WorldWideScience

Sample records for 144ce fission fragments

  1. Chromatographic isolation of 144Ce and 144Pr from the wastes of irradiated uranium treatment

    A two-step chromatographic technique was elaborated to isolate 144Ce, 144Pr from a solution of uranium fission products in 6M HNO3. The oxidation to Ce(III) by bromate and selective adsorption of 144Ce(IV) on anion exchange column were used to concentrate and purify 144Ce. Some impurities of uranium, 95Zr, 95Nb, 106Ru remain in 144Ce solution after the first step of its isolation. The final purification is achieved by passing the 6M HNO3 solution of 144Ce(IV) through the HDEHP-coated teflon column. The decontamination factors of 144Ce from main fission products are given. 7.2 mCi of (144Ce+144Pr) are recovered from each gram of irradiated uranium trioxide with the yield greater than 99%. An improvement of known generator was carried out to elute a purer 144Pr from maternal 144Ce(IV) adsorbed on the anion exchange column. (author)

  2. Fission fragment rocket concept

    A new propulsion scheme is outlined which may permit interstellar missions for spacecraft. This scheme is based on the idea of allowing fission fragments to escape from the core of a nuclear reactor. (orig.)

  3. Fission Fragments Discriminator

    Nuclear fission reaction between Uranium-235 nucleus and thermal neutron caused the high energy fission fragments with uncertainly direction. The particle direction discrimination was determined. The 2.5 x 3.0 mm2 polyethylene gratings with 1-6 mm thickness were used. The grating was placed between uranium screen that fabricated from ammonium-diurinate compound and polycarbonate nuclear track film recorder irradiated by neutron from Thai Research Reactor (TRR-1/M1) facility. The nuclear track density was inversely with grating thickness. It's only fission fragments normal to uranium screen pass through film recorder when grating thickness was 4-6 mm

  4. Fission fragment angular distributions

    Recently a Letter appeared (Phys. Rev. Lett., 522, 414(1984)) claiming that the usual expression for describing the angula distribution of fission fragments from compound nuclear decay is not a necessarily valid limit of a more general expression. In this comment we wish to point out that the two expressions arise from distinctly different models, and that the new expression as used in the cited reference is internally inconsistent

  5. The spectroscopy of fission fragments

    High-resolution measurements on γ rays from fission fragments have provided a rich source of information, unobtainable at the moment in any other way, on the spectroscopy of neutron-rich nuclei. In recent years important data have been obtained on the yrast- and near yrast-structure of neutron-rich fission fragments. We discuss the scope of measurements which can be made on prompt gamma rays from secondary fission fragments, the techniques used in the experiments and some results recently obtained. (author)

  6. The spectroscopy of fission fragments

    Phillips, W.R. [Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL (United Kingdom); Collaboration: La Direction des Sciences de la Matiere du CEA (FR); Le Fonds National de la Recherche Scientifique de Belgique (BE)

    1998-12-31

    High-resolution measurements on {gamma} rays from fission fragments have provided a rich source of information, unobtainable at the moment in any other way, on the spectroscopy of neutron-rich nuclei. In recent years important data have been obtained on the yrast- and near yrast-structure of neutron-rich fission fragments. We discuss the scope of measurements which can be made on prompt gamma rays from secondary fission fragments, the techniques used in the experiments and some results recently obtained. (author) 24 refs., 8 figs., 1 tab.

  7. Chemical Production using Fission Fragments

    Some reactor design considerations of the use of fission recoil fragment energy for the production of chemicals of industrial importance have been discussed previously in a paper given at the Second United Nations International Conference on the Peaceful Uses of Atomic Energy [A/Conf. 15/P.76]. The present paper summarizes more recent progress made on this topic at AERE, Harwell. The range-energy relationship for fission fragments is discussed in the context of the choice of fuel system for a chemical production reactor, and the experimental observation of a variation of chemical effect along the length of a fission fragment track is described for the irradiation of nitrogen-oxygen mixtures. Recent results are given on the effect of fission fragments on carbon monoxide-hydrogen gas mixtures and on water vapour. No system investigated to date shows any outstanding promise for large-scale chemical production. (author)

  8. Fission fragment driven neutron source

    Miller, Lowell G.; Young, Robert C.; Brugger, Robert M.

    1976-01-01

    Fissionable uranium formed into a foil is bombarded with thermal neutrons in the presence of deuterium-tritium gas. The resulting fission fragments impart energy to accelerate deuterium and tritium particles which in turn provide approximately 14 MeV neutrons by the reactions t(d,n).sup.4 He and d(t,n).sup.4 He.

  9. Velocity fluctuations of fission fragment.

    Llanes Estrada, Felipe José; Martínez Carmona, Belén; Muñoz Martínez, José L.

    2016-01-01

    We propose event by event velocity fluctuations of nuclear fission fragments as an additional interesting observable that gives access to the nuclear temperature in an independent way from spectral measurements and relates the diffusion and friction coefficients for the relative fragment coordinate in Kramers-like models (in which some aspects of fission can be understood as the diffusion of a collective variable through a potential barrier). We point out that neutron emission by the heavy fr...

  10. Laser spectroscopy of fission fragments

    The study of the nuclear structure of fission fragments is discussed. They are neutron-rich nuclei the structure of which possesses some peculiarities. Two regions of fission fragments are discussed: near the shell closures N = 50 and N = 82 and at the boundary of the deformation. A view on the optical properties of these elements is presented and different laser spectroscopic methods for their investigation are proposed. (author)

  11. Velocity fluctuations of fission fragments

    Llanes-Estrada, Felipe J; Martinez, Jose L Muñoz

    2015-01-01

    We propose event by event velocity fluctuations of nuclear fission fragments as an additional interesting observable that gives access to the nuclear temperature in an independent way from spectral measurements and relates the diffusion and friction coefficients for the relative fragment coordinate in Kramer-like models (in which some aspects of fission can be understood as the diffusion of a collective variable through a potential barrier). We point out that neutron emission by the heavy fragments can be treated in effective theory if corrections to the velocity distribution are needed.

