole collimator.However the ideal pinhole collimator must keep a compromise between spatial resolution and sensitivity.In order to design a pinhole collimator with an optimized sensitivity and spatial resolution,the spatial resolution and the geometric sensitivity response as a function of the source to collimator distance has been obtained by means of Monte-Carlo simulation for a small field of view gamma camera with a pinhole collimator of various-hole diameters.The results show that the camera with pinhole of 1 mm,1.5 mm and 2 mm diameter has respectively spatial resolution of 1.5 mm,2.25 mm and 3 mm and geometric sensitivity of 0.016%,0.022% and 0.036%,while the source to collimator distance is 3 cm.We chose the pinhole collimator with hole diameter size of 1.2 mm for our the gamma camera designed based on the wade-off between sensitivity and resolution.

  12. Thermomechanical assessment of the effects of a jaw-beam angle during beam impact on Large Hadron Collider collimators

    Science.gov (United States)

    Cauchi, Marija; Assmann, R. W.; Bertarelli, A.; Carra, F.; Lari, L.; Rossi, A.; Mollicone, P.; Sammut, N.

    2015-02-01

    The correct functioning of a collimation system is crucial to safely and successfully operate high-energy particle accelerators, such as the Large Hadron Collider (LHC). However, the requirements to handle high-intensity beams can be demanding, and accident scenarios must be well studied in order to assess if the collimator design is robust against possible error scenarios. One of the catastrophic, though not very probable, accident scenarios identified within the LHC is an asynchronous beam dump. In this case, one (or more) of the 15 precharged kicker circuits fires out of time with the abort gap, spraying beam pulses onto LHC machine elements before the machine protection system can fire the remaining kicker circuits and bring the beam to the dump. If a proton bunch directly hits a collimator during such an event, severe beam-induced damage such as magnet quenches and other equipment damage might result, with consequent downtime for the machine. This study investigates a number of newly defined jaw error cases, which include angular misalignment errors of the collimator jaw. A numerical finite element method approach is presented in order to precisely evaluate the thermomechanical response of tertiary collimators to beam impact. We identify the most critical and interesting cases, and show that a tilt of the jaw can actually mitigate the effect of an asynchronous dump on the collimators. Relevant collimator damage limits are taken into account, with the aim to identify optimal operational conditions for the LHC.

  13. A Combined Global and Local Approach to Elucidate Spatial Organization of the Mycobacterial ParB-parS Partition

    Energy Technology Data Exchange (ETDEWEB)

    Chaudhuri, Barnali [University of Buffalo, The State University of New York; Gupta, Sayan [Case Western Reserve University; Urban, Volker S [ORNL; Chance, Mark [Case Western Reserve University; D' Mello, Rhijuta [Case Western Reserve University; Smith, Lauren [University of Buffalo, The State University of New York; Lyons, Kelly [University of Buffalo, The State University of New York; Gee, Jessica [University of Buffalo, The State University of New York

    2010-01-01

    Combining diverse sets of data at global (size, shape) and local (residue) scales is an emerging trend for elucidating the organization and function of the cellular assemblies. We used such a strategy, combining data from X-ray and neutron scattering with H/D-contrast variation and X-ray footprinting with mass spectrometry, to elucidate the spatial organization of the ParB-parS assembly from Mycobacterium tuberculosis. The ParB-parS participates in plasmid and chromosome segregation and condensation in predivisional bacterial cells. ParB polymerizes around the parS centromere(s) to form a higher-order assembly that serves to recruit cyto-skeletal ParA ATPases and SMC proteins for chromosome segregation. A hybrid model of the ParB-parS was built by combining and correlating computational models with experiment-derived information about size, shape, position of the symmetry axis within the shape, internal topology, DNA-protein interface, exposed surface patches, and prior knowledge. This first view of the ParB-parS leads us to propose how ParB spread on the chromosome to form a larger assembly.

  14. A Combined Global and Local Approach to Elucidate Spatial Organization of the Mycobacterial ParB-parS Partition Assembly

    Energy Technology Data Exchange (ETDEWEB)

    B Chaudhuri; S Gupta; V Urban; M Chance; R DMello; L Smith; K Lyons; J Gee

    2011-12-31

    Combining diverse sets of data at global (size, shape) and local (residue) scales is an emerging trend for elucidating the organization and function of the cellular assemblies. We used such a strategy, combining data from X-ray and neutron scattering with H/D-contrast variation and X-ray footprinting with mass spectrometry, to elucidate the spatial organization of the ParB-parS assembly from Mycobacterium tuberculosis. The ParB-parS participates in plasmid and chromosome segregation and condensation in predivisional bacterial cells. ParB polymerizes around the parS centromere(s) to form a higher-order assembly that serves to recruit cyto-skeletal ParA ATPases and SMC proteins for chromosome segregation. A hybrid model of the ParB-parS was built by combining and correlating computational models with experiment-derived information about size, shape, position of the symmetry axis within the shape, internal topology, DNA-protein interface, exposed surface patches, and prior knowledge. This first view of the ParB-parS leads us to propose how ParB spread on the chromosome to form a larger assembly.

  15. A combined global and local approach to elucidate spatial organization of the Mycobacterial ParB-parS partition assembly.

    Science.gov (United States)

    Chaudhuri, Barnali N; Gupta, Sayan; Urban, Volker S; Chance, Mark R; D'Mello, Rhijuta; Smith, Lauren; Lyons, Kelly; Gee, Jessica

    2011-03-22

    Combining diverse sets of data at global (size, shape) and local (residue) scales is an emerging trend for elucidating the organization and function of the cellular assemblies. We used such a strategy, combining data from X-ray and neutron scattering with H/D-contrast variation and X-ray footprinting with mass spectrometry, to elucidate the spatial organization of the ParB-parS assembly from Mycobacterium tuberculosis. The ParB-parS participates in plasmid and chromosome segregation and condensation in predivisional bacterial cells. ParB polymerizes around the parS centromere(s) to form a higher-order assembly that serves to recruit cyto-skeletal ParA ATPases and SMC proteins for chromosome segregation. A hybrid model of the ParB-parS was built by combining and correlating computational models with experiment-derived information about size, shape, position of the symmetry axis within the shape, internal topology, DNA-protein interface, exposed surface patches, and prior knowledge. This first view of the ParB-parS leads us to propose how ParB spread on the chromosome to form a larger assembly.

  16. Host response biomarker in sepsis: suPAR detection.

    Science.gov (United States)

    Giamarellos-Bourboulis, Evangelos J; Georgitsi, Marianna

    2015-01-01

    Recent studies of our group have shown that suPAR may complement APACHE II score for risk assessment in sepsis. suPAR may be measured in serum of patients by an enzyme immunosorbent assay developed by Virogates (suPARnostic™). Production of suPAR from circulating neutrophils and monocytes may be assessed after isolation of neutrophils and monocytes and ex vivo culture. This is followed by measurement of suPAR in culture supernatants.

  17. The effect of laser beam size in a zig-zag collimator on transverse cooling of a krypton atomic beam

    Indian Academy of Sciences (India)

    Vivek Singh; V B Tiwari; S Singh; S R Mishra; H S Rawat

    2014-07-01

    The effect of size of a cooling laser beam in a zig-zag atomic beam collimator on transverse cooling of a krypton atomic beam is investigated. The simulation results show that discreteness in the interaction between the cooling laser beam and atomic beam, arising due to finite size and incidence angle of the cooling laser beam, significantly reduces the value of transverse velocity capture range of the collimator. The experimental observations show the trend similar to that obtained from simulations. Our study can be particularly useful where a small zig-zag collimator is required.

  18. Controlling the self-collimation characteristics of a near-infrared two-dimensional metallic photonic crystal

    Institute of Scientific and Technical Information of China (English)

    Feng Shuai; Ren Cheng; Wang Wen-Zhong; Wang Yi-Quan

    2012-01-01

    Self-collimation characteristics of the two-dimensional square-lattice photonic crystal (PC) consisting of metal rods immersed in silicon are studied by the finite-difference time-domain method.The Drude dispersion model is adopted to describe the metal rod,and the self-collimation behaviours of the near-infrared light through the PC are studied.The frequency region and the tolerance of incident angle for the self-collimation behaviour can be controlled by changing the shape of the metal rods.

  19. Copenhagen uPAR prostate cancer (CuPCa) database

    DEFF Research Database (Denmark)

    Lippert, Solvej; Berg, Kasper D; Høyer-Hansen, Gunilla

    2016-01-01

    AIM: Urokinase plasminogen activator receptor (uPAR) plays a central role during cancer invasion by facilitating pericellular proteolysis. We initiated the prospective 'Copenhagen uPAR Prostate Cancer' study to investigate the significance of uPAR levels in prostate cancer (PCa) patients. METHODS...

  20. Phosphorylation of Mycobacterium tuberculosis ParB participates in regulating the ParABS chromosome segregation system.

    Directory of Open Access Journals (Sweden)

    Grégory Baronian

    Full Text Available Here, we present for the first time that Mycobacterium tuberculosis ParB is phosphorylated by several mycobacterial Ser/Thr protein kinases in vitro. ParB and ParA are the key components of bacterial chromosome segregation apparatus. ParB is a cytosolic conserved protein that binds specifically to centromere-like DNA parS sequences and interacts with ParA, a weak ATPase required for its proper localization. Mass spectrometry identified the presence of ten phosphate groups, thus indicating that ParB is phosphorylated on eight threonines, Thr32, Thr41, Thr53, Thr110, Thr195, and Thr254, Thr300, Thr303 as well as on two serines, Ser5 and Ser239. The phosphorylation sites were further substituted either by alanine to prevent phosphorylation or aspartate to mimic constitutive phosphorylation. Electrophoretic mobility shift assays revealed a drastic inhibition of DNA-binding by ParB phosphomimetic mutant compared to wild type. In addition, bacterial two-hybrid experiments showed a loss of ParA-ParB interaction with the phosphomimetic mutant, indicating that phosphorylation is regulating the recruitment of the partitioning complex. Moreover, fluorescence microscopy experiments performed in the surrogate Mycobacterium smegmatis ΔparB strain revealed that in contrast to wild type Mtb ParB, which formed subpolar foci similar to M. smegmatis ParB, phoshomimetic Mtb ParB was delocalized. Thus, our findings highlight a novel regulatory role of the different isoforms of ParB representing a molecular switch in localization and functioning of partitioning protein in Mycobacterium tuberculosis.

  1. Phosphorylation of Mycobacterium tuberculosis ParB participates in regulating the ParABS chromosome segregation system.

    Science.gov (United States)

    Baronian, Grégory; Ginda, Katarzyna; Berry, Laurence; Cohen-Gonsaud, Martin; Zakrzewska-Czerwińska, Jolanta; Jakimowicz, Dagmara; Molle, Virginie

    2015-01-01

    Here, we present for the first time that Mycobacterium tuberculosis ParB is phosphorylated by several mycobacterial Ser/Thr protein kinases in vitro. ParB and ParA are the key components of bacterial chromosome segregation apparatus. ParB is a cytosolic conserved protein that binds specifically to centromere-like DNA parS sequences and interacts with ParA, a weak ATPase required for its proper localization. Mass spectrometry identified the presence of ten phosphate groups, thus indicating that ParB is phosphorylated on eight threonines, Thr32, Thr41, Thr53, Thr110, Thr195, and Thr254, Thr300, Thr303 as well as on two serines, Ser5 and Ser239. The phosphorylation sites were further substituted either by alanine to prevent phosphorylation or aspartate to mimic constitutive phosphorylation. Electrophoretic mobility shift assays revealed a drastic inhibition of DNA-binding by ParB phosphomimetic mutant compared to wild type. In addition, bacterial two-hybrid experiments showed a loss of ParA-ParB interaction with the phosphomimetic mutant, indicating that phosphorylation is regulating the recruitment of the partitioning complex. Moreover, fluorescence microscopy experiments performed in the surrogate Mycobacterium smegmatis ΔparB strain revealed that in contrast to wild type Mtb ParB, which formed subpolar foci similar to M. smegmatis ParB, phoshomimetic Mtb ParB was delocalized. Thus, our findings highlight a novel regulatory role of the different isoforms of ParB representing a molecular switch in localization and functioning of partitioning protein in Mycobacterium tuberculosis.

  2. Enhanced proton beam collimation in the ultra-intense short pulse regime

    Science.gov (United States)

    Green, J. S.; Dover, N. P.; Borghesi, M.; Brenner, C. M.; Cameron, F. H.; Carroll, D. C.; Foster, P. S.; Gallegos, P.; Gregori, G.; McKenna, P.; Murphy, C. D.; Najmudin, Z.; Palmer, C. A. J.; Prasad, R.; Romagnani, L.; Quinn, K. E.; Schreiber, J.; Streeter, M. J. V.; Ter-Avetisyan, S.; Tresca, O.; Zepf, M.; Neely, D.

    2014-08-01

    The collimation of proton beams accelerated during ultra-intense laser irradiation of thin aluminum foils was measured experimentally whilst varying laser contrast. Increasing the laser contrast using a double plasma mirror system resulted in a marked decrease in proton beam divergence (20° to <10°), and the enhanced collimation persisted over a wide range of target thicknesses (50 nm-6 µm), with an increased flux towards thinner targets. Supported by numerical simulation, the larger beam divergence at low contrast is attributed to the presence of a significant plasma scale length on the target front surface. This alters the fast electron generation and injection into the target, affecting the resultant sheath distribution and dynamics at the rear target surface. This result demonstrates that careful control of the laser contrast will be important for future laser-driven ion applications in which control of beam divergence is crucial.

  3. A novel method involving Matlab coding to determine the distribution of a collimated ionizing radiation beam

    Science.gov (United States)

    Ioan, M.-R.

    2016-08-01

    In ionizing radiation related experiments, precisely knowing of the involved parameters it is a very important task. Some of these experiments are involving the use of electromagnetic ionizing radiation such are gamma rays and X rays, others make use of energetic charged or not charged small dimensions particles such are protons, electrons, neutrons and even, in other cases, larger accelerated particles such are helium or deuterium nuclei are used. In all these cases the beam used to hit an exposed target must be previously collimated and precisely characterized. In this paper, a novel method to determine the distribution of the collimated beam involving Matlab coding is proposed. The method was implemented by using of some Pyrex glass test samples placed in the beam where its distribution and dimension must be determined, followed by taking high quality pictures of them and then by digital processing the resulted images. By this method, information regarding the doses absorbed in the exposed samples volume are obtained too.

  4. Simulation of the in-flight calibration of the collimator alignment and PSF for HXMT

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The Hard X-ray Modulation Telescope(HXMT) is an X-ray astronomical satellite in 1-250 keV,consisting of three collimated instruments.We present the in-flight calibration approach of the collimator alignment and Point Spread Function(PSF) for HXMT,using both the direct fitting method and the imaging method.According to observational simulations of the Crab Nebula,we find that these two methods produce almost the same calibration accuracy of the alignment,and with a one-day scanning observation,the alignment can be calibrated to better than 0.45’ and 0.1’ along the wide and narrow directions of the Field of View(FOV) for a detector module,which corresponds to a localization accuracy of better than 0.1’ and meets the scientific requirement.

  5. Solar concentrator with integrated tracking and light delivery system with collimation

    Energy Technology Data Exchange (ETDEWEB)

    Maxey, Lonnie Curt

    2015-06-09

    A solar light distribution system includes a solar light concentrator that is affixed externally to a light transfer tube. Solar light waves are processed by the concentrator into a collimated beam of light, which is then transferred through a light receiving port and into the light transfer tube. A reflector directs the collimated beam of light through the tube to a light distribution port. The interior surface of the light transfer tube is highly reflective so that the light transfers through the tube with minimal losses. An interchangeable luminaire is attached to the light distribution port and distributes light inside of a structure. A sun tracking device rotates the concentrator and the light transfer tube to optimize the receiving of solar light by the concentrator throughout the day. The system provides interior lighting, uses only renewable energy sources, and releases no carbon dioxide emissions into the atmosphere.

