Rapid ionization of the environment of SN 1987A

International Nuclear Information System (INIS)

Raga, A.C.

1987-01-01

It has been suggested by some authors that IUE observations of the supernova SN 1987A show the presence of a strong component of the interstellar C IV 1550 and Si IV 1393 absorption lines at a velocity that approximately corresponds to the velocity of the LMC. It is possible that this component might come from originally neutral (or at least not very highly ionized) gas which has been photoionized by the initially very strong ionizing radiation field of the supernova. Theoretical considerations of this scenario lead to the study of fast (with velocities of about c) ionization fronts. It is shown that for reasonable model parameters it is possible to obtain considerably large C IV column densities, in agreement with the IUE observations. On the other hand, the models do not so easily predict the large Si IV column densities that are also obtained from the IUE observations. It is found that only models in which the interstellar medium surrounding SN 1987A is initially composed of already ionized hydrogen and helium predict substantial Si IV column densities. This result provides an interesting prediction of the ionization state of the environment of the presupernova star. 9 references

Rapid ionization of the environment of SN 1987A

Science.gov (United States)

Raga, A. C.

1987-01-01

It has been suggested by some authors that IUE observations of the supernova SN 1987A show the presence of a strong component of the interstellar C IV 1550 and Si IV 1393 absorption lines at a velocity that approximately corresponds to the velocity of the LMC. It is possible that this component might come from originally neutral (or at least not very highly ionized) gas which has been photoionized by the initially very strong ionizing radiation field of the supernova. Theoretical considerations of this scenario lead to the study of fast (with velocities of about c) ionization fronts. It is shown that for reasonable model parameters it is possible to obtain considerably large C IV column densities, in agreement with the IUE observations. On the other hand, the models do not so easily predict the large Si IV column densities that are also obtained from the IUE observations. It is found that only models in which the interstellar medium surrounding SN 1987A is initially composed of already ionized hydrogen and helium predict substantial Si IV column densities. This result provides an interesting prediction of the ionization state of the environment of the presupernova star.

Large single-crystal diamond substrates for ionizing radiation detection

Energy Technology Data Exchange (ETDEWEB)

Girolami, Marco; Bellucci, Alessandro; Calvani, Paolo; Trucchi, Daniele M. [Istituto di Struttura della Materia (ISM), Consiglio Nazionale delle Ricerche (CNR), Sede Secondaria di Montelibretti, Monterotondo Stazione, Roma (Italy)

2016-10-15

The need for large active volume detectors for ionizing radiations and particles, with both large area and thickness, is becoming more and more compelling in a wide range of applications, spanning from X-ray dosimetry to neutron spectroscopy. Recently, 8.0 x 8.0 mm{sup 2} wide and 1.2 mm thick single-crystal diamond plates have been put on the market, representing a first step to the fabrication of large area monolithic diamond detectors with optimized charge transport properties, obtainable up to now only with smaller samples. The more-than-double thickness, if compared to standard plates (typically 500 μm thick), demonstrated to be effective in improving the detector response to highly penetrating ionizing radiations, such as γ-rays. Here we report on the first measurements performed on large active volume single-crystal diamond plates, both in the dark and under irradiation with optical wavelengths (190-1100 nm), X-rays, and radioactive γ-emitting sources ({sup 57}Co and {sup 22}Na). (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Increasing the applicability of density functional theory. V. X-ray absorption spectra with ionization potential corrected exchange and correlation potentials

Energy Technology Data Exchange (ETDEWEB)

Verma, Prakash; Bartlett, Rodney J., E-mail: bartlett@qtp.ufl.edu [Quantum Theory Project, University of Florida, Gainesville, Florida 32611 (United States)

2016-07-21

Core excitation energies are computed with time-dependent density functional theory (TD-DFT) using the ionization energy corrected exchange and correlation potential QTP(0,0). QTP(0,0) provides C, N, and O K-edge spectra to about an electron volt. A mean absolute error (MAE) of 0.77 and a maximum error of 2.6 eV is observed for QTP(0,0) for many small molecules. TD-DFT based on QTP (0,0) is then used to describe the core-excitation spectra of the 22 amino acids. TD-DFT with conventional functionals greatly underestimates core excitation energies, largely due to the significant error in the Kohn-Sham occupied eigenvalues. To the contrary, the ionization energy corrected potential, QTP(0,0), provides excellent approximations (MAE of 0.53 eV) for core ionization energies as eigenvalues of the Kohn-Sham equations. As a consequence, core excitation energies are accurately described with QTP(0,0), as are the core ionization energies important in X-ray photoionization spectra or electron spectroscopy for chemical analysis.

Increasing the applicability of density functional theory. V. X-ray absorption spectra with ionization potential corrected exchange and correlation potentials.

Science.gov (United States)

Verma, Prakash; Bartlett, Rodney J

2016-07-21

Core excitation energies are computed with time-dependent density functional theory (TD-DFT) using the ionization energy corrected exchange and correlation potential QTP(0,0). QTP(0,0) provides C, N, and O K-edge spectra to about an electron volt. A mean absolute error (MAE) of 0.77 and a maximum error of 2.6 eV is observed for QTP(0,0) for many small molecules. TD-DFT based on QTP (0,0) is then used to describe the core-excitation spectra of the 22 amino acids. TD-DFT with conventional functionals greatly underestimates core excitation energies, largely due to the significant error in the Kohn-Sham occupied eigenvalues. To the contrary, the ionization energy corrected potential, QTP(0,0), provides excellent approximations (MAE of 0.53 eV) for core ionization energies as eigenvalues of the Kohn-Sham equations. As a consequence, core excitation energies are accurately described with QTP(0,0), as are the core ionization energies important in X-ray photoionization spectra or electron spectroscopy for chemical analysis.

Impact ionization in GaAs: A screened exchange density-functional approach

International Nuclear Information System (INIS)

Picozzi, S.; Asahi, R.; Geller, C.B.; Continenza, A.; Freeman, A.J.

2001-01-01

Results are presented of a fully ab initio calculation of impact ionization rates in GaAs within the density functional theory framework, using a screened-exchange formalism and the highly precise all-electron full-potential linearized augmented plane wave method. The calculated impact ionization rates show a marked orientation dependence in k space, indicating the strong restrictions imposed by the conservation of energy and momentum. This anisotropy diminishes as the impacting electron energy increases. A Keldysh type fit performed on the energy-dependent rate shows a rather soft edge and a threshold energy greater than the direct band gap. The consistency with available Monte Carlo and empirical pseudopotential calculations shows the reliability of our approach and paves the way to ab initio calculations of pair production rates in new and more complex materials

Ionization Potentials of Chemical Warfare Agents and Related Compounds Determined with Density Functional Theory

National Research Council Canada - National Science Library

Wright, J

2000-01-01

...) agents at contaminated sites. Reported herein are theoretical ionization potentials for CW agents and their related compounds calculated using density functional theory at the B3LYP/6-311+G(2d,p) level of theory...

Studies on the propagation of relativistic plasma waves in high density plasmas produced by hypersonic ionizing shock waves

International Nuclear Information System (INIS)

Williams, R.L.; Johnson, J.A. III

1993-01-01

The feasibility of using an ionizing shock wave to produce high density plasmas suitable for the propagation large amplitude relativistic plasma waves is being investigated. A 20 kv arc driven shock tube of coaxial geometry produces a hypersonic shock wave (10 p > 10 17 cm -3 ). The shock can be made to reflect off the end of the tube, collide with its wake, and thus increase the plasma density further. After reflecting, the plasma is at rest. The shock speed is measured using piezoelectric pressure probes and the ion density is measured using laser induced fluorescence (LIF) techniques on argon 488.0 nm and 422.8 nm lines. The future plans are to excite large amplitude relativistic plasma waves in this plasma by either injecting a short pulse laser (Laser Wake Field Scheme), two beating lasers (Plasma Beat Wave Scheme), or a short bunch of relativistic electrons (Plasma Wake Field Scheme). Results of recent computational and theoretical studies, as well as initial experimental measurements on the plasma using LIF, are reported. Implications for the application of high density plasmas produced in this way to such novel schemes as the plasma wave accelerator, photon accelerator, plasma wave undulator, and also plasma lens, are discussed. The effect of plasma turbulence is also discussed

Simulation of ionization effects for high-density positron drivers in future plasma wakefield experiments

International Nuclear Information System (INIS)

Bruhwiler, D.L.; Dimitrov, D.A.; Cary, J.R.; Esarey, E.; Leemans, W.P.

2003-01-01

The plasma wakefield accelerator (PWFA) concept has been proposed as a potential energy doubler for present or future electron-positron colliders. Recent particle-in-cell (PIC) simulations have shown that the self-fields of the required electron beam driver can tunnel ionize neutral Li, leading to plasma wake dynamics differing significantly from that of a preionized plasma. It has also been shown, for the case of a preionized plasma, that the plasma wake of a positron driver differs strongly from that of an electron driver. We will present new PIC simulations, using the OOPIC code, showing the effects of tunneling ionization on the plasma wake generated by high-density positron drivers. The results will be compared to previous work on electron drivers with tunneling ionization and positron drivers without ionization. Parameters relevant to the energy doubler and the upcoming E-164x experiment at the Stanford Linear Accelerator Center will be considered

On the ionization and burnout processes of a magnetically confined plasma

International Nuclear Information System (INIS)

Lehnert, B.

1977-10-01

The particle and heat balance during plasma start-up are investigates, to specify the conditions for reaching various ion density ranges and high plasma temperatures in cases of a limited heating power. Particular attention is paid to the permeable-impermeable transition regime of plasmas being subject to Ohmic heating and confined in closed or open bottles with a main poloidal field. The ionization and burnout conditions are found to depend critically on the confinement and the filling density. They become optimal in closed bottles under symmetric and stable conditions, where the transition into a fully ionized state should be reached even at moderately large ionization rates, burnout powers and currents. Start-up methods based on constant as well as on variable filling densities are discussed as means of ion density control.(author)

Ion density in ionizing beams

International Nuclear Information System (INIS)

Knuyt, G.K.; Callebaut, D.K.

1978-01-01

The equations defining the ion density in a non-quasineutral plasma (chasma) are derived for a number of particular cases from the general results obtained in paper 1. Explicit calculations are made for a fairly general class of boundaries: all tri-axial ellipsoids, including cylinders with elliptic cross-section and the plane parallel case. The results are very simple. When the ion production and the beam intensity are constant then the steady state ion space charge is also constant in space, it varies over less than 10% for the various geometries, it may exceed the beam density largely for comparatively high pressures (usually still less than about 10 -3 Torr), it is tabulated for a number of interesting cases and moreover it can be calculated precisely and easily by some simple formulae for which also approximations are elaborated. The total potential is U =-ax 2 -by 2 -cz 2 , a, b and c constants which can be calculated immediately from the space charge density and the geometry; the largest coefficient varies at most over a factor four for various geometries; it is tabulated for a number of interesting cases. (author)

Assessment of Real-Time Time-Dependent Density Functional Theory (RT-TDDFT) in Radiation Chemistry: Ionized Water Dimer.

Science.gov (United States)

Chalabala, Jan; Uhlig, Frank; Slavíček, Petr

2018-03-29

Ionization in the condensed phase and molecular clusters leads to a complicated chain of processes with coupled electron-nuclear dynamics. It is difficult to describe such dynamics with conventional nonadiabatic molecular dynamics schemes since the number of states swiftly increases as the molecular system grows. It is therefore attractive to use a direct electron and nuclear propagation such as the real-time time-dependent density functional theory (RT-TDDFT). Here we report a RT-TDDFT benchmark study on simulations of singly and doubly ionized states of a water monomer and dimer as a prototype for more complex processes in a condensed phase. We employed the RT-TDDFT based Ehrenfest molecular dynamics with a generalized gradient approximate (GGA) functional and compared it with wave-function-based surface hopping (SH) simulations. We found that the initial dynamics of a singly HOMO ionized water dimer is similar for both the RT-TDDFT/GGA and the SH simulations but leads to completely different reaction channels on a longer time scale. This failure is attributed to the self-interaction error in the GGA functionals and it can be avoided by using hybrid functionals with large fraction of exact exchange (represented here by the BHandHLYP functional). The simulations of doubly ionized states are reasonably described already at the GGA level. This suggests that the RT-TDDFT/GGA method could describe processes following the autoionization processes such as Auger emission, while its applicability to more complex processes such as intermolecular Coulombic decay remains limited.

Local clouds ionization, temperatures, electron densities and interfaces, from GHRS and IMAPS spectra of epsilon Canis Majoris

CERN Document Server

Gry, C; Gry, Cecile; Jenkins, Edward B.

2001-01-01

The composition and physical properties of several local clouds, including the Local Interstellar Cloud (LIC) in which the Sun is embedded, are derived from absorption features in the UV spectrum of the star epsilon CMa. We derive temperatures and densities for three components by combining our interpretations of the ionization balance of magnesium and the relative population of C II in an excited fine-structure level. We find that for the LIC n(e) = 0.12 +/-0.05 cm-3 and T = 7000 +/-1200 K. We derive the ionization fractions of hydrogen and discuss the ionizing processes. In particular the hydrogen and helium ionizations in the LIC are compatible with photoionization by the local EUV radiation fields from the hot stars and the cloud interface with the hot gas. We confirm the detection of high ionization species : Si III is detected in all clouds and C IV in two of them, including the LIC, suggesting the presence of ionized interfaces around the local clouds.

Ring magnetron ionizer

International Nuclear Information System (INIS)

Alessi, J.G.

1986-01-01

A ring magnetron D - charge exchange ionizer has been built and tested. An H - current of 500 μA was extracted with an estimated H 0 density in the ionizer of 10 12 cm -3 . This exceeds the performance of ionizers presently in use on polarized H - sources. The ionizer will soon be tested with a polarized atomic beam

Self-interaction error in density functional theory: a mean-field correction for molecules and large systems

International Nuclear Information System (INIS)

Ciofini, Ilaria; Adamo, Carlo; Chermette, Henry

2005-01-01

Corrections to the self-interaction error which is rooted in all standard exchange-correlation functionals in the density functional theory (DFT) have become the object of an increasing interest. After an introduction reminding the origin of the self-interaction error in the DFT formalism, and a brief review of the self-interaction free approximations, we present a simple, yet effective, self-consistent method to correct this error. The model is based on an average density self-interaction correction (ADSIC), where both exchange and Coulomb contributions are screened by a fraction of the electron density. The ansatz on which the method is built makes it particularly appealing, due to its simplicity and its favorable scaling with the size of the system. We have tested the ADSIC approach on one of the classical pathological problem for density functional theory: the direct estimation of the ionization potential from orbital eigenvalues. A large set of different chemical systems, ranging from simple atoms to large fullerenes, has been considered as test cases. Our results show that the ADSIC approach provides good numerical values for all the molecular systems, the agreement with the experimental values increasing, due to its average ansatz, with the size (conjugation) of the systems

Localized electron density enhancements in the high-altitude polar ionosphere and their relationships with storm-enhanced density (SED plumes and polar tongues of ionization (TOI

Directory of Open Access Journals (Sweden)

Y. Kitanoya

2011-02-01

Full Text Available Events of localized electron density increase in the high-altitude (>3000 km polar ionosphere are occasionally identified by the thermal plasma instruments on the Akebono satellite. In this paper, we investigate the vertical density structure in one of such events in detail using simultaneous observations by the Akebono and DMSP F15 satellites, the SuperDARN radars, and a network of ground Global Positioning System (GPS receivers, and the statistical characteristics of a large number (>10 000 of such events using Akebono data over half of an 11-year solar cycle. At Akebono altitude, the parallel drift velocity is remarkably low and the O+ ion composition ratio remarkably high, inside the high plasma-density regions at high altitude. Detailed comparisons between Akebono, DMSP ion velocity and density, and GPS total electron content (TEC data suggest that the localized plasma density increase observed at high altitude on Akebono was likely connected with the polar tongue of ionization (TOI and/or storm enhanced density (SED plume observed in the F-region ionosphere. Together with the SuperDARN plasma convection map these data suggest that the TOI/SED plume penetrated into the polar cap due to anti-sunward convection and the plume existed in the same convection channel as the dense plasma at high altitude; in other words, the two were probably connected to each other by the convecting magnetic field lines. The observed features are consistent with the observed high-density plasma being transported from the mid-latitude ionosphere or plasmasphere and unlikely a part of the polar wind population.

New upper limits on the local metagalactic ionizing radiation density

Science.gov (United States)

Vogel, Stuart N.; Weymann, Ray; Rauch, Michael; Hamilton, Tom

1995-01-01

We have obtained H-alpha observations with the Maryland-Caltech Fabry-Perot Spectrometer attached to the Cassegrain focus of the 1.5 m telescope at Palomer Observatory in order to set limits on the number of ionizing photons from the local metagalactic radiation field. We have observed the SW component of the Haynes-Giovanelli cloud H I 1225+01, an intergalactic cloud which should be optimum for measuring the metagalactic flux because it is nearly opaque to ionizing photons, it does not appear to be significantly shielded from the metagalactic radiation field, and the limits on embedded or nearby ionizing sources are unusually low. For the area of the cloud with an H I column density greater than 10(exp 19)/sq cm we set a 2 sigma limit of 1.1 x 10(exp -19) ergs/sq cm/s/sq arcsec (20 mR) for the surface brightness of diffuse H-alpha. This implies a 2 sigma upper limit on the incident one-sided ionizing flux of Phi(sub ex) is less than 3 x 10(exp 4)/sq cm/s. For a radiation field of the form J(sub nu) is approximately nu(exp -1.4), this yields a firm 2 sigma upper limit on the local metagalactic photoionization rate of Gamma is less than 2 x 10(exp -13)/s, and an upper limit for the radiation field J(sub nu) at the Lyman limit of J(sub nu0) is less than 8 x 10(exp -23) ergs/sq cm/Hz/sr. We discuss previous efforts to constrain the metagalactic ionizing flux using H-alpha surface brightness observations and also other methods, and conclude that our result places the firmest upper limit on this flux. We also observed the 7 min diameter region centered on 3C 273 in which H-alpha emission at a velocity of approximately 1700 km/s was initially reported by Williams and Schommer. In agreement with T. B. Williams (private communication) we find the initial detection was spurious. We obtain a 2 sigma upper limit of 1.8 x 10(exp -19) ergs/sq cm/s/sq arcsec (32 mR) for the mean surface brightness of diffuse H-alpha, about a factor of 6 below the published value.

Ionization of cloud and intercloud hydrogen by O and B stars

International Nuclear Information System (INIS)

Elmergreen, B.G.

1975-01-01

Lyman continuum radiation from OB stars may be the primary source of ionization of interstellar hydrogen. Eighty percent of Lyman continuum photons produced by these stars comes from a very small number of 05 and 06 stars, however, and if this radiation is ionized to interstellar hydrogen with the high degree of uniformity indicated by pulsar dispersion measures or by the diffuse background of Hα emission, then each 05 or 06 star must be able to maintain an H II region over a distance of several hundred parsecs. The cloudy structure of interstellar space prevents such long range ionization, however, and a large fraction of the stellar Lyman continuum photons will be converted to Balmer photons in the high-density ionized surfaces of the exposed clouds. Two questions concerning this cloudy obscuration naturally arise: what will be the consequences of a cloud's exposure to Lyman continuum radiation, and to what extent can low-density, intercloud hydrogen be ionized in the obscured regions. These questions are considered

Simulation study of the ionizing front in the critical ionization velocity phenomenon

International Nuclear Information System (INIS)

Machida, S.; Goertz, C.K.; Lu, G.

1988-01-01

Simulations of the Critical Ionization Velocity (CIV) for a neutral gas cloud moving across the static magnetic field are made. We treat a low-β plasma and use a 2-1/2 D electrostatic code linked with our Plasma and Neutral Interaction Code (PANIC). Our study is focused on the understanding of the interface between the neutral gas cloud and the surrounding plasma where the strong interaction takes place. We assume the existence of some hot electrons in the ambient plasma to provide a seed ionization for CIV. When the ionization starts a sheath-like structure is formed at the surface of the neutral gas (Ionizing Front). In that region the crossfield component of the electric field causes the electron to E x B drift with a velocity of the order of the neutral gas velocity times the square root of the ion to electron mass ratio. Thus the kinetic energy of the drifting electrons can be large enough for electron impact ionization. In addition a diamagnetic drift of the electron occurs due to the number density and temperature inhomogeneity in the ionization front. These drift currents excite the lower-hybrid waves with the wave k-vectors almost perpendicular to the neutral flow and magnetic field again resulting in electron heating and additional ionization. The overall structure is studied by developing a simple analytic model as well as making simulation runs. (author)

Ionized gas at the edge of the central molecular zone

Science.gov (United States)

Langer, W. D.; Goldsmith, P. F.; Pineda, J. L.; Velusamy, T.; Requena-Torres, M. A.; Wiesemeyer, H.

2015-04-01

Context. The edge of the central molecular zone (CMZ) is the location where massive dense molecular clouds with large internal velocity dispersions transition to the surrounding more quiescent and lower CO emissivity region of the Galaxy. Little is known about the ionized gas surrounding the molecular clouds and in the transition region. Aims: We determine the properties of the ionized gas at the edge of the CMZ near Sgr E using observations of N+ and C+. Methods: We observed a small portion of the edge of the CMZ near Sgr E with spectrally resolved [C ii] 158 μm and [N ii] 205 μm fine structure lines at six positions with the GREAT instrument on SOFIA and in [C ii] using Herschel HIFI on-the-fly strip maps. We use the [N ii] spectra along with a radiative transfer model to calculate the electron density of the gas and the [C ii] maps to illuminate the morphology of the ionized gas and model the column density of CO-dark H2. Results: We detect two [C ii] and [N ii] velocity components, one along the line of sight to a CO molecular cloud at - 207 km s-1 associated with Sgr E and the other at -174 km s-1 outside the edge of another CO cloud. From the [N ii] emission we find that the average electron density is in the range of ~5 to 21 cm-3 for these features. This electron density is much higher than that of the disk's warm ionized medium, but is consistent with densities determined for bright diffuse H ii nebula. The column density of the CO-dark H2 layer in the -207 km s-1 cloud is ~1-2 × 1021 cm-2 in agreement with theoretical models. The CMZ extends further out in Galactic radius by ~7 to 14 pc in ionized gas than it does in molecular gas traced by CO. Conclusions: The edge of the CMZ likely contains dense hot ionized gas surrounding the neutral molecular material. The high fractional abundance of N+ and high electron density require an intense EUV field with a photon flux of order 106 to 107 photons cm-2 s-1, and/or efficient proton charge exchange with

The dependence of C IV broad absorption line properties on accompanying Si IV and Al III absorption: relating quasar-wind ionization levels, kinematics, and column densities

Energy Technology Data Exchange (ETDEWEB)

Filiz Ak, N.; Brandt, W. N.; Schneider, D. P.; Trump, J. R. [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States); Hall, P. B. [Department of Physics and Astronomy, York University, 4700 Keele Street, Toronto, Ontario M3J 1P3 (Canada); Anderson, S. F. [Astronomy Department, University of Washington, Seattle, WA 98195 (United States); Hamann, F. [Department of Astronomy, University of Florida, Gainesville, FL 32611-2055 (United States); Myers, Adam D. [Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States); Pâris, I. [Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago (Chile); Petitjean, P. [Institut d' Astrophysique de Paris, Universite Paris 6, F-75014 Paris (France); Ross, Nicholas P. [Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Shen, Yue [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); York, Don, E-mail: nfilizak@astro.psu.edu [Department of Astronomy and Astrophysics, The University of Chicago, Chicago, IL 60637 (United States)

2014-08-20

We consider how the profile and multi-year variability properties of a large sample of C IV Broad Absorption Line (BAL) troughs change when BALs from Si IV and/or Al III are present at corresponding velocities, indicating that the line of sight intercepts at least some lower ionization gas. We derive a number of observational results for C IV BALs separated according to the presence or absence of accompanying lower ionization transitions, including measurements of composite profile shapes, equivalent width (EW), characteristic velocities, composite variation profiles, and EW variability. We also measure the correlations between EW and fractional-EW variability for C IV, Si IV, and Al III. Our measurements reveal the basic correlated changes between ionization level, kinematics, and column density expected in accretion-disk wind models; e.g., lines of sight including lower ionization material generally show deeper and broader C IV troughs that have smaller minimum velocities and that are less variable. Many C IV BALs with no accompanying Si IV or Al III BALs may have only mild or no saturation.

Line intensity ratios of helium atom in an ionizing plasma

International Nuclear Information System (INIS)

Sasaki, Satoshi; Goto, Motoshi; Kato, Takako; Takamura, Shuichi

1998-10-01

Effective emission rate coefficients C em eff (λ), line intensity ratios, C em eff (λ 1 )/C em eff (λ 2 ), and S eff /C em eff (λ), with S eff the ionization rate coefficient, are obtained by the collisional radiative model for an ionizing plasma using new excitation and ionization rate coefficients. In the plasma with electron density n e > 10 4 cm -3 , C em eff (λ) for various lines are enlarged, since the normalized population densities for the metastable states, n(2 1,3 S)/n He , becomes large, and the excitation rate coefficients from 2 1,3 S, C 21,3S→i , are large compared to that from the ground state C 11S→i . In high n e plasma (n e > 10 12 cm -3 ), with frequent electron impacts on the excited heliums, n(i)/n He become constant to n e , which results in the decrease of C em eff (λ). Hot electrons and resonance scattering, which are often important for the experimental applications, are included in this model. A small amount of hot electrons (several percents) can enhance the line emission and ionization rates for low electron temperature plasma with T e (T e 1 S - n 1 P) and enlarges n 1 P and 2 1 S populations when the column density of helium gas n He x L exceeds 2x10 13 [cm -2 ]. (author)

Development of a spatially uniform fast ionization wave in a large-volume discharge

International Nuclear Information System (INIS)

Zatsepin, D.V.; Starikovskaya, S.M.; Starikovskii, A.Yu.

1998-01-01

A study is made of a high-voltage nanosecond breakdown in the form of a fast ionization wave produced in a large-volume (401) discharge chamber. The propagation speed of the wave front and the integral energy deposition in a plasma are measured for various regimes of the air discharge at pressures of 10 -2 -4 Torr. A high degree of both the spatial uniformity of the discharge and the reproducibility of the discharge parameters is obtained. The possibility of the development of a fast ionization wave in an electrodeless system is demonstrated. A transition of the breakdown occurring in the form of a fast ionization wave into the streamer breakdown is observed. It is shown that such discharges are promising for technological applications

Current-voltage characteristic of parallel-plane ionization chamber with inhomogeneous ionization

International Nuclear Information System (INIS)

Stoyanov, D G

2007-01-01

The balances of particles and charges in the volume of parallel-plane ionization chamber are considered. Differential equations describing the distribution of current densities in the chamber volume are obtained. As a result of the differential equations solution an analytical form of the current-voltage characteristic of parallel-plane ionization chamber with inhomogeneous ionization in the volume is obtained

Current-voltage characteristic of parallel-plane ionization chamber with inhomogeneous ionization

Energy Technology Data Exchange (ETDEWEB)

Stoyanov, D G [Faculty of Engineering and Pedagogy in Sliven, Technical University of Sofia, 59, Bourgasko Shaussee Blvd, 8800 Sliven (Bulgaria)

2007-08-15

The balances of particles and charges in the volume of parallel-plane ionization chamber are considered. Differential equations describing the distribution of current densities in the chamber volume are obtained. As a result of the differential equations solution an analytical form of the current-voltage characteristic of parallel-plane ionization chamber with inhomogeneous ionization in the volume is obtained.

A novel method for producing multiple ionization of noble gas

International Nuclear Information System (INIS)

Wang Li; Li Haiyang; Dai Dongxu; Bai Jiling; Lu Richang

1997-01-01

We introduce a novel method for producing multiple ionization of He, Ne, Ar, Kr and Xe. A nanosecond pulsed electron beam with large number density, which could be energy-controlled, was produced by incidence a focused 308 nm laser beam onto a stainless steel grid. On Time-of-Flight Mass Spectrometer, using this electron beam, we obtained multiple ionization of noble gas He, Ne, Ar and Xe. Time of fight mass spectra of these ions were given out. These ions were supposed to be produced by step by step ionization of the gas atoms by electron beam impact. This method may be used as a ideal soft ionizing point ion source in Time of Flight Mass Spectrometer

Positive streamers in air of varying density : experiments on the scaling of the excitation density

NARCIS (Netherlands)

Dubrovin, D.; Nijdam, S.; Clevis, T.T.J.; Heijmans, L.C.J.; Ebert, U.; Yair, Y.; Price, C.

2015-01-01

Streamers are rapidly extending ionized finger-like structures that dominate the initial breakdown of large gas volumes in the presence of a sufficiently strong electric field. Their macroscopic parameters are described by simple scaling relations, where the densities of electrons and of excited

Optical observations on critical ionization velocity experiments in space

International Nuclear Information System (INIS)

Stenbaek-Nielsen, H.C.

1993-01-01

A number of Critical Ionization Velocity (CIV) experiments have been performed in space. CIV has been observed in laboratory experiments, but experiments in space have been inconclusive. Most space experiments have used barium which ionizes easily, and with emission lines from both neutrals and ions in the visible optical observations can be made from the ground. Also other elements, such as xenon, strontium and calcium, have been used. High initial ionization in some barium release experiments has been claimed due to CIV. However, a number of reactions between barium and the ambient plasma have been suggested as more likely processes. Currently the most popular process in this debate is charge exchange with O + . This process has a large cross section, but is it large enough? The cross section for charge exchange with calcium should be even larger, but in a double release of barium and calcium (part of the NASA CRRES release experiments) most ionization was observed from the barium release. Moreover, if charge exchange is the dominant process, the amount of ionization should relate to the oxygen ion density, and that does not appear to be the case. Other processes, such as associative ionization, have also been proposed, but yields are uncertain because the reaction rates are very poorly known

[Ionization energies and infrared spectra studies of histidine using density functional theory].

Science.gov (United States)

Hu, Qiong; Wang, Guo-Ying; Liu, Gang; Ou, Jia-Ming; Wang, Rui-Li

2010-05-01

Histidines provide axial ligands to the primary electron donors in photosynthetic reaction centers (RCs) and play an important role in the protein environments of these donors. In this paper the authors present a systematic study of ionization energies and vibrational properties of histidine using hybrid density functional theory (DFT). All calculations were undertaken by using B3LYP method in combination with four basis sets: 6-31G(d), 6-31G(df, p), 6-31+G(d) and 6-311+G(2d, 2p) with the aim to investigate how the basis sets influence the calculation results. To investigate solvent effects and gain a detailed understanding of marker bands of histidine, the ionization energies of histidine and the vibrational frequencies of histidine which are unlabeled and 13C, 15N, and 2H labeled in the gas phase, CCl4, protein environment, THF and water solution, which span a wide range of dielectric constant, were also calculated. Our results showed that: (1) The main geometry parameters of histidine were impacted by basis sets and mediums, and C2-N3 and N3-C4 bond of imidazole ring of histidine side chain display the maximum bond lengths in the gas phase; (2) single point energies and frequencies calculated were decreased while ionization energies increased with the increasing level of basis sets and diffuse function applied in the same solvent; (3) with the same computational method, the higher the dielectric constant of the solvent used, the lower the ionization energy and vibrational frequency and the higher the intensity obtained. In addition, calculated ionization energy in the gas phase and marker bands of histidine as well as frequency shift upon 13C and 15N labeling at the computationally more expensive 6-311+G(2d, 2p) level are in good agreement with experimental observations available in literatures. All calculations indicated that the results calculated by using higher level basis set with diffuse function were more accurate and closer to the experimental value. In

Simultaneous atomization and ionization of large organic molecules using femtosecond laser ablation

International Nuclear Information System (INIS)

Kurata-Nishimura, Mizuki; Tokanai, Fuyuki; Matsuo, Yukari; Kobayashi, Tohru; Kawai, Jun; Kumagai, Hiroshi; Midorikawa, Katsumi; Tanihata, Isao; Hayashizaki, Yoshihide

2002-01-01

We have experimentally demonstrated femtosecond laser ablation for simultaneous atomization and ionization (fs-SAI) of organic molecules on solid substrates. We find most of the constituent atoms of organic molecules are atomized and ionized non-resonantly by femtosecond laser ablation. This observation is in contrast with that for the photoionization of cyclic aromatic hydrocarbons by femtosecond laser in the gas phase where little fragmentation has been observed. Crucial contribution of ablation plasma of solid sample to fs-SAI process is suggested. The ratio of natural abundance of stable isotopes contained in sample molecules is well reproduced, which confirms fs-SAI can be applied to the quantitative chemical analysis of isotope-labeled large organic molecules

Multiple neutral density measurements in the lower thermosphere with cold-cathode ionization gauges

Science.gov (United States)

Lehmacher, G. A.; Gaulden, T. M.; Larsen, M. F.; Craven, J. D.

2013-01-01

Cold-cathode ionization gauges were used for rocket-borne measurements of total neutral density and temperature in the aurorally forced lower thermosphere between 90 and 200 km. A commercial gauge was adapted as a low-cost instrument with a spherical antechamber for measurements in molecular flow conditions. Three roll-stabilized payloads on different trajectories each carried two instruments for measurements near the ram flow direction along the respective upleg and downleg segments of a flight path, and six density profiles were obtained within a period of 22 min covering spatial separations up to 200 km. The density profiles were integrated below 125 km to yield temperatures. The mean temperature structure was similar for all six profiles with two mesopause minima near 110 and 101 km, however, for the downleg profiles, the upper minimum was warmer and the lower minimum was colder by 20-30 K indicating significant variability over horizontal scales of 100-200 km. The upper temperature minimum coincided with maximum horizontal winds speeds, exceeding 170 m/s.

Collisional ionization

International Nuclear Information System (INIS)

Arnaud, M.

1985-07-01

In low density, thin plasmas (such as stellar coronae, interstellar medium, intracluster medium) the ionization process is governed by collision between electrons and ions in their ground state. In view of the recent improvements we thought an updating of ionization rates was really needed. The work is based on both experimental data and theoretical works and give separate estimates for the direct and autoionization rates

Laser-supported ionization wave in under-dense gases and foams

International Nuclear Information System (INIS)

Gus'kov, S. Yu.; Limpouch, J.; Nicolaie, Ph.; Tikhonchuk, V. T.

2011-01-01

Propagation of laser-supported ionization wave in homogeneous and porous materials with a mean density less than the critical plasma density is studied theoretically in the one-dimensional geometry. It is shown that the velocity of the ionization wave in a foam is significantly decreased in comparison with the similar wave in a homogeneous fully ionized plasma of the same density. That difference is attributed to the ionization and hydro-homogenization processes forming an under-critical density environment in the front of ionization wave. The rate of energy transfer from laser to plasma is found to be in a good agreement with available experimental data.

Propagation of ionizing waves in glow discharge

International Nuclear Information System (INIS)

Suzuki, T.

1977-01-01

Ionizing waves were produced along the positive column of a glow discharge in air by applying an impulse voltage to an electrode at one end of the column. Five photomultipliers and three current-sensing coils were used to observe how the waves were affected by the rise time and the magnitude of the applied impulses and by the electron density in the positive column of the glow discharge. It is shown that the speed of the ionizing waves increases with the slope of the applied impulses and with the preexisting electron density. The electron density is augmented about 100--200 times due to the buildup of ionization at the front of the waves. The theory was developed to explain the property of ionizing waves

Study of combinations of TL/OSL single dosimeters for mixed high/low ionization density radiation fields

International Nuclear Information System (INIS)

Oster, L.; Druzhyna, S.; Orion, I.; Horowitz, Y.S.

2013-01-01

In this paper we discuss and compare the potential application of combined OSL/TL measurements using 6 LiF:Mg,Ti (TLD-600 is enriched of isotope 6 Li which has a high cross-section for the reaction with slow neutrons) or 7 LiF:Mg,Ti ( TLD-700 is enriched of 7 Li isotope) and TLD-100 (natural isotopic composition) detectors. The OSL/TL duel readout of LiF:Mg,Ti as an ionization density discriminator avoids some of the difficulties inherent to the various types of discrimination mixed-field passive dosimeters, and in addition has several advantages. The preferential excitation of OSL compared to TL following high ionization density (HID) alpha irradiation, naturally explained via the identification of OSL with the “two-hit” F 2 or F 3 center, whereas the major component of composite TL glow peak 5 is believed to arise from a ''one-hit'' complex defect. This evidence allows near-total discrimination between HID radiation and low-ionization density (LID) radiation. Beta and alpha particle irradiations were carried out with 90 Sr/ 90 Y (∼500 keV average energy) and 241 Am sources (4.7 MeV) respectively and neutron irradiations were carried out at the PTB (Germany) (E n = 5 MeV) and RARAF (Columbia University, USA) (E n = 6 MeV) accelerator facilities. The highest values of the FOM obtained was ∼30 for neutron/gamma discrimination and ∼110 for alpha/gamma discrimination using OSL/TL – peak 5 measurements in TLD-700. -- Highlights: ► The increased response of OSL compared to TL following HID irradiation is observed. ► This evidence is explained via the identification of OSL with the ''two-hit'' F2 centers. ► The potential application of combined OSL/TL in discrimination dosimetry is discussed. ► The values of FOM were 110 for alpha/gamma and 30 for neutron/gamma discrimination

Air density dependence of the response of the PTW SourceCheck 4pi ionization chamber for 125I brachytherapy seeds.

Science.gov (United States)

Torres Del Río, J; Tornero-López, A M; Guirado, D; Pérez-Calatayud, J; Lallena, A M

2017-06-01

To analyze the air density dependence of the response of the new SourceCheck 4pi ionization chamber, manufactured by PTW. The air density dependence of three different SourceCheck 4pi chambers was studied by measuring 125 I sources. Measurements were taken by varying the pressure from 746.6 to 986.6hPa in a pressure chamber. Three different HDR 1000 Plus ionization chambers were also analyzed under similar conditions. A linear and a potential-like function of the air density were fitted to experimental data and their achievement in describing them was analyzed. SourceCheck 4pi chamber response showed a residual dependence on the air density once the standard pressure and temperature factor was applied. The chamber response was overestimated when the air density was below that under normal atmospheric conditions. A similar dependence was found for the HDR 1000 Plus chambers analyzed. A linear function of the air density permitted a very good description of this residual dependence, better than with a potential function. No significant variability between the different specimens of the same chamber model studied was found. The effect of overestimation observed in the chamber responses once they are corrected for the standard pressure and temperature may represent a non-negligible ∼4% overestimation in high altitude cities as ours (700m AMSL). This overestimation behaves linearly with the air density in all cases analyzed. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Acceleration of electrons and supplementary ionization during parametrical plasma heating

International Nuclear Information System (INIS)

Grach, S.M.; Mityakov, N.A.; Trakhtengerts, V.Yu.; AN SSSR, Gor'kij. Inst. Prikladnoj Fiziki)

1986-01-01

Acceleration of electrons by plasma waves in partially ionized plasma is considered with provision for the effects of turbulent scattering and formation of secondary electrons, which are produced in the process of electron shock ionization. It is shown that the avalanche density growth of electrons accelerated up to 1-2 ionization potential (instability) takes place beginning from some critical density of plasma waves. Density of fast electrons is found out along with plasma wave energy density at the stage of instability saturation. Additional concentration of a background plasma, which manifests itself due to ionization, is evaluated

Storm-enhanced plasma density and polar tongue of ionization development during the 15 May 2005 superstorm

Science.gov (United States)

Horvath, Ildiko; Lovell, Brian C.

2015-06-01

We investigate the ionosphere's global response to the 15 May 2005 superstorm in terms of storm evolution and ionospheric electrodynamics. Our aim is to study the global distribution of plasma and the resultant large-scale ionospheric features including the equatorial ionization anomaly (EIA), storm-enhanced density (SED), and polar tongue of ionization (TOI). We have combined multi-instrument ionospheric data, solar and terrestrial magnetic data, and polar convection maps. Results reveal the prompt penetration of the interplanetary electric field to the polar region and then to the equator with a dusk-to-dawn polarity during the initial phase and with a dawn-to-dusk polarity during the main phase. This drove during the initial phase a weak eastward equatorial electrojet (EEJ) in the American sector at nighttime and a weak westward EEJ in the Indian-Australian sector at daytime. During the main phase, these EEJs intensified and changed polarities. SED and polar TOI development was observed prior to and during the initial phase at evening-premidnight hours over North America and during the main phase in the south at afternoon-evening hours in the Australian sector. During the main phase and early in the recovery phase, the EIA-SED structure was well formed in the Asian longitude sector. Then, polar TOI development was absent in the north because of the long distance from the magnetic pole but was supported in the south because of the closeness of daytime cusp and magnetic pole. Thus, the EIA-SED-TOI structure developed twice but each time in a different longitude sector and with different characteristics.

Surface-ionization field mass-spectrometry studies of nonequilibrium surface ionization

International Nuclear Information System (INIS)

Blashenkov, Nikolai M; Lavrent'ev, Gennadii Ya

2007-01-01

The ionization of polyatomic molecules on tungsten and tungsten oxide surfaces is considered for quasiequilibrium or essentially nonequilibrium conditions (in the latter case, the term nonequilibrium surface ionization is used for adsorbate ionization). Heterogeneous reactions are supposed to proceed through monomolecular decay of polyatomic molecules or fragments of multimolecular complexes. The nonequilibrium nature of these reactions is established. The dependences of the current density of disordered ions on the surface temperature, electric field strength, and ionized particle energy distribution are obtained in analytical form. Heterogeneous dissociation energies, the ionization potentials of radicals, and the magnitude of reaction departure from equilibrium are determined from experimental data, as are energy exchange times between reaction products and surfaces, the number of molecules in molecular complexes, and the number of effective degrees of freedom in molecules and complexes. In collecting the data a new technique relying on surface-ionization field mass-spectrometry was applied. (instruments and methods of investigation)

Large-scale density structures in the outer heliosphere

Science.gov (United States)

Belcher, J. W.; Lazarus, A. J.; Mcnutt, R. L., Jr.; Gordon, G. S., Jr.

1993-01-01

The Plasma Science experiment on the Voyager 2 spacecraft has measured the solar wind density from 1 to 38 AU. Over this distance, the solar wind density decreases as the inverse square of the heliocentric distance. However, there are large variations in this density at a given radius. Such changes in density are the dominant cause of changes in the solar wind ram pressure in the outer heliosphere and can cause large perturbations in the location of the termination shock of the solar wind. Following a simple model suggested by Suess, we study the non-equilibrium, dynamic location of the termination shock as it responds to these pressure changes. The results of this study suggest that the termination shock is rarely if ever at its equilibrium distance and may depart from that distance by as much as 50 AU at times.

Parametrization of the average ionization and radiative cooling rates of carbon plasmas in a wide range of density and temperature

International Nuclear Information System (INIS)

Gil, J.M.; Rodriguez, R.; Florido, R.; Rubiano, J.G.; Mendoza, M.A.; Nuez, A. de la; Espinosa, G.; Martel, P.; Minguez, E.

2013-01-01

In this work we present an analysis of the influence of the thermodynamic regime on the monochromatic emissivity, the radiative power loss and the radiative cooling rate for optically thin carbon plasmas over a wide range of electron temperature and density assuming steady state situations. Furthermore, we propose analytical expressions depending on the electron density and temperature for the average ionization and cooling rate based on polynomial fittings which are valid for the whole range of plasma conditions considered in this work. -- Highlights: ► We compute the average ionization, cooling rates and emissivities of carbon plasmas. ► We compare LTE and NLTE calculations of these magnitudes. ► We perform a parametrization of these magnitudes in a wide range of plasma conditions. ► We provide information about where LTE regime assumption is accurate

Battery-powered pulsed high density inductively coupled plasma source for pre-ionization in laboratory astrophysics experiments.

Science.gov (United States)

Chaplin, Vernon H; Bellan, Paul M

2015-07-01

An electrically floating radiofrequency (RF) pre-ionization plasma source has been developed to enable neutral gas breakdown at lower pressures and to access new experimental regimes in the Caltech laboratory astrophysics experiments. The source uses a customized 13.56 MHz class D RF power amplifier that is powered by AA batteries, allowing it to safely float at 3-6 kV with the electrodes of the high voltage pulsed power experiments. The amplifier, which is capable of 3 kW output power in pulsed (<1 ms) operation, couples electrical energy to the plasma through an antenna external to the 1.1 cm radius discharge tube. By comparing the predictions of a global equilibrium discharge model with the measured scalings of plasma density with RF power input and axial magnetic field strength, we demonstrate that inductive coupling (rather than capacitive coupling or wave damping) is the dominant energy transfer mechanism. Peak ion densities exceeding 5 × 10(19) m(-3) in argon gas at 30 mTorr have been achieved with and without a background field. Installation of the pre-ionization source on a magnetohydrodynamically driven jet experiment reduced the breakdown time and jitter and allowed for the creation of hotter, faster argon plasma jets than was previously possible.

MAGNETIC RECONNECTION IN NON-EQUILIBRIUM IONIZATION PLASMA

International Nuclear Information System (INIS)

Imada, S.; Shimizu, T.; Murakami, I.; Watanabe, T.; Hara, H.

2011-01-01

We have studied the effect of time-dependent ionization and the recombination processes on magnetic reconnection in the solar corona. Petschek-type steady reconnection, in which the magnetic energy is mainly converted at the slow-mode shocks, was assumed. We carried out the time-dependent ionization calculation in the magnetic reconnection structure. We only calculated the transient ionization of iron; the other species were assumed to be in ionization equilibrium. The intensity of line emissions at specific wavelengths was also calculated for comparison with Hinode or other observations in future. We found the following: (1) iron is mostly in non-equilibrium ionization in the reconnection region; (2) the intensity of line emission estimated by the time-dependent ionization calculation is significantly different from that determined from the ionization equilibrium assumption; (3) the effect of time-dependent ionization is sensitive to the electron density in the case where the electron density is less than 10 10 cm –3 ; (4) the effect of thermal conduction lessens the time-dependent ionization effect; and (5) the effect of radiative cooling is negligibly small even if we take into account time-dependent ionization.

Quench protection and design of large high-current-density superconducting magnets

International Nuclear Information System (INIS)

Green, M.A.

1981-03-01

Although most large superconducting magnets have been designed using the concept of cryostability, there is increased need for large magnets which operate at current densities above the cryostable limit (greater than 10 8 Am -2 ). Large high current density superconducting magnets are chosen for the following reasons: reduced mass, reduced coil thickness or size, and reduced cost. The design of large high current density, adiabatically stable, superconducting magnets requires a very different set of design rules than either large cryostable superconducting magnets or small self-protected high current density magnets. The problems associated with large high current density superconducting magnets fall into three categories; (a) quench protection, (b) stress and training, and (c) cryogenic design. The three categories must be considered simultaneously. The paper discusses quench protection and its implication for magnets of large stored energies (this includes strings of smaller magnets). Training and its relationship to quench protection and magnetic strain are discussed. Examples of magnets, built at the Lawrence Berkeley Laboratory and elsewhere using the design guidelines given in this report, are presented

Parametrization of the average ionization and radiative cooling rates of carbon plasmas in a wide range of density and temperature

OpenAIRE

Gil de la Fe, Juan Miguel; Rodriguez Perez, Rafael; Florido, Ricardo; Garcia Rubiano, Jesus; Mendoza, M.A.; Nuez, A. de la; Espinosa, G.; Martel Escobar, Carlos; Mínguez Torres, Emilio

2013-01-01

In this work we present an analysis of the influence of the thermodynamic regime on the monochromatic emissivity, the radiative power loss and the radiative cooling rate for optically thin carbon plasmas over a wide range of electron temperature and density assuming steady state situations. Furthermore, we propose analytical expressions depending on the electron density and temperature for the average ionization and cooling rate based on polynomial fittings which are valid for the whole range...

Simplified large African carnivore density estimators from track indices

Directory of Open Access Journals (Sweden)

Christiaan W. Winterbach

2016-12-01

Full Text Available Background The range, population size and trend of large carnivores are important parameters to assess their status globally and to plan conservation strategies. One can use linear models to assess population size and trends of large carnivores from track-based surveys on suitable substrates. The conventional approach of a linear model with intercept may not intercept at zero, but may fit the data better than linear model through the origin. We assess whether a linear regression through the origin is more appropriate than a linear regression with intercept to model large African carnivore densities and track indices. Methods We did simple linear regression with intercept analysis and simple linear regression through the origin and used the confidence interval for ß in the linear model y = αx + ß, Standard Error of Estimate, Mean Squares Residual and Akaike Information Criteria to evaluate the models. Results The Lion on Clay and Low Density on Sand models with intercept were not significant (P > 0.05. The other four models with intercept and the six models thorough origin were all significant (P < 0.05. The models using linear regression with intercept all included zero in the confidence interval for ß and the null hypothesis that ß = 0 could not be rejected. All models showed that the linear model through the origin provided a better fit than the linear model with intercept, as indicated by the Standard Error of Estimate and Mean Square Residuals. Akaike Information Criteria showed that linear models through the origin were better and that none of the linear models with intercept had substantial support. Discussion Our results showed that linear regression through the origin is justified over the more typical linear regression with intercept for all models we tested. A general model can be used to estimate large carnivore densities from track densities across species and study areas. The formula observed track density = 3.26�

Determination of dislocation densities in InN

Energy Technology Data Exchange (ETDEWEB)

Ardali, Sukru; Tiras, Engin [Department of Physics, Faculty of Science, Anadolu University, Yunus Emre Campus, Eskisehir 26470 (Turkey); Gunes, Mustafa; Balkan, Naci [School of Computer Science and Electronic Engineering, University of Essex, Wivenhoe Park, Colchester CO4 3SQ (United Kingdom); Ajagunna, Adebowale Olufunso; Iliopoulos, Eleftherios; Georgakilas, Alexandros [Microelectronics Research Group, IESL, FORTH and Physics Department, University of Crete, P.O. Box 1385, 71110 Heraklion-Crete (Greece)

2012-03-15

The magneto-transport measurements, carried out at magnetic fields up to 11 T and in the temperature range between 1.8 K and 300 K, are used to investigate the scattering mechanisms in GaN/InN/AlN double heterojunctions. Theoretical modeling is based on a variational approach to solving Boltzmann transport equation. It is found that dislocation scattering is the dominant scattering mechanisms at low temperatures because of the large lattice mismatch with the substrate and hence the high density of dislocations in these material systems. Nevertheless, InN epilayers are characterized by a high background carrier density, probably associated with unwanted impurities. Therefore, we also included in our calculations the ionized impurity scattering. However, the effect of ionized impurity scattering as well as the acoustic phonon scattering, remote- background-ionized impurity scattering, and interface roughness scattering on electron mobility are much smaller than that of dislocation scattering. The dislocation densities, in samples with InN thicknesses of 0.4, 0.6 and 0.8 {mu}m, are then determined from the best fit to the experimental data for the low-temperature transport mobility (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Masses and densities determination of meteoroids by radio-echo observations considering processes which influence the form of meteor ionization curves

International Nuclear Information System (INIS)

Bibarsov, R.Sh.; Narziev, M.; Chebotarev, R.P.

1990-01-01

Influence division of account and other factors (such as coefficient figure changing and methorin heat conductivity lengthways trajectories, structure and meteoroid comic structure) during of their weight and density definition on an angular ionization figure from one item on radar-tracking supervision is resulted

Testing an excited-state energy density functional and the associated potential with the ionization potential theorem

International Nuclear Information System (INIS)

Hemanadhan, M; Shamim, Md; Harbola, Manoj K

2014-01-01

The modified local spin density (MLSD) functional and the related local potential for excited states is tested by employing the ionization potential theorem. The exchange functional for an excited state is constructed by splitting k-space. Since its functional derivative cannot be obtained easily, the corresponding exchange potential is given by an analogy to its ground-state counterpart. Further, to calculate the highest occupied orbital energy ϵ max accurately, the potential is corrected for its asymptotic behaviour by employing the van Leeuwen and Baerends (LB) correction to it. ϵ max so obtained is then compared with the ΔSCF ionization energy calculated using the MLSD functional with self-interaction correction for the orbitals involved in the transition. It is shown that the two match quite accurately. The match becomes even better by tuning the LB correction with respect to a parameter in it. (paper)

Energy vs. density on paths toward more exact density functionals.

Science.gov (United States)

Kepp, Kasper P

2018-03-14

Recently, the progression toward more exact density functional theory has been questioned, implying a need for more formal ways to systematically measure progress, i.e. a "path". Here I use the Hohenberg-Kohn theorems and the definition of normality by Burke et al. to define a path toward exactness and "straying" from the "path" by separating errors in ρ and E[ρ]. A consistent path toward exactness involves minimizing both errors. Second, a suitably diverse test set of trial densities ρ' can be used to estimate the significance of errors in ρ without knowing the exact densities which are often inaccessible. To illustrate this, the systems previously studied by Medvedev et al., the first ionization energies of atoms with Z = 1 to 10, the ionization energy of water, and the bond dissociation energies of five diatomic molecules were investigated using CCSD(T)/aug-cc-pV5Z as benchmark at chemical accuracy. Four functionals of distinct designs was used: B3LYP, PBE, M06, and S-VWN. For atomic cations regardless of charge and compactness up to Z = 10, the energy effects of the different ρ are energy-wise insignificant. An interesting oscillating behavior in the density sensitivity is observed vs. Z, explained by orbital occupation effects. Finally, it is shown that even large "normal" problems such as the Co-C bond energy of cobalamins can use simpler (e.g. PBE) trial densities to drastically speed up computation by loss of a few kJ mol -1 in accuracy. The proposed method of using a test set of trial densities to estimate the sensitivity and significance of density errors of functionals may be useful for testing and designing new balanced functionals with more systematic improvement of densities and energies.

Characteristics of a Dry Fog Ionizer

International Nuclear Information System (INIS)

Murata, Y; Kudo, Y; Yonezawa, M

2008-01-01

The newly developed 'Dry Fog Ionizer' generates charged dry fog. The dry fog consists of very fine water droplets 8μm in mean diameter. This system consists of a dry fog nozzle (H.Ikeuchi and Co., LTD.), a ring electrode for induction charging (50mm outside diameter, and 10mm thick) in front of the nozzle, and a fan for dissipating charged dry fog. The ring electrode is DC or AC-biased and fine droplets ejected from the nozzle are electrified by induction charging. The particle size of the charged water droplets are reduced through evaporation during the transporting process by air flow, and completely evaporate approximately 2m from the nozzle under normal atmospheric conditions (25 deg. C, 60%R.H.) leaving high density ions. Using this system, high density ionic space charge can be realized in a remote spot from the ionizer. By this principle, the Dry Fog Ionizer shows strong charge-eliminating ability in the region away from the ionizer. When a dc bias of 5kV was applied to a ring electrode with the rate of water flow from the nozzle being 21/h, an ionic space-charge density of 1200nC /m 3 was able to be obtained at a distance 2m away from the ionizer, which was 10 2 times the value produced by an ordinary corona-type ionizer with an air blower.

Laws governing the energy conversion of ionization curves

International Nuclear Information System (INIS)

Gorgoskii, V.I.

1986-01-01

The author attempts to determine if ionization curves are structured or smooth, the cause of the smoothing of the curves, the possibility of the curves having maxima and why, how many maxima are on the ionization curve, and which of these maxima is the fundamental maxima. The study shows that ionization curves without and additional maximum, i.e., with one fundamental maximum, can be obtained for potassium, rubidium, and cesium. This requires reduction of the density of the electrons in the stream and the density of the atoms of the target gas. It is also shown that in order to obtain ionization curves with additional maxima in the cases of neon, argon, and krypton, the measurements must be carried out at high densities of the electrons in the stream and of the atoms of the target gas

Electron acceleration by a radially polarized laser pulse during ionization of low density gases

Directory of Open Access Journals (Sweden)

Kunwar Pal Singh

2011-03-01

Full Text Available The acceleration of electrons by a radially polarized intense laser pulse has been studied. The axial electric field of the laser is responsible for electron acceleration. The axial electric field increases with decreasing laser spot size; however, the laser pulse gets defocused sooner for smaller values and the electrons do not experience high electric field for long, reducing the energy they can reach. The electron remains confined in the electric field of the laser for longer and the electron energy peaks for the normalized laser spot size nearly equal to the normalized laser intensity parameter. Electron energy peaks for initial laser phase ϕ_{0}=π due to accelerating laser phase and decreases with transverse initial position of the electrons. The energy and angle of the emittance spectrum of the electrons generated during ionization of krypton and argon at low densities have been obtained and a right choice of laser parameters has been suggested to obtain high energy quasimonoenergetic collimated electron beams. It has been found that argon is more suitable than krypton to obtain high energy electron beams due to higher ionization potential of inner shells for the former.

The computation of ionization potentials for second-row elements by ab initio and density functional theory methods

International Nuclear Information System (INIS)

Jursic, B.S.