  12. Velocity fluctuations of fission fragments

    Llanes-Estrada, Felipe J.; Carmona, Belén Martínez; Martínez, Jose L. Muñoz

    2016-02-01

    We propose event by event velocity fluctuations of nuclear fission fragments as an additional interesting observable that gives access to the nuclear temperature in an independent way from spectral measurements and relates the diffusion and friction coefficients for the relative fragment coordinate in Kramers-like models (in which some aspects of fission can be understood as the diffusion of a collective variable through a potential barrier). We point out that neutron emission by the heavy fragments can be treated in effective theory if corrections to the velocity distribution are needed.

  13. Ternary fission of nuclei into comparable fragments

    Karpeshin, F. F., E-mail: fkarpeshin@gmail.com [D.I. Mendeleev Institute forMetrology (VNIIM) (Russian Federation)

    2015-07-15

    The problem of nuclear fission into three comparable fragments is considered. A mechanism of true ternary fission is proposed. In contrast to sequential fission, where the three fragments arise upon two sequential events of binary fission, the mechanism in question relies on a scenario that originally involves fission into three fragments. This mechanism is driven by a hexadecapole deformation of the fissioning nucleus, in contrast to binary fission associated with quadrupole vibrations of the nuclear surface. The fragment-mass ratios are estimated. The dynamics of formation of collinear fragments and their subsequent motion in opposite directions is traced. The calculated probability of true ternary fission complies with observed values.

  14. Ternary fission of nuclei into comparable fragments

    The problem of nuclear fission into three comparable fragments is considered. A mechanism of true ternary fission is proposed. In contrast to sequential fission, where the three fragments arise upon two sequential events of binary fission, the mechanism in question relies on a scenario that originally involves fission into three fragments. This mechanism is driven by a hexadecapole deformation of the fissioning nucleus, in contrast to binary fission associated with quadrupole vibrations of the nuclear surface. The fragment-mass ratios are estimated. The dynamics of formation of collinear fragments and their subsequent motion in opposite directions is traced. The calculated probability of true ternary fission complies with observed values

  15. The VERDI fission fragment spectrometer

    Frégeau M.O.; Bryś T.; Gamboni Th.; Geerts W.; Oberstedt S.; Oberstedt A.; Borcea R.

    2013-01-01

    The VERDI time-of-flight spectrometer is dedicated to measurements of fission product yields and of prompt neutron emission data. Pre-neutron fission-fragment masses will be determined by the double time-of-flight (TOF) technique. For this purpose an excellent time resolution is required. The time of flight of the fragments will be measured by electrostatic mirrors located near the target and the time signal coming from silicon detectors located at 50 cm on both sides of the target. This conf...

  16. Energy production using fission fragment rockets

    Chapline, G.; Matsuda, Y.

    1991-08-01

    Fission fragment rockets are nuclear reactors with a core consisting of thin fibers in a vacuum, and which use magnetic fields to extract the fission fragments from the reactor core. As an alternative to ordinary nuclear reactors, fission fragment rockets would have the following advantages: approximately twice the efficiency if the fission fragment energy can be directly converted into electricity; reduction of the buildup of a fission fragment inventory in the reactor could avoid a Chernobyl type disaster; and collection of the fission fragments outside the reactor could simplify the waste disposal problem.

  17. Energy production using fission fragment rockets

    Fission fragment rockets are nuclear reactors with a core consisting of thin fibers in a vacuum, and which use magnetic fields to extract the fission fragments from the reactor core. As an alternative to ordinary nuclear reactors, fission fragment rockets would have the following advantages: Approximately twice as efficient if one can directly convert the fission fragment energy into electricity; by reducing the buildup of a fission fragment inventory in the reactor one could avoid a Chernobyl type disaster; and collecting the fission fragments outside the reactor could simplify the waste disposal problem. 6 refs., 4 figs., 2 tabs

  18. The VERDI fission fragment spectrometer

    The VERDI time-of-flight spectrometer is dedicated to measurements of fission product yields and of prompt neutron emission data. Pre-neutron fission-fragment masses will be determined by the double time-of-flight (TOF) technique. For this purpose an excellent time resolution is required. The time of flight of the fragments will be measured by electrostatic mirrors located near the target and the time signal coming from silicon detectors located at 50 cm on both sides of the target. This configuration, where the stop detector will provide us simultaneously with the kinetic energy of the fragment and timing information, significantly limits energy straggling in comparison to legacy experimental setup where a thin foil was usually used as a stop detector. In order to improve timing resolution, neutron transmutation doped silicon will be used. The high resistivity homogeneity of this material should significantly improve resolution in comparison to standard silicon detectors. Post-neutron fission fragment masses are obtained form the time-of-flight and the energy signal in the silicon detector. As an intermediary step a diamond detector will also be used as start detector located very close to the target. Previous tests have shown that poly-crystalline chemical vapour deposition (pCVD) diamonds provides a coincidence time resolution of 150 ps not allowing complete separation between very low-energy fission fragments, alpha particles and noise. New results from using artificial single-crystal diamonds (sCVD) show similar time resolution as from pCVD diamonds but also sufficiently good energy resolution. (authors)

  19. The VERDI fission fragment spectrometer

    Frégeau M.O.