  6. Improvement in QEPAS system based on miniaturized collimator and flat mirror

    Science.gov (United States)

    Wang, Fupeng; Chang, Jun; Wang, Qiang; Liu, Yuanyuan; Liu, Zhaojun; Qin, Zengguang; Zhu, Cunguang

    2016-12-01

    An improved QEPAS (quartz enhanced photo-acoustic spectroscopy) system based on an optical structure comprising miniaturized collimator and flat mirror is proposed. The beam diameter of the miniaturized collimator is designed less than 0.2 mm in a 20 mm working distance. Experiments are set up to compare the beam quality and photo-acoustic performance of three optical structures (this one, fiber lead mode and conventional focus mode). By virtue of the micro-resonator tubes and flat mirror, the new proposed structure achieves a SNR of 260 for a 3000 ppmv water vapor sample, which is much better than 183 for the fiber lead mode and 193 for the conventional focus mode respectively. This test is achieved by using the same self-designed circuit with the same parameters. The proposed optical structure is simpler and easier for optical alignment, and provides an alternative way in improving and simplifying the QEPAS system for industrial applications.

  7. Mode-mismatched confocal thermal-lens microscope with collimated probe beam

    Energy Technology Data Exchange (ETDEWEB)

    Cabrera, Humberto, E-mail: hcabrera@ictp.it [SPIE-ICTP Anchor Research Laboratory, International Centre for Theoretical Physics (ICTP), Strada Costiera 11, Trieste (Italy); Centro Multidisciplinartio de Ciencias, Instituto Venezolano de Investigaciones Científicas (IVIC), Mérida 5101 (Venezuela, Bolivarian Republic of); Korte, Dorota; Franko, Mladen [Laboratory for Environmental Research, University of Nova Gorica, Vipavska 13, 5000 Nova Gorica (Slovenia)

    2015-05-15

    We report a thermal lens microscope (TLM) based on an optimized mode-mismatched configuration. It takes advantage of the coaxial counter propagating tightly focused excitation and collimated probe beams, instead of both focused at the sample, as it is in currently known TLM setups. A simple mathematical model that takes into account the main features of the instrument is presented. The confocal detection scheme and the introduction of highly collimated probe beam allow enhancing the versatility, limit of detection (LOD), and sensitivity of the instrument. The theory is experimentally verified measuring ethanol’s absorption coefficient at 532.8 nm. Additionally, the presented technique is applied for detection of ultra-trace amounts of Cr(III) in liquid solution. The achieved LOD is 1.3 ppb, which represents 20-fold enhancement compared to transmission mode spectrometric techniques and a 7.5-fold improvement compared to previously reported methods for Cr(III) based on thermal lens effect.

  8. A Collimation Scheme for Ions Changing Charge State in the LEIR Ring

    CERN Document Server

    Pasternak, Jaroslaw; Carli, Christian; Chanel, Michel; Mahner, Edgar

    2005-01-01

    Avalanche-like pressure rise and an associated decrease of the beam life-time, caused by (i) beam loss due to charge exchange interactions with rest gas molecules and (ii) electron capture from the electron beam of the electron cooler and (iii) ion impact induced outgassing, is a potential limitation for heavy ion accelerators. The vacuum system of the LEIR ring as to be upgraded to reach the dynamical vacuum pressure in the low 10-12 Torr range necessary to reach design performance. A collimation system to intercept lost ions by absorber blocks made of low beam-induced outgassing material will be installed. This paper reviews the collimation scheme and simulations of beam loss patterns around the ring.

  9. The New Transfer Line Collimation System for the LHC High Luminosity Era

    Energy Technology Data Exchange (ETDEWEB)

    Kain, Verena [CERN; Bracco, Chiara [CERN; Goddard, Brennan [CERN; Maciariello, Fausto [CERN; Meddahi, Malika [CERN; Mereghetti, Alessio [CERN; Steele, Genevieve [CERN; Velotti, Francesco [CERN; Gianfelice-Wendt, Eliana [Fermilab

    2014-07-01

    A set of passive absorbers is located at the end of each of the 3 km long injection lines to protect the LHC in case of failures during the extraction process from the LHC’s last pre-injector or the beam transfer itself. In case of an erroneous extraction, the absorbers have to attenuate the beam to a safe level and be robust enough themselves to survive the impact. These requirements are difficult to fulfil with the very bright and intense beams produced by the LHC injectors for the high luminosity era. This paper revisits the requirements for the SPS-to-LHC transfer line collimation system and the adapted strategy to fulfill these for the LHC high luminosity operation. A possible solution for the new transfer line collimation system is presented.

  10. Operational Experience with a LHC Collimator Prototype in the CERN SPS

    CERN Document Server

    Redaelli, S; Assmann, R; Dehning, B; Bracco, C; Jonker, M; Masi, A; Losito, R; Sapinski, M; Weiler, T; Zamantzas, C

    2010-01-01

    A full-scale prototype of the Large Hadron Collider (LHC) collimator was installed in 2004 in the CERN Super Proton Synchrotron (SPS) and has been extensively used for beam tests, for control tests and also LHC simulation benchmarking during four years of operation. This operational experience has been extremely valuable in view of the final LHC implementation as well as for estimating the LHC operational scenarios, most notably to establish procedures for the beam-based alignment of the collimators with respect to the circulating beam. These studies were made possible by installing in the SPS a first prototype of the LHC beam loss monitoring system. The operational experience gained at the SPS and the lessons learnt for the LHC operation are presented.

  11. OPERATIONAL EXPERIENCE WITH A LHC COLLIMATOR PROTOTYPE IN THE CERN SPS

    CERN Document Server

    Redaelli, S; Assmann, R; Dehning, B; Bracco, C; Jonker, M; Masi, A; Losito, R; Sapinski, M; Weiler, T; Zamantzas, C

    2009-01-01

    A full-scale prototype of the Large Hadron Collider (LHC) collimator was installed in 2004 in the CERN Super Proton Synchrotron (SPS) and has been extensively used for beam tests, for control tests and also LHC simulation benchmarking during four years of operation. This operational experience has been extremely valuable in view of the final LHC implementation as well as for estimating the LHC operational scenarios, most notably to establish procedures for the beam-based alignment of the collimators with respect to the circulating beam. These studies were made possible by installing in the SPS a first prototype of the LHC beam loss monitoring system. The operational experience gained at the SPS and the lessons learnt for the LHC operation are presented.

  12. Magnetic collimation of relativistic jets: the role of the black hole spin

    Science.gov (United States)

    Globus, N.; Sauty, C.; Cayatte, V.

    2011-06-01

    An ideal engine for producing ultrarelativistic jets is a rapidly rotating black hole threaded by a magnetic field. Following the 3+1 decomposion of spacetime of Thorne et al. (1986), we use a local inertial frame of reference attached to an observer comoving with the frame-dragging of the Kerr black hole (ZAMO) to write the GRMHD equations. Assuming θ-self similarity, analytical solutions for jets can be found for which the streamline shape is calculated exactly. Calculating the total energy variation between a non polar streamline and the polar axis, we have extended to the Kerr metric the simple criterion for the magnetic collimation of jets developed by Sauty et al. (1999). We show that the black hole rotation induces a more efficient magnetic collimation of the jet.

  13. Formation and collimation of relativistic MHD jets - simulations and radio maps

    CERN Document Server

    Fendt, Christian; Sheikhnezami, Somayeh

    2013-01-01

    We present results of magnetohydrodynamic (MHD) simulations of jet formation and propagation, discussing a variety of astrophysical setups. In the first approach we consider simulations of relativistic MHD jet formation, considering jets launched from the surface of a Keplerian disk, demonstrating numerically - for the first time - the self-collimating ability of relativistic MHD jets. We obtain Lorentz factors up to about 10 while acquiring a high degree of collimation of about 1 degree. We then present synchrotron maps calculated from the intrinsic jet structure derived from the MHD jet formation simulation. We finally present (non-relativistic) MHD simulations of jet lauching, treating the transition between accretion and ejection. These setups include a physical magnetic diffusivity which is essential for loading the accretion material onto the outflow. We find relatively high mass fluxes in the outflow, of the order of 20-40 % of the accretion rate.

  14. Leaf trajectory calculation for dynamic multileaf collimation to realize optimized fluence profiles

    Energy Technology Data Exchange (ETDEWEB)

    Dirkx, M.L.P.; Heijmen, B.J.M.; Santvoort, J.P.C. van [University Hospital Rotterdam/Daniel den Hoed Cancer Center, Groene Hilledijk 301, 3075 EA Rotterdam (Netherlands)

    1998-05-01

    An algorithm for the calculation of the required leaf trajectories to generate optimized intensity modulated beam profiles by means of dynamic multileaf collimation is presented. This algorithm iteratively accounts for leaf transmission and collimator scatter and fully avoids tongue-and-groove underdosage effects. Tests on a large number of intensity modulated fields show that only a limited number of iterations, generally less than 10, are necessary to minimize the differences between optimized and realized fluence profiles. To assess the accuracy of the algorithm in combination with the dose calculation algorithm of the Cadplan 3D treatment planning system, predicted absolute dose distributions for optimized fluence profiles were compared with dose distributions measured on the MM50 Racetrack Microtron and resulting from the calculated leaf trajectories. Both theoretical and clinical cases yield an agreement within 2%, or within 2 mm in regions with a high dose gradient, showing that the accuracy is adequate for clinical application. (author)

  15. The treatment planning of segmental, conformal stereotactic radiosurgery utilizing a standard multileaf collimator.

    Science.gov (United States)

    Archer, P G; Balter, J M; Ross, D A; Hayman, J A; Sandler, H M

    1999-01-01

    Over a period of approximately 3 years, our institution has implemented and refined a system of Stereotactic Radiosurgery (SRS) which utilizes the standard multi leaf collimator (MLC) of the Scanditronix MM50 Racetrack Microtron and treats in an arrangement of segmental "pseudo-arcs." This system employs a commercial BRW based stereotactic frame which is mounted to the treatment table. With the exception of the table-mounted frame hardware there have been no modifications to the treatment machine to accommodate these treatments. By use of standard evaluation parameters (e.g., treatment time, planning time, dose conformance and dose heterogeneity ratios) this system compares quite favorably with reported data from institutions treating SRS with either a GammaKnife or a standard linear accelerator with tertiary collimators.

  16. Leaf trajectory calculation for dynamic multileaf collimation to realize optimized fluence profiles

    Science.gov (United States)

    Dirkx, M. L. P.; Heijmen, B. J. M.; van Santvoort, J. P. C.

    1998-05-01

    An algorithm for the calculation of the required leaf trajectories to generate optimized intensity modulated beam profiles by means of dynamic multileaf collimation is presented. This algorithm iteratively accounts for leaf transmission and collimator scatter and fully avoids tongue-and-groove underdosage effects. Tests on a large number of intensity modulated fields show that only a limited number of iterations, generally less than 10, are necessary to minimize the differences between optimized and realized fluence profiles. To assess the accuracy of the algorithm in combination with the dose calculation algorithm of the Cadplan 3D treatment planning system, predicted absolute dose distributions for optimized fluence profiles were compared with dose distributions measured on the MM50 Racetrack Microtron and resulting from the calculated leaf trajectories. Both theoretical and clinical cases yield an agreement within 2%, or within 2 mm in regions with a high dose gradient, showing that the accuracy is adequate for clinical application.

  17. Freeform lens collimating spectrum-folded Hadamard transform near-infrared spectrometer

    Science.gov (United States)

    Wang, Xiaoduo; Liu, Hua; Juschkin, Larissa; Li, Yunpeng; Xu, Jialin; Quan, Xiangqian; Lu, Zhenwu

    2016-12-01

    A novel Hadamard transform spectrometer collimated by a freeform lens has been designed, which doubles the working spectral range while the spectral resolution is maintained. The freeform lens is designed to redistribute the broadband spectra of the source from 800 nm to 2400 nm into two collimated beams with different wavelengths and different tilting angles, to achieve the folding of spectra on the digital micro-mirror devices (DMD). It is constructed by solving two partial differential equations. The grating diffraction efficiency of the two split beams are more uniform and higher compared with the traditional method. The simulation results show that the bandwidth of the spectrometer is doubled and the spectral resolution is better than 10 nm. The optical system becomes more compact, and the energy efficiency is improved by 11.98% by folding the spectra with one freeform lens and one grating.

  18. Research and development of novel advanced materials for next-generation collimators

    CERN Document Server

    Bertarelli, A; Carra, F; Dallocchio, A; Gil Costa, M; Mariani, N

    2011-01-01

    The study of innovative collimators is essential to handle the high energy particle beams required to explore unknown territory in basic research. This calls for the development of novel advanced materials, as no existing metal-based or carbon-based material possesses the combination of physical, thermal, electrical and mechanical properties, imposed by collimator extreme working conditions. A new family of materials, with promising features, has been identified: metal-diamond composites. These materials are to combine the outstanding thermal and physical properties of diamond with the electrical and mechanical properties of metals. The best candidates are Copper-Diamond (Cu-CD) and Molybdenum-Diamond (Mo-CD). In particular, Mo-CD may provide interesting properties as to mechanical strength, melting temperature, thermal shock resistance and, thanks to its balanced material density, energy absorption. The research program carried out on these materials at CERN and collaborating partners is presented, mainly fo...

  19. X-ray collimation by the parabolic cylinder mirror in SPring-8/BL29XUL.

    Science.gov (United States)

    Takei, Dai; Kohmura, Yoshiki; Senba, Yasunori; Ohashi, Haruhiko; Tamasaku, Kenji; Ishikawa, Tetsuya

    2016-01-01

    A combination of plane and threefold-shape X-ray mirrors was installed in SPring-8 BL29XUL. The second mirror has parabolic cylinder surfaces that collimate X-rays in the vertical direction. A performance test was conducted, yielding highly collimated 8 keV photon beams with an effective angular divergence of 0.4 µrad, below only 5% of that of the original beams. The double-mirror system preserved 70% of the total incident flux and nearly tripled the flux density at 988 m from the light source. The values of the observations were almost similar to those of our ray-tracing simulation. Based on the results a discussion of future prospects of the mirror system is included.

  20. Jets from Young Stars: The Need for MHD Collimation and Acceleration Processes

    Science.gov (United States)

    Cabrit, Sylvie

    This lecture revisits in the light of recent data the main lines of evidence indicating that MHD processes play a crucial role in jets from young stars. Measurements of jet collimation and jet ejection-accretion efficiencies are reviewed and compared at various evolutionary stages (from protostars to optically revealed objects). It is then shown that they cannot satisfactorily be accounted for by purely hydrodynamical processes. MHD magneto-centrifugal ejection (combining magnetic self-collimation and magnetic acceleration) appears as the most effective mechanism able to reproduce the observed jet properties at all evolutionary phases. The jets would then be intimately linked to angular momentum extraction from the accreting disk and/or star.

  1. Construction and bench testing of a prototype rotatable collimator for the LHC

    CERN Document Server

    Markiewicz, T; Keller, L; Aberle, O; Bertarelli, A; Gradassi, P; Marsili, A; Redaelli, S; Rossi, A; Salvachua, B; Valentino, G

    2014-01-01

    A second generation prototype rotatable collimator has been fabricated at SLAC and delivered to CERN for further vacuum, metrology, function and impedance tests. The design features two cylindrical Glidcop jaws designed to each absorb 12 kW of beam in steady state and up to 60 kW in transitory beam loss with no damage and minimal thermal distortion [1]. The design is motivated by the use of a radiation resistant high Z low impedance readily available material. A vacuum rotation mechanism using the standard LHC collimation jaw positioning motor system allows each jaw to be rotated to present a new 2 cm high surface to the beam if the jaw surface were to be damaged by multiple full intensity beam bunch impacts in a asynchronous beam abort. Design modifications to improve on the first generation prototype, pre-delivery functional tests performed at SLAC and post-delivery test results at CERN are presented.

  2. Modeling of a slanted-hole collimator in a compact endo-cavity gamma camera.

    Science.gov (United States)

    Kamuda, Mark; Cui, Yonggang; Lall, Terry; Ionson, Jim; Camarda, Giuseppe S.; Hossain, Anwar; Yang, Ge; Roy, Utpal N.; James, Ralph B.