1996-01-01

Up to four ionization potentials of elements from the second-row of the periodic table were computed using the ab initio (HF, MP2, MP3, MP4, QCISD, GI, G2, and G2MP2) and DFT (B3LY, B3P86, B3PW91, XALPHA, HFS, HFB, BLYP, BP86, BPW91, BVWN, XAPLY, XAP86, XAPW91, XAVWN, SLYR SP86, SPW91 and SVWN) methods. In all of the calculations, the large 6-311++G(3df,3pd) gaussian type of basis set was used. The computed values were compared with the experimental results and suitability of the ab initio and DFF methods were discussed, in regard to reproducing the experimental data. From the computed ionization potentials of the second-row elements, it can be concluded that the HF ab initio computation is not capable of reproducing the experimental results. The computed ionization potentials are too low. However, by using the ab initio methods that include electron correlation, the computed IPs are becoming much closer to the experimental values. In all cases, with the exception of the first ionization potential for oxygen, the G2 computation result produces ionization potentials that are indistinguishable from the experimental results

The ionization effects from nuclear explosions in high-altitude and their effect to radio propagation

International Nuclear Information System (INIS)

Guan Rongsheng; Li Qin

1997-01-01

A high-altitude nuclear explosions releases large quantities of energetic particles and electromagnetic radiation capable of producing ionization in the atmosphere. These particles and rays radiation character in the atmosphere are discussed. Ionizations due to explosion X rays, γ rays, neutrons and β particles are considered separately. The time-space distribution of additional electron density is computed and its nature is analyzed. The effects of explosion-induced ionization on the absorption of radio wave is considered and the dependence of the absorption on explosion characteristics, distance from the earth's atmosphere, and frequency of the radio wave is determined

Observed departures from LTE ionization equilibrium in late-type giants

International Nuclear Information System (INIS)

Ramsey, L.W.

1977-01-01

Photoelectric scans of the Ca I line at 6572 A and the forbidden Ca II transition at 7323 A are studied in the K giant α Tau, the M supergiant α Ori, and the M giants β And, α Cet, μ Gem, and β Peg. The relative strengths of these lines are shown to be indicative of the ratio of the relative number densities of the neutral and ionized species in the photosphere. The analysis indicates an overionization relative to LTE in qualitative agreement with the theoretical calculations of Auman and Woodrow for the K and M giants. The M supergiant α Ori exhibits a large over-ionization relative to LTE

Theory for the asymmetry in the auroral ionization density profile for the generation of auroral infrasonic waves

International Nuclear Information System (INIS)

Goodwin, P.A.

1979-01-01

Traveling pressure waves with periods from 10 to 100 seconds are generated in the lower ionosphere by auroral electrojet current filaments as they move supersonically in an equatorward direction. The infrasonic waves produced by the auroral motions propagate to the ground as highly directional bow waves that can be detected by infrasonic microphones on the surface. There is an asymmetry in the reception of auroral infrasonic waves (AIW) with respect to whether the auroral arcs are moving equatorward to poleward. In the literature it is suggested that the asymmetry may be due to anisotropic propagation conditions along the acoustic ray path from the E-region, where AIW are produced, to the surface. Some intrinsic property of the AIW generation mechanism itself has also been suggested as a possible explanation. In this thesis anisotropic propagation is eliminated as the cause of the AIW reception asymmetry. Theoretical calculations, beginning with a model of an auroral precipitation region, are presented to show that there can be a significant difference in the transverse ionization density profiles between an auroral arc that is moving equatorward and an arc that is moving poleward, for a given equatorward-directed E-region ambient electric field. The calculation has been accomplished by solving the equations of motion and continuity for the cross-sectional ionization density profile associated with the transverse motion of a filamentary auroral electrojet. Thus, it is shown that there is an asymmetry in the ionization profiles associated with moving arcs, and in their coupling, that is related to the relative direction of motion of the arc with respect to the ambient electric field, and that it is this asymmetry that is probably the cause of the observed AIW reception asymmetry

Total Ionizing Dose Effects on Threshold Switching in 1T-Tantalum Disulfide Charge-Density-Wave Devices

OpenAIRE

Liu, G.; Zhang, E. X.; Liang, C. D.; Bloodgood, M. A.; Salguero, T. T.; Fleetwood, D. M.; Balandin, A. A.

2017-01-01

The 1T polytype of TaS2 exhibits voltage-triggered threshold switching as a result of a phase transition from nearly commensurate to incommensurate charge density wave states. Threshold switching, persistent above room temperature, can be utilized in a variety of electronic devices, e.g., voltage controlled oscillators. We evaluated the total-ionizing-dose response of thin film 1T-TaS2 at doses up to 1 Mrad(SiO2). The threshold voltage changed by less than 2% after irradiation, with persisten...

Analytical form of current-voltage characteristic of parallel-plane, cylindrical and spherical ionization chambers with homogeneous ionization

Energy Technology Data Exchange (ETDEWEB)

Stoyanov, D G [Faculty of Engineering and Pedagogy in Sliven, Technical University of Sofia, 59, Bourgasko Shaussee Blvd, 8800 Sliven (Bulgaria)

2007-11-15

The elementary processes taking place in the formation of charged particles and their flow in parallel-plane, cylindrical and spherical geometry cases of ionization chamber are considered. On the basis of particles and charges balance a differential equation describing the distribution of current densities in the ionization chamber volume is obtained. As a result of the differential equation solution an analytical form of the current-voltage characteristic of an ionization chamber with homogeneous ionization is obtained. For the parallel-plane case comparision with experimental data is performed.

Analytical form of current-voltage characteristic of parallel-plane, cylindrical and spherical ionization chambers with homogeneous ionization

International Nuclear Information System (INIS)

Stoyanov, D G

2007-01-01

The elementary processes taking place in the formation of charged particles and their flow in parallel-plane, cylindrical and spherical geometry cases of ionization chamber are considered. On the basis of particles and charges balance a differential equation describing the distribution of current densities in the ionization chamber volume is obtained. As a result of the differential equation solution an analytical form of the current-voltage characteristic of an ionization chamber with homogeneous ionization is obtained. For the parallel-plane case comparision with experimental data is performed

Electron density reactivity indexes of the tautomeric/ionization forms of thiamin diphosphate.

Science.gov (United States)

Jaña, Gonzalo A; Delgado, Eduardo J

2013-09-01

The generation of the highly reactive ylide in thiamin diphosphate catalysis is analyzed in terms of the nucleophilicity of key atoms, by means of density functional calculations at X3LYP/6-31++G(d,p) level of theory. The Fukui functions of all tautomeric/ionization forms are calculated in order to assess their reactivity. The results allow to conclude that the highly conserved glutamic residue does not protonate the N1' atom of the pyrimidyl ring, but it participates in a strong hydrogen bonding, stabilizing the eventual negative charge on the nitrogen, in all forms involved in the ylide generation. This condition provides the necessary reactivity on key atoms, N4' and C2, to carry out the formation of the ylide required to initiate the catalytic cycle of ThDP-dependent enzymes. This study represents a new approach for the ylide formation in ThDP catalysis.

Reduction of plasma density in the Helicity Injected Torus with Steady Inductance experiment by using a helicon pre-ionization source

International Nuclear Information System (INIS)

Hossack, Aaron C.; Jarboe, Thomas R.; Victor, Brian S.; Firman, Taylor; Prager, James R.; Ziemba, Timothy; Wrobel, Jonathan S.

2013-01-01

A helicon based pre-ionization source has been developed and installed on the Helicity Injected Torus with Steady Inductance (HIT-SI) spheromak. The source initiates plasma breakdown by injecting impurity-free, unmagnetized plasma into the HIT-SI confinement volume. Typical helium spheromaks have electron density reduced from (2–3) × 10 19 m −3 to 1 × 10 19 m −3 . Deuterium spheromak formation is possible with density as low as 2 × 10 18 m −3 . The source also enables HIT-SI to be operated with only one helicity injector at injector frequencies above 14.5 kHz. A theory explaining the physical mechanism driving the reduction of breakdown density is presented

Initial events in the cellular effects of ionizing radiations: clustered damage in DNA

International Nuclear Information System (INIS)

Goodhead, D.T.

1994-01-01

Ionizing radiations produce many hundreds of different simple chemical products in DNA and also multitudes of possible clustered combinations. The simple products, including single-strand breaks, tend to correlate poorly with biological effectiveness. Even for initial double-strand breaks, as a broad class, there is apparently little or no increase in yield with increasing ionization density, in contrast with the large rise in relative biological effectiveness for cellular effects. Track structure analysis has revealed that clustered DNA damage of severity greater than simple double-strand breaks is likely to occur at biologically relevant frequencies with all ionizing radiations. Studies are in progress to describe in more detail the chemical nature of these clustered lesions and to consider the implications for cellular repair. (author)

Increasing the applicability of density functional theory. IV. Consequences of ionization-potential improved exchange-correlation potentials.

Science.gov (United States)

Verma, Prakash; Bartlett, Rodney J

2014-05-14

This paper's objective is to create a "consistent" mean-field based Kohn-Sham (KS) density functional theory (DFT) meaning the functional should not only provide good total energy properties, but also the corresponding KS eigenvalues should be accurate approximations to the vertical ionization potentials (VIPs) of the molecule, as the latter condition attests to the viability of the exchange-correlation potential (VXC). None of the prominently used DFT approaches show these properties: the optimized effective potential VXC based ab initio dft does. A local, range-separated hybrid potential cam-QTP-00 is introduced as the basis for a "consistent" KS DFT approach. The computed VIPs as the negative of KS eigenvalue have a mean absolute error of 0.8 eV for an extensive set of molecule's electron ionizations, including the core. Barrier heights, equilibrium geometries, and magnetic properties obtained from the potential are in good agreement with experiment. A similar accuracy with less computational efforts can be achieved by using a non-variational global hybrid variant of the QTP-00 approach.

Electronegative Plasma Equilibria with Spatially-Varying Ionization

Science.gov (United States)

Lieberman, M. A.; Kawamura, E.; Lichtenberg, A. J.

2012-10-01

Electronegative inductive discharges in higher pressure ranges typically exhibit localized ionization near the coil structure, with decay of the ionization into the central discharge. We use a two-dimensional fluid code [1] with chlorine feedstock to determine the spatial profiles of the plasma parameters in a cylindrical transformer-coupled plasma device excited by a planar coil. To compare with one-dimensional (1D) analytic modeling, the results are area-averaged. The ionization is found to decay roughly exponentially along the axial direction, allowing the ansatz of an exponentially decaying ionization to be used in a 1D computational model. The model captures the main features of the axial variations of the area-averaged fluid simulation, indicating that the main diffusion mechanisms act along the axial direction. A simple analytic global discharge model is developed, accounting for the asymmetric density and ionization profiles. The global model gives the scalings with power and pressure of volume-averaged densities, electron temperature, and ionization decay rate, also in reasonable agreement with the scalings obtained by averaging the simulation results. [4pt] [1] E. Kawamura, D.B. Graves, and M.A. Lieberman, Plasma Sources Sci. Technol. 20, 035009 (2012)

Ionization chamber for high dose measurements

International Nuclear Information System (INIS)

Rodrigues Junior, Ary de Araujo

2005-01-01

Industrial gamma irradiators facilities are designed for processing large amounts of products, which are exposed to large doses of gamma radiation. The irradiation, in industrial scale, is usually carried out in a dynamic form, where the products go through a 60 Co gamma source with activity of TBq to P Bq (k Ci to MCi). The dose is estimated as being directly proportional to the time that the products spend to go through the source. However, in some situations, mainly for research purposes or for validation of customer process following the ISO 11137 requirements, it is required to irradiate small samples in a static position with fractional deliver doses. The samples are put inside the irradiation room at a fixed distance from the source and the dose is usually determined using dosimeters. The dose is only known after the irradiation, by reading the dosimeter. Nevertheless, in the industrial irradiators, usually different kinds of products with different densities go through between the source and the static position samples. So, the dose rate varies in function of the product density. A suitable methodology would be to monitor the samples dose in real time, measuring the dose on line with a radiation detector, which would improve the dose accuracy and avoid the overdose. A cylindrical ionization chamber of 0.9 cm 3 has been developed for high-doses real-time monitoring, during the sample irradiation at a static position in a 60 Co gamma industrial plant. Nitrogen and argon gas at pressure of 10 exp 5 Pa (1 bar) was utilized to fill the ionization chamber, for which an appropriate configuration was determined to be used as a detector for high-dose measurements. To transmit the signal generated in the ionization chamber to the associated electronic and processing unit, a 20 m mineral insulated cable was welded to the ionization chamber. The signal to noise ratio produced by the detector was about 100. The dosimeter system was tested at a category I gamma

First-principles investigations on ionization and thermal conductivity of polystyrene for inertial confinement fusion applications

Energy Technology Data Exchange (ETDEWEB)

Hu, S. X., E-mail: shu@lle.rochester.edu; Goncharov, V. N.; McCrory, R. L.; Skupsky, S. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Collins, L. A.; Kress, J. D. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2016-04-15

Using quantum molecular-dynamics (QMD) methods based on the density functional theory, we have performed first-principles investigations of the ionization and thermal conductivity of polystyrene (CH) over a wide range of plasma conditions (ρ = 0.5 to 100 g/cm{sup 3} and T = 15 625 to 500 000 K). The ionization data from orbital-free molecular-dynamics calculations have been fitted with a “Saha-type” model as a function of the CH plasma density and temperature, which gives an increasing ionization as the CH density increases even at low temperatures (T < 50 eV). The orbital-free molecular dynamics method is only used to gauge the average ionization behavior of CH under the average-atom model in conjunction with the pressure-matching mixing rule. The thermal conductivities (κ{sub QMD}) of CH, derived directly from the Kohn–Sham molecular-dynamics calculations, are then analytically fitted with a generalized Coulomb logarithm [(lnΛ){sub QMD}] over a wide range of plasma conditions. When compared with the traditional ionization and thermal conductivity models used in radiation–hydrodynamics codes for inertial confinement fusion simulations, the QMD results show a large difference in the low-temperature regime in which strong coupling and electron degeneracy play an essential role in determining plasma properties. Hydrodynamic simulations of cryogenic deuterium–tritium targets with CH ablators on OMEGA and the National Ignition Facility using the QMD-derived ionization and thermal conductivity of CH have predicted ∼20% variation in target performance in terms of hot-spot pressure and neutron yield (gain) with respect to traditional model simulations.

Comparison of Atmospheric Pressure Chemical Ionization and Field Ionization Mass Spectrometry for the Analysis of Large Saturated Hydrocarbons.

Science.gov (United States)

Jin, Chunfen; Viidanoja, Jyrki; Li, Mingzhe; Zhang, Yuyang; Ikonen, Elias; Root, Andrew; Romanczyk, Mark; Manheim, Jeremy; Dziekonski, Eric; Kenttämaa, Hilkka I

2016-11-01

Direct infusion atmospheric pressure chemical ionization mass spectrometry (APCI-MS) was compared to field ionization mass spectrometry (FI-MS) for the determination of hydrocarbon class distributions in lubricant base oils. When positive ion mode APCI with oxygen as the ion source gas was employed to ionize saturated hydrocarbon model compounds (M) in hexane, only stable [M - H] + ions were produced. Ion-molecule reaction studies performed in a linear quadrupole ion trap suggested that fragment ions of ionized hexane can ionize saturated hydrocarbons via hydride abstraction with minimal fragmentation. Hence, APCI-MS shows potential as an alternative of FI-MS in lubricant base oil analysis. Indeed, the APCI-MS method gave similar average molecular weights and hydrocarbon class distributions as FI-MS for three lubricant base oils. However, the reproducibility of APCI-MS method was found to be substantially better than for FI-MS. The paraffinic content determined using the APCI-MS and FI-MS methods for the base oils was similar. The average number of carbons in paraffinic chains followed the same increasing trend from low viscosity to high viscosity base oils for the two methods.

Reduction of plasma density in the Helicity Injected Torus with Steady Inductance experiment by using a helicon pre-ionization source

Energy Technology Data Exchange (ETDEWEB)

Hossack, Aaron C.; Jarboe, Thomas R.; Victor, Brian S. [Department of Aeronautics and Astronautics, University of Washington, Seattle, Washington 98195 (United States); Firman, Taylor; Prager, James R.; Ziemba, Timothy [Eagle Harbor Technologies, Inc., 119 W. Denny Way, Suite 210, Seattle, Washington 98119 (United States); Wrobel, Jonathan S. [979B West Moorhead Circle, Boulder, Colorado 80305 (United States)

2013-10-15

A helicon based pre-ionization source has been developed and installed on the Helicity Injected Torus with Steady Inductance (HIT-SI) spheromak. The source initiates plasma breakdown by injecting impurity-free, unmagnetized plasma into the HIT-SI confinement volume. Typical helium spheromaks have electron density reduced from (2–3) × 10{sup 19} m{sup −3} to 1 × 10{sup 19} m{sup −3}. Deuterium spheromak formation is possible with density as low as 2 × 10{sup 18} m{sup −3}. The source also enables HIT-SI to be operated with only one helicity injector at injector frequencies above 14.5 kHz. A theory explaining the physical mechanism driving the reduction of breakdown density is presented.

Ionization of Interstellar Hydrogen

Science.gov (United States)

Whang, Y. C.

1996-09-01

Interstellar hydrogen can penetrate through the heliopause, enter the heliosphere, and may become ionized by photoionization and by charge exchange with solar wind protons. A fluid model is introduced to study the flow of interstellar hydrogen in the heliosphere. The flow is governed by moment equations obtained from integration of the Boltzmann equation over the velocity space. Under the assumption that the flow is steady axisymmetric and the pressure is isotropic, we develop a method of solution for this fluid model. This model and the method of solution can be used to study the flow of neutral hydrogen with various forms of ionization rate β and boundary conditions for the flow on the upwind side. We study the solution of a special case in which the ionization rate β is inversely proportional to R2 and the interstellar hydrogen flow is uniform at infinity on the upwind side. We solve the moment equations directly for the normalized density NH/NN∞, bulk velocity VH/VN∞, and temperature TH/TN∞ of interstellar hydrogen as functions of r/λ and z/λ, where λ is the ionization scale length. The solution is compared with the kinetic theory solution of Lallement et al. The fluid solution is much less time-consuming than the kinetic theory solutions. Since the ionization rate for production of pickup protons is directly proportional to the local density of neutral hydrogen, the high-resolution solution of interstellar neutral hydrogen obtained here will be used to study the global distribution of pickup protons.

Large magnitude gridded ionization chamber for impurity identification in alpha emitting radioactive samples

International Nuclear Information System (INIS)

Santos, R.N. dos.

1992-01-01

This paper refers to a large magnitude gridded ionization chamber with high resolution used in the identification of α radioactive samples. The chamber and the electrode have been described in terms of their geometry and dimensions, as well as the best results listed accordingly. Several α emitting radioactive samples were used with a gas mixture of 90% Argon plus 10% Methane. We got α energy spectrum with resolution around 22,14 KeV in agreement to the best results available in the literature. The spectrum of α energy related to 92 U 233 was gotten using the ionization chamber mentioned in this work; several values were found which matched perfectly well adjustment curve of the chamber. Many other additional measures using different kinds of adjusted detectors were successfully obtained in order to confirm the results gotten in the experiments, thus leading to the identification of some elements of the 92 U 233 radioactive series. Such results show the possibility of using the chamber mentioned for measurements of α low activity contamination. (author)

The Gaia-ESO Survey: dynamics of ionized and neutral gas in the Lagoon nebula (M 8)

Science.gov (United States)

Damiani, F.; Bonito, R.; Prisinzano, L.; Zwitter, T.; Bayo, A.; Kalari, V.; Jiménez-Esteban, F. M.; Costado, M. T.; Jofré, P.; Randich, S.; Flaccomio, E.; Lanzafame, A. C.; Lardo, C.; Morbidelli, L.; Zaggia, S.

2017-08-01

Aims: We present a spectroscopic study of the dynamics of the ionized and neutral gas throughout the Lagoon nebula (M 8), using VLT-FLAMES data from the Gaia-ESO Survey. The new data permit exploration of the physical connections between the nebular gas and the stellar population of the associated star cluster NGC 6530. Methods: We characterized through spectral fitting emission lines of Hα, [N II] and [S II] doublets, [O III], and absorption lines of sodium D doublet, using data from the FLAMES-Giraffe and UVES spectrographs, on more than 1000 sightlines toward the entire face of the Lagoon nebula. Gas temperatures are derived from line-width comparisons, densities from the [S II] doublet ratio, and ionization parameter from Hα/[N II] ratio. Although doubly-peaked emission profiles are rarely found, line asymmetries often imply multiple velocity components along the same line of sight. This is especially true for the sodium absorption, and for the [O III] lines. Results: Spatial maps for density and ionization are derived, and compared to other known properties of the nebula and of its massive stars 9 Sgr, Herschel 36 and HD 165052 which are confirmed to provide most of the ionizing flux. The detailed velocity fields across the nebula show several expanding shells, related to the cluster NGC 6530, the O stars 9 Sgr and Herschel 36, and the massive protostar M 8East-IR. The origins of kinematical expansion and ionization of the NGC 6530 shell appear to be different. We are able to put constrains on the line-of-sight (relative or absolute) distances between some of these objects and the molecular cloud. The data show that the large obscuring band running through the middle of the nebula is being compressed by both sides, which might explain its enhanced density. We also find an unexplained large-scale velocity gradient across the entire nebula. At larger distances, the transition from ionized to neutral gas is studied using the sodium lines. Based on observations

Core fueling to produce peaked density profiles in large tokamaks

International Nuclear Information System (INIS)

Mikkelsen, D.R.; McGuire, K.M.; Schmidt, G.L.; Zweben, S.J.

1994-06-01

Peaking the density profile increases the usable bootstrap current and the average fusion power density; this could reduce the current drive power and increase the net output of power producing tokamaks. The use of neutral beams and pellet injection to produce peaked density profiles is assessed. We show that with radially ''hollow'' diffusivity profiles (and no particle pinch) moderately peaked density profiles can be produced by particle source profiles which are peaked off-axis. The fueling penetration requirements can therefore be relaxed and this greatly improves the feasibility of generating peaked density profiles in large tokamaks. In particular, neutral beam fueling does not require MeV particle energy. Even with beam voltages of ∼200 keV, however, exceptionally good particle confinement, τ p much-gt τ E is required to achieve net electrical power generation. In system with no power production requirement (e.g., neutron sources) neutral beam fueling should be capable of producing peaked density profiles in devices as large as ITER. Fueling systems with low energy cost per particle (such as cryogenic pellet injection) must be used in power producing tokamaks when τ p ∼ τ E . Simulations with pellet injection speeds of 7 km/sec show the peaking factor, n eo /left-angle n e right-angle, approaching 2

Direct Analysis of Large Living Organism by Megavolt Electrostatic Ionization Mass Spectrometry

Science.gov (United States)

Ng, Kwan-Ming; Tang, Ho-Wai; Man, Sin-Heng; Mak, Pui-Yuk; Choi, Yi-Ching; Wong, Melody Yee-Man

2014-09-01

A new ambient ionization method allowing the direct chemical analysis of living human body by mass spectrometry (MS) was developed. This MS method, namely Megavolt Electrostatic Ionization Mass Spectrometry, is based on electrostatic charging of a living individual to megavolt (MV) potential, illicit drugs, and explosives on skin/glove, flammable solvent on cloth/tissue paper, and volatile food substances in breath were readily ionized and detected by a mass spectrometer.

Effects of ionizing scrape-off layers on local recycling in Tore Supra pump limiter experiments

International Nuclear Information System (INIS)

Chatelier, M.; Loarer, T.

1992-01-01

A series of ohmic discharges with active pumping in the Tore Supra outboard pump limiter has been analyzed with the DEGAS neutrals transport code and an analytic scrape-off layer (SOL) plasma model. Pumping speed and plenum pressure measurements indicated 5-10 torr.L/s throughput with only modest effects on density. A model is developed in which large exhaust fluxes, with little attendant effect on core plasma density, are explained in terms of SOL ionization of recycled and wall-desorbed neutrals. Particle balance with active pumping and constant line density requires that the wall return flux exceed the incident flux by approximately the pump throughput in the absence of external fueling. The radial profile of the H + source rate from ionization and dissociation of wall-desorbed molecules is seen to peak very near the radial position of the limiter throat. Consequently, a strong recycling vortex is created in the region of the limiter, with the ion flux amplified by factors of 2 at the outer limiter surfaces and > 3 within the limiter throat. The calculations indicate that less than 30% of the pump throughput is due to first-generation ions from the core efflux, with the balance from local recycling in the strongly ionizing SOL

An open-flow pulse ionization chamber for alpha spectrometry of large-area samples

International Nuclear Information System (INIS)

Johansson, L.; Roos, B.; Samuelsson, C.

1992-01-01

The presented open-flow pulse ionization chamber was developed to make alpha spectrometry on large-area surfaces easy. One side of the chamber is left open, where the sample is to be placed. The sample acts as a chamber wall and therby defeins the detector volume. The sample area can be as large as 400 cm 2 . To prevent air from entering the volume there is a constant gas flow through the detector, coming in at the bottom of the chamber and leaking at the sides of the sample. The method results in good energy resolution and has considerable applicability in the retrospective radon research. Alpha spectra obtained in the retrospective measurements descend from 210 Po, built up in the sample from the radon daughters recoiled into a glass surface. (au)

Suitability of tunneling ionization produced plasmas for the plasma beat wave accelerator

International Nuclear Information System (INIS)

Leeman, W.P.; Clayton, C.E.; Marsh, K.A.; Dyson, A.; Joshi, C.

1991-01-01

Tunneling ionization can be thought of as the high intensity, low frequency limit of multi-photon ionization (MPI). Extremely uniform plasmas were produced by the latter process at Rutherford lab for beat wave excitation experiments using a 0.5 μm laser. Plasmas with 100% ionization were produced with densities exceeding 10 17 cm -3 . The experiment uses a CO 2 laser (I max ∼ 5 x 10 14 W/cm 2 ) which allows the formation of plasmas via the tunneling process. For the experiments the authors need plasmas with densities in the range of 5 to 10 x 10 16 cm -3 . Using Thomson scattering as a diagnostic they have explored the density and temperature regime of tunneling ionization produced plasmas. They find that plasmas with densities up to 10 16 cm -3 can indeed be produced and that these plasmas are hot. Beyond this density strong refraction of laser radiation occurs due to the radial profile of the plasma. Implications of this work to the Beat Wave Accelerator program will be discussed

Core fuelling to produce peaked density profiles in large tokamaks

International Nuclear Information System (INIS)

Mikkelsen, D.R.; McGuire, K.M.; Schmidt, G.L.; Zweben, S.J.

1995-01-01

Peaking the density profile increases the usable bootstrap current and the average fusion power density; this could reduce the current drive power and increase the net output of power producing tokamaks. The use of neutral beams and pellet injection to produce peaked density profiles is assessed. It is shown that with radially 'hollow' diffusivity profiles (and no particle pinch) moderately peaked density profiles can be produced by particle source profiles that are peaked off-axis. The fuelling penetration requirements can therefore be relaxed and this greatly improves the feasibility of generating peaked density profiles in large tokamaks. In particular, neutral beam fuelling does not require Megavolt particle energies. Even with beam voltages of ∼ 200 keV, however, exceptionally good particle confinement is needed to achieve net electrical power generation. The required ratio of particle to thermal diffusivities is an order of magnitude outside the range reported for tokamaks. In a system with no power production requirement (e.g., neutron sources) neutral beam fuelling should be capable of producing peaked density profiles in devices as large as ITER. Fuelling systems with low energy cost per particle - such as cryogenic pellet injection - must be used in power producing tokamaks when τ P ∼ τ E . Simulations with pellet injection speeds of 7 km/s show that the peaking factor, n e0 / e >, approaches 2. (author). 65 refs, 8 figs

Compatibility of polyamide 6.6 and low density polyethylene polymeric blend using electron beam ionizing radiation

International Nuclear Information System (INIS)

Feitosa, Marcos Antonio Fernandes

2008-01-01

The plastic industry has recognized that mixture of polymers, called polymeric blends, yields new materials with improve properties and better features of those of the polymer blended. In most of the cases, blends are formed by immiscible components presenting separated phases, micro-structures or morphologies. One of the main factors for good mechanical performance is the interfacial adhesion of the blend components. The improvement of miscibility between the polymer components and the enhancement of blend performance is denominated of compatibility. This compatibility can be achieved by chemical methods or using ionizing radiation. The present work has as a main objective the study of the effect of the ionizing radiation from electron beam in the compatibility of the polyamide (PA) 6.6 and low density polyethylene (LDPE) 75%/25% wt blend, in the range of applied doses from 50 to 250 kGy. The compatibility effect was evaluated by mechanical test, which has shown improvement in the tensile strength and hardness properties and a reduction of the impact resistant. This mechanical behavior can be considered as a combination effect of the cross-linking, induced in the molecular structure on the polymers, and the increase of the miscibility of the blend components. The degree of compatibility was evaluated by the behavior of the glass transition temperatures (T g ) for the blend components obtained by dynamic mechanical analysis (DMA) measurements. The results have shown that the values of T g for PA 6.6 and LDPE get near by 8 deg C showing that the ionizing radiation have promoted a compatibility effect on the irradiated blend. (author)

Modification of K-line emission profiles in laser-created solid-density plasmas

International Nuclear Information System (INIS)

Sengebusch, A.; Reinholz, H.; Roepke, G.

2010-01-01

Complete text of publication follows. X-ray emissions in the keV energy range have shown to be suitable radiation to investigate the properties of laser-created solid-density plasmas. We use the modifications of inner shell transitions due to the environment to characterize these plasmas. A theoretical treatment of spectral line profiles based on a self-consistent ion sphere model is applied on moderately ionized mid-Z materials, such as titanium, silicon and chlorine. We observe large contributions of satellite transitions due to M-shell ionization and excitation. To determine the composition a mixture of various excited and ionized ionic states embedded in a plasma has to be considered. Plasma polarization effects that cause shifts of the emission and ionization energies are taken into account. K-line profiles are calculated for bulk temperatures up to 100 eV and free electron densities up to 10 24 cm -3 in order to analyze recent measurements with respect to the plasma parameters of electron heated target regions. Moreover, in high-intensity laser-matter interactions, inevitable prepulses are likely to create preplasma and shocks within the target before the main pulse arrives. We investigate the influence of density gradients due to prepulses on the spectral profiles. Further, radial bulk temperature distributions as well the composition of the created warm dense matter are inferred.

Modelling high density phenomena in hydrogen fibre Z-pinches

International Nuclear Information System (INIS)

Chittenden, J.P.

1990-09-01

The application of hydrogen fibre Z-pinches to the study of the radiative collapse phenomenon is studied computationally. Two areas of difficulty, the formation of a fully ionized pinch from a cryogenic fibre and the processes leading to collapse termination, are addressed in detail. A zero-D model based on the energy equation highlights the importance of particle end losses and changes in the Coulomb logarithm upon collapse initiation and termination. A 1-D Lagrangian resistive MHD code shows the importance of the changing radial profile shapes, particularly in delaying collapse termination. A 1-D, three fluid MHD code is developed to model the ionization of the fibre by thermal conduction from a high temperature surface corona to the cold core. Rate equations for collisional ionization, 3-body recombination and equilibration are solved in tandem with fluid equations for the electrons, ions and neutrals. Continuum lowering is found to assist ionization at the corona-core interface. The high density plasma phenomena responsible for radiative collapse termination are identified as the self-trapping of radiation and free electron degeneracy. A radiation transport model and computational analogues for the effects of degeneracy upon the equation of state, transport coefficients and opacity are implemented in the 1-D, single fluid model. As opacity increases the emergent spectrum is observed to become increasingly Planckian and a fall off in radiative cooling at small radii and low frequencies occurs giving rise to collapse termination. Electron degeneracy terminates radiative collapse by supplementing the radial pressure gradient until the electromagnetic pinch force is balanced. Collapse termination is found to be a hybrid process of opacity and degeneracy effects across a wide range of line densities with opacity dominant at large line densities but with electron degeneracy becoming increasingly important at lower line densities. (author)

Large-Area Neutron Detector based on Li-6 Pulse Mode Ionization Chamber

International Nuclear Information System (INIS)

Chung, K.; Ianakiev, K.D.; Swinhoe, M.T.; Makela, M.F.

2005-01-01

Prototypes of a Li-6 Pulse Mode Ionization Chamber (LiPMIC) have been in development for the past two years for the purpose of providing large-area neutron detector. this system would be suitable for remote deployment for homeland security and counterterrorism needs at borders, ports, and nuclear facilities. A prototype of LiPMIC is expected to provide a similar level of performance to the current industry-standard, He-3 proportional counters, while keeping the initial cost of procurement down by an order of magnitude, especially where large numbers of detectors are required. The overall design aspect and the efficiency optimization process is discussed. Specifically, the MCNP simulations of a single-cell prototype were performed and benchmarked with the experimental results. MCNP simulations of a three dimensional array design show intrinsic efficiency comparable to that of an array of He-3 proportional counters. LiPMIC has shown steady progress toward fulfilling the design expectations and future design modification and optimization are discussed.

Alpha radioactivity monitor using ionized air transport technology for large size uranium waste (2). Simulation model reinforcement for practical apparatus design

International Nuclear Information System (INIS)

Asada, Takatoshi; Hirata, Yosuke; Naito, Susumu; Izumi, Mikio; Yoshimura, Yukio

2011-01-01

In alpha radioactivity measurement using ionized air transportation (AMAT), conversion from ion currents to radioactivity accurate is required. An ion transport simulation provides ways of complementarily determining conversion factors. We have developed an ion transport simulation model. Simulation results were compared with experiments with air speeds, faster than 1 m/s, achieving good agreement. In a practical AMAT apparatus, the air-flow at the alpha source may be slower than 1 m/s, and ion loss is likely to be large. Reinforcement of the ion transport model to cover the lower air speed region is effective. Ions are generated by an alpha particle in a very thin column. Since the ion density at this temporal stage is high, the recombination loss, proportional to the square of ion density, is dominant within a few milli-seconds. The spatial and temporal scales of this columnar recombination are too small for CFD simulation. We solve an ion transport equation during the period of columnar recombination with diffusion and recombination terms and incorporated the relation between ion loss and turbulent parameters into CFD. Using this model, simulations have been done for various air speeds and targets. Those for simulation results agree with experiments, showing improvement of simulation accuracy. (author)

Effect of ionizing radiation on mechanical and thermal properties of low-density polyethylene containing pro-degradant agents

International Nuclear Information System (INIS)

Bardi, Marcelo A.G.; Kodama, Yasko; Machado, Luci D.B.; Giovedi, Claudia; Rosa, Derval S.

2009-01-01

The wide use of plastics on packages of short-lifetime products has presented harmful consequences for the environment due to their low degradation rate. By this way, improved results to the bio-assimilation of polyolefins have been achieved by the incorporation of pro-oxidant components. The aim of this work is to evaluate the mechanical and thermal behavior of low-density polyethylene (LDPE) modified by those agents and submitted to ionizing radiation by gamma rays. LDPE was modified using a masterbatch containing calcium stearate (CaSt), or magnesium stearate (MgSt) or Clariant R commercial metallic complex. The final amount of stearate in modified LDPE was 0.2%. The films were obtained by compression molding. Samples were gamma irradiated at absorbed doses of 15 kGy and 100 kGy. Differential scanning calorimetry (DSC) and thermogravimetry (TG) were performed on samples, as well as mechanical analysis by universal testing machine. Thermal properties of samples presenting pro-degradant agents were affected by the ionizing radiation in the dose range studied, and some of the mechanical properties were clearly modified by reducing their values of tensile strength at break and elongation at break. (author)

Effect of ionizing radiation on mechanical and thermal properties of low-density polyethylene containing pro-degradant agents

Energy Technology Data Exchange (ETDEWEB)

Bardi, Marcelo A.G.; Kodama, Yasko; Machado, Luci D.B., E-mail: magbardi@ipen.b, E-mail: ykodama@ipen.b, E-mail: lmachado@ipen.b [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil); Giovedi, Claudia, E-mail: giovedi@ctmsp.mar.mil.b [Centro Tecnologico da Marinha em Sao Paulo (CTMSP), Sao Paulo, SP (Brazil); Rosa, Derval S., E-mail: derval.rosa@ufabc.edu.b [Universidade Federal do ABC (UFABC), Santo Andre, SP (Brazil)

2009-07-01

The wide use of plastics on packages of short-lifetime products has presented harmful consequences for the environment due to their low degradation rate. By this way, improved results to the bio-assimilation of polyolefins have been achieved by the incorporation of pro-oxidant components. The aim of this work is to evaluate the mechanical and thermal behavior of low-density polyethylene (LDPE) modified by those agents and submitted to ionizing radiation by gamma rays. LDPE was modified using a masterbatch containing calcium stearate (CaSt), or magnesium stearate (MgSt) or Clariant{sup R} commercial metallic complex. The final amount of stearate in modified LDPE was 0.2%. The films were obtained by compression molding. Samples were gamma irradiated at absorbed doses of 15 kGy and 100 kGy. Differential scanning calorimetry (DSC) and thermogravimetry (TG) were performed on samples, as well as mechanical analysis by universal testing machine. Thermal properties of samples presenting pro-degradant agents were affected by the ionizing radiation in the dose range studied, and some of the mechanical properties were clearly modified by reducing their values of tensile strength at break and elongation at break. (author)

Ionizing and non-ionizing radiations

International Nuclear Information System (INIS)

1994-01-01

The monograph is a small manual to get a knowledge of ionizing and non-ionizing radiations. The main chapters are: - Electromagnetic radiations - Ionizing and non-ionizing radiations - Non-ionizing electromagnetic radiations - Ionizing electromagnetic radiation - Other ionizing radiations - Ionizing radiation effects - The Nuclear Safety Conseil

Propagation of an ionizing surface electromagnetic wave

Energy Technology Data Exchange (ETDEWEB)

Boev, A.G.; Prokopov, A.V.

1976-11-01

The propagation of an rf surface wave in a plasma which is ionized by the wave itself is analyzed. The exact solution of the nonlinear Maxwell equations is discussed for the case in which the density of plasma electrons is an exponential function of the square of the electric field. The range over which the surface wave exists and the frequency dependence of the phase velocity are found. A detailed analysis is given for the case of a plasma whose initial density exceeds the critical density at the wave frequency. An increase in the wave amplitude is shown to expand the frequency range over which the plasma is transparent; The energy flux in the plasma tends toward a certain finite value which is governed by the effective ionization field.

Propagation of electromagnetic waves in a weak collisional and fully ionized dusty plasma

Energy Technology Data Exchange (ETDEWEB)

Jia, Jieshu; Yuan, Chengxun, E-mail: yuancx@hit.edu.cn; Gao, Ruilin; Wang, Ying; Zhou, Zhong-Xiang [Department of Physics, Harbin Institute of Technology, Harbin 150001 (China); Liu, Sha; Yue, Feng [Shanghai Institute of Spaceflight Control Technology, Shanghai 200233 (China); Wu, Jian [China Research Institute of Radio wave Propagation, Beijing 102206 (China); Li, Hui [Department of Physics, Harbin Institute of Technology, Harbin 150001 (China); China Research Institute of Radio wave Propagation, Beijing 102206 (China)

2016-04-15

The propagation properties of electromagnetic (EM) waves in fully ionized dusty plasmas is the subject of this study. The dielectric relationships for EM waves propagating in a fully ionized dusty plasma was derived from the Boltzmann distribution law, taking into consideration the collision and charging effects of the dust grains. The propagation properties of the EM waves in a dusty plasma were numerically calculated and studied. The study results indicated that the dusty grains with an increased radius and charge were more likely to impede the penetration of EM waves. Dust grains with large radii and high charge cause the attenuation of the EM wave in the dusty plasma. The different density of the dust in the plasma appeared to have no obvious effect on the transmission of the EM waves. The propagation of the EM waves in a weakly ionized dusty plasma varies from that in a fully ionized dusty plasma. The results are helpful to analyze the effects of dust in dusty plasmas and also provide a theoretical basis for future studies.

Propagation of electromagnetic waves in a weak collisional and fully ionized dusty plasma

International Nuclear Information System (INIS)

Jia, Jieshu; Yuan, Chengxun; Gao, Ruilin; Wang, Ying; Zhou, Zhong-Xiang; Liu, Sha; Yue, Feng; Wu, Jian; Li, Hui

2016-01-01

The propagation properties of electromagnetic (EM) waves in fully ionized dusty plasmas is the subject of this study. The dielectric relationships for EM waves propagating in a fully ionized dusty plasma was derived from the Boltzmann distribution law, taking into consideration the collision and charging effects of the dust grains. The propagation properties of the EM waves in a dusty plasma were numerically calculated and studied. The study results indicated that the dusty grains with an increased radius and charge were more likely to impede the penetration of EM waves. Dust grains with large radii and high charge cause the attenuation of the EM wave in the dusty plasma. The different density of the dust in the plasma appeared to have no obvious effect on the transmission of the EM waves. The propagation of the EM waves in a weakly ionized dusty plasma varies from that in a fully ionized dusty plasma. The results are helpful to analyze the effects of dust in dusty plasmas and also provide a theoretical basis for future studies.

Density-functional theory simulation of large quantum dots

Science.gov (United States)

Jiang, Hong; Baranger, Harold U.; Yang, Weitao

2003-10-01

Kohn-Sham spin-density functional theory provides an efficient and accurate model to study electron-electron interaction effects in quantum dots, but its application to large systems is a challenge. Here an efficient method for the simulation of quantum dots using density-function theory is developed; it includes the particle-in-the-box representation of the Kohn-Sham orbitals, an efficient conjugate-gradient method to directly minimize the total energy, a Fourier convolution approach for the calculation of the Hartree potential, and a simplified multigrid technique to accelerate the convergence. We test the methodology in a two-dimensional model system and show that numerical studies of large quantum dots with several hundred electrons become computationally affordable. In the noninteracting limit, the classical dynamics of the system we study can be continuously varied from integrable to fully chaotic. The qualitative difference in the noninteracting classical dynamics has an effect on the quantum properties of the interacting system: integrable classical dynamics leads to higher-spin states and a broader distribution of spacing between Coulomb blockade peaks.

SUPPRESSION OF DIELECTRONIC RECOMBINATION DUE TO FINITE DENSITY EFFECTS

International Nuclear Information System (INIS)

Nikolić, D.; Gorczyca, T. W.; Korista, K. T.; Ferland, G. J.; Badnell, N. R.

2013-01-01

We have developed a general model for determining density-dependent effective dielectronic recombination (DR) rate coefficients in order to explore finite-density effects on the ionization balance of plasmas. Our model consists of multiplying by a suppression factor those highly-accurate total zero-density DR rate coefficients which have been produced from state-of-the-art theoretical calculations and which have been benchmarked by experiment. The suppression factor is based upon earlier detailed collision-radiative calculations which were made for a wide range of ions at various densities and temperatures, but used a simplified treatment of DR. A general suppression formula is then developed as a function of isoelectronic sequence, charge, density, and temperature. These density-dependent effective DR rate coefficients are then used in the plasma simulation code Cloudy to compute ionization balance curves for both collisionally ionized and photoionized plasmas at very low (n e = 1 cm –3 ) and finite (n e = 10 10 cm –3 ) densities. We find that the denser case is significantly more ionized due to suppression of DR, warranting further studies of density effects on DR by detailed collisional-radiative calculations which utilize state-of-the-art partial DR rate coefficients. This is expected to impact the predictions of the ionization balance in denser cosmic gases such as those found in nova and supernova shells, accretion disks, and the broad emission line regions in active galactic nuclei.

Possible ionization ''ignition'' in laser-driven clusters

International Nuclear Information System (INIS)

Rose-Petruck, C.; Schafer, K.J.; Barty, C.P.J.

1995-01-01

The authors use Classical Trajectory Monte Carlo (CTMC) simulations to study the ionization of small rare gas clusters in short pulse, high intensity laser fields. They calculate, for a cluster of 25 neon atoms, the ionization stage reached and the average kinetic energy of the ionized electrons as functions of time and peak laser intensity. The CTMC calculations mimic the results of the much simpler barrier suppression model in the limit of isolated atoms. At solid density the results give much more ionization in the cluster than that predicted by the barrier suppression model. They find that when the laser intensity reaches a threshold value such that on average one electron is ionized from each atom, the cluster atoms rapidly move to higher ionization stages, approaching Ne +8 in a few femtoseconds. This ignition process creates an ultrafast pulse of energetic electrons in the cluster at quite modest laser intensities

Assessment of hydrogen bonding effect on ionization of water from ambient to supercritical region–MD simulation approach

International Nuclear Information System (INIS)

Swiatla-Wojcik, D.; Mozumder, A.

2014-01-01

We present a novel, molecular dynamics (MD) simulation based, strategy to analyze how the degree of hydrogen bonding may influence the ionization and dissociation of water upon heating from ambient to supercritical temperatures. Calculations show a negligible change in the ionization energy up to 200 °C. At higher temperatures the ionization energy increases due to the decreasing degree of hydrogen bonding. The influence of density (pressure) is pronounced in the supercritical region. The ionization is more energy consuming in the less dense fluid. We also show that high temperature and low density may promote dissociation of the electronically excited water molecules. Implications on the initial radiation chemical yields of the hydrated electron, hydrogen atom and hydroxyl radical are discussed. - Highlights: • Up to 200 °C changes in the vertical and adiabatic ionization potentials are negligible. • At higher temperatures ionization is more energy consuming. • Ionization potential increases with decreasing density of supercritical water. • High temperature and low density promote dissociation of the excited molecules

Controlling branching in streamer discharge by laser background ionization

International Nuclear Information System (INIS)

Takahashi, E; Kato, S; Furutani, H; Sasaki, A; Kishimoto, Y

2011-01-01

Irradiation with a KrF laser controlled the positive streamer branching in atmospheric argon gas. This laser irradiation changed the amount of background ionization before the streamer discharge. Measuring the ionization current allowed us to evaluate the initial electron density formed by the KrF laser. We observed characteristic feather-like branching structure and found that it was only suppressed in the irradiated region. The threshold of ionization density which can influence the branching was evaluated to be 5 x 10 5 cm -3 . The relationship between the size of avalanche head and mean distance between initial electrons explained this suppression behaviour. These experimental results support that the feather-like structure originates from the branching model of Loeb-Meek, a probabilistic merging of individual avalanches.

Production of a large, quiescent, magnetized plasma

Science.gov (United States)

Landt, D. L.; Ajmera, R. C.

1976-01-01

An experimental device is described which produces a large homogeneous quiescent magnetized plasma. In this device, the plasma is created in an evacuated brass cylinder by ionizing collisions between electrons emitted from a large-diameter electron gun and argon atoms in the chamber. Typical experimentally measured values of the electron temperature and density are presented which were obtained with a glass-insulated planar Langmuir probe. It is noted that the present device facilitates the study of phenomena such as waves and diffusion in magnetized plasmas.

Dwarf galaxies with ionizing radiation feedback. II. Spatially resolved star formation relation

International Nuclear Information System (INIS)

Kim, Ji-hoon; Krumholz, Mark R.; Goldbaum, Nathan J.; Wise, John H.; Turk, Matthew J.; Abel, Tom

2013-01-01

We investigate the spatially resolved star formation relation using a galactic disk formed in a comprehensive high-resolution (3.8 pc) simulation. Our new implementation of stellar feedback includes ionizing radiation as well as supernova explosions, and we handle ionizing radiation by solving the radiative transfer equation rather than by a subgrid model. Photoheating by stellar radiation stabilizes gas against Jeans fragmentation, reducing the star formation rate (SFR). Because we have self-consistently calculated the location of ionized gas, we are able to make simulated, spatially resolved observations of star formation tracers, such as Hα emission. We can also observe how stellar feedback manifests itself in the correlation between ionized and molecular gas. Applying our techniques to the disk in a galactic halo of 2.3 × 10 11 M ☉ , we find that the correlation between SFR density (estimated from mock Hα emission) and H 2 density shows large scatter, especially at high resolutions of ≲75 pc that are comparable to the size of giant molecular clouds (GMCs). This is because an aperture of GMC size captures only particular stages of GMC evolution and because Hα traces hot gas around star-forming regions and is displaced from the H 2 peaks themselves. By examining the evolving environment around star clusters, we speculate that the breakdown of the traditional star formation laws of the Kennicutt-Schmidt type at small scales is further aided by a combination of stars drifting from their birthplaces and molecular clouds being dispersed via stellar feedback.

Dwarf galaxies with ionizing radiation feedback. II. Spatially resolved star formation relation

Energy Technology Data Exchange (ETDEWEB)

Kim, Ji-hoon; Krumholz, Mark R.; Wise, John H.; Turk, Matthew J.; Goldbaum, Nathan J.; Abel, Tom

2013-11-15

AWe investigate the spatially resolved star formation relation using a galactic disk formed in a comprehensive high-resolution (3.8 pc) simulation. Our new implementation of stellar feedback includes ionizing radiation as well as supernova explosions, and we handle ionizing radiation by solving the radiative transfer equation rather than by a subgrid model. Photoheating by stellar radiation stabilizes gas against Jeans fragmentation, reducing the star formation rate (SFR). Because we have self-consistently calculated the location of ionized gas, we are able to make simulated, spatially resolved observations of star formation tracers, such as Hα emission. We can also observe how stellar feedback manifests itself in the correlation between ionized and molecular gas. Applying our techniques to the disk in a galactic halo of 2.3 × 10¹¹ M _⊙, we find that the correlation between SFR density (estimated from mock Hα emission) and H₂ density shows large scatter, especially at high resolutions of ≲ 75 pc that are comparable to the size of giant molecular clouds (GMCs). This is because an aperture of GMC size captures only particular stages of GMC evolution and because Hα traces hot gas around star-forming regions and is displaced from the H₂ peaks themselves. By examining the evolving environment around star clusters, we speculate that the breakdown of the traditional star formation laws of the Kennicutt-Schmidt type at small scales is further aided by a combination of stars drifting from their birthplaces and molecular clouds being dispersed via stellar feedback.

III. Penning ionization, associative ionization and chemi-ionization processes

International Nuclear Information System (INIS)

Cermak, V.

1975-01-01

Physical mechanisms of three important ionization processes in a cold plasma and the methods of their experimental study are discussed. An apparatus for the investigation of the Penning ionization using ionization processes of long lived metastable rare gas atoms is described. Methods of determining interaction energies and ionization rates from the measured energy spectra of the originating electrons are described and illustrated by several examples. Typical associative ionization processes are listed and the ionization rates are compared with those of the Penning ionization. Interactions with short-lived excited particles and the transfer of excitation without ionization are discussed. (J.U.)

Ionization beam scanner

CERN Multimedia

CERN PhotoLab

1973-01-01

Inner structure of an ionization beam scanner, a rather intricate piece of apparatus which permits one to measure the density distribution of the proton beam passing through it. On the outside of the tank wall there is the coil for the longitudinal magnetic field, on the inside, one can see the arrangement of electrodes creating a highly homogeneous transverse electric field.

Differential analysis of the inactivation of yeast cells induced by irradiation with various ionization densities

International Nuclear Information System (INIS)

Grundler, W.

1979-03-01

A quantitative investigation is presented on the radiation-induced inactivation of yeast cells in the first generations as a function of dose, repair, and various ionization densities. The study has been made to solve two main questions, i.e.: How do these cells reproduce, and how do they look like at the end of the investigation. Finding the answer to these questions, it was hoped, would lead to a description of survival in the colony test by defining the final fate of the cells which represent the stationary end state. The experiments were to clarify to what extent the dose-response curve yields only relatively general information on radiation-induced damage, or what kind of damage is mainly and best described. This supplementary information will help to improve the interpretation of many experiments having been made with this strain. (orig./MG) [de

CIFOG: Cosmological Ionization Fields frOm Galaxies

Science.gov (United States)

Hutter, Anne

2018-03-01

CIFOG is a versatile MPI-parallelised semi-numerical tool to perform simulations of the Epoch of Reionization. From a set of evolving cosmological gas density and ionizing emissivity fields, it computes the time and spatially dependent ionization of neutral hydrogen (HI), neutral (HeI) and singly ionized helium (HeII) in the intergalactic medium (IGM). The code accounts for HII, HeII, HeIII recombinations, and provides different descriptions for the photoionization rate that are used to calculate the residual HI fraction in ionized regions. This tool has been designed to be coupled to semi-analytic galaxy formation models or hydrodynamical simulations. The modular fashion of the code allows the user to easily introduce new descriptions for recombinations and the photoionization rate.

Density limit studies in the large helical device

International Nuclear Information System (INIS)

Peterson, B.J.; Miyazawa, J.; Nishimura, K.

2005-01-01

Steady state densities of up to 1.6 x 10 20 m -3 have been sustained using gas puff fuelling and NBI heating up to 11 MW in the Large Helical Device (LHD). The density limit in LHD is observed to be ∼ 1.6 times the Sudo limit. The density is ultimately limited by radiative collapse which is attributed to the onset of a radiative thermal instability of the light impurities in the edge region of the plasma based on several observations. First of all the onset of the radiative thermal instability is tied to a certain edge temperature threshold. Secondly, the onset of thermal instability occurs first in oxygen and then carbon as expected from their cooling rate temperature dependencies. Finally, radiation profiles show that as the temperature drops and the plasma collapses the radiating zone broadens and moves inward. In addition, comparison with the total radiated power behaviour indicates that Carbon is the dominant radiator. Two dimensional tomographic inversions of AXUVD array data and comparison of modelling with images of radiation brightness from imaging bolometers and indicate that the poloidal asymmetry which accompanies the radiative collapse is toroidally symmetric. Ain addition to the operational density limit where the discharge is terminated by radiative collapse, a confinement limit has been recognized in LHD. This confinement limit appears at lower density than the operational density limit, similar to the saturated ohmic confinement observed in tokamaks. To investigate the physics behind this degradation, the parameter dependence of the thermal diffusivity, χ, has been investigated. While the temperature dependence in ISS95 is as strong as the gyro-Bohm model of χ ∝ T e 1.5 , weaker T e dependence of χ ∝ T e 0.5 appears in the high-density regime. Such weak T e dependence results in the weak density dependence of the global energy confinement as τ E ∝ n e 13 -bar. (author)

The ratio of double to single ionization of helium: The relationship of photon and bare charged particle impact ionization

International Nuclear Information System (INIS)

Manson, S.T.

1994-01-01

In this paper the author derives expressions for the ratio of double to single ionization of helium from its ground state, by both single photons, and charged particle impact. He shows that in the limit of large reduced incident energy T of a charged particle, that the ratio of the double to single ionization cross sections at some energy transfer ΔE is equal to the ratio of photoionization cross sections for a photon of energy hν = ΔE, independent of T. He then goes on to find a relationship for this ionization ratio which is not restricted to some specific energy transfer, and shows that the double to single ionization cross section ratio approaches an asymtotic limit for large enough T

Ionization loss in BGO

International Nuclear Information System (INIS)

Bakken, J.A.; Denes, P.; Piroue, P.A.; Stickland, D.P.; Sumner, R.L.; Taylor, C.; Barone, L.; Borgia, B.; Diemoz, M.; Dionisi, C.; Falciano, S.; Ferroni, F.; Gratta, G.; Longo, E.; Luminari, L.; Morganti, S.; Valente, E.; Blaising, J.J.; Boutigny, D.; Coignet, G.; Karyotakis, Y.; Sauvage, G.; Schneegans, M.; Vivargent, M.; Extermann, P.; Morand, G.; Ossmann, J.; Ruckstuhl, W.; Schaad, T.P.; Lecoq, P.; Walk, W.; Li, P.J.; Micke, M.; Micke, U.; Schmitz, D.

1988-01-01

We report on a precise measurement of the energy loss through ionization by pions in bismuth germanate performed at several values of the incident particles momentum with a prototype of the L3 electromagnetic calorimeter. The experimental results are in good agreement with theoretical predictions showing the relativistic rise modified by density effect. (orig.)

Arrays of Synthetic Atoms: Nanocapacitor Batteries with Large Energy Density and Small Leak Currents

Science.gov (United States)

2017-11-28

AFRL-RV-PS- AFRL-RV-PS- TR-2017-0169 TR-2017-0169 ARRAYS OF SYNTHETIC ATOMS: NANOCAPACITOR BATTERIES WITH LARGE ENERGY DENSITY AND SMALL LEAK...1-0247 Arrays of Synthetic Atoms: Nanocapacitor Batteries with Large Energy Density and Small Leak Currents 5b. GRANT NUMBER 5c. PROGRAM ELEMENT...large dielectric strength to a nanoscale rechargeable battery . We fabricated arrays of one-, two- and three-dimensional synthetic atoms and comparison

High Power Density Power Electronic Converters for Large Wind Turbines

DEFF Research Database (Denmark)

Senturk, Osman Selcuk

. For these VSCs, high power density is required due to limited turbine nacelle space. Also, high reliability is required since maintenance cost of these remotely located wind turbines is quite high and these turbines operate under harsh operating conditions. In order to select a high power density and reliability......In large wind turbines (in MW and multi-MW ranges), which are extensively utilized in wind power plants, full-scale medium voltage (MV) multi-level (ML) voltage source converters (VSCs) are being more preferably employed nowadays for interfacing these wind turbines with electricity grids...... VSC solution for wind turbines, first, the VSC topology and the switch technology to be employed should be specified such that the highest possible power density and reliability are to be attained. Then, this qualitative approach should be complemented with the power density and reliability...

Large density amplification measured on jets ejected from a magnetized plasma gun

OpenAIRE

Yun, Gunsu S.; You, Setthivoine; Bellan, Paul M.

2007-01-01

Observation of a large density amplification in the collimating plasma jet ejected from a coplanar coaxial plasma gun is reported. The jet velocity is ~30 km s^-1 and the electron density increases from ~10^20 to 10^(22–23) m^-3. In previous spheromak experiments, electron density of the order 10^(19–21) m^-3 had been measured in the flux conserver region, but no density measurement had been reported for the source gun region. The coplanar geometry of our electrodes permits direct observation...

L-subshell ionization studies in Au and Bi for 19F and 28Si large-ion bombardment

International Nuclear Information System (INIS)

Padhi, H.C.; Dhal, B.B.; Nanal, V.; Prasad, K.G.; Tandon, P.N.; Trautmann, D.