    2013-12-01

    Full Text Available The VERDI time-of-flight spectrometer is dedicated to measurements of fission product yields and of prompt neutron emission data. Pre-neutron fission-fragment masses will be determined by the double time-of-flight (TOF technique. For this purpose an excellent time resolution is required. The time of flight of the fragments will be measured by electrostatic mirrors located near the target and the time signal coming from silicon detectors located at 50 cm on both sides of the target. This configuration, where the stop detector will provide us simultaneously with the kinetic energy of the fragment and timing information, significantly limits energy straggling in comparison to legacy experimental setup where a thin foil was usually used as a stop detector. In order to improve timing resolution, neutron transmutation doped silicon will be used. The high resistivity homogeneity of this material should significantly improve resolution in comparison to standard silicon detectors. Post-neutron fission fragment masses are obtained form the time-of-flight and the energy signal in the silicon detector. As an intermediary step a diamond detector will also be used as start detector located very close to the target. Previous tests have shown that poly-crystalline chemical vapour deposition (pCVD diamonds provides a coincidence time resolution of 150 ps not allowing complete separation between very low-energy fission fragments, alpha particles and noise. New results from using artificial single-crystal diamonds (sCVD show similar time resolution as from pCVD diamonds but also sufficiently good energy resolution.

  20. Fission fragment excited laser system

    McArthur, David A.; Tollefsrud, Philip B.

    1976-01-01

    A laser system and method for exciting lasing action in a molecular gas lasing medium which includes cooling the lasing medium to a temperature below about 150 K and injecting fission fragments through the lasing medium so as to preferentially excite low lying vibrational levels of the medium and to cause population inversions therein. The cooled gas lasing medium should have a mass areal density of about 5 .times. 10.sup.-.sup.3 grams/square centimeter, relaxation times of greater than 50 microseconds, and a broad range of excitable vibrational levels which are excitable by molecular collisions.

  1. Correlation measurements of fission-fragment properties

    Oberstedt A.; Martinez T.; Kis Z.; Karlsson J.; Hambsch F.-J.; Cano-Ott D.; Göök A.; Borcea R.; Billnert R.; Belgya T.; Oberstedt S.; Szentmiklosi L.; Takác K.

    2010-01-01

    For the development of future nuclear fission applications and for a responsible handling of nuclear waste the a-priori assessment of the fission-fragments’ heat production and toxicity is a fundamental necessity. The success of an indispensable modelling of the fission process strongly depends on a good understanding of the particular mechanism of scission, the mass fragmentation and partition of excitation energy. Experimental observables are fission-fragment properties like mass- and energ...

  2. Shell effects and fission fragments angular anisotropy

    The impact of the shell corrections attenuation effect with growth of the fissionable nuclei temperature on the angular anisotropy of the fission fragments is considered. The experimental data on the anisotropy of the fission fragments angular distributions of the compound nucleus, formed in the 4He + 238U reactions, are analyzed within the frames of the transition states model in the fission barriers saddle point and statistic theory of nuclear reactions. The obvious kind of the shell corrections attenuation function is obtained

  3. Detection of fission fragments by secondary emission

    This fission fragment detecting apparatus is based on the principle that fragments traversing a thin foil will cause emission of secondary electrons. These electrons are then accelerated (10 kV) and directly detected by means of a plastic scintillator and associated photomultiplier. Some of the advantages of such a detector are, its rapidity, its discriminating power between alpha particles and fission fragments, its small energy loss in detecting the fragments and the relatively great amount of fissionable material which it can contain. This paper is subdivided as follows: a) theoretical considerations b) constructional details of apparatus and some experimental details and c) a study of the secondary emission effect itself. (author)

  4. A new 144Ce/144Pr radioisotope generator system

    A miniaturized generator system was developed containing manganese dioxide-coated alumina on which 144Ce is deposited and from which 144Pr is eluted with an aqueous solution of 1% KIO3 in 1 N nitric acid. More than 60% of the 144Pr was recovered with a 99.9% radionuclide purity even after 2000 ml eluant and 1000 1 or air had been passed through the column. (author)

  5. Fission fragment angular distribution in heavy ion induced fission

    S. Soheyli

    2006-06-01

    Full Text Available   We have calculated the fission fragment angular anisotropy for 16O + 232Th,12C + 236U , 11B + 237 Np , 14 N + 232 Th , 11B + 235U , 12C + 232Th systems with the saddle point statistical model and compared the fission fragment angular anisotropy for these systems. This comparison was done with two methods a without neutron correction and b with neutron correction. Also we studied normal and anomalous behavior of the fission fragment angular anisotropy. Finally, we have predicted the average emitted neutron from compound nuclei considering the best fit for each system.

  6. Fission fragment angular distribution in heavy ion induced fission

    S. Soheyli; I. Ziaeian

    2006-01-01

      We have calculated the fission fragment angular anisotropy for 16O + 232Th,12C + 236U , 11B + 237 Np , 14 N + 232 Th , 11B + 235U , 12C + 232Th systems with the saddle point statistical model and compared the fission fragment angular anisotropy for these systems. This comparison was done with two methods a) without neutron correction and b) with neutron correction. Also we studied normal and anomalous behavior of the fission fragment angular anisotropy. Finally, we have predicted the averag...

  7. Correlation measurements of fission-fragment properties

    Oberstedt A.