    2013-09-01

    Having the ability to take an accurate 3D image of a tumor greatly helps doctors diagnose it and then create a treatment plan for a patient. One way to accomplish molecular imaging is to inject a radioactive tracer into a patient and then measure the gamma rays emitted from regions with high-uptake of the tracer, viz., the cancerous tissues. In large, expensive PET- or SPECT-imaging systems, the 3D imaging easily is accomplished by rotating the gamma-ray detectors and then employing software to reconstruct the 3D images from the multiple 2D projections at different angles of view. However, this method is impractical in a very compact imaging system due to anatomical considerations, e.g., the transrectal gamma camera under development at Brookhaven National Laboratory (BNL) for detection of intra-prostatic tumors. The camera uses pixilated cadmium zinc telluride (CdZnTe or CZT) detectors with matched parallel-hole collimator. Our research investigated the possibility of using a collimator with slanted holes to create 3D pictures of a radioactive source. The underlying concept is to take 2D projection images at different angles of view by adjusting the slant angle of the collimator, then using the 2D projection images to reconstruct the 3D image. To do this, we first simulated the response of a pixilated CZT detector to radiation sources placed in the field of view of the camera. Then, we formulated an algorithm to use the simulation results as prior knowledge and estimate the distribution of a shaped source from its 2D projection images. From the results of the simulation, we measured the spatial resolution of the camera as ~7-mm at a depth of 13.85-mm when using a detector with 2.46-mm pixel pitch and a collimator with 60° slant angle.

  3. Impact of large x-ray beam collimation on image quality

    Science.gov (United States)

    Racine, Damien; Ba, Alexandre; Ott, Julien G.; Bochud, François O.; Verdun, Francis R.

    2016-03-01

    Large X-ray beam collimation in computed tomography (CT) opens the way to new image acquisition techniques and improves patient management for several clinical indications. The systems that offer large X-ray beam collimation enable, in particular, a whole region of interest to be investigated with an excellent temporal resolution. However, one of the potential drawbacks of this option might be a noticeable difference in image quality along the z-axis when compared with the standard helical acquisition mode using more restricted X-ray beam collimations. The aim of this project is to investigate the impact of the use of large X-ray beam collimation and new iterative reconstruction on noise properties, spatial resolution and low contrast detectability (LCD). An anthropomorphic phantom and a custom made phantom were scanned on a GE Revolution CT. The images were reconstructed respectively with ASIR-V at 0% and 50%. Noise power spectra, to evaluate the noise properties, and Target Transfer Functions, to evaluate the spatial resolution, were computed. Then, a Channelized Hotelling Observer with Gabor and Dense Difference of Gaussian channels was used to evaluate the LCD using the Percentage correct as a figure of merit. Noticeable differences of 3D noise power spectra and MTF have been recorded; however no significant difference appeared when dealing with the LCD criteria. As expected the use of iterative reconstruction, for a given CTDIvol level, allowed a significant gain in LCD in comparison to ASIR-V 0%. In addition, the outcomes of the NPS and TTF metrics led to results that would contradict the outcomes of CHO model observers if used for a NPWE model observer (Non- Prewhitening With Eye filter). The unit investigated provides major advantages for cardiac diagnosis without impairing the image quality level of standard chest or abdominal acquisitions.

  4. Wavefront sensing and adaptive control in phased array of fiber collimators

    Science.gov (United States)

    Lachinova, Svetlana L.; Vorontsov, Mikhail A.

    2011-03-01

    A new wavefront control approach for mitigation of atmospheric turbulence-induced wavefront phase aberrations in coherent fiber-array-based laser beam projection systems is introduced and analyzed. This approach is based on integration of wavefront sensing capabilities directly into the fiber-array transmitter aperture. In the coherent fiber array considered, we assume that each fiber collimator (subaperture) of the array is capable of precompensation of local (onsubaperture) wavefront phase tip and tilt aberrations using controllable rapid displacement of the tip of the delivery fiber at the collimating lens focal plane. In the technique proposed, this tip and tilt phase aberration control is based on maximization of the optical power received through the same fiber collimator using the stochastic parallel gradient descent (SPGD) technique. The coordinates of the fiber tip after the local tip and tilt aberrations are mitigated correspond to the coordinates of the focal-spot centroid of the optical wave backscattered off the target. Similar to a conventional Shack-Hartmann wavefront sensor, phase function over the entire fiber-array aperture can then be retrieved using the coordinates obtained. The piston phases that are required for coherent combining (phase locking) of the outgoing beams at the target plane can be further calculated from the reconstructed wavefront phase. Results of analysis and numerical simulations are presented. Performance of adaptive precompensation of phase aberrations in this laser beam projection system type is compared for various system configurations characterized by the number of fiber collimators and atmospheric turbulence conditions. The wavefront control concept presented can be effectively applied for long-range laser beam projection scenarios for which the time delay related with the double-pass laser beam propagation to the target and back is compared or even exceeds the characteristic time of the atmospheric turbulence change

  5. Calculations of safe collimator settings and β^{*} at the CERN Large Hadron Collider

    Directory of Open Access Journals (Sweden)

    R. Bruce

    2015-06-01

    Full Text Available The first run of the Large Hadron Collider (LHC at CERN was very successful and resulted in important physics discoveries. One way of increasing the luminosity in a collider, which gave a very significant contribution to the LHC performance in the first run and can be used even if the beam intensity cannot be increased, is to decrease the transverse beam size at the interaction points by reducing the optical function β^{*}. However, when doing so, the beam becomes larger in the final focusing system, which could expose its aperture to beam losses. For the LHC, which is designed to store beams with a total energy of 362 MJ, this is critical, since the loss of even a small fraction of the beam could cause a magnet quench or even damage. Therefore, the machine aperture has to be protected by the collimation system. The settings of the collimators constrain the maximum beam size that can be tolerated and therefore impose a lower limit on β^{*}. In this paper, we present calculations to determine safe collimator settings and the resulting limit on β^{*}, based on available aperture and operational stability of the machine. Our model was used to determine the LHC configurations in 2011 and 2012 and it was found that β^{*} could be decreased significantly compared to the conservative model used in 2010. The gain in luminosity resulting from the decreased margins between collimators was more than a factor 2, and a further contribution from the use of realistic aperture estimates based on measurements was almost as large. This has played an essential role in the rapid and successful accumulation of experimental data in the LHC.

  6. Advanced Simulator for Pilot Training: Effects of Collimation on Accommodation and Vergence

    Science.gov (United States)

    1985-09-01

    Training ( ASPT ), used for training R&D by AFHRL, employs seven collimated display windows to provide a virtual image covering a 300 degree horizontal by...with relatively low luminance and contrast. One potential solution to the limited lumirance and contrast of the ASPT display system is simply to remove...while viewing ASPT imagery through a ILIOS. Measurements were made while the observer viewed a dynamic computer-generated scene representing the pilot’s

  7. The design, construction and performance of a variable collimator for epithermal neutron capture therapy beams

    Science.gov (United States)

    Riley, K. J.; Binns, P. J.; Ali, S. J.; Harling, O. K.

    2004-05-01

    A patient collimator for the fission converter based epithermal neutron beam (FCB) at the Massachusetts Institute of Technology Research Reactor (MITR-II) was built for clinical trials of boron neutron capture therapy (BNCT). A design was optimized by Monte Carlo simulations of the entire beam line and incorporates a modular construction for easy modifications in the future. The device was formed in-house by casting a mixture of lead spheres (7.6 mm diameter) in epoxy resin loaded with either 140 mg cm-3 of boron carbide or 210 mg cm-3 of lithium fluoride (95% enriched in 6Li). The cone shaped collimator allows easy field placement anywhere on the patient and is equipped with a laser indicator of central axis, beam's eye view optics and circular apertures of 80, 100, 120 and 160 mm diameter. Beam profiles and the collateral dose in a half-body phantom were measured for the 160 mm field using fission counters, activation foils as well as tissue equivalent (A-150) and graphite walled ionization chambers. Leakage radiation through the collimator contributes less than 10% to the total collateral dose up to 0.15 m beyond the edge of the aperture and becomes relatively more prominent with lateral displacement. The measured whole body dose equivalent of 24 ± 2 mSv per Gy of therapeutic dose is comparable to doses received during conventional therapy and is due principally (60-80%) to thermal neutron capture reactions with boron. These findings, together with the dose distributions for the primary beam, demonstrate the suitability of this patient collimator for BNCT.

  8. The design, construction and performance of a variable collimator for epithermal neutron capture therapy beams.

    Science.gov (United States)

    Riley, K J; Binns, P J; Ali, S J; Harling, O K

    2004-05-21

    A patient collimator for the fission converter based epithermal neutron beam (FCB) at the Massachusetts Institute of Technology Research Reactor (MITR-II) was built for clinical trials of boron neutron capture therapy (BNCT). A design was optimized by Monte Carlo simulations of the entire beam line and incorporates a modular construction for easy modifications in the future. The device was formed in-house by casting a mixture of lead spheres (7.6 mm diameter) in epoxy resin loaded with either 140 mg cm(-3) of boron carbide or 210 mg cm(-3) of lithium fluoride (95% enriched in 6Li). The cone shaped collimator allows easy field placement anywhere on the patient and is equipped with a laser indicator of central axis, beam's eye view optics and circular apertures of 80, 100, 120 and 160 mm diameter. Beam profiles and the collateral dose in a half-body phantom were measured for the 160 mm field using fission counters, activation foils as well as tissue equivalent (A-150) and graphite walled ionization chambers. Leakage radiation through the collimator contributes less than 10% to the total collateral dose up to 0.15 m beyond the edge of the aperture and becomes relatively more prominent with lateral displacement. The measured whole body dose equivalent of 24 +/- 2 mSv per Gy of therapeutic dose is comparable to doses received during conventional therapy and is due principally (60-80%) to thermal neutron capture reactions with boron. These findings, together with the dose distributions for the primary beam, demonstrate the suitability of this patient collimator for BNCT.

  9. Unsolved Problems of AGN Jets in Sub Parsec Scale: Acceleration, Collimation, and Stability Properties

    Science.gov (United States)

    Nakamura, M.; Meier, D. L.

    2009-08-01

    What can we expect in the VSOP-2 mission to reveal the sub parsec scale structures of AGN jets? Based on the MHD process of jet formation and evolution, we discuss about unsolved problems of sub parsec AGN jets in terms of the acceleration, the collimation, and the stability properties. Several key features will be proved by the VSOP-2 observations; they play an important role in determining how the MHD process will work in the jet dynamics.

  10. Three-dimensional collimated self-accelerating beam through acoustic metascreen

    OpenAIRE

    Yong Li; M. Badreddine Assouar

    2015-01-01

    We report the generation of three-dimensional acoustic collimated self-accelerating beam in non-paraxial region with sourceless metascreen. Acoustic metascreen with deep subwavelength spatial resolution, composed of hybrid structures combining four Helmholtz resonators and a straight pipe, transmitting sound efficiently and shifting fully the local phase is evidenced. With an extra phase profile provided by the metascreen, the transmitted sound can be tuned to propagate along arbitrary causti...

  11. Matching of electron and photon beams with a multi-leaf collimator.

    Science.gov (United States)

    Karlsson, M; Zackrisson, B

    1993-12-01

    Multi-leaf collimators (MLCs) are offered as an accessory to many accelerators for radiation therapy. However, beam edges generated with these collimators are not as smooth as can be achieved with individually made blocks. The clinical drawbacks and benefits of this ripple were evaluated both for single field treatments and for combined adjacent fields of different beam qualities. In this investigation the MLC-collimated beams of the MM50 racetrack microtron were studied. The distance between the field edge and the 90% isodose was measured at the reference depth for four beam qualities (20 MV photons and 10, 20 and 50 MeV electrons). This distance was found to vary from approximately 6 mm for straight beam edges (i.e., all collimator leaves aligned) to approximately 2 mm from the tip of the leaves for a saw-tooth shaped beam edge. The over- and under-dosage in the joint between combined adjacent fields was found to be typically +/- 10% in small volumes. Improved clinical techniques using adjacent photon and electron fields with the same isocentre and source position (without moving the gantry) have been developed. For treatments of the breast, including the mammary chain, a uniform dose distribution was created with special attention given to the irradiation of the heart and lung outside the target volume. A method for head and neck treatments was optimised to give uniform dose distribution in the joint between the photon and electron fields and a method of treating the mediastinum, including the chest wall in front of the left lung, was analysed with respect to dose uniformity in the tumour and shielding of the lung.

  12. Shaping of light beams with photonic crystals : spatial filtering, beam collimation and focusing

    OpenAIRE

    2014-01-01

    The research developed in the framework of this PhD thesis is a theoretical, numerical and experimental study of light beam shaping (spatial filtering, beam collimation and focusing) in the visible frequency range using photonic crystal structures. Photonic crystals (PhCs) are materials with periodic, spatially modulated refractive index on the wavelength scale. They are primarily known for their chromatic dispersion properties. However, they can also modify the spatial dispersion, which allo...

  13. COLLIMATION AND SCATTERING OF THE ACTIVE GALACTIC NUCLEUS EMISSION IN THE SOMBRERO GALAXY

    Energy Technology Data Exchange (ETDEWEB)

    Menezes, R. B.; Steiner, J. E.; Ricci, T. V., E-mail: robertobm@astro.iag.usp.br [Instituto de Astronomia Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Cidade Universitaria, Sao Paulo, SP CEP 05508-090 (Brazil)

    2013-03-10

    We present an analysis of a data cube of the central region of M104, the Sombrero galaxy, obtained with the GMOS-IFU of the Gemini-South telescope, and report the discovery of collimation and scattering of the active galactic nucleus (AGN) emission in the circumnuclear region of this galaxy. Analysis with PCA Tomography and spectral synthesis revealed the existence of collimation and scattering of the AGN featureless continuum and also of a broad component of the H{alpha} emission line. The collimation and scattering of this broad H{alpha} component was also revealed by fitting the [N II] {lambda}{lambda}6548, 6583 and H{alpha} emission lines as a sum of Gaussian functions. The spectral synthesis, together with a V-I image obtained with the Hubble Space Telescope, showed the existence of circumnuclear dust, which may cause the light scattering. We also identify a dusty feature that may be interpreted as a torus/disk structure. The existence of two opposite regions with featureless continuum (P.A. = -18 Degree-Sign {+-} 13 Degree-Sign and P.A. = 162 Degree-Sign {+-} 13 Degree-Sign ) along a direction perpendicular to the torus/disk (P.A. = 72 Degree-Sign {+-} 14 Degree-Sign ) suggests that this structure is approximately edge-on and collimates the AGN emission. The edge-on torus/disk also hides the broad-line region. The proposed scenario is compatible with the unified model and explains why only a weak broad component of the H{alpha} emission line is visible and also why many previous studies detected no broad H{alpha}. The technique used here proved to be an efficient method not only for detecting scattered light, but also for testing the unified model in low-luminosity AGNs.

  14. A study on the performance evaluation of small gamma camera collimators using detective quantun efficiency

    Energy Technology Data Exchange (ETDEWEB)

    Jeon, Ho Sang

    2008-02-15

    The anger-type gamma camera and novel marker compound using Tc-99m were firstly introduced in 1963. The gamma camera systems have being improved and applied to various fields, for example, medical, industrial, and environmental fields. Gamma camera is mainly composed of collimator, detector, and signal processor. And the radiative source is namely the imaging object. The collimator is essential component of gamma camera system because the imaging performance of system is mainly dependent on the collimator. The performance evaluation of collimators can be done by using evaluating factors. In this study, the novel factors for gamma camera evaluation are suggested. The established evaluating factors by NEMA are FWHM, sensitivity, and uniformity. They have some limitations in spite of their usefulness. Firstly, performance evaluation by those factors give insensitive and indirect results only. Secondly, the evaluation of noise property is ambiguous. Thirdly, there is no synthetic evaluation of system performance. Simulation with Monte Carlo code and experiment with a small camera camera were simultaenuously performed to verify novel evaluating factors. For the evaluation of spatial resolution, MTF was applied instead of FWHM. The MTF values presents excellent linear relationship with FWHM values. The NNPS was applied instead of uniformity and sensitivity for the evaluation of noise fluctuation. The NNPS values also presents linear relationship with sensitivity and unifomity. Moreover, these novel factors give quantities as the function of spatial frequencies. Finally, the DQE values were given by calculations with MTF, NNPS, and input SNR. DQE effectively presents the synthetic evaluation of gamma camera performance. It is the conclusion that MTF, NNPS, and DQE can be novel evaluating factors for gamma camera systems and the new factor for synthetic evaluation is derived.

  15. Radiative transfer in participating media with collimated short-pulse Gaussian irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Okutucu, Tuba; Yener, Yaman [Mechanical and Industrial Engineering Department, Northeastern University, Boston, MA 02115 (United States)

    2006-05-07

    Radiative transfer in a one-dimensional absorbing and isotropically scattering plane-parallel grey medium with a collimated short-pulse Gaussian irradiation on one of its boundaries is studied. The medium is non-emitting and the boundaries are non-reflecting and non-refracting. The Galerkin method is extended for the solution of the transient radiative transfer problem. The transient transmittance and reflectance of the medium are evaluated for various optical thicknesses, scattering albedos and pulse durations.