1996-01-01

L x-ray production and subshell ionization cross sections of Au and Bi have been measured for the bombardment of 19 F and 28 Si ions in the energy range 30 endash 57 MeV and 36 endash 84 MeV, respectively. Comparison of the Lα x-ray production cross sections of Au with the earlier data by Malhi and Gray [Phys. Rev. A 44, 7199 (1991)] shows reasonable agreement for 19 F impact and their data are consistently higher for 28 Si at all energies. The measured Lα line energy shows a shift towards higher energy, which appears to be proportional to the square of the projectile atomic number at all impact energies. This shift suggests the presence of multiple ionization in the L and M shells with a simultaneous production of four M holes in Au at the impact energy of 3 MeVu -1 of 28 Si. The L-subshell ionization cross sections obtained from the measured x-ray production cross sections have been compared with the semiclassical approximation and perturbed stationary state theory with energy loss, Coulomb deflection, and relativistic correction for the electron motion calculations, which show large deviations for the L 1 subshell. The L 2 - and L 3 -subshell ionization cross sections are underestimated by both the theories by a factor of 1.2 endash 4.0 for 28 Si impact whereas for the 19 F case there is reasonable agreement for the L 3 cross section but the L 2 cross section is underestimated by 20 endash 30%. copyright 1996 The American Physical Society

Approximate thermodynamic state relations in partially ionized gas mixtures

International Nuclear Information System (INIS)

Ramshaw, John D.

2004-01-01

Thermodynamic state relations for mixtures of partially ionized nonideal gases are often approximated by artificially partitioning the mixture into compartments or subvolumes occupied by the pure partially ionized constituent gases, and requiring these subvolumes to be in temperature and pressure equilibrium. This intuitively reasonable procedure is easily shown to reproduce the correct thermal and caloric state equations for a mixture of neutral (nonionized) ideal gases. The purpose of this paper is to point out that (a) this procedure leads to incorrect state equations for a mixture of partially ionized ideal gases, whereas (b) the alternative procedure of requiring that the subvolumes all have the same temperature and free electron density reproduces the correct thermal and caloric state equations for such a mixture. These results readily generalize to the case of partially degenerate and/or relativistic electrons, to a common approximation used to represent pressure ionization effects, and to two-temperature plasmas. This suggests that equating the subvolume electron number densities or chemical potentials instead of pressures is likely to provide a more accurate approximation in nonideal plasma mixtures

Biological effects of low-level ionizing and non-ionizing radiation

International Nuclear Information System (INIS)

Upton, A.C.

1986-01-01

Early in this century it was recognized that large doses of ionizing radiation could injure almost any tissue in the body, but small doses were generally thought to be harmless. By the middle of the century however it came to be suspected that even the smallest doses of ionizing radiation to the gonads might increase the risk of hereditary disease in subsequently-conceived offspring. Since then the hypothesis that carcinogenic and teratogenic effects also have no threshold has been adopted for purposes of radiological protection. It is estimated nevertheless that the risks that may be associated with natural background levels of ionizing irradiation are too small to be detectable. Hence validation of such risk estimates will depend on further elucidation of the dose-effect relationships and mechanisms of the effects in question, through studies at higher dose levels. In contrast to the situation with ionizing radiation, exposure to natural background levels of ultraviolet radiation has been implicated definitively in the etiology of skin cancers in fair-skinned individuals. Persons with inherited effects in DNA repair capacity are particularly susceptible. Non-ionizing radiations of other types can also affect health at high dose levels, but whether they can cause injury at low levels of exposure is not known

An approximate method to calculate ionization of LTE and non-LTE plasma

International Nuclear Information System (INIS)

Zhang Jun; Gu Peijun

1987-01-01

When matter, especially high Z element, is heated to high temperature, it will be ionized many times. The degree of ionization has a strong effect on many plasma properties. So an approximate method to calculate the mean ionization degree is needed for solving many practical problems. An analytical expression which is convenient for the approximate numerical calculation is given by fitting it to the scaling law and numerical results of the ionization potential of Thomas-Fermi statistical model. In LTE case, the ionization degree of Au calculated by using the approximate method is in agreement with that of the average ion model. By extending the approximate method to non-LTE case, the ionization degree of Au is similarly calculated according to Corona model and Collision-Radiatoin model(C-R). The results of Corona model agree with the published data quite well, while the results of C-R approach those of Corona model as the density is reduced and approach those of LTE as the density is increased. Finally, all approximately calculated results of ionization degree of Au and the comparision of them are given in figures and tables

Hydrodynamic optical-field-ionized plasma channels

Science.gov (United States)

Shalloo, R. J.; Arran, C.; Corner, L.; Holloway, J.; Jonnerby, J.; Walczak, R.; Milchberg, H. M.; Hooker, S. M.

2018-05-01

We present experiments and numerical simulations which demonstrate that fully ionized, low-density plasma channels could be formed by hydrodynamic expansion of plasma columns produced by optical field ionization. Simulations of the hydrodynamic expansion of plasma columns formed in hydrogen by an axicon lens show the generation of 200 mm long plasma channels with axial densities of order ne(0 ) =1 ×1017cm-3 and lowest-order modes of spot size WM≈40 μ m . These simulations show that the laser energy required to generate the channels is modest: of order 1 mJ per centimeter of channel. The simulations are confirmed by experiments with a spherical lens which show the formation of short plasma channels with 1.5 ×1017cm-3≲ne(0 ) ≲1 ×1018cm-3 and 61 μ m ≳WM≳33 μ m . Low-density plasma channels of this type would appear to be well suited as multi-GeV laser-plasma accelerator stages capable of long-term operation at high pulse repetition rates.

Effects of ionizing radiation on vitamins

International Nuclear Information System (INIS)

Thayer, D.W.; Fox, J.B. Jr.; Lakritz, L.

1991-01-01

Vitamins are known to be sensitive to the effects of ionizing radiation. Since most foods contain a large proportion of water, the most probable reaction of the ionizing radiation would be with water; and as vitamins are present in very small amounts compared with other substances in the food they will be affected indirectly by the radiation. This chapter discusses the effect of ionizing radiation on water soluble vitamins and fat soluble vitamins. (author)

Re-ionization of a partially ionized plasma by an Alfven wave of moderate amplitude

International Nuclear Information System (INIS)

Brennan, M.H.; Sawley, M.L.

1980-01-01

The use of forced magnetic-acoustic oscillations to investigate the effect of a torsional hydromagnetic (Alfven) wave pulse of moderate amplitude on the properties of a partially ionized afterglow helium plasma is reported. Observations of the magnetic flux associated with the oscillations, measured at a number of frequencies are used to determine radial density profiles and to provide estimates of plasma temperature. The torsional wave is shown to cause significant re-ionization of the plasma with no corresponding increase in the plasma temperature. The presence of a number of energetic particles is evidenced by the production of a significant number of doubly charged helium ions. (author)

Surface Ionization and Soft Landing Techniques in Mass Spectrometry

International Nuclear Information System (INIS)

Futrell, Jean H.; Laskin, Julia

2010-01-01

The advent of soft ionization techniques, notably electrospray and laser desorption ionization methods, has extended mass spectrometric methods to large molecules and molecular complexes. This both greatly expands applications of mass spectrometry and makes the activation and dissociation of complex ions an integral part of large molecule mass spectrometry. A corollary of the much greater number of internal degrees of freedom and high density of states associated with molecular complexity is that internal energies much higher than the dissociation energies for competing fragmentation processes are required for observable fragmentation in time scales sampled by mass spectrometers. This article describes the kinetics of surface-induced dissociation (SID), a particularly efficient activation method for complex ions. Two very important characteristics of SID are very rapid, sub-picosecond activation and precise control of ion internal energy by varying ion collision energy. The nature of the surface plays an important role in SID, determining both efficiency and mechanism of ion activation. Surface composition and morphology strongly influence the relative importance of competing reactions of SID, ion capture (soft-landing), surface reaction and neutralization. The important features of SID and ion soft-landing are described briefly in this review and more fully in the recommended reading list.

Secondary ionization processes in laser induced breakdown of electronegative gases

International Nuclear Information System (INIS)

Gamal Yosr, E.E.D.; Shafik, M.S.; Abdel-Moneim, H.M.

1990-08-01

This paper presents an investigation of the stepwise ionization processes which occur during the interaction of laser radiation with electronegative gases. Calculations are carried out adopting a modified version of the electron cascade model previously developed by Evans and Gamal. The modifications of the model are performed for the case of molecular oxygen to account for electron attachment losses. Particular attention is devoted to molecular oxygen at a pressure of 2.8 x 10 4 Torr irradiated by 10 ns pulse of Nd:YAG laser (λ=1.064 μm) at a peak intensity of 1.7x10 11 Wcm -2 . The calculations consider the effect of the secondary ionization processes on the electron energy distribution function and its parameters (evolution of the density of the excited molecules, electrons density as well as the electron mean energy during the laser flash). This analysis shows how the removal of slow electrons by attachment to oxygen molecules creates a strong competition between the stepwise ionization processes. These processes namely photoionization and collisional ionization deplete the electronic excited states and contribute eventually to the ionization growth rate in laser induced breakdown of electronegative gases. (author). 7 refs, 6 figs, 1 tab

Two-center interference effects in (e, 2e) ionization of H2 and CO2 at large momentum transfer

Science.gov (United States)

Yamazaki, Masakazu; Nakajima, Isao; Satoh, Hironori; Watanabe, Noboru; Jones, Darryl; Takahashi, Masahiko

2015-09-01

In recent years, there has been considerable interest in understanding quantum mechanical interference effects in molecular ionization. Since this interference appears as a consequence of coherent electron emission from the different molecular centers, it should depend strongly on the nature of the ionized molecular orbital. Such molecular orbital patterns can be investigated by means of binary (e, 2e) spectroscopy, which is a kinematically-complete electron-impact ionization experiment performed under the high-energy Bethe ridge conditions. In this study, two-center interference effects in the (e, 2e) cross sections of H2 and CO2 at large momentum transfer are demonstrated with a high-statistics experiment, in order to elucidate the relationship between molecular orbital patterns and the interference structure. It is shown that the two-center interference is highly sensitive to the phase, spatial pattern, symmetry of constituent atomic orbital, and chemical bonding nature of the molecular orbital. This work was partially supported by Grant-in-Aids for Scientific Research (S) (No. 20225001) and for Young Scientists (B) (No. 21750005) from the Ministry of Education, Culture, Sports, Science and Technology.

Ionization equilibrium in dense plasmas

International Nuclear Information System (INIS)

Ying, R.

1987-01-01

The average degree of ionization for a strongly coupled plasma is investigated and calculated. Two widely used approaches: the Saha equation method and the Thomas-Fermi (TF) statistical atomic model are adopted to determine the degree of ionization. Both methods are modified in a number of ways to include the strong-coupling effect in the plasma. In the Saha equation approach, the strong-coupling effects are introduced through: (i) a replacement of the Coulomb potential by a screened Debye potential; (ii) adoption of the Planck-Larkin partition function; (iii) description of the electron component by Fermi-Dirac statistics. The calculated degree of ionization exceeds that obtained from the original Saha equation, exhibits a minimum as a function of the density and shows an abrupt phase transition from weakly ionized to a fully ionized state. The zero-temperature TF model for compressed ions and the finite-temperature TF model for ions are investigated for the first time. In order to take into account the strong-coupling effect in a systematic way, a strong-coupling TF model is set up. Favorable results with the relatively simple approximations indicate that the newly established strong-coupling TF model is a more systematic and physically consistent approach

Effects of multiple electronic shells on strong-field multiphoton ionization and high-order harmonic generation of diatomic molecules with arbitrary orientation: An all-electron time-dependent density-functional approach

International Nuclear Information System (INIS)

Telnov, Dmitry A.; Chu, S.-I

2009-01-01

We present a time-dependent density-functional theory approach with proper long-range potential for an ab initio study of the effect of correlated multielectron responses on the multiphoton ionization (MPI) and high-order harmonic generation (HHG) of diatomic molecules N 2 and F 2 in intense short laser pulse fields with arbitrary molecular orientation. We show that the contributions of inner molecular orbitals to the total MPI probability can be sufficiently large or even dominant over the highest-occupied molecular orbital, depending on detailed electronic structure and symmetry, laser field intensity, and orientation angle. The multielectron effects in HHG are also very important. They are responsible for enhanced HHG at some orientations of the molecular axis. Even strongly bound electrons may have a significant influence on the HHG process.

Molecular evidence for the induction of large interstitial deletions on mouse chromosome 8 by ionizing radiation

International Nuclear Information System (INIS)

Turker, Mitchell S.; Pieretti, Maura; Kumar, Sudha

1997-01-01

The P19H22 mouse embryonal carcinoma cell line is characterized by a hemizygous deficiency for the chromosome 8 encoded aprt (adenine phosphoribosyltransferase) gene and heterozygosity for many chromosome 8 loci. We have previously demonstrated that this cell line is suitable for mutational studies because it is permissive of events ranging in size from base-pair substitutions at the aprt locus to apparent loss of chromosome 8. Large mutational events, defined by loss of the remaining aprt allele, were found to predominate in spontaneous mutants and those induced by ionizing radiation. In this study we have used a PCR based assay to screen for loss of heterozygosity at microsatellite loci both proximal and distal to aprt in 137 Cs-induced and spontaneous aprt mutants. This approach allowed us to distinguish apparent interstitial deletional events from apparent recombinational events. Significantly, 32.5% (26 of 80) of the mutational events induced by 137 Cs appeared to be interstitial deletions as compared with 7.7% (6 of 78) in the spontaneous group. This difference was statistically significant (p 137 Cs caused a significant number of deletion mutations. Most 137 Cs-induced interstitial deletions were larger than 6 cM, whereas none of the spontaneous deletions were larger than 6 cM. These results provide further support for the notion that ionizing radiation induces deletion mutations and validate the use of the P19H22 cell line for the study of events induced by ionizing radiation

Quantitative analysis of copolymers : influence of the structure of the monomer on the ionization efficiency in electrospray ionization FTMS

NARCIS (Netherlands)

Koster, S.; Mulder, B.; Duursma, M.C.; Boon, J.J.; Philipsen, H.J.A.; Velde, J.W.; Nielen, M.W.F.; Koster, de C.G.; Heeren, R.M.A.

2002-01-01

The influence of the ionization efficiency on the measured copolymer sequence distribution is presented. Large differences in ionization efficiency were observed for mixtures of homopolyesters containing dipropoxylated bisphenol A/adipic acid and dipropoxylated bisphenol A/isophthalic acid and the

Male density affects large-male advantage in the golden silk spider, Nephila clavipes

OpenAIRE

Clare C. Rittschof

2010-01-01

Across a variety of animal taxa, the outcome of male--male contests depends on male body size; winners are usually the larger males or the males with bigger weapons. However, high male density can either increase or reverse large-male advantage because density changes the frequency and intensity of male--male interactions. In the golden orb-web spider Nephila clavipes, large males have a competitive advantage in male--male contests. However, this species shows more than 2-fold variation in ma...

Order made in implementation of Section 23 of Decree no 75-306 of 28 April 1975 on the protection of workers against the hazards of ionizing radiations in large nuclear installations

International Nuclear Information System (INIS)

1977-01-01

This Order was made in implementation of Decree No 75-306 of 28 April 1975 on the Protection of Workers Against the Hazards of Ionizing Radiations in Large Nuclear Installations and approves the methods for controlling radiation sources and the atmosphere in large nuclear installations which are elaborated by the Central Service for Protection Against Ionizing Radiations. (NEA) [fr

Geomagnetic control of mesospheric nitric oxide concentration from simultaneous D and F region ionization measurements

International Nuclear Information System (INIS)

Pradhan, S.N.; Shirke, J.S.

1978-01-01

Investigations are made of D-region electron density profiles derived from 'partial reflection' measurements over a low latitude station (Ahmedabad) during a year of low solar activity. The index relating the electron density with the solar zenith angle is found to increase towards lower zenith angles suggesting both diurnal and seasonal variations in the Nitric oxide concentration. A close correlation is also found between the electron density at 80 km and the maximum ionization density in the F region above. This is interpreted as due to concomitant variation of a sizeable fraction of the Nitric oxide concentration in the mesosphere and lower thermosphere with the overhead F region ionization. A simplified global model is presented for the mesospheric Nitric oxide concentration based on the morphological features of F region and the relationship existing between the ionization levels in F and D regions. Many observed features of the D region ionization including the solar zenith angle dependence, latitudinal and geomagnetic anomaly and long term variability are explained on the basis of this model

Multiconfiguration Pair-Density Functional Theory Is Free From Delocalization Error.

Science.gov (United States)

Bao, Junwei Lucas; Wang, Ying; He, Xiao; Gagliardi, Laura; Truhlar, Donald G

2017-11-16

Delocalization error has been singled out by Yang and co-workers as the dominant error in Kohn-Sham density functional theory (KS-DFT) with conventional approximate functionals. In this Letter, by computing the vertical first ionization energy for well separated He clusters, we show that multiconfiguration pair-density functional theory (MC-PDFT) is free from delocalization error. To put MC-PDFT in perspective, we also compare it with some Kohn-Sham density functionals, including both traditional and modern functionals. Whereas large delocalization errors are almost universal in KS-DFT (the only exception being the very recent corrected functionals of Yang and co-workers), delocalization error is removed by MC-PDFT, which bodes well for its future as a step forward from KS-DFT.

Ionization Efficiency in the Dayside Martian Upper Atmosphere

Science.gov (United States)

Cui, J.; Wu, X.-S.; Xu, S.-S.; Wang, X.-D.; Wellbrock, A.; Nordheim, T. A.; Cao, Y.-T.; Wang, W.-R.; Sun, W.-Q.; Wu, S.-Q.; Wei, Y.

2018-04-01

Combining the Mars Atmosphere and Volatile Evolution measurements of neutral atmospheric density, solar EUV/X-ray flux, and differential photoelectron intensity made during 240 nominal orbits, we calculate the ionization efficiency, defined as the ratio of the secondary (photoelectron impact) ionization rate to the primary (photon impact) ionization rate, in the dayside Martian upper atmosphere under a range of solar illumination conditions. Both the CO2 and O ionization efficiencies tend to be constant from 160 km up to 250 km, with respective median values of 0.19 ± 0.03 and 0.27 ± 0.04. These values are useful for fast calculation of the ionization rate in the dayside Martian upper atmosphere, without the need to construct photoelectron transport models. No substantial diurnal and solar cycle variations can be identified, except for a marginal trend of reduced ionization efficiency approaching the terminator. These observations are favorably interpreted by a simple scenario with ionization efficiencies, as a first approximation, determined by a comparison between relevant cross sections. Our analysis further reveals a connection between regions with strong crustal magnetic fields and regions with high ionization efficiencies, which are likely indicative of more efficient vertical transport of photoelectrons near magnetic anomalies.

Effects of ionizing radiation and partial hepatectomy on messenger RNA synthesis

International Nuclear Information System (INIS)

Abdel-Halim, M.N.

1979-01-01

Newly synthesized messenger RNA, as measured by a 40 min uptake of the radioactive precursor (6- 14 C) orotic acid, was studied in the regenerating livers of non-irradiated and gamma-irradiated (1800 rad) adrenal-intact and adrenalectomized rats 24 and 48 hours after partial hepatectomy. Two groups of rats, one with and one without adrenal glands were each divided into four subgroups: (1) control rats, (2) irradiated rats, (3) partially hepatectomized rats and (4) irradiated, partially hepatectomized rats. The radioactive profile of polyribosome formation and distribution was determined by sucrose density gradient centrifugation (10 to 40 per cent). The result of this study indicates that ionizing radiation decreases the synthesis of newly formed messenger RNA in regenerating livers of adrenal-intact rats. However, adrenalectomy largely abolished that inhibition. These data suggest that the decrease in messenger RNA synthesis may be explained by the disturbance of adrenal hormones induced by partial hepatectomy and ionizing radiation. (author)

Gasdynamics of H II regions. V. The interaction of weak R ionization fronts with dense clouds

Energy Technology Data Exchange (ETDEWEB)

Tenorio-Tagle, G; Bedijn, P J

1981-06-01

The interaction of weak R-type ionization fronts with a density enhancement is calculated numerically as a function of time within the framework of the champagne model of the evolution of H II regions. Calculations are performed under the assumption of plane-parallel geometry for various relative densities of the cloud in which the exciting star is formed and a second cloud with which an ionization front from the first cloud interacts. The supersonic ionization front representing the outer boundary of an H II region experiencing the champagne phase is found to either evolve into a D-type front or remain of type R, depending on the absolute number of photons leaving the H II region that undergoes the champagne phase. Recombinations in the ionized gas eventually slow the ionization front, however photon fluxes allow it to speed up again, resulting in oscillatory propagation of the front. Front-cloud interactions are also shown to lead to the development of a backward-facing shock, a forward-facing shock, and a density maximum in the ionized gas. The results can be used to explain the origin of bright rims in H II regions.

Benchmark study of ionization potentials and electron affinities of armchair single-walled carbon nanotubes using density functional theory

Science.gov (United States)

Zhou, Bin; Hu, Zhubin; Jiang, Yanrong; He, Xiao; Sun, Zhenrong; Sun, Haitao

2018-05-01

The intrinsic parameters of carbon nanotubes (CNTs) such as ionization potential (IP) and electron affinity (EA) are closely related to their unique properties and associated applications. In this work, we demonstrated the success of optimal tuning method based on range-separated (RS) density functionals for both accurate and efficient prediction of vertical IPs and electron affinities (EAs) of a series of armchair single-walled carbon nanotubes C20n H20 (n  =  2–6) compared to the high-level IP/EA equation-of-motion coupled-cluster method with single and double substitutions (IP/EA-EOM-CCSD). Notably, the resulting frontier orbital energies (–ε HOMO and –ε LUMO) from the tuning method exhibit an excellent approximation to the corresponding IPs and EAs, that significantly outperform other conventional density functionals. In addition, it is suggested that the RS density functionals that possess both a fixed amount of exact exchange in the short-range and a correct long-range asymptotic behavior are suitable for calculating electronic structures of finite-sized CNTs. Next the performance of density functionals for description of various molecular properties such as chemical potential, hardness and electrophilicity are assessed as a function of tube length. Thanks to the efficiency and accuracy of this tuning method, the related behaviors of much longer armchair single-walled CNTs until C200H20 were studied. Lastly, the present work is proved to provide an efficient theoretical tool for future materials design and reliable characterization of other interesting properties of CNT-based systems.

Determination of electron temperature and density at plasma edge in the Large Helical Device with opacity-incorporated helium collisional-radiative model

International Nuclear Information System (INIS)

Goto, M.; Sawada, K.

2014-01-01

Spectra of neutral helium in the visible wavelength range are measured for a discharge in the Large Helical Device (LHD). The electron temperature (T e ) and density (n e ) are derived from the intensity distribution of helium emission lines. For that purpose, a collisional-radiative model developed by Sawada et al. [Plasma and Fusion Res. 2010;5:001] which takes the reabsorption effect into account is used. It is found that incorporation of the reabsorption effect is necessary to obtain a set of T e and n e giving consistent line intensity distribution with the measurement, and that those parameters obtained vary as the line-averaged n e changes in the course of time. The position where the helium line emission dominantly takes place is located with the help of T e and n e profiles measured by the Thomson scattering system. The result indicates that the emission position is almost fixed at the place where the connection length of the magnetic field lines to the divertor plate leaps beyond 10 m. Because intense neutral atom line emission suggests the vigorous ionization of neutral atoms, the helium line emission location determined here can be regarded as the effective boundary of the plasma. - Highlights: • The reabsorption effect is included in the helium collisional-radiative model. • Electron temperature and density are derived for the Large Helical Device (LHD). • Line emission location is found to be little changed during the discharge. • This measurement method can be used to determine the position of effective plasma boundary

Environmental gamma radiation monitoring system with a large volume air ionization chamber

International Nuclear Information System (INIS)

Duftschmid, K.E.; Strachotinsky, C.; Witzani, J.

1986-01-01

An improved environmental monitoring system has been designed and tested consisting of an ionization chamber with 120 l sensitive volume, operated at atmospheric pressure, and a commercial electrometer amplifier with digital voltmeter. The system is controlled by a desk calculator with printer for automated operation and calculation of dose and doserate. The ionization chamber provides superior dosimetric performance as compared to usual GM-counters and high pressure chambers. The system has been field-tested during the 'European Intercomparison Programme for Environmental Monitoring Instruments' organized by the Commission of the European Communities. (Author)

RUNAWAY STARS AND THE ESCAPE OF IONIZING RADIATION FROM HIGH-REDSHIFT GALAXIES

International Nuclear Information System (INIS)

Conroy, Charlie; Kratter, Kaitlin M.

2012-01-01

Approximately 30% of all massive stars in the Galaxy are runaways with velocities exceeding 30 km s –1 . Their high speeds allow them to travel ∼0.1-1 kpc away from their birthplace before they explode at the end of their several Myr lifetimes. At high redshift, when galaxies were much smaller than in the local universe, runaways could venture far from the dense inner regions of their host galaxies. From these large radii, and therefore low column densities, much of their ionizing radiation is able to escape into the intergalactic medium. Runaways may therefore significantly enhance the overall escape fraction of ionizing radiation, f esc , from small galaxies at high redshift. We present simple models of the high-redshift runaway population and its impact on f esc as a function of halo mass, size, and redshift. We find that the inclusion of runaways enhances f esc by factors of ≈1.1-8, depending on halo mass, galaxy geometry, and the mechanism of runaway production, implying that runaways may contribute 50%-90% of the total ionizing radiation escaping from high-redshift galaxies. Runaways may therefore play an important role in reionizing the universe.

Many-electron model for multiple ionization in atomic collisions

International Nuclear Information System (INIS)

Archubi, C D; Montanari, C C; Miraglia, J E

2007-01-01

We have developed a many-electron model for multiple ionization of heavy atoms bombarded by bare ions. It is based on the transport equation for an ion in an inhomogeneous electronic density. Ionization probabilities are obtained by employing the shell-to-shell local plasma approximation with the Levine and Louie dielectric function to take into account the binding energy of each shell. Post-collisional contributions due to Auger-like processes are taken into account by employing recent photoemission data. Results for single-to-quadruple ionization of Ne, Ar, Kr and Xe by protons are presented showing a very good agreement with experimental data

Many-electron model for multiple ionization in atomic collisions

Energy Technology Data Exchange (ETDEWEB)

Archubi, C D [Instituto de AstronomIa y Fisica del Espacio, Casilla de Correo 67, Sucursal 28 (C1428EGA) Buenos Aires (Argentina); Montanari, C C [Instituto de AstronomIa y Fisica del Espacio, Casilla de Correo 67, Sucursal 28 (C1428EGA) Buenos Aires (Argentina); Miraglia, J E [Instituto de AstronomIa y Fisica del Espacio, Casilla de Correo 67, Sucursal 28 (C1428EGA) Buenos Aires (Argentina)

2007-03-14

We have developed a many-electron model for multiple ionization of heavy atoms bombarded by bare ions. It is based on the transport equation for an ion in an inhomogeneous electronic density. Ionization probabilities are obtained by employing the shell-to-shell local plasma approximation with the Levine and Louie dielectric function to take into account the binding energy of each shell. Post-collisional contributions due to Auger-like processes are taken into account by employing recent photoemission data. Results for single-to-quadruple ionization of Ne, Ar, Kr and Xe by protons are presented showing a very good agreement with experimental data.

Comparison of laser-induced surface damage density measurements with small and large beams: toward representativeness

International Nuclear Information System (INIS)

Lamaignere, Laurent; Dupuy, Gabriel; Donval, Thierry; Grua, Pierre; Bercegol, Herve

2011-01-01

Pulsed laser damage density measurements obtained with diverse facilities are difficult to compare, due to the interplay of numerous parameters, such as beam area and pulse geometry, which, in operational large beam conditions, are very different from laboratory measurements. This discrepancy could have a significant impact; if so, one could not even pretend that laser damage density control is a real measurement process. In this paper, this concern is addressed. Tests with large beams of centimeter size on a high-power laser facility have beam performed according to a parametric study and are compared to small beam laboratory tests. It is shown that laser damage densities obtained with large and small beams are equal, within calculated error bars.

Accessible light detection and ranging: estimating large tree density for habitat identification

Science.gov (United States)

Heather A. Kramer; Brandon M. Collins; Claire V. Gallagher; John Keane; Scott L. Stephens; Maggi Kelly

2016-01-01

Large trees are important to a wide variety of wildlife, including many species of conservation concern, such as the California spotted owl (Strix occidentalis occidentalis). Light detection and ranging (LiDAR) has been successfully utilized to identify the density of large-diameter trees, either by segmenting the LiDAR point cloud into...

A statistical mechanical model for equilibrium ionization

International Nuclear Information System (INIS)

Macris, N.; Martin, P.A.; Pule, J.

1990-01-01

A quantum electron interacts with a classical gas of hard spheres and is in thermal equilibrium with it. The interaction is attractive and the electron can form a bound state with the classical particles. It is rigorously shown that in a well defined low density and low temperature limit, the ionization probability for the electron tends to the value predicted by the Saha formula for thermal ionization. In this regime, the electron is found to be in a statistical mixture of a bound and a free state. (orig.)

A mesh density study for application to large deformation rolling process evaluation

International Nuclear Information System (INIS)

Martin, J.A.

1997-12-01

When addressing large deformation through an elastic-plastic analysis the mesh density is paramount in determining the accuracy of the solution. However, given the nonlinear nature of the problem, a highly-refined mesh will generally require a prohibitive amount of computer resources. This paper addresses finite element mesh optimization studies considering accuracy of results and computer resource needs as applied to large deformation rolling processes. In particular, the simulation of the thread rolling manufacturing process is considered using the MARC software package and a Cray C90 supercomputer. Both mesh density and adaptive meshing on final results for both indentation of a rigid body to a specified depth and contact rolling along a predetermined length are evaluated

Ionization and fragmentation of DNA-RNA bases: a density functional theory study

International Nuclear Information System (INIS)

Sadr-Arani, Leila

2014-01-01

Ionizing radiation (IR) cross human tissue, deposit energy and dissipate fragmenting molecules. The resulting fragments may be highlighted by mass spectrometry. Despite the amount of information obtained experimentally by the interpretation of the mass spectrum, experience alone cannot answer all the questions of the mechanism of fragmentation of DNA/RNA bases and a theoretical study is a complement to this information. A theoretical study allows us to know the weakest bonds in the molecule during ionization and thus may help to provide mechanisms of dissociation and produced fragments. The purpose of this work, using the DFT with the PBE functional, is to study the ionization and fragmentation mechanisms of DNA/RNA bases (Uracil, Cytosine, Adenine and Guanine) and to identify the cations corresponding to each peak in mass spectra. For all RNA bases, the retro Diels-Alder reaction (elimination of HNCO or NCO*) is a major route for dissociating, with the exception of adenine for which there is no atom oxygen in its structure. Loss of NH 3 (NH 2 *) molecule is another common way to all bases that contain amine group. The possibility of the loss of hydrogen from the cations is also investigated, as well as the dissociation of dehydrogenated cations and protonated uracil. This work shows the interest of providing DFT calculation in the interpretation of mass spectra of DNA bases. (author)

Kinetics of swelling of polyelectrolyte gels: Fixed degree of ionization

Science.gov (United States)

Sen, Swati; Kundagrami, Arindam

2015-12-01

The swelling kinetics of uncharged and charged polymer (polyelectrolyte) gels in salt-free conditions is studied in one dimension by solving the constitutive equation of motion (Newton's law for the elementary gel volume) of the displacement variable by two theoretical methods: one in which the classical definition of stress is used with the bulk modulus taken as a parameter, and the other in which a phenomenological expression of the osmotic stress as a function of polymer density and degree of ionization is taken as an input to the dynamics. The time-evolution profiles for spatially varying polymer density and stress, along with the location of the gel-solvent interface, are obtained from the two methods. We show that both the polymer density (volume fraction) and stress inside the gel follow expected behaviours of being maximum for the uniformly shrunken gel, and relaxing slowly to the lowest values as the gel approaches equilibrium. We further show that, by comparing the temporal profiles of the gel-solvent interface and other variables between the two methods, one may attempt to assign an effective bulk modulus to the polyelectrolyte gel as a function of the degree of ionization and other parameters of the gel such as hydrophobicity, cross-link density, and the temperature. The major result we get is that the effective bulk modulus of a polyelectrolyte gel increases monotonically with its degree of ionization. In the process of identifying the parameters for a monotonic swelling, we calculated using a well-known expression of the free energy the equilibrium results of two-phase co-existence and the critical point of a polyelectrolyte gel with a fixed degree of ionization.

Parametric study of x-ray pre-ionizer with plasma cathode

International Nuclear Information System (INIS)

Bollanti, S.; Di Lazzaro, P.; Flora, F.; Giordano, G.; Letardi, T.; Schina, G.; Zheng, C.

1993-01-01

The construction characteristics and the performance of an x-ray diode working at 200 Hz are described. The temporal behavior of both the plasma cathode emission and the diode discharge was studied, including the measurements of vacuum effects on the repetition rate and lifetime capability, pre-ionization versus electrical features, and ionization density versus dosage. This simple and low-cost x-ray diode was used to uniformly pre-ionize a half-liter XeCl laser, delivering an output laser energy of 800 mJ/shot at a 100-Hz repetition rate

Multiphoton ionization for hydrogen plasma diagnostics

International Nuclear Information System (INIS)

Bonnie, J.H.M.

1987-01-01

In this thesis the processes leading to the formation of negative ions (H - ) in hydrogen discharges are studied. These ions enable efficient production of a beam of fast neutral particles. Such beams are applied in nuclear fusion research. A model has been generally accepted in which H - is formed by means of dissociative attachment (DA) of electrons to vibrationally excited hydrogen molecules [H 2 (υ'')] molecule: when υ'' is low, electron emission is most probable, but when υ'' is high, H - production dominates. A necessary preliminary to the DA process is the presence of sufficient [H 2 (υ'')] molecules with υ'' > 4. By determining the densities of hydrogen molecules in the various vibrational levels as a function of the various discharge parameters (scaling laws), insight can be gained into the extent to which the DA process contributes to H - formation. Since the de-excitation of [H 2 (υ'')] molecules by H atoms is expected to have a large cross section, it is also relevant to determine the scaling laws for atomic hydrogen. This thesis gives an account of the development of an experimental setup for obtaining such measurements, and reports the first results achieved. In view of the anticipated density of the vibrationally excited molecules and the detection limit considered feasible, the diagnostic chosen was resonance-enhanced multiphoton ionization (REMPI). The principle is based on state-selective ionization with REMPI of particles effusing from the discharge chamber through an aperture in the wall. The ions produced in the REMPI-process are then detected. The use of both an electric and a magnetic field makes it possible to distinguish the REMPI ions from those originating elsewhere, such as plasma ions or photodesorption ions. 145 refs.; 25 figs.; 6 tabs

Measurement of the Lyman-alpha radiation at ionization manometers for determination of the hydrogen atom number density in fusion experiments

International Nuclear Information System (INIS)

Loercher, M.

1990-01-01

Codes like DEGAS which simulate the interaction of neutral gas with plasma (e.g. in a divertor), not only deliver the global density and flux of neutral particles, but also allow one, in addition, to distinguish between atoms and molecules. Whereas the global parameters of the neutral gas in a divertor can be measured by, for example, special ion gauges like those, which are installed in the divertor chamber, there has until now been no possibility of measuring the atomic and molecular density independently. In the frame of a diploma thesis (M. Loercher) an ASDEX neutral pressure gauge was modified in such a way that it delivers not only the global density of neutral particles (molecules and atoms) by ionization, but also the density of the atoms by measurement of the Lα-radiation produced by electron impact exitation. Owing to the very weak intensity the main effort was dedicated to developing a detector-filter combination which allows the Lα-radiation to be separated from, the H 2 bands in the VUV and be measured with a time resolution of at least of few ms. Several versions were tested theoretically and practically. The best solution was found to be a combination of an O 2 filter using MgF 2 windows and a multichannel plate. The arrangement was tested and calibrated with an atomic beam of known intensity from an oven. (orig.)

Balance of ionization and recombination of carbon ions in high density peripheral plasmas of the JT-60 U tokamak

International Nuclear Information System (INIS)

Nakano, T.; Kubo, H.; Asakura, N.; Shimizu, K.

2009-01-01

In high density and low temperature peripheral plasmas of JT-60 U, i.e. detached divertor plasmas, C III and C IV lines were observed by a visible and VUV spectrometers in order to investigate dominant radiators, radiation power and particle balance between the radiators. An emission peak was found between the inner strike and the X-point. With increasing electron density, the emission peak moved to the X-point with a constant electron temperature of ∼7 eV. In the case the emission peak was located on the X-point, the dominant radiators in the emission peak were C 2+ and C 3+ , which contributed 30% and 60% to the total radiative power. It was found that C 3+ was produced by the ionization of C 2+ and the volume recombination of C 4+ at a similar rates. However, the loss flux of C 3+ was lower by two orders of magnitude than the C 3+ production flux, indicating that another loss mechanism such as transport loss around the X-point was significant.

HIGH-TEMPERATURE IONIZATION IN PROTOPLANETARY DISKS

Energy Technology Data Exchange (ETDEWEB)

Desch, Steven J. [School of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ 85287-1404 (United States); Turner, Neal J. [Jet Propulsion Laboratory, Mail Stop 169-506, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)

2015-10-01

We calculate the abundances of electrons and ions in the hot (≳500 K), dusty parts of protoplanetary disks, treating for the first time the effects of thermionic and ion emission from the dust grains. High-temperature ionization modeling has involved simply assuming that alkali elements such as potassium occur as gas-phase atoms and are collisionally ionized following the Saha equation. We show that the Saha equation often does not hold, because free charges are produced by thermionic and ion emission and destroyed when they stick to grain surfaces. This means the ionization state depends not on the first ionization potential of the alkali atoms, but rather on the grains’ work functions. The charged species’ abundances typically rise abruptly above about 800 K, with little qualitative dependence on the work function, gas density, or dust-to-gas mass ratio. Applying our results, we find that protoplanetary disks’ dead zone, where high diffusivities stifle magnetorotational turbulence, has its inner edge located where the temperature exceeds a threshold value ≈1000 K. The threshold is set by ambipolar diffusion except at the highest densities, where it is set by Ohmic resistivity. We find that the disk gas can be diffusively loaded onto the stellar magnetosphere at temperatures below a similar threshold. We investigate whether the “short-circuit” instability of current sheets can operate in disks and find that it cannot, or works only in a narrow range of conditions; it appears not to be the chondrule formation mechanism. We also suggest that thermionic emission is important for determining the rate of Ohmic heating in hot Jupiters.

HIGH-TEMPERATURE IONIZATION IN PROTOPLANETARY DISKS

International Nuclear Information System (INIS)

Desch, Steven J.; Turner, Neal J.

2015-01-01

We calculate the abundances of electrons and ions in the hot (≳500 K), dusty parts of protoplanetary disks, treating for the first time the effects of thermionic and ion emission from the dust grains. High-temperature ionization modeling has involved simply assuming that alkali elements such as potassium occur as gas-phase atoms and are collisionally ionized following the Saha equation. We show that the Saha equation often does not hold, because free charges are produced by thermionic and ion emission and destroyed when they stick to grain surfaces. This means the ionization state depends not on the first ionization potential of the alkali atoms, but rather on the grains’ work functions. The charged species’ abundances typically rise abruptly above about 800 K, with little qualitative dependence on the work function, gas density, or dust-to-gas mass ratio. Applying our results, we find that protoplanetary disks’ dead zone, where high diffusivities stifle magnetorotational turbulence, has its inner edge located where the temperature exceeds a threshold value ≈1000 K. The threshold is set by ambipolar diffusion except at the highest densities, where it is set by Ohmic resistivity. We find that the disk gas can be diffusively loaded onto the stellar magnetosphere at temperatures below a similar threshold. We investigate whether the “short-circuit” instability of current sheets can operate in disks and find that it cannot, or works only in a narrow range of conditions; it appears not to be the chondrule formation mechanism. We also suggest that thermionic emission is important for determining the rate of Ohmic heating in hot Jupiters

Excitation and ionization of ethylene by charged projectiles

International Nuclear Information System (INIS)

Wang Zhiping; Wang Jing; Zhang Fengshou

2010-01-01

Using the time dependent local density approximation, applied to valence electrons, coupled non-adiabatically to molecular dynamics of ions, the collision process between ethylene and fast charged projectiles is studied in the microscopic way. The impact of ionic motion on the ionization is explored to show the importance of treating electronic and ionic degrees of freedom simultaneously. The number of escaped electrons, ionization probabilities are obtained. Furthermore, it is found that the ionic extensions in different directions show the different patterns. (authors)

Solving large nonlinear generalized eigenvalue problems from Density Functional Theory calculations in parallel

DEFF Research Database (Denmark)

Bendtsen, Claus; Nielsen, Ole Holm; Hansen, Lars Bruno

2001-01-01

The quantum mechanical ground state of electrons is described by Density Functional Theory, which leads to large minimization problems. An efficient minimization method uses a self-consistent field (SCF) solution of large eigenvalue problems. The iterative Davidson algorithm is often used, and we...

Time-resolved spectroscopy of nonequilibrium ionization in laser-produced plasmas

International Nuclear Information System (INIS)

Marjoribanks, R.S.

1988-01-01

The highly transient ionization characteristic of laser-produced plasmas at high energy densities has been investigated experimentally, using x-ray spectroscopy with time resolution of less than 20 ps. Spectroscopic diagnostics of plasma density and temperature were used, including line ratios, line profile broadening and continuum emission, to characterize the plasma conditions without relying immediately on ionization modeling. The experimentally measured plasma parameters were used as independent variables, driving an ionization code, as a test of ionization modeling, divorced from hydrodynamic calculations. Several state-of-the-art streak spectrographs, each recording a fiducial of the laser peak along with the time-resolved spectrum, characterized the laser heating of thin signature layers of different atomic numbers imbedded in plastic targets. A novel design of crystal spectrograph, with a conically curved crystal, was developed. Coupled with a streak camera, it provided high resolution (λ/ΔΛ > 1000) and a collection efficiency roughly 20-50 times that of planar crystal spectrographs, affording improved spectra for quantitative reduction and greater sensitivity for the diagnosis of weak emitters. Experimental results were compared to hydrocode and ionization code simulations, with poor agreement. The conclusions question the appropriateness of describing electron velocity distributions by a temperature parameter during the time of laser illumination and emphasis the importance of characterizing the distribution more generally

Effects of previous ionization and excitation on the ionization wave propagation along the dielectric tube

International Nuclear Information System (INIS)

Xia, Yang; Liu, Dongping; Bi, Zhenhua; Wang, Xueyang; Niu, Jinhai; Ji, Longfei; Song, Ying; Qi, Zhihua; Wang, Wenchun

2016-01-01

In this paper, by using a high precision synchronization system, the ignition time, velocity, and propagation properties of the ionization waves (IWs) have been investigated in detail from the 1st high voltage (HV) pulse to the sequential ones over a large range of the pulse-off time. In order to clarify the effects of previous ionization and excitation on the IW propagation, the density of the residual charges are controlled by varying the pulse-off time from 199 μs to 15 μs. The results show that the formation and propagation of IWs can be strongly affected by previous discharge. For a longer pulse-off time (100 μs–190 μs), the propagation velocity of plasma bullets are decreased from the 1st to the 10th HV pulse, then increased after the 10th pulse, and finally become stable after about 500 pulses. When the pulse-off time is reduced to 15 μs, the propagation velocity of plasma bullets will rapidly increase and become stable after the 1st HV pulse. The ignition voltage is significantly reduced after the 1st HV pulse with the decrease in pulse-off time. Consequently, the generation and propagation of IWs in the tube are strongly affected by the accumulation of long-lived metastable helium (He) species and residual charges from previous discharges, which is important for understanding the plasma bullet behavior. (paper)

H II regions ionized by sigma and tau Sco

Energy Technology Data Exchange (ETDEWEB)

Gaylard, M J [Council for Scientific and Industrial Research, Pretoria (South Africa). National Inst. for Telecommunications Research

1984-11-15

The H142..cap alpha.. line has been detected in Sharpless 9, which is ionized by sigmaSco, and in RCW 129, ionized by tau Sco. The electron temperatures in the two H II regions are 5700 +- 340 K and 4200 +- 600 K respectively. The thermal radio emission from S9 is asymmetric with respect to the stellar position, and the emission peak coincides with the position of the optical red emission features to the north and west of the star. There is no evidence for collisional excitation. S9 is a density-bounded H II region in the champagne phase, the bright rims and radio peak marking the ionization front.

Procedure of non-contacting local mass density and mass density distribution measurements

International Nuclear Information System (INIS)

Menzel, M.; Winkler, K.

1985-01-01

The invention has been aimed at a procedure of non-contacting local mass density and/or mass density distribution measurements i.e. without the interfering influence of sensors or probes. It can be applied to installations, apparatuses and pipings of chemical engineering, to tank constructions and transportation on extreme temperature and/or pressure conditions and aggressive media influences respectively. The procedure has utilized an ionizing quantum radiation whereby its unknown weakening and scattering is compensated by a suitable combination of scattering and transmission counter rate measurements in such a way that the local mass densities and the mass density distribution respectively are determinable

Ionization chamber correction factors for MR-linacs.

Science.gov (United States)

Pojtinger, Stefan; Dohm, Oliver Steffen; Kapsch, Ralf-Peter; Thorwarth, Daniela

2018-06-07

Previously, readings of air-filled ionization chambers have been described as being influenced by magnetic fields. To use these chambers for dosimetry in magnetic resonance guided radiotherapy (MRgRT), this effect must be taken into account by introducing a correction factor k B . The purpose of this study is to systematically investigate k B for a typical reference setup for commercially available ionization chambers with different magnetic field strengths. The Monte Carlo simulation tool EGSnrc was used to simulate eight commercially available ionization chambers in magnetic fields whose magnetic flux density was in the range of 0-2.5 T. To validate the simulation, the influence of the magnetic field was experimentally determined for a PTW30013 Farmer-type chamber for magnetic flux densities between 0 and 1.425 T. Changes in the detector response of up to 8% depending on the magnetic flux density, on the chamber geometry and on the chamber orientation were obtained. In the experimental setup, a maximum deviation of less than 2% was observed when comparing measured values with simulated values. Dedicated values for two MR-linac systems (ViewRay MRIdian, ViewRay Inc, Cleveland, United States, 0.35 T/ 6 MV and Elekta Unity, Elekta AB, Stockholm, Sweden, 1.5 T/7 MV) were determined for future use in reference dosimetry. Simulated values for thimble-type chambers are in good agreement with experiments as well as with the results of previous publications. After further experimental validation, the results can be considered for definition of standard protocols for purposes of reference dosimetry in MRgRT.

Ionization chamber correction factors for MR-linacs

Science.gov (United States)

Pojtinger, Stefan; Steffen Dohm, Oliver; Kapsch, Ralf-Peter; Thorwarth, Daniela

2018-06-01

Previously, readings of air-filled ionization chambers have been described as being influenced by magnetic fields. To use these chambers for dosimetry in magnetic resonance guided radiotherapy (MRgRT), this effect must be taken into account by introducing a correction factor k B. The purpose of this study is to systematically investigate k B for a typical reference setup for commercially available ionization chambers with different magnetic field strengths. The Monte Carlo simulation tool EGSnrc was used to simulate eight commercially available ionization chambers in magnetic fields whose magnetic flux density was in the range of 0–2.5 T. To validate the simulation, the influence of the magnetic field was experimentally determined for a PTW30013 Farmer-type chamber for magnetic flux densities between 0 and 1.425 T. Changes in the detector response of up to 8% depending on the magnetic flux density, on the chamber geometry and on the chamber orientation were obtained. In the experimental setup, a maximum deviation of less than 2% was observed when comparing measured values with simulated values. Dedicated values for two MR-linac systems (ViewRay MRIdian, ViewRay Inc, Cleveland, United States, 0.35 T/ 6 MV and Elekta Unity, Elekta AB, Stockholm, Sweden, 1.5 T/7 MV) were determined for future use in reference dosimetry. Simulated values for thimble-type chambers are in good agreement with experiments as well as with the results of previous publications. After further experimental validation, the results can be considered for definition of standard protocols for purposes of reference dosimetry in MRgRT.

Motion of ionizing electric-field solitons in a bounded plasma

International Nuclear Information System (INIS)

Lagar'kov, A.; Rutkevich, I.

1981-01-01

A theory is derived for the motion of fast ionization waves along a plane slab of a weakly ionized plasma. The properties of the ionization wave are shown to be closely related to the motion of a two-dimensional surface-charge wave along the slab boundaries. As a result, the ionization wave is quite different from a one-dimensional wave. A quasi-one-dimensional description is used for the wave motion, in which the initial equations are averaged over the transverse coordinate. The relationship between the normal component of the current density at the plasma boundary and the amplitude of the electric potential from the linear theory for a surface wave is used to close the system of averaged equations. Self-similar solutions are derived for these equations; the solutions describe space-charge solitons and electric-field solitons which ionize the plasma. The theory is used to explain the motion of fast ionization waves in long discharge tubes

Hydrogenic ionization model for mixtures in non-LTE plasmas

International Nuclear Information System (INIS)

Djaoui, A.

1999-01-01

The Hydrogenic Ionization Model for Mixtures (HIMM) is a non-Local Thermodynamic Equilibrium (non-LTE), time-dependent ionization model for laser-produced plasmas containing mixtures of elements (species). In this version, both collisional and radiative rates are taken into account. An ionization distribution for each species which is consistent with the ambient electron density is obtained by use of an iterative procedure in a single calculation for all species. Energy levels for each shell having a given principal quantum number and for each ion stage of each species in the mixture are calculated using screening constants. Steady-state non-LTE as well as LTE solutions are also provided. The non-LTE rate equations converge to the LTE solution at sufficiently high densities or as the radiation temperature approaches the electron temperature. The model is particularly useful at low temperatures where convergence problems are usually encountered in our previous models. We apply our model to typical situation in x-ray laser research, laser-produced plasmas and inertial confinement fusion. Our results compare well with previously published results for a selenium plasma. (author)

Health consequences of ionizing radiation exposure

International Nuclear Information System (INIS)

Dalci, D.; Dorter, G.; Guclu, I.

2004-01-01

The increasing use of ionizing radiations all over the world induces an ever increasing interest of the professionals as well as of the whole society in health protection and the risk due to these practices. Shortly after its discovery, it was recognized that ionizing radiation can have adverse health effects and knowledge of its detrimental effects has accumulated. The fact that ionizing radiation produces biological damage has been known for many years. The biological effects of ionizing radiation for radiation protection considerations are grouped into two categories: The deterministic and the stochastic ones. Deterministic radiation effects can be clinically diagnosed in the exposed individual and occur when above a certain 'threshold' an appropriately high dose is absorbed in the tissues and organs to cause the death of a large number of cells and consequently to impair tissue or organ functions early after exposure. A clinically observable biological effect (Acute Radiation Syndromes, ARS) that occurs days to months after an acute radiation dose. ARS is a complex of acute injury manifestations that occur after a sufficiently large portion of a person's body is exposed to a high dose of ionizing radiation. Such irradiation initially injures all organs to some extent, but the timing and extent of the injury manifestations depend upon the type, rate, and dose of radiation received. Stochastic radiation effects are the chronic effects of radiation result from relatively low exposure levels delivered over long periods of time. These are sort of effects that might result from occupational exposure, or to the background exposure levels (includes radioactive pollution). Such late effects might be the development of malignant (cancerous) disease and of the hereditary consequences. These effects may be observed many years after the radiation exposure. There is a latent period between the initial radiation exposure and the development of the biological effect. In this

Characteristics of the self-excited ionization waves in a magnetized positive column

International Nuclear Information System (INIS)

Maruyama, Takeo; Yamamura, Yasuhiro; Takano, Saburo; Miura, Kosuke; Imazu, Shingo.

1979-01-01

In the past, metastable atoms were not considered in the investigations of ionization waves generated in a positive column weakly ionized. However, metastable atoms seem to be important for the generation of ionization waves, and there are many unknown factors. In this paper, the fundamental equations and dispersion relation are explained under the assumption of axi-symmetrical positive column plasma placed in a uniform magnetic field, and the direct ionization frequency and excitation frequency, cumulative ionization coefficient, electron density and metastable atom density, the energy loss factor for electrons, the dependence of plasma quantities on magnetic field and dispersion characteristics are calculated. Experiments have been conducted using Ne gas in a discharge tube of 80 cm long and 1 cm radius with heated oxide cathode. Magnetic field was obtained with a solenoid coil of 75 cm long, 9 cm I.D. and 27 cm O.D. The axially uniform magnetic field was in the range of 35 to 40 cm. As the results, the following points have become clear. (1) The number of waves, angular frequency and phase velocity of ionization waves decrease with the increase of magnetic field. (2) By the consideration of the presence of metastable atoms, the theoretical values were improved pretty well and agreed with the experimental values qualitatively and quantitatively. (3) Longitudinal magnetic field has the effect of suppressing the growth of ionization waves because of the reduction of time and spatial growth rates with the increase of magnetic field. (Wakatsuki, Y.)

Reproductive survival and hypoxic protection as a function of radiation ionization density. Further studies with murine leukemia cells irradiated in vitro with monoenergetic accelerated charged particles and assayed in vivo

International Nuclear Information System (INIS)

Berry, R.J.

1977-01-01

Murine lymphocytic leukemia P-388 cells have been irradiated in vitro under aerobic or hypoxic conditions with monoenergetic track segments of beams of accelerated helium or boron ions, and survival of their reproductive capacity assessed in vivo. These cells showed a maximum cell killing per rad at a relatively low ionization density (ca. 60--80 keV/μm) and their response ceased to depend on the presence or absence of oxygen at all LET values above ea. 100 keV/μm. This is similar to the LET dependence of cell killing reported recently for human lymphocytes which die a nonreproductive interphase death, and differs from the response of human kidney-derived cells which have been studied in vitro by other workers. The significance of these differences in predicting the response of cells and tissues to radiations such as fast neutrons or pi - mesons which produce wide spectra of ionization densities is discussed briefly

Excitation and Ionization of Ethylene by Charged Projectiles

International Nuclear Information System (INIS)

Zhi-Ping, Wang; Jing, Wang; Feng-Shou, Zhang

2010-01-01

Using the time dependent local density approximation, applied to valence electrons, coupled non-adiabatically to molecular dynamics of ions, the collision process between ethylene and fast charged projectiles is studied in the microscopic way. The impact of ionic motion on the ionization is explored to show the importance of treating electronic and ionic degrees of freedom simultaneously. The number of escaped electrons, ionization probabilities are obtained. Furthermore, it is found that the ionic extensions in different directions show the different patterns. (atomic and molecular physics)

Effects of temperature and ionization density in medical luminescence dosimetry using Al2O3:C

International Nuclear Information System (INIS)

Morgenthaler Edmund, J.

2007-11-01

A new system containing small crystals of aluminum oxide doped with carbon (Al 2 O 3 :C) attached to optical fiber cables has recently been introduced. During irradiation, the system monitors the radioluminescence (RL)from the crystals and after irradiation, an optically stimulated luminescence (OSL) signal can be read out by stimulating the crystal with light. This thesis applies the initial part and the total area of the resulting OSL decay curve for dosimetry measurements and investigates the effects of temperature and proton energy, i.e. ionization density, on the RL and OSL signals from Al 2 O 3 :C. In the temperature study, it was found that the OSL signal depends on both irradiation and stimulation temperature while the RL signal is effected only by the irradiation temperature. The initial OSL signal is increasing with temperature whereas the total OSL area is decreasing. Therefore, if the irradiation temperature is kept constant, one can find an integration time which provides an OSL signal independent of stimulation temperature. Overall, the RL and OSL signals vary between -0.2 to 0.6% per C. Thermal effects were simulated with a band structure model and indicated that the temperature effects are caused by the combined efforts of energetic shallow traps and thermal excitation from intermediate states in deeper traps. In the study of ionization density, we investigated protons with energies between 10 and 60 MeV (4.57 to 1.08 keV/μm in water). Experimentally, we observed that the initial OSL signalprovided a signal independent of linear energy transfer (LET) for allenergies at 0.3 Gy. The total OSL area showed an LET dependent behavior atall doses and energies. We used track structure theory (TST) to give possible explanations for the LET dependence of the OSL signal. From these calculations, we found that the initial OSL signal is, in general, not LET independent which makes Al2O3:C unsuitable for OSL proton dosimetry. The initial OSL signal can, however

Saha's ionization equation for high Z elements

International Nuclear Information System (INIS)

Godwal, B.K.; Sikka, S.K.

1977-01-01

Saha's ionization equation has been solved for high Z elements with the aim of providing input for opacity calculations. Results are presented for two elements, tungsten and uranium. The ionization potentials have been evaluated using the simple Bhor's formula with suitable effective charges for ions. The reliability of the free electron density, ion concentrations, etc., obtained from the Saha's equation solutions has been checked by comparing the P and E computed from them with those given by the Thomas-Fermi-Dirac equation of state. The agreement between the two is good from temperatures above 0.2 keV. (author)

MODEL OF THE TOKAMAK EDGE DENSITY PEDESTAL INCLUDING DIFFUSIVE NEUTRALS

International Nuclear Information System (INIS)

BURRELL, K.H.

2003-01-01

OAK-B135 Several previous analytic models of the tokamak edge density pedestal have been based on diffusive transport of plasma plus free-streaming of neutrals. This latter neutral model includes only the effect of ionization and neglects charge exchange. The present work models the edge density pedestal using diffusive transport for both the plasma and the neutrals. In contrast to the free-streaming model, a diffusion model for the neutrals includes the effect of both charge exchange and ionization and is valid when charge exchange is the dominant interaction. Surprisingly, the functional forms for the electron and neutral density profiles from the present calculation are identical to the results of the previous analytic models. There are some differences in the detailed definition of various parameters in the solution. For experimentally relevant cases where ionization and charge exchange rate are comparable, both models predict approximately the same width for the edge density pedestal

REIONIZATION ON LARGE SCALES. I. A PARAMETRIC MODEL CONSTRUCTED FROM RADIATION-HYDRODYNAMIC SIMULATIONS

International Nuclear Information System (INIS)

Battaglia, N.; Trac, H.; Cen, R.; Loeb, A.