    2010-10-01

    Full Text Available For the development of future nuclear fission applications and for a responsible handling of nuclear waste the a-priori assessment of the fission-fragments’ heat production and toxicity is a fundamental necessity. The success of an indispensable modelling of the fission process strongly depends on a good understanding of the particular mechanism of scission, the mass fragmentation and partition of excitation energy. Experimental observables are fission-fragment properties like mass- and energy-distributions, and the prompt neutron as well as γ-ray multiplicities and emission spectra. The latter quantities should preferably be known as a function of fragment mass and excitation energy. Those data are highly demanded as published by the OECD-NEA in its high priority data request list. With the construction of the double (v, E spectrometer VERDI we aim at measuring pre- and post-neutron masses directly and simultaneously to avoid prompt neutron corrections. From the simultaneous measurement of pre- and post-neutron fission-fragment data the prompt neutron multiplicity may then be inferred fully correlated with fragment mass yield and total kinetic energy. Using an ultra-fast fission event trigger spectral prompt fission γ-ray measurements may be performed. For that purpose recently developed lanthanum-halide detectors, with excellent timing characteristics, were coupled to the VERDI spectrometer allowing for a very good discrimination of fission γ-rays and prompt neutrons due to their different time-of-flight.

  8. Antiproton Induced Fission and Fragmentation of Nuclei

    2002-01-01

    The annihilation of slow antiprotons with nuclei results in a large highly localized energy deposition primarily on the nuclear surface. \\\\ \\\\ The study of antiproton induced fission and fragmentation processes is expected to yield new information on special nuclear matter states, unexplored fission modes, multifragmentation of nuclei, and intranuclear cascades.\\\\ \\\\ In order to investigate the antiproton-nucleus interaction and the processes following the antiproton annihilation at the nucleus, we propose the following experiments: \\item A)~Measurement of several fragments from fission and from multifragmentation in coincidence with particle spectra, especially neutrons and kaons. \\item B)~Precise spectra of $\\pi$, K, n, p, d and t with time-of-flight techniques. \\item C)~Installation of the Berlin 4$\\pi$ neutron detector with a 4$\\pi$ Si detector placed inside for fragments and charged particles. This yields neutron multiplicity distributions and consequently distributions of thermal excitation energies and...

  9. Brownian shape motion: Fission fragment mass distributions

    Sierk Arnold J.; Randrup Jørgen; Möller Peter

    2012-01-01

    It was recently shown that remarkably accurate fission-fragment mass distributions can be obtained by treating the nuclear shape evolution as a Brownian walk on previously calculated five-dimensional potential-energy surfaces; the current status of this novel method is described here.

  10. Fission fragment rockets - A new frontier

    A new reactor concept is described which would enable fission fragments to be continuously extracted from the reactor. Such a reactor has the potential of enabling extremely energetic and ambitious deep space missions. In this talk the basic physics issues involved in the operation of this type of reactor are outlined, and some possible applications to space exploration are described

  11. Brownian shape motion: Fission fragment mass distributions

    Sierk Arnold J.

    2012-02-01

    Full Text Available It was recently shown that remarkably accurate fission-fragment mass distributions can be obtained by treating the nuclear shape evolution as a Brownian walk on previously calculated five-dimensional potential-energy surfaces; the current status of this novel method is described here.

  12. Isoscaling of the Fission Fragments with Langevin Equation

    WANG Kun; TIAN Wen-Dong; ZHONG Chen; ZHOU Xing-Fei; MA Yu-Gang; WEI Yi-Bin; CAI Xiang-Zhou; CHEN Jin-Gen; FANG De-Qing; GUO Wei; MA Guo-Liang; SHEN Wen-Qing

    2005-01-01

    @@ The Langevin equation is used to simulate the fission process of 112Sn + 112Sn and 116Sn + 116Sn. The mass distribution of the fission fragments are given by assuming the process of symmetric fission or asymmetric fission with the Gaussian probability sampling. The isoscaling behaviour has been observed from the analysis of fission fragments of both the reactions, and the isoscaling parameter α seems to be sensitive to the width of fission probability and the beam energy.

  13. Isoscaling of the Fission Fragments with Langevin Equation

    Wang, K.; Ma, Y. G.; Wei, Y. B.; Cai, X. Z.; Chen, J. G.; Fang, D Q; Guo, W; Ma, G. L.; Shen, W.Q.(Shanghai Institute of Applied Physics, Shanghai, 201800, China); Tian, W.D.; Zhong, C.; Zhou, X. F.

    2004-01-01

    Langevin equation is used to simulate the fission process of $^{112}$Sn + $^{112}$Sn and $^{116}$Sn + $^{116}$Sn. The mass distribution of the fission fragments are given by assuming the process of symmetric fission or asymmetric fission with the Gaussian probability sampling. Isoscaling behavior has been observed from the analysis of fission fragments of both reactions and the isoscaling parameter $\\alpha$ seems to be sensitive to the width of fission probability and the beam energy.

  14. Influence of spin on fission fragments anisotropy

    Ghodsi Omid N.

    2005-01-01

    Full Text Available An analysis of selected fission fragment angular distribution when at least one of the spins of the projectile or target is appreciable in induced fission was made by using the statistical scission model. The results of this model predicate that the spins of the projectile or target are affected on the nuclear level density of the compound nucleus. The experimental data was analyzed by means of the couple channel spin effect formalism. This formalism suggests that the projectile spin is more effective on angular anisotropies within the limits of energy near the fusion barrier.