  16. Study of Collimated Neutron Flux Monitors for MAST and MAST Upgrade

    OpenAIRE

    Sangaroon, Siriyaporn

    2014-01-01

    Measurements of the neutron emission, resulting from nuclear fusion reactions between the hydrogen isotopes deuterium and tritium, can provide a wealth of information on the confinement properties of fusion plasmas and how these are affected by Magneto-Hydro-Dynamic (MHD) instabilities. This thesis describes work aimed to develop neutron measurement techniques for nuclear fusion plasma experiments, specifically regarding the performance and design of collimated neutron flux monitors (neutron ...

  17. LHC physics debris collimation studies and their impact on AFP detectors acceptance

    CERN Document Server

    Roncarolo, F; Potter, K; Bussey, P; Bracco, C

    2011-01-01

    The ATLAS Forward Proton (AFP) group is proposing to upgrade the forward region of ATLAS by installing forward proton detectors at 220 m and 420 m from the interaction point on both sides of the LHC ATLAS experiment. For this purpose, at both the 420 m and 220 m locations, it is proposed to install movable beam pipes which will host silicon tracking and fast timing detectors (i.e. four independent detector stations). The experimental acceptance at 220 m is dependent upon the setting of two collimators designed to protect the LHC straight section and dispersion suppressor around ATLAS (and CMS) from the physics debris generated at the two high luminosity experiments. This note presents the result of tracking studies showing that the installation of a new collimator in front of the Q6 magnet (or the displacement at this of location of the second of the already existing collimators) would ensure an improved protection of the LHC machine while allowing the AFP experiment at 220m.

  18. Investigation of optimal acquisition time of myocardial perfusion scintigraphy using cardiac focusing-collimator

    Science.gov (United States)

    Niwa, Arisa; Abe, Shinji; Fujita, Naotoshi; Kono, Hidetaka; Odagawa, Tetsuro; Fujita, Yusuke; Tsuchiya, Saki; Kato, Katsuhiko

    2015-03-01

    Recently myocardial perfusion SPECT imaging acquired using the cardiac focusing-collimator (CF) has been developed in the field of nuclear cardiology. Previously we have investigated the basic characteristics of CF using physical phantoms. This study was aimed at determining the acquisition time for CF that enables to acquire the SPECT images equivalent to those acquired by the conventional method in 201TlCl myocardial perfusion SPECT. In this study, Siemens Symbia T6 was used by setting the torso phantom equipped with the cardiac, pulmonary, and hepatic components. 201TlCl solution were filled in the left ventricular (LV) myocardium and liver. Each of CF, the low energy high resolution collimator (LEHR), and the low medium energy general purpose collimator (LMEGP) was set on the SPECT equipment. Data acquisitions were made by regarding the center of the phantom as the center of the heart in CF at various acquisition times. Acquired data were reconstructed, and the polar maps were created from the reconstructed images. Coefficient of variation (CV) was calculated as the mean counts determined on the polar maps with their standard deviations. When CF was used, CV was lower at longer acquisition times. CV calculated from the polar maps acquired using CF at 2.83 min of acquisition time was equivalent to CV calculated from those acquired using LEHR in a 180°acquisition range at 20 min of acquisition time.

  19. Aspheric surface lens for LED collimating illumination with low Fresnel loss

    Science.gov (United States)

    Chen, Xindu; Lin, Jiaping; Liu, Zhanji; Wu, Peixuan; Wang, Han

    2016-12-01

    An aspheric surface lens is presented to realize collimating illumination with low Fresnel loss based on Fresnel equations and Snell's law. The smooth 2D contour of refractive optical surface is constructed from a set of cubic Bézier segments, whose control points are computed by deCasteljau algorithm. Simulation results show that the optical efficiency of 90.82% is achieved under a divergence angle of ±2.87° for an extended light-emitting diode (LED) source with chip size of 1 mm × 1 mm and the Fresnel loss is only 8.76%, whose optical efficiency has improved 14.3% than traditional collimating lens. By employing this proposed surface construction method, the largest divergence angle of collimating lens for point source is only 0.26° with 15 feature points on each refractive surface, while more than 2° for the traditional method. Therefore, the beams are well controlled with fewer feature data points. Tolerance analyses are also conducted in detail.

  20. Aspheric surface lens for LED collimating illumination with low Fresnel loss

    Science.gov (United States)

    Chen, Xindu; Lin, Jiaping; Liu, Zhanji; Wu, Peixuan; Wang, Han

    2017-02-01

    An aspheric surface lens is presented to realize collimating illumination with low Fresnel loss based on Fresnel equations and Snell's law. The smooth 2D contour of refractive optical surface is constructed from a set of cubic Bézier segments, whose control points are computed by deCasteljau algorithm. Simulation results show that the optical efficiency of 90.82% is achieved under a divergence angle of ±2.87° for an extended light-emitting diode (LED) source with chip size of 1 mm × 1 mm and the Fresnel loss is only 8.76%, whose optical efficiency has improved 14.3% than traditional collimating lens. By employing this proposed surface construction method, the largest divergence angle of collimating lens for point source is only 0.26° with 15 feature points on each refractive surface, while more than 2° for the traditional method. Therefore, the beams are well controlled with fewer feature data points. Tolerance analyses are also conducted in detail.

  1. Characteristic and quality control test in sector collimator gamma knife perfexion at Siloam hospital

    Science.gov (United States)

    Wesly Manik, Jhon; Hidayanto, Eko; Sutanto, Heri

    2017-01-01

    In this study conducted to evaluate the collimator 4 mm, 8 mm, 16 mm to determine the level of precision Gamma Knife Perfexion there three years and eight months has not carried out measurements after the first year and verify the alignment of sector 1-8. Measurement with three axes (x-axis, y-axis, z-axis) using the film Gafcromic EBT-3, which will be signaled to a central point in the film to be measured and given a dose of 5 Gy for 10 minutes and then scanned and analyzed using ImageJ softwere 1.50 and dose rate in film comparison with measurent dose rate using electrometer. Alignment of Patient-Positioning System (PPS) with Radiation Focal Point (RFP) determination of quality control testing each collimator 4 mm in the standard test with 0.4 mm passive voice AAPM 54. The results of the standard are still in conformity item 0.21 mm for 4 mm and corelasi dose rate film and measurent using electrometer collimator 4 mm = 0.965, 8 mm = 0.964, 16 mm = 0.959.

  2. Dosimetric characterization of a bi-directional micromultileaf collimator for stereotactic applications.

    Science.gov (United States)

    Bucciolini, M; Russo, S; Banci Buonamici, F; Pini, S; Silli, P

    2002-07-01

    A 6 MV photon beam from Linac SL75-5 has been collimated with a new micromultileaf device that is able to shape the field in the two orthogonal directions with four banks of leaves. This is the first clinical installation of the collimator and in this paper the dosimetric characterization of the system is reported. The dosimetric parameters required by the treatment planning system used for the dose calculation in the patient are: tissue maximum ratios, output factors, transmission and leakage of the leaves, penumbra values. Ionization chambers, silicon diode, radiographic films, and LiF thermoluminescent dosimeters have been employed for measurements of absolute dose and beam dosimetric data. Measurements with different dosimeters supply results in reasonable agreement among them and consistent with data available in literature for other models of micromultileaf collimator; that permits the use of the measured parameters for clinical applications. The discrepancies between results obtained with the different detectors (around 2%) for the analyzed parameters can be considered an indication of the accuracy that can be reached by current stereotactic dosimetry.

  3. Beam profile investigation of the new collimator system for the J-PET detector

    CERN Document Server

    Kubicz, E; Wieczorek, A; Alfs, D; Bednarski, T; Białas, P; Czerwiński, E; Gajos, A; Głowacz, B; Jasińska, B; Kamińska, D; Korcyl, G; Kowalski, P; Kozik, T; Krzemień, W; Mohammed, M; Moskal, I; Niedźwiecki, S; Pawlik-Niedźwiecka, M; Raczyński, L; Rudy, Z; Strzelecki, A; Wiślicki, W; Zieliński, M; Zgardzińska, B; Moskal, P

    2016-01-01

    Jagiellonian Positron Emission Tomograph (J-PET) is a multi-purpose detector which will be used for search for discrete symmetries violations in the decays of positronium atoms and for investigations with positronium atoms in life-sciences and medical diagnostics. In this article we present three methods for determination of the beam profile of collimated annihilation gamma quanta. Precise monitoring of this profile is essential for time and energy calibration of the J-PET detector and for the determination of the library of model signals used in the hit-time and hit-position reconstruction. We have we have shown that usage of two lead bricks with dimensions of 5x10x20 cm^3 enables to form a beam of annihilation quanta with Gaussian profile characterized by 1 mm FWHM. Determination of this characteristic is essential for designing and construction the collimator system for the 24-module J-PET prototype. Simulations of the beam profile for different collimator dimensions were performed. This allowed us to choo...

  4. Development and validation of a BEAMnrc component module for a miniature multileaf collimator.

    Science.gov (United States)

    Doerner, E; Hartmann, G H

    2012-05-21

    A new component module (CM) named mini multileaf collimator (mMLC) was developed for the Monte Carlo code BEAMnrc. It models the geometry of the add-on miniature multileaf collimator ModuLeaf (MRC Systems GmbH, Heidelberg, Germany, now part of Siemens, Erlangen, Germany). The new CM is partly based on the existing CM called DYNVMLC. The development was performed using a modified EGSnrc platform which enables us to work in the Microsoft Visual Studio environment. In order to validate the new CM, the PRIMUS linac with 6 MV x-rays (Siemens OCS, Concord, CA, USA) equipped with the ModuLeaf mMLC was modelled. Validation was performed by two methods: (a) a ray-tracing method to check the correct geometry of the multileaf collimator (MLC) and (b) a comparison of calculated and measured results of the following dosimetrical parameters: output factors, dose profiles, field edge position penumbra, MLC interleaf leakage and transmission values. Excellent agreement was found for all parameters. It was, in particular, found that the relationship between leaf position and field edge depending on the shape of the leaf ends can be investigated with a higher accuracy by this new CM than by measurements demonstrating the usefulness of the new CM.

  5. Radiation Transport Calculation of the UGXR Collimators for the Jules Horowitz Reactor (JHR)

    Science.gov (United States)

    Chento, Yelko; Hueso, César; Zamora, Imanol; Fabbri, Marco; Fuente, Cristina De La; Larringan, Asier

    2017-09-01

    Jules Horowitz Reactor (JHR), a major infrastructure of European interest in the fission domain, will be built and operated in the framework of an international cooperation, including the development and qualification of materials and nuclear fuel used in nuclear industry. For this purpose UGXR Collimators, two multi slit gamma and X-ray collimation mechatronic systems, will be installed at the JHR pool and at the Irradiated Components Storage pool. Expected amounts of radiation produced by the spent fuel and X-ray accelerator implies diverse aspects need to be verified to ensure adequate radiological zoning and personnel radiation protection. A computational methodology was devised to validate the Collimators design by means of coupling different engineering codes. In summary, several assessments were performed by means of MCNP5v1.60 to fulfil all the radiological requirements in Nominal scenario (TEDE < 25µSv/h) and in Maintenance scenario (TEDE < 2mSv/h) among others, detailing the methodology, hypotheses and assumptions employed.

  6. Dosimetric effects of beam size and collimation of epithermal neutrons for boron neutron capture therapy.

    Science.gov (United States)

    Yanch, J C; Harling, O K

    1993-08-01

    A series of studies of "ideal" beams has been carried out using Monte Carlo simulation with the goal of providing guidance for the design of epithermal beams for boron neutron capture therapy (BNCT). An "ideal" beam is defined as a monoenergetic, photon-free source of neutrons with user-specified size, shape and angular dependence of neutron current. The dosimetric behavior of monoenergetic neutron beams in an elliptical phantom composed of brain-equivalent material has been assessed as a function of beam diameter and neutron emission angle (beam angle), and the results are reported here. The simulation study indicates that substantial differences exist in the dosimetric behavior of small and large neutron beams (with respect to the phantom) as a function of the extent of beam collimation. With a small beam, dose uniformity increases as the beam becomes more isotropic (less collimated); the opposite is seen with large beams. The penetration of thermal neutrons is enhanced as the neutron emission angle is increased with a small beam; again the opposite trend is seen with large beams. When beam size is small, the dose delivered per neutron is very dependent on the extent of beam collimation; this does not appear to be the case with a larger beam. These trends in dose behavior are presented graphically and discussed in terms of their effect on several figures of merit, the advantage depth, the advantage ratio, and the advantage depth-dose rate. Tables giving quick summaries of these results are provided.

  7. QUASI-STATIC MODEL OF MAGNETICALLY COLLIMATED JETS AND RADIO LOBES. II. JET STRUCTURE AND STABILITY

    Energy Technology Data Exchange (ETDEWEB)

    Colgate, Stirling A.; Li, Hui [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Fowler, T. Kenneth [University of California, Berkeley, CA 94720 (United States); Hooper, E. Bickford [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); McClenaghan, Joseph; Lin, Zhihong [University of California, Irvine, CA 92697 (United States)

    2015-11-10

    This is the second in a series of companion papers showing that when an efficient dynamo can be maintained by accretion disks around supermassive black holes in active galactic nuclei, it can lead to the formation of a powerful, magnetically driven, and mediated helix that could explain both the observed radio jet/lobe structures and ultimately the enormous power inferred from the observed ultrahigh-energy cosmic rays. In the first paper, we showed self-consistently that minimizing viscous dissipation in the disk naturally leads to jets of maximum power with boundary conditions known to yield jets as a low-density, magnetically collimated tower, consistent with observational constraints of wire-like currents at distances far from the black hole. In this paper we show that these magnetic towers remain collimated as they grow in length at nonrelativistic velocities. Differences with relativistic jet models are explained by three-dimensional magnetic structures derived from a detailed examination of stability properties of the tower model, including a broad diffuse pinch with current profiles predicted by a detailed jet solution outside the collimated central column treated as an electric circuit. We justify our model in part by the derived jet dimensions in reasonable agreement with observations. Using these jet properties, we also discuss the implications for relativistic particle acceleration in nonrelativistically moving jets. The appendices justify the low jet densities yielding our results and speculate how to reconcile our nonrelativistic treatment with general relativistic MHD simulations.

  8. Small animal imaging by single photon emission using pinhole and coded aperture collimation

    Energy Technology Data Exchange (ETDEWEB)

    Garibaldi, F.; Accorsi, R.; Cinti, M.N.; Colilli, S.; Cusanno, F.; De Vincentis, G.; Fortuna, A.; Girolami, B.; Giuliani, F.; Gricia, M.; Lanza, R.; Loizzo, A.; Loizzo, S.; Lucentini, M.; Majewski, S.; Santavenere, F.; Pani, R.; Pellegrini, R.; Signore, A.; Scopinaro, F.

    2005-06-01

    The aim of this paper is to investigate the basic properties and limits of the small animal imaging systems based on single photon detectors. The detectors for radio imaging of small animals are challenging because of the very high spatial resolution needed, possibly coupled with high efficiency to allow dynamic studies. These performances are hardly attainable with single photon technique because of the collimator that limits both spatial resolution and sensitivity. In this paper we describe a simple desktop detector based on pixellated NaI(Tl) scintillator array coupled with a pinhole collimator and a PSPMT, the Hamamatsu R2486. The limits of such systems as well as the way to overcome them will be shown. In fact better light sampling at the anode level would allow better pixel identification for higher number of pixel that is one of the parameters defining the image quality. Also the spatial resolution would improve. The performances of such layout are compared with others using PSPMTs differing from R2486 for the light sampling at the anode level and different areas. We show how a further step, namely the substitution of the pinhole collimator with a coded aperture, will allow a great improvement in system sensitivity while maintaining very good spatial resolution, possibly submillimetric. Calculations and simulations show that sensitivity would improve by a factor of 50.