2013-01-01

We present a new method for modeling inhomogeneous cosmic reionization on large scales. Utilizing high-resolution radiation-hydrodynamic simulations with 2048 3 dark matter particles, 2048 3 gas cells, and 17 billion adaptive rays in a L = 100 Mpc h –1 box, we show that the density and reionization redshift fields are highly correlated on large scales (∼> 1 Mpc h –1 ). This correlation can be statistically represented by a scale-dependent linear bias. We construct a parametric function for the bias, which is then used to filter any large-scale density field to derive the corresponding spatially varying reionization redshift field. The parametric model has three free parameters that can be reduced to one free parameter when we fit the two bias parameters to simulation results. We can differentiate degenerate combinations of the bias parameters by combining results for the global ionization histories and correlation length between ionized regions. Unlike previous semi-analytic models, the evolution of the reionization redshift field in our model is directly compared cell by cell against simulations and performs well in all tests. Our model maps the high-resolution, intermediate-volume radiation-hydrodynamic simulations onto lower-resolution, larger-volume N-body simulations (∼> 2 Gpc h –1 ) in order to make mock observations and theoretical predictions

NON-EQUILIBRIUM CHEMISTRY OF DYNAMICALLY EVOLVING PRESTELLAR CORES. II. IONIZATION AND MAGNETIC FIELD

International Nuclear Information System (INIS)

Tassis, Konstantinos; Willacy, Karen; Yorke, Harold W.; Turner, Neal J.

2012-01-01

We study the effect that non-equilibrium chemistry in dynamical models of collapsing molecular cloud cores has on measurements of the magnetic field in these cores, the degree of ionization, and the mean molecular weight of ions. We find that OH and CN, usually used in Zeeman observations of the line-of-sight magnetic field, have an abundance that decreases toward the center of the core much faster than the density increases. As a result, Zeeman observations tend to sample the outer layers of the core and consistently underestimate the core magnetic field. The degree of ionization follows a complicated dependence on the number density at central densities up to 10 5 cm –3 for magnetic models and 10 6 cm –3 in non-magnetic models. At higher central densities, the scaling approaches a power law with a slope of –0.6 and a normalization which depends on the cosmic-ray ionization rate ζ and the temperature T as (ζT) 1/2 . The mean molecular weight of ions is systematically lower than the usually assumed value of 20-30, and, at high densities, approaches a value of 3 due to the asymptotic dominance of the H + 3 ion. This significantly lower value implies that ambipolar diffusion operates faster.

Simulations of Hall reconnection in partially ionized plasmas

Science.gov (United States)

Innocenti, Maria Elena; Jiang, Wei; Lapenta, Giovanni

2017-04-01

Magnetic reconnection occurs in the Hall, partially ionized regime in environments as diverse as molecular clouds, protostellar disks and regions of the solar chromosphere. While much is known about Hall reconnection in fully ionized plasmas, Hall reconnection in partially ionized plasmas is, in comparison, still relatively unexplored. This notwithstanding the fact that partial ionization is expected to affect fundamental processes in reconnection such as the transition from the slow, fluid to the fast, kinetic regime, the value of the reconnection rate and the dimensions of the diffusion regions [Malyshkin and Zweibel 2011 , Zweibel et al. 2011]. We present here the first, to our knowledge, fully kinetic simulations of Hall reconnection in partially ionized plasmas. The interaction of electrons and ions with the neutral background is realistically modelled via a Monte Carlo plug-in coded into the semi-implicit, fully kinetic code iPic3D [Markidis 2010]. We simulate a plasma with parameters compatible with the MRX experiments illustrated in Zweibel et al. 2011 and Lawrence et al. 2013, to be able to compare our simulation results with actual experiments. The gas and ion temperature is T=3 eV, the ion to electron temperature ratio is Tr=0.44, ion and electron thermal velocities are calculated accordingly resorting to a reduced mass ratio and a reduced value of the speed of light to reduce the computational costs of the simulations. The initial density of the plasma is set at n= 1.1 1014 cm-3 and is then left free to change during the simulation as a result of gas-plasma interaction. A set of simulations with initial ionisation percentage IP= 0.01, 0.1, 0.2, 0.6 is presented and compared with a reference simulation where no background gas is present (full ionization). In this first set of simulations, we assume to be able to externally control the initial relative densities of gas and plasma. Within this parameter range, the ion but not the electron population is

Accurate density-functional calculations on large systems: Fullerenes and magnetic clusters

International Nuclear Information System (INIS)

Dunlap, B.I.

1996-01-01

Efforts to accurately compute all-electron density-functional energies for large molecules and clusters using Gaussian basis sets will be reviewed. The foundation of this effort, variational fitting, will be described and followed by three applications of the method. The first application concerns fullerenes. When first discovered, C 60 is quite unstable relative to the higher fullerenes. In addition, to raising questions about the relative abundance of the various fullerenes, this work conflicted with the then state-of-the art density-funcitonal calculations on crystalline graphite. Now high accuracy molecular and band structure calculations are in fairly good agreement. Second, we have used these methods to design transition metal clusters having the highest magnetic moment by maximizing the symmetry-required degeneracy of the one-electron orbitals. Most recently, we have developed accurate, variational generalized-gradient approximation (GGA) forces for use in geometry optimization of clusters and in molecular-dynamics simulations of friction. The GGA optimized geometries of a number of large clusters will be given

55-68 Impact of Area Enclosures on Density and Diversity of Large ...

African Journals Online (AJOL)

1Department of Land Resources Management and Environmental Protection, Mekelle University, ... The enclosures have higher density and diversity of large wild mammals ..... in it. Figure 4 Human interference in enclosures of the study area ...

Space-charge-limited ion flow through an ionizing neutral layer

International Nuclear Information System (INIS)

Duvall, R.E.; Litwin, C.; Maron, Y.

1993-01-01

Space-charge-limited ion flow through an ionizing layer of neutral atoms is studied. The ion flow is between two parallel conducting plates (anode and cathode) with an externally applied voltage between them. An expanding layer of neutral atoms is adjacent to the anode surface, extending a finite distance into the anode--cathode gap. All ions originate either from the anode surface or from the ionization of neutrals; electrons originate only from ionization. Electrons are strongly magnetized by an externally applied, time-independent direct current (dc) magnetic field directed across the ion flow. The ions are unmagnetized, all motion being perpendicular to the conducting plates. Two different models of the anode layer were used to analyze this problem: a multifluid steady-state model and a single fluid time-dependent model. From both models it was found that the anode surface becomes shielded after the ion flux from the ionizing layer becomes larger than the space-charge-limited flux of the reduced gap between the neutral layer and cathode. Comparison was made between the time-dependent model and results from magnetically insulated ion beam diode (MID) experiments. Using an initial areal density of neutral hydrogen and carbon equal to the final observed electron areal density, comparison was made between calculated plasma shielding times and upper bounds on the shielding time observed in experiments. It was found that a layer of neutral hydrogen must contain a minimum of 15% carbon (by number density) to explain the rapid electric field screening observed in experiments

Large plasma density enhancements occurring in the northern polar region during the 6 April 2000 superstorm

Science.gov (United States)

Horvath, Ildiko; Lovell, Brian C.

2014-06-01

We focus on the ionospheric response of northern high-latitude region to the 6 April 2000 superstorm and aim to investigate how the storm-enhanced density (SED) plume plasma became distributed in the regions of auroral zone and polar cap plus to study the resultant ionospheric features and their development. Multi-instrument observational results combined with model-generated, two-cell convection maps permitted identifying the high-density plasma's origin and the underlying plasma transportation processes. Results show the plasma density feature of polar cap enhancement (PCE; 600 × 103 i+/cm3) appearing for 7 h during the main phase and characterized by increases reaching up to 6 times of the quiet time values. Meanwhile, strong westward convections ( 17,500 m/s) created low plasma densities in a wider region of the dusk cell. Oppositely, small ( 750 m/s) but rigorous westward drifts drove the SED plume plasma through the auroral zone, wherein plasma densities doubled. As the SED plume plasma traveled along the convection streamlines and entered the polar cap, a continuous enhancement of the tongue of ionization (TOI) developed under steady convection conditions. However, convection changes caused slow convections and flow stagnations and thus segmented the TOI feature by locally depleting the plasma in the affected regions of the auroral zone and polar cap. From the strong correspondence of polar cap potential drop and subauroral polarization stream (SAPS), we conclude that the SAPS E-field strength remained strong, and under its prolonged influence, the SED plume provided a continuous supply of downward flowing high-density plasma for the development and maintenance of PCEs.

Experimental Studies for the Evaluation of Non-Ionizing Radiation Levels

International Nuclear Information System (INIS)

Nasr, A.; Ashour, M.

2008-01-01

This article concerns the characteristic studies of non-ionizing; microwave, radiations. The power density levels, frequency ranges, modulation types, and the Fast Fourier Transform (FFT) are discussed. The experimental data are collected from the Egyptian Atomic Energy Authority (EAEA) locations in Nasr city and Anshas. This study has been carried out by Spectrum analyzer (SA) system, which implied radio frequency coaxial cable and horn antenna with height holders. The horn antenna was adjusted to scan all directions for investigating the signal strength. From this study, we obtain two main non-ionizing signals at center frequencies 900, and 1800 MHz, which are exploited by mobile communications networks. During the silence state, the measured maximum power densities levels for both frequencies are 0.553 μ W/cm 2 and 0.0191μW/cm 2 , respectively. While the measured maximum power densities, during alarm (ringing) state, are 98.67μ W/cm 2 and 2.961μ W/cm 2 for considered two frequencies, correspondingly. One can notice that the power densities are multiplied 178 times and 155 times for the same mentioned frequencies in that order. Moreover, these non-ionizing signals are analyzed theoretically and experimentally by utilizing FFT functions to clarify the Amplitude Modulations (AM) ratios and voltage strengths of these signals. Furthermore, the Occupied Band Width (OBW) ratio, and the division from the center frequency of the channel, (δFc) are clarified

THE ESCAPE FRACTION OF IONIZING RADIATION FROM GALAXIES

International Nuclear Information System (INIS)

Benson, Andrew; Venkatesan, Aparna; Shull, J. Michael

2013-01-01

The escape of ionizing radiation from galaxies plays a critical role in the evolution of gas in galaxies, and the heating and ionization history of the intergalactic medium. We present semi-analytic calculations of the escape fraction of ionizing radiation for both hydrogen and helium from galaxies ranging from primordial systems to disk-type galaxies that are not heavily dust-obscured. We consider variations in the galaxy density profile, source type, location, and spectrum, and gas overdensity/distribution factors. For sufficiently hard first-light sources, the helium ionization fronts closely track or advance beyond that of hydrogen. Key new results in this work include calculations of the escape fractions for He I and He II ionizing radiation, and the impact of partial ionization from X-rays from early active galactic nuclei or stellar clusters on the escape fractions from galaxy halos. When factoring in frequency-dependent effects, we find that X-rays play an important role in boosting the escape fractions for both hydrogen and helium, but especially for He II. We briefly discuss the implications of these results for recent observations of the He II reionization epoch at low redshifts, as well as the UV data and emission-line signatures from early galaxies anticipated from future satellite missions.

Electron ionization and dissociation of aliphatic amino acids

Science.gov (United States)

Papp, P.; Shchukin, P.; Kočíšek, J.; Matejčík, Š.

2012-09-01

We present experimental and theoretical study of electron ionization and dissociative ionization to the gas phase amino acids valine, leucine, and isoleucine. A crossed electron/molecular beams technique equipped with quadrupole mass analyzer has been applied to measure mass spectra and ion efficiency curves for formation of particular ions. From experimental data the ionization energies of the molecules and the appearance energies of the fragment ions were determined. Ab initio calculations (Density Functional Theory and G3MP2 methods) were performed in order to calculate the fragmentation paths and interpret the experimental data. The experimental ionization energies of parent molecules [P]+ 8.91 ± 0.05, 8.85 ± 0.05, and 8.79 ± 0.05 eV and G3MP2 ionization energies (adiabatic) of 8.89, 8.88, and 8.81 eV were determined for valine, leucine, and isoleucine, respectively, as well as the experimental and theoretical threshold energies for dissociative ionization channels. The comparison of experimental data with calculations resulted in identification of the ions as well as the neutral fragments formed in the dissociative reactions. Around 15 mass/charge ratio fragments were identified from the mass spectra by comparison of experimental appearance energies with calculated reaction enthalpies for particular dissociative reactions.

THE ESCAPE FRACTION OF IONIZING RADIATION FROM GALAXIES

Energy Technology Data Exchange (ETDEWEB)

Benson, Andrew [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Venkatesan, Aparna [Department of Physics and Astronomy, University of San Francisco, San Francisco, CA 94117 (United States); Shull, J. Michael, E-mail: abenson@obs.carnegiescience.edu, E-mail: avenkatesan@usfca.edu, E-mail: michael.shull@colorado.edu [CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309 (United States)

2013-06-10

The escape of ionizing radiation from galaxies plays a critical role in the evolution of gas in galaxies, and the heating and ionization history of the intergalactic medium. We present semi-analytic calculations of the escape fraction of ionizing radiation for both hydrogen and helium from galaxies ranging from primordial systems to disk-type galaxies that are not heavily dust-obscured. We consider variations in the galaxy density profile, source type, location, and spectrum, and gas overdensity/distribution factors. For sufficiently hard first-light sources, the helium ionization fronts closely track or advance beyond that of hydrogen. Key new results in this work include calculations of the escape fractions for He I and He II ionizing radiation, and the impact of partial ionization from X-rays from early active galactic nuclei or stellar clusters on the escape fractions from galaxy halos. When factoring in frequency-dependent effects, we find that X-rays play an important role in boosting the escape fractions for both hydrogen and helium, but especially for He II. We briefly discuss the implications of these results for recent observations of the He II reionization epoch at low redshifts, as well as the UV data and emission-line signatures from early galaxies anticipated from future satellite missions.

Ultra fast atomic process in X-ray emission by inner-shell ionization

Energy Technology Data Exchange (ETDEWEB)

Moribayashi, Kengo; Sasaki, Akira [Japan Atomic Energy Research Inst., Neyagawa, Osaka (Japan). Kansai Research Establishment; Tajima, T

1998-03-01

An ultra-fast atomic process together with X-ray emission by inner-shell ionization using high intensity (10{sup 18} W/cm{sup 2}) short pulse (20fs) X-ray is studied. A new class of experiment is proposed and a useful pumping source is suggested. In this method, it is found that the gain value of X-ray laser amounts to larger than 1000(1/cm) with use of the density of 10{sup 22}/cm{sup 3} of carbon atom. Electron impact ionization effect and initial density effect as well as intensity of pumping source effect are also discussed. (author)

Ionized calcium measurements are influenced by albumin - should ionized calcium be corrected?

DEFF Research Database (Denmark)

Larsen, Trine R; Galthen-Sørensen, Mathias; Antonsen, Steen

2014-01-01

Abstract Measurement of ionized calcium (CaI) has been reported to be dependent on albumin concentration. We examined the correlation between albumin and CaI measured on different ion selective electrode analyzers and in different groups of patients in a large dataset, extracted from the laboratory...

A large area position-sensitive ionization chamber for heavy-ion-induced reaction studies

CERN Document Server

Pant, L M; Dinesh, B V; Thomas, R G; Saxena, A; Sawant, Y S; Choudhury, R K

2002-01-01

A large area position-sensitive ionization chamber with a wide dynamic range has been developed to measure the mass, charge and energy of the heavy ions and the fission fragments produced in heavy-ion-induced reactions. The split anode geometry of the detector makes it suitable for both particle identification and energy measurements for heavy ions and fission fragments. The detector has been tested with alpha particles from sup 2 sup 4 sup 1 Am- sup 2 sup 3 sup 9 Pu source, fission fragments from sup 2 sup 5 sup 2 Cf and the heavy-ion beams from the 14UD Mumbai Pelletron accelerator facility. Using this detector, measurements on mass and total kinetic energy distributions in heavy-ion-induced fusion-fission reactions have been carried out for a wide range of excitation energies. Results on deep inelastic collisions and mass-energy correlations on different systems using this detector setup are discussed.

Propagation characteristics of electromagnetic waves in dusty plasma with full ionization

Science.gov (United States)

Dan, Li; Guo, Li-Xin; Li, Jiang-Ting

2018-01-01

This study investigates the propagation characteristics of electromagnetic (EM) waves in fully ionized dusty plasmas. The propagation characteristics of fully ionized plasma with and without dust under the Fokker-Planck-Landau (FPL) and Bhatnagar-Gross-Krook (BGK) models are compared to those of weakly ionized plasmas by using the propagation matrix method. It is shown that the FPL model is suitable for the analysis of the propagation characteristics of weakly collisional and fully ionized dusty plasmas, as is the BGK model. The influence of varying the dust parameters on the propagation properties of EM waves in the fully ionized dusty plasma was analyzed using the FPL model. The simulation results indicated that the densities and average radii of dust grains influence the reflection and transmission coefficients of fully ionized dusty plasma slabs. These results may be utilized to analyze the effects of interaction between EM waves and dusty plasmas, such as those associated with hypersonic vehicles.

Statistical measurement of power spectrum density of large aperture optical component

International Nuclear Information System (INIS)

Xu Jiancheng; Xu Qiao; Chai Liqun

2010-01-01

According to the requirement of ICF, a method based on statistical theory has been proposed to measure the power spectrum density (PSD) of large aperture optical components. The method breaks the large-aperture wavefront into small regions, and obtains the PSD of the large-aperture wavefront by weighted averaging of the PSDs of the regions, where the weight factor is each region's area. Simulation and experiment demonstrate the effectiveness of the proposed method. They also show that, the obtained PSDs of the large-aperture wavefront by statistical method and sub-aperture stitching method fit well, when the number of small regions is no less than 8 x 8. The statistical method is not sensitive to translation stage's errors and environment instabilities, thus it is appropriate for PSD measurement during the process of optical fabrication. (authors)

Study of ionization process of matrix molecules in matrix-assisted laser desorption ionization

Energy Technology Data Exchange (ETDEWEB)

Murakami, Kazumasa; Sato, Asami; Hashimoto, Kenro; Fujino, Tatsuya, E-mail: fujino@tmu.ac.jp

2013-06-20

Highlights: ► Proton transfer and adduction reaction of matrix in MALDI were studied. ► Hydroxyl group forming intramolecular hydrogen bond was related to the ionization. ► Intramolecular proton transfer in the electronic excited state was the initial step. ► Non-volatile analytes stabilized protonated matrix in the ground state. ► A possible mechanism, “analyte support mechanism”, has been proposed. - Abstract: Proton transfer and adduction reaction of matrix molecules in matrix-assisted laser desorption ionization were studied. By using 2,4,6-trihydroxyacetophenone (THAP), 2,5-dihydroxybenzoic acid (DHBA), and their related compounds in which the position of a hydroxyl group is different, it was clarified that a hydroxyl group forming an intramolecular hydrogen bond is related to the ionization of matrix molecules. Intramolecular proton transfer in the electronic excited state of the matrix and subsequent proton adduction from a surrounding solvent to the charge-separated matrix are the initial steps for the ionization of matrix molecules. Nanosecond pump–probe NIR–UV mass spectrometry confirmed that the existence of analyte molecules having large dipole moment in their structures is necessary for the stabilization of [matrix + H]{sup +} in the electronic ground state.

Time expansion chamber and single ionization cluster measurement

International Nuclear Information System (INIS)

Walenta, A.H.

1978-10-01

The time expansion chamber (TEC), a new type of drift chamber, allows the measurement of microscopic details of ionization. The mean drift time interval from subsequent sngle ionization clusters of a relativistic particle in the TEC can be made large enough compared to the width of a anode signal to allow the recording of the clusters separately. Since single primary electrons can be detected, the cluster counting would allow an improved particle separation using the relativistic rise of primary ionization. In another application, very high position accuracy for track detectors or improved energy resolution may be obtained. Basic ionization phenomena and drift properties can be measured at the single electron level

Calculation of large ion densities under HVdc transmission lines by the finite difference method

International Nuclear Information System (INIS)

Suda, Tomotaka; Sunaga, Yoshitaka

1995-01-01

A calculation method for large ion densities (charged aerosols) under HVdc transmission lines was developed considering both the charging mechanism of aerosols by small ions and the drifting process by wind. Large ion densities calculated by this method agreed well with the ones measured under the Shiobara HVdc test line on the lateral profiles at ground level up to about 70m downwind from the line. Measured values decreased more quickly than calculated ones farther downwind from the line. Considering the effect of point discharge from ground cover (earth corona) improved the agreement in the farther downwind region

Liquid ionizing radiaion detector

International Nuclear Information System (INIS)

deGaston, A.N.

1979-01-01

A normally nonconducting liquid such as liquid hydrocarbon is encased between a pair of electrodes in an enclosure so that when the liquid is subjected to ionizing radiation, the ion pairs so created measurably increase the conductivity of the fluid. The reduced impedance between the electrodes is detectable with a sensitive ohm-meter and indicates the amount of ionizing radiation. The enclosure, the electrodes and the fluid can be constructed of materials that make the response of the detector suitable for calibrating a large range of radiation energy levels. The detector is especially useful in medical applications where tissue equivalent X ray detectors are desired

Laser ionization installation for measurement of atomic beam parameters

CERN Document Server

Tukhlibaev, O; Khalilov, E E; Alimov, U Z

2002-01-01

The design of the laser ionization installation for determination of the atomic beam intensity, density and spatial structure is described. The method of the atoms laser resonance staged photoionization is applied in the installation. The above installation consists of two lasers on the dyestuffs, the atomizer, the ionization system and the ion signals registration system. The results of studies on the spatial structure of the In atoms beam are presented. The proposed method provides for the spatial resolution at the level of 10-100 mu m

A compact neutron generator using a field ionization source.

Science.gov (United States)

Persaud, Arun; Waldmann, Ole; Kapadia, Rehan; Takei, Kuniharu; Javey, Ali; Schenkel, Thomas

2012-02-01

Field ionization as a means to create ions for compact and rugged neutron sources is pursued. Arrays of carbon nano-fibers promise the high field-enhancement factors required for efficient field ionization. We report on the fabrication of arrays of field emitters with a density up to 10(6) tips∕cm(2) and measure their performance characteristics using electron field emission. The critical issue of uniformity is discussed, as are efforts towards coating the nano-fibers to enhance their lifetime and surface properties.

Analysis of laser ablation: Contribution of ionization energy to the plasma and shock wave properties

International Nuclear Information System (INIS)

Wen, S.-B.; Mao Xianglei; Greif, Ralph; Russo, Richard E.

2007-01-01

By fitting simulation results with experimentally measured trajectories of the shock wave and the vapor/background gas contact surface, we found that inclusion of ionization energy in the analysis leads to a change in the evolution of the pressure, mass density, electron number density, and temperature of the vapor plume. The contribution of ionization energy to both the plasma and shock wave has been neglected in most studies of laser ablation. Compared to previous simulations, the densities, pressures, and temperatures are lower shortly after the laser pulse ( 50 ns). The predicted laser energy conversion ratio also showed about a 20% increase (from 35% to 45%) when the ionization energy is considered. The changes in the evolution of the physical quantities result from the retention of the ionization energy in the vapor plume, which is then gradually transformed to kinetic and thermal energies. When ionization energy is included in the simulation, the vapor plume attains higher expansion speeds and temperatures for a longer time after the laser pulse. The better determination of the temperature history of the vapor plume not only improves the understanding of the expansion process of the laser induced vapor plume but also is important for chemical analysis. The accurate temperature history provides supplementary information which enhances the accuracy of chemical analysis based on spectral emission measurements (e.g., laser induced breakdown spectroscopy)

Pressure of a partially ionized hydrogen gas : numerical results from exact low temperature expansions

OpenAIRE

Alastuey , Angel; Ballenegger , Vincent

2010-01-01

8 pages; International audience; We consider a partially ionized hydrogen gas at low densities, where it reduces almost to an ideal mixture made with hydrogen atoms in their ground-state, ionized protons and ionized electrons. By performing systematic low-temperature expansions within the physical picture, in which the system is described as a quantum electron-proton plasma interacting via the Coulomb potential, exact formulae for the first five leading corrections to the ideal Saha equation ...

Experimental Studies of Ar{sup n+} ionization using an EBIS

Energy Technology Data Exchange (ETDEWEB)

Lee, Seunghyun; Kim, Han-Sung; Kwon, Hyeok-Jung; Cho, Yong-Sub [Korea Atomic Energy Research Institute, Gyeongju (Korea, Republic of)

2016-10-15

Electron beam ion source (EBIS) has been one of widely used table-top devices for the production of highly charged ions by electron impact ionization. EBIS employs a magnetically compressed, high energy and density electron beam to sequentially ionize atoms or ions in a low charge state. Combination of an EBIS and a Radio frequency quadrupole (RFQ) is a suitable means of heavy ion beam production at low energies. With EBIS, beams of any element can be prepared including uranium and spin-polarized {sup 3}He with a narrow charge distribution. It has demonstrated its reliability and flexibility as a pre-injector used at several accelerators and collider facilities such as Brookhaven National Laboratory, Relative Heavy Ion Collider, NASA Space Radiation Laboratory, Argonne National Laboratory and Large Hadron Collider. At Korea Multi-purpose Accelerator Complex (KOMAC), we have a compact EBIS, operated at room temperature. It is additionally constructed with a dipole bending magnet and a Faraday Cup to separate the charge distribution and measure charge spectra of an ion beam from the EBIS. Using this setup, helium (He) and argon (Ar) gases have been tested to produce charge spectra. An EBIS is employed to produce ions in multiply charged states. We measure an Ar ion spectrum and identify it till 16{sup th} charge state. A detailed experimental study of Ar{sup 1+} and Ar{sup 2+} ions is performed to characterize the effects of electron beam for ionization.

Occurrence of the dayside three-peak density structure in the F2 and the topside ionosphere

Science.gov (United States)

Astafyeva, Elvira; Zakharenkova, Irina; Pineau, Yann

2016-07-01

In this work, we discuss the occurrence of the dayside three-peak electron density structure in the ionosphere. We first use a set of ground-based and satellite-borne instruments to demonstrate the development of a large-amplitude electron density perturbation at the recovery phase of a moderate storm of 11 October 2008. The perturbation developed in the F2 and low topside ionospheric regions over the American sector; it was concentrated on the north from the equatorial ionization anomaly (EIA) but was clearly separated from it. At the F2 region height, the amplitude of the observed perturbation was comparable or even exceeded that of the EIA. Further analysis of the observational data together with the Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics model simulation results showed that a particular local combination of the thermospheric wind surges provided favorable conditions for the generation of the three-peak EIA structure. We further proceed with a statistical study of occurrence of the three-peak density structure in the ionosphere in general. Based on the analysis of 7 years of the in situ data from CHAMP satellite, we found that such three-peak density structure occurs sufficiently often during geomagnetically quiet time. The third ionization peak develops in the afternoon hours in the summer hemisphere at solstice periods. Based on analysis of several quiet time events, we conclude that during geomagnetically quiet time, the prevailing summer-to-winter thermospheric circulation acts in similar manner as the storm-time enhanced thermospheric winds, playing the decisive role in generation of the third ionization peak in the daytime ionosphere.

RZP 202 - a modular system for surface density measurement

International Nuclear Information System (INIS)

Severa, L.; Merinsky, J.

The sensing element is an ionization chamber of the type that has maximum sensitivity to beta radiation of the used radionuclide ( 147 Pm, 85 Kr, 90 Sr- 90 Y) or to gamma radiation of radionuclide 241 Am. Collimation shields were developed for the said sources. Measurement of the ionization currents is made with an electrometer with a vibration capacitor. Invariable configuration is secured by a measuring arm. The modular units are of the CAMAC system design. The surface density meters measure deviations from the rated surface density. The scale for inputting surface density is linear. The configuration, functional continuity of the individual parts and the possibility of variant designs of surface density meters are described and the technical parameters of RZP 202 and its configuration and design are given

Theory of warm ionized gases: equation of state and kinetic Schottky anomaly.

Science.gov (United States)

Capolupo, A; Giampaolo, S M; Illuminati, F

2013-10-01

Based on accurate Lennard-Jones-type interaction potentials, we derive a closed set of state equations for the description of warm atomic gases in the presence of ionization processes. The specific heat is predicted to exhibit peaks in correspondence to single and multiple ionizations. Such kinetic analog in atomic gases of the Schottky anomaly in solids is enhanced at intermediate and low atomic densities. The case of adiabatic compression of noble gases is analyzed in detail and the implications on sonoluminescence are discussed. In particular, the predicted plasma electron density in a sonoluminescent bubble turns out to be in good agreement with the value measured in recent experiments.

Matrix-assisted laser desorption/ionization-time of flight mass spectrometry identification of large colony beta-hemolytic streptococci containing Lancefield groups A, C, and G

DEFF Research Database (Denmark)

Salgård Jensen, Christian; Dam-Nielsen, Casper; Arpi, Magnus

2015-01-01

BACKGROUND: The aim of this study was to investigate whether large colony beta-hemolytic streptococci containing Lancefield groups A, C, and G can be adequately identified using matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-ToF). Previous studies show varying...

Multiphoton ionization of many-electron atoms and highly-charged ions in intense laser fields: a relativistic time-dependent density functional theory approach

Science.gov (United States)

Tumakov, Dmitry A.; Telnov, Dmitry A.; Maltsev, Ilia A.; Plunien, Günter; Shabaev, Vladimir M.

2017-10-01

We develop an efficient numerical implementation of the relativistic time-dependent density functional theory (RTDDFT) to study multielectron highly-charged ions subject to intense linearly-polarized laser fields. The interaction with the electromagnetic field is described within the electric dipole approximation. The resulting time-dependent relativistic Kohn-Sham (RKS) equations possess an axial symmetry and are solved accurately and efficiently with the help of the time-dependent generalized pseudospectral method. As a case study, we calculate multiphoton ionization probabilities of the neutral argon atom and argon-like xenon ion. Relativistic effects are assessed by comparison of our present results with existing non-relativistic data.

PHYSICS OF A PARTIALLY IONIZED GAS RELEVANT TO GALAXY FORMATION SIMULATIONS—THE IONIZATION POTENTIAL ENERGY RESERVOIR

International Nuclear Information System (INIS)

Vandenbroucke, B.; De Rijcke, S.; Schroyen, J.; Jachowicz, N.

2013-01-01

Simulation codes for galaxy formation and evolution take on board as many physical processes as possible beyond the standard gravitational and hydrodynamical physics. Most of this extra physics takes place below the resolution level of the simulations and is added in a ''sub-grid'' fashion. However, these sub-grid processes affect the macroscopic hydrodynamical properties of the gas and thus couple to the ''on-grid'' physics that is explicitly integrated during the simulation. In this paper, we focus on the link between partial ionization and the hydrodynamical equations. We show that the energy stored in ions and free electrons constitutes a potential energy term which breaks the linear dependence of the internal energy on temperature. Correctly taking into account ionization hence requires modifying both the equation of state and the energy-temperature relation. We implemented these changes in the cosmological simulation code GADGET2. As an example of the effects of these changes, we study the propagation of Sedov-Taylor shock waves through an ionizing medium. This serves as a proxy for the absorption of supernova feedback energy by the interstellar medium. Depending on the density and temperature of the surrounding gas, we find that up to 50% of the feedback energy is spent ionizing the gas rather than heating it. Thus, it can be expected that properly taking into account ionization effects in galaxy evolution simulations will drastically reduce the effects of thermal feedback. To the best of our knowledge, this potential energy term is not used in current simulations of galaxy formation and evolution.

Coupled Cluster Studies of Ionization Potentials and Electron Affinities of Single-Walled Carbon Nanotubes

Energy Technology Data Exchange (ETDEWEB)

Peng, Bo; Govind, Niranjan; Apra, Edoardo; Klemm, Michael; Hammond, Jeff R.; Kowalski, Karol

2017-02-03

In this paper we apply equation-of-motion coupled cluster (EOMCC) methods in studies of vertical ionization potentials (IP) and electron affinities (EA) for sin- gled walled carbon nanotubes. EOMCC formulations for ionization potentials and electron affinities employing excitation manifolds spanned by single and double ex- citations (IP/EA-EOMCCSD) are used to study IPs and EAs of nanotubes as a function of nanotube length. Several armchair nanotubes corresponding to C20nH20 models with n = 2 - 6 have been used in benchmark calculations. In agreement with previous studies, we demonstrate that the electronegativity of C20nH20 systems remains, to a large extent, independent of nanotube length. We also compare IP/EA- EOMCCSD results with those obtained with the coupled cluster models with single and double excitations corrected by perturbative triples, CCSD(T), and density func- tional theory (DFT) using global and range-separated hybrid exchange-correlation functionals.

High density high performance plasma with internal diffusion barrier in Large Helical Device

International Nuclear Information System (INIS)

Sakamoto, R.; Kobayashi, M.; Miyazawa, J.

2008-10-01

A attractive high density plasma operational regime, namely an internal diffusion barrier (IDB), has been discovered in the intrinsic helical divertor configuration on the Large Helical Device (LHD). The IDB which enables core plasma to access a high density/high pressure regime has been developed. It is revealed that the IDB is reproducibly formed by pellet fueling in the magnetic configurations shifted outward in major radius. Attainable central plasma density exceeds 1x10 21 m -3 . Central pressure reaches 1.5 times atmospheric pressure and the central β value becomes fairly high even at high magnetic field, i.e. β(0)=5.5% at B t =2.57 T. (author)

Neutral Atom Diffusion in a Partially Ionized Prominence Plasma

Science.gov (United States)

Gilbert, Holly

2010-01-01

The support of solar prominences is normally described in terms of a magnetic force on the prominence plasma that balances the solar gravitational force. Because the prominence plasma is only partially ionized. it is necessary to consider in addition the support of the neutral component of the prominence plasma. This support is accomplished through a frictional interaction between the neutral and ionized components of the plasma, and its efficacy depends strongly on the degree of ionization of the plasma. More specifically, the frictional force is proportional to the relative flow of neutral and ion species, and for a sufficiently weakly ionized plasma, this flow must be relatively large to produce a frictional force that balances gravity. A large relative flow, of course, implies significant draining of neutral particles from the prominence. We evaluate the importance of this draining effect for a hydrogen-helium plasma, and consider the observational evidence for cross-field diffusion of neutral prominence material,

Conversion of ionization measurements to radiation absorbed dose in non-water density material

International Nuclear Information System (INIS)

El-Khatib, E.; Connors, S.

1992-01-01

In bone-equivalent materials two different calculations of absorbed dose are possible: the absorbed dose to soft tissue plastic (polystyrene) within bone-equivalent material and the dose to the bone-equivalent material itself. Both can be calculated from ionization measurements in phantoms. These two calculations result in significantly different doses in a heterogeneous phantom composed of polystyrene and aluminium (a bone substitute). The dose to a thin slab of polystyrene in aluminium is much higher than the dose to the aluminium itself at the same depth in the aluminium. Monte Carlo calculations confirm that the calculation of dose to polystyrene in aluminium can be accurately carried out using existing dosimetry protocols. However, the conversion of ionization measurements to absorbed dose to high atomic number materials cannot be accurately carried out with existing protocols and appropriate conversion factors need to be determined. (author)

Radar measurements of the latitudinal variation of auroral ionization

International Nuclear Information System (INIS)

Vondrak, R.R.; Baron, M.J.

1976-01-01

The Chatanika, Alaska, incoherent scatter radar has been used to measure the spatial variation of auroral ionization. A two-dimensional (altitude, latitude) cross-sectional map of electron densities in the ionosphere is produced by scanning in the geomagnetic meridian plane. The altitutde variation of ionization is used to infer the differential energy distribution of the incident auroral electrons. The latitudinal variation of this energy distribution and the total energy input are obtained by use of the meridian-scanning technique. Examples are shown of observations made during an active aurora

Lattice Boltzmann method for weakly ionized isothermal plasmas

International Nuclear Information System (INIS)

Li Huayu; Ki, Hyungson

2007-01-01

In this paper, a lattice Boltzmann method (LBM) for weakly ionized isothermal plasmas is presented by introducing a rescaling scheme for the Boltzmann transport equation. Without using this rescaling, we found that the nondimensional relaxation time used in the LBM is too large and the LBM does not produce physically realistic results. The developed model was applied to the electrostatic wave problem and the diffusion process of singly ionized helium plasmas with a 1-3% degree of ionization under an electric field. The obtained results agree well with theoretical values

Ionization and recombination in attosecond electric field pulses

International Nuclear Information System (INIS)

Dimitrovski, Darko; Solov'ev, Eugene A.; Briggs, John S.

2005-01-01

Based on the results of a previous communication [Dimitrovski et al., Phys. Rev. Lett. 93, 083003 (2004)], we study ionization and excitation of a hydrogenic atom from the ground and first excited states in short electric field pulses of several cycles. A process of ionization and recombination which occurs periodically in time is identified, for both small and extremely large peak electric field strengths. In the limit of large electric peak fields closed-form analytic expressions for the population of the initial state after single- and few-cycle pulses are derived. These formulas, strictly valid for asymptotically large momentum transfer from the field, give excellent agreement with fully numerical calculations for all momentum transfers

Mass flow and the validity of ionization equilibrium on the sun

International Nuclear Information System (INIS)

Joselyn, J.; Munro, R.H.; Holzer, T.E.

1979-01-01

Ionization equilibrium is a useful assumption which allows temperatures and other plasma properties to be deduced from spectral observations. Inherent to this assumption is the premise that the ion stage densities are determined solely by atomic processes which are local functions of the plasma temperature and electron density. However, if the time scale of plasma flow through a temperature gradient is less than the characteristic time scale for an important atomic process, deviations from the ionization stage densities expected for equilibrium will occur which could introduce serious errors into subsequent analyses. In the past few years, significant flow velocities in the upper solar atmosphere have been inferred from observations of emission lines originating in the transition region (about 10 4 -10 6 K) and corona. In this paper, 3 models of the solar atmosphere (quiet Sun, coronal hole, and a network model) are examined to determine if the emission expected from these model atmospheres could be produced from equilibrium ion populations when steady flows of several kilometers per second are assumed. If the flows are quasi-periodic instead of steady, spatial and temporal averaging inherent in the observations may allow for the construction of satisfactory models based on the assumption of ionization equilibrium. Representative emission lines are analysed for the following ions: C III, IV, O IV, V, VI, Ne VII, VIII, Mg IX, X, Si XII, Fe IX-XIV. Two principle conclusions are drawn. First, only the iron ions are generally in equilibrium for steady flows of 20 kms -1 . For carbon and oxygen, ionization equilibrium is not a valid assumption for steady flows as small as 1 kms -1 . Second, the 3 models representing different solar conditions behave in a qualitatively similar manner, implying that these results are not particularly model dependent over the range of temperature gradients and electron densities thus far inferred for the Sun. In view of the flow velocities

Local thermodynamic equilibrium in rapidly heated high energy density plasmas

International Nuclear Information System (INIS)

Aslanyan, V.; Tallents, G. J.

2014-01-01

Emission spectra and the dynamics of high energy density plasmas created by optical and Free Electron Lasers (FELs) depend on the populations of atomic levels. Calculations of plasma emission and ionization may be simplified by assuming Local Thermodynamic Equilibrium (LTE), where populations are given by the Saha-Boltzmann equation. LTE can be achieved at high densities when collisional processes are much more significant than radiative processes, but may not be valid if plasma conditions change rapidly. A collisional-radiative model has been used to calculate the times taken by carbon and iron plasmas to reach LTE at varying densities and heating rates. The effect of different energy deposition methods, as well as Ionization Potential Depression are explored. This work shows regimes in rapidly changing plasmas, such as those created by optical lasers and FELs, where the use of LTE is justified, because timescales for plasma changes are significantly longer than the times needed to achieve an LTE ionization balance

Exploring the temporally resolved electron density evolution in extreme ultra-violet induced plasmas

International Nuclear Information System (INIS)

Van der Horst, R M; Beckers, J; Nijdam, S; Kroesen, G M W

2014-01-01

We measured the electron density in an extreme ultra-violet (EUV) induced plasma. This is achieved in a low-pressure argon plasma by using a method called microwave cavity resonance spectroscopy. The measured electron density just after the EUV pulse is 2.6 × 10 16  m −3 . This is in good agreement with a theoretical prediction from photo-ionization, which yields a density of 4.5 × 10 16  m −3 . After the EUV pulse the density slightly increases due to electron impact ionization. The plasma (i.e. electron density) decays in tens of microseconds. (fast track communication)

K-shell ionization and double-ionization of Au atoms with 1.33 MeV photons

International Nuclear Information System (INIS)

Belkacem, A.; Dauvergne, D.; Feinberg, B.; Ionescu, D.; Maddi, J.; Sorensen, A.H.

2000-01-01

At relativistic energies, the cross section for the atomic photoelectric effect drops off as does the cross section for liberating any bound electron through Compton scattering. However, when the photon energy exceeds twice the rest mass of the electron, ionization may proceed via electron-positron pair creation. We used 1.33 MeV photons impinging on Au thin foils to study double K-shell ionization and vacuum-assisted photoionization. The preliminary results yield a ratio of vacuum-assisted photoionization and pair creation of 2x10 -3 , a value that is substantially higher than the ratio of photo double ionization to single photoionization that is found to be 0.5-1x10 -4 . Because of the difficulties and large error bars associated with the small cross sections additional measurements are needed to minimize systematic errors

Gas chromatography/chemical ionization triple quadrupole mass spectrometry analysis of anabolic steroids: ionization and collision-induced dissociation behavior.

Science.gov (United States)

Polet, Michael; Van Gansbeke, Wim; Van Eenoo, Peter; Deventer, Koen

2016-02-28

The detection of new anabolic steroid metabolites and new designer steroids is a challenging task in doping analysis. Switching from electron ionization gas chromatography triple quadrupole mass spectrometry (GC/EI-MS/MS) to chemical ionization (CI) has proven to be an efficient way to increase the sensitivity of GC/MS/MS analyses and facilitate the detection of anabolic steroids. CI also extends the possibilities of GC/MS/MS analyses as the molecular ion is retained in its protonated form due to the softer ionization. In EI it can be difficult to find previously unknown but expected metabolites due to the low abundance or absence of the molecular ion and the extensive (and to a large extent unpredictable) fragmentation. The main aim of this work was to study the CI and collision-induced dissociation (CID) behavior of a large number of anabolic androgenic steroids (AAS) as their trimethylsilyl derivatives in order to determine correlations between structures and CID fragmentation. Clarification of these correlations is needed for the elucidation of structures of unknown steroids and new metabolites. The ionization and CID behavior of 65 AAS have been studied using GC/CI-MS/MS with ammonia as the reagent gas. Glucuronidated AAS reference standards were first hydrolyzed to obtain their free forms. Afterwards, all the standards were derivatized to their trimethylsilyl forms. Full scan and product ion scan analyses were used to examine the ionization and CID behavior. Full scan and product ion scan analyses revealed clear correlations between AAS structure and the obtained mass spectra. These correlations were confirmed by analysis of multiple hydroxylated, methylated, chlorinated and deuterated analogs. AAS have been divided into three groups according to their ionization behavior and into seven groups according to their CID behavior. Correlations between fragmentation and structure were revealed and fragmentation pathways were postulated. Copyright © 2016 John Wiley

Thermodynamics of aqueous association and ionization reactions at high temperatures and pressures

International Nuclear Information System (INIS)

Mesmer, R.E.; Marshall, W.L.; Palmer, D.A.; Simonson, J.M.; Holmes, H.F.

1990-01-01

Electrochemical and electrical conductance cells have been widely used at ORNL over the years to quantitatively determine equilibrium constants and their salt effects to 300 degree C (EMF) and 800 degree C (conductance) at the saturation pressure of water (EMF) and to 4000 bars (conductance). The most precise results to 300 degree C for a large number of weak acids and bases show very similar thermodynamic behavior, which will be discussed. Results for the ionization constants of water, NH 3 (aq), HCl(aq), and NaCl(aq), which extend well into the supercritical region, have been fitted in terms of a model with dependence on density and temperature. The entropy change is found to be the driving force for ion-association reactions and this tendency increases (as it must) with increasing temperature at a given pressure. Also, the variation of all thermodynamic properties is greatly reduced at high fixed densities. Considerable variation occurs at low densities. From this analysis, the dependence of the reaction thermodynamics on the P-V-T properties of the solvent is shown, and the implication of large changes in hydration for solutes in the vicinity of the critical temperature will be discussed. Finally, the change in the molar compressibility coefficient for all reactions in water is shown to be the same and dependent only on the compressibility of the solvent

Electron Impact Ionization of C60

International Nuclear Information System (INIS)

Duenser, B.; Lezius, M.; Scheier, P.; Deutsch, H.; Maerk, T.D.

1995-01-01

Absolute partial and total cross sections for the electron impact ionization of C 60 have been measured using a novel approach for the absolute calibration. The results obtained reveal not only an anomalous large parent ion cross section (as compared to the other ionization channels), but also anomalies for the production of multiply charged parent and fragment ions. This special behavior has its origin in the specific electronic and geometric structure of C 60 . Semiclassical calculations for singly charged ions support the measured data

ASYMMETRIC MAGNETIC RECONNECTION IN WEAKLY IONIZED CHROMOSPHERIC PLASMAS

International Nuclear Information System (INIS)

Murphy, Nicholas A.; Lukin, Vyacheslav S.

2015-01-01

Realistic models of magnetic reconnection in the solar chromosphere must take into account that the plasma is partially ionized and that plasma conditions within any two magnetic flux bundles undergoing reconnection may not be the same. Asymmetric reconnection in the chromosphere may occur when newly emerged flux interacts with pre-existing, overlying flux. We present 2.5D simulations of asymmetric reconnection in weakly ionized, reacting plasmas where the magnetic field strengths, ion and neutral densities, and temperatures are different in each upstream region. The plasma and neutral components are evolved separately to allow non-equilibrium ionization. As in previous simulations of chromospheric reconnection, the current sheet thins to the scale of the neutral–ion mean free path and the ion and neutral outflows are strongly coupled. However, the ion and neutral inflows are asymmetrically decoupled. In cases with magnetic asymmetry, a net flow of neutrals through the current sheet from the weak-field (high-density) upstream region into the strong-field upstream region results from a neutral pressure gradient. Consequently, neutrals dragged along with the outflow are more likely to originate from the weak-field region. The Hall effect leads to the development of a characteristic quadrupole magnetic field modified by asymmetry, but the X-point geometry expected during Hall reconnection does not occur. All simulations show the development of plasmoids after an initial laminar phase

Indirect processes in electron impact ionization of Kr24+ and Kr25+

International Nuclear Information System (INIS)

Chen, M.H.; Reed, K.J.

1992-09-01

Electron-impact ionization cross sections have been calculated for magnesiumlike Kr 24+ and sodiumlike Kr 25+ . Electron-impact ionization is an important atomic process in hot dense plasmas. It can affect the ionization balance, electron temperature, electron density, and level population in the plasma. In the past decade, theoretical and experimental studies have revealed that indirect processes can make significant contributions to the cross sections for electron impact ionization of positive ions. The most important indirect process is excitation of an inner-shell electron followed by Auger emission. Higher-order processes such as resonant excitation followed by sequential double Auger emission, can also contribute significantly. The contributions of excitation-autoionization and resonant excitation double autoionization (REDA) were included, in addition to the cross sections for direct ionization of a 3s electron. The calculations were carried out using the relativistic distorted wave methods and the multiconfiguration Dirac-Fock model. For Kr 25+ , the total cross section is about 5 times the direct ionization cross section. For the Kr 24+ , the indirect contribution is about 2.5 times the direct ionization cross section. The REDA process produces many strong resonances and contributes about 20% to the average ionization cross section

The Evolution of the Large-Scale ISM: Bubbles, Superbubbles and Non-Equilibrium Ionization

Science.gov (United States)

de Avillez, M. A.; Breitschwerdt, D.

2010-12-01

The ISM, powered by SNe, is turbulent and permeated by a magnetic field (with a mean and a turbulent component). It constitutes a frothy medium that is mostly out of equilibrium and is ram pressure dominated on most of the temperature ranges, except for T 106K, where magnetic and thermal pressures dominate, respectively. Such lack of equilibrium is also imposed by the feedback of the radiative processes into the ISM flow. Many models of the ISM or isolated phenomena, such as bubbles, superbubbles, clouds evolution, etc., take for granted that the flow is in the so-called collisional ionization equilibrium (CIE). However, recombination time scales of most of the ions below 106 K are longer than the cooling time scale. This implies that the recombination lags behind and the plasma is overionized while it cools. As a consequence cooling deviates from CIE. This has severe implications on the evolution of the ISM flow and its ionization structure. Here, besides reviewing several models of the ISM, including bubbles and superbubbles, the validity of the CIE approximation is discussed, and a presentation of recent developments in modeling the ISM by taking into account the time-dependent ionization structure of the flow in a full-blown numerical 3D high resolution simulation is presented.

Azimuthal angle correlations at large rapidities. Revisiting density variation mechanism

Energy Technology Data Exchange (ETDEWEB)

Gotsman, E. [Tel Aviv University, Department of Particle Physics, Raymond and Beverly Sackler Faculty of Exact Science, School of Physics and Astronomy, Tel Aviv (Israel); Levin, E. [Tel Aviv University, Department of Particle Physics, Raymond and Beverly Sackler Faculty of Exact Science, School of Physics and Astronomy, Tel Aviv (Israel); Universidad Tecnica Federico Santa Maria, Departemento de Fisica, Valparaiso (Chile); Centro Cientifico-Tecnologico de Valparaiso, Valparaiso (Chile)

2017-11-15

We discuss the angular correlation present in hadron-hadron collisions at large rapidity difference (anti α{sub S}y{sub 12} >> 1). We find that in the CGC/saturation approach the largest contribution stems from the density variation mechanism. Our principal results are that the odd Fourier harmonics (v{sub 2n+1}) decrease substantially as a function of y{sub 12}, while the even harmonics (v{sub 2n}) increase considerably with the growth of y{sub 12}. (orig.)

Density effects on electronic configurations in dense plasmas

Science.gov (United States)

Faussurier, Gérald; Blancard, Christophe

2018-02-01

We present a quantum mechanical model to describe the density effects on electronic configurations inside a plasma environment. Two different approaches are given by starting from a quantum average-atom model. Illustrations are shown for an aluminum plasma in local thermodynamic equilibrium at solid density and at a temperature of 100 eV and in the thermodynamic conditions of a recent experiment designed to characterize the effects of the ionization potential depression treatment. Our approach compares well with experiment and is consistent in that case with the approach of Stewart and Pyatt to describe the ionization potential depression rather than with the method of Ecker and Kröll.

PHYSICS OF A PARTIALLY IONIZED GAS RELEVANT TO GALAXY FORMATION SIMULATIONS-THE IONIZATION POTENTIAL ENERGY RESERVOIR

Energy Technology Data Exchange (ETDEWEB)

Vandenbroucke, B.; De Rijcke, S.; Schroyen, J. [Department of Physics and Astronomy, Ghent University, Krijgslaan 281, S9, B-9000 Gent (Belgium); Jachowicz, N. [Department of Physics and Astronomy, Ghent University, Proeftuinstraat 86, B-9000 Gent (Belgium)

2013-07-01

Simulation codes for galaxy formation and evolution take on board as many physical processes as possible beyond the standard gravitational and hydrodynamical physics. Most of this extra physics takes place below the resolution level of the simulations and is added in a ''sub-grid'' fashion. However, these sub-grid processes affect the macroscopic hydrodynamical properties of the gas and thus couple to the ''on-grid'' physics that is explicitly integrated during the simulation. In this paper, we focus on the link between partial ionization and the hydrodynamical equations. We show that the energy stored in ions and free electrons constitutes a potential energy term which breaks the linear dependence of the internal energy on temperature. Correctly taking into account ionization hence requires modifying both the equation of state and the energy-temperature relation. We implemented these changes in the cosmological simulation code GADGET2. As an example of the effects of these changes, we study the propagation of Sedov-Taylor shock waves through an ionizing medium. This serves as a proxy for the absorption of supernova feedback energy by the interstellar medium. Depending on the density and temperature of the surrounding gas, we find that up to 50% of the feedback energy is spent ionizing the gas rather than heating it. Thus, it can be expected that properly taking into account ionization effects in galaxy evolution simulations will drastically reduce the effects of thermal feedback. To the best of our knowledge, this potential energy term is not used in current simulations of galaxy formation and evolution.

Foundations of high-energy-density physics physical processes of matter at extreme conditions

CERN Document Server

Larsen, Jon

2017-01-01

High-energy-density physics explores the dynamics of matter at extreme conditions. This encompasses temperatures and densities far greater than we experience on Earth. It applies to normal stars, exploding stars, active galaxies, and planetary interiors. High-energy-density matter is found on Earth in the explosion of nuclear weapons and in laboratories with high-powered lasers or pulsed-power machines. The physics explored in this book is the basis for large-scale simulation codes needed to interpret experimental results whether from astrophysical observations or laboratory-scale experiments. The key elements of high-energy-density physics covered are gas dynamics, ionization, thermal energy transport, and radiation transfer, intense electromagnetic waves, and their dynamical coupling. Implicit in this is a fundamental understanding of hydrodynamics, plasma physics, atomic physics, quantum mechanics, and electromagnetic theory. Beginning with a summary of the topics and exploring the major ones in depth, thi...

THE IMPLICATIONS OF A HIGH COSMIC-RAY IONIZATION RATE IN DIFFUSE INTERSTELLAR CLOUDS

International Nuclear Information System (INIS)

Indriolo, Nick; Fields, Brian D.; McCall, Benjamin J.

2009-01-01

Diffuse interstellar clouds show large abundances of H + 3 which can only be maintained by a high ionization rate of H 2 . Cosmic rays are the dominant ionization mechanism in this environment, so the large ionization rate implies a high cosmic-ray flux, and a large amount of energy residing in cosmic rays. In this paper, we find that the standard propagated cosmic-ray spectrum predicts an ionization rate much lower than that inferred from H + 3 . Low-energy (∼10 MeV) cosmic rays are the most efficient at ionizing hydrogen, but cannot be directly detected; consequently, an otherwise unobservable enhancement of the low-energy cosmic-ray flux offers a plausible explanation for the H + 3 results. Beyond ionization, cosmic rays also interact with the interstellar medium by spalling atomic nuclei and exciting atomic nuclear states. These processes produce the light elements Li, Be, and B, as well as gamma-ray lines. To test the consequences of an enhanced low-energy cosmic-ray flux, we adopt two physically motivated cosmic-ray spectra which by construction reproduce the ionization rate inferred in diffuse clouds, and investigate the implications of these spectra on dense cloud ionization rates, light-element abundances, gamma-ray fluxes, and energetics. One spectrum proposed here provides an explanation for the high ionization rate seen in diffuse clouds while still appearing to be broadly consistent with other observables, but the shape of this spectrum suggests that supernovae remnants may not be the predominant accelerators of low-energy cosmic rays.

Ionization balance in Titan's nightside ionosphere

Science.gov (United States)

Vigren, E.; Galand, M.; Yelle, R. V.; Wellbrock, A.; Coates, A. J.; Snowden, D.; Cui, J.; Lavvas, P.; Edberg, N. J. T.; Shebanits, O.; Wahlund, J.-E.; Vuitton, V.; Mandt, K.

2015-03-01

Based on a multi-instrumental Cassini dataset we make model versus observation comparisons of plasma number densities, nP = (nenI)1/2 (ne and nI being the electron number density and total positive ion number density, respectively) and short-lived ion number densities (N+, CH2+, CH3+, CH4+) in the southern hemisphere of Titan's nightside ionosphere over altitudes ranging from 1100 and 1200 km and from 1100 to 1350 km, respectively. The nP model assumes photochemical equilibrium, ion-electron pair production driven by magnetospheric electron precipitation and dissociative recombination as the principal plasma neutralization process. The model to derive short-lived-ion number densities assumes photochemical equilibrium for the short-lived ions, primary ion production by electron-impact ionization of N2 and CH4 and removal of the short-lived ions through reactions with CH4. It is shown that the models reasonably reproduce the observations, both with regards to nP and the number densities of the short-lived ions. This is contrasted by the difficulties in accurately reproducing ion and electron number densities in Titan's sunlit ionosphere.

On interaction of large dust grains with fusion plasma

International Nuclear Information System (INIS)

Krasheninnikov, S. I.; Smirnov, R. D.

2009-01-01

So far the models used to study dust grain-plasma interactions in fusion plasmas neglect the effects of dust material vapor, which is always present around dust in rather hot and dense edge plasma environment in fusion devices. However, when the vapor density and/or the amount of ionized vapor atoms become large enough, they can alter the grain-plasma interactions. Somewhat similar processes occur during pellet injection in fusion plasma. In this brief communication the applicability limits of the models ignoring vapor effects in grain-plasma interactions are obtained.