  15. Fission fragment angular distributions and fission cross section validation

    The present knowledge of angular distributions of neutron-induced fission is limited to a maximal energy of 15 MeV, with large discrepancies around 14 MeV. Only 238U and 232Th have been investigated up to 100 MeV in a single experiment. The n-TOF Collaboration performed the fission cross section measurement of several actinides (232Th, 235U, 238U, 234U, 237Np) at the n-TOF facility using an experimental set-up made of Parallel Plate Avalanche Counters (PPAC), extending the energy domain of the incident neutron above hundreds of MeV. The method based on the detection of the 2 fragments in coincidence allowed to clearly disentangle the fission reactions among other types of reactions occurring in the spallation domain. I will show the methods we used to reconstruct the full angular resolution by the tracking of fission fragments. Below 10 MeV our results are consistent with existing data. For example in the case of 232Th, below 10 MeV the results show clearly the variation occurring at the first (1 MeV) and second (7 MeV) chance fission, corresponding to transition states of given J and K (total spin and its projection on the fission axis), and a much more accurate energy dependence at the 3. chance threshold (14 MeV) has been obtained. In the spallation domain, above 30 MeV we confirm the high anisotropy revealed in 232Th by the single existing data set. I'll discuss the implications of this finding, related to the low anisotropy exhibited in proton-induced fission. I also explore the critical experiments which is valuable checks of nuclear data. The 237Np neutron-induced fission cross section has recently been measured in a large energy range (from eV to GeV) at the n-TOF facility at CERN. When compared to previous measurements, the n-TOF fission cross section appears to be higher by 5-7 % beyond the fission threshold. To check the relevance of n-TOF data, we simulate a criticality experiment performed at Los Alamos with a 6 kg sphere of 237Np. This sphere was

  16. Understanding of fission dynamics from fragment mass distribution studies

    Nuclear fission is a complex process involving large scale collective rearrangement of nuclear matter. The shape of the fissioning nucleus evolves in the multidimensional space of relative separation, neck opening, mass asymmetry and deformation of the fragments. Various types of nuclear shape deformation have been observed from the fission fragment spectroscopy studies, which provide crucial information in the understanding of the dynamics of the fission process. The fission fragment mass and charge distributions are decided during saddle to scission transition and are directly related to the scission configuration. Several nuclear models have been put forward to describe the fission fragment mass distribution as well as shape deformation of the fragments. The width of the fission fragment mass distribution is related to the fission process and provides information on the type of fission reactions

  17. Fission fragment rockets -- a potential breakthrough

    A new reactor concept which has the potential of enabling extremely energetic and ambitious space propulsion missions is described. Fission fragments are directly utilized as the propellant by guiding them out of a very low density core using magnetic fields. The very high fission fragment exhaust velocities yield specific impulses of approximately a million seconds while maintaining respectable thrust levels. Specific impulses of this magnitude allow acceleration of significant payload masses to several percent of the velocity of light and enable a variety of interesting missions, e.g., payloads to the nearest star, Alpha Centauri, in about a hundred years or very rapid solar system transport. The parameters reported in this paper are based on a very preliminary analysis. Considerable trade-off studies will be required to find the optimum system

  18. Fission Fragment characterization with FALSTAFF at NFS

    Pancin J.

    2013-03-01

    Full Text Available The Neutrons for Science (NFS facility will be one of the first installations of the SPIRAL2 facility. NFS will be composed of a time-of-flight baseline and irradiation stations and will allow studying neutron-induced reactions for energies going from some hundreds of keV up to 40 MeV. Continuous and quasi-monoenergetic energy neutron beams will be available. Taking advantage of this new installation, the development of an experimental setup for a full characterization of actinide fission fragments in this energy domain has been undertaken. To achieve this goal a new detection system called FALSTAFF (Four Arm cLover for the STudy of Actinide Fission Fragments in under development. In this paper, the characteristics of the NFS facility will be exposed and the motivations for the FALSTAFF experiment will be presented. The experimental setup will be described and the expected resolutions based on realistic GEANT4 simulations will be discussed.

  19. Fission Fragment characterization with FALSTAFF at NFS

    Doré, D.; Farget, F.; Lecolley, F.-R.; Ledoux, X.; Lehaut, G.; Materna, T.; Pancin, J.; Panebianco, S.

    2013-03-01

    The Neutrons for Science (NFS) facility will be one of the first installations of the SPIRAL2 facility. NFS will be composed of a time-of-flight baseline and irradiation stations and will allow studying neutron-induced reactions for energies going from some hundreds of keV up to 40 MeV. Continuous and quasi-monoenergetic energy neutron beams will be available. Taking advantage of this new installation, the development of an experimental setup for a full characterization of actinide fission fragments in this energy domain has been undertaken. To achieve this goal a new detection system called FALSTAFF (Four Arm cLover for the STudy of Actinide Fission Fragments) in under development. In this paper, the characteristics of the NFS facility will be exposed and the motivations for the FALSTAFF experiment will be presented. The experimental setup will be described and the expected resolutions based on realistic GEANT4 simulations will be discussed.

  20. Measurement of fission fragments energy loss

    Benetti, P; Calligarich, E; Cesana, A; Dolfini, R; Ioppolo, T; Raselli, G L; Terrani, M

    2002-01-01

    The mean energy of sup 2 sup 5 sup 2 Cf fission fragments emerging from an absorber and the determination of the capture rate in the absorber itself have been measured using two independent and complementary nuclear techniques. The results can be applied to the measurement of the energy self-absorption in a non-zero thickness source and can be used to validate simulation programs.