  9. A Highly Collimated, Young and Fast CO(2-1) Outflow in OMC1 South

    CERN Document Server

    Zapata, L A; Ho, P T P; Zhang, Q; Qi, C; Kurtz, S E; Zapata, Luis A.; Rodriguez, Luis F.; Ho, Paul T.P.; Zhang, Qizhou; Qi, Chunhua

    2005-01-01

    We present high angular resolution (~ 1''), sensitive CO(2-1) line observations of the region OMC1 South in the Orion Nebula made using the Submillimeter Array (SMA). We detect the CO(2-1) high velocity outflow that was first found by Rodriguez-Franco et al. (1999a) with the IRAM 30 m. Our observations resolve the outflow, whose velocity-integrated emission has a deconvolved width of 0.89'' \\pm 0.06'' (490 AU) and a projected length of ~ 48'' (21,000 AU) with very high redshifted and blueshifted gas with velocities of about \\pm 80 km/s. This outflow is among the most collimated (~ 3 degrees) and youngest outflows (600 yr) that have been reported. The data show that this collimated outflow has been blowing in the same direction during the last 600 yr. At high velocities, the CO(2-1) outflow traces an extremely collimated jet, while at lower velocities the CO emission traces an envelope possibly produced by entrainment of ambient gas. Furthermore, we also detect for the first time a millimeter wavelength contin...

  10. Collimation and scattering of the active galactic nucleus emission in the Sombrero galaxy

    CERN Document Server

    Menezes, R B; Ricci, T V; 10.1088/2041-8205/765/2/L40

    2013-01-01

    We present an analysis of a data cube of the central region of M104, the Sombrero galaxy, obtained with the GMOS-IFU of the Gemini-South telescope, and report the discovery of collimation and scattering of the active galactic nucleus (AGN) emission in the circumnuclear region of this galaxy. Analysis with PCA Tomography and spectral synthesis revealed the existence of collimation and scattering of the AGN featureless continuum and also of a broad component of the H{\\alpha} emission line. The collimation and scattering of this broad H{\\alpha} component was also revealed by fitting the [NII] {\\lambda}{\\lambda}6548,6583 and H{\\alpha} emission lines as a sum of Gaussian functions. The spectral synthesis, together with a V-I image obtained with the Hubble Space Telescope, showed the existence of circumnuclear dust, which may cause the light scattering. We also identify a dusty feature that may be interpreted as a torus/disk structure. The existence of two opposite regions with featureless continuum (P.A. = -18{\\de...

  11. Use of Apollo 17 Epoch Neutron Spectrum as a Benchmark in Testing LEND Collimated Sensor

    Science.gov (United States)

    Chin, Gordon; Sagdeev, R.; Milikh, G.

    2011-01-01

    The Apollo 17 neutron experiment LPNE provided a unique set of data on production of neutrons in the Lunar soil bombarded by Galactic Cosmic Rays (GCR). It serves as valuable "ground-truth" in the age of orbital remote sensing. We used the neutron data attributed to Apollo 17 epoch as a benchmark for testing the LEND's collimated sensor, as introduced by the geometry of collimator and efficiency of He3 counters. The latter is defined by the size of gas counter and pressure inside it. The intensity and energy spectrum of neutrons escaping the lunar surface are dependent on incident flux of Galactic Cosmic Rays (GCR) whose variability is associated with Solar Cycle and its peculiarities. We obtain first the share of neutrons entering through the field of view of collimator as a fraction of the total neutron flux by using the angular distribution of neutron exiting the Moon described by our Monte Carlo code. We computed next the count rate of the 3He sensor by using the neutron energy spectrum from McKinney et al. [JGR, 2006] and by consider geometry and gas pressure of the LEND sensor. Finally the neutron count rate obtained for the Apollo 17 epoch characterized by intermediate solar activity was adjusted to the LRO epoch characterized by low solar activity. It has been done by taking into account solar modulation potential, which affects the GCR flux, and in turn changes the neutron albedo flux.

  12. Radiation Transport Calculation of the UGXR Collimators for the Jules Horowitz Reactor (JHR

    Directory of Open Access Journals (Sweden)

    Chento Yelko

    2017-01-01

    Full Text Available Jules Horowitz Reactor (JHR, a major infrastructure of European interest in the fission domain, will be built and operated in the framework of an international cooperation, including the development and qualification of materials and nuclear fuel used in nuclear industry. For this purpose UGXR Collimators, two multi slit gamma and X-ray collimation mechatronic systems, will be installed at the JHR pool and at the Irradiated Components Storage pool. Expected amounts of radiation produced by the spent fuel and X-ray accelerator implies diverse aspects need to be verified to ensure adequate radiological zoning and personnel radiation protection. A computational methodology was devised to validate the Collimators design by means of coupling different engineering codes. In summary, several assessments were performed by means of MCNP5v1.60 to fulfil all the radiological requirements in Nominal scenario (TEDE < 25µSv/h and in Maintenance scenario (TEDE < 2mSv/h among others, detailing the methodology, hypotheses and assumptions employed.

  13. Objective comparison of lesion detectability in low and medium-energy collimator iodine-123 mIBG images using a channelized Hotelling observer

    Science.gov (United States)

    Gregory, Rebecca A.; Murray, Iain; Gear, Jonathan; Aldridge, Matthew D.; Levine, Daniel; Fowkes, Lucy; Waddington, Wendy A.; Chua, Sue; Flux, Glenn

    2017-01-01

    Iodine-123 mIBG imaging is widely regarded as a gold standard for diagnostic studies of neuroblastoma and adult neuroendocrine cancer although the optimal collimator for tumour imaging remains undetermined. Low-energy (LE) high-resolution (HR) collimators provide superior spatial resolution. However due to septal penetration of high-energy photons these provide poorer contrast than medium-energy (ME) general-purpose (GP) collimators. LEGP collimators improve count sensitivity. The aim of this study was to objectively compare the lesion detection efficiency of each collimator to determine the optimal collimator for diagnostic imaging. The septal penetration and sensitivity of each collimator was assessed. Planar images of the patient abdomen were simulated with static scans of a Liqui-Phil™ anthropomorphic phantom with lesion-shaped inserts, acquired with LE and ME collimators on 3 different manufacturers’ gamma camera systems (Skylight (Philips), Intevo (Siemens) and Discovery (GE)). Two-hundred normal and 200 single-lesion abnormal images were created for each collimator. A channelized Hotelling observer (CHO) was developed and validated to score the images for the likelihood of an abnormality. The areas under receiver-operator characteristic (ROC) curves, Az, created from the scores were used to quantify lesion detectability. The CHO ROC curves for the LEHR collimators were inferior to the GP curves for all cameras. The LEHR collimators resulted in statistically significantly smaller Azs (p  <  0.05), of on average 0.891  ±  0.004, than for the MEGP collimators, 0.933  ±  0.004. In conclusion, the reduced background provided by MEGP collimators improved 123I mIBG image lesion detectability over LEHR collimators that provided better spatial resolution.

  14. The polarization-based collimated beam combiner and the proposed NOVA fringe tracker (NFT) for the VLTI

    NARCIS (Netherlands)

    Meisner, J.A.; Jaffe, W.J.; Le Poole, R.S.; Pereira, S.F.; Quirrenbach, A.; Raban, D.; Vosteen, A.

    2010-01-01

    The Polarization-Based Collimated Beam Combiner efficiently produces pairwise interference between beams from multiple telescopes. An important feature is achieving ”Photometric Symmetry” whereby interference measurements have no first-order sensitivity to wavefront perturbations (or photometric var

  15. The polarization-based collimated beam combiner and the proposed NOVA fringe tracker (NFT) for the VLTI

    NARCIS (Netherlands)

    Meisner, J.A.; Jaffe, W.J.; Poole, R.S. le; Pereira, S.F.; Quirrenbach, A.; Raban, D.; Vosteen, L.L.A.

    2010-01-01

    The Polarization-Based Collimated Beam Combiner efficiently produces pairwise interference between beams from multiple telescopes. An important feature is achieving "Photometric Symmetry" whereby interference measurements have no first-order sensitivity to wavefront perturbations (or photometric var

  16. VLBI collimation-tower technique for time-delay studies of a large ground-station communications antenna

    Science.gov (United States)

    Otoshi, T. Y.; Young, L. E.; Rusch, W. V. T.

    1985-01-01

    A need for an accurate but inexpensive method for measuring and evaluating time delays of large ground antennas for VLBI applications motivated the development of the collimation tower technique. Supporting analytical work which was performed primarily to verify time delay measurement results obtained for a large antenna when the transmitter was at a collimation distance of 1/25 of the usual far field criterion is discussed. Comparisons of theoretical and experimental results are also given.

  17. A comparison of two prompt gamma imaging techniques with collimator-based cameras for range verification in proton therapy

    Science.gov (United States)

    Lin, Hsin-Hon; Chang, Hao-Ting; Chao, Tsi-Chian; Chuang, Keh-Shih

    2017-08-01

    In vivo range verification plays an important role in proton therapy to fully utilize the benefits of the Bragg peak (BP) for delivering high radiation dose to tumor, while sparing the normal tissue. For accurately locating the position of BP, camera equipped with collimators (multi-slit and knife-edge collimator) to image prompt gamma (PG) emitted along the proton tracks in the patient have been proposed for range verification. The aim of the work is to compare the performance of multi-slit collimator and knife-edge collimator for non-invasive proton beam range verification. PG imaging was simulated by a validated GATE/GEANT4 Monte Carlo code to model the spot-scanning proton therapy and cylindrical PMMA phantom in detail. For each spot, 108 protons were simulated. To investigate the correlation between the acquired PG profile and the proton range, the falloff regions of PG profiles were fitted with a 3-line-segment curve function as the range estimate. Factors including the energy window setting, proton energy, phantom size, and phantom shift that may influence the accuracy of detecting range were studied. Results indicated that both collimator systems achieve reasonable accuracy and good response to the phantom shift. The accuracy of range predicted by multi-slit collimator system is less affected by the proton energy, while knife-edge collimator system can achieve higher detection efficiency that lead to a smaller deviation in predicting range. We conclude that both collimator systems have potentials for accurately range monitoring in proton therapy. It is noted that neutron contamination has a marked impact on range prediction of the two systems, especially in multi-slit system. Therefore, a neutron reduction technique for improving the accuracy of range verification of proton therapy is needed.

  18. Design consideration of a multipinhole collimator with septa for ultra high-resolution silicon drift detector modules

    Energy Technology Data Exchange (ETDEWEB)

    Min, Byung Jun [Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Ilwon-Dong, Gangnam-Gu, Seoul 135-710 (Korea, Republic of); Choi, Yong [Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Ilwon-Dong, Gangnam-Gu, Seoul 135-710 (Korea, Republic of)], E-mail: ychoi@skku.edu; Lee, Nam-Yong [School of Computer Aided Science, Institute of Basic Science, Inje University, Gimhae, Gyeongnam 621-749 (Korea, Republic of); Lee, Kisung [Department of Radiologic Science, Korea University, Seoul 136-703 (Korea, Republic of); Ahn, Young Bok [Department of Electronic Engineering, Konkuk University, Seoul 143-701 (Korea, Republic of); Joung, Jinhun [Molecular Imaging, Siemens Medical Solutions USA, Inc., Hoffman Estates, IL 60195 (United States)

    2009-07-21

    The aim of this study was to design a multipinhole (MP) collimator with lead vertical septa coupled to a high-resolution detector module containing silicon drift detectors (SDDs) with an intrinsic resolution approaching the sub-millimeter level. Monte Carlo simulations were performed to determine pinhole parameters such as pinhole diameter, focal length, and number of pinholes. Effects of parallax error and collimator penetration were investigated for the new MP collimator design. The MP detector module was evaluated using reconstructed images of resolution and mathematical cardiac torso (MCAT) phantoms. In addition, the reduced angular sampling effect was investigated over 180 deg. The images were reconstructed using dedicated maximum likelihood expectation maximization (MLEM) algorithm. An MP collimator with 81-pinhole was designed with a 2-mm-diameter pinhole and a focal length of 40 mm . Planar sensitivity and resolution obtained using the devised MP collimator were 3.9 cps/{mu}Ci and 6 mm full-width at half-maximum (FWHM) at a 10 cm distance. The parallax error and penetration ratio were significantly improved using the proposed MP collimation design. The simulation results demonstrated that the proposed MP detector provided enlarged imaging field of view (FOV) and improved the angular sampling effect in resolution and MCAT phantom studies. Moreover, the novel design enables tomography images by simultaneously obtaining eight projections with eight-detector modules located along the 180 deg. orbit surrounding a patient, which allows designing of a stationary cardiac SPECT. In conclusion, the MP collimator with lead vertical septa was designed to have comparable system resolution and sensitivity to those of the low-energy high-resolution (LEHR) collimator per detector. The system sensitivity with an eight-detector configuration would be four times higher than that with a standard dual-detector cardiac SPECT.

  19. Transcriptional program induced by factor VIIa-tissue factor, PAR1 and PAR2 in MDA-MB-231 cells

    DEFF Research Database (Denmark)

    Albrektsen, T; Sørensen, B B; Hjortø, G M

    2007-01-01

    -regulated genes was also regulated by a PAR1 agonist peptide suggesting extensive redundancy between FVIIa/PAR2 signaling and thrombin/PAR1 signaling. The FVIIa regulated genes encode cytokines, chemokines and growth factors, and the gene repertoire induced by FVIIa in MDA-MB-231 cells is consistent...... with a role for TF-FVIIa signaling in regulation of a wound healing type of response. Interestingly, a number of genes regulated exclusively by FVIIa/PAR2-mediated cell signaling in MDA-MB-231 cells were regulated by thrombin and a PAR1 agonist, but not by FVIIa, in the TF-expressing glioblastoma U373 cell...

  20. Micro-collimators fabricated by chemical etching of thin polyallyldiglycol carbonate polymer films exposed to oxygen ions

    Energy Technology Data Exchange (ETDEWEB)

    Choi, V.W.Y.; Ng, C.K.M.; Nikezic, D. [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong (Hong Kong); Konishi, T. [National Institute of Radiological Sciences, Department of Technical Support and Development, Chiba 263-8555 (Japan); Yu, K.N., E-mail: peter.yu@cityu.edu.h [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong (Hong Kong)

    2011-03-01

    One approach for {alpha} particle radiobiological experiments is to use solid-state nuclear track detectors (SSNTDs) as support substrates to record the {alpha} particle hit positions on the targets. To facilitate accurate characterization of the hit positions as well as the incident {alpha} particle energies, micro-collimators are required in these experiments to restrict the incident {alpha} particles to those with small deviations from normal incidence with respect to the collimator. In the present paper, we fabricated micro-collimators, which restricted {alpha} particles to those with deviations as low as 12{sup o}. Specially etched polyallyldiglycol carbonate (PADC) films, which are a kind of SSNTD, with a thickness 70 {mu}m were prepared from commercially available PADC films. These were then irradiated by 4.83 MeV/n oxygen ions generated from the heavy-ion medical accelerator in Chiba (HIMAC), Japan. The irradiated films were chemically etched for at least 2.7 h to achieve etched-through air channels to form the micro-collimators. The micro-collimators formed by etching the irradiated films for 2.7, 3.0 and 4.0 h were experimentally shown to be able to restrict {alpha} particles to those very close to normal incidence. In contrast, the micro-collimator formed by etching the irradiated film for 4.5 h started to allow {alpha} particles with larger deviations from normal incidence to pass through, which is likely due to overlapping of air channels from excessive etching.

  1. Study of collimator array based on single collimating lens%基于单准直透镜的阵列准直器研究

    Institute of Scientific and Technical Information of China (English)

    袁志林; 杨睿; 杨柳; 宋丽丹; 孙莉萍; 马雨虹; 王猛; 陈定康; 郭金平; 唐丽红

    2012-01-01

    提出了一种基于单准直透镜和光纤阵列的阵列准直器,深入研究了此种方案的光路无胶和光路有胶的两种实现方式:并基于高斯光束传输矩阵和q参数相关理论,从理论上详细地计算、推导了各变量之间的关系,并进行了模拟仿真及实验验证,得到了理论和实验一致的结果.对两种实现方式的结构及封装设计也进行了初步的摸索和实验,并制作出了性能良好的阵列准直器.理论和实验表明,该方案具有易加工、低成本、易封装、性能优等特点,也易于扩展成多维阵列准直器,可为可重构光分插复用器系统和光交叉连接系统的发展提供强有力的器件支撑.%A new collimator array based on single collimating lens and fiber array is proposed in the paper. An in-depth study is conducted on the two realizing methods, one is with glue in the optical path and the other is without glue in the optical path. Based on Gauss optics transmission matrix and q parameter theory, the relationship among the variables is deduced and computed theoretically, simulated virtually and confirmed experimentally. Good agreement between theoretical results and simulation, experimental results is obtained. The mechanical and packaging designs of the two realizing methods are first studied, then the proposed collimator arrays, with good performance are made. Both the theoretical and experimental results show that the scheme has the merits of easy-to-make, low cost, easy-to-package, good performance, good scalability, etc., which can strongly support the development of reconfigurable optical add- drop multiplexer system and optical cross-connect system.