Novel target configurations for selective ionization state studies in molybdenum

International Nuclear Information System (INIS)

Ilcisin, K.J.; Feldman, U.; Schwob, J.L.; Wouters, A.; Suckewer, S.; Princeton Univ., NJ

1990-03-01

Details of experiments aimed at achieving low ionization state selectivity in molybdenum are presented. Targets are excited with a 10 J CO 2 laser and the resultant VUV spectrum (300--700 Angstrom) has been studied. Combinations of focal spot size, target depth, and target geometries are compared. Simple attenuation of energy is shown not to vary ionization stage composition significantly. Experiments conducted with grazing incidence targets result only in a hot plasma. Modular targets with cooling cylinders of various radii demonstrated good selectivity of the ionization states, but with low absolute signals. Finally, results from combinations of focal spot adjustment and radiative cooling illustrate increased control over desired plasma temperature and density for spectroscopic studies of molybdenum. 7 refs., 14 figs

A model for steady-state large-volume plasma generation

International Nuclear Information System (INIS)

Uhm, H.S.; Miller, J.D.; Schneider, R.F.

1991-01-01

In this paper, a simple, new scheme to generate a uniform, steady-state, large-volume plasma is presented. The weakly magnetized plasma is created by direct ionization of the background gas by low-energy electrons generated from thermionic filaments. An annular arrangement of the filaments ensures a uniform plasma density in the radial direction as predicted by theory. Experiments have been performed to characterize the plasma generated in such a configuration. In order to explain the experimental observation, we develop a bulk plasma theory based on plasma transport via cross-field diffusion. As assumed in the theoretical model, the experimental measurements indicate a uniform plasma density along the axis. Both the theory and experiment indicate that the plasma density is a function of the square of the external magnetic field. The theory also predicts the plasma density to be proportional to the neutral density to the two-thirds power in agreement with the experimental data. We also observe the experimental data to agree remarkably well with theoretical prediction for a broad range of system parameters

About particular use of ionizing radiations

International Nuclear Information System (INIS)

2001-01-01

Different uses of ionizing radiations are reviewed: tracers techniques, nuclear gauges, dating by carbon 14, silica doping, use of gamma irradiation for the density measurement in civil engineering, use of a electron capture detector to study by gas chromatography chlorinated contaminants in environment, neutron activation as environmental gauge, analysis of lead in paint and pollutants in ground and dusts, help for work of art valuation by x spectrometry. (N.C.)

Structure of anode plasma of gas discharge taking into account gas ionization burnout

International Nuclear Information System (INIS)

Zharinov, A.V.; Shumilin, V.P.

2006-01-01

One deals with a structure of an anode plasma of a gas discharge with intensive ionization ( b urnout ) of neutral atoms (neutrals). One derived analytical solutions of the quasi-neutrality equation for potential distribution, as well as, a condition of anode plasma existence in a unidimensional case at the arbitrary dependences of neutral burnout frequency and of electron concentration on the potential. One studied particular cases of the level frequency of neutral burnout, of ionization by the Maxwell electrons and of ionization by the intensive beam at collision-free motion of ions and the Boltzmann distribution of thermal electrons. Solutions for the first two cases at zero parameter of burnout, that is, at the level concentration of a gas coincide with the solutions obtained [1] by the power series expansion. It is shown that in case of ionization by the Maxwell electrons, anode plasma at the rational flow rates of a working gas may be produced under rather high temperature of electrons (if, for example, xenon serves as a working gas, so T e ≥5 eV). The stationary solutions of the quasi-neutrality at ionization by the intensive electron beam are found exclusively when the ratio between the electron beam density and the maximum density of thermal neutrons does not exceed a certain limiting value [ru

Critical ionization velocity as a mechanism for producing Titan's plasma tail

International Nuclear Information System (INIS)

Galeev, A.A.; Khabibrakhmanov, I.KH.

1984-01-01

The phenomenon of a critical ionization velocity may explain the anomalous interaction between the magnetospheric plasma corotating with Saturn and the atmosphere of Titan. Although the dominant role will be played by the lower-hybrid instability due to the counterstreaming of the magnetospehric plasma and newly formed atmospheric ions, charge-separation effects caused by the very large Larmor radius of the new nitrogen ions also may trigger instability. The kinetic energy of the newly formed ions will be conveyed to the electrons by plasma waves generated in the counterflow, thereby exciting the atmospheric atoms to emit radiation. The limiting plasma density and electron temperature in Titan's plasma tail and the frequency spectrum of the waves that develop are determined and compared against the Voyager measurements. 11 references

Ionizing collisions: a new diagnostic for Bose-Einstein condensates of metastable helium

International Nuclear Information System (INIS)

Sirjean, O.

2003-06-01

At this writing, metastable helium (23S1) is the only example of Bose-Einstein condensation of an atom in an excited electronic state. The corresponding internal energy permits efficient and fast electronic detection of the atoms using a micro-channel plate detector (MCP). Moreover, this energy is responsible for ionizing collisions inside the magnetically trapped cloud (Penning ionization). These ions are also easily detected by the MCP. This thesis begins by describing the characteristics of the MCP detector. Next, the experimental procedure to achieve Bose-Einstein condensation is presented. These preliminaries are followed by a description of the experiments performed in order to determine the origin of the ions produced and by a presentation of some of the new experimental possibilities provided by the ion signal. For clouds with a low enough density, ions are mainly produced by collisions with the residual gas, and the signal is proportional to the number of trapped atoms. For clouds with a sufficiently high density, for example close to the condensation threshold, ions are mainly produced by 2- and 3-body collisions. In this case, the ion signal is also related to the density of the cloud. Depending on the density, the signal gives a real-time and 'non-destructive' measurement of these different characteristics. In particular, we have shown it is a valuable indicator of the onset of condensation, because it signals the sudden increase of density which then occurs. By studying the ion rate versus the density and the number of atoms for pure condensates and for thermal clouds at critical temperature, we have measured the collision rate constants for these ionizing processes. Our results are in agreement with theoretical predictions. (author)

Gauging Metallicity of Diffuse Gas under an Uncertain Ionizing Radiation Field

Science.gov (United States)

Chen, Hsiao-Wen; Johnson, Sean D.; Zahedy, Fakhri S.; Rauch, Michael; Mulchaey, John S.

2017-06-01

Gas metallicity is a key quantity used to determine the physical conditions of gaseous clouds in a wide range of astronomical environments, including interstellar and intergalactic space. In particular, considerable effort in circumgalactic medium (CGM) studies focuses on metallicity measurements because gas metallicity serves as a critical discriminator for whether the observed heavy ions in the CGM originate in chemically enriched outflows or in more chemically pristine gas accreted from the intergalactic medium. However, because the gas is ionized, a necessary first step in determining CGM metallicity is to constrain the ionization state of the gas which, in addition to gas density, depends on the ultraviolet background radiation field (UVB). While it is generally acknowledged that both the intensity and spectral slope of the UVB are uncertain, the impact of an uncertain spectral slope has not been properly addressed in the literature. This Letter shows that adopting a different spectral slope can result in an order of magnitude difference in the inferred CGM metallicity. Specifically, a harder UVB spectrum leads to a higher estimated gas metallicity for a given set of observed ionic column densities. Therefore, such systematic uncertainties must be folded into the error budget for metallicity estimates of ionized gas. An initial study shows that empirical diagnostics are available for discriminating between hard and soft ionizing spectra. Applying these diagnostics helps reduce the systematic uncertainties in CGM metallicity estimates.

Gauging Metallicity of Diffuse Gas under an Uncertain Ionizing Radiation Field

Energy Technology Data Exchange (ETDEWEB)

Chen, Hsiao-Wen; Zahedy, Fakhri S. [Department of Astronomy and Astrophysics, The University of Chicago, 5640 S Ellis Avenue, Chicago, IL 60637 (United States); Johnson, Sean D. [Department of Astrophysics, Princeton University, Princeton, NJ (United States); Rauch, Michael; Mulchaey, John S., E-mail: hchen@oddjob.uchicago.edu [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)

2017-06-20

Gas metallicity is a key quantity used to determine the physical conditions of gaseous clouds in a wide range of astronomical environments, including interstellar and intergalactic space. In particular, considerable effort in circumgalactic medium (CGM) studies focuses on metallicity measurements because gas metallicity serves as a critical discriminator for whether the observed heavy ions in the CGM originate in chemically enriched outflows or in more chemically pristine gas accreted from the intergalactic medium. However, because the gas is ionized, a necessary first step in determining CGM metallicity is to constrain the ionization state of the gas which, in addition to gas density, depends on the ultraviolet background radiation field (UVB). While it is generally acknowledged that both the intensity and spectral slope of the UVB are uncertain, the impact of an uncertain spectral slope has not been properly addressed in the literature. This Letter shows that adopting a different spectral slope can result in an order of magnitude difference in the inferred CGM metallicity. Specifically, a harder UVB spectrum leads to a higher estimated gas metallicity for a given set of observed ionic column densities. Therefore, such systematic uncertainties must be folded into the error budget for metallicity estimates of ionized gas. An initial study shows that empirical diagnostics are available for discriminating between hard and soft ionizing spectra. Applying these diagnostics helps reduce the systematic uncertainties in CGM metallicity estimates.

Determination of the fine structure in the ionization plots obtained from a mass spectrometer with a large energy dispersion

International Nuclear Information System (INIS)

Deruaz, Daniel.

1974-01-01

The precise determination of ionization potentials, fragment ion appearance potentials and different excited state levels of the positive ions formed, together with phenomena due to an electron impact, were studied from ionization efficiency curves obtained by mass spectrometry. A standard ion source and an analytical method of electron energy dispersion reduction were used to study fine structures of ionization efficiency curves. Since the mass spectrometer was not adapted for the acquisition of ionization efficiency curve data an electronic system was designed to record these curves automatically. A precise stepwise potential variation of 45+-0.04mV was obtained, and for each step an intensity proportional to the number of ions created by the fragment considered, the additional gain being 4.4 and the linearity greater than 1% over a 13-volt region. Before each set of measurements the scattering was determined by calculation of the second derivative of a logistic function deduced from the cubic regression of the experimental helium function ionization efficiency curve values. The precision, given by the variance analysis SNEDECOR F test, is higher than 1/1000. For each series of recordings the numerical values were processed by a computer to raise by twenty the signal to noise ratio and calculate the ionization efficiency curve values by the energy difference method and the iterative unfolding method. In this way a high sensitivity was obtained for the determination of the curves near the ionization threshold, and a precision below 50MeV (at least equivalent to that given by ionization cells with quasi-monoenergetic electron beams) for the values of the ionization potentials, the appearance potentials and the excited state energy levels. In order to judge the reliability of the technique the ionization potentials of a set of eleven complex molecules were determined and compared with the results obtained by photoionization and photoelectron spectrometry [fr

Effects of temperature and ionization density in medical luminescence dosimetry using Al{sub 2}O{sub 3}:C

Energy Technology Data Exchange (ETDEWEB)

Morgenthaler Edmund, J.

2007-11-15

A new system containing small crystals of aluminum oxide doped with carbon (Al{sub 2}O{sub 3}:C) attached to optical fiber cables has recently been introduced. During irradiation, the system monitors the radioluminescence (RL)from the crystals and after irradiation, an optically stimulated luminescence (OSL) signal can be read out by stimulating the crystal with light. This thesis applies the initial part and the total area of the resulting OSL decay curve for dosimetry measurements and investigates the effects of temperature and proton energy, i.e. ionization density, on the RL and OSL signals from Al{sub 2}O{sub 3}:C. In the temperature study, it was found that the OSL signal depends on both irradiation and stimulation temperature while the RL signal is effected only by the irradiation temperature. The initial OSL signal is increasing with temperature whereas the total OSL area is decreasing. Therefore, if the irradiation temperature is kept constant, one can find an integration time which provides an OSL signal independent of stimulation temperature. Overall, the RL and OSL signals vary between -0.2 to 0.6% per C. Thermal effects were simulated with a band structure model and indicated that the temperature effects are caused by the combined efforts of energetic shallow traps and thermal excitation from intermediate states in deeper traps. In the study of ionization density, we investigated protons with energies between 10 and 60 MeV (4.57 to 1.08 keV/mum in water). Experimentally, we observed that the initial OSL signalprovided a signal independent of linear energy transfer (LET) for allenergies at 0.3 Gy. The total OSL area showed an LET dependent behavior atall doses and energies. We used track structure theory (TST) to give possible explanations for the LET dependence of the OSL signal. From these calculations, we found that the initial OSL signal is, in general, not LET independent which makes Al2O3:C unsuitable for OSL proton dosimetry. The initial OSL

LARGE-SCALE SHOCK-IONIZED AND PHOTOIONIZED GAS IN M83: THE IMPACT OF STAR FORMATION

International Nuclear Information System (INIS)

Hong, Sungryong; Calzetti, Daniela; Dopita, Michael A.; Blair, William P.; Whitmore, Bradley C.; Bond, Howard E.; Balick, Bruce; Carollo, Marcella; Disney, Michael J.; Frogel, Jay A.; Hall, Donald; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.; O'Connell, Robert W.; Paresce, Francesco; Saha, Abhijit; Silk, Joseph I.; Trauger, John T.; Walker, Alistair R.

2011-01-01

We investigate the ionization structure of the nebular gas in M83 using the line diagnostic diagram, [O III](5007 A)/Hβ versus [S II](6716 A+6731 A)/Hα, with the newly available narrowband images from the Wide Field Camera 3 (WFC3) of the Hubble Space Telescope (HST). We produce the diagnostic diagram on a pixel-by-pixel (0.''2 x 0.''2) basis and compare it with several photo- and shock-ionization models. We select four regions from the center to the outer spiral arm and compare them in the diagnostic diagram. For the photoionized gas, we observe a gradual increase of the log ([O III]/Hβ) ratios from the center to the spiral arm, consistent with the metallicity gradient, as the H II regions go from super-solar abundance to roughly solar abundance from the center out. Using the diagnostic diagram, we separate the photoionized from the shock-ionized component of the gas. We find that the shock-ionized Hα emission ranges from ∼2% to about 15%-33% of the total, depending on the separation criteria used. An interesting feature in the diagnostic diagram is a horizontal distribution around log ([O III]/Hβ) ∼ 0. This feature is well fit by a shock-ionization model with 2.0 Z sun metallicity and shock velocities in the range of 250-350 km s -1 . A low-velocity shock component, -1 , is also detected and is spatially located at the boundary between the outer ring and the spiral arm. The low-velocity shock component can be due to (1) supernova remnants located nearby, (2) dynamical interaction between the outer ring and the spiral arm, and (3) abnormal line ratios from extreme local dust extinction. The current data do not enable us to distinguish among those three possible interpretations. Our main conclusion is that, even at the HST resolution, the shocked gas represents a small fraction of the total ionized gas emission at less than 33% of the total. However, it accounts for virtually all of the mechanical energy produced by the central starburst in M83.

Ionization impact on molecular clouds and star formation: Numerical simulations and observations

International Nuclear Information System (INIS)

Tremblin, Pascal

2012-01-01

At all the scales of Astrophysics, the impact of the ionization from massive stars is a crucial issue. At the galactic scale, the ionization can regulate star formation by supporting molecular clouds against gravitational collapse and at the stellar scale, indications point toward a possible birth place of the Solar System close to massive stars. At the molecular cloud scale, it is clear that the hot ionized gas compresses the surrounding cold gas, leading to the formation of pillars, globules, and shells of dense gas in which some young stellar objects are observed. What are the formation mechanisms of these structures? Are the formation of these young stellar objects triggered or would have they formed anyway? Do massive stars have an impact on the distribution of the surrounding gas? Do they have an impact on the mass distribution of stars (the initial mass function, IMF)? This thesis aims at shedding some light on these questions, by focusing especially on the formation of the structures between the cold and the ionized gas. We present the state of the art of the theoretical and observational works on ionized regions (H II regions) and we introduce the numerical tools that have been developed to model the ionization in the hydrodynamic simulations with turbulence performed with the HERACLES code. Thanks to the simulations, we present a new model for the formation of pillars based on the curvature and collapse of the dense shell on itself and a new model for the formations of cometary globules based on the turbulence of the cold gas. Several diagnostics have been developed to test these new models in the observations. If pillars are formed by the collapse of the dense shell on itself, the velocity spectrum of a nascent pillar presents a large spectra with a red-shifted and a blue-shifted components that are caused by the foreground and background parts of the shell that collapse along the line of sight. If cometary globules emerge because of the turbulence of

Shock velocity in weakly ionized nitrogen, air, and argon

International Nuclear Information System (INIS)

Siefert, Nicholas S.

2007-01-01

The goal of this research was to determine the principal mechanism(s) for the shock velocity increase in weakly ionized gases. This paper reports experimental data on the propagation of spark-generated shock waves (1< Mach<3) into weakly ionized nitrogen, air, and argon glow discharges (1 < p<20 Torr). In order to distinguish between effects due solely to the presence of electrons and effects due to heating of the background gas via elastic collisions with electrons, the weakly ionized discharge was pulsed on/off. Laser deflection methods determined the shock velocity, and the electron number density was collected using a microwave hairpin resonator. In the afterglow of nitrogen, air, and argon discharges, the shock velocity first decreased, not at the characteristic time for electrons to diffuse to the walls, but rather at the characteristic time for the centerline gas temperature to equilibrate with the wall temperature. These data support the conclusion that the principal mechanism for the increase in shock velocity in weakly ionized gases is thermal heating of the neutral gas species via elastic collisions with electrons

Ionization potential depression in an atomic-solid-plasma picture

Science.gov (United States)

Rosmej, F. B.

2018-05-01

Exotic solid density matter such as heated hollow crystals allow extended material studies while their physical properties and models such as the famous ionization potential depression are presently under renewed controversial discussion. Here we develop an atomic-solid-plasma (ASP) model that permits ionization potential depression studies also for single and multiple core hole states. Numerical calculations show very good agreement with recently available data not only in absolute values but also for Z-scaled properties while currently employed methods fail. For much above solid density compression, the ASP model predicts increased K-edge energies that are related to a Fermi surface rising. This is in good agreement with recent quantum molecular dynamics simulations. For hot dense matter a quantum number dependent optical electron finite temperature ion sphere model is developed that fits well with line shift and line disappearance data from dense laser produced plasma experiments. Finally, the physical transparency of the ASP picture allows a critical discussion of current methods.

Study on the Properties of Ionized Metal Plasma Methodology on Titanium

International Nuclear Information System (INIS)

Leow, M. T.; Hassan, Z.; Lee, K. E.; Omar, G.; Lim, S. P.; Chan, C. F.; Siew, E. T.; Chuah, Z. M.

2010-01-01

Ionized Metal Plasma (IMP) deposition was used in depositing metal interconnection of titanium metal film. Inductively coupled plasma (ICP) was attached to chamber wall where it creates an electromagnetic field, thus, ionizing the sputtered metal atoms from target. The film morphology was observed by scanning electron microscope (SEM). Acoustic measurement of titanium film thickness showed that there was a comparable result with film resistance measured by 4-point probe. Results show that higher plasma density would cause tensile properties on the film stress.

Supersonic propagation of ionization waves in an underdense, laser-produced plasma

International Nuclear Information System (INIS)

Constantin, C.; Back, C.A.; Fournier, K.B.; Gregori, G.; Landen, O.L.; Glenzer, S.H.; Dewald, E.L.; Miller, M.C.

2005-01-01

A laser-driven supersonic ionization wave propagating through a millimeter-scale plasma of subcritical density up to 2-3 keV electron temperatures was observed. Propagation velocities initially ten times the sound speed were measured by means of time-resolved x-ray imaging diagnostics. The measured ionization wave trajectory is modeled analytically and by a two-dimensional radiation-hydrodynamics code. The comparison to the modeling suggests that nonlocal heat transport effects may contribute to the attenuation of the heat-wave propagation

Experimental investigation of the triple differential cross section for electron impact ionization of N{sub 2} and CO{sub 2} molecules at intermediate impact energy and large ion recoil momentum

Energy Technology Data Exchange (ETDEWEB)

Lahmam-Bennani, A; Staicu Casagrande, E M; Naja, A, E-mail: azzedine.bennani@u-psud.f [Universite Paris-Sud 11, Laboratoire des Collisions Atomiques et Moleculaires (LCAM), Bat. 351, 91405 Orsay Cedex (France)

2009-12-14

The (e,2e) triple differential cross sections (TDCS) are measured for the ionization of nitrogen and carbon dioxide molecules in a coplanar asymmetric geometry for a wide range of ejected electron energies and at an incident energy about 500-700 eV. This kinematics corresponds to a large momentum imparted to the ion, and is meant to enhance the recoil scattering. The experimental binary and recoil angular distributions of the TDCS are characterized both by a shift towards larger angles with respect to the momentum transfer direction and by a large intensity in the recoil region, in particular for the ionization of the 'inner' N{sub 2}(2{sigma}{sub g}) molecular orbital. The data are compared with the results of calculations using the first Born approximation-two centre continuum (FBA-TCC) theoretical model for treating differential electron impact ionization. The experimentally observed shifts and recoil intensity enhancement are not predicted by the model calculations, which rather yield a TDCS symmetrically distributed around the momentum transfer direction, and completely fail in describing the recoil distribution. It is hoped that these new results will stimulate the development of more refined theories for correctly modelling single ionization of molecules.

Equation of state of partially-ionized dense plasmas

International Nuclear Information System (INIS)

Rogers, F.J.

1989-01-01

This paper describes methods for calculating the equation of state of partially-ionized dense plasmas. The term dense plasma is used rather than strongly coupled plasma, since it is possible that at plasma conditions such that only a few levels can be observed spectroscopically the plasma coupling parameters are not large. Due mainly to their importance in theoretical astrophysics, the properties of partially ionized plasmas have been of interest for a long while. More recently, this interest has intensified due to the development of methods for producing partially ionized plasmas in the laboratory. This has opened up large programs of experimental investigation and of practical application. In this paper we consider detailed statistical mechanical methods that explicitly treat the distribution over ionic species and their energy level structure. These detailed approaches are generally characterized as being in the ''chemical picture'' when a free energy expression is minimized or in the ''physical picture'' when the starting point is the grand canonical ensemble. 52 refs., 2 tabs

Bio-dosimetry of ionizing radiation

International Nuclear Information System (INIS)

Hadjidekova, V.; Kristova, R.; Stainova, A.; Deleva, S.; Popova, L.; Georgieva, D.

2013-01-01

Full text: Introduction: The impact of ionizing radiation in medical, occupational and accidental human exposure leads to adverse side effects such as increased mortality and carcinogenesis. Information about the level of absorbed dose is important for risk assessment and for implementation of appropriate therapy. In most cases of actual or suspected exposure to ionizing radiation biological dosimetry is the only way to assess the absorbed dose. What you will learn: In this work we discuss the methods for biodosimetry and technological developments in their application in various emergency situations. The application of biological dosimetry and assessment of the influence of external factors in the conduct of epidemiological studies of radiation effects in protracted low-dose ionizing radiation on humans is presented. Discussion: The results of cytogenetic analysis and biological evaluation of absorbed dose based on the analysis of dicentrics in peripheral blood lymphocytes of five people injured in a severe radiation accident in Bulgaria in 2011 are presented. The assessed individual doses of the injured persons are in the range of 1.2 to 5,2 Gy acute homogeneous irradiation and are in line with the estimates of international experts. Conclusion: An algorithm to conduct a biological assessment of the dose in limited radiation accidents and in large scale radiation accidents with large number irradiated or suspected for exposure persons is proposed

MICROWAVE INTERACTIONS WITH INHOMOGENEOUS PARTIALLY IONIZED PLASMA

Energy Technology Data Exchange (ETDEWEB)

Kritz, A. H.

1962-11-15

Microwave interactions with inhomogeneous plasmas are often studied by employing a simplified electromagnetic approach, i.e., by representing the effects of the plasma by an effective dielectric coefficient. The problems and approximations associated with this procedure are discussed. The equation describing the microwave field in an inhomogeneous partially ionized plasma is derived, and the method that is applied to obtain the reflected, transmitted, and absorbed intensities in inhomogeneous plasmas is presented. The interactions of microwaves with plasmas having Gaussian electron density profiles are considered. The variation of collision frequency with position is usually neglected. In general, the assumption of constant collision frequency is not justified; e.g., for a highly ionized plasma, the electron density profile determines, in part, the profile of the electron-ion collision frequency. The effect of the variation of the collision frequency profile on the interaction of microwaves with inhomogeneous plasmas is studied in order to obtain an estimate of the degree of error that may result when constant collision frequency is assumed instead of a more realistic collision frequency profile. It is shown that the degree of error is of particular importance when microwave analysis is used as a plasma diagnostic. (auth)

Threshold law for ionization cross sections in the Temkin-Poet model

International Nuclear Information System (INIS)

Macek, J.H.; Ihra, W.

1997-01-01

An integral representation of wave functions for the Temkin-Poet model of electron impact on atomic hydrogen is given. Approximate wave functions are evaluated analytically for large hyperradius to extract the ionization S-matrix element. An ionization cross section of the form exp[-aE -1/6 +bE 1/6 ], where a and b are positive constants, is derived. The exponential suppression of ionization for small E appears to be the quantum counterpart of the delayed onset of ionization in the classical theory for this model. copyright 1997 The American Physical Society

Laser-enhanced ionization spectroscopy around the ionization limit

International Nuclear Information System (INIS)

Axner, O.; Berglind, T.; Sjoestroem, S.

1986-01-01

Laser-induced photoionization and Laser-Enhanced collision Ionization (LEI) of Na, Tl, and Li in flames are detected by measuring the production of charges following a laser excitation. The ionization signal is investigated for excitations of the atoms from lower lying states both to Rydberg states close to the ionization limit, as well as to continuum states, i.e. the process of collision ionization is compared with that of photoionization. The qualitative behaviour of the ionization signal when scanning across the ionization limit is studied. It is shown that the ionization signal has a smooth behaviour when passing from bound states into continuum states. The laser-induced photoionization signal strength of atoms in flames is both calculated and measured and a good agreement is obtained. A calculation of wavelength dependent photoionization signal strengths for a number of elements is also presented. Photoionization is used to determine flame- and geometry-dependent parameters. An implication of photoionization in connection with LEI spectrometry for trace element analysis is that there will be a significant increase in background noise if the sample contains high concentrations of easily photoionizing elements and short wavelength light is used. (orig.)

Energetic particles and ionization in the nighttime middle and low latitude ionosphere

International Nuclear Information System (INIS)

Voss, H.D.; Smith, L.G.

1977-01-01

Seven Nike Apache rockets, each equipped with an energetic particle spectrometer (12 E 80 keV) and electron-density experiments, were launched from Wallops Island, Virginia and Chilca, Peru, under varying geomagnetic conditions near midnight. At Wallops Island the energetic particle flux (E 40 keV) is found to be strongly dependent on Kp. The pitch-angle distribution is asymmetrical about a peak at 90 D signifying a predominately quasi-trapped flux and explaining the linear increase of count rate with altitute in the altitude region 120 to 200 km. The height-averaged ionization rates derived from the electron-density profiles are consistent with the rates calculated from the observed total particle flux for magnetic index Kp 3. In the region 90 to 110 km it is found that the nighttime ionization is primarily a result of Ly-beta radiation from the geocorona and interplanetary hydrogen for even very disturbed conditions. Below 90 km during rather disturbed conditions energetic electrons can be a significant ionization source. Two energetic particle precipitation zones have been identified at midlatitudes

Energetic particles and ionization in the nighttime middle and low latitude ionosphere

Science.gov (United States)

Voss, H. D.; Smith, L. G.

1977-01-01

Seven Nike Apache rockets, each equipped with an energetic particle spectrometer (12 E 80 keV) and electron-density experiments, were launched from Wallops Island, Virginia and Chilca, Peru, under varying geomagnetic conditions near midnight. At Wallops Island the energetic particle flux (E 40 keV) is found to be strongly dependent on Kp. The pitch-angle distribution is asymmetrical about a peak at 90 D signifying a predominately quasi-trapped flux and explaining the linear increase of count rate with altitute in the altitude region 120 to 200 km. The height-averaged ionization rates derived from the electron-density profiles are consistent with the rates calculated from the observed total particle flux for magnetic index Kp 3. In the region 90 to 110 km it is found that the nighttime ionization is primarily a result of Ly-beta radiation from the geocorona and interplanetary hydrogen for even very disturbed conditions. Below 90 km during rather disturbed conditions energetic electrons can be a significant ionization source. Two energetic particle precipitation zones have been identified at midlatitudes.

Absolute density measurements in the middle atmosphere

Directory of Open Access Journals (Sweden)

M. Rapp

2001-05-01

Full Text Available In the last ten years a total of 25 sounding rockets employing ionization gauges have been launched at high latitudes ( ~ 70° N to measure total atmospheric density and its small scale fluctuations in an altitude range between 70 and 110 km. While the determination of small scale fluctuations is unambiguous, the total density analysis has been complicated in the past by aerodynamical disturbances leading to densities inside the sensor which are enhanced compared to atmospheric values. Here, we present the results of both Monte Carlo simulations and wind tunnel measurements to quantify this aerodynamical effect. The comparison of the resulting ‘ram-factor’ profiles with empirically determined density ratios of ionization gauge measurements and falling sphere measurements provides excellent agreement. This demonstrates both the need, but also the possibility, to correct aerodynamical influences on measurements from sounding rockets. We have determined a total of 20 density profiles of the mesosphere-lower-thermosphere (MLT region. Grouping these profiles according to season, a listing of mean density profiles is included in the paper. A comparison with density profiles taken from the reference atmospheres CIRA86 and MSIS90 results in differences of up to 40%. This reflects that current reference atmospheres are a significant potential error source for the determination of mixing ratios of, for example, trace gas constituents in the MLT region.Key words. Middle atmosphere (composition and chemistry; pressure, density, and temperature; instruments and techniques

Absolute density measurements in the middle atmosphere

Directory of Open Access Journals (Sweden)

M. Rapp

Full Text Available In the last ten years a total of 25 sounding rockets employing ionization gauges have been launched at high latitudes ( ~ 70° N to measure total atmospheric density and its small scale fluctuations in an altitude range between 70 and 110 km. While the determination of small scale fluctuations is unambiguous, the total density analysis has been complicated in the past by aerodynamical disturbances leading to densities inside the sensor which are enhanced compared to atmospheric values. Here, we present the results of both Monte Carlo simulations and wind tunnel measurements to quantify this aerodynamical effect. The comparison of the resulting ‘ram-factor’ profiles with empirically determined density ratios of ionization gauge measurements and falling sphere measurements provides excellent agreement. This demonstrates both the need, but also the possibility, to correct aerodynamical influences on measurements from sounding rockets. We have determined a total of 20 density profiles of the mesosphere-lower-thermosphere (MLT region. Grouping these profiles according to season, a listing of mean density profiles is included in the paper. A comparison with density profiles taken from the reference atmospheres CIRA86 and MSIS90 results in differences of up to 40%. This reflects that current reference atmospheres are a significant potential error source for the determination of mixing ratios of, for example, trace gas constituents in the MLT region.

Key words. Middle atmosphere (composition and chemistry; pressure, density, and temperature; instruments and techniques

Radiative transfer calculations of the diffuse ionized gas in disc galaxies with cosmic ray feedback

Science.gov (United States)

Vandenbroucke, Bert; Wood, Kenneth; Girichidis, Philipp; Hill, Alex S.; Peters, Thomas

2018-05-01

The large vertical scale heights of the diffuse ionized gas (DIG) in disc galaxies are challenging to model, as hydrodynamical models including only thermal feedback seem to be unable to support gas at these heights. In this paper, we use a three-dimensional Monte Carlo radiation transfer code to post-process disc simulations of the Simulating the Life-Cycle of Molecular Clouds project that include feedback by cosmic rays. We show that the more extended discs in simulations including cosmic ray feedback naturally lead to larger scale heights for the DIG which are more in line with observed scale heights. We also show that including a fiducial cosmic ray heating term in our model can help to increase the temperature as a function of disc scale height, but fails to reproduce observed DIG nitrogen and sulphur forbidden line intensities. We show that, to reproduce these line emissions, we require a heating mechanism that affects gas over a larger density range than is achieved by cosmic ray heating, which can be achieved by fine tuning the total luminosity of ionizing sources to get an appropriate ionizing spectrum as a function of scale height. This result sheds a new light on the relation between forbidden line emissions and temperature profiles for realistic DIG gas distributions.

Excitation of an instability by neutral particle ionization induced fluxes in the tokamak edge plasma

International Nuclear Information System (INIS)

Bachmann, P.; Sunder, D.

1991-01-01

Strong density and potential fluctuations in the edge plasma of toroidal nuclear fusion devices can lead to anomalously fast particle and energy transport. There are some reasons to assume the level of these fluctuations to be connected with neutral particles which enter the plasma by gas puffing or recycling processes. The influence of neutral particles on the behaviour of electrostatic drift modes was investigated. Using the ballooning transformation the excitation of dissipative drift waves in tokamak was studied taking ionization and charge exchange into consideration. Ionization driven drift wave turbulence was analyzed. The higher the neutral particle density is the more important the plasma-wall interaction and the less important the action of the limiter becomes. Instabilities localized in the edge plasma and far from the limiter can be one of the reasons of such a phenomenon. In the present paper we show that such an instability may exist. Usually the neutral particle density is large in the vicinity of the limiter and decreases rapidly with the distance from it. Plasma particles generated by ionization of these neutrals outside the limiter shadow, move along the magnetic field lines into a region without neutrals and diffuse slowly across the magnetic field. We solve the stability problem for modes with a perpendicular wave length that is much larger than the ion Larmor radius with electron temperature, and much smaller than the minor plasma radius. The excitation of such modes localized far from the limiter is investigated. A one-dimensional differential equation is derived in the cold ion approximation without taking shear and toroidal effects into consideration. In the case of low flow velocities a nearly aperiodic instability is found analytically. Its growth rate is proportional to the equilibrium plasma velocity at the boundary of the neutral particle's free region and to the inverse of the extension of this zone. This mode is localized in the edge

The QTP family of consistent functionals and potentials in Kohn-Sham density functional theory

Energy Technology Data Exchange (ETDEWEB)

Jin, Yifan; Bartlett, Rodney J., E-mail: bartlett@qtp.ufl.edu [Quantum Theory Project and Departments of Chemistry and Physics, University of Florida, Gainesville, Florida 32611 (United States)

2016-07-21

This manuscript presents the second, consistent density functional in the QTP (Quantum Theory Project) family, that is, the CAM-QTP(01). It is a new range-separated exchange-correlation functional in which the non-local exchange contribution is 100% at large separation. It follows the same basic principles of this family that the Kohn-Sham eigenvalues of the occupied orbitals approximately equal the vertical ionization energies, which is not fulfilled by most of the traditional density functional methods. This new CAM-QTP(01) functional significantly improves the accuracy of the vertical excitation energies especially for the Rydberg states in the test set. It also reproduces many other properties such as geometries, reaction barrier heights, and atomization energies.

Quantitative study of the ionization-induced refraction of picosecond laser pulses in gas-jet targets

International Nuclear Information System (INIS)

Mackinnon, A.J.; Borghesi, M.; Iwase, A.; Jones, M.W.; Pert, G.J.; Rae, S.; Burnett, K.; Willi, O.

1996-01-01

A quantitative study of refractive whole beam defocusing and small scale breakup induced by optical ionization of subpicosecond and picosecond, 0.25 and 1 μm, laser pulses in gas-jet targets at densities above 1x10 19 cm -3 has been carried out. A significant reduction of the incident laser intensity was observed due to refraction from ionization-induced density gradients. The level of refraction measured with optical probing correlated well with the fraction of energy transmitted through the plasma. The numerical and analytical models were found to agree well with experimental observations. copyright 1996 The American Physical Society

Review Ionizing Radiation In The Environment

International Nuclear Information System (INIS)

Hassan, K.M.

2007-01-01

Our environment is pervaded by ionizing radiation of natural origin including terrestrial radionuclides and extra-terrestrial sources but man's activities can increase radiation levels by acting on natural sources or by producing artificial radionuclides. The energy released by radionuclides can be measured. The amount of energy generated in our bodies from the radioactive decay of within- body radionuclides is called internal dose. External dose results from gamma rays emitted by terrestrial sources such as the ground, building materials and from extraterrestrial sources. The major contributors to human exposure are radon and its daughters in the air that we breathe. Ionizing radiation can penetrate into matter and thus, causing damage by interacting with the atoms and molecules of the medium. If the medium is living tissue, damage to cells can take place. Very large doses of radiation will result in serious tissue, damage that may lead to death of the organism. Lower doses may also be harmful and do not cause the immediate damage of high doses but instead act to increase the likelihood of developing cancer. So, exposure to ionizing radiation can have health consequences, which is why we are concerned about and, to a large extent, is why this review paper was written. Exposure to ionizing radiation should be kept as minimum as practically possible. People are advised to monitor the concentrations of radon in their houses. In addition, the levels of radionuclides in drinking water should also be monitored in accordance with the guidelines used in the USA

[Ionizing and non-ionizing radiation (comparative risk estimations)].

Science.gov (United States)

Grigor'ev, Iu G

2012-01-01

The population has widely used mobile communication for already more than 15 years. It is important to note that the use of mobile communication has sharply changed the conditions of daily exposure of the population to EME We expose our brain daily for the first time in the entire civilization. The mobile phone is an open and uncontrollable source of electromagnetic radiation. The comparative risk estimation for the population of ionizing and non-ionizing radiation was carried out taking into account the real conditions of influence. Comparison of risks for the population of ionizing and non-ionizing radiation leads us to a conclusion that EMF RF exposure in conditions of wide use of mobile communication is potentially more harmful than ionizing radiation influence.

Ionization in matrix-assisted laser desorption/ionization: singly charged molecular ions are the lucky survivors.

Science.gov (United States)

Karas, M; Glückmann, M; Schäfer, J

2000-01-01

A new model for the ionization processes in UV matrix-assisted laser desorption/ionization (MALDI) which accounts for the major phenomena observed is presented and discussed. The model retains elements of earlier approaches, such as photoionization and photochemical reactions, but it redefines these in the light of new working questions, most importantly why only singly charged ions are detected. Based on experimental evidence, the formation of singly and multiply charged clusters by a deficiency/excess of ions and also by photoionization and subsequent photochemical processes is pointed out to be the major ionization processes, which typically occur in parallel. The generation of electrons and their partial loss into the surrounding vacuum and solid, on the one hand, results in a positively charged ion-neutral plume facilitating a high overall ionization yield. On the other hand, these electrons, and also the large excess of protonated matrix ions in the negative ion mode, induce effective ion reneutralization in the plume. These neutralization processes are most effective for the highly charged cluster ions initially formed. Their fragmentation behaviour is evidenced in fast metastable fragmentation characteristics and agrees well with an electron capture dissociation mechanism and the enthalpy transfer upon neutralization forms the rationale for the prominent fragmentation and intense chemical noise accompanying successful MALDI. Within the course of the paper, cross-correlations with other desorption/ionization techniques and with earlier discussions on their mechanisms are drawn. Copyright 2000 John Wiley & Sons, Ltd.

PIC simulations of post-pulse field reversal and secondary ionization in nanosecond argon discharges

Science.gov (United States)

Kim, H. Y.; Gołkowski, M.; Gołkowski, C.; Stoltz, P.; Cohen, M. B.; Walker, M.

2018-05-01

Post-pulse electric field reversal and secondary ionization are investigated with a full kinetic treatment in argon discharges between planar electrodes on nanosecond time scales. The secondary ionization, which occurs at the falling edge of the voltage pulse, is induced by charge separation in the bulk plasma region. This process is driven by a reverse in the electric field from the cathode sheath to the formerly driven anode. Under the influence of the reverse electric field, electrons in the bulk plasma and sheath regions are accelerated toward the cathode. The electron movement manifests itself as a strong electron current generating high electron energies with significant electron dissipated power. Accelerated electrons collide with Ar molecules and an increased ionization rate is achieved even though the driving voltage is no longer applied. With this secondary ionization, in a single pulse (SP), the maximum electron density achieved is 1.5 times higher and takes a shorter time to reach using 1 kV 2 ns pulse as compared to a 1 kV direct current voltage at 1 Torr. A bipolar dual pulse excitation can increase maximum density another 50%–70% above a SP excitation and in half the time of RF sinusoidal excitation of the same period. The first field reversal is most prominent but subsequent field reversals also occur and correspond to electron temperature increases. Targeted pulse designs can be used to condition plasma density as required for fast discharge applications.

Visualization and measurement of gas-liquid metal two-phase flow with large density difference using thermal neutrons as microscopic probes

International Nuclear Information System (INIS)

Saito, Y.; Hibiki, T.; Mishima, K.; Nishihara, H.; Yamamoto, A.; Kanda, K.; Tobita, Y.; Konishi, K.; Matsubayashi, M.

1998-01-01

In a core melt accident of a fast breeder reactor there is a possibility of boiling of fuel-steel mixture in the containment pool. In relation to safety evaluation on severe accident, it is indispensable to evaluate the recriticality of melted core. Gas-liquid two-phase flow with a large density difference is formed due to the boiling of fuel-steel mixture. Although the large density difference may affect the basic characteristics of two-phase flow, little work has been performed so far on two-phase flow with large density difference has not been performed well. In this study, visualization and void fraction measurement of gas-liquid metal two-phase flow were performed by using neutron radiography. The effect of the large density difference between gas and liquid phases on the basic flow characteristics of two-phase flow was clarified. (author)

Density dependence of dielectronic recombination in selenium

International Nuclear Information System (INIS)

Hagelstein, P.L.; Rosen, M.D.; Jacobs, V.L.

1986-01-01

Dielectronic recombination has been found to be the dominant recombination process in the determination of the ionization balance of selenium near the Ne-like sequence under conditions relevant to the exploding-foil EUV laser plasmas. The dielectronic recombination process tends to populate excited levels, and these levels in turn are more susceptible to subsequent excitation and ionization than are the ground-state ions. If one defines an effective recombination rate which includes, in addition to the primary recombination, the subsequent excitation and ionization of the additional excited-state population due to the primary recombination, then this effective recombination rate can be density-sensitive at relatively low electron density. We present results for this effective dielectronic recombination rate at an electron density of 3 x 10/sup 20/ electrons/cm 3 for recombination from Ne-like to Na-like selenium and from F-like to Ne-like selenium. In the former case, the effective recombination rate coefficient is found to be 1.8 x 10/sup -11/ cm 3 /sec at 1.0 keV, which is to be compared with the zero-density value of 2.8 x 10/sup -11/ cm 3 /sec. In the latter case (F-like to Ne-like), the effective recombination rate coefficient is found to be 1.3 x 10/sup -11/ cm 3 /sec, which is substantially reduced from the zero-density result of 3.3 x 10/sup -11/ cm 3 /sec. We have examined the effects of dielectronic recombination on the laser gain of the dominant Ne-like 3p-3s transitions and have compared our results with those presented by Whitten et al. [Phys. Rev. A 33, 2171 (1986)

Two-dimensional kinetic analysis on the ionization waves in a low current discharge

International Nuclear Information System (INIS)

Yamazaki, Tsutomu; Fujii, Masaharu; Noda, Shozou; Miura, Kousuke; Imazu, Shingo.

1982-01-01

In the research on the ionization waves produced in the positive column in a low pressure discharge, theoretical analyses have been made since long ago using mainly the fluid theory. However, the experimental properties that cannot be explained with the fluid theory have been found lately. For example, it has been shown experimentally that the product of longitudinal electric field E and the wavelength lambda of ionization waves becomes some specific values depending on the kinds of gas as one of the characteristics of the ionization waves produced in the positive column plasma in rare gas glow discharge, but these specific values of E-lambda cannot be explained with the fluid theory. In this paper, the perturbation component of electron energy distribution function accompanying ionization waves was derived from a two-dimensional Boltzmann equation which takes the radial non-uniformity into account, to consider the E-lambda values of ionization waves from the relative equation between electron density and the perturbation component of an electric field. The following results were obtained. The relative equation between electron density and the perturbation component of an electric field, which cannot be derived from the fluid theory, was able to be obtained; the values of E-lambda product agreed with the experimental results better than one-dimensional analysis; The steeper the shape of radial potential distribution, the more likely the resonance occurrence and the larger the E-lambda product; and so forth. (Wakatsuki, Y.)

Multiphoton ionization of H2+ in xuv laser pulses

International Nuclear Information System (INIS)

Guan Xiaoxu; Secor, Ethan B.; Bartschat, Klaus; Schneider, Barry I.

2011-01-01

We consider the ionization of the hydrogen molecular ion after one-, two-, and three-photon absorption over a large range of photon energies between 9 and 40 eV in the fixed-nuclei approximation. The temporal development of the system is obtained in a fully ab initio time-dependent grid-based approach in prolate spheroidal coordinates. The alignment dependence of the one-photon ionization amplitude is highlighted in the framework of time-dependent perturbation theory. For one-photon ionization as a function of the nuclear separation, the calculations reveal a significant minimum in the ionization probability. The suppressed ionization is attributed to a Cooper-type minimum, which is similar, but not identical, to the cancellation effect observed in photoionization cross sections of some noble-gas atoms. The effect of the nonspherical two-center Coulomb potential is analyzed. For two- and three-photon ionization, the angle-integrated cross sections clearly map out intermediate-state resonances, and the predictions of the current computations agree very well with those from time-independent calculations. The dominant emission modes for two-photon ionization are found to be very similar in both resonance and off-resonance regions.

A study of fast electron energy transport in relativistically intense laser-plasma interactions with large density scalelengths

Energy Technology Data Exchange (ETDEWEB)

Scott, R. H. H.; Norreys, P. A. [Department of Physics, Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2AZ (United Kingdom); Central Laser Facility, STFC Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxford OX11 0QX (United Kingdom); Perez, F.; Baton, S. D. [LULI, Ecole Polytechnique, UMR 7605, CNRS/CEA/UPMC, Route de Saclay, 91128 Palaiseau (France); Santos, J. J.; Nicolai, Ph.; Hulin, S. [Univ. Bordeaux/CNRS/CEA, CELIA, UMR 5107, 33405 Talence (France); Ridgers, C. P. [Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Department of Physics, Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2AZ (United Kingdom); Davies, J. R. [GoLP, Instituto de Plasmas e Fusao Nuclear - Laboratorio Associado, Instituto Superior Tecnico, 1049-001 Lisboa (Portugal); Lancaster, K. L.; Trines, R. M. G. M. [Central Laser Facility, STFC Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxford OX11 0QX (United Kingdom); Bell, A. R.; Tzoufras, M. [Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Central Laser Facility, STFC Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxford OX11 0QX (United Kingdom); Rose, S. J. [Department of Physics, Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2AZ (United Kingdom)

2012-05-15

A systematic experimental and computational investigation of the effects of three well characterized density scalelengths on fast electron energy transport in ultra-intense laser-solid interactions has been performed. Experimental evidence is presented which shows that, when the density scalelength is sufficiently large, the fast electron beam entering the solid-density plasma is best described by two distinct populations: those accelerated within the coronal plasma (the fast electron pre-beam) and those accelerated near or at the critical density surface (the fast electron main-beam). The former has considerably lower divergence and higher temperature than that of the main-beam with a half-angle of {approx}20 Degree-Sign . It contains up to 30% of the total fast electron energy absorbed into the target. The number, kinetic energy, and total energy of the fast electrons in the pre-beam are increased by an increase in density scalelength. With larger density scalelengths, the fast electrons heat a smaller cross sectional area of the target, causing the thinnest targets to reach significantly higher rear surface temperatures. Modelling indicates that the enhanced fast electron pre-beam associated with the large density scalelength interaction generates a magnetic field within the target of sufficient magnitude to partially collimate the subsequent, more divergent, fast electron main-beam.

Optically-ionized plasma recombination x-ray lasers

International Nuclear Information System (INIS)

Amendt, P.; Eder, D.C.; Wilks, S.C.; Dunning, M.J.; Keane, C.J.

1991-01-01

Design studies for recombination x-ray lasers based on plasmas ionized by high intensity, short pulse optical lasers are presented. Transient lasing on n = 3 to n = 2 transitions in Lithium-like Neon allows for moderately short wavelengths (≤ 100 angstrom) without requiring ionizing intensities associated with relativistic electron quiver energies. The electron energy distribution following the ionizing pulse affects directly the predicted gains for this resonance transition. Efficiencies of 10 -6 or greater are found for plasma temperatures in the vicinity of 40 eV. Simulation studies of parametric heating phenomena relating to stimulated Raman and Compton scattering are presented. For electron densities less than about 2.5 x 10 20 cm -3 and peak driver intensity of 2 x 10 17 W/cm 2 at 0.25 μm with pulse length of 100 fsec, the amount of electron heating is found to be marginally significant. For Lithium-like Aluminum, the required relativistic ionizing intensity gives excessive electron heating and reduced efficiency, thereby rendering this scheme impractical for generating shorter wavelength lasing (≤ 50 angstrom) in the transient case. Following the transient lasing phase, a slow hydrodynamic expansion into the surrounding cool plasma is accompanied by quasi-static gain on the n = 4 to n = 3 transition in Lithium-like Neon. Parametric heating effects on gain optimization in this regime are also discussed. 18 refs., 6 figs

Field-dependent molecular ionization and excitation energies: Implications for electrically insulating liquids

Directory of Open Access Journals (Sweden)

N. Davari

2014-03-01

Full Text Available The molecular ionization potential has a relatively strong electric-field dependence as compared to the excitation energies which has implications for electrical insulation since the excited states work as an energy sink emitting light in the UV/VIS region. At some threshold field, all the excited states of the molecule have vanished and the molecule is a two-state system with the ground state and the ionized state, which has been hypothesized as a possible origin of different streamer propagation modes. Constrained density-functional theory is used to calculate the field-dependent ionization potential of different types of molecules relevant for electrically insulating liquids. The low singlet-singlet excitation energies of each molecule have also been calculated using time-dependent density functional theory. It is shown that low-energy singlet-singlet excitation of the type n → π* (lone pair to unoccupied π* orbital has the ability to survive at higher fields. This type of excitation can for example be found in esters, diketones and many color dyes. For alkanes (as for example n-tridecane and cyclohexane on the other hand, all the excited states, in particular the σ → σ* excitations vanish in electric fields higher than 10 MV/cm. Further implications for the design of electrically insulating dielectric liquids based on the molecular ionization potential and excitation energies are discussed.

Ionization effects in electronic inner-shells of ionized atoms

International Nuclear Information System (INIS)

Shchornak, G.

1983-01-01

A review of the atomic physics of ionization atoms has been presented. Interaction and structure effects in atomic shells, correlated to the occurrence of vacancies in several subshells of the atom have been considered. The methods of calculations of atomic states and wave functions have been reviewed. The energy shift of characteristic X-rays is discussed as a function of the ionization stage of the atom. The influence of inner and outer-shell vacancies on the energy of the X-rays is shown in detail. The influence of chemical effects on the parameters of X-rays is also taken into account. Further on, the change of transition probabilities in radiative and non-radiative transitions by changing stage of ionization is discussed; and among them the leading part of Auger and Coster-Kronig transitions by the arearrangement of the atomic states is shown. The influence of non-radiative electronic transitions on ionization cross-sections for multiple ionization is discussed. Using these results, ionization cross-sections for direct and indirect processes for several ionization stages are given

Cosmological streaming velocities and large-scale density maxima

International Nuclear Information System (INIS)

Peacock, J.A.; Lumsden, S.L.; Heavens, A.F.

1987-01-01

The statistical testing of models for galaxy formation against the observed peculiar velocities on 10-100 Mpc scales is considered. If it is assumed that observers are likely to be sited near maxima in the primordial field of density perturbations, then the observed filtered velocity field will be biased to low values by comparison with a point selected at random. This helps to explain how the peculiar velocities (relative to the microwave background) of the local supercluster and the Rubin-Ford shell can be so similar in magnitude. Using this assumption to predict peculiar velocities on two scales, we test models with large-scale damping (i.e. adiabatic perturbations). Allowed models have a damping length close to the Rubin-Ford scale and are mildly non-linear. Both purely baryonic universes and universes dominated by massive neutrinos can account for the observed velocities, provided 0.1 ≤ Ω ≤ 1. (author)

Heavy component of spent nuclear fuel: Efficiency of model-substance ionization by electron-induced discharge

Energy Technology Data Exchange (ETDEWEB)

Antonov, N. N., E-mail: antonovnickola@gmail.com; Gavrikov, A. V.; Samokhin, A. A.; Smirnov, V. P. [Russian Academy of Sciences, High Energy Density Research Center, Joint Institute for High Temperatures (Russian Federation)

2016-12-15

The method of plasma separation of spent nuclear fuel can be tested with a model substance which has to be transformed from the condensed to plasma state. For this purpose, electron-induced discharge in lead vapor injected into the interelectrode gap is simulated using the kinetic approach. The ionization efficiency, the electrostatic-potential distribution, and those of the ion and electron densities in the discharge gap are derived as functions of the discharge-current density and concentration of the vapor of the model substance. Given a discharge-current density of 3.5 A/cm{sup 2} and a lead-vapor concentration of 2 × 10{sup 12} cm{sup –3}, the simulated ionization efficiency proves to be nearly 60%. The discharge in lead vapor is also investigated experimentally.

Non-equilibrium hydrogen ionization in 2D simulations of the solar atmosphere

Science.gov (United States)

Leenaarts, J.; Carlsson, M.; Hansteen, V.; Rutten, R. J.

2007-10-01

Context: The ionization of hydrogen in the solar chromosphere and transition region does not obey LTE or instantaneous statistical equilibrium because the timescale is long compared with important hydrodynamical timescales, especially of magneto-acoustic shocks. Since the pressure, temperature, and electron density depend sensitively on hydrogen ionization, numerical simulation of the solar atmosphere requires non-equilibrium treatment of all pertinent hydrogen transitions. The same holds for any diagnostic application employing hydrogen lines. Aims: To demonstrate the importance and to quantify the effects of non-equilibrium hydrogen ionization, both on the dynamical structure of the solar atmosphere and on hydrogen line formation, in particular Hα. Methods: We implement an algorithm to compute non-equilibrium hydrogen ionization and its coupling into the MHD equations within an existing radiation MHD code, and perform a two-dimensional simulation of the solar atmosphere from the convection zone to the corona. Results: Analysis of the simulation results and comparison to a companion simulation assuming LTE shows that: a) non-equilibrium computation delivers much smaller variations of the chromospheric hydrogen ionization than for LTE. The ionization is smaller within shocks but subsequently remains high in the cool intershock phases. As a result, the chromospheric temperature variations are much larger than for LTE because in non-equilibrium, hydrogen ionization is a less effective internal energy buffer. The actual shock temperatures are therefore higher and the intershock temperatures lower. b) The chromospheric populations of the hydrogen n = 2 level, which governs the opacity of Hα, are coupled to the ion populations. They are set by the high temperature in shocks and subsequently remain high in the cool intershock phases. c) The temperature structure and the hydrogen level populations differ much between the chromosphere above photospheric magnetic elements

Radiatively-driven winds: model improvements, ionization balance and the infared spectrum

International Nuclear Information System (INIS)

Castor, J.I.

1979-01-01

Recent improvements to theoretical stellar wind models and the results of empirical modelling of the ionization balance and the infrared continuum are discussed. The model of a wind driven by radiation pressure in spectral lines is improved by accounting for overlap of the driving lines, dependence of ionization balance on density, and stellar rotation. These effects produce a softer velocity law than that given by Castor, Abbott and Klein (1975). The ionization balance in zeta Puppis is shown to agree with that estimated for an optically thick wind at a gas temperature of 60,000 K. The ionization model is not unique. The infrared continuum of zeta Pup measured by Barlow and Cohen is fitted to a cool model with a linear rise of velocity with radius; this fit is also not unique. It is concluded that one should try to find a model that fits several kinds of evidence simultaneously. (Auth.)

Influence of Ionization Degrees on the Evolutions of Charged Particles in Atmospheric Plasma at Low Altitude

International Nuclear Information System (INIS)

Pang Xuexia; Deng Zechao; Jia Pengying; Liang Weihua; Li Xia

2012-01-01

A zero-dimensional model which includes 56 species of reactants and 427 reactions is used to study the behavior of charged particles in atmospheric plasmas with different ionization degrees at low altitude (near 0 km). The constant coefficient nonlinear equations are solved by using the Quasi-steady-state approximation method. The electron lifetimes are obtained for afterglow plasma with different initial values, and the temporal evolutions of the main charged species are presented, which are dominant in reaction processes. The results show that the electron number density decays quickly. The lifetimes of electrons are shortened by about two orders with increasing ionization degree. Electrons then attach to neutral particles and produce negative ions. When the initial electron densities are in the range of 10 10 ∼ 10 14 cm −3 , the negative ions have sufficiently high densities and long lifetimes for air purification, disinfection and sterilization. Electrons, O 2 − , O 4 − , CO 4 − and CO 3 − are the dominant negative species when the initial electron density n e0 ≤ 10 13 cm −3 , and only electrons and CO 3 − are left when n e0 ≥ 10 15 cm −3 · N + 2 , N + 4 and O + 2 are dominant in the positive charges for any ionization degree. Other positive species, such as O + 4 , N + 3 , NO + , NO + 2 , Ar + 2 and H 3 O + ·H 2 O, are dominant only for a certain ionization degree and in a certain period. (low temperature plasma)

Nighttime ionization by energetic particles at Wallops Island in the altitude region 120 to 200 km

International Nuclear Information System (INIS)

Voss, H.D.; Smith, L.G.

1979-01-01

Five Nike Apache rockets, each including an energetic particle spectrometer and an electron density-electron temperature experiment, have been launched from Wallops Island (L=2.6) near midnight under varying geomagnetic conditions. On the most recent of these (5 January 1978) an additional spectrometer with a broom magnet, and a 391.4 nm photometer were flown. The data from this flight indicate that the energetic particle flux consists predominantly of protons, neutral hydrogen and possibly other energetic nuclei. The energy spectrum becomes much softer and the flux more intense with increasing Kp for 10 0 indicating that the majority of particles are near their mirroring altitude. Ionization rates are calculated based on the measured energy spectrum and mirror height distribution. The resulting ionization rate profile is found to be nearly constant with altitude in the region 120 to 200 km. The measured energetic particle flux and calculated ionization rate from the five flights are found to vary with magnetic activity (based on the Kp and Dst indexes) in the same way as the independently derived ionization rates deduced from the electron density profile

Determination of equilibrium composition of thermally ionized monoatomic gas under different physical conditions

Science.gov (United States)

Romanova, M. S.; Rydalevskaya, M. A.