  1. MAFF - the Munich accelerator for fission fragments

    At the new high flux reactor FRM-II in Munich the accelerator MAFF (Munich Accelerator for Fission Fragments) is under design. In the high neutron flux of 1014 n/cm2 s up to 1014 neutron-rich fission fragments per second are produced in the 1 g 235 U target. Ions with an energy of 30 keV are extracted from the ion source. In the mass separator two isotopes can be selected. One of the beams is used for low energy experiments, the other one is injected into an ECRIS (or EBIS) for charge breeding to a q/A ≥ 0.16. A gas filled RFQ cooler is used for emittance improvement. The subsequent LINAC delivers beams with an energy ranging from 3.7 MeV/u to 5.9 MeV/u. New IH structures are being developed at the Munich tandem laboratory. A small storage ring is planned in a further stage to recycle the fission fragments. A thin target foil can be placed into this ring, e.g., for synthesis of super-heavy elements. The through-going beam tube has been installed in the heavy water tank of the reactor. Tests of the target ion source in a special oven to test long term stability and safety tests were in progress. (author)

  2. Toxicity of 144Ce inhaled in a relatively insoluble form by immature beagle dogs. VI

    Immature Beagle dogs (approximately equal to 3 months of age at exposure) have been exposed by inhalation to a relatively insoluble form of 144Ce (in fused aluminosilicate particles) to compare the resulting patterns of metabolism, dosimetry and biological effects with those seen in dogs exposed at 12 and 14 months of age and at 8 to 10.5 years of age. Five blocks of longevity animals, each consisting of 10 exposed dogs and one control, are currently on experiment. The initial lung burdens of the 144Ce-exposed dogs range from 0.004 to 140 μCi 144Ce/kg body weight. Three dogs with initial lung burdens of 73 to 120 μCi 144Ce/kg body weight died at 66 to 121 days after exposure with pulmonary injury and congestive heart failure. One dog with an initial lung burden of 140 μCi 144Ce/kg body weight died at 91 days after exposure with severe radiation pneumonitis and minimal pulmonary fibrosis and another dog whose initial lung burden was 70 μCi 144Ce/kg body weight died at 511 days after exposure with pulmonary injury that was mainly fibrotic in nature. Two dogs with initial lung burdens of 52 and 64 μCi 144Ce/kg body weight had primary pulmonary hemangiosarcomas and died at 618 and 689 days, respectively, with cumulative average absorbed beta doses to lung of 23,000 and 29,000 rads. One dog with an initial lung burden of 28 μCi 144Ce/kg body weight was euthanized at 1227 days after exposure with a hemangiosarcoma of the mediastinum, and another dog with an initial lung burden of 12 μCi 144Ce/kg body weight died at 1520 days after exposure from epilepsy. Serial observations are continuing on the surviving 40 exposed and five control dogs

  3. Revisiting the even-odd staggering in fission fragment yields

    Caamano, M.; Rejmund, F.; Schmidt, K. -H.

    2009-01-01

    The even-odd staggering observed in the experimental fission-fragment nuclear-charge yields is investigated over a wide systematics of fission fragments measured at Lohengrin in direct kinematics and at GSI in inverse kinematics. The general increase of the even-odd staggering in the fission-fragment charge yields towards asymmetric charge splits is explained by the absorption of the unpaired nucleons by the heavy fragment. As a consequence, the well established trend of evenodd staggering in...

  4. Toxicity of 144Ce inhaled in a relatively insoluble form by immature Beagle dogs. XVII

    Immature Beagle dogs (3-mo old) received a single, brief inhalation exposure to 144Ce in fused aluminosilicate particles as part of a series of studies designed to study the effects of age on dose response relationships for inhaled radionuclides. Forty-nine dogs inhaled graded levels of 144Ce that resulted in initial lung burdens ranging from 0.004-140 μCi/kg 0.15-5200 kBq/kg) body weight. Five control dogs inhaled nonradioactive fused aluminosilicate particles. Forty-one of the 144Ce-exposed dogs have died: 11 with lung tumors 4 with tumors of the tracheobronchial lymph nodes, with a nasal cavity tumor, and 9 with non neoplastic diseases of the respiratory tract. Observations are continuing on the 8 144Ce-exposed dogs that are surviving at this time. (author)

  5. DSP Algorithms for Fission Fragment and Prompt Fission Neutron Spectroscopy

    Zeynalova, O.; Zeynalov, Sh.; Hambsch, F.-J.; Oberstedt, S.; Fabry, I.

    2009-10-01

    Digital signal processing (DSP) algorithms are in high demand for modern nuclear fission investigation due to importance of increase the accuracy of fissile nuclear data for new generation of nuclear power stations. DSP algorithms for fission fragment (FF) and prompt fission neutron (PFN) spectroscopy are described in the present work. The twin Frisch-grid ionization chamber (GTIC) is used to measure the kinetic energy-, mass- and angular distributions of the FF in the 252Cf(SF) reaction. Along with the neutron time-of-flight (TOF) measurement the correlation between neutron emission and FF mass and energy is investigated. The TOF is measured between common cathode of the GTIC and the neutron detector (ND) pulses. Waveform digitizers (WFD) having 12 bit amplitude resolution and 100 MHz sampling frequency are used for the detector pulse sampling. DSP algorithms are developed as recursive procedures to perform the signal processing, similar to those available in various nuclear electronics modules, such as constant fraction discriminator (CFD), pulse shape discriminator (PSD), peak-sensitive analogue-to-digital converter (pADC) and pulse shaping amplifier (PSA). To measure the angle between FF and the cathode plane normal to the GTIC a new algorithm is developed having advantage over the traditional analogue pulse processing schemes. Algorithms are tested by comparing the numerical simulation of the data analysis of the 252Cf(SF) reaction with data available from literature.