  2. Simulating technetium-99m cerebral perfusion studies with a three-dimensional Hoffman brain phantom. Collimator and filter selection in SPECT neuroimaging

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hee-Joung; Yang, Seoung-Oh; Moon, Dae-Hyuk; Lee, Hee-Kyung [Asan Medical Center, Seoul (Korea, Republic of); Karp, J.S.; Mozley, P.D.; Kung, H.F.; Alavi, A.

    1996-02-01

    The choice of a collimator and the selection of a filter can affect the quality of clinical SPECT images of the brain. The compromises that 4 different collimators make between spatial resolution and sensitivity were studied by imaging a three-dimensional Hoffman brain phantom. The planar data were acquired with each collimator on a three-headed SPECT system and were reconstructed with both a standard Butterworth filter and a Wiener pre-filter. The reconstructed images were then evaluated by specialists in nuclear medicine and were also quantitatively analyzed with specific regions of interest (ROI) in the brain. All observers preferred the Wiener filter reconstructed images regardless of the collimator used to acquire the planar images. With this filter, the ultrahigh-resolution fan-beam collimator was the most subjectively preferable and quantitatively produced the highest contrast ratios. The findings support suggestions that higher resolution collimators are preferable to higher sensitivity collimators, and indicate that fan-beam collimators are preferable to parallel-hole collimators for clinical SPECT studies of cerebral perfusion. The results also suggest that the Wiener filter enhances the quality of SPECT brain images regardless of which collimator is used to acquire the data. (author).

  3. The actinobacterial signature protein ParJ (SCO1662) regulates ParA polymerization and affects chromosome segregation and cell division during Streptomyces sporulation.

    Science.gov (United States)

    Ditkowski, Bartosz; Troć, Paulina; Ginda, Katarzyna; Donczew, Magdalena; Chater, Keith F; Zakrzewska-Czerwińska, Jolanta; Jakimowicz, Dagmara

    2010-12-01

    Bacterial chromosome segregation usually involves cytoskeletal ParA proteins, ATPases which can form dynamic filaments. In aerial hyphae of the mycelial bacterium Streptomyces coelicolor, ParA filaments extend over tens of microns and are responsible for segregation of dozens of chromosomes. We have identified a novel interaction partner of S. coelicolor ParA, ParJ. ParJ negatively regulates ParA polymerization in vitro and is important for efficient chromosome segregation in sporulating aerial hyphae. ParJ-EGFP formed foci along aerial hyphae even in the absence of ParA. ParJ, which is encoded by sco1662, turned out to be one of the five actinobacterial signature proteins, and another of the five is a ParJ paralogue. We hypothesize that polar growth, which is characteristic not only of streptomycetes, but even of simple Actinobacteria, may be interlinked with ParA polymer assembly and its specific regulation by ParJ.

  4. A Conserved Mode of Protein Recognition and Binding in a ParD−ParE Toxin−Antitoxin Complex

    Energy Technology Data Exchange (ETDEWEB)

    Dalton, Kevin M.; Crosson, Sean (UC)

    2010-05-06

    Toxin-antitoxin (TA) systems form a ubiquitous class of prokaryotic proteins with functional roles in plasmid inheritance, environmental stress response, and cell development. ParDE family TA systems are broadly conserved on plasmids and bacterial chromosomes and have been well characterized as genetic elements that promote stable plasmid inheritance. We present a crystal structure of a chromosomally encoded ParD-ParE complex from Caulobacter crescentus at 2.6 {angstrom} resolution. This TA system forms an {alpha}{sub 2}{beta}{sub 2} heterotetramer in the crystal and in solution. The toxin-antitoxin binding interface reveals extensive polar and hydrophobic contacts of ParD antitoxin helices with a conserved recognition and binding groove on the ParE toxin. A cross-species comparison of this complex structure with related toxin structures identified an antitoxin recognition and binding subdomain that is conserved between distantly related members of the RelE/ParE toxin superfamily despite a low level of overall primary sequence identity. We further demonstrate that ParD antitoxin is dimeric, stably folded, and largely helical when not bound to ParE toxin. Thus, the paradigmatic model in which antitoxin undergoes a disorder-to-order transition upon toxin binding does not apply to this chromosomal ParD-ParE TA system.

  5. A new model for estimating boreal forest fPAR

    Science.gov (United States)

    Majasalmi, Titta; Rautiainen, Miina; Stenberg, Pauline

    2014-05-01

    Life on Earth is continuously sustained by the extraterrestrial flux of photosynthetically active radiation (PAR, 400-700 nm) from the sun. This flux is converted to biomass by chloroplasts in green vegetation. Thus, the fraction of absorbed PAR (fPAR) is a key parameter used in carbon balance studies, and is listed as one of the Essential Climate Variables (ECV). Temporal courses of fPAR for boreal forests are difficult to measure, because of the complex 3D structures. Thus, they are most often estimated based on models which quantify the dependency of absorbed radiation on canopy structure. In this study, we adapted a physically-based canopy radiation model into a fPAR model, and compared modeled and measured fPAR in structurally different boreal forest stands. The model is based on the spectral invariants theory, and uses leaf area index (LAI), canopy gap fractions and spectra of foliage and understory as input data. The model differs from previously developed more detailed fPAR models in that the complex 3D structure of coniferous forests is described using an aggregated canopy parameter - photon recollision probability p. The strength of the model is that all model inputs are measurable or available through other simple models. First, the model was validated with measurements of instantaneous fPAR obtained with the TRAC instrument in nine Scots pine, Norway spruce and Silver birch stands in a boreal forest in southern Finland. Good agreement was found between modeled and measured fPAR. Next, we applied the model to predict temporal courses of fPAR using data on incoming radiation from a nearby flux tower and sky irradiance models. Application of the model to simulate diurnal and seasonal values of fPAR indicated that the ratio of direct-to-total incident radiation and leaf area index are the key factors behind the magnitude and variation of stand-level fPAR values.

  6. THE FIRST ''WATER FOUNTAIN'' COLLIMATED OUTFLOW IN A PLANETARY NEBULA

    Energy Technology Data Exchange (ETDEWEB)

    Gómez, José F.; Miranda, Luis F.; Guerrero, Martín A. [Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, E-18008 Granada (Spain); Suárez, Olga; Bendjoya, Philippe; Lagadec, Eric [Laboratoire Lagrange, UMR 7293, Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d' Azur, F-06304 Nice (France); Rizzo, J. Ricardo; García-García, Enrique [Centro de Astrobiología (INTA-CSIC), Ctra. M-108, km. 4, E-28850 Torrejón de Ardoz (Spain); Green, James A. [CSIRO Astronomy and Space Science, Australia Telescope National Facility, P.O. Box 76, Epping, NSW 1710 (Australia); Uscanga, Lucero [Institute of Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, 15236 Athens (Greece); Ramos-Larios, Gerardo [Instituto de Astronomía y Meteorología, Av. Vallarta No. 2602, Col. Arcos Vallarta, C.P. 44130 Guadalajara, Jalisco (Mexico)

    2015-02-01

    ''Water fountains'' (WFs) are evolved objects showing high-velocity, collimated jets traced by water maser emission. Most of them are in the post-asymptotic giant branch (post-AGB) and they may represent one of the first manifestations of collimated mass loss in evolved stars. We present water maser, carbon monoxide, and mid-infrared spectroscopic data (obtained with the Australia Telescope Compact Array, Herschel Space Observatory, and the Very Large Telescope, respectively) toward IRAS 15103–5754, a possible planetary nebula (PN) with WF characteristics. Carbon monoxide observations show that IRAS 15103–5754 is an evolved object, while the mid-IR spectrum displays unambiguous [Ne II] emission, indicating that photoionization has started and thus, its nature as a PN is confirmed. Water maser spectra show several components spreading over a large velocity range (≅ 75 km s{sup –1}) and tracing a collimated jet. This indicates that the object is a WF, the first WF known that has already entered the PN phase. However, the spatial and kinematical distribution of the maser emission in this object are significantly different from those in other WFs. Moreover, the velocity distribution of the maser emission shows a ''Hubble-like'' flow (higher velocities at larger distances from the central star), consistent with a short-lived, explosive mass-loss event. This velocity pattern is not seen in other WFs (which are presumably in earlier evolutionary stages). We therefore suggest that we are witnessing a fundamental change of mass-loss processes in WFs, with water masers being pumped by steady jets in post-AGB stars, but tracing explosive/ballistic events as the object enters the PN phase.

  7. A clinical gamma camera-based pinhole collimated system for high resolution small animal SPECT imaging

    Directory of Open Access Journals (Sweden)

    J. Mejia

    2010-12-01

    Full Text Available The main objective of the present study was to upgrade a clinical gamma camera to obtain high resolution tomographic images of small animal organs. The system is based on a clinical gamma camera to which we have adapted a special-purpose pinhole collimator and a device for positioning and rotating the target based on a computer-controlled step motor. We developed a software tool to reconstruct the target’s three-dimensional distribution of emission from a set of planar projections, based on the maximum likelihood algorithm. We present details on the hardware and software implementation. We imaged phantoms and heart and kidneys of rats. When using pinhole collimators, the spatial resolution and sensitivity of the imaging system depend on parameters such as the detector-to-collimator and detector-to-target distances and pinhole diameter. In this study, we reached an object voxel size of 0.6 mm and spatial resolution better than 2.4 and 1.7 mm full width at half maximum when 1.5- and 1.0-mm diameter pinholes were used, respectively. Appropriate sensitivity to study the target of interest was attained in both cases. Additionally, we show that as few as 12 projections are sufficient to attain good quality reconstructions, a result that implies a significant reduction of acquisition time and opens the possibility for radiotracer dynamic studies. In conclusion, a high resolution single photon emission computed tomography (SPECT system was developed using a commercial clinical gamma camera, allowing the acquisition of detailed volumetric images of small animal organs. This type of system has important implications for research areas such as Cardiology, Neurology or Oncology.

  8. A clinical gamma camera-based pinhole collimated system for high resolution small animal SPECT imaging

    Energy Technology Data Exchange (ETDEWEB)

    Mejia, J.; Galvis-Alonso, O.Y., E-mail: mejia_famerp@yahoo.com.b [Faculdade de Medicina de Sao Jose do Rio Preto (FAMERP), SP (Brazil). Dept. de Biologia Molecular; Castro, A.A. de; Simoes, M.V. [Faculdade de Medicina de Sao Jose do Rio Preto (FAMERP), SP (Brazil). Dept. de Clinica Medica; Leite, J.P. [Universidade de Sao Paulo (FMRP/USP), Ribeirao Preto, SP (Brazil). Fac. de Medicina. Dept. de Neurociencias e Ciencias do Comportamento; Braga, J. [Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP (Brazil). Div. de Astrofisica

    2010-11-15

    The main objective of the present study was to upgrade a clinical gamma camera to obtain high resolution tomographic images of small animal organs. The system is based on a clinical gamma camera to which we have adapted a special-purpose pinhole collimator and a device for positioning and rotating the target based on a computer-controlled step motor. We developed a software tool to reconstruct the target's three-dimensional distribution of emission from a set of planar projections, based on the maximum likelihood algorithm. We present details on the hardware and software implementation. We imaged phantoms and heart and kidneys of rats. When using pinhole collimators, the spatial resolution and sensitivity of the imaging system depend on parameters such as the detector-to-collimator and detector-to-target distances and pinhole diameter. In this study, we reached an object voxel size of 0.6 mm and spatial resolution better than 2.4 and 1.7 mm full width at half maximum when 1.5- and 1.0-mm diameter pinholes were used, respectively. Appropriate sensitivity to study the target of interest was attained in both cases. Additionally, we show that as few as 12 projections are sufficient to attain good quality reconstructions, a result that implies a significant reduction of acquisition time and opens the possibility for radiotracer dynamic studies. In conclusion, a high resolution single photon emission computed tomography (SPECT) system was developed using a commercial clinical gamma camera, allowing the acquisition of detailed volumetric images of small animal organs. This type of system has important implications for research areas such as Cardiology, Neurology or Oncology. (author)

  9. Poster — Thur Eve — 19: Performance assessment of a 160-leaf beam collimation system

    Energy Technology Data Exchange (ETDEWEB)

    Ali, E. S. M.; La Russa, D. J.; Vandervoort, E. [The Ottawa Hospital Cancer Centre, Ottawa (Canada)

    2014-08-15

    In this study, the performance of the new beam collimation system with 160 leaves, each with a 5 mm leaf width projected at isocenter, is evaluated in terms of positional accuracy and plan/delivery quality. Positional accuracy was evaluated using a set of static and dynamic MLC/jaw delivery patterns at different gantry angles, dose rates, and MLC/jaw speeds. The impact on IMRT plan quality was assessed by comparing against a previous generation collimation system using the same optimization parameters, while delivery quality was quantified using a combination of patient-specific QA measurements with ion chambers, film, and a bi-planar diode array. Positional accuracy for four separate units was comparable. The field size accuracy, junction width, and total displacement over 16 cm leaf travel are 0.3 ± 0.2 mm, 0.4 ± 0.3 mm, and 0.5 ± 0.2 mm, respectively. The typical leaf minor offset is 0.05 ± 0.04 mm, and MLC hysteresis effects are 0.2 ± 0.1 mm over 16 cm travel. The dynamic output is linear with MU and MLC/jaw speed, and is within 0.7 ± 0.3 % of the planning system value. Plan quality is significantly improved both in terms of target coverage and OAR sparing due, in part, to the larger allowable MLC and jaw speeds. γ-index pass rates for the patient-specific QA measurements exceeded 97% using criteria of 2%/2 mm. In conclusion, the performance of the Agility system is consistent among four separate installations, and is superior to its previous generations of collimation systems.

  10. Physical properties of new collimator cone system for stereotactic radiation therapy developed in samsung medical center.

    Science.gov (United States)

    Kim, D Y; Ahn, Y C; Oh, D G; Choi, D R; Ju, S G; Yeo, I H; Huh, S J

    2000-09-01

    A new collimator cone system has been developed at the Samsung Medical Center that overcomes some of the limitations of present commercially supplied collimator cones. The physical properties of the newly developed cone system are described in this report. The new cones have relatively larger aperture sizes (3.0-7.0 cm in diameter) and are 16 cm in length. Each new cone is fabricated with cerrobend alloy melted and poured into a stainless steel housing that is permanently fixed to a mounting plate. The mounting plate of the new cone is designed to insert into the wedge mount slot of the gantry head. The mechanical accuracy of the central axis of the cone pointing to the isocenter was tested using film, a steel ball positioned at the isocenter by the mechanical isocenter device. For the evaluation of beam flatness and penumbra, off-axis ratios at 5 cm depth were measured by film dosimetry using polystyrene phantom. The average error of the mechanical isocenter was 0.27 mm (+/- 0.16 mm). The beam flatness was excellent in the central region of the beam, and the average penumbra width was 3.35 mm (+/- 0.25 mm). The new cone design has more clearance between the patient's head and the gantry, and can more easily be removed from the gantry head because it slides in and out of the wedge slot. This facilitates changing cone sizes during one treatment session, and makes the process of double exposure port films easier. A new collimator cone system for stereotactic radiation therapy has been developed. The mechanical accuracy and physical properties are satisfactory for clinical use, and the new design permits a wider range of clinical applications for stereotactic radiation therapy.