2017-05-01

Perfect gas mixtures that result from thermal ionization of spatially and chemically homogeneous monoatomic gases are considered. Equilibrium concentrations of the components of such mixtures are determined using integration over the momentum space and summation with respect to energy levels of the distribution functions that maximize the entropy of system under condition for constancy of the total number of nuclei and electrons. It is demonstrated that such a method allows significant simplification of the calculation of the equilibrium composition for ionized mixtures at different temperatures and makes it possible to study the degree of ionization of gas versus gas density and number in the periodic table of elements.

Large discrepancies observed in theoretical studies of ion-impact ionization of the atomic targets at large momentum transfer

Science.gov (United States)

Ghorbani, Omid; Ghanbari-Adivi, Ebrahim

2017-12-01

A full quantum mechanical version of the three-body distorted wave-eikonal initial state (3DW-EIS) theory is developed to study of the single ionization of the atomic targets by ion impact at different momentum transfers. The calculations are performed both with and without including the internuclear interaction in the transition amplitude. For 16 \\text{Mev} \\text{O}7+ \\text{-He}~(1s2 ) and 24 \\text{Mev} \\text{O}8+\\text{-Li}~(2s ) collisions, the emission of the active electron into the scattering plane is considered and the fully differential cross-sections (FDCSs) are calculated for a fixed value of the ejected electron energy and a variety of momentum transfers. For both the specified collision systems, the obtained results are compared with the experimental data and with the cross-sections obtained using the semi-classical continuum distorted wave-eikonal initial state (CDW-EIS) approach. For 16 \\text{Mev} \\text{O}7+ \\text{-He}~(1s^2) , we also compared the results with those of a four-body three-Coulomb-wave (3CW) model. In general, we find some large discrepancies between the results obtained by different theories. These discrepancies are much more significant at larger momentum transfers. Also, for some ranges of the electron emission angles the results are much more sensitive to the internuclear interaction to be either turned on or off.

A Novel Highly Ionizing Particle Trigger using the ATLAS Transition Radiation Tracker

CERN Document Server

Penwell, J; The ATLAS collaboration

2011-01-01

The ATLAS Transition Radiation Tracker (TRT) is an important part of the experiment’s charged particle tracking system. It also provides the ability to discriminate electrons from pions efficiently using large signal amplitudes induced in the TRT straw tubes by transition radiation. This amplitude information can also be used to identify heavily ionizing particles, such as monopoles, or Q-balls, that traverse the straws. Because of their large ionization losses, these particles can range out before they reach the ATLAS calorimeter, making them difficult to identify by the experiment’s first level trigger. Much of this inefficiency could be regained by making use of a feature of the TRT electronics that allows fast access to information on whether large-amplitude signals were produced in regions of the detector. A modest upgrade to existing electronics could allow triggers sensitive to heavily ionizing particles at level-1 to be constructed by counting such large-amplitude signals in roads corresponding to...

Inclusive and exclusive cross sections for multiple ionization by fast, highly charged ions in the independent-electron approximation

International Nuclear Information System (INIS)

Ben-Itzhak, I.; Gray, T.J.; Legg, J.C.; McGuire, J.H.

1988-01-01

Cross sections for the ionization of n of N electrons with equal single-electron ionization probability P are considered. When both N and the projectile charge q are large, the cross sections for single and double ionization are both found to be approximately linear in q at 1 MeVamu. The ratio of double-to-single-ionization cross sections is independent of q. Moreover, first-order perturbation theory for the single-electron ionization probability P, which varies as q 2 , is found to be applicable due to the damping of contributions with large P caused by factors of (1-P)/sup N/ - /sup n/. For large P there are differences between the inclusive probability P and the probability NP commonly used for a target with N electrons. Both of these probabilities differ significantly from the exclusive probability NP(1-P)/sup N/ -1 for the ionization of only one electron. For large N and large q, the exclusive ionization probabilities for removing exactly n of the N electrons tend to be concentrated in somewhat separate ranges of impact parameters b, defining impact-parameter ''windows.'' The windows which we obtain using the quantum-mechanical semiclassical-Coulomb-approximation (SCA) probabilities are similar to those using classical Monte Carlo calculations. Model calculations, based on analytic fits to the SCA probabilities, are used to obtain approximate analytic expressions for single- and double-ionization cross sections and for the impact-parameter windows

Threshold law for electron-atom impact ionization

International Nuclear Information System (INIS)

Temkin, A.

1982-01-01

The threshold law for electron-atom ionization is derived on the basis of the Coulomb-dipole theory. The result is a modulated quasilinear law for the yield: QproportionalE(lnE) -2 [1+C sin(αlnE+μ)]. The derivation depends on a more accurate description of the dipole moment seen by the outer electron as the distance of the inner electron from the nucleus. The derivation also implies Capprox. =α -1 , and it also suggests that α is large. The same law also applies to positron-atom impact ionization

The multiphoton ionization of uranium hexafluoride

International Nuclear Information System (INIS)

Armstrong, D.P.

1992-05-01

Multiphoton ionization (MPI) time-of-flight mass spectroscopy and photoelectron spectroscopy studies of UF 6 have been conducted using focused light from the Nd:YAG laser fundamental (λ=1064 nm) and its harmonics (λ=532, 355, or 266 nm), as well as other wavelengths provided by a tunable dye laser. The MPI mass spectra are dominated by the singly and multiply charged uranium ions rather than by the UF x + fragment ions even at the lowest laser power densities at which signal could be detected. The laser power dependence of U n+ ions signals indicates that saturation can occur for many of the steps required for their ionization. In general, the doubly-charged uranium ion (U 2+ ) intensity is much greater than that of the singly-charged uranium ion (U + ). For the case of the tunable dye laser experiments, the U n+ (n = 1- 4) wavelength dependence is relatively unstructured and does not show observable resonance enhancement at known atomic uranium excitation wavelengths. The dominance of the U 2+ ion and the absence or very small intensities of UF x + fragments, along with the unsaturated wavelength dependence, indicate that mechanisms may exist other than ionization of bare U atoms after the stepwise photodissociation of F atoms from the parent molecule

AN EXPLANATION FOR THE DIFFERENT X-RAY TO OPTICAL COLUMN DENSITIES IN THE ENVIRONMENTS OF GAMMA RAY BURSTS: A PROGENITOR EMBEDDED IN A DENSE MEDIUM

International Nuclear Information System (INIS)

Krongold, Yair; Prochaska, J. Xavier

2013-01-01

We study the ∼> 10 ratios in the X-ray to optical column densities inferred from afterglow spectra of gamma ray bursts (GRBs) due to gas surrounding their progenitors. We present time-evolving photoionization calculations for these afterglows and explore different conditions of their environment. We find that homogenous models of the environment (constant density) predict X-ray columns similar to those found in the optical spectra, with the bulk of the opacity being produced by neutral material at large distances from the burst. This result is independent of gas density or metallicity. Only models assuming a progenitor immersed in a dense (∼10 2-4 cm –3 ) cloud of gas (with radius ∼10 pc), with a strong, declining gradient of density for the surrounding interstellar medium (ISM) are able to account for the large X-ray to optical column density ratios. However, to avoid an unphysical correlation between the size of this cloud and the size of the ionization front produced by the GRB, the models also require that the circumburst medium is already ionized prior to the burst. The inferred cloud masses are ∼ 6 M ☉ , even if low metallicities in the medium are assumed (Z ∼ 0.1 Z ☉ ). These cloud properties are consistent with those found in giant molecular clouds and our results support a scenario in which the progenitors reside within intense star formation regions of galaxies. Finally, we show that modeling over large samples of GRB afterglows may offer strong constraints on the range of properties in these clouds, and the host galaxy ISM

Development of alpha radioactivity measurement using ionized air transportation technology

International Nuclear Information System (INIS)

Kanemoto, Shigeru; Naito, Susumu; Sano, Akira; Sato, Mitsuyoshi; Fukumoto, Masahiko; Miyamoto, Yasuaki; Nanbu, Kenichi; Takahashi, Hiroyuki

2005-01-01

Alpha radioactivity Measurement using ionized Air Transportation technology (AMAT) is developed to measure alpha contaminated wastes with large and complex surfaces. An outline of this project was described in this text. A major problem of AMAT technology is that the theoretical relation between alpha radioactivity and observed ion current is unclear because of the complicated behavior of ionized air molecules. An ion current prediction model covering from ionization of air molecules to ion detection was developed based on atmospheric electrodynamics. This model was described in this text, too. (author)

Local Fitting of the Kohn-Sham Density in a Gaussian and Plane Waves Scheme for Large-Scale Density Functional Theory Simulations.

Science.gov (United States)

Golze, Dorothea; Iannuzzi, Marcella; Hutter, Jürg

2017-05-09

A local resolution-of-the-identity (LRI) approach is introduced in combination with the Gaussian and plane waves (GPW) scheme to enable large-scale Kohn-Sham density functional theory calculations. In GPW, the computational bottleneck is typically the description of the total charge density on real-space grids. Introducing the LRI approximation, the linear scaling of the GPW approach with respect to system size is retained, while the prefactor for the grid operations is reduced. The density fitting is an O(N) scaling process implemented by approximating the atomic pair densities by an expansion in one-center fit functions. The computational cost for the grid-based operations becomes negligible in LRIGPW. The self-consistent field iteration is up to 30 times faster for periodic systems dependent on the symmetry of the simulation cell and on the density of grid points. However, due to the overhead introduced by the local density fitting, single point calculations and complete molecular dynamics steps, including the calculation of the forces, are effectively accelerated by up to a factor of ∼10. The accuracy of LRIGPW is assessed for different systems and properties, showing that total energies, reaction energies, intramolecular and intermolecular structure parameters are well reproduced. LRIGPW yields also high quality results for extended condensed phase systems such as liquid water, ice XV, and molecular crystals.

Visualization and measurement of gas-liquid metal two-phase flow with large density difference using thermal neutrons as microscopic probes

International Nuclear Information System (INIS)

Mishima, K.; Hibiki, T.; Saito, Y.; Nishihara, H.; Tobita, Y.; Konishi, K.; Matsubayashi, M.

1999-01-01

In a core melt accident of a fast breeder reactor, there is a possibility of boiling of the fuel-steel mixture in the containment pool. In relation to safety evaluation on severe accident, it is indispensable to evaluate the possibility of re-criticality of melted core. Gas-liquid two-phase flow with a large liquid-to-gas density ratio is formed due to the boiling of fuel-steel mixture. Although it is anticipated that the large density ratio may affect the basic characteristics of two-phase flow, little work has been performed so far on two-phase flow with a large liquid-to-gas density ratio. In this study, visualization and void fraction measurement of gas-liquid metal two-phase flow were performed by using neutron radiography and image processing techniques. Then, the effect of large density difference between gas and liquid phases on the basic flow characteristics of two-phase flow was clarified

Simulated Measurements of Cooling in Muon Ionization Cooling Experiment

Energy Technology Data Exchange (ETDEWEB)

Mohayai, Tanaz [IIT, Chicago; Rogers, Chris [Rutherford; Snopok, Pavel [Fermilab

2016-06-01

Cooled muon beams set the basis for the exploration of physics of flavour at a Neutrino Factory and for multi-TeV collisions at a Muon Collider. The international Muon Ionization Cooling Experiment (MICE) measures beam emittance before and after an ionization cooling cell and aims to demonstrate emittance reduction in muon beams. In the current MICE Step IV configuration, the MICE muon beam passes through low-Z absorber material for reducing its transverse emittance through ionization energy loss. Two scintillating fiber tracking detectors, housed in spectrometer solenoid modules upstream and downstream of the absorber are used for reconstructing position and momentum of individual muons for calculating transverse emittance reduction. However, due to existence of non-linear effects in beam optics, transverse emittance growth can be observed. Therefore, it is crucial to develop algorithms that are insensitive to this apparent emittance growth. We describe a different figure of merit for measuring muon cooling which is the direct measurement of the phase space density.

Development of large high current density superconducting solenoid magnets for use in high energy physics experiments

International Nuclear Information System (INIS)

Green, M.A.

1977-05-01

The development of a unique type of large superconducting solenoid magnet, characterized by very high current density windings and a two-phase helium tubular cooling system is described. The development of the magnet's conceptual design and the construction of two test solenoids are described. The successful test of the superconducting coil and its tubular cooling refrigeration system is presented. The safety, environmental and economic impacts of the test program on future developments in high energy physics are shown. Large solid angle particle detectors for colliding beam physics will analyze both charged and neutral particles. In many cases, these detectors will require neutral particles, such as gamma rays, to pass through the magnet coil with minimum interaction. The magnet coils must be as thin as possible. The use of superconducting windings allows one to minimize radiation thickness, while at the same time maximizing charged particle momentum resolution and saving substantial quantities of electrical energy. The results of the experimental measurements show that large high current density solenoid magnets can be made to operate at high stored energies. The superconducting magnet development described has a positive safety and environmental impact. The use of large high current density thin superconducting solenoids has been proposed in two high energy physics experiments to be conducted at the Stanford Linear Accelerator Center and Cornell University as a result of the successful experiments described

Theory of strong-field ionization of aligned CO₂

DEFF Research Database (Denmark)

Abu-Samha, Mahmoud; Madsen, Lars Bojer

2009-01-01

resonance states, and the alignment-dependent ionization yields do not follow the electron density of the initial states. The theory explains the breakdown of semianalytical theories, such as the molecular tunneling theory and strong-field approximation, where excited electronic structure is neglected....

On the effect of electron's runaway in partially ionized hydrogen semiclassical nonideal plasma

International Nuclear Information System (INIS)

Turekhanova, K.M.

2011-01-01

Complete text of publication follows. The effect of runaway electrons occurs frequently in tokamak plasmas. The majority of experiments in tokamak research have been devoted to the study of confinement properties of runaway electrons. Runaway electrons are reason of various destroying untolarance in tokamak plasmas. At high plasma density, when the critical energy is comparable with the rest energy the multiplication of runaway electrons accelerate at the sacrifice of increase of plasma density. The plasma conductivity is determined by electrons with energy several times higher than the thermal one and does not practically depend on slower electrons distribution. It is important to analyze the probability of runaway electrons at investigation of physical properties of nonideal plasmas under external electric field and running numerical simulations of their. The present paper is devoted to the investigation of effect of runaway electrons in partially ionized hydrogen dense plasma using the effective potentials of particle's interaction. At the investigation of composition of plasma we used the Saha equation with corrections to nonideality (lowering of ionization potentials). The Saha equation was solved for obtaining of plasma ionization stages at the different number density and temperature. As well, when take into account quantum-mechanical diffraction and screening effects, whereas free path of electrons increases with increase of plasma coupling parameter. The condition for appearance of runaway electrons in semiclassical partially ionized plasma is more favorable in regime of dense plasma. In summary it means that the probability of runaway electron in dense plasma is more than the same in rarified plasma that is possibly connected with formation of some ordered structures in dense plasma.

Recent attoclock measurements of strong field ionization

International Nuclear Information System (INIS)

Pfeiffer, Adrian N.; Cirelli, Claudio; Smolarski, Mathias; Keller, Ursula

2013-01-01

Highlights: ► The attoclock measures time by electron streaking with elliptically polarized light. ► Precision measurements reveal details about the laser-induced tunneling current flow. ► Multielectron effects play an important role when the polarizability is large. ► Double ionization experiments show evidence of novel electron correlation mechanisms. - Abstract: The attoclock is a powerful, new, and unconventional experimental tool to study fundamental attosecond dynamics on an atomic scale. We have demonstrated the first attoclock with the goal to measure the tunneling delay time in laser-induced ionization of helium and argon atoms, with surprising results. It was found that the time delay in tunneling is zero for helium and argon atoms within the experimental uncertainties of a few 10’s of attoseconds. Furthermore we showed that the single active electron approximation is not sufficient even for atoms such as argon and the parent-ion interaction is much more complex than normally assumed. For double ionization of argon we found again surprising results because the ionization time of the first electron is in good agreement with the predictions, whereas the ionization of the second electron occurs significantly earlier than predicted and the two electrons exhibit some unexpected correlation

Recent attoclock measurements of strong field ionization

Energy Technology Data Exchange (ETDEWEB)

Pfeiffer, Adrian N., E-mail: apfeiff@phys.ethz.ch [Physics Department, ETH Zurich, 8093 Zurich (Switzerland); Cirelli, Claudio; Smolarski, Mathias; Keller, Ursula [Physics Department, ETH Zurich, 8093 Zurich (Switzerland)

2013-03-12

Highlights: ► The attoclock measures time by electron streaking with elliptically polarized light. ► Precision measurements reveal details about the laser-induced tunneling current flow. ► Multielectron effects play an important role when the polarizability is large. ► Double ionization experiments show evidence of novel electron correlation mechanisms. - Abstract: The attoclock is a powerful, new, and unconventional experimental tool to study fundamental attosecond dynamics on an atomic scale. We have demonstrated the first attoclock with the goal to measure the tunneling delay time in laser-induced ionization of helium and argon atoms, with surprising results. It was found that the time delay in tunneling is zero for helium and argon atoms within the experimental uncertainties of a few 10’s of attoseconds. Furthermore we showed that the single active electron approximation is not sufficient even for atoms such as argon and the parent-ion interaction is much more complex than normally assumed. For double ionization of argon we found again surprising results because the ionization time of the first electron is in good agreement with the predictions, whereas the ionization of the second electron occurs significantly earlier than predicted and the two electrons exhibit some unexpected correlation.

Disordered strictly jammed binary sphere packings attain an anomalously large range of densities

Science.gov (United States)

Hopkins, Adam B.; Stillinger, Frank H.; Torquato, Salvatore

2013-08-01

Previous attempts to simulate disordered binary sphere packings have been limited in producing mechanically stable, isostatic packings across a broad spectrum of packing fractions. Here we report that disordered strictly jammed binary packings (packings that remain mechanically stable under general shear deformations and compressions) can be produced with an anomalously large range of average packing fractions 0.634≤ϕ≤0.829 for small to large sphere radius ratios α restricted to α≥0.100. Surprisingly, this range of average packing fractions is obtained for packings containing a subset of spheres (called the backbone) that are exactly strictly jammed, exactly isostatic, and also generated from random initial conditions. Additionally, the average packing fractions of these packings at certain α and small sphere relative number concentrations x approach those of the corresponding densest known ordered packings. These findings suggest for entropic reasons that these high-density disordered packings should be good glass formers and that they may be easy to prepare experimentally. We also identify an unusual feature of the packing fraction of jammed backbones (packings with rattlers excluded). The backbone packing fraction is about 0.624 over the majority of the α-x plane, even when large numbers of small spheres are present in the backbone. Over the (relatively small) area of the α-x plane where the backbone is not roughly constant, we find that backbone packing fractions range from about 0.606 to 0.829, with the volume of rattler spheres comprising between 1.6% and 26.9% of total sphere volume. To generate isostatic strictly jammed packings, we use an implementation of the Torquato-Jiao sequential linear programming algorithm [Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.82.061302 82, 061302 (2010)], which is an efficient producer of inherent structures (mechanically stable configurations at the local maxima in the density landscape). The identification and

Effective ionization coefficient of C5 perfluorinated ketone and its mixtures with air

Science.gov (United States)

Aints, Märt; Jõgi, Indrek; Laan, Matti; Paris, Peeter; Raud, Jüri

2018-04-01

C5 perfluorinated ketone (C5 PFK with UIPAC chemical name 1,1,1,3,4,4,4-heptafluoro-3-(trifluoromethyl)-2-butanone and sold by 3M as Novec™ 5110) has a high dielectric strength and a low global warming potential, which makes it interesting as an insulating gas in medium and high-voltage applications. The study was carried out to determine the effective Townsend ionization coefficient α eff as a function of electric field strength and gas density for C5 PFK and for its mixtures with air. The non-self-sustained Townsend discharge between parallel plate electrodes was initiated by illuminating the cathode by UV radiation. The discharge current, I, was measured as a function of inter-electrode distance, d, at different gas densities, N, and electric field strengths, E. The effective ionization coefficient α eff was determined from the semi-logarithmic plots of I/I 0 against d. For each tested gas mixture, the density normalized effective ionization coefficient α eff/N was found to be a unique function of reduced electric field strength E/N. The measurements were carried out in the absolute pressure range of 0.05-1.3 bar and E/N range of 150-1200 Td. The increasing fraction of C5 PFK in air resulted in the decrease of effective ionization coefficient. The limiting electric field strength (E/N)lim where the effective ionization coefficient α eff became zero was 770 Td (190 kV cm-1 at 1 bar) for pure C5 PFK and decreased to 225 Td (78 kV cm-1 at 1.4 bar) for 7.6% C5 PFK/air mixture. The latter value of (E/N)lim is still more than two times higher than the (E/N)lim value of synthetic air and about two-thirds of the value corresponding to pure SF6. The investigated gas mixtures have the potential to become an alternative to SF6 in numerous high- and medium-voltage applications.

Density Structures, Dynamics, and Seasonal and Solar Cycle Modulations of Saturn's Inner Plasma Disk

Science.gov (United States)

Holmberg, M. K. G.; Shebanits, O.; Wahlund, J.-E.; Morooka, M. W.; Vigren, E.; André, N.; Garnier, P.; Persoon, A. M.; Génot, V.; Gilbert, L. K.

2017-12-01

We present statistical results from the Cassini Radio and Plasma Wave Science (RPWS) Langmuir probe measurements recorded during the time interval from orbit 3 (1 February 2005) to 237 (29 June 2016). A new and improved data analysis method to obtain ion density from the Cassini LP measurements is used to study the asymmetries and modulations found in the inner plasma disk of Saturn, between 2.5 and 12 Saturn radii (1 RS=60,268 km). The structure of Saturn's plasma disk is mapped, and the plasma density peak, nmax, is shown to be located at ˜4.6 RS and not at the main neutral source region at 3.95 RS. The shift in the location of nmax is due to that the hot electron impact ionization rate peaks at ˜4.6 RS. Cassini RPWS plasma disk measurements show a solar cycle modulation. However, estimates of the change in ion density due to varying EUV flux is not large enough to describe the detected dependency, which implies that an additional mechanism, still unknown, is also affecting the plasma density in the studied region. We also present a dayside/nightside ion density asymmetry, with nightside densities up to a factor of 2 larger than on the dayside. The largest density difference is found in the radial region 4 to 5 RS. The dynamic variation in ion density increases toward Saturn, indicating an internal origin of the large density variability in the plasma disk rather than being caused by an external source origin in the outer magnetosphere.

Theoretical investigation of dielectric corona pre-ionization TEA nitrogen laser based on transmission line method

Science.gov (United States)

Bahrampour, Alireza; Fallah, Robabeh; Ganjovi, Alireza A.; Bahrampour, Abolfazl

2007-07-01

This paper models the dielectric corona pre-ionization, capacitor transfer type of flat-plane transmission line traveling wave transverse excited atmospheric pressure nitrogen laser by a non-linear lumped RLC electric circuit. The flat-plane transmission line and the pre-ionizer dielectric are modeled by a lumped linear RLC and time-dependent non-linear RC circuit, respectively. The main discharge region is considered as a time-dependent non-linear RLC circuit where its resistance value is also depends on the radiated pre-ionization ultra violet (UV) intensity. The UV radiation is radiated by the resistance due to the surface plasma on the pre-ionizer dielectric. The theoretical predictions are in a very good agreement with the experimental observations. The electric circuit equations (including the ionization rate equations), the equations of laser levels population densities and propagation equation of laser intensities, are solved numerically. As a result, the effects of pre-ionizer dielectric parameters on the electrical behavior and output laser intensity are obtained.

High microvessel density determines a poor outcome in patients with diffuse large B-cell lymphoma treated with rituximab plus chemotherapy

Science.gov (United States)

Cardesa-Salzmann, Teresa M.; Colomo, Luis; Gutierrez, Gonzalo; Chan, Wing C.; Weisenburger, Dennis; Climent, Fina; González-Barca, Eva; Mercadal, Santiago; Arenillas, Leonor; Serrano, Sergio; Tubbs, Ray; Delabie, Jan; Gascoyne, Randy D.; Connors, Joseph M; Mate, Jose L.; Rimsza, Lisa; Braziel, Rita; Rosenwald, Andreas; Lenz, Georg; Wright, George; Jaffe, Elaine S.; Staudt, Louis; Jares, Pedro; López-Guillermo, Armando; Campo, Elias

2011-01-01

Background Diffuse large B-cell lymphoma is a clinically and molecularly heterogeneous disease. Gene expression profiling studies have shown that the tumor microenvironment affects survival and that the angiogenesis-related signature is prognostically unfavorable. The contribution of histopathological microvessel density to survival in diffuse large B-cell lymphomas treated with immunochemotherapy remains unknown. The purpose of this study is to assess the prognostic impact of histopathological microvessel density in two independent series of patients with diffuse large B-cell lymphoma treated with immunochemotherapy. Design and Methods One hundred and forty-seven patients from the Leukemia Lymphoma Molecular Profiling Project (training series) and 118 patients from the Catalan Lymphoma-Study group-GELCAB (validation cohort) were included in the study. Microvessels were immunostained with CD31 and quantified with a computerized image analysis system. The stromal scores previously defined in 110 Leukemia Lymphoma Molecular Profiling Project cases were used to analyze correlations with microvessel density data. Results Microvessel density significantly correlated with the stromal score (r=0.3209; P<0.001). Patients with high microvessel density showed significantly poorer overall survival than those with low microvessel density both in the training series (4-year OS 54% vs. 78%; P=0.004) and in the validation cohort (57% vs. 81%; P=0.006). In multivariate analysis, in both groups high microvessel density was a statistically significant unfavorable prognostic factor independent of international prognostic index [training series: international prognostic index (relative risk 2.7; P=0.003); microvessel density (relative risk 1.96; P=0.002); validation cohort: international prognostic index (relative risk 4.74; P<0.001); microvessel density (relative risk 2.4; P=0.016)]. Conclusions These findings highlight the impact of angiogenesis in the outcome of patients with

Microscopic theory of warm ionized gases: equation of state and kinetic Schottky anomaly

International Nuclear Information System (INIS)

Capolupo, A; Giampaolo, S M; Illuminati, F

2013-01-01

Based on accurate Lennard-Jones type interaction potentials, we derive a closed set of state equations for the description of warm atomic gases in the presence of ionization processes. The specific heat is predicted to exhibit peaks in correspondence to single and multiple ionizations. Such kinetic analogue in atomic gases of the Schottky anomaly in solids is enhanced at intermediate and low atomic densities. The case of adiabatic compression of noble gases is analyzed in detail and the implications on sonoluminescence are discussed.

Light focusing from large refractive indices in ionized air

International Nuclear Information System (INIS)

Robledo-Martinez, A.; Sobral, H.; Villagran-Muniz, M.; Bredice, F.

2008-01-01

The sheath that surrounds a laser-induced plasma in air was investigated with a light probe. The sheath is a 3-mm-thick halo of ionized gas created by ultraviolet light emitted from the plasma core. A beam of laser light tracked with a streak camera was employed to probe it. It was found that in the first hundreds of a nanosecond after plasma inception, the beam is deflected towards the plasma center. This result points to a high refractive index inside the sheath. The index values obtained (up to 2.0) are due to an increased susceptibility caused by a bulk electric polarization. Using previous results on the sheath's electric polarizability values, the refractive index was calculated and was found to agree with the observed indices. The application of the electric polarization model to the guiding of laser beams and to plasma lenses is also discussed.

L-shell ionization studies of Pb and Bi with α particles

International Nuclear Information System (INIS)

Dhal, B.B.; Nandi, T.; Padhi, H.C.

1994-01-01

Ionization cross sections for the L subshells of Pb and Bi by α-particle bombardment (2.2--8.2 MeV) have been determined from the experimental data and the currently available radiative transition probabilities, fluorescence yields, and Coster-Kronig factors. The measured ionization cross sections and their ratios are compared with the results of ECPSSR calculations [ECPSSR denotes perturbed-stationary-state (PSS) theory with energy-loss (E), Coulomb deflection (C), and relativistic (R) corrections]. The measured individual cross sections for L 1 and L 2 subshells deviated in opposite directions from the theory, whereas their sum shows good agreement. The L 3 and total ionization cross sections obtained from the data also show good agreement with the ECPSSR theory. The ionization cross-section ratios σ L1 /σ L2 and σ L3 /σ L2 show large deviations from the ECPSSR theory. The experimental x-ray production cross-section ratios are found to be in better agreement with the theoretical results obtained from using ECPSSR ionization cross sections and the decay yield data of Xu and Xu [J. Phys. B 25, 695 (1992)] rather than those obtained from using the decay yield data of Krause [J. Phys. Chem. Ref. Data 8, 307 (1979)]. The x-ray production cross sections, however, are in better agreement with the theoretical results obtained from using the decay yield data of Krause. The measured centroid energy of the Lγ lines of Pb shows large deviations at high projectile energy, whereas for Bi large deviations are found at the low-energy region

Power Spectral Density Specification and Analysis of Large Optical Surfaces

Science.gov (United States)

Sidick, Erkin

2009-01-01

The 2-dimensional Power Spectral Density (PSD) can be used to characterize the mid- and the high-spatial frequency components of the surface height errors of an optical surface. We found it necessary to have a complete, easy-to-use approach for specifying and evaluating the PSD characteristics of large optical surfaces, an approach that allows one to specify the surface quality of a large optical surface based on simulated results using a PSD function and to evaluate the measured surface profile data of the same optic in comparison with those predicted by the simulations during the specification-derivation process. This paper provides a complete mathematical description of PSD error, and proposes a new approach in which a 2-dimentional (2D) PSD is converted into a 1-dimentional (1D) one by azimuthally averaging the 2D-PSD. The 1D-PSD calculated this way has the same unit and the same profile as the original PSD function, thus allows one to compare the two with each other directly.

Possible influence of the Kuramoto length in a photo-catalytic water splitting reaction revealed by Poisson-Nernst-Planck equations involving ionization in a weak electrolyte

Science.gov (United States)

Suzuki, Yohichi; Seki, Kazuhiko

2018-03-01

We studied ion concentration profiles and the charge density gradient caused by electrode reactions in weak electrolytes by using the Poisson-Nernst-Planck equations without assuming charge neutrality. In weak electrolytes, only a small fraction of molecules is ionized in bulk. Ion concentration profiles depend on not only ion transport but also the ionization of molecules. We considered the ionization of molecules and ion association in weak electrolytes and obtained analytical expressions for ion densities, electrostatic potential profiles, and ion currents. We found the case that the total ion density gradient was given by the Kuramoto length which characterized the distance over which an ion diffuses before association. The charge density gradient is characterized by the Debye length for 1:1 weak electrolytes. We discuss the role of these length scales for efficient water splitting reactions using photo-electrocatalytic electrodes.

Optical observations on the CRIT-II Critical Ionization Velocity Experiment

International Nuclear Information System (INIS)

Stenbaek-Nielsen, H.C.; Wescott, E.M.; Haerendel, G.; Valenzuela, A.

1990-01-01

A rocket borne Critical Ionization Velocity (CIV) experiment was carried out from Wallops Island at dusk on May 4, 1989. Two barium shaped charges were released below the solar terminator (to prevent photoionization) at altitudes near 400 km. The ambient ionospheric electron density was 5x10 5 cm -3 . The neutral barium jet was directed upwards and at an angle of nominally 45 degrees to B which gives approximately 3x10 23 neutrals with super critical velocity. Ions created by a CIV process in the region of the neutral jet would travel up along B into sunlight where they can be detected optically. Well defined ion clouds (max. brightness 750 R) were observed in both releases. An ionization rate of 0.8%s -1 (125s ionization time constant) can account for the observed ion cloud near the release field line, but the ionization rate falls off with increasing distance from the release. It is concluded that a CIV process was present in the neutral jet out to about 50 km from the release, which is significantly further than allowed by current theories

The GBT Diffuse Ionized Gas Survey (GDIGS)

Science.gov (United States)

Luisi, Matteo; Anderson, Loren Dean; Liu, Bin; Bania, Thomas; Balser, Dana; Wenger, Trey; Haffner, Lawrence Matthew

2018-01-01

Diffuse ionized gas in the Galactic mid-plane known as the "Warm Ionized Medium" (WIM) makes up ~20% of the gas mass of the Milky Way and >90% of its ionized gas. It is the last major component of the interstellar medium (ISM) that has not yet been studied at high spatial and spectral resolution, and therefore many of its fundamental properties remain unclear. The Green Bank Telescope (GBT) Diffuse Ionized Gas Survey (GDIGS) is a new large survey of the Milky Way disk at C-band (4-8 GHz). The main goals of GDIGS are to investigate the properties of the WIM and to determine the connection between the WIM and high-mass star formation over the Galactic longitude and latitude range of 32 deg > l > -5 deg, |b| resolution of 0.5 km/s and rms sensitivities of ~3 mJy per beam. GDIGS observations are currently underway and are expected to be completed by late 2018. These data will allow us to: 1) Study for the first time the inner-Galaxy WIM unaffected by confusion from discrete HII regions, 2) determine the distribution of the inner Galaxy WIM, 3) investigate the ionization state of the WIM, 4) explore the connection between the WIM and HII regions, and 5) analyze the effect of leaked photons from HII regions on ISM dust temperatures.

Ionization and scintillation response of high-pressure xenon gas to alpha particles

International Nuclear Information System (INIS)

Álvarez, V; Cárcel, S; Cervera, A; Díaz, J; Ferrario, P; Gil, A; Gómez-Cadenas, J J; Borges, F I G; Conde, C A N; Fernandes, L M P; Freitas, E D C; Cebrián, S; Dafni, T; Gómez, H; Egorov, M; Gehman, V M; Goldschmidt, A; Esteve, R; Evtoukhovitch, P; Ferreira, A L

2013-01-01

High-pressure xenon gas is an attractive detection medium for a variety of applications in fundamental and applied physics. In this paper we study the ionization and scintillation detection properties of xenon gas at 10 bar pressure. For this purpose, we use a source of alpha particles in the NEXT-DEMO time projection chamber, the large scale prototype of the NEXT-100 neutrinoless double beta decay experiment, in three different drift electric field configurations. We measure the ionization electron drift velocity and longitudinal diffusion, and compare our results to expectations based on available electron scattering cross sections on pure xenon. In addition, two types of measurements addressing the connection between the ionization and scintillation yields are performed. On the one hand we observe, for the first time in xenon gas, large event-by-event correlated fluctuations between the ionization and scintillation signals, similar to that already observed in liquid xenon. On the other hand, we study the field dependence of the average scintillation and ionization yields. Both types of measurements may shed light on the mechanism of electron-ion recombination in xenon gas for highly-ionizing particles. Finally, by comparing the response of alpha particles and electrons in NEXT-DEMO, we find no evidence for quenching of the primary scintillation light produced by alpha particles in the xenon gas.

COMPLETE IONIZATION OF THE NEUTRAL GAS: WHY THERE ARE SO FEW DETECTIONS OF 21 cm HYDROGEN IN HIGH-REDSHIFT RADIO GALAXIES AND QUASARS

Energy Technology Data Exchange (ETDEWEB)

Curran, S. J. [Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006 (Australia); Whiting, M. T., E-mail: sjc@physics.usyd.edu.au [CSIRO Astronomy and Space Science, P.O. Box 76, Epping, NSW 1710 (Australia)

2012-11-10

From the first published z {approx}> 3 survey of 21 cm absorption within the hosts of radio galaxies and quasars, Curran et al. found an apparent dearth of cool neutral gas at high redshift. From a detailed analysis of the photometry, each object is found to have a {lambda} = 1216 A continuum luminosity in excess of L {sub 1216} {approx} 10{sup 23} W Hz{sup -1}, a critical value above which 21 cm has never been detected at any redshift. At these wavelengths, and below, hydrogen is excited above the ground state so that it cannot absorb in 21 cm. In order to apply the equation of photoionization equilibrium, we demonstrate that this critical value also applies to the ionizing ({lambda} {<=} 912 A) radiation. We use this to show, for a variety of gas density distributions, that upon placing a quasar within a galaxy of gas, there is always an ultraviolet luminosity above which all of the large-scale atomic gas is ionized. While in this state, the hydrogen cannot be detected or engage in star formation. Applying the mean ionizing photon rate of all of the sources searched, we find, using canonical values for the gas density and recombination rate coefficient, that the observed critical luminosity gives a scale length (3 kpc) similar that of the neutral hydrogen (H I) in the Milky Way, a large spiral galaxy. Thus, this simple yet physically motivated model can explain the critical luminosity (L {sub 912} {approx} L {sub 1216} {approx} 10{sup 23} W Hz{sup -1}), above which neutral gas is not detected. This indicates that the non-detection of 21 cm absorption is not due to the sensitivity limits of current radio telescopes, but rather that the lines of sight to the quasars, and probably the bulk of the host galaxies, are devoid of neutral gas.

Microparticle charging in dry air plasma created by an external ionization source

International Nuclear Information System (INIS)

Derbenev, I N; Filippov, A V

2015-01-01

In the present paper the dust particle charging is studied in a dry air plasma created by an external ionization source. The ionization rate is changed in the range 10 1 -10 20 cm -3 s -1 . It is found that the main positive ion of the plasma is O + 4 and the main negative ones are O − 2 and O − 4 . The point sink model based on the diffusion-drift approach shows that the screening potential distribution around a dust particle is a superposition of four Debye-like exponentials with four different spatial scales. The first scale almost coincides with the Debye radius. The second one is the distance, passed by positive and negative plasma components due to ambipolar diffusion in their recombination time. The third one is defined by the negative ion conversion and diffusion. The fourth scale is described by the electron attachment, recombination and diffusion at low gas ionization rates and by the recombination and diffusion of negative diatomic ions at high ionization rates. It is also shown that the electron flux defines the microparticle charge at high ionization rates, whereas the electron number density is much less than the ion one. (paper)

Electron ionization and spin polarization control of Fe atom adsorbed graphene irradiated by a femtosecond laser

International Nuclear Information System (INIS)

Yu, Dong; Jiang, Lan; Wang, Feng; Li, Xin; Qu, Liangti; Lu, Yongfeng

2015-01-01

We investigate the structural properties and ionized spin electrons of an Fe–graphene system, in which the time-dependent density functional theory (TDDFT) within the generalized gradient approximation is used. The electron dynamics, including electron ionization and ionized electron spin polarization, is described for Fe atom adsorbed graphene under femtosecond laser irradiation. The theoretical results show that the electron ionization and ionized electron spin polarization are sensitive to the laser parameters, such as the incident angle and the peak intensity. The spin polarization presents the maximum value under certain laser parameters, which may be used as a source of spin-polarized electrons. - Highlights: • The structural properties of Fe–graphene system are investigated. • The electron dynamics of Fe–graphene system under laser irradiation are described. • The Fe–graphene system may be used as a source of spin-polarized electrons

Predicting Ionization Rates from SEP and Solar Wind Proton Precipitation into the Martian Atmosphere

Science.gov (United States)

Jolitz, R.; Dong, C.; Lee, C. O.; Curry, S.; Lillis, R. J.; Brain, D.; Halekas, J. S.; Larson, D. E.; Bougher, S. W.; Jakosky, B. M.

2017-12-01

Precipitating energetic particles ionize planetary atmospheres and increase total electron content. At Mars, the solar wind and solar energetic particles (SEPs) can precipitate directly into the atmosphere because solar wind protons can charge exchange to become neutrals and pass through the magnetosheath, while SEPs are sufficiently energetic to cross the magnetosheath unchanged. In this study we will present predicted ionization rates and resulting electron densities produced by solar wind and SEP proton ionization during nominal solar activity and a CME shock front impact event on May 16 2016. We will use the Atmospheric Scattering of Protons and Energetic Neutrals (ASPEN) model to compare ionization by SEP and solar wind protons currently measured by the SWIA (Solar Wind Ion Analyzer) and SEP instruments aboard the MAVEN spacecraft. Results will help to quantify how the ionosphere responds to extreme solar events during solar minimum.

Propagation of electromagnetic waves in a weakly ionized dusty plasma

International Nuclear Information System (INIS)

Jia, Jieshu; Yuan, Chengxun; Gao, Ruilin; Wang, Ying; Liu, Yaoze; Gao, Junying; Zhou, Zhongxiang; Sun, Xiudong; Li, Hui; Wu, Jian; Pu, Shaozhi

2015-01-01

Propagation properties of electromagnetic (EM) waves in weakly ionized dusty plasmas are the subject of this study. Dielectric relation for EM waves propagating at a weakly ionized dusty plasma is derived based on the Boltzmann distribution law while considering the collision and charging effects of dust grains. The propagation properties of EM energy in dusty plasma of rocket exhaust are numerically calculated and studied, utilizing the parameters of rocket exhaust plasma. Results indicate that increase of dust radius and density enhance the reflection and absorption coefficient. High dust radius and density make the wave hardly transmit through the dusty plasmas. Interaction enhancements between wave and dusty plasmas are developed through effective collision frequency improvements. Numerical results coincide with observed results by indicating that GHz band wave communication is effected by dusty plasma as the presence of dust grains significantly affect propagation of EM waves in the dusty plasmas. The results are helpful to analyze the effect of dust in plasmas and also provide a theoretical basis for the experiments. (paper)

NON-EQUILIBRIUM IONIZATION MODELING OF THE CURRENT SHEET IN A SIMULATED SOLAR ERUPTION

International Nuclear Information System (INIS)

Shen Chengcai; Reeves, Katharine K.; Raymond, John C.; Murphy, Nicholas A.; Ko, Yuan-Kuen; Lin Jun; Mikić, Zoran; Linker, Jon A.

2013-01-01

The current sheet that extends from the top of flare loops and connects to an associated flux rope is a common structure in models of coronal mass ejections (CMEs). To understand the observational properties of CME current sheets, we generated predictions from a flare/CME model to be compared with observations. We use a simulation of a large-scale CME current sheet previously reported by Reeves et al. This simulation includes ohmic and coronal heating, thermal conduction, and radiative cooling in the energy equation. Using the results of this simulation, we perform time-dependent ionization calculations of the flow in a CME current sheet and construct two-dimensional spatial distributions of ionic charge states for multiple chemical elements. We use the filter responses from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory and the predicted intensities of emission lines to compute the count rates for each of the AIA bands. The results show differences in the emission line intensities between equilibrium and non-equilibrium ionization. The current sheet plasma is underionized at low heights and overionized at large heights. At low heights in the current sheet, the intensities of the AIA 94 Å and 131 Å channels are lower for non-equilibrium ionization than for equilibrium ionization. At large heights, these intensities are higher for non-equilibrium ionization than for equilibrium ionization inside the current sheet. The assumption of ionization equilibrium would lead to a significant underestimate of the temperature low in the current sheet and overestimate at larger heights. We also calculate the intensities of ultraviolet lines and predict emission features to be compared with events from the Ultraviolet Coronagraph Spectrometer on the Solar and Heliospheric Observatory, including a low-intensity region around the current sheet corresponding to this model

Numerical double layer solutions with ionization

International Nuclear Information System (INIS)

Andersson, D.; Soerensen, J.

1982-08-01

Maxwell's equation div D = ro in one dimension is solved numerically, taking ionization into account. Time independent anode sheath and double layer solutions are obtained. By varying voltage, neutral gas pressure, temperature of the trapped ions on the cathode side and density and temperature of the trapped electrones on the anode side, diagrams are constructed that show permissible combinations of these parameters. Results from a recent experiment form a subset. Distribution functions, the Langmuir condition, some scaling laws and a possible application to the lower ionosphere are discussed. (Authors)

Ultra-low emittance beam generation using two-color ionization injection in a CO2 laser-driven plasma accelerator

International Nuclear Information System (INIS)

Schroeder, Carl; Benedetti, Carlo; Bulanov, Stepan; Chen, Min; Esarey, Eric; Geddes, Cameron; Vay, J.; Yu, Lule; Leemans, Wim

2015-01-01

Ultra-low emittance (tens of nm) beams can be generated in a plasma accelerator using ionization injection of electrons into a wakefield. An all-optical method of beam generation uses two laser pulses of different colors. A long-wavelength drive laser pulse (with a large ponderomotive force and small peak electric field) is used to excite a large wakefield without fully ionizing a gas, and a short-wavelength injection laser pulse (with a small ponderomotive force and large peak electric field), co-propagating and delayed with respect to the pump laser, to ionize a fraction of the remaining bound electrons at a trapped wake phase, generating an electron beam that is accelerated in the wake. The trapping condition, the ionized electron distribution, and the trapped bunch dynamics are discussed. Expressions for the beam transverse emittance, parallel and orthogonal to the ionization laser polarization, are presented. An example is shown using a 10-micron CO 2 laser to drive the wake and a frequency-doubled Ti:Al 2 O 3 laser for ionization injection.

Ionization processes in the Fe 27 region of hot iron plasma in the field of hard gamma radiation

International Nuclear Information System (INIS)

Illarionov, A.F.

1989-01-01

A highly ionized hot plasma of an iron 26 56 Fe-type heavy element in the field of hard ionizing gamma-ray radiation is considered. The processes of ionization and recombination are discussed for a plasma consisting of the fully ionized Fe 27 and the hydrogen-like Fe 26 ions of iron in the case of large optical depth of the plasma with respect to the photoionization by gamma-ray quanta. The self-ionization process of a hot plasma with the temperature kT ≅ I (I being the ionization potential), due to the production of the own ionizing gamma-ray quanta, by the free-free (ff) and recombination (fb) radiation mechanisms, is investigated. It is noted that in the stationary situation the process of self-ionization of a hot plasma imposes the restriction upon the plasma temperature, kT<1.5 I. It is shown that the ionization of heavy-ion plasma by the impact of thermal electrons is dominating over the processes of ff- and fb-selfionization of plasma only by the large concentration of hydrogen-like iron at the periphery of the region of fully ionized iron Fe 27

Stokes-attenuated tunneling ionization of molecules

Science.gov (United States)

Kornev, Aleksei S.; Zon, Boris A.

2018-03-01

We set forth the quantum theory of ionic vibrational-level population by means of tunneling ionization of a molecule. Specific calculations are carried out for the H2 molecule. The results are in qualitative agreement with the experimental data [X. Urbain et al., Phys. Rev. Lett. 92, 163004 (2004), 10.1103/PhysRevLett.92.163004]. Our account for the excited vibrational levels reveals an interplay of two tendencies which contribute to the ionization rate: (i) It decreases due to additional energy absorption needed to populate these states and (ii) it increases together with the Franck-Condon factors which are large for these states. We show that these two tendencies practically compensate each other. The average quantitative disagreement between the theory and experiment amounts to ˜30 %. The same disagreement takes place when using the frozen approximation for the description of the nuclei motion. We demonstrated that the light-dressing effect for H2 leads to the dependence of the ionization rate on the angle between the molecule axis and the polarization vector of the radiation.

The mean free path of hydrogen ionizing photons during the epoch of reionization

Science.gov (United States)

Rahmati, Alireza; Schaye, Joop

2018-05-01

We use the Aurora radiation-hydrodynamical simulations to study the mean free path (MFP) for hydrogen ionizing photons during the epoch of reionization. We directly measure the MFP by averaging the distance 1 Ry photons travel before reaching an optical depth of unity along random lines-of-sight. During reionization the free paths tend to end in neutral gas with densities near the cosmic mean, while after reionization the end points tend to be overdense but highly ionized. Despite the increasing importance of discrete, over-dense systems, the cumulative contribution of systems with NHI ≲ 1016.5 cm-2 suffices to drive the MFP at z ≈ 6, while at earlier times higher column densities are more important. After reionization the typical size of HI systems is close to the local Jeans length, but during reionization it is much larger. The mean free path for photons originating close to galaxies, {MFP_{gal}}, is much smaller than the cosmic MFP. After reionization this enhancement can remain significant up to starting distances of ˜1 comoving Mpc. During reionization, however, {MFP_{gal}} for distances ˜102 - 103 comoving kpc typically exceeds the cosmic MFP. These findings have important consequences for models that interpret the intergalactic MFP as the distance escaped ionizing photons can travel from galaxies before being absorbed and may cause them to under-estimate the required escape fraction from galaxies, and/or the required emissivity of ionizing photons after reionization.

Photoionization and High Density Gas

Science.gov (United States)

Kallman, T.; Bautista, M.; White, Nicholas E. (Technical Monitor)

2002-01-01

We present results of calculations using the XSTAR version 2 computer code. This code is loosely based on the XSTAR v.1 code which has been available for public use for some time. However it represents an improvement and update in several major respects, including atomic data, code structure, user interface, and improved physical description of ionization/excitation. In particular, it now is applicable to high density situations in which significant excited atomic level populations are likely to occur. We describe the computational techniques and assumptions, and present sample runs with particular emphasis on high density situations.

The role of exciton ionization processes in bulk heterojunction organic photovoltaic cells

Science.gov (United States)

Zou, Yunlong; Holmes, Russell

2015-03-01

Dissociating photogenerated excitons into their constituent charges is essential for efficient photoconversion in organic semiconductors. Organic photovoltaics cells (OPV) widely adopt a heterojunction architecture where dissociation is facilitated by charge transfer at a donor-acceptor (D-A) interface. Interestingly, recent work on MoOx/C60 Schottky OPVs has demonstrated that excitons in C60 may also undergo bulk-ionization to generate photocurrent, driven by the built-in field at the MoOx/C60 interface. Here, we show that bulk-ionization processes also contribute to the photocurrent in bulk heterojunction (BHJ) OPVs with fullerene-rich compositions. The short-circuit current density (JSC) in a MoOx/C60 Schottky OPVs shows almost no dependence on temperature down to 80 K. This characteristic of bulk-ionization allows the use of temperature-dependent measurements of JSC to distinguish dissociation by bulk-ionization from charge transfer at a D-A interface. For BHJ OPVs constructed using the D-A pairing of boron subphthalocyanine chloride (SubPc)-C60, bulk-ionization is found to contribute >10% of the total photocurrent and >30% of the photocurrent from C60. We further find that fullerene-rich SubPc-C60 BHJ OPVs show a larger open-circuit voltage (VOC) than evenly mixed BHJs due to the presence of bulk-ionization. This talk will examine the dependence of JSC and VOC on the relative fraction of dissociation by charge transfer and bulk-ionization processes.

Effects of air humidity on ionization chamber response

International Nuclear Information System (INIS)

Meger, C.; DeLuca, P.M. Jr.; Pearson, D.W.; Venci, R.

1983-01-01

A study of the effect of air humidity on four different ionization chamber cap materials verified earlier studies (Kristensen and Sundbom, 1981; Mijnheer et al., 1983) and extended our understanding of the problem. We found nylon and A-150 plastic caps swell as they absorb water from the air. This accounts for as much as 2.5% increase in ionization response. Graphite chambers readily absorb and desorb water from the air. This creates a problem in maintaining dry air in a wet graphite chamber. Humid air has a different density and W value than dry air (Niatel, 1969, 1975). This decreases the charge collected in a wet graphite chamber. We observe a decrease in response of approximately 2%, a value greater than can be accounted for by these effects alone. Polyethylene chambers are unaffected by humid air. 4 refs., 9 figs

Ionization mechanism of cesium plasma produced by irradiation of dye laser

International Nuclear Information System (INIS)

Yamada, Jun; Shibata, Kohji; Uchida, Yoshiyuki; Hioki, Yoshiaki; Sahashi, Toshio.

1992-01-01

When a cesium vapor was irradiated by a dye laser which was tuned to the cesium atomic transition line, the number of charged particles produced by the laser radiation was observed. Several sharp peaks in the number of charged particles were observed, which corresponded to the atomic transition where the lower level was the 6P excited atom. The ionization mechanism of the laser-produced cesium plasma has been discussed. An initial electron is produced by laser absorptions of the cesium dimer. When the cesium density is high, many 6P excited atoms are excited by electron collisions. The 6P excited atom further absorbs the laser photon and is ionized through the higher-energy state. As the cesium vapor pressure increases, the resonance effect becomes observable. The 6P excited atom plays dominant role in the ionization mechanism of the laser-produced cesium plasma. (author)

SURFACE LAYER ACCRETION IN CONVENTIONAL AND TRANSITIONAL DISKS DRIVEN BY FAR-ULTRAVIOLET IONIZATION

International Nuclear Information System (INIS)

Perez-Becker, Daniel; Chiang, Eugene

2011-01-01

Whether protoplanetary disks accrete at observationally significant rates by the magnetorotational instability (MRI) depends on how well ionized they are. Disk surface layers ionized by stellar X-rays are susceptible to charge neutralization by small condensates, ranging from ∼0.01 μm sized grains to angstrom-sized polycyclic aromatic hydrocarbons (PAHs). Ion densities in X-ray-irradiated surfaces are so low that ambipolar diffusion weakens the MRI. Here we show that ionization by stellar far-ultraviolet (FUV) radiation enables full-blown MRI turbulence in disk surface layers. Far-UV ionization of atomic carbon and sulfur produces a plasma so dense that it is immune to ion recombination on grains and PAHs. The FUV-ionized layer, of thickness 0.01-0.1 g cm -2 , behaves in the ideal magnetohydrodynamic limit and can accrete at observationally significant rates at radii ∼> 1-10 AU. Surface layer accretion driven by FUV ionization can reproduce the trend of increasing accretion rate with increasing hole size seen in transitional disks. At radii ∼<1-10 AU, FUV-ionized surface layers cannot sustain the accretion rates generated at larger distance, and unless turbulent mixing of plasma can thicken the MRI-active layer, an additional means of transport is needed. In the case of transitional disks, it could be provided by planets.

Estimate of electrical potential difference between plasmas with different degrees of ionization

Energy Technology Data Exchange (ETDEWEB)

Chang, Chong [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2017-01-12

The electrical potential difference has been estimated across the mixing region of two plasmas with different degrees of ionization. The estimation has been carried out in two different contexts of a charge neutral mixing region and a charge non-neutral sheath. Ion energy gained due to the potential difference has also been estimated. In both analyses, ion energy gain is proportional to the degree of ionization, and a fairly large ionization appears to be needed for overcoming the potential energy barrier of strongly coupled plasmas.

Code of Practice for the Use of Ionizing Radiations in Secondary Schools.

Science.gov (United States)

National Health and Medical Research Council, Canberra (Australia).

The appreciation of the potential hazard of ionizing radiation led to the setting up of national, and later, international commissions for the defining of standards of protection for the occupationally exposed worker in the use of ionizing radiation. However, in the last twenty years, with the large scale development of nuclear energy, the need…

Multiphoton ionization of H{sub 2}{sup +} in xuv laser pulses

Energy Technology Data Exchange (ETDEWEB)

Guan Xiaoxu; Secor, Ethan B.; Bartschat, Klaus [Department of Physics and Astronomy, Drake University, Des Moines, Iowa 50311 (United States); Schneider, Barry I. [Office of Cyberinfrastructure, National Science Foundation, Arlington, Virgina 22230 (United States)

2011-09-15

We consider the ionization of the hydrogen molecular ion after one-, two-, and three-photon absorption over a large range of photon energies between 9 and 40 eV in the fixed-nuclei approximation. The temporal development of the system is obtained in a fully ab initio time-dependent grid-based approach in prolate spheroidal coordinates. The alignment dependence of the one-photon ionization amplitude is highlighted in the framework of time-dependent perturbation theory. For one-photon ionization as a function of the nuclear separation, the calculations reveal a significant minimum in the ionization probability. The suppressed ionization is attributed to a Cooper-type minimum, which is similar, but not identical, to the cancellation effect observed in photoionization cross sections of some noble-gas atoms. The effect of the nonspherical two-center Coulomb potential is analyzed. For two- and three-photon ionization, the angle-integrated cross sections clearly map out intermediate-state resonances, and the predictions of the current computations agree very well with those from time-independent calculations. The dominant emission modes for two-photon ionization are found to be very similar in both resonance and off-resonance regions.

Ionization

International Nuclear Information System (INIS)

2002-01-01

This document reprints the text of the French by-law from January 8, 2002 relative to the approval and to the controls and verifications of facilities devoted to the ionizing of food products for human beings and animals. The by-law imposes the operators of such facilities to perform measurements and dosimetric verifications all along the ionization process. (J.S.)

Safety instruction for execution tasks involving ionizing radiations

International Nuclear Information System (INIS)

Fonseca, G.

1985-01-01

Basic directives are presented allow operations with ionizing radiations in industrial areas with high levels of safety. Contractual, technical, operational and administrative criteria are established for the safe performance of x-rays and gamographies and the use of fixed radiation based equipment (indicators of level, density, flow, etc) as well as precautions to be taken during project, procurement, transportation, assembly and maintenance of such equipment. Finally procedures are suggested for emergencies involving radioactive sources. (author)

MOSFET and MOS capacitor responses to ionizing radiation

Science.gov (United States)

Benedetto, J. M.; Boesch, H. E., Jr.

1984-01-01

The ionizing radiation responses of metal oxide semiconductor (MOS) field-effect transistors (FETs) and MOS capacitors are compared. It is shown that the radiation-induced threshold voltage shift correlates closely with the shift in the MOS capacitor inversion voltage. The radiation-induced interface-state density of the MOSFETs and MOS capacitors was determined by several techniques. It is shown that the presence of 'slow' states can interfere with the interface-state measurements.

Ionizing radiation

International Nuclear Information System (INIS)

Kruger, J.