  6. Toxicity of inhaled 144CeCl3 in beagle dogs. VIII

    Studies on the metabolism, dosimetry, and effects of inhaled 144CeCl3 in the Beagle dog are continuing to provide information that will aid in assessing the biological consequences of inhaling 144Ce such as might be released in certain nuclear accidents. Studies on the tissue distribution of inhaled 144CeCl3 have shown that the 144Ce deposited in lung is translocated at a moderately rapid rate to liver and skeleton and that significant radiation doses are accumulated by all three organs. Fifty-five dogs that inhaled 144CeCl3 and 15 control dogs were placed in a longevity study and are being observed for their lifespan. The 144Ce dogs had long-term retained burdens with values ranging from 20 to 2900 μCi. Thirty-one of the dogs exposed to 144CeCl3 have died; 8 at 21 to 44 days after inhalation with signs attributed to severe bone marrow damage and associated pancytopenia; 2 at 138 and 144 days with radiation pneumonitis; 3 at 309 to 874 days with hepatic necrosis; 1 at 510 days with marrow aplasia; 1 at 375 days with pulmonary fibrosis; and 16 at 799 to 3081 days, most with neoplasms or myeloproliferative disorders. In this last group, 1 dog had an osteosarcoma, 3 had squamous cell carcinomas of the maxilla, 2 of the latter also having primary pulmonary neoplasms, 5 had hemangiosarcomas of the liver, 1 had a hemangiosarcoma of the nasal cavity, 2 had myelogenous leukemia, 1 had myelofibrosis with myeloid metaplasia, 1 had spinal cord ependymomas, and 2 did not have neoplasms. One of these had severe myelomalacia and the other diffuse hepatic lipidosis with severe degeneration. Two controls died; 1 with a thyroid carcinoma and 1 with aspiration pneumonia. Serial observations are continuing on the 24 surviving 144CeCl3 dogs and 13 control dogs. (U.S.)

  7. Fission fragment characterization with FALSTAFF at NFS

    The Neutrons for Science (NFS) facility will be one of the first installations of the SPIRAL2 facility. NFS will be composed of a time-of-flight baseline and irradiation stations and will allow studying neutron-induced reactions for energies going from some hundreds of keV up to 40 MeV. Continuous and quasi-monoenergetic energy neutron beams will be available. Taking advantage of this new installation, the development of an experimental setup for a full characterization of actinide fission fragments in this energy domain has been undertaken. To achieve this goal a new detection system called FALSTAFF (Four Arm clover for the Study of Actinide Fission Fragments) in under development. Charge and mass distribution measurements in FALSTAFF are based on residual energy and velocity measurements. The 2V and EV methods are used to determine the fragment mass before and after neutron evaporation. In this paper, the characteristics of the NFS facility will be exposed and the motivations for the FALSTAFF experiment will be presented. The experimental setup will be described and the expected resolutions based on realistic GEANT4 simulations will be discussed. Simulations show that the foreseen experimental setup is able to provide the required precision. The building construction is almost finished and the beginning of the commissioning is planned for mid-2014

  8. Fusion – fission dynamics: fragment mass distribution studies

    Bhattacharya S; Chaudhuri A.; Ghosh T. K.; Banerjee K; Bhattacharya C.; Kundu S.; Mukherjee G; Rana T. K.; Roy P; Pandey R; Bhattacharya P

    2015-01-01

    Using the major accelerator facilities available in India, detailed experimental studies have been made to understand the mechanism of quasi-fission and role of nuclear shell effect in heavy nuclei. Fission fragment mass distribution has been used as the probe to explore the role of entrance channel effects on fusion-fission and quasifission dynamics. Fission fragment mass distribution has also been demonstrated to be useful to identify the phenomenon of ‘washing out’ of nuclear shell effect ...

  9. About total kinetic energy distribution between fragments of binary fission

    At the investigation of binary fission reactions one of the main characteristic of process is total kinetic energy (TKE) of fission fragments and it distribution between them. From the values of these characteristics it is possible to extract the information about structure of fission fragments in the break up point of initial fissionable nuclear system. In our work TKE dependence from the deformation parameters of shape and density distribution of charge in the fission fragments are investigated. In the end of paper some generalizations of obtaining results are carried out and presented in the form of tables and figures

  10. Alkaline glass as induced fission fragment detectors

    The slide glass, registered trade marks INLAB, INVICT and PERFECTA were compared. For the three kinds of glasses the following studies were done: chemical composition; general dissolution rate for hydrofluoric acid solutions of concentrations between 1 and 10M, at 300C and ultrasound shaking; relative efficiency for recording fission fragment tracks from 252Cf. The INLAB glass was selected due to the better quality of its surface after chemical etching. The HF concentration 2.5M was determined for chemical etching of INLAB glass, and the optimum etching time was chosen between 8 and 10 minutes. The thermal attenuation of latent tracks in the environmental temperature was observed for intervals uo to 31 days between the detector exposure to the fission fragment source and etching of tracks. Several methods were used for determining the detector parameters, such as: critical angle, angle of the cone and efficiency of etching. The effects of gamma irradiation from 60Co and reactor neutrons in material properties as track detector were studied. Attenuation of latent tracks and saturation of color centers were observed for doses over 100M Rad. Since this kind of material contains uranium as impurity, uniformely distributed, slide glass were calibrated to be applied as a monitor of thermal neutron flux in nuclear reactor. (Author)

  11. Fission fragment detector by thin film capacitors. Pt. 2

    Fission fragments produce current pulses in thin film capacitors at applied electric fields lower than those required for the induction of breakdowns by such charged particles. This paper describes the use of silicon dioxide capacitors for the detection of fission fragments by these current pulses. With capacitor areas of 2 x 10-2 cm2, the pulses are not detectable when the oxide is relatively thin, but with 3,800 A thick oxide, fission fragments produce pulses of about 10-15C. The mechanisms producing the current pulses by fission fragments are finally discussed. (orig.)