  11. THE INNERMOST COLLIMATION STRUCTURE OF THE M87 JET DOWN TO ∼10 SCHWARZSCHILD RADII

    Energy Technology Data Exchange (ETDEWEB)

    Hada, Kazuhiro; Giroletti, Marcello; Giovannini, Gabriele [INAF Istituto di Radioastronomia, via Gobetti 101, I-40129 Bologna (Italy); Kino, Motoki; Doi, Akihiro [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara 252-5210 (Japan); Nagai, Hiroshi; Honma, Mareki; Hagiwara, Yoshiaki; Kawaguchi, Noriyuki [National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588 (Japan)

    2013-09-20

    We investigated the detailed inner jet structure of M87 using Very Long Baseline Array data at 2, 5, 8.4, 15, 23.8, 43, and 86 GHz, especially focusing on the multi-frequency properties of the radio core at the jet base. First, we measured the size of the core region transverse to the jet axis, defined as W{sub c}, at each frequency ν, and found a relation between W{sub c} and ν: W{sub c}(ν)∝ν{sup –0.71±0.05}. Then, by combining W{sub c}(ν) and the frequency dependence of the core position r{sub c}(ν), which was obtained in our previous study, we constructed a collimation profile of the innermost jet W{sub c}(r) down to ∼10 Schwarzschild radii (R{sub s}) from the central black hole. We found that W{sub c}(r) smoothly connects with the width profile of the outer edge-brightened, parabolic jet and then follows a similar radial dependence down to several tens of R{sub s}. Closer to the black hole, the measured radial profile suggests a possible change in the jet collimation shape from the outer parabolic one, where the jet shape tends to become more radially oriented. This result could be related to a magnetic collimation process or/and interactions with surrounding materials at the jet base. The present results shed light on the importance of higher-sensitivity/resolution imaging studies of M87 at 86, 43, and 22 GHz; these studies should be examined more rigorously.

  12. Tune shift induced by nonlinear resistive wall wake field of flat collimator

    CERN Document Server

    Zimmermann, Frank; Assmann, R W; Burkhardt, H; Caspers, Friedhelm; Gasior, M; Jones, R; Kroyer, T; Métral, E; Redaelli, S; Robert-Démolaize, G; Roncarolo, F; Rumolo, Giovanni; Steinhagen, Ralph J; Wenninger, J

    2006-01-01

    We present formulae for the coherent and incoherent tune shifts due to the nonlinear resistive wall wake field for a single beam traveling between two parallel plates. In particular, we demonstrate that the nonlinear terms of the resistive-wall wake field become important if the gap between the plates is comparable to the transverse rms beam size. We also compare the theoretically predicted tune shift as a function of gap size with measurements for an LHC prototype graphite collimator in the CERN SPS and with simulations.

  13. HOLLOW ELECTRON BEAM COLLIMATION FOR HL-LHC - EFFECT ON THE BEAM CORE

    Energy Technology Data Exchange (ETDEWEB)

    Fitterer, M. [Fermilab; Stancari, G. [Fermilab; Valishev, A. [Fermilab; Bruce, R. [CERN; Papadopoulou, S. [CERN; Papotti, G. [CERN; Pellegrini, D. [CERN; Pellegrini, S. [CERN; Valuch, D. [CERN; Wagner, J. F. [CERN

    2016-10-05

    Collimation with hollow electron beams or lenses (HEL) is currently one of the most promising concepts for active halo control in HL-LHC. In previous studies it has been shown that the halo can be efficiently removed with a hollow electron lens. Equally important as an efficient removal of the halo, is also to demonstrate that the core stays unperturbed. In this paper, we present a summary of the experiment at the LHC and simulations in view of the effect of the HEL on the beam core in case of a pulsed operation.

  14. Magnetic collimation of meridional-self-similar general relativistic MHD flows

    Science.gov (United States)

    Globus, Noemie; Sauty, Christophe; Cayatte, Véronique; Celnikier, Ludwik M.

    2014-06-01

    We present a model for the spine of relativistic Magnetohydrodynamics outflows in the Kerr geometry. Meridional self-similarity is invoked to derive semianalytical solutions close to the polar axis. The study of the energy conservation along a particular field line gives a simple criterion for the collimation of jets. Such parameter have already been derived in the classical case by Sauty et al. 1999 and also extended to the Schwarzschild metric by Meliani et al. 2006. We generalize the same study to the Kerr metric. We show that the rotation of the black hole increases the magnetic self-confinement.

  15. Magnetic collimation of meridional-self-similar general relativistic MHD flows

    CERN Document Server

    Globus, Noemie; Cayatte, Véronique; Celnikier, Ludwik M

    2014-01-01

    We present a model for the spine of relativistic MHD outflows in the Kerr geometry. Meridional self-similarity is invoked to derive semi-analytical solutions close to the polar axis. The study of the energy conservation along a particular field line gives a simple criterion for the collimation of jets. Such parameter have already been derived in the classical case by Sauty et al. 1999 and also extended to the Schwarzschild metric by Meliani et al. 2006. We generalize the same study to the Kerr metric. We show that the rotation of the black hole increases the magnetic self-confinement.

  16. Tunable Goos-Haenchen shift for self-collimated beams in two-dimensional photonic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Matthews, Aaron [Nonlinear Physics Centre and Centre for Ultra-high Bandwidth Devices for Optical Systems (CUDOS), Research School of Physical Sciences and Engineering, Australian National University, Canberra ACT 0200 (Australia)], E-mail: afm124@rsphysse.anu.edu.au; Kivshar, Yuri [Nonlinear Physics Centre and Centre for Ultra-high Bandwidth Devices for Optical Systems (CUDOS), Research School of Physical Sciences and Engineering, Australian National University, Canberra ACT 0200 (Australia)

    2008-04-21

    We present finite-difference time-domain studies of the Goos-Haenchen effect observed at the reflection of a self-collimated beam from the surface of a two-dimensional photonic crystal. We describe a method of tuning the shift of the reflected beam in photonic crystals through the modification of the surface, first structurally, as a change in the radius of the surface rods, and then all-optically, with the addition of nonlinear material to the surface layer. We demonstrate all-optical tunability and intensity-dependent control of the beam shift.

  17. Polarization Beam Splitter Based on Self-Collimation Effect in Two-Dimensional Photonics Crystal

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jie; ZHAO De-Yin; ZHOU Chnan-Hong; JIANG Xun-Ya

    2007-01-01

    A photonic crystal polarization beam splitter based on the self-collimation effect is proposed. By means of the plane wave expansion method and the finite-difference time-domain method, we analyse the splitting mechanism in two alternative ways: performing a band gap structure analysis and simulating the field distribution. The results indicate that two beams of different polarizations can be split with an extinction ratio of nearly 20 dB in a wavelength range of 90nm. The splitter may have practical applications in integrated photonic circuits.

  18. Proton-Nucleus Scattering Approximations and Implications for LHC Crystal Collimation

    Energy Technology Data Exchange (ETDEWEB)

    Noble, Robert; /SLAC

    2010-06-07

    In particle accelerators, scattered protons with energies close to the incident particles may travel considerable distances with the beam before impacting on accelerator components downstream. To analyze such problems, angular deflection and energy loss of scattered particles are the main quantities to be simulated since these lead to changes in the beam's phase space distribution and particle loss. Simple approximations for nuclear scattering processes causing limited energy loss to high-energy protons traversing matter are developed which are suitable for rapid estimates and reduced-description Monte Carlo simulations. The implications for proton loss in the Large Hadron Collider due to nuclear scattering on collimation crystals are discussed.

  19. Hydrogen cracking and stress corrosion of pipeline steels. Contribution of the cracking mechanisms study to the understanding of the in-service damage and to the definition of a ranking test; Fissuration assistee par l'hydrogene et corrosion sous contrainte des aciers de pipelines. Apports de l'etude des mecanismes de fissuration a la comprehension de l'endommagement de service et a la definition d'un test de classification

    Energy Technology Data Exchange (ETDEWEB)

    Le Friant, D.

    2000-12-19

    This work is based on the study of the cracking of a French oil transmission pipeline protected by a cathodic protection system. The objective is to identify field parameters, which contribute to the cracks propagation, and to assess changes in the operating conditions, which could lead to a mitigation of the phenomenon. We have focused on the study of the micro-mechanisms by means of slow strain rate tests. Then, cyclic loading tests were carried out to investigate cracks propagation mechanisms. Smooth and pre-notched specimens were tested at free and cathodic potential. Hydrogen is responsible for crack advance through changes in the local steels properties. Such effects take place when two phenomenons occur: favourable conditions for hydrogen entry and, a localisation of hydrogen and its effects. In particular, we have shown the essential role of a dynamic loading in promoting hydrogen entry into the steel (especially at the very crack tip). At cathodic potential, hydrogen-related effects are exacerbated by the presence of MnS inclusions which leads to the initiation of internal cracks (HIC) and to a SOHIC-like crack morphology. At free potential, the lesser amount of available hydrogen give localisation-related effects a greater importance. Cracking is then related to a hydrogen-induced SCC mechanism. Three parameters are involved in the field cracking: operating pressure variations, period of over-protection and a sensitive steels microstructure (MnS). Cathodic protection appears to be the most efficient field parameter to mitigate the phenomenon: it requires a better control of the polarisation level. Finally, a ranking test is outlined from the study of the cracking mechanisms. (author)

  20. Transcriptional program induced by factor VIIa-tissue factor, PAR1 and PAR2 in MDA-MB-231 cells

    DEFF Research Database (Denmark)

    Albrektsen, Tatjana; Sørensen, B B; Hjortø, G M

    2007-01-01

    -activated receptor 1 (PAR1) or PAR2 agonists using MDA-MB-231 breast carcinoma cells that constitutively express TF, PAR1 and PAR2. RESULTS AND CONCLUSIONS: Out of 8500 genes, FVIIa stimulation induced differential regulation of 39 genes most of which were not previously recognized as FVIIa regulated. All genes...... regulated genes encode cytokines, chemokines and growth factors, and the gene repertoire induced by FVIIa in MDA-MB-231 cells is consistent with a role for TF-FVIIa signaling in regulation of a wound healing type of response. Interestingly, a number of genes regulated exclusively by FVIIa/PAR2-mediated cell...... signaling in MDA-MB-231 cells were regulated by thrombin and a PAR1 agonist, but not by FVIIa, in the TF-expressing glioblastoma U373 cell line....

  1. Simultaneous Tc-99m/I-123 Dual Radionuclide Myocardial Perfusion/Innervation Imaging Using Siemens IQ-SPECT with SMARTZOOM Collimator

    OpenAIRE

    Du, Yong; Bhattacharya, Manojeet; Frey, Eric C.

    2014-01-01

    Simultaneous dual-radionuclide myocardial perfusion/innervation SPECT imaging can provide important information about mismatch between scar tissue and denervated regions. The Siemens IQ-SPECT system developed for cardiac imaging uses a multifocal SMARTZOOM collimator to achieve a four-fold sensitivity for the cardiac region compared to a typical parallel-hole low-energy high-resolution collimator but without the data truncation that can result with conventional converging-beam collimators. Th...

  2. Design a freeform microlens array module for any arbitrary-shape collimated beam shaping and color mixing

    Science.gov (United States)

    Chen, Enguo; Wu, Rengmao; Guo, Tailiang

    2014-06-01

    Collimated beam shaping with freeform surface usually employs a predefined mapping to tailor one or multiple freeform surfaces. Limitation on those designs is that the source, the freeform optics and the target are in fixed one-to-one correspondence with each other. To overcome this drawback, this paper presents a kind of freeform microlens array module integrated with an ultra-thin freeform microlens array and a condenser lens to reshape any arbitrary-shape collimated beam into a prescribed uniform rectangular illumination and achieve color mixing. The design theory is explicitly given, and some key issues are addressed. Several different application examples are given, and the target is obtained with high uniformity and energy efficiency. This freeform microlens array module, which shows better flexibility and practicality than the regular designs, can be used not only to reshape any arbitrary-shape collimated beam (or a collimated beam integrated with several sub-collimated beams), but also most importantly to achieve color mixing. With excellent optical performance and ultra-compact volume, this optical module together with the design theory can be further introduced into other applications and will have a huge market potential in the near future.

  3. Collimating Montel mirror as part of a multi-crystal analyzer system for resonant inelastic x-ray scattering

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jungho; Shi, Xianbo; Casa, Diego; Qian, Jun; Huang, XianRong; Gog, Thomas

    2016-07-01

    Advances in resonant inelastic x-ray scattering (RIXS) have come in lockstep with improvements in energy resolution. Currently, the best energy resolution at the Ir-L3 edge stands at ~25 meV, which is achieved using a diced Si spherical analyzer. An angular dispersion analyzer system using multiple flat crystals provides a promising way to achieve higher energy resolution, namely 10 meV or better, thereby overcoming the intrinsic energy resolution limit of diced spherical crystal analyzers. One essential component for a practical use of such multi-crystal systems is the xray collimation optics. In this work, a laterally graded, parabolic collimation Montel mirror was designed with larger than 10 mrad acceptance, collimating the x-ray beam to smaller than 100 μrad divergence at the Ir-L3 absorption energy. The x-ray collimation performance was investigated at beamline 27-ID of the Advanced Photon Source, using incident photons from a Diamond (111) monochromator illuminating a controlled 40 mrad divergence scattering source of 5 μm diameter. A flat Si (111) crystal served as the analyzer. It is found from experimental data and ray-tracing simulations, combined with metrology results, that the manufactured Montel mirror satisfies the required specifications of angular acceptance and collimated x-ray divergence for a high resolution RIXS spectrometer at the Ir-L3 edge.

  4. Angular response of a W-collimated room-temperature-operated CdZnTe Frisch collar spectrometer

    Energy Technology Data Exchange (ETDEWEB)

    Kargar, Alireza [S.M.A.R.T. Laboratory, Department of Mechanical and Nuclear Engineering, Kansas State University, Manhattan, KS 66506 (United States); Jones, Andrew M. [S.M.A.R.T. Laboratory, Department of Mechanical and Nuclear Engineering, Kansas State University, Manhattan, KS 66506 (United States); McNeil, Walter J. [S.M.A.R.T. Laboratory, Department of Mechanical and Nuclear Engineering, Kansas State University, Manhattan, KS 66506 (United States); Harrison, Mark J. [S.M.A.R.T. Laboratory, Department of Mechanical and Nuclear Engineering, Kansas State University, Manhattan, KS 66506 (United States); McGregor, Douglas S. [S.M.A.R.T. Laboratory, Department of Mechanical and Nuclear Engineering, Kansas State University, Manhattan, KS 66506 (United States)]. E-mail: mcgregor@ksu.edu

    2006-06-15

    The spatial resolution of a collimated CdZnTe Frisch collar detector was experimentally investigated for two different tungsten collimator designs using a {sup 198}Au gamma-ray source at 412 keV. A two-dimensional model for the detector-collimator-source geometry was developed and applied with some simplifying assumptions. The CdZnTe detector was fabricated from a single crystal using a copper shim as the Frisch collar. The detector fabrication process is briefly described. Pulse height spectra were collected from {sup 241}Am, {sup 198}Au and {sup 137}Cs using a 3.4x3.4x5.8 mm{sup 3} CdZnTe detector utilizing an insulated Frisch collar mounted inside a tungsten collimator. The resulting energy spectra are presented. Room-temperature energy resolution of 1.72% full-width at half-maximum (FWHM) was obtained for {sup 137}Cs at 662 keV without electronic correction. The two-dimensional model reasonably predicts the angular response of the CdZnTe detectors when inserted into two different collimators.

  5. Taare Zameen Par and dyslexic savants

    Science.gov (United States)

    Chakravarty, Ambar

    2009-01-01

    The film Taare Zameen Par (Stars upon the Ground) portrays the tormented life at school and at home of a child with dyslexia and his eventual success after his artistic talents are discovered by his art teacher at the boarding school. The film hints at a curious neurocognitive phenomenon of creativity in the midst of language disability, as exemplified in the lives of people like Leonardo da Vinci and Albert Einstein, both of whom demonstrated extraordinary creativity even though they were probably affected with developmental learning disorders. It has been hypothesized that a developmental delay in the dominant hemisphere most likely ‘disinhibits’ the nondominant parietal lobe, unmasking talents—artistic or otherwise—in some such individuals. It has been suggested that, in remedial training, children with learning disorders be encouraged to develop such hidden talents to full capacity, rather than be subjected to the usual overemphasis on the correction of the disturbed coded symbol operations. PMID:20142854

  6. Parálisis cerebral Cerebral palsy

    OpenAIRE

    Jorge Malagon Valdez

    2007-01-01

    El término parálisis cerebral (PC) engloba a un gran número de síndromes neurológicos clínicos, de etiología diversa. Estos síndromes se caracterizan por tener una sintomatología común: los trastornos motores. Algunos autores prefieren manejar términos como "encefalopatía fija", "encefalopatías no evolutivas". Se mencionan la utilidad de programas de intervención temprana y métodos especiales de rehabilitación, así como el manejo de las deficiencias asociadas como la epilepsia, deficiencia me...