1989-01-01

Ionizing radiation results in biological damage that differs from other hazardous substances and is highly dangerous to man. Ionizing radiation cannot be perceived by man's sense organs and the biological damage cannot be detected immediately afterwards (except in very high doses). Every human being is exposed to low doses of radiation. The structure of the atom; sources of ionizing radiation; radiation units; biological effects; norms for radiation protection; and the national control in South Africa are discussed. 1 fig., 5 refs

Charge Dynamics in near-Surface, Variable-Density Ensembles of Nitrogen-Vacancy Centers in Diamond.

Science.gov (United States)

Dhomkar, Siddharth; Jayakumar, Harishankar; Zangara, Pablo R; Meriles, Carlos A

2018-06-13

Although the spin properties of superficial shallow nitrogen-vacancy (NV) centers have been the subject of extensive scrutiny, considerably less attention has been devoted to studying the dynamics of NV charge conversion near the diamond surface. Using multicolor confocal microscopy, here we show that near-surface point defects arising from high-density ion implantation dramatically increase the ionization and recombination rates of shallow NVs compared to those in bulk diamond. Further, we find that these rates grow linearly, not quadratically, with laser intensity, indicative of single-photon processes enabled by NV state mixing with other defect states. Accompanying these findings, we observe NV ionization and recombination in the dark, likely the result of charge transfer to neighboring traps. Despite the altered charge dynamics, we show that one can imprint rewritable, long-lasting patterns of charged-initialized, near-surface NVs over large areas, an ability that could be exploited for electrochemical biosensing or to optically store digital data sets with subdiffraction resolution.

Large aperture contact ionized Cs+1 ion source for an induction linac

International Nuclear Information System (INIS)

Abbott, S.; Chupp, W.; Faltens, A.; Herrmannsfeldt, W.; Hoyer, E.; Keefe, D.; Kim, C.H.; Rosenblum, S.; Shiloh, J.

1979-03-01

A 500 KeV one-ampere Cs +1 ion beam has been generated by contact ionization with a 30 cm dia. iridium hot plate. Reproducibility of space charge limited ion current wave forms at repetition rates up to 1 Hz has been verified. The beam is characterized to be very bright and suitable as an ion source for the induction linac based heavy ion fusion scheme. The hot anode plate was found to be reliable and self-cleaning during the operation

Electron ionization and the Compton effect in double ionization of helium

International Nuclear Information System (INIS)

Samson, J.

1994-01-01

The author discusses ionization phenomena in helium, both photoionization and electron ionization. In particular he compares double ionization cross sections with total cross sections, as a function of electron energy, and photon energy. Data is discussed over the energy range up to 10 keV

Vinyl acetate polymerization by ionizing radiation

International Nuclear Information System (INIS)

Mesquita, Andrea Cercan

2002-01-01

The aim of this work is the synthesis and characterization of the poly(vinyl acetate) using the ionizing radiation. Six polymerizations of vinyl acetate were carried out using three techniques of polymerization: in bulk, emulsion and solution. In the technique of solution polymerization were used two solvents, the alcohol ethyl and the methylethylketone, in two proportions 1:0.5 and 1:1 related to the monomer. The solutions were irradiated with gamma rays from a 60 Co source, with dose rate between 5.25 kGy/h and 6.26 kGy/h. The polymers obtained were characterized by Fourier Transform Infrared Spectroscopy (FTIR). The glass transition temperature (Tg) was investigated by Differential Scanning Calorimeter (DSC). The molecular weight was analyzed by the technique of Gel Permeation Chromatography (GPC). Tests of density, hardness and Vicat softening temperature were carried out. The infrared spectroscopy and others results confirmed that the polymers obtained by polymerization of vinyl acetate in bulk, emulsion and solution, using ionizing radiation, really correspond at poly(vinyl acetate). (author)

Multiple ionization effects in M X-ray emission induced by heavy ions

International Nuclear Information System (INIS)

Wang, Xing; Zhao, Yongtao; Cheng, Rui; Zhou, Xianming; Xu, Ge; Sun, Yuanbo; Lei, Yu; Wang, Yuyu; Ren, Jieru; Yu, Yang; Li, Yongfeng; Zhang, Xiaoan; Li, Yaozong; Liang, Changhui; Xiao, Guoqing

2012-01-01

M-shell ionization of tungsten by Ar 12+ ions were investigated in the energy range of 1.2–3.0 MeV. The measurements were also implemented for H, He and Xe ions as a comparative study. A significant shift of the M X-ray lines to the higher energy side caused by multiple ionizations, which was verified by the analysis of the intensity ratios of M γ and M αβ , was observed. The total experimental cross sections of tungsten were compared with the PWBA and ECPSSR theoretical predictions, which are based on two extreme assumptions, namely, single ionization and full ionization. -- Highlights: ► Projectiles with low velocity (near Bohr velocity). ► A significant shift of the M X-ray lines to the higher energy side. ► A large enhancement in the M 3 fluorescence yield. ► Theoretical predictions based on single ionization and full ionization.

Highly ionized physical vapor deposition plasma source working at very low pressure

Science.gov (United States)

Stranak, V.; Herrendorf, A.-P.; Drache, S.; Cada, M.; Hubicka, Z.; Tichy, M.; Hippler, R.

2012-04-01

Highly ionized discharge for physical vapor deposition at very low pressure is presented in the paper. The discharge is generated by electron cyclotron wave resonance (ECWR) which assists with ignition of high power impulse magnetron sputtering (HiPIMS) discharge. The magnetron gun (with Ti target) was built into the single-turn coil RF electrode of the ECWR facility. ECWR assistance provides pre-ionization effect which allows significant reduction of pressure during HiPIMS operation down to p = 0.05 Pa; this is nearly more than an order of magnitude lower than at typical pressure ranges of HiPIMS discharges. We can confirm that nearly all sputtered particles are ionized (only Ti+ and Ti++ peaks are observed in the mass scan spectra). This corresponds well with high plasma density ne ˜ 1018 m-3, measured during the HiPIMS pulse.

Highly ionized physical vapor deposition plasma source working at very low pressure

International Nuclear Information System (INIS)

Stranak, V.; Herrendorf, A.-P.; Drache, S.; Hippler, R.; Cada, M.; Hubicka, Z.; Tichy, M.

2012-01-01

Highly ionized discharge for physical vapor deposition at very low pressure is presented in the paper. The discharge is generated by electron cyclotron wave resonance (ECWR) which assists with ignition of high power impulse magnetron sputtering (HiPIMS) discharge. The magnetron gun (with Ti target) was built into the single-turn coil RF electrode of the ECWR facility. ECWR assistance provides pre-ionization effect which allows significant reduction of pressure during HiPIMS operation down to p = 0.05 Pa; this is nearly more than an order of magnitude lower than at typical pressure ranges of HiPIMS discharges. We can confirm that nearly all sputtered particles are ionized (only Ti + and Ti ++ peaks are observed in the mass scan spectra). This corresponds well with high plasma density n e ∼ 10 18 m -3 , measured during the HiPIMS pulse.

Application of soft x-ray laser interferometry to study large-scale-length, high-density plasmas

International Nuclear Information System (INIS)

Wan, A.S.; Barbee, T.W., Jr.; Cauble, R.

1996-01-01

We have employed a Mach-Zehnder interferometer, using a Ne-like Y x- ray laser at 155 Angstrom as the probe source, to study large-scale- length, high-density colliding plasmas and exploding foils. The measured density profile of counter-streaming high-density colliding plasmas falls in between the calculated profiles using collisionless and fluid approximations with the radiation hydrodynamic code LASNEX. We have also performed simultaneous measured the local gain and electron density of Y x-ray laser amplifier. Measured gains in the amplifier were found to be between 10 and 20 cm -1 , similar to predictions and indicating that refraction is the major cause of signal loss in long line focus lasers. Images showed that high gain was produced in spots with dimensions of ∼ 10 μm, which we believe is caused by intensity variations in the optical drive laser. Measured density variations were smooth on the 10-μm scale so that temperature variations were likely the cause of the localized gain regions. We are now using the interferometry technique as a mechanism to validate and benchmark our numerical codes used for the design and analysis of high-energy-density physics experiments. 11 refs., 6 figs

The alteration of chromatin domains during damage repair induced by ionizing radiation

International Nuclear Information System (INIS)

Cress, A.E.; Olson, K.M.; Olson, G.B.

1995-01-01

Several groups previously have reported the ability of chromatin structure to influence the production of damage induced by ionizing radiation. The authors' interest has been to determine whether chromatin structural alterations exist after ionizing radiation during a repair interval. The earlier work investigated this question using biochemical techniques. The crosslinking of nuclear structural proteins to DNA after ionizing radiation was observed. In addition, they found that the chromatin structure in vitro as measured by sucrose density gradient sedimentation, was altered after ionizing radiation. These observations added to earlier studies in which digital imaging techniques showed an alteration in feulgen-positive DNA after irradiation prompted the present study. The object of this study was to detect whether the higher order structure of DNA into chromatin domains within interphase human cells was altered in interphase cells in response to a radiation induced damage. The present study takes advantage of the advances in the detection of chromatin domains in situ using DNA specific dyes and digital image processing of established human T and B cell lines

Nighttime ionization by energetic particles at Wallops Island in the altitude region 120 to 200 km

Science.gov (United States)

Voss, H. D.; Smith, L. G.

1979-01-01

Five Nike Apache rockets, each including an energetic particle spectrometer and an electron density-electron temperature experiment, have been launched from Wallops Island (L = 2.6) near midnight under varying geomagnetic conditions. On the most recent of these (5 January 1978) an additional spectrometer with a broom magnet, and a 391.4 nm photometer were flown. The data from this flight indicate that the energetic particle flux consists predominantly of protons, neutral hydrogen and possibly other energetic nuclei. The energy spectrum becomes much softer and the flux more intense with increasing Kp for 10-100 keV. The pitch angle distribution at 180 km is asymmetrical with a peak at 90 deg indicating that the majority of particles are near their mirroring altitude. Ionization rates are calculated based on the measured energy spectrum and mirror height distribution. The resulting ionization rate profile is found to be nearly constant with altitude in the region 120 to 200 km. The measured energetic particle flux and calculated ionization rate from the five flights are found to vary with magnetic activity (based on the Kp and Dst indexes) in the same way as the independently derived ionization rates deduced from the electron density profile.

Large, Tunable Magnetoresistance in Nonmagnetic III-V Nanowires.

Science.gov (United States)

Li, Sichao; Luo, Wei; Gu, Jiangjiang; Cheng, Xiang; Ye, Peide D; Wu, Yanqing

2015-12-09

Magnetoresistance, the modulation of resistance by magnetic fields, has been adopted and continues to evolve in many device applications including hard-disk, memory, and sensors. Magnetoresistance in nonmagnetic semiconductors has recently raised much attention and shows great potential due to its large magnitude that is comparable or even larger than magnetic materials. However, most of the previous work focus on two terminal devices with large dimensions, typically of micrometer scales, which severely limit their performance potential and more importantly, scalability in commercial applications. Here, we investigate magnetoresistance in the impact ionization region in InGaAs nanowires with 20 nm diameter and 40 nm gate length. The deeply scaled dimensions of these nanowires enable high sensibility with less power consumption. Moreover, in these three terminal devices, the magnitude of magnetoresistance can be tuned by the transverse electric field controlled by gate voltage. Large magnetoresistance between 100% at room temperature and 2000% at 4.3 K can be achieved at 2.5 T. These nanoscale devices with large magnetoresistance offer excellent opportunity for future high-density large-scale magneto-electric devices using top-down fabrication approaches, which are compatible with commercial silicon platform.

Characterization of reticulated vitreous carbon foam using a frisch-grid parallel-plate ionization chamber

Science.gov (United States)

Edwards, Nathaniel S.; Conley, Jerrod C.; Reichenberger, Michael A.; Nelson, Kyle A.; Tiner, Christopher N.; Hinson, Niklas J.; Ugorowski, Philip B.; Fronk, Ryan G.; McGregor, Douglas S.

2018-06-01

The propagation of electrons through several linear pore densities of reticulated vitreous carbon (RVC) foam was studied using a Frisch-grid parallel-plate ionization chamber pressurized to 1 psig of P-10 proportional gas. The operating voltages of the electrodes contained within the Frisch-grid parallel-plate ionization chamber were defined by measuring counting curves using a collimated 241Am alpha-particle source with and without a Frisch grid. RVC foam samples with linear pore densities of 5, 10, 20, 30, 45, 80, and 100 pores per linear inch were separately positioned between the cathode and anode. Pulse-height spectra and count rates from a collimated 241Am alpha-particle source positioned between the cathode and each RVC foam sample were measured and compared to a measurement without an RVC foam sample. The Frisch grid was positioned in between the RVC foam sample and the anode. The measured pulse-height spectra were indiscernible from background and resulted in negligible net count rates for all RVC foam samples. The Frisch grid parallel-plate ionization chamber measurement results indicate that electrons do not traverse the bulk of RVC foam and consequently do not produce a pulse.

Specific cationic emission of cisplatin following ionization by swift protons

International Nuclear Information System (INIS)

Moretto-Capelle, P.; Champeaux, J.P.; Deville, C.; Sence, M.; Cafarelli, P.

2016-01-01

We have investigated collision-induced ionization and fragmentation by 100 keV protons of the radio sensitizing molecule cisplatin, which is used in cancer treatments. A large emission of HCl"+ and NH_2"+ is observed, but surprisingly, no cationic fragments containing platinum are detected, in contrast to ionization-dissociation induced by electronic collision. Theoretical investigations show that the ionization processes take place on platinum and on chlorine atoms. We propose new ionization potentials for cisplatin. Dissociation limits corresponding to the measured fragmentation mass spectrum have been evaluated and the theoretical results show that the non-observed cationic fragments containing platinum are mostly associated with low dissociation energies. We have also investigated the reaction path for the hydrogen transfer from the NH_3 group to the Cl atom, as well as the corresponding dissociation limits from this tautomeric form. Here again the cations containing platinum correspond to lower dissociation limits. Thus, the experimental results suggest that excited states, probably formed via inner-shell ionization of the platinum atom of the molecule, correlated to higher dissociation limits are favored. (authors)

Specific cationic emission of cisplatin following ionization by swift protons

Science.gov (United States)

Moretto-Capelle, Patrick; Champeaux, Jean-Philippe; Deville, Charlotte; Sence, Martine; Cafarelli, Pierre

2016-05-01

We have investigated collision-induced ionization and fragmentation by 100 keV protons of the radio sensitizing molecule cisplatin, which is used in cancer treatments. A large emission of HCl+ and NH2+ is observed, but surprisingly, no cationic fragments containing platinum are detected, in contrast to ionization-dissociation induced by electronic collision. Theoretical investigations show that the ionization processes take place on platinum and on chlorine atoms. We propose new ionization potentials for cisplatin. Dissociation limits corresponding to the measured fragmentation mass spectrum have been evaluated and the theoretical results show that the non-observed cationic fragments containing platinum are mostly associated with low dissociation energies. We have also investigated the reaction path for the hydrogen transfer from the NH3 group to the Cl atom, as well as the corresponding dissociation limits from this tautomeric form. Here again the cations containing platinum correspond to lower dissociation limits. Thus, the experimental results suggest that excited states, probably formed via inner-shell ionization of the platinum atom of the molecule, correlated to higher dissociation limits are favored.

The effect of random matter density perturbations on the large mixing angle solution to the solar neutrino problem

Science.gov (United States)

Guzzo, M. M.; Holanda, P. C.; Reggiani, N.

2003-08-01

The neutrino energy spectrum observed in KamLAND is compatible with the predictions based on the Large Mixing Angle realization of the MSW (Mikheyev-Smirnov-Wolfenstein) mechanism, which provides the best solution to the solar neutrino anomaly. From the agreement between solar neutrino data and KamLAND observations, we can obtain the best fit values of the mixing angle and square difference mass. When doing the fitting of the MSW predictions to the solar neutrino data, it is assumed the solar matter do not have any kind of perturbations, that is, it is assumed the the matter density monothonically decays from the center to the surface of the Sun. There are reasons to believe, nevertheless, that the solar matter density fluctuates around the equilibrium profile. In this work, we analysed the effect on the Large Mixing Angle parameters when the density matter randomically fluctuates around the equilibrium profile, solving the evolution equation in this case. We find that, in the presence of these density perturbations, the best fit values of the mixing angle and the square difference mass assume smaller values, compared with the values obtained for the standard Large Mixing Angle Solution without noise. Considering this effect of the random perturbations, the lowest island of allowed region for KamLAND spectral data in the parameter space must be considered and we call it very-low region.

Large high current density superconducting solenoids for use in high energy physics experiments

International Nuclear Information System (INIS)

Green, M.A.; Eberhard, P.H.; Taylor, J.D.

1976-05-01

Very often the study of high energy physics in colliding beam storage-rings requires a large magnetic field volume in order to detect and analyze charged particles which are created from the collision of two particle beams. Large superconducting solenoids which are greater than 1 meter in diameter are required for this kind of physics. In many cases, interesting physics can be done outside the magnet coil, and this often requires that the amount of material in the magnet coil be minimized. As a result, these solenoids should have high current density (up to 10 9 A m -2 ) superconducting windings. The methods commonly used to stabilize large superconducting magnets cannot be employed because of this need to minimize the amount of material in the coils. A description is given of the Lawrence Berkeley Laboratory program for building and testing prototype solenoid magnets which are designed to operate at coil current densities in excess of 10 9 A m -2 with magnetic stored energies which are as high as 1.5 Megajoules per meter of solenoid length. The coils use intrinsically stable multifilament Nb--Ti superconductors. Control of the magnetic field quench is achieved by using a low resistance aluminum bore tube which is inductively coupled to the coil. The inner cryostat is replaced by a tubular cooling system which carries two phase liquid helium. The magnet coil, the cooling tubes, and aluminum bore tube are cast in epoxy to form a single unified magnet and cryogenic system which is about 2 centimeters thick. The results of the magnet coil tests are discussed

Numerical simulation of the ionization effects of low- and high-altitude nuclear explosions

International Nuclear Information System (INIS)

Zhao Zhengyu; Wang Xiang

2007-01-01

Low-altitude and high-altitude nuclear explosions are sources of intensive additional ionization in ionosphere. In this paper, in terms of the ionization equilibrium equation system and the equation of energy deposition of radiation in atmosphere, and considering the influence of atmosphere, the temporal and spatial distribution of ionization effects caused by atmospheric nuclear detonation are investigated. The calculated results show that the maximum of additional free electron density produced by low-altitude nuclear explosion is greater than that by the high-altitude nuclear burst. As to the influence of instant nuclear radiation, there is obvious difference between the low-altitude and the high-altitude explosions. The influence range and the continuance time caused by delayed nuclear radiation is less for the low-altitude nuclear detonation than that for the high-altitude one. (authors)

Ionization detector

International Nuclear Information System (INIS)

Solomon, E.E.

1980-01-01

A safe and reliable apparatus for detecting products of combustion and aerosols in the atmosphere was developed which uses a beta source. It is easy to adjust for optimum performance. The ionization detector comprises a double chamber; one of the chambers is the basic sensing chamber. The sensing chamber is ported to both the secondary chambers to account for slow ambient changes in the atmosphere outside of the chamber. The voltages from the ionization chamber are adjusted with electrodes in each chamber. The ionization chamber contains baffles to direct the air to be sensed as well as an electrostatic screen. A unique electronic circuit provides an inexpensive and reliable means for detecting the signal change which occurs in the ionization chamber. The decision level of the alarm circuit can be adjusted to allow for any desired sensitivity. (D.N.)

Effect of ionizing radiation on nanocomposites of high density polyethylene with pseudoboehmite obtained by sol-gel process

International Nuclear Information System (INIS)

Miranda, Leila F.; Munhoz Junior, Antonio H.; Terence, Mauro C.; Alves, Alexandre P.

2009-01-01

Nanocomposites are polymeric hybrid materials where inorganic substances of nanometric dimensions are dispersed in a polymeric matrix. The fillers present area of raised surface, promoting better dispersion in the polymeric matrix and therefore an improvement of the physical properties of the composite that depends on the homogeneity of the material. The nanocomposites preparation with polymeric matrix allows in many cases to find a relation enters a low cost, due to the use of minor amount of filler, and a raised performance level. Nanocomposites were obtained with pseudoboehmite synthesized by sol-gel process and high density polyethylene with different concentrations of pseudoboehmite. The aim of this work was to study the effects of ionizing radiation on the properties of the nanocomposites obtained. The nanocomposites were prepared by melt intercalation technique and subsequently, the samples were molded by injection, irradiated and submitted to thermal and mechanical tests. The mechanical properties (impact strength and tensile strength), temperature of thermal distortion (HDT) and Vicat softening temperature of the non irradiated and irradiated nanocomposites were determined. The irradiation doses were of 30, 50 and 100kGy in a gamma cell. The results showed an increase in the values of tensile strength; a decrease in the impact strength and an increase in the temperature of thermal distortion (HDT) evidencing the interaction of nanofiller with the polymeric matrix. (author)

Plasma density enhancements created by the ionization of the Earth's upper atmosphere by artificial electron beams

DEFF Research Database (Denmark)

Neubert, Torsten; Banks, P.M.

line) and down-going differential energy flux. The equations are solved numerically, using the MSIS atmospheric model and the IRI ionospheric model. The results from the model compare well with recent observations from the CHARGE 2 sounding rocket experiment. Two aspects of the beam-neutral atmosphere...... interaction are discussed: First we investigate the limits on the electron beam current that can be emitted from a space. craft without substantial spacecraft charging. This question is important because the charging of the spacecraft to positive potentials limits the current and the escape energy of the beam...... electrons and thereby limits the ionization of the neutral atmosphere. As an example we find from CHARGE 2 observations and from the model calculations that below about 180 km, secondary electrons generated through the ionization of the neutral atmosphere by 1-10 keV electron beams from sounding rockets...

Ionizing radiation in environment

International Nuclear Information System (INIS)

Jandl, J.; Petr, I.

1988-01-01

The basic terms are explained such as the atom, radioactivity, nuclear reaction, interaction of ionizing radiation with matter, etc. The basic dosimetric variables and units and properties of radionuclides and ionizing radiation are given. Natural and artificial sources of ionizing radiation are discussed with regard to the environment and the propagation and migration of radionuclides is described in the environment to man. The impact is explained of ionizing radiation on the cell and the somatic and genetic effects of radiation on man are outlined. Attention is devoted to protection against ionizing radiation and to radiation limits, also to the detection, dosimetry and monitoring of ionizing radiation in the environment. (M.D.). 92 figs., 40 tabs. 74 refs

Ionizing gas breakdown waves in strong electric fields.

Science.gov (United States)

Klingbeil, R.; Tidman, D. A.; Fernsler, R. F.

1972-01-01

A previous analysis by Albright and Tidman (1972) of the structure of an ionizing potential wave driven through a dense gas by a strong electric field is extended to include atomic structure details of the background atoms and radiative effects, especially, photoionization. It is found that photoionization plays an important role in avalanche propagation. Velocities, electron densities, and temperatures are presented as a function of electric field for both negative and positive breakdown waves in nitrogen.

A study of tungsten spectra using large helical device and compact electron beam ion trap in NIFS

Science.gov (United States)

Morita, S.; Dong, C. F.; Goto, M.; Kato, D.; Murakami, I.; Sakaue, H. A.; Hasuo, M.; Koike, F.; Nakamura, N.; Oishi, T.; Sasaki, A.; Wang, E. H.

2013-07-01

Tungsten spectra have been observed from Large Helical Device (LHD) and Compact electron Beam Ion Trap (CoBIT) in wavelength ranges of visible to EUV. The EUV spectra with unresolved transition array (UTA), e.g., 6g-4f, 5g-4f, 5f-4d and 5p-4d transitions for W+24-+33, measured from LHD plasmas are compared with those measured from CoBIT with monoenergetic electron beam (≤2keV). The tungsten spectra from LHD are well analyzed based on the knowledge from CoBIT tungsten spectra. The C-R model code has been developed to explain the UTA spectra in details. Radial profiles of EUV spectra from highly ionized tungsten ions have been measured and analyzed by impurity transport simulation code with ADPAK atomic database code to examine the ionization balance determined by ionization and recombination rate coefficients. As the first trial, analysis of the tungsten density in LHD plasmas is attempted from radial profile of Zn-like WXLV (W44+) 4p-4s transition at 60.9Å based on the emission rate coefficient calculated with HULLAC code. As a result, a total tungsten ion density of 3.5×1010cm-3 at the plasma center is reasonably obtained. In order to observe the spectra from tungsten ions in lower-ionized charge stages, which can give useful information on the tungsten influx in fusion plasmas, the ablation cloud of the impurity pellet is directly measured with visible spectroscopy. A lot of spectra from neutral and singly ionized tungsten are observed and some of them are identified. A magnetic forbidden line from highly ionized tungsten ions has been examined and Cd-like WXXVII (W26+) at 3893.7Å is identified as the ground-term fine-structure transition of 4f23H5-3H4. The possibility of α particle diagnostic in D-T burning plasmas using the magnetic forbidden line is discussed.

A study of tungsten spectra using large helical device and compact electron beam ion trap in NIFS

International Nuclear Information System (INIS)

Morita, S.; Goto, M.; Murakami, I.; Dong, C. F.; Kato, D.; Sakaue, H. A.; Oishi, T.; Hasuo, M.; Koike, F.; Nakamura, N.; Sasaki, A.; Wang, E. H.

2013-01-01

Tungsten spectra have been observed from Large Helical Device (LHD) and Compact electron Beam Ion Trap (CoBIT) in wavelength ranges of visible to EUV. The EUV spectra with unresolved transition array (UTA), e.g., 6g-4f, 5g-4f, 5f-4d and 5p-4d transitions for W +24-+33 , measured from LHD plasmas are compared with those measured from CoBIT with monoenergetic electron beam (≤2keV). The tungsten spectra from LHD are well analyzed based on the knowledge from CoBIT tungsten spectra. The C-R model code has been developed to explain the UTA spectra in details. Radial profiles of EUV spectra from highly ionized tungsten ions have been measured and analyzed by impurity transport simulation code with ADPAK atomic database code to examine the ionization balance determined by ionization and recombination rate coefficients. As the first trial, analysis of the tungsten density in LHD plasmas is attempted from radial profile of Zn-like WXLV (W 44+ ) 4p-4s transition at 60.9Å based on the emission rate coefficient calculated with HULLAC code. As a result, a total tungsten ion density of 3.5×10 10 cm −3 at the plasma center is reasonably obtained. In order to observe the spectra from tungsten ions in lower-ionized charge stages, which can give useful information on the tungsten influx in fusion plasmas, the ablation cloud of the impurity pellet is directly measured with visible spectroscopy. A lot of spectra from neutral and singly ionized tungsten are observed and some of them are identified. A magnetic forbidden line from highly ionized tungsten ions has been examined and Cd-like WXXVII (W 26+ ) at 3893.7Å is identified as the ground-term fine-structure transition of 4f 23 H 5 - 3 H 4 . The possibility of α particle diagnostic in D-T burning plasmas using the magnetic forbidden line is discussed

A study of tungsten spectra using large helical device and compact electron beam ion trap in NIFS

Energy Technology Data Exchange (ETDEWEB)

Morita, S.; Goto, M.; Murakami, I. [National Institute for Fusion Science, Toki 509-5292, Gifu (Japan); Department of Fusion Science, Graduate University for Advanced Studies, Toki 509-5292, Gifu (Japan); Dong, C. F.; Kato, D.; Sakaue, H. A.; Oishi, T. [National Institute for Fusion Science, Toki 509-5292, Gifu (Japan); Hasuo, M. [Department of Mechanical Engineering and Science, Graduate School of Engineering, Kyoto University, Kyoto 606-8501 (Japan); Koike, F. [Physics Laboratory, School of Medicine, Kitasato University, Sagamihara 252-0374 (Japan); Nakamura, N. [Institute of Laser Science, University of Electro-Communications, Tokyo 182-8585 (Japan); Sasaki, A. [Quantum Beam Science Directorate, Japan Atomic Energy Research Agency, Kizugawa 619-0215, Kyoto (Japan); Wang, E. H. [Department of Fusion Science, Graduate University for Advanced Studies, Toki 509-5292, Gifu (Japan)

2013-07-11

Tungsten spectra have been observed from Large Helical Device (LHD) and Compact electron Beam Ion Trap (CoBIT) in wavelength ranges of visible to EUV. The EUV spectra with unresolved transition array (UTA), e.g., 6g-4f, 5g-4f, 5f-4d and 5p-4d transitions for W{sup +24-+33}, measured from LHD plasmas are compared with those measured from CoBIT with monoenergetic electron beam ({<=}2keV). The tungsten spectra from LHD are well analyzed based on the knowledge from CoBIT tungsten spectra. The C-R model code has been developed to explain the UTA spectra in details. Radial profiles of EUV spectra from highly ionized tungsten ions have been measured and analyzed by impurity transport simulation code with ADPAK atomic database code to examine the ionization balance determined by ionization and recombination rate coefficients. As the first trial, analysis of the tungsten density in LHD plasmas is attempted from radial profile of Zn-like WXLV (W{sup 44+}) 4p-4s transition at 60.9A based on the emission rate coefficient calculated with HULLAC code. As a result, a total tungsten ion density of 3.5 Multiplication-Sign 10{sup 10}cm{sup -3} at the plasma center is reasonably obtained. In order to observe the spectra from tungsten ions in lower-ionized charge stages, which can give useful information on the tungsten influx in fusion plasmas, the ablation cloud of the impurity pellet is directly measured with visible spectroscopy. A lot of spectra from neutral and singly ionized tungsten are observed and some of them are identified. A magnetic forbidden line from highly ionized tungsten ions has been examined and Cd-like WXXVII (W{sup 26+}) at 3893.7A is identified as the ground-term fine-structure transition of 4f{sup 23}H{sub 5}-{sup 3}H{sub 4}. The possibility of {alpha} particle diagnostic in D-T burning plasmas using the magnetic forbidden line is discussed.

Battery-Powered RF Pre-Ionization System for the Caltech Magnetohydrodynamically-Driven Jet Experiment: RF Discharge Properties and MHD-Driven Jet Dynamics

Science.gov (United States)

Chaplin, Vernon H.

This thesis describes investigations of two classes of laboratory plasmas with rather different properties: partially ionized low pressure radiofrequency (RF) discharges, and fully ionized high density magnetohydrodynamically (MHD)-driven jets. An RF pre-ionization system was developed to enable neutral gas breakdown at lower pressures and create hotter, faster jets in the Caltech MHD-Driven Jet Experiment. The RF plasma source used a custom pulsed 3 kW 13.56 MHz RF power amplifier that was powered by AA batteries, allowing it to safely float at 4-6 kV with the cathode of the jet experiment. The argon RF discharge equilibrium and transport properties were analyzed, and novel jet dynamics were observed. Although the RF plasma source was conceived as a wave-heated helicon source, scaling measurements and numerical modeling showed that inductive coupling was the dominant energy input mechanism. A one-dimensional time-dependent fluid model was developed to quantitatively explain the expansion of the pre-ionized plasma into the jet experiment chamber. The plasma transitioned from an ionizing phase with depressed neutral emission to a recombining phase with enhanced emission during the course of the experiment, causing fast camera images to be a poor indicator of the density distribution. Under certain conditions, the total visible and infrared brightness and the downstream ion density both increased after the RF power was turned off. The time-dependent emission patterns were used for an indirect measurement of the neutral gas pressure. The low-mass jets formed with the aid of the pre-ionization system were extremely narrow and collimated near the electrodes, with peak density exceeding that of jets created without pre-ionization. The initial neutral gas distribution prior to plasma breakdown was found to be critical in determining the ultimate jet structure. The visible radius of the dense central jet column was several times narrower than the axial current channel

Track reconstruction in liquid hydrogen ionization chamber

International Nuclear Information System (INIS)

Balbekov, V.I.; Baranov, A.M.; Krasnokutski, R.N.; Perelygin, V.P.; Rasuvaev, E.A.; Shuvalov, R.S.; Zhigunov, V.P.; Lebedenko, V.N.; Stern, B.E.

1979-01-01

It is shown that particle track parameters can be reconstructed by the currents in the anode cells of the ionization chamber. The calculations are carried out for the chamber with 10 cm anode-cathode gap width. For simplicity a two-dimensional chamber model is used. To make the calculations simpler the charge density along the track is considered to be constant and equal to 10 4 electrons/mm. The drift velocity of electrons is assumed to be 5x10 6 cm/s. The anode is devided into cells 2 cm in width. The events in the chamber is defined with the coordinates X and Z of the event vertex, polar angles THETA of each track and track length l. The coordinates x, y and track angle THETA are reconstructed by currents with errors of up to millimetre and milliradian. The reconstruction errors are proportional to noise levels of electronics and also depend on the track geometry and argon purification. The energy resolution of the chamber is calculated for high energy electrons by means of computer program based on a Monter-Carlo method. The conclusion is made that the energy resolution depends on the gap width as a square root. Two ways to solve the track reconstruction problem are considered: 1. the initial charge density is determined by measuring the charges induced in anode strips at some discrete moments of time; 2. the evaluation of the parameters ia made by traditional minimization technique. The second method is applicable only for a not very large number of hypothesis, but it is less time consuming

Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Analysis of Large Polymerases Chain Reaction Products

International Nuclear Information System (INIS)

Wunschel, David S.; Pasa Tolic, Ljiljana; Feng, Bingbing; Smith, Richard D.

2000-01-01

We have attempted to expand the size range of PCR products that can be analyzed by electroscopy ionization (ESI) Fourier transformion cyclotron resonance (FTICR) mass spectrometry. The mass measurement accuracy obtained illustrates that a signel base substitution could be identified at the size of PCR product with a 7 tesla ESI-FTICR

Large Eddy Simulations of Compositional Density Currents Flowing Over a Mobile Bed

Science.gov (United States)

Kyrousi, Foteini; Zordan, Jessica; Leonardi, Alessandro; Juez, Carmelo; Zanello, Francesca; Armenio, Vincenzo; Franca, Mário J.

2017-04-01

Density currents are a ubiquitous phenomenon caused by natural events or anthropogenic activities, and play an important role in the global sediment cycle; they are agents of long distance sediment transport in lakes, seas and oceans. Density gradients induced by salinity, temperature differences, or by the presence of suspended material are all possible triggers of a current. Such flows can travel long distances while eroding or depositing bed materials. This can provoke rapid topological changes, which makes the estimation of their transport capacity of prime interest for environmental engineering. Despite their relevance, field data regarding their dynamics is limited due to density currents scattered and unpredictable occurrence in nature. For this reason, laboratory experiments and numerical simulations have been a preferred way to investigate sediment transport processes associated to density currents. The study of entrainment and deposition processes requires detailed data of velocities spatial and temporal distributions in the boundary layer and bed shear stress, which are troublesome to obtain in laboratory. Motivated by this, we present 3D wall-resolved Large Eddy Simulations (LES) of density currents generated by lock-exchange. The currents travel over a smooth flat bed, which includes a section composed by erodible fine sediment susceptible of eroding. Several sediment sizes and initial density gradients are considered. The grid is set to resolve the velocity field within the boundary layer of the current (a tiny fraction of the total height), which in turn allows to obtain predictions of the bed shear stress. The numerical outcomes are compared with experimental data obtained with an analogous laboratory setting. In laboratory experiments salinity was chosen for generating the initial density gradient in order to facilitate the identification of entrained particles, since salt does not hinder the possibility to track suspended particles. Under these

The Influence of Non-Equilibrium Excitation on the Electron Density in One-Dimensional MFD Channel Flow

Energy Technology Data Exchange (ETDEWEB)

Eichert, K.; Kaeppeler, H. J. [Institut fuer Plasmaforschung der Technischen Hochschule Stuttgart, Federal Republic of Germany (Germany)

1966-10-15

In previous publications, a system of equations was derived from the gas-kinetic description of a multi-component reacting plasma and employed for the calculation of one-dimensional subsonic flows. This system is now extended to include non-equilibrium excitation. No thermal or chemical equilibrium between the various components of the plasma is assumed. The components of the plasma considered are a non-reacting working fluid, an alkali metal vapour as a seeding material, ions of this seeding substance, and electrons. Three levels for the excited states are introduced. The reactions considered are excitation and ionization by electron collisions, and photo-ionization, as well as the corresponding reverse processes. For the reaction velocities, analytical equations are introduced permitting insertion of any excitation or ionization cross-sections of either experimental or theoretical origin. The method employed had been previously suggested by one of the authors. As examples, the degrees of excitation and ionization in the flow of a helium working fluid with 1% caesium seeding through a channel against transverse magnetic fields of 15 and 40 kg at Mach numbers of 0.7 and 0.8, respectively, were calculated. The results of the calculations show that for relatively small magnetic fields there is no rapid rise of the ionization to Saha-equilibrium as a function of electron temperature. A comparison with the results of a calculation neglecting excitation shows that especially for relatively large magnetic fields non-equilibrium excitation has an essential influence on the electron density and its approach to equilibrium. Neglecting excitation, there results a nearly frozen behaviour of the degree of ionization within channel lengths of technical interest for small magnetic fields. (author)

Doubly resonant multiphoton ionization

International Nuclear Information System (INIS)

Crance, M.

1978-01-01

A particular case of doubly resonant multiphoton ionization is theoretically investigated. More precisely, two levels quasi-resonant with two successive harmonics of the field frequency are considered. The method used is based on the effective operator formalism first introduced for this problem by Armstrong, Beers and Feneuille. The main result is to show the possibility of observing large interference effects on the width of the resonances. Moreover this treatment allows us to make more precise the connection between effective operator formalism and standard perturbation theory

Study of the ionization of sodium vapor in the presence of resonant laser radiation

International Nuclear Information System (INIS)

Carre, B.

1986-06-01

Ionization of a diffuse sodium jet, excited by laser radiation (D2 resonance), either continuous or pulsed, is studied by electron spectroscopy. Results show: associative ionization (AI) in the collision of two Na(3p) excited atoms; occupancy of highly excited nl states in energy association collisions of two Na(3p) followed by Penning collisional ionization (CI) in the system Na(nl) + Na(3p); heating of electrons by 1, 2, or 3 superelastic collisions with Na(3p). For both the excitation cases (continuous or pulsed source) analysis of experiment results leads to a description of the whole of the ionized medium, characterized as being low density and the site of the ambipolar diffusion of charged particles. A highly simplified model describes the kinetic and electrokinetic equilibrium (continuous case) in which the different populations of distinct nonthermalized energy (low energy primary electrons, hot electrons) play specific roles. The cross sections associated with AI and CI are estimated from experiment results using the model [fr

Measurements of ion velocity separation and ionization in multi-species plasma shocks

Science.gov (United States)

Rinderknecht, Hans G.; Park, H.-S.; Ross, J. S.; Amendt, P. A.; Wilks, S. C.; Katz, J.; Hoffman, N. M.; Kagan, G.; Vold, E. L.; Keenan, B. D.; Simakov, A. N.; Chacón, L.

2018-05-01

The ion velocity structure of a strong collisional shock front in a plasma with multiple ion species is directly probed in laser-driven shock-tube experiments. Thomson scattering of a 263.25 nm probe beam is used to diagnose ion composition, temperature, and flow velocity in strong shocks ( M ˜6 ) propagating through low-density ( ρ˜0.1 mg/cc) plasmas composed of mixtures of hydrogen (98%) and neon (2%). Within the preheat region of the shock front, two velocity populations of ions are observed, a characteristic feature of strong plasma shocks. The ionization state of the Ne is observed to change within the shock front, demonstrating an ionization-timescale effect on the shock front structure. The forward-streaming proton feature is shown to be unexpectedly cool compared to predictions from ion Fokker-Planck simulations; the neon ionization gradient is evaluated as a possible cause.

Enhancement of phase space density by increasing trap anisotropy in a magneto-optical trap with a large number of atoms

International Nuclear Information System (INIS)

Vengalattore, M.; Conroy, R.S.; Prentiss, M.G.

2004-01-01

The phase space density of dense, cylindrical clouds of atoms in a 2D magneto-optic trap is investigated. For a large number of trapped atoms (>10 8 ), the density of a spherical cloud is limited by photon reabsorption. However, as the atom cloud is deformed to reduce the radial optical density, the temperature of the atoms decreases due to the suppression of multiple scattering leading to an increase in the phase space density. A density of 2x10 -4 has been achieved in a magneto-optic trap containing 2x10 8 atoms

IONIZATION IN ATMOSPHERES OF BROWN DWARFS AND EXTRASOLAR PLANETS. V. ALFVÉN IONIZATION

International Nuclear Information System (INIS)

Stark, C. R.; Helling, Ch.; Rimmer, P. B.; Diver, D. A.

2013-01-01

Observations of continuous radio and sporadic X-ray emission from low-mass objects suggest they harbor localized plasmas in their atmospheric environments. For low-mass objects, the degree of thermal ionization is insufficient to qualify the ionized component as a plasma, posing the question: what ionization processes can efficiently produce the required plasma that is the source of the radiation? We propose Alfvén ionization as a mechanism for producing localized pockets of ionized gas in the atmosphere, having sufficient degrees of ionization (≥10 –7 ) that they constitute plasmas. We outline the criteria required for Alfvén ionization and demonstrate its applicability in the atmospheres of low-mass objects such as giant gas planets, brown dwarfs, and M dwarfs with both solar and sub-solar metallicities. We find that Alfvén ionization is most efficient at mid to low atmospheric pressures where a seed plasma is easier to magnetize and the pressure gradients needed to drive the required neutral flows are the smallest. For the model atmospheres considered, our results show that degrees of ionization of 10 –6 -1 can be obtained as a result of Alfvén ionization. Observable consequences include continuum bremsstrahlung emission, superimposed with spectral lines from the plasma ion species (e.g., He, Mg, H 2 , or CO lines). Forbidden lines are also expected from the metastable population. The presence of an atmospheric plasma opens the door to a multitude of plasma and chemical processes not yet considered in current atmospheric models. The occurrence of Alfvén ionization may also be applicable to other astrophysical environments such as protoplanetary disks

Ionization and photofragmentation of Ru3(CO)12 and Os3(CO)12

International Nuclear Information System (INIS)

Schalk, Oliver; Josefsson, Ida; Odelius, Michael; Richter, Robert; Prince, Kevin C.; Mucke, Melanie

2015-01-01

In this paper, we use a combination of photoelectron spectroscopy, mass spectrometry, and density functional theory calculations to get a detailed understanding of valence single and double ionization and the subsequent dissociation processes. This is exemplified on benchmark systems, trimetallo-dodecacarbonyls M 3 (CO) 12 with M = Ru, Os, where the energy remaining in the molecule after photoionization can be retrieved by measuring the degree of fragmentation of the molecular ion. The intensity of different mass peaks can thus be directly related to ionization cross sections obtained by photoelectron spectroscopy. We find that the M—CO dissociation energy rises as the number of CO ligands decreases due to dissociation. Moreover, ionization of the CO ligands has a higher cross section than that of the metal center for both single and double ionization. After advanced fragmentation, a CO bond can break and the carbon atom remains bonded to the metal core. In addition, we found that the valence ionization cross sections of M 3 (CO) 12 are maximal at about 40 eV photon energy thus showing a more pronounced shape resonance than Ru and Os-complexes with a single metal atom center. Finally, an np → nd giant resonance absorption causes a significant increase of the ionization cross section above 50 eV for Ru 3 (CO) 12

Hole dynamics and spin currents after ionization in strong circularly polarized laser fields

International Nuclear Information System (INIS)

Barth, Ingo; Smirnova, Olga

2014-01-01

We apply the time-dependent analytical R-matrix theory to develop a movie of hole motion in a Kr atom upon ionization by strong circularly polarized field. We find rich hole dynamics, ranging from rotation to swinging motion. The motion of the hole depends on the final energy and the spin of the photoelectron and can be controlled by the laser frequency and intensity. Crucially, hole rotation is a purely non-adiabatic effect, completely missing in the framework of quasistatic (adiabatic) tunneling theories. We explore the possibility to use hole rotation as a clock for measuring ionization time. Analyzing the relationship between the relative phases in different ionization channels we show that in the case of short-range electron-core interaction the hole is always initially aligned along the instantaneous direction of the laser field, signifying zero delays in ionization. Finally, we show that strong-field ionization in circular fields creates spin currents (i.e. different flow of spin-up and spin-down density in space) in the ions. This phenomenon is intimately related to the production of spin-polarized electrons in strong laser fields Barth and Smirnova (2013 Phys. Rev. A 88 013401). We demonstrate that rich spin dynamics of electrons and holes produced during strong field ionization can occur in typical experimental conditions and does not require relativistic intensities or strong magnetic fields. (paper)

The Pulsed High Density Experiment (PHDX) Final Report

Energy Technology Data Exchange (ETDEWEB)

Slough, John P. [Univ. of Washington, Seattle, WA (United States); Andreason, Samuel [Univ. of Washington, Seattle, WA (United States)

2017-04-27

The purpose of this paper is to present the conclusions that can be drawn from the Field Reversed Configuration (FRC) formation experiments conducted on the Pulsed High Density experiment (PHD) at the University of Washington. The experiment is ongoing. The experimental goal for this first stage of PHD was to generate a stable, high flux (>10 mWb), high energy (>10 KJ) target FRC. Such results would be adequate as a starting point for several later experiments. This work focuses on experimental implementation and the results of the first four month run. Difficulties were encountered due to the initial on-axis plasma ionization source. Flux trapping with this ionization source acting alone was insufficient to accomplish experimental objectives. Additional ionization methods were utilized to overcome this difficulty. A more ideal plasma source layout is suggested and will be explored during a forthcoming work.

Biological Effects of Ionizing Radiation

Science.gov (United States)

Ingram, M.; Mason, W. B.; Whipple, G. H.; Howland, J. W.

1952-04-07

This report presents a review of present knowledge and concepts of the biological effects of ionizing radiations. Among the topics discussed are the physical and chemical effects of ionizing radiation on biological systems, morphological and physiological changes observed in biological systems subjected to ionizing radiations, physiological changes in the intact animal, latent changes following exposure of biological systems to ionizing radiations, factors influencing the biological response to ionizing radiation, relative effects of various ionizing radiations, and biological dosimetry.

Ionization chambers

International Nuclear Information System (INIS)

Boag, J.W.

1987-01-01

Although a variety of solid-state and chemical methods for measuring radiation dose have been developed in recent decades and calorimetry can now provide an absolute standard of reference, ionization dosimetry retains its position as the most widely used, most convenient, and, in most situations, most accurate method of measuring either exposure or absorbed dose. The ionization chamber itself is the central element in this system of dosimetry. In this chapter the principles governing the construction and operation of ionization chambers of various types are examined. Since the ionization chambers now in general use are nearly all of commercial manufacture, the emphasis is on operating characteristics and interpretation of measurements rather than on details of construction, although some knowledge of the latter is often required when applying necessary corrections to the measured quantities. Examples are given of the construction of typical chambers designed for particular purposes, and the methods of calibrating them are discussed

Electron density measurements during ion beam transport on Gamble II

International Nuclear Information System (INIS)

Weber, B.V.; Hinshelwood, D.D.; Neri, J.M.; Ottinger, P.F.; Rose, D.V.; Stephanakis, S.J.; Young, F.C.

1999-01-01

High-sensitivity laser interferometry was used to measure the electron density created when an intense proton beam (100 kA, 1 MeV, 50 ns) from the Gamble II generator was transported through low-pressure gas as part of a project investigating Self-Pinched Transport (SPT) of intense ion beams. This measurement is non-perturbing and sufficiently quantitative to allow benchmarking of codes (particularly IPROP) used to model beam-gas interaction and ion-beam transport. Very high phase sensitivity is required for this measurement. For example, a 100-kA, 1-MeV, 10-cm-radius proton beam with uniform current density has a line-integrated proton density equal to n b L = 3 x 10 13 cm -2 . An equal electron line-density, n e L = n b L, (expected for transport in vacuum) will be detected as a phase shift of the 1.064 microm laser beam of only 0.05degree, or an optical path change of 1.4 x 10 -4 waves (about the size of a hydrogen atom). The time-history of the line-integrated electron density, measured across a diameter of the transport chamber at 43 cm from the input aperture, starts with the proton arrival time and decays differently depending on the gas pressure. The gas conditions included vacuum (10 -4 Torr air), 30 to 220 mTorr He, and 1 Torr air. The measured densities vary by three orders of magnitude, from 10 13 to 10 16 cm -2 for the range of gas pressures investigated. In vacuum, the measured electron densities indicate only co-moving electrons (n e L approximately n b L). In He, when the gas pressure is sufficient for ionization by beam particles and SPT is observed, n e L increases to about 10 n b L. At even higher pressures where electrons contribute to ionization, even higher electron densities are observed with an ionization fraction of about 2%. The diagnostic technique as used on the SPT experiment will be described and a summary of the results will be given. The measurements are in reasonable agreement with theoretical predictions from the IPROP code

Large thermoelectric efficiency of doped polythiophene junction: A density functional study

Science.gov (United States)

Golsanamlou, Zahra; Bagheri Tagani, Meysam; Rahimpour Soleimani, Hamid

2018-06-01

The thermoelectric properties of polythiophene (PT) coupled to the Au (111) electrodes are studied based on density functional theory with nonequilibrium Green function formalism. Specially, the effect of Li and Cl adsorbents on the thermoelectric efficiency of the PT junction is investigated in different concentrations of the dopants for two lengths of the PT. Results show that the presence of dopants can bring the structural changes in the oligomer and modify the arrangement of the molecular levels leading to the dramatic changes in the transmission spectra of the junction. Therefore, the large enhancement in thermopower and consequently figure of merit is obtained by dopants which makes the doped PT junction as a beneficial thermoelectric device.

Determination of Nerve Agent Metabolites by Ultraviolet Femtosecond Laser Ionization Mass Spectrometry.

Science.gov (United States)

Hamachi, Akifumi; Imasaka, Tomoko; Nakamura, Hiroshi; Li, Adan; Imasaka, Totaro

2017-05-02

Nerve agent metabolites, i.e., isopropyl methylphosphonic acid (IMPA) and pinacolyl methylphosphonic acid (PMPA), were derivatized by reacting them with 2,3,4,5,6-pentafluorobenzyl bromide (PFBBr) and were determined by mass spectrometry using an ultraviolet femtosecond laser emitting at 267 and 200 nm as the ionization source. The analytes of the derivatized compounds, i.e., IMPA-PFB and PMPA-PFB, contain a large side-chain, and molecular ions are very weak or absent in electron ionization mass spectrometry. The use of ultraviolet femtosecond laser ionization mass spectrometry, however, resulted in the formation of a molecular ion, even for compounds such as these that contain a highly bulky functional group. The signal intensity was larger at 200 nm due to resonance-enhanced two-photon ionization. In contrast, fragmentation was suppressed at 267 nm (nonresonant two-photon ionization) especially for PMPA-PFB, thus resulting in a lower background signal. This favorable result can be explained by the small excess energy in ionization at 267 nm and by the low-frequency vibrational mode of a bulky trimethylpropyl group in PMPA.

Ionization-potential depression and dynamical structure factor in dense plasmas

Science.gov (United States)

Lin, Chengliang; Röpke, Gerd; Kraeft, Wolf-Dietrich; Reinholz, Heidi

2017-07-01

The properties of a bound electron system immersed in a plasma environment are strongly modified by the surrounding plasma. The modification of an essential quantity, the ionization energy, is described by the electronic and ionic self-energies, including dynamical screening within the framework of the quantum statistical theory. Introducing the ionic dynamical structure factor as the indicator for the ionic microfield, we demonstrate that ionic correlations and fluctuations play a critical role in determining the ionization potential depression. This is, in particular, true for mixtures of different ions with large mass and charge asymmetry. The ionization potential depression is calculated for dense aluminum plasmas as well as for a CH plasma and compared to the experimental data and more phenomenological approaches used so far.

DRIVING TURBULENCE AND TRIGGERING STAR FORMATION BY IONIZING RADIATION

International Nuclear Information System (INIS)

Gritschneder, Matthias; Naab, Thorsten; Walch, Stefanie; Burkert, Andreas; Heitsch, Fabian

2009-01-01

We present high-resolution simulations on the impact of ionizing radiation of massive O stars on the surrounding turbulent interstellar medium (ISM). The simulations are performed with the newly developed software iVINE which combines ionization with smoothed particle hydrodynamics (SPH) and gravitational forces. We show that radiation from hot stars penetrates the ISM, efficiently heats cold low-density gas and amplifies overdensities seeded by the initial turbulence. The formation of observed pillar-like structures in star-forming regions (e.g. in M16) can be explained by this scenario. At the tip of the pillars gravitational collapse can be induced, eventually leading to the formation of low-mass stars. Detailed analysis of the evolution of the turbulence spectra shows that UV radiation of O stars indeed provides an excellent mechanism to sustain and even drive turbulence in the parental molecular cloud.

Ionization versus displacement damage effects in proton irradiated CMOS sensors manufactured in deep submicron process

International Nuclear Information System (INIS)

Goiffon, V.; Magnan, P.; Saint-Pe, O.; Bernard, F.; Rolland, G.

2009-01-01

Proton irradiation effects have been studied on CMOS image sensors manufactured in a 0.18μm technology dedicated to imaging. The ionizing dose and displacement damage effects were discriminated and localized thanks to 60 Co irradiations and large photodiode reverse current measurements. The only degradation observed was a photodiode dark current increase. It was found that ionizing dose effects dominate this rise by inducing generation centers at the interface between shallow trench isolations and depleted silicon regions. Displacement damages are is responsible for a large degradation of dark current non-uniformity. This work suggests that designing a photodiode tolerant to ionizing radiation can mitigate an important part of proton irradiation effects.

F--Ray: A new algorithm for efficient transport of ionizing radiation

Science.gov (United States)

Mao, Yi; Zhang, J.; Wandelt, B. D.; Shapiro, P. R.; Iliev, I. T.

2014-04-01

We present a new algorithm for the 3D transport of ionizing radiation, called F2-Ray (Fast Fourier Ray-tracing method). The transfer of ionizing radiation with long mean free path in diffuse intergalactic gas poses a special challenge to standard numerical methods which transport the radiation in position space. Standard methods usually trace each individual ray until it is fully absorbed by the intervening gas. If the mean free path is long, the computational cost and memory load are likely to be prohibitive. We have developed an algorithm that overcomes these limitations and is, therefore, significantly more efficient. The method calculates the transfer of radiation collectively, using the Fast Fourier Transform to convert radiation between position and Fourier spaces, so the computational cost will not increase with the number of ionizing sources. The method also automatically combines parallel rays with the same frequency at the same grid cell, thereby minimizing the memory requirement. The method is explicitly photon-conserving, i.e. the depletion of ionizing photons is guaranteed to equal the photoionizations they caused, and explicitly obeys the periodic boundary condition, i.e. the escape of ionizing photons from one side of a simulation volume is guaranteed to be compensated by emitting the same amount of photons into the volume through the opposite side. Together, these features make it possible to numerically simulate the transfer of ionizing photons more efficiently than previous methods. Since ionizing radiation such as the X-ray is responsible for heating the intergalactic gas when first stars and quasars form at high redshifts, our method can be applied to simulate thermal distribution, in addition to cosmic reionization, in three-dimensional inhomogeneous cosmological density field.

Phase-field-based lattice Boltzmann modeling of large-density-ratio two-phase flows

Science.gov (United States)

Liang, Hong; Xu, Jiangrong; Chen, Jiangxing; Wang, Huili; Chai, Zhenhua; Shi, Baochang

2018-03-01

In this paper, we present a simple and accurate lattice Boltzmann (LB) model for immiscible two-phase flows, which is able to deal with large density contrasts. This model utilizes two LB equations, one of which is used to solve the conservative Allen-Cahn equation, and the other is adopted to solve the incompressible Navier-Stokes equations. A forcing distribution function is elaborately designed in the LB equation for the Navier-Stokes equations, which make it much simpler than the existing LB models. In addition, the proposed model can achieve superior numerical accuracy compared with previous Allen-Cahn type of LB models. Several benchmark two-phase problems, including static droplet, layered Poiseuille flow, and spinodal decomposition are simulated to validate the present LB model. It is found that the present model can achieve relatively small spurious velocity in the LB community, and the obtained numerical results also show good agreement with the analytical solutions or some available results. Lastly, we use the present model to investigate the droplet impact on a thin liquid film with a large density ratio of 1000 and the Reynolds number ranging from 20 to 500. The fascinating phenomena of droplet splashing is successfully reproduced by the present model and the numerically predicted spreading radius exhibits to obey the power law reported in the literature.

Spatially resolved spectroscopy analysis of the XMM-Newton large program on SN1006

Science.gov (United States)

Li, Jiang-Tao; Decourchelle, Anne; Miceli, Marco; Vink, Jacco; Bocchino, Fabrizio

2016-04-01

We perform analysis of the XMM-Newton large program on SN1006 based on our newly developed methods of spatially resolved spectroscopy analysis. We extract spectra from low and high resolution meshes. The former (3596 meshes) is used to roughly decompose the thermal and non-thermal components and characterize the spatial distributions of different parameters, such as temperature, abundances of different elements, ionization age, and electron density of the thermal component, as well as photon index and cutoff frequency of the non-thermal component. On the other hand, the low resolution meshes (583 meshes) focus on the interior region dominated by the thermal emission and have enough counts to well characterize the Si lines. We fit the spectra from the low resolution meshes with different models, in order to decompose the multiple plasma components at different thermal and ionization states and compare their spatial distributions. In this poster, we will present the initial results of this project.