  12. The multi-step prompt particle emission from fission fragments

    The purpose of this work is the study of non-equilibrium high-energy gamma emission from 252 Cf. In the framework of the formalism of statistical multi-step compound processes in nuclear reactions. A relation was found between the shape of the high-energy part of the gamma spectrum and different mechanisms of excitation of the fission fragments. Agreement with experimental data for different groups of fission fragments was obtained. The analysis of the experimental high-energy part of gamma spectra yields information about the mechanism of excitation of fission fragments. The influence of dissipation of the deformation excess on intrinsic excitation of fission fragments was studied. (authors)

  13. Conservation of Isospin in Neutron-rich Fission Fragments

    On the occasion of the 75th anniversary of the fission phenomenon, we present a surprisingly simple result which highlights the important role of isospin and its conservation in neutron rich fission fragments. We have analysed the fission fragment mass distribution from two recent heavyion reactions 238U(18O,f) and 208Pb(18O,f) as well as a thermal neutron fission reaction 245Cm(nth,f). We find that the conservation of the total isospin explains the overall trend in the observed relative yields of fragment masses in each fission pair partition. The isospin values involved are very large making the effect dramatic. The findings open the way for more precise calculations of fission fragment distributions in heavy nuclei and may have far reaching consequences for the drip line nuclei, HI fusion reactions, and calculation of decay heat in the fission phenomenon

  14. Conservation of Isospin in Neutron-rich Fission Fragments

    Jain, A. K.; Choudhury, D.; Maheshwari, B.

    2014-06-01

    On the occasion of the 75th anniversary of the fission phenomenon, we present a surprisingly simple result which highlights the important role of isospin and its conservation in neutron rich fission fragments. We have analysed the fission fragment mass distribution from two recent heavyion reactions 238U(18O,f) and 208Pb(18O,f) as well as a thermal neutron fission reaction 245Cm(nth,f). We find that the conservation of the total isospin explains the overall trend in the observed relative yields of fragment masses in each fission pair partition. The isospin values involved are very large making the effect dramatic. The findings open the way for more precise calculations of fission fragment distributions in heavy nuclei and may have far reaching consequences for the drip line nuclei, HI fusion reactions, and calculation of decay heat in the fission phenomenon.

  15. Conservation of Isospin in Neutron-Rich Fission Fragments

    Jain, Ashok Kumar; Maheshwari, Bhoomika

    2014-01-01

    On the occasion of the $75^{th}$ anniversary of the fission phenomenon, we present a surprisingly simple result which highlights the important role of isospin and its conservation in neutron rich fission fragments. We have analysed the fission fragment mass distribution from two recent heavy-ion reactions $^{238}$U($^{18}$O,f) and $^{208}$Pb($^{18}$O,f) as well as a thermal neutron fission reaction $^{245}$Cm(n$^{th}$,f). We find that the conservation of the total isospin explains the overall trend in the observed relative yields of fragment masses in each fission pair partition. The isospin values involved are very large making the effect dramatic. The findings open the way for more precise calculations of fission fragment distributions in heavy nuclei and may have far reaching consequences for the drip line nuclei, HI fusion reactions, and calculation of decay heat in the fission phenomenon.

  16. Toxicity of inhaled 144CeCl3 in beagle dogs. XI

    Studies on the metabolism, dosimetry and effects of inhaled 144CeCl3 in Beagle dogs are being conducted to assess the biological consequences of inhaling 144Ce such as might be released in certain nuclear accidents. Studies on the organ distribution of inhaled 144CeCl3 have shown that the 144Ce deposited in the lung is translocated at a moderately rapid rate to liver and skeleton and that significant radiation doses are accumulated by all three organs. Fifty-five dogs that inhaled 144CeCl3 and 15 control dogs are being observed for their life span. The 144Ce dogs have long-term retained burdens with values ranging from 20 to 2900 μCi. Forty-five of the dogs exposed to 144CeCl3 have died; eight from 21 to 44 days after inhalation with severe bone marrow damage and associated pancytopenia; two at 138 and 144 days with radiation pneumonitis; three from 309 to 874 days with hepatic necrosis; one at 510 days with marrow aplasia; one at 375 days with pulmonary fibrosis; and 30 from 799 to 4085 days, most with neoplasms or myeloproliferative disorders. In this last group, one dog had an osteosarcoma, five had squamous cell carcinomas of the nasal cavity (two also having primary pulmonary neoplasms), six had hemangiosarcomas of the liver, one had a hemangiosarcoma of the nasal cavity, two had myelogenous leukemia, one had myelofibrosis with myeloid metaplasia, one had spinal cord ependymomas, one had a malignant melanoma (also an ependymoma) and two had mammary adenocarcinomas. Three dogs had primary pulmonary neoplasms including two with bronchogenic adenocarcinomas and one with an adenoma. Seven did not have malignant neoplasms. Two of these had severe myelomalacia, one had pulmonary edema, three had congestive heart failure and one had diffuse hepatic lipidosis with severe hepatic degeneration

  17. Fission fragments transport by gaseous flow with aerosols

    Paper describes a pilot facility for fission fragment transport by gaseous flow with aerosols. This facility designed for fragment transport consists of a reaction chamber with irradiated target, receipt chamber to collect fragments, aerosol generator, roughing pump to pump put gas and a capillary connecting these units of facility. Paper presents the results of facility testing with fragments of 238U photofission by microtron Bremsstrahlung. The obtained parameters of facility (up to 70% efficiency of transport, up to 0.1 s time of transport at 1 m distance) enable to use it efficiently in experiments