  7. Taare Zameen Par and dyslexic savants

    Directory of Open Access Journals (Sweden)

    Chakravarty Ambar

    2009-01-01

    Full Text Available The film Taare Zameen Par (Stars upon the Ground portrays the tormented life at school and at home of a child with dyslexia and his eventual success after his artistic talents are discovered by his art teacher at the boarding school. The film hints at a curious neurocognitive phenomenon of creativity in the midst of language disability, as exemplified in the lives of people like Leonardo da Vinci and Albert Einstein, both of whom demonstrated extraordinary creativity even though they were probably affected with developmental learning disorders. It has been hypothesized that a developmental delay in the dominant hemisphere most likely ′disinhibits′ the nondominant parietal lobe, unmasking talents-artistic or otherwise-in some such individuals. It has been suggested that, in remedial training, children with learning disorders be encouraged to develop such hidden talents to full capacity, rather than be subjected to the usual overemphasis on the correction of the disturbed coded symbol operations.

  8. Magnetar Driven Bubbles and the Origin of Collimated Outflows from GRBs

    CERN Document Server

    Bucciantini, N; Arons, J; Metzger, B D; Thompson, Todd A

    2007-01-01

    We model the interaction between the wind from a newly formed rapidly rotating magnetar and the surrounding progenitor. In the first few seconds after core collapse the magnetar inflates a bubble of plasma and magnetic fields behind the supernova shock, which expands asymmetrically because of the pinching effect of the toroidal magnetic field, as in PWNe, even if the host star is spherically symmetric. The degree of asymmetry depends on the ratio of the magnetic energy to the total energy in the bubble. We assume that the wind by newly formed magnetars inflating these bubbles is more magnetized than for PWNe. We show that for a magnetic to total power supplied by the central magnetar $\\sim 0.1$ the bubble expands relatively spherically while for values greater than 0.3, most of the pressure in the bubble is exerted close to the rotation axis, driving a collimated outflow out through the host star. This can account for the collimation inferred from observations of long-duration gamma-ray bursts (GRBs). Given t...

  9. Optical nanostructures in 2D for wide-diameter and broadband beam collimation

    Science.gov (United States)

    Clark, James; Anguita, José V.; Chen, Ying; Silva, S. Ravi P.

    2016-01-01

    Eliminating curved refracting lensing components used in conventional projection, imaging and sensing optical assemblies, is critical to enable compactness and miniaturisation of optical devices. A suitable means is replacing refracting lenses with two-dimensional optical media in flat-slab form, to achieve an equivalent optical result. One approach, which has been the focus of intense research, uses a Veselago lens which features a negative-index metamaterial. However, practical implementations rely on resonance techniques, thus broadband operation at optical frequencies imposes significant technical challenges that have been difficult to overcome. Here, we demonstrate a highly-collimated, broadband, wide-diameter beam from a compact source in flat-slab form, based on light collimation using nanomaterials ordered in patterns and embedded into flexible polymers. These provide a highly anisotropic absorption coefficient due to patterns created by vertical carbon nanotube structures grown on glass, and the anisotropic electrical conductivity of the nanotubes. We show this nanostructure strongly absorbs unwanted off-axis light rays, whilst transmitting the desired on-axis rays, to achieve the required optical effect over broadband, from visible to short-infrared, thus circumventing some technical limitations of negative-index metamaterials. We further show a low substrate-temperature system for nanotube growth, allowing direct implementation into heat-sensitive large-area devices.

  10. Radiative transport produced by oblique illumination of turbid media with collimated beams.

    Science.gov (United States)

    Gardner, Adam R; Kim, Arnold D; Venugopalan, Vasan

    2013-06-01

    We examine the general problem of light transport initiated by oblique illumination of a turbid medium with a collimated beam. This situation has direct relevance to the analysis of cloudy atmospheres, terrestrial surfaces, soft condensed matter, and biological tissues. We introduce a solution approach to the equation of radiative transfer that governs this problem, and develop a comprehensive spherical harmonics expansion method utilizing Fourier decomposition (SHEF(N)). The SHEF(N) approach enables the solution of problems lacking azimuthal symmetry and provides both the spatial and directional dependence of the radiance. We also introduce the method of sequential-order smoothing that enables the calculation of accurate solutions from the results of two sequential low-order approximations. We apply the SHEF(N) approach to determine the spatial and angular dependence of both internal and boundary radiances from strongly and weakly scattering turbid media. These solutions are validated using more costly Monte Carlo simulations and reveal important insights regarding the evolution of the radiant field generated by oblique collimated beams spanning ballistic and diffusely scattering regimes.

  11. Polarization Beam Splitter Based on a Self-Collimation Michelson Interferometer in a Silicon Photonic Crystal

    Institute of Scientific and Technical Information of China (English)

    CHEN Xi-Yao; LIN Gui-Min; LI Jun-Jun; XU Xiao-Fu; JIANG Jun-Zhen; QIANG Ze-Xuan; QIU Yi-Shen; LI Hui

    2012-01-01

    A polarization beam splitter based on a self-collimation Michelson interferometer (SMI) in a hole-type silicon photonic crystal is proposed and numerically demonstrated.Utilizing the polarization dependence of the transmission spectra of the SMI and polarization peak matching method,the SMI can work as a polarization beam splitter (PBS) by selecting an appropriate path length difference in the structure.Based on its novel polarization beam splitting mechanics,the polarization extinction ratios (PERs) for TM and TE modes are as high as 18.4 dB and 24.3 dB,respectively.Since its dimensions are only several operating wavelengths,the PBS may have practical applications in photonic integrated circuits.%A polarization beam splitter based on a self-collimation Michelson interferometer (SMI) in a hole-type silicon photonic crystal is proposed and numerically demonstrated. Utilizing the polarization dependence of the transmission spectra of the SMI and polarization peak matching method, the SMI can work as a polarization beam splitter (PBS) by selecting an appropriate path length difference in the structure. Based on its novel polarization beam splitting mechanics, the polarization extinction ratios (PERs) for TM and TE modes are as high as 18.4 dB and 24.3 dB, respectively. Since its dimensions are only several operating wavelengths, the PBS may have practical applications in photonic integrated circuits.

  12. Interaction of the CERN Large Hadron Collider (LHC) Beam with Carbon Collimators

    CERN Document Server

    Schmidt, R; Hoffmann, Dieter H H; Kadi, Y; Shutov, A; Piriz, AR

    2006-01-01

    The LHC will operate at an energy of 7 TeV with a luminosity of 1034cm-2s-1. This requires two beams, each with 2808 bunches. The energy stored in each beam of 362 MJ. In a previous paper the mechanisms causing equipment damage in case of a failure of the machine protection system was discussed, assuming that the entire beam is deflected into a copper target [1, 2]. Another failure scenario is the deflection of beam into carbon material. Carbon collimators and beam absorbers are installed in many locations around the LHC to diffuse or absorb beam losses. Since the collimator jaws are close to the beam, it is very likely that they are hit first when the beam is accidentally deflected. Here we present the results of two-dimensional hydrodynamic simulations of the heating of a solid carbon cylinder irradiated by the LHC beam with nominal parameters, carried out using the BIG-2 computer code [3] while the energy loss of the 7 TeV protons in carbon is calculated using the well known FLUKA code [4]. Our calculation...

  13. A simple model for the efficient correction of collimator blur in 3D SPECT imaging

    Science.gov (United States)

    Boccacci, P.; Bonetto, P.; Calvini, P.; Formiconi, A. R.

    1999-08-01

    The problem of performing an efficient compensation of collimator blur in the three-dimensional (3D) reconstruction of SPECT data acquired in parallel beam geometry is tackled. An approximate model for data acquisition is developed, which leads to the construction of the corresponding projector-backprojector pair. In order to perform some numerical tests, the model is customized to a state-of-the-art neuro-SPECT scanner, which is supplied with a three-segmented parallel beam collimator. Some reconstruction algorithms based on this customization are presented and their results are compared, in terms of quality and timing requirements, with the outcome generated by the corresponding fully 3D model. According to this numerical simulation, where voxel-driven (back-)projectors are used, the conclusion can be drawn that the approximate model produces reconstructions as good as the ones generated by the fully 3D model in a time which is one order of magnitude shorter. In the case that (back-)projectors based on the rotation of the emission matrix are used, the proposed approximate model is evaluated to be about four times faster than the corresponding fully 3D model.

  14. Implementation of strip-area system model for fan-beam collimator SPECT reconstruction

    Science.gov (United States)

    Ye, Hongwei; Krol, Andrzej; Feiglin, David H.; Lipson, Edward D.; Lee, Wei; Coman, Ioana L.

    2006-03-01

    We have implemented a more accurate physical system representation, a strip-area system model (SASM), for improved fan-beam collimator (FBC) SPECT reconstruction. This approach required implementation of modified ray tracing and attenuation compensation in comparison to a line-length system model (LLSM). We have compared performance of SASM with LLSM using Monte Carlo and analytical simulations of FBC SPECT from a thorax phantom. OSEM reconstruction was performed with OS=3 in a 64×64 matrix with attenuation compensation (assuming uniform attenuation of 0.13 cm -1). Scatter correction and smoothing were not applied. We observe overall improvement in SPECT image bias, visual image quality and an improved hot myocardium contrast for SASM vs. LLSM. In contrast to LLSM, the sensitivity pattern artifacts are not present in the SASM reconstruction. In both reconstruction methods, cross-talk image artifacts (e.g. inverse images of the lungs) can be observed, due to the uniform attenuation map used. SASM applied to fan-beam collimator SPECT results in better image quality and improved hot target contrast, as compared to LLSM, but at the expense of 1.5-fold increase in reconstruction time.

  15. Collimated Fast Wind in the Pre-Planetary Nebula CRL 618

    CERN Document Server

    Lee, Chin-Fei; Sahai, Raghvendra

    2009-01-01

    Collimated fast winds (CFWs) have been proposed to operate during the post-AGB evolutionary phase (and even earlier during the late AGB phase), responsible for the shaping of pre-planetary nebulae (PPNs) and young planetary nebulae (PNs). This paper is a follow-up to our previous study of CFW models for the well-studied PPN CRL 618. Previously, we compared our CFW models with optical observations of CRL 618 in atomic and ionic lines and found that a CFW with a small opening angle can readily reproduce the highly collimated shape of the northwestern (W1) lobe of CRL 618 and the bow-like structure seen at its tip. In this paper, we compare our CFW models with recent observations of CRL 618 in CO J=2-1, J=6-5, and H2 1-0 S(1). In our models, limb-brightened shell structures are seen in CO and H2 at low velocity arising from the shocked AGB wind in the shell, and can be identified as the low-velocity (LV) components in the observations. However, the shell structure in CO J=2-1 is significantly less extended than ...

  16. Design and Performance Optimization of the LHC Collimation System (CERN-THESIS-2006-069)

    CERN Document Server

    Robert-Démolaize, G

    2006-01-01

    The Large Hadron Collider (LHC) is presently under construction at CERN. The LHC is a circular accelerator that stores proton beams and accelerates them to a 7 TeV beam energy. The required bending fields are achieved with super-conducting magnets. The stored proton beams are collided in experimental detectors and produce a design luminosity of 1034 cm−2s−1. Every storage ring encounters unavoidable proton losses. The protons that diffuse into the so-called beam halo can touch accelerator components. In order to avoid quenches of the superconducting magnets, the halo protons must be removed before reaching the magnets. This is achieved with a multi-stage cleaning system, built out of two-sided collimators that are located at adequate positions in the machine. Due to the high stored beam intensity (required for high luminosity), the efficiency of the LHC beam cleaning must be much better than in any other exisiting machine: not more than 0.00002 % of protons hitting the collimators may escape and imp...

  17. Induced radioactivity in a patient-specific collimator used in proton therapy

    CERN Document Server

    Silari, M; Mauro, Egidio; Silari, Marco

    2010-01-01

    This paper discusses the activation of a patient-specific collimator, calculating dose rates, total activities and activities per unit mass of the mixture of radionuclides generated by proton irradiation in the energy range 100-250 MeV. Monte Carlo simulations were first performed for a generic case, using an approximate geometry and on the basis of assumptions on beam intensity and irradiation profile. A collimator used for a prostate cancer treatment was obtained from the MD Anderson Cancer Center (MDACC), Houston, USA, from which a number of samples were cut and analyzed by gamma spectrometry. The results of the gamma spectrometry are compared with the results of Monte Carlo simulations performed using geometrical and irradiation data specific to the unit. The assumptions made for the simulations and their impact on the results are discussed. Dose rate measurements performed in a low-background area at CERN and routine radiation protection measurements at the MDACC are also reported. It is shown that it sh...

  18. Performance evaluation of a parallel-hole collimated detector module for animal SPECT imaging

    Institute of Scientific and Technical Information of China (English)

    HUANG Xian-Chao; WANG Ying-Jie; WEI Long; SHAN Bao-Ci; WANG Bao-Yi; ZHANG Zhi-Ming; LI Dao-Wu; TANG Hao-Hui; LI Ting; LIAO Yan-Fei; LIU Jun-Hui; WANG Pei-Lin; CHEN Yan

    2011-01-01

    We have built and investigated a detector module for animal SPECT imaging,especially for use in large field of view (FOV) conditions.The module consists of a PMT-based detector and a parallel-hole collimator with an effective area of 80 mm × 80 mm.The detector is composed of a NaI scintillation crystal array coupled to four H8500 position sensitive photomultiplier tubes (PS-PMT).The intrinsic energy resolution of the detector is 11.5% at 140 keV on average.The planar spatial resolution of the module changes from 2.2 mm to 5.1 mm at different source-to-collimator distances with an unchanged sensitivity of about 34cps/MBq.Additionally,the SPECT Micro Deluxe Phantom imaging was performed with a radius of rotation (ROR)of 40 mm.Using the FBP reconstruction algorithm,a high performance image was obtained,indicating the feasibility of this detector module.

  19. A quality assurance technique for the static multileaf collimator mode based on intrinsic base lines

    Directory of Open Access Journals (Sweden)

    Kareem Ahmed El-Maraghy

    2014-04-01

    Full Text Available The inspection of the static leaf positions of Multileaf Collimator (MLC devices is essential for safe radiotherapy deliveries in both static and dynamic modes. The purpose of this study was to develop a robust, accurate and generic algorithm to measure the individual static MLC leaf positions. This was performed by extracting leaf tip locations from the radiographic film image and measuring their relative distance from a reference line on the film. The reference line was created with a selected set of MLC leaf sides. The film scaling was created and verified using the physical leaf width. The average measured distance corresponds to a leaf width of 10 mm was 9.95 ± 0.09 mm. The estimated reproducibility of the leaf tips location was ±0.26 mm. The code accuracy was checked by intentionally positioning set of leaves with small errors (1 mm, and the detected deviations from the expected positions ranged from −0.25 mm and +0.32 mm. The algorithm includes two self testing functions in order to detect failures of leaf positioning due to poor film quality and to avoid the potential systematic errors attributable to the improper collimator setting. The code is promising to be more efficient with Gafchromic and Electronic Portal Imaging Device (EPID.

  20. Lumbar spine radiography — poor collimation practices after implementation of digital technology

    Science.gov (United States)

    Zetterberg, L G; Espeland, A

    2011-01-01

    Objectives The transition from analogue to digital radiography may have reduced the motivation to perform proper collimation, as digital techniques have made it possible to mask areas irradiated outside the area of diagnostic interest (ADI). We examined the hypothesis that collimation practices have deteriorated since digitalisation. Methods After defining the ADI, we compared the proportion of the irradiated field outside the ADI in 86 digital and 86 analogue frontal lumbar spine radiographs using the Mann–Whitney test. 50 digital images and 50 analogue images were from a Norwegian hospital and the remainder from a Danish hospital. Consecutive digital images were compared with analogue images (from the hospitals' archives) produced in the 4 years prior to digitalisation. Both hospitals' standard radiographic procedures remained unchanged during the study. For digital images, the irradiated field was assessed using non-masked raw-data images. Results The proportion of the irradiated field outside the ADI was larger in digital than in analogue images (mean 61.7% vs 42.4%, pdigital than in analogue images (791 cm2 vs 541 cm2). Conclusion Following the implementation of digital radiography, considerably larger areas were irradiated. This causes unnecessarily high radiation doses to patients. PMID:21606070