The ionizing treatment of food

International Nuclear Information System (INIS)

1998-01-01

This book of proceedings contains the talks given by the members of the Society of chemical experts of France (SECF) and by various specialists of the ionizing treatment during the scientific days of September 25-26, 1997. The aim of this meeting was to reconsider the effects of ionization from a scientific point of view and apart from the polemics generated by this domain. The following topics were discussed successively: source and characterization of a ionizing treatment, biological effects of ionization on food and the expected consequences, the ionizing treatment and the reduction of the vitamin C content of fruits and vegetables, is it safe to eat irradiated food?, the organoleptic modifications of food after ionization, quality assurance of dosimetry measurements in an industrial installation of food ionization, the French and European regulations in food ionization, the detection of irradiated foodstuffs, processed food and complex lipid matrices, sterilization of dishes for immuno-depressed patients using ionization. (J.S.)

Large model-space calculation of the nuclear level density parameter

International Nuclear Information System (INIS)

Agrawal, B.K.; Samaddar, S.K.; De, J.N.; Shlomo, S.

1998-01-01

Recently, several attempts have been made to obtain nuclear level density (ρ) and level density parameter (α) within the microscopic approaches based on path integral representation of the partition function. The results for the inverse level density parameter K es and the level density as a function of excitation energy are presented

Preferential enrichment of large-sized very low density lipoprotein populations with transferred cholesteryl esters

International Nuclear Information System (INIS)

Eisenberg, S.

1985-01-01

The effect of lipid transfer proteins on the exchange and transfer of cholesteryl esters from rat plasma HDL2 to human very low (VLDL) and low density (LDL) lipoprotein populations was studied. The use of a combination of radiochemical and chemical methods allowed separate assessment of [ 3 H]cholesteryl ester exchange and of cholesteryl ester transfer. VLDL-I was the preferred acceptor for transferred cholesteryl esters, followed by VLDL-II and VLDL-III. LDL did not acquire cholesteryl esters. The contribution of exchange of [ 3 H]cholesteryl esters to total transfer was highest for LDL and decreased in reverse order along the VLDL density range. Inactivation of lecithin: cholesterol acyltransferase (LCAT) and heating the HDL2 for 60 min at 56 degrees C accelerated transfer and exchange of [ 3 H]cholesteryl esters. Addition of lipid transfer proteins increased cholesterol esterification in all systems. The data demonstrate that large-sized, triglyceride-rich VLDL particles are preferred acceptors for transferred cholesteryl esters. It is suggested that enrichment of very low density lipoproteins with cholesteryl esters reflects the triglyceride content of the particles

Elves and associated electron density changes due to cloud-to-ground and in-cloud lightning discharges

Science.gov (United States)

Marshall, R. A.; Inan, U. S.; Glukhov, V. S.

2010-04-01

A 3-D finite difference time domain model is used to simulate the lightning electromagnetic pulse (EMP) and its interaction with the lower ionosphere. Results agree with the frequently observed, doughnut-shaped optical signature of elves but show that the structure exhibits asymmetry due to the presence of Earth's ambient magnetic field. Furthermore, in-cloud (horizontal) lightning channels produce observable optical emissions without the doughnut shape and, in fact, produce a much stronger optical output for the same channel current. Electron density perturbations associated with elves are also calculated, with contributions from attachment and ionization. Results presented as a function of parameters such as magnetic field direction, dipole current orientation, altitude and amplitude, and ambient ionospheric density profile demonstrate the highly nonlinear nature of the EMP-ionosphere interaction. Ionospheric effects of a sequence of in-cloud discharges are calculated, simulating a burst of in-cloud lightning activity and resulting in large density changes in the overlying ionosphere.

Ionization Waves in a Fast, Hollow-Cathode-Assisted Capillary Discharge

International Nuclear Information System (INIS)

Rutkevich, I.; Mond, M.; Kaufman, Y.; Choi, P.; Favre, M.

1999-01-01

The initial, low-current stage of the evolution of a soft x-ray emitting, hollow-cathode-assisted capillary discharge initiated by a steep high-voltage pulse is investigated. The capillary is surrounded by a shield having the cathode potential. The mean electric field E of the order of 10 kV/cm and the low gas pressure (P<1Torr) provide conditions for extensive electron runaway. This is taken into account in the formulation of the theoretical approach by retaining the inertial terms in the momentum equation for the electrons. In addition, the ionization rate is calculated by considering the cross section for ionization by high-energy electrons. The two-dimensional system of the basic equations is reduced to a system of one-dimensional equations for the axial distributions of the physical quantities by introducing appropriate radial profiles of the electric potential, and the electron gas parameters and satisfying the electrodynamic boundary conditions at the capillary wall and at the shield. The resulting system of equations admits solutions in the form of stationary ionization waves transferring the anode potential to the cathode end. Numerical calculations of such solutions for argon show that the wave velocity V increases with the gas pressure P and with the density of initial electron beam ejected from the cathode hole ahead of the ionization front, while the dependence of V on the applied voltage is weak. At the instant when the virtual anode reaches the cathode hole, the plasma in the capillary is not yet fully ionized. The traverse time of the ionization wave along the capillary calculated for various gas pressures is in reasonable agreement with experimentally registered time delay for a high-current stage resulting in voltage collapse and soft x-ray emission

'Saddle-point' ionization

International Nuclear Information System (INIS)

Gay, T.J.; Hale, E.B.; Irby, V.D.; Olson, R.E.; Missouri Univ., Rolla; Berry, H.G.

1988-01-01

We have studied the ionization of rare gases by protons at intermediate energies, i.e., energies at which the velocities of the proton and the target-gas valence electrons are comparable. A significant channel for electron production in the forward direction is shown to be 'saddle-point' ionization, in which electrons are stranded on or near the saddle-point of electric potential between the receding projectile and the ionized target. Such electrons yield characteristic energy spectra, and contribute significantly to forward-electron-production cross sections. Classical trajectory Monte Carlo calculations are found to provide qualitative agreement with our measurements and the earlier measurements of Rudd and coworkers, and reproduce, in detail, the features of the general ionization spectra. (orig.)

Heating and ionization in MHD shock waves propagating into partially ionized plasma

International Nuclear Information System (INIS)

Bighel, L.; Collins, A.R.; Cramer, N.F.; Watson-Munro, C.N.

1975-09-01

A model of the structure of MHD switch-on shocks propagating in a partially ionized plasma, in which the primary dissipation mechanism is friction between ions and neutrals, is here compared favourably with experimental results. Four degrees of upstream ionization were studied, ranging from almost complete to very small ionization. (author)

Heating and ionization in MHD shock wave propagating into partially ionized plasma

International Nuclear Information System (INIS)

Bighel, L.; Collins, A.R.; Cramer, N.F.; Watson-Munro, C.N.

1975-09-01

A model of the structure of MHD switch-on shocks propagating in a partially ionized plasma, in which the primary dissipation mechanism is friction between ions and neutrals, is here compared favourably with experimental results. Four degrees of upstream ionization were studied, ranging from almost complete to very small ionization. (author)

Five-photon ionization of atomic hydrogen at wavelengths around the threshold for four-photon ionization

International Nuclear Information System (INIS)

Gontier, Y.; Trahin, M.; Wolff-Rottke, B.; Rottke, H.; Welge, K.H.; Feldmann, D.

1992-01-01

Theoretical and experimental studies show the strong influence of the three-photon nearly resonant 2p state on four- and five-photon ionization of atomic hydrogen near the threshold for four-photon ionization. Changes in five-photon ionization occur when the four-photon ionization channel opens. The angular distributions of photoelectrons from five-photon ionization of H are studied at five wavelengths which cover the range from four-photon resonance with high-lying Rydberg states (n≥10) to direct four-photon ionization into the continuum. The role of resonances in this ionization process is discussed. A fair agreement is found in comparing experimental and theoretical results

Equipment for handling ionization chamber

International Nuclear Information System (INIS)

Altmann, J.

1988-01-01

The device consists of an ionization channel with an ionization chamber, of a support ring, axial and radial bearings, a sleeve, a screw gear and an electric motor. The ionization chamber is freely placed on the bottom of the ionization channel. The bottom part of the channel deviates from the vertical axis. The support ring propped against the axial bearing in the sleeve is firmly fixed to the top part of the ionization channel. The sleeve is fixed to the reactor lid. Its bottom part is provided with a recess for the radial bearing which is propped against a screw wheel firmly connected to the ionization channel. In measuring neutron flux, the screw wheel is rotated by the motor, thus rotating the whole ionization channel such that the ionization chamber is displaced into the reactor core.(J.B.). 1 fig

Foodstuffs preservation by ionization

International Nuclear Information System (INIS)

1991-12-01

This document contains all the papers presented at the meeting on foodstuffs preservation by ionization. These papers deal especially with the food ionization process, its development and the view of the food industry on ionization. Refs and figs (F.M.)

Impact ionization dynamics in silicon by MV/cm THz fields

DEFF Research Database (Denmark)

Tarekegne, Abebe Tilahun; Hirori, Hideki; Tanaka, Koichiro

2017-01-01

We investigate the dynamics of the impact ionization (IMI) process in silicon in extremely high fields in the MV/cm range and at low initial carrier concentrations; conditions that are not accessible with conventional transport measurements. We use ultrafast measurements with high-intensity terah......We investigate the dynamics of the impact ionization (IMI) process in silicon in extremely high fields in the MV/cm range and at low initial carrier concentrations; conditions that are not accessible with conventional transport measurements. We use ultrafast measurements with high......-intensity terahertz pulses to show that IMI is significantly more efficient at lower than at higher initial carrier densities. Specifically, in the case of silicon with an intrinsic carrier concentration (∼1010 cm−3), the carrier multiplication process can generate more than 108 electrons from just a single free...

Ambient ionization mass spectrometry: A tutorial

Energy Technology Data Exchange (ETDEWEB)

Huang, Min-Zong; Cheng, Sy-Chi; Cho, Yi-Tzu [Department of Chemistry, National Sun Yat-Sen University, Kaohsiung, Taiwan (China); Shiea, Jentaie, E-mail: jetea@fac.nsysu.edu.tw [Department of Chemistry, National Sun Yat-Sen University, Kaohsiung, Taiwan (China); Cancer Center, Kaohsiung Medical University, Kaohsiung, Taiwan (China)

2011-09-19

Highlights: {yields} Ambient ionization technique allows the direct analysis of sample surfaces with little or no sample pretreatment. {yields} We sort ambient ionization techniques into three main analytical strategies, direct ionization, direct desorption/ionization, and two-step ionization. {yields} The underlying principles of operation, ionization processes, detecting mass ranges, sensitivity, and representative applications of these techniques are described and compared. - Abstract: Ambient ionization is a set of mass spectrometric ionization techniques performed under ambient conditions that allows the direct analysis of sample surfaces with little or no sample pretreatment. Using combinations of different types of sample introduction systems and ionization methods, several novel techniques have been developed over the last few years with many applications (e.g., food safety screening; detection of pharmaceuticals and drug abuse; monitoring of environmental pollutants; detection of explosives for antiterrorism and forensics; characterization of biological compounds for proteomics and metabolomics; molecular imaging analysis; and monitoring chemical and biochemical reactions). Electrospray ionization and atmospheric pressure chemical ionization are the two main ionization principles most commonly used in ambient ionization mass spectrometry. This tutorial paper provides a review of the publications related to ambient ionization techniques. We describe and compare the underlying principles of operation, ionization processes, detecting mass ranges, sensitivity, and representative applications of these techniques.

Ambient ionization mass spectrometry: A tutorial

International Nuclear Information System (INIS)

Huang, Min-Zong; Cheng, Sy-Chi; Cho, Yi-Tzu; Shiea, Jentaie

2011-01-01

Highlights: → Ambient ionization technique allows the direct analysis of sample surfaces with little or no sample pretreatment. → We sort ambient ionization techniques into three main analytical strategies, direct ionization, direct desorption/ionization, and two-step ionization. → The underlying principles of operation, ionization processes, detecting mass ranges, sensitivity, and representative applications of these techniques are described and compared. - Abstract: Ambient ionization is a set of mass spectrometric ionization techniques performed under ambient conditions that allows the direct analysis of sample surfaces with little or no sample pretreatment. Using combinations of different types of sample introduction systems and ionization methods, several novel techniques have been developed over the last few years with many applications (e.g., food safety screening; detection of pharmaceuticals and drug abuse; monitoring of environmental pollutants; detection of explosives for antiterrorism and forensics; characterization of biological compounds for proteomics and metabolomics; molecular imaging analysis; and monitoring chemical and biochemical reactions). Electrospray ionization and atmospheric pressure chemical ionization are the two main ionization principles most commonly used in ambient ionization mass spectrometry. This tutorial paper provides a review of the publications related to ambient ionization techniques. We describe and compare the underlying principles of operation, ionization processes, detecting mass ranges, sensitivity, and representative applications of these techniques.

Effect of negative ions on current growth and ionizing wave propagation in air

International Nuclear Information System (INIS)

Kline, L.E.

1975-01-01

The spatiotemporal development of electron and ion densities, electric fields, and luminosity are calculated for electron pulse experiments in overvolted parallel-plane gaps by numerically solving continuity equations together with Poisson's equation. Experimental coefficients for primary ionization, cathode photoemission, photoionization, and luminosity are used. Unambiguous determination of the coefficients for attachment, detachment, and charge transfer is not possible from available experimental results. Therefore, the calculations are repeated for three sets of coefficients for these processes, corresponding to the following assumptions: unstable negative ions, stable negative ions, and no negative ions. The results of the calculations show, in each case, that the electron pulse initiates an avalanche which grows exponentially until the onset of space-charge effects. The calculated growth rate is strongly affected by the assumed attachment, detachment, and charge-transfer coefficients. When the total number of electrons in the avalanche reaches approx.10 8 , anode- and cathode-directed ionizing waves, or streamers, develop from the avalanche and produce a weakly ionized filamentary plasma. The calculated ionizing wave velocities are strongly increasing functions of the space-charge--enhanced electric field within the waves and are insensitive to the assumed attachment, detachment, and charge-transfer coefficients. The numerically calculated ionizing wave velocities are in approximate agreement with a simple analytical theory

Fueling with edge recycling to high-density in DIII-D

Energy Technology Data Exchange (ETDEWEB)

Leonard, A.W., E-mail: leonard@fusion.gat.com [General Atomics, P.O. Box 85608, San Diego, CA 92186-5608 (United States); Elder, J.D. [University of Toronto Institute of Aerospace Studies, Toronto, Canada M3H 5T6 (Canada); Canik, J.M. [Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831 (United States); Groebner, R.J.; Osborne, T.H. [General Atomics, P.O. Box 85608, San Diego, CA 92186-5608 (United States)

2013-07-15

Pedestal fueling through edge recycling is examined with the interpretive OEDGE code for high-density discharges in DIII-D. A high current, high-density discharge is found to have a similar radial ion flux profile through the pedestal to a lower current, lower density discharge. The higher density discharge, however, has a greater density gradient indicating a pedestal particle diffusion coefficient that scales near linear with 1/I{sub p}. The time dependence of density profile is taken into account in the analysis of a discharge with low frequency ELMs. The time-dependent analysis indicates that the inferred neutral ionization source is inadequate to account for the increase in the density profile between ELMs, implying an inward density convection, or density pinch, near the top of the pedestal.

Spatiotemporal characterization of ionizing radiation induced DNA damage foci and their relation to chromatin organization

Energy Technology Data Exchange (ETDEWEB)

Costes, Sylvain V; Chiolo, Irene; Pluth, Janice M.; Barcellos-Hoff, Mary Helen; Jakob, Burkhard

2009-09-15

DNA damage sensing proteins have been shown to localize to the sites of DSB within seconds to minutes following ionizing radiation (IR) exposure, resulting in the formation of microscopically visible nuclear domains referred to as radiation-induced foci (RIF). This review characterizes the spatio-temporal properties of RIF at physiological doses, minutes to hours following exposure to ionizing radiation, and it proposes a model describing RIF formation and resolution as a function of radiation quality and nuclear densities. Discussion is limited to RIF formed by three interrelated proteins ATM (Ataxia telangiectasia mutated), 53BP1 (p53 binding protein 1) and ?H2AX (phosphorylated variant histone H2AX). Early post-IR, we propose that RIF mark chromatin reorganization, leading to a local nuclear scaffold rigid enough to keep broken DNA from diffusing away, but open enough to allow the repair machinery. We review data indicating clear kinetic and physical differences between RIF emerging from dense and uncondensed regions of the nucleus. At later time post-IR, we propose that persistent RIF observed days following exposure to ionizing radiation are nuclear ?scars? marking permanent disruption of the chromatin architecture. When DNA damage is resolved, such chromatin modifications should not necessarily lead to growth arrest and it has been shown that persistent RIF can replicate during mitosis. Thus, heritable persistent RIF spanning over tens of Mbp may affect the transcriptome of a large progeny of cells. This opens the door for a non DNA mutation-based mechanism of radiation-induced phenotypes.

Experiments with Highly-Ionized Atoms in Unitary Penning Traps

Directory of Open Access Journals (Sweden)

Shannon Fogwell Hoogerheide

2015-08-01

Full Text Available Highly-ionized atoms with special properties have been proposed for interesting applications, including potential candidates for a new generation of optical atomic clocks at the one part in 1019 level of precision, quantum information processing and tests of fundamental theory. The proposed atomic systems are largely unexplored. Recent developments at NIST are described, including the isolation of highly-ionized atoms at low energy in unitary Penning traps and the use of these traps for the precise measurement of radiative decay lifetimes (demonstrated with a forbidden transition in Kr17+, as well as for studying electron capture processes.

Spectral density of electron concentration fluctuations in ionospheric D region

International Nuclear Information System (INIS)

Martynenko, S.I.

1989-01-01

Expression for spectral density of electron concentration fluctuations in D-region with regard to the effect of ionization-recombination proceses and negative ions is obtained in terms of atmospheric turbulence model which obeys Kolmogorov-Obukhov 2/3 law

Ionization of food products

International Nuclear Information System (INIS)

Vasseur, J.P.

1991-01-01

After general remarks on foods preservation, on international works and on ionization future prospects, main irradiation sources are described. Recalls on radioactivity, on radiation-matter interaction, on toxicology of ionized foods and on ionized foods detection are given. Ionization applications to various products are reviewed, especially in: - Poultry meat - Fishing products - Fresh fruits and vegetables - Dry fruits and vegetables - spices, tea, infusion - prepacked products... An evaluation of economics and sociocultural impacts is presented in connection with recent experiments [fr

Ionization asymmetry effects on the properties modulation of atmospheric pressure dielectric barrier discharge sustained by tailored voltage waveforms

Science.gov (United States)

Zhang, Z. L.; Nie, Q. Y.; Zhang, X. N.; Wang, Z. B.; Kong, F. R.; Jiang, B. H.; Lim, J. W. M.

2018-04-01

The dielectric barrier discharge (DBD) is a promising technology to generate high density and uniform cold plasmas in atmospheric pressure gases. The effective independent tuning of key plasma parameters is quite important for both application-focused and fundamental studies. In this paper, based on a one-dimensional fluid model with semi-kinetics treatment, numerical studies of ionization asymmetry effects on the properties modulation of atmospheric DBD sustained by tailored voltage waveforms are reported. The driving voltage waveform is characterized by an asymmetric-slope fundamental sinusoidal radio frequency signal superimposing one or more harmonics, and the effects of the number of harmonics, phase shift, as well as the fluctuation of harmonics on the sheath dynamics, impact ionization of electrons and key plasma parameters are investigated. The results have shown that the electron density can exhibit a substantial increase due to the effective electron heating by a spatially asymmetric sheath structure. The strategic modulation of harmonics number and phase shift is capable of raising the electron density significantly (e.g., nearly three times in this case), but without a significant increase in the gas temperature. Moreover, by tailoring the fluctuation of harmonics with a steeper slope, a more profound efficiency in electron impact ionization can be achieved, and thus enhancing the electron density effectively. This method then enables a novel alternative approach to realize the independent control of the key plasma parameters under atmospheric pressure.

LUMINOUS RED GALAXY HALO DENSITY FIELD RECONSTRUCTION AND APPLICATION TO LARGE-SCALE STRUCTURE MEASUREMENTS

International Nuclear Information System (INIS)

Reid, Beth A.; Spergel, David N.; Bode, Paul

2009-01-01

The nontrivial relationship between observations of galaxy positions in redshift space and the underlying matter field complicates our ability to determine the linear theory power spectrum and extract cosmological information from galaxy surveys. The Sloan Digital Sky Survey (SDSS) luminous red galaxy (LRG) catalog has the potential to place powerful constraints on cosmological parameters. LRGs are bright, highly biased tracers of large-scale structure. However, because they are highly biased, the nonlinear contribution of satellite galaxies to the galaxy power spectrum is large and fingers-of-God (FOGs) are significant. The combination of these effects leads to a ∼10% correction in the underlying power spectrum at k = 0.1 h Mpc -1 and ∼40% correction at k = 0.2 h Mpc -1 in the LRG P(k) analysis of Tegmark et al., thereby compromising the cosmological constraints when this potentially large correction is left as a free parameter. We propose an alternative approach to recovering the matter field from galaxy observations. Our approach is to use halos rather than galaxies to trace the underlying mass distribution. We identify FOGs and replace each FOG with a single halo object. This removes the nonlinear contribution of satellite galaxies, the one-halo term. We test our method on a large set of high-fidelity mock SDSS LRG catalogs and find that the power spectrum of the reconstructed halo density field deviates from the underlying matter power spectrum at the ≤1% level for k ≤ 0.1 h Mpc -1 and ≤4% at k = 0.2 h Mpc -1 . The reconstructed halo density field also removes the bias in the measurement of the redshift space distortion parameter β induced by the FOG smearing of the linear redshift space distortions.

Direct evidence for radiative charge transfer after inner-shell excitation and ionization of large clusters

Science.gov (United States)

Hans, Andreas; Stumpf, Vasili; Holzapfel, Xaver; Wiegandt, Florian; Schmidt, Philipp; Ozga, Christian; Reiß, Philipp; Ben Ltaief, Ltaief; Küstner-Wetekam, Catmarna; Jahnke, Till; Ehresmann, Arno; Demekhin, Philipp V.; Gokhberg, Kirill; Knie, André

2018-01-01

We directly observe radiative charge transfer (RCT) in Ne clusters by dispersed vacuum-ultraviolet photon detection. The doubly ionized Ne2+-{{{N}}{{e}}}n-1 initial states of RCT are populated after resonant 1s-3p photoexcitation or 1s photoionization of Ne n clusters with ≈ 2800. These states relax further producing Ne+-Ne+-{{{N}}{{e}}}n-2 final states, and the RCT photon is emitted. Ab initio calculations assign the observed RCT signal to the{}{{{N}}{{e}}}2+(2{{{p}}}-2{[}1{{D}}]){--}{{{N}}{{e}}}n-1 initial state, while transitions from other possible initial states are proposed to be quenched by competing relaxation processes. The present results are in agreement with the commonly discussed scenario, where the doubly ionized atom in a noble gas cluster forms a dimer which dissipates its vibrational energy on a picosecond timescale. Our study complements the picture of the RCT process in weakly bound clusters, providing information which is inaccessible by charged particle detection techniques.

Quantum-mechanical predictions of DNA and RNA ionization by energetic proton beams.

Science.gov (United States)

Galassi, M E; Champion, C; Weck, P F; Rivarola, R D; Fojón, O; Hanssen, J

2012-04-07

Among the numerous constituents of eukaryotic cells, the DNA macromolecule is considered as the most important critical target for radiation-induced damages. However, up to now ion-induced collisions on DNA components remain scarcely approached and theoretical support is still lacking for describing the main ionizing processes. In this context, we here report a theoretical description of the proton-induced ionization of the DNA and RNA bases as well as the sugar-phosphate backbone. Two different quantum-mechanical models are proposed: the first one based on a continuum distorted wave-eikonal initial state treatment and the second perturbative one developed within the first Born approximation with correct boundary conditions (CB1). Besides, the molecular structure information of the biological targets studied here was determined by ab initio calculations with the Gaussian 09 software at the restricted Hartree-Fock level of theory with geometry optimization. Doubly, singly differential and total ionization cross sections also provided by the two models were compared for a large range of incident and ejection energies and a very good agreement was observed for all the configurations investigated. Finally, in comparison with the rare experiment, we have noted a large underestimation of the total ionization cross sections of uracil impacted by 80 keV protons,whereas a very good agreement was shown with the recently reported ionization cross sections for protons on adenine, at both the differential and the total scale.

Nonequilibrium response of an electron-mediated charge density wave ordered material to a large dc electric field

Science.gov (United States)

Matveev, O. P.; Shvaika, A. M.; Devereaux, T. P.; Freericks, J. K.

2016-01-01

Using the Kadanoff-Baym-Keldysh formalism, we employ nonequilibrium dynamical mean-field theory to exactly solve for the nonlinear response of an electron-mediated charge-density-wave-ordered material. We examine both the dc current and the order parameter of the conduction electrons as the ordered system is driven by the electric field. Although the formalism we develop applies to all models, for concreteness, we examine the charge-density-wave phase of the Falicov-Kimball model, which displays a number of anomalous behaviors including the appearance of subgap density of states as the temperature increases. These subgap states should have a significant impact on transport properties, particularly the nonlinear response of the system to a large dc electric field.

A Si IV/O IV Electron Density Diagnostic for the Analysis of IRIS Solar Spectra

Science.gov (United States)

Young, P. R.; Keenan, F. P.; Milligan, R. O.; Peter, H.

2018-04-01

Solar spectra of ultraviolet bursts and flare ribbons from the Interface Region Imaging Spectrograph (IRIS) have suggested high electron densities of > {10}12 cm‑3 at transition region temperatures of 0.1 MK, based on large intensity ratios of Si IV λ1402.77 to O IV λ1401.16. In this work, a rare observation of the weak O IV λ1343.51 line is reported from an X-class flare that peaked at 21:41 UT on 2014 October 24. This line is used to develop a theoretical prediction of the Si IV λ1402.77 to O IV λ1401.16 ratio as a function of density that is recommended to be used in the high-density regime. The method makes use of new pressure-dependent ionization fractions that take account of the suppression of dielectronic recombination at high densities. It is applied to two sequences of flare kernel observations from the October 24 flare. The first shows densities that vary between 3× {10}12 and 3× {10}13 cm‑3 over a seven-minute period, while the second location shows stable density values of around 2× {10}12 cm‑3 over a three-minute period.

Effect of Thermospheric Neutral Density upon Inner Trapped-belt Proton Flux

Science.gov (United States)

Wilson, Thomas L.; Lodhi, M. A. K.; Diaz, Abel B.

2007-01-01

We wish to point out that a secular change in the Earth's atmospheric neutral density alters charged-particle lifetime in the inner trapped radiation belts, in addition to the changes recently reported as produced by greenhouse gases. Heretofore, changes in neutral density have been of interest primarily because of their effect on the orbital drag of satellites. We extend this to include the orbital lifetime of charged particles in the lower radiation belts. It is known that the charged-belt population is coupled to the neutral density of the atmosphere through changes induced by solar activity, an effect produced by multiple scattering off neutral and ionized atoms along with ionization loss in the thermosphere where charged and neutral populations interact. It will be shown here that trapped-belt flux J is bivariant in energy E and thermospheric neutral density , as J(E,rho). One can conclude that proton lifetimes in these belts are also directly affected by secular changes in the neutral species populating the Earth s thermosphere. This result is a consequence of an intrinsic property of charged-particle flux, that flux is not merely a function of E but is dependent upon density rho when a background of neutrals is present.

Investigation of the Hall MHD channel operating with the ionized instable plasma of inert gases

International Nuclear Information System (INIS)

Vasi'leva, R.V.; D'yakova, E.A.; Erofeev, A.V.; Zuev, A.D.; Lapushkina, T.A.; Markhotok, A.A.

1997-01-01

Possibility of applying ionization-instable plasma of pure inert gases as perspective working substance for closed-cycle MHD generators is studied. The experiment was produced in the model of the disk Hall MHD channel. The ionized gas flux was produced in a shock tube. Xenon was used as a working substance. Gas pressure, flux velocity, electron concentration and temperature, azimuthal current density, potential distribution in the channel and near-electrode voltage drop values were measured in the experiment. Volt-ampere characteristics were taken by various indices of magnetic field and load resistance

Chemical data on ionizing and non-ionizing angiographic contrast materials

International Nuclear Information System (INIS)

Bonati, F.

1980-01-01

The cardiovascular effects of ionizing and non-ionizing contrast media are compared in experimental animals and in isolated heart preparations. The following parameters were recorded: peripheric arterial diastolic pressure, heart rate, duration of asystolic period, respiratory rate, contractility of the myocardium (dp/dt, LVSP, Vsub(max), EDV, ESV, SV). The observed changes are mainly due to the higher osmotic activity of the contrast media, as similar alterations were recorded after the injection of hyperosmotic glucose solution. It is concluded that administration of non-ionizing contrast media results in significantly less cardiovascular side effects. (L.E.)

Downstream plasma transport and metal ionization in a high-powered pulsed-plasma magnetron

International Nuclear Information System (INIS)

Meng, Liang; Szott, Matthew M.; McLain, Jake T.; Ruzic, David N.; Yu, He

2014-01-01

Downstream plasma transport and ionization processes in a high-powered pulsed-plasma magnetron were studied. The temporal evolution and spatial distribution of electron density (n e ) and temperature (T e ) were characterized with a 3D scanning triple Langmuir probe. Plasma expanded from the racetrack region into the downstream region, where a high n e peak was formed some time into the pulse-off period. The expansion speed and directionality towards the substrate increased with a stronger magnetic field (B), largely as a consequence of a larger potential drop in the bulk plasma region during a relatively slower sheath formation. The fraction of Cu ions in the deposition flux was measured on the substrate using a gridded energy analyzer. It increased with higher pulse voltage. With increased B field from 200 to 800 Gauss above racetrack, n e increased but the Cu ion fraction decreased from 42% to 16%. A comprehensive model was built, including the diffusion of as-sputtered Cu flux, the Cu ionization in the entire plasma region using the mapped n e and T e data, and ion extraction efficiency based on the measured plasma potential (V p ) distribution. The calculations matched the measurements and indicated the main causes of lower Cu ion fractions in stronger B fields to be the lower T e and inefficient ion extraction in a larger pre-sheath potential.

Enhanced ionized impurity scattering in nanowires

Science.gov (United States)

Oh, Jung Hyun; Lee, Seok-Hee; Shin, Mincheol

2013-06-01

The electronic resistivity in silicon nanowires is investigated by taking into account scattering as well as the donor deactivation from the dielectric mismatch. The effects of poorly screened dopant atoms from the dielectric mismatch and variable carrier density in nanowires are found to play a crucial role in determining the nanowire resistivity. Using Green's function method within the self-consistent Born approximation, it is shown that donor deactivation and ionized impurity scattering combined with the charged interface traps successfully to explain the increase in the resistivity of Si nanowires while reducing the radius, measured by Björk et al. [Nature Nanotech. 4, 103 (2009)].

Significance of Environmental Density in Shocked Poststarburst Galaxy Evolution

Science.gov (United States)

Jaliff, Laura

2018-01-01

The Shocked POstarbusrt Galaxy Survey (SPOGS) comprises 1,066 galaxies undergoing the transformation from blue cloud late-type spirals to red sequence non-star-forming early-type ellipticals and lenticulars. They are selected via spectral analysis of ionized gas line ratios, which indicate shocked objects, and Balmer H-δ equivalent width, which select recently formed stars, but not active star formation. E+A galaxies (Zabludoff et al. 1996), like SPOGs, contain young stars but, unlike SPOGs, no emission lines consistent with star formation. They differ in that the quality used to discern SPOGs, their shocks, produces H-α lines that prevent them from being found via the same criteria as E+As. Thus, SPOGs can be found before being entirely stripped of their gas, and, while E+As are largely red and dead, found leaving the green valley, SPOGS are mostly entering it. The environmental density data for SPOGs was retrieved via the NASA Extragalactic Database (NED) radial velocity constrained cone tool, which provides counts and densities within spheres of radii 1, 5, and 10 Mpc from the center of search as well as relative positions and redshifts of objects. The kinematic morphology-density relation (Cappellari et al. 2011) is employed as a point of comparison for how SPOGs’ environmental densities might relate to morphological and spectroscopic factors, including tidal features, asymmetry, and color, in order to fully understand the role of environmental factors in SPOGS object evolution.

Determination of Hydrogen Density by Swift Heavy Ions.

Science.gov (United States)

Xu, Ge; Barriga-Carrasco, M D; Blazevic, A; Borovkov, B; Casas, D; Cistakov, K; Gavrilin, R; Iberler, M; Jacoby, J; Loisch, G; Morales, R; Mäder, R; Qin, S-X; Rienecker, T; Rosmej, O; Savin, S; Schönlein, A; Weyrich, K; Wiechula, J; Wieser, J; Xiao, G Q; Zhao, Y T

2017-11-17

A novel method to determine the total hydrogen density and, accordingly, a precise plasma temperature in a lowly ionized hydrogen plasma is described. The key to the method is to analyze the energy loss of swift heavy ions interacting with the respective bound and free electrons of the plasma. A slowly developing and lowly ionized hydrogen theta-pinch plasma is prepared. A Boltzmann plot of the hydrogen Balmer series and the Stark broadening of the H_{β} line preliminarily defines the plasma with a free electron density of (1.9±0.1)×10^{16}  cm^{-3} and a free electron temperature of 0.8-1.3 eV. The temperature uncertainty results in a wide hydrogen density, ranging from 2.3×10^{16} to 7.8×10^{18}  cm^{-3}. A 108 MHz pulsed beam of ^{48}Ca^{10+} with a velocity of 3.652  MeV/u is used as a probe to measure the total energy loss of the beam ions. Subtracting the calculated energy loss due to free electrons, the energy loss due to bound electrons is obtained, which linearly depends on the bound electron density. The total hydrogen density is thus determined as (1.9±0.7)×10^{17}  cm^{-3}, and the free electron temperature can be precisely derived as 1.01±0.04  eV. This method should prove useful in many studies, e.g., inertial confinement fusion or warm dense matter.

Ionizing radiations

International Nuclear Information System (INIS)

Anon.

1999-01-01

This is an update about the radiological monitoring in base nuclear installations. A departmental order of the 23. march 1999 (J.O.28. april, p.6309) determines the enabling rules by the Office of Protection against Ionizing Radiations of person having at one's disposal the results with names of individual exposure of workers put through ionizing radiations. (N.C.)

Atmospheric Gaseous Plasma with Large Dimensions

Science.gov (United States)

Korenev, Sergey

2012-10-01

The forming of atmospheric plasma with large dimensions using electrical discharge typically uses the Dielectric Barrier Discharge (DBD). The study of atmospheric DBD was shown some problems related to homogeneous volume plasma. The volume of this plasma determines by cross section and gas gap between electrode and dielectric. The using of electron beam for volume ionization of air molecules by CW relativistic electron beams was shown the high efficiency of this process [1, 2]. The main advantage of this approach consists in the ionization of gas molecules by electrons in longitudinal direction determines by their kinetic energy. A novel method for forming of atmospheric homogeneous plasma with large volume dimensions using ionization of gas molecules by pulsed non-relativistic electron beams is presented in the paper. The results of computer modeling for delivered doses of electron beams in gases and ionization are discussed. The structure of experimental bench with plasma diagnostics is considered. The preliminary results of forming atmospheric plasma with ionization gas molecules by pulsed nanosecond non-relativistic electron beam are given. The analysis of potential applications for atmospheric volume plasma is presented. Reference: [1] S. Korenev. ``The ionization of air by scanning relativistic high power CW electron beam,'' 2002 IEEE International Conference on Plasma Science. May 2002, Alberta, Canada. [2] S. Korenev, I. Korenev. ``The propagation of high power CW scanning electron beam in air.'' BEAMS 2002: 14th International Conference on High-Power Particle Beams, Albuquerque, New Mexico (USA), June 2002, AIP Conference Proceedings Vol. 650(1), pp. 373-376. December 17.

Probing photo-ionization: experiments on positive streamers in pure gases and mixtures

International Nuclear Information System (INIS)

Nijdam, S; Van de Wetering, F M J H; Blanc, R; Van Veldhuizen, E M; Ebert, U

2010-01-01

Positive streamers are thought to propagate by photo-ionization; the parameters of photo-ionization depend on the nitrogen : oxygen ratio. Therefore we study streamers in nitrogen with 20%, 0.2% and 0.01% oxygen and in pure nitrogen as well as in pure oxygen and argon. Our new experimental set-up guarantees contamination of the pure gases to be well below 1 ppm. Streamers in oxygen are difficult to measure as they emit considerably less light in the sensitivity range of our fast ICCD camera than the other gases. Streamers in pure nitrogen and in all nitrogen-oxygen mixtures look generally similar, but become somewhat thinner and branch more with decreasing oxygen content. In pure nitrogen the streamers can branch so much that they resemble feathers. This feature is even more pronounced in pure argon, with approximately 10 2 hair tips cm -3 in the feathers at 200 mbar; this density can be interpreted as the free electron density creating avalanches towards the streamer stem. It is remarkable that the streamer velocity is essentially the same for similar voltage and pressure in all nitrogen-oxygen mixtures as well as in pure nitrogen, while the oxygen concentration and therefore the photo-ionization lengths vary by more than five orders of magnitude. Streamers in argon have essentially the same velocity as well. The physical similarity of streamers at different pressures is confirmed in all gases; the minimal diameters are smaller than in earlier measurements.

Probing photo-ionization: experiments on positive streamers in pure gases and mixtures

Energy Technology Data Exchange (ETDEWEB)

Nijdam, S; Van de Wetering, F M J H; Blanc, R; Van Veldhuizen, E M; Ebert, U, E-mail: s.nijdam@tue.n [Eindhoven University of Technology, Department Applied Physics, PO Box 513, 5600 MB Eindhoven (Netherlands)

2010-04-14

Positive streamers are thought to propagate by photo-ionization; the parameters of photo-ionization depend on the nitrogen : oxygen ratio. Therefore we study streamers in nitrogen with 20%, 0.2% and 0.01% oxygen and in pure nitrogen as well as in pure oxygen and argon. Our new experimental set-up guarantees contamination of the pure gases to be well below 1 ppm. Streamers in oxygen are difficult to measure as they emit considerably less light in the sensitivity range of our fast ICCD camera than the other gases. Streamers in pure nitrogen and in all nitrogen-oxygen mixtures look generally similar, but become somewhat thinner and branch more with decreasing oxygen content. In pure nitrogen the streamers can branch so much that they resemble feathers. This feature is even more pronounced in pure argon, with approximately 10{sup 2} hair tips cm{sup -3} in the feathers at 200 mbar; this density can be interpreted as the free electron density creating avalanches towards the streamer stem. It is remarkable that the streamer velocity is essentially the same for similar voltage and pressure in all nitrogen-oxygen mixtures as well as in pure nitrogen, while the oxygen concentration and therefore the photo-ionization lengths vary by more than five orders of magnitude. Streamers in argon have essentially the same velocity as well. The physical similarity of streamers at different pressures is confirmed in all gases; the minimal diameters are smaller than in earlier measurements.

Ion collection efficiency of ionization chambers in electron beams

International Nuclear Information System (INIS)

Garcia, S.; Cecatti, E.R.

1984-01-01

When ionization chambers are used in pulsed radiation beams the high-density of ions produced per pulse permits ion recombination, demanding the use of a correction factor. An experimental technique using the charge collected at two different voltages permits the calculation of the ion collection efficiency. The ion collection efficiency of some common ionization chambers in pulsed electron beams were studied as a function of electron energy, dose rate and depth. Accelerators with magnetic scanning system, in which the instantaneous dose rate is much greater than the average dose rate, present a smaller collection efficiency than accelerators with scattering foil. The results lead to the introduction of a correction factor for ion recombination that is the reciprocal of the ion collection efficiency. It is also suggested a simple technique to connect an external variable DC power supply in a Baldwin Farmer dosemeter. (Author) [pt

Adaptive finite-element ballooning analysis of bipolar ionized fields

International Nuclear Information System (INIS)

Al-Hamouz, Z.M.

1995-01-01

This paper presents an adaptive finite-element iterative method for the analysis of the ionized field around high-voltage bipolar direct-current (HVDC) transmission line conductors without resort to Deutsch's assumption. A new iterative finite-element ballooning technique is proposed to solve Poisson's equation wherein the commonly used artificial boundary around the transmission line conductors is simulated at infinity. Unlike all attempts reported in the literature for the solution of ionized field, the constancy of the conductors' surface field at the corona onset value is directly implemented in the finite-element formulation. In order to investigate the effectiveness of the proposed method, a laboratory model was built. It has been found that the calculated V-I characteristics and the ground-plane current density agreed well with those measured experimentally. The simplicity in computer programming in addition to the low number of iterations required to achieve convergence characterize this method of analysis

Valence one-electron and shake-up ionization bands of fluorene, carbazole and dibenzofuran

International Nuclear Information System (INIS)

Reza Shojaei, S.H.; Morini, Filippo; Deleuze, Michael S.

2013-01-01

Highlights: • The photoelectron spectra of the title compounds are assigned in details. • Shake-up lines are found to severely contaminate both π- and σ-ionization bands. • σ-ionization onsets are subject to severe vibronic coupling complications. • We compare the results of OVGF, ADC(3) and TDDFT calculations. - Abstract: A comprehensive study of the He (I) ultra-violet photoelectron spectra of fluorene, carbazole and dibenzofuran is presented with the aid of one-particle Green’s Function calculations employing the outer-valence Green’s Function (OVGF) approach and the third-order algebraic diagrammatic construction [ADC(3)] scheme, along with Dunning’s correlation consistent basis sets of double and triple zeta quality (cc-pVDZ, cc-pVTZ). Extrapolations of the ADC(3) results for the outermost one-electron π-ionization energies to the cc-pVTZ basis set enable theoretical insights into He (I) measurements within ∼0.15 eV accuracy, up to the σ-ionization onset. The lower ionization energy of carbazole is the combined result of mesomeric and electronic relaxation effects. OVGF/cc-pVDZ or OVGF/cc-pVTZ pole strengths smaller than 0.85 systematically corroborate a breakdown of the orbital picture of ionization at the ADC(3) level. Comparison is made with calculations of the lowest doublet–doublet excitation energies of the radical cation of fluorene, by means of time-dependent density functional theory (TDDFT)

Enhanced Responsivity of Photodetectors Realized via Impact Ionization

Directory of Open Access Journals (Sweden)

De-Zhen Shen

2012-01-01

Full Text Available To increase the responsivity is one of the vital issues for a photodetector. By employing ZnO as a representative material of ultraviolet photodetectors and Si as a representative material of visible photodetectors, an impact ionization process, in which additional carriers can be generated in an insulating layer at a relatively large electric field, has been employed to increase the responsivity of a semiconductor photodetector. It is found that the responsivity of the photodetectors can be enhanced by tens of times via this impact ionization process. The results reported in this paper provide a general route to enhance the responsivity of a photodetector, thus may represent a step towards high-performance photodetectors.

Temporal evolution of plasma density in femtosecond light filaments

International Nuclear Information System (INIS)

Wang Haitao; Fan Chengyu; Shen Hong; Qiao Chunhong; Zhang Jinghui; Zhang Pengfei; Ma Huimin; Xu Huiling

2012-01-01

By using a legible and comprehensive physical model describing the generation and evolvement of ion densities in the plasma channel induced by intense femtosecond laser pulse, the work studied the temporal evolution of the plasma densities in femtosecond light filaments. It shows that the contribution of the ionization of oxygen and nitrogen molecules to the total electron densities varies much for different laser pulse shapes, and the pulse shapes have more effects on the lifetime of the higher density plasma. It is necessary to control the pulse shape for efficient using of the plasma channel. Pulses of long duration and short wavelength can obtain a plasma channel with higher electron density, but the channel lifetime thoroughly depends on the later evolution of the self-guided channel. (authors)

Ab initio dynamics and photoionization mass spectrometry reveal ion-molecule pathways from ionized acetylene clusters to benzene cation.

Science.gov (United States)

Stein, Tamar; Bandyopadhyay, Biswajit; Troy, Tyler P; Fang, Yigang; Kostko, Oleg; Ahmed, Musahid; Head-Gordon, Martin

2017-05-23

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion-molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (C 2 H 2 ) n + , just like ionized acetylene clusters. The fragmentation products result from reactive ion-molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C 4 H 4 + and C 6 H 6 + structures solvated with one or more neutral acetylene molecules. Such species contain large amounts (>2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C 2 H 2 ) n + isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C 6 H 6 + isomers. These results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM.

Ab initio dynamics and photoionization mass spectrometry reveal ion–molecule pathways from ionized acetylene clusters to benzene cation

Science.gov (United States)

Stein, Tamar; Bandyopadhyay, Biswajit; Troy, Tyler P.; Fang, Yigang; Kostko, Oleg

2017-01-01

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion–molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (C2H2)n+, just like ionized acetylene clusters. The fragmentation products result from reactive ion–molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C4H4+ and C6H6+ structures solvated with one or more neutral acetylene molecules. Such species contain large amounts (>2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C2H2)n+ isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C6H6+ isomers. These results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM. PMID:28484019

Low-frequency observations of Galactic supernova remnants and the distribution of low-density ionized gas in the interstellar medium

International Nuclear Information System (INIS)

Kassim, N.E.

1989-01-01

New long-wavelength observations of Galactic SNRs at 30.9 and 57.5 MHz are used to derive detailed low-frequency radio spectra for 32 SNRs. Of these, about two-thirds show turnovers at low frequencies, implying the presence of a widespread, but inhomogeneous, ionized absorbing medium along the lines of sight. These observations are combined with other low-frequency data to derive free-free optical depths toward 457 SNRs and to constrain the physical properties of the ionized gas responsible for the absorption. These optical depths are consistent with the expected absorbing properties of extended H II region envelopes. 43 refs

A drift-ordered short mean-free path description of a partially ionized magnetized plasma

International Nuclear Information System (INIS)

Simakov, Andrei N

2009-01-01

Neutral particles that are present at the edge of plasma magnetic confinement devices can play an important role in energy and momentum transport, and their effects should be accounted for. This work uses the drift ordering to derive a closed fluid description for a collisional, magnetized, partially ionized plasma. Charge-exchange, ionization and recombination processes are taken into account. It is assumed that electron distribution function is unaffected by atomic processes, so that electron-ion momentum and energy exchange are described by the usual expressions for a fully ionized plasma, and that neutral-neutral collisions are unimportant. The collisional fluid equations derived herein generalize the drift-ordered description of a fully ionized collisional plasma (Catto P J et al 2004 Phys. Plasmas 11 90), agree with the MHD-ordered description of a partially ionized plasma (Helander P et al 1994 Phys. Plasmas 1 3174) in the large-flow limit and can be used to describe both turbulent and collisional behavior of a partially ionized plasma.

Ionization of large homogeneous and heterogeneous clusters generated in acetylene–Ar expansions: Cluster ion polymerization

Czech Academy of Sciences Publication Activity Database

Kočišek, Jaroslav; Lengyel, Jozef; Fárník, Michal

2013-01-01

Roč. 138, č. 12 (2013), s. 124306 ISSN 0021-9606 R&D Projects: GA ČR GA203/09/0422 EU Projects: European Commission(XE) 238671 - ICONIC Institutional support: RVO:61388955 Keywords : argon * electron impact ionization * evaporation Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.122, year: 2013

Exact differential equation for the density and ionization energy of a many-particle system

Science.gov (United States)

Levy, M.; Perdew, J. P.; Sahni, V.

1984-01-01

The present investigation is concerned with relations studied by Hohenberg and Kohn (1964) and Kohn and Sham (1965). The properties of a ground-state many-electron system are determined by the electron density. The correct differential equation for the density, as dictated by density-functional theory, is presented. It is found that the ground-state density n of a many-electron system obeys a Schroedinger-like differential equation which may be solved by standard Kohn-Sham programs. Results are connected to the traditional exact Kohn-Sham theory. It is pointed out that the results of the current investigations are readily extended to spin-density functional theory.

Assessment of Density-Functional Tight-Binding Ionization Potentials and Electron Affinities of Molecules of Interest for Organic Solar Cells Against First-Principles GW Calculations

Directory of Open Access Journals (Sweden)

Ala Aldin M. H. M. Darghouth

2015-12-01

Full Text Available Ionization potentials (IPs and electron affinities (EAs are important quantities input into most models for calculating the open-circuit voltage (Voc of organic solar cells. We assess the semi-empirical density-functional tight-binding (DFTB method with the third-order self-consistent charge (SCC correction and the 3ob parameter set (the third-order DFTB (DFTB3 organic and biochemistry parameter set against experiments (for smaller molecules and against first-principles GW (Green’s function, G, times the screened potential, W calculations (for larger molecules of interest in organic electronics for the calculation of IPs and EAs. Since GW calculations are relatively new for molecules of this size, we have also taken care to validate these calculations against experiments. As expected, DFTB is found to behave very much like density-functional theory (DFT, but with some loss of accuracy in predicting IPs and EAs. For small molecules, the best results were found with ΔSCF (Δ self-consistent field SCC-DFTB calculations for first IPs (good to ± 0.649 eV. When considering several IPs of the same molecule, it is convenient to use the negative of the orbital energies (which we refer to as Koopmans’ theorem (KT IPs as an indication of trends. Linear regression analysis shows that KT SCC-DFTB IPs are nearly as accurate as ΔSCF SCC-DFTB eigenvalues (± 0.852 eV for first IPs, but ± 0.706 eV for all of the IPs considered here for small molecules. For larger molecules, SCC-DFTB was also the ideal choice with IP/EA errors of ± 0.489/0.740 eV from ΔSCF calculations and of ± 0.326/0.458 eV from (KT orbital energies. Interestingly, the linear least squares fit for the KT IPs of the larger molecules also proves to have good predictive value for the lower energy KT IPs of smaller molecules, with significant deviations appearing only for IPs of 15–20 eV or larger. We believe that this quantitative analysis of errors in SCC-DFTB IPs and EAs may be of

Estimating large carnivore populations at global scale based on spatial predictions of density and distribution – Application to the jaguar (Panthera onca)

Science.gov (United States)

Robinson, Hugh S.; Abarca, Maria; Zeller, Katherine A.; Velasquez, Grisel; Paemelaere, Evi A. D.; Goldberg, Joshua F.; Payan, Esteban; Hoogesteijn, Rafael; Boede, Ernesto O.; Schmidt, Krzysztof; Lampo, Margarita; Viloria, Ángel L.; Carreño, Rafael; Robinson, Nathaniel; Lukacs, Paul M.; Nowak, J. Joshua; Salom-Pérez, Roberto; Castañeda, Franklin; Boron, Valeria; Quigley, Howard

2018-01-01

Broad scale population estimates of declining species are desired for conservation efforts. However, for many secretive species including large carnivores, such estimates are often difficult. Based on published density estimates obtained through camera trapping, presence/absence data, and globally available predictive variables derived from satellite imagery, we modelled density and occurrence of a large carnivore, the jaguar, across the species’ entire range. We then combined these models in a hierarchical framework to estimate the total population. Our models indicate that potential jaguar density is best predicted by measures of primary productivity, with the highest densities in the most productive tropical habitats and a clear declining gradient with distance from the equator. Jaguar distribution, in contrast, is determined by the combined effects of human impacts and environmental factors: probability of jaguar occurrence increased with forest cover, mean temperature, and annual precipitation and declined with increases in human foot print index and human density. Probability of occurrence was also significantly higher for protected areas than outside of them. We estimated the world’s jaguar population at 173,000 (95% CI: 138,000–208,000) individuals, mostly concentrated in the Amazon Basin; elsewhere, populations tend to be small and fragmented. The high number of jaguars results from the large total area still occupied (almost 9 million km2) and low human densities (conservation actions. PMID:29579129

A multi purpose 4 π counter spherical ionization chamber type

International Nuclear Information System (INIS)

Calin, Marian Romeo; Calin, Adrian Cantemir

2004-01-01

A pressurized ionization chamber detector able to measure radioactive sources in internal 2π or 4π geometry was built in order to characterize alpha and beta radioactive sources, i.e. to calibrate these sources by relative method and to test the behavior of gas mixtures in pressurized-gas radiation detectors. The detector we made is of spherical shape and works by collecting in a uniform electric field the ionization charges resulting from the interaction of ionizing radiation with gas in the sensitive volume of the chamber. An ionizing current proportional to the activity of the radioactive source to be measured is obtained. In this paper a gas counter with a spherical symmetry is described. This detector can work in a very satisfactory manner, either as a flow counter or as a ionization chamber reaching in the latter case a good α pulse height resolution, even with large emitting sources. Calculations are made in order to find the dependence of the pulse shape on the direction of emission of an α-particle by a point source in the chamber (finite track). A good agreement is found between these calculations and the experimental tests performed, which show that this dependence can be employed in high efficiency measurements of angular α-γ correlations. (authors)

Stochastic substitute for coupled rate equations in the modeling of highly ionized transient plasmas

International Nuclear Information System (INIS)

Eliezer, S.; Falquina, R.; Minguez, E.

1994-01-01

Plasmas produced by intense laser pulses incident on solid targets often do not satisfy the conditions for local thermodynamic equilibrium, and so cannot be modeled by transport equations relying on equations of state. A proper description involves an excessively large number of coupled rate equations connecting many quantum states of numerous species having different degrees of ionization. Here we pursue a recent suggestion to model the plasma by a few dominant states perturbed by a stochastic driving force. The driving force is taken to be a Poisson impulse process, giving a Langevin equation which is equivalent to a Fokker-Planck equation for the probability density governing the distribution of electron density. An approximate solution to the Langevin equation permits calculation of the characteristic relaxation rate. An exact stationary solution to the Fokker-Planck equation is given as a function of the strength of the stochastic driving force. This stationary solution is used, along with a Laplace transform, to convert the Fokker-Planck equation to one of Schroedinger type. We consider using the classical Hamiltonian formalism and the WKB method to obtain the time-dependent solution

X-RAY SIGNATURES OF NON-EQUILIBRIUM IONIZATION EFFECTS IN GALAXY CLUSTER ACCRETION SHOCK REGIONS

International Nuclear Information System (INIS)

Wong, Ka-Wah; Sarazin, Craig L.; Ji Li

2011-01-01

The densities in the outer regions of clusters of galaxies are very low, and the collisional timescales are very long. As a result, heavy elements will be under-ionized after they have passed through the accretion shock. We have studied systematically the effects of non-equilibrium ionization for relaxed clusters in the ΛCDM cosmology using one-dimensional hydrodynamic simulations. We found that non-equilibrium ionization effects do not depend on cluster mass, but depend strongly on redshift which can be understood by self-similar scaling arguments. The effects are stronger for clusters at lower redshifts. We present X-ray signatures such as surface brightness profiles and emission lines in detail for a massive cluster at low redshift. In general, soft emission (0.3-1.0 keV) is enhanced significantly by under-ionization, and the enhancement can be nearly an order of magnitude near the shock radius. The most prominent non-equilibrium ionization signature we found is the O VII and O VIII line ratio. The ratios for non-equilibrium ionization and collisional ionization equilibrium models are different by more than an order of magnitude at radii beyond half of the shock radius. These non-equilibrium ionization signatures are equally strong for models with different non-adiabatic shock electron heating efficiencies. We have also calculated the detectability of the O VII and O VIII lines with the future International X-ray Observatory (IXO). Depending on the line ratio measured, we conclude that an exposure of ∼130-380 ks on a moderate-redshift, massive regular cluster with the X-ray Microcalorimeter Spectrometer (XMS) on the IXO will be sufficient to provide a strong test for the non-equilibrium ionization model.

Highly ionized plasma plume generation by long-pulse CO2 laser irradiation of solid targets in strong axial magnetic fields

International Nuclear Information System (INIS)

Hoffman, A.L.; Crawford, E.A.

1982-01-01

The present work utilizes high f number optics and is directed primarily at controlling the conditions in the magnetically confined plume. Typically, fully ionized carbon plasmas have been produced with 10 18 cm -3 electron densities and 100 to 150 eV electron temperatures. These carbon plasmas have been doped with high Z atoms in order to study ionization and emission rates at the above conditions

Schwinger variational calculation of ionization of hydrogen atoms for ...

Indian Academy of Sciences (India)

Schwinger variational calculation of ionization of hydrogen atoms for large momentum transfers. K CHAKRABARTI. Department of Mathematics, Scottish Church College, 1 & 3 Urquhart Square,. Kolkata 700 006, India. MS received 7 July 2001; revised 10 October 2001. Abstract. Schwinger variational principle is used here ...

H TO Zn IONIZATION EQUILIBRIUM FOR THE NON-MAXWELLIAN ELECTRON κ-DISTRIBUTIONS: UPDATED CALCULATIONS

International Nuclear Information System (INIS)

Dzifčáková, E.; Dudík, J.

2013-01-01

New data for the calculation of ionization and recombination rates have been published in the past few years, most of which are included in the CHIANTI database. We used these data to calculate collisional ionization and recombination rates for the non-Maxwellian κ-distributions with an enhanced number of particles in the high-energy tail, which have been detected in the solar transition region and the solar wind. Ionization equilibria for elements H to Zn are derived. The κ-distributions significantly influence both the ionization and recombination rates and widen the ion abundance peaks. In comparison with the Maxwellian distribution, the ion abundance peaks can also be shifted to lower or higher temperatures. The updated ionization equilibrium calculations result in large changes for several ions, notably Fe VIII-Fe XIV. The results are supplied in electronic form compatible with the CHIANTI database.

Body mass of prefledging Emperor Geese Chen canagica: Large-scale effects of interspecific densities and food availability

Science.gov (United States)

Lake, B.C.; Schmutz, J.A.; Lindberg, M.S.; Ely, Craig R.; Eldridge, W.D.; Broerman, F.J.

2008-01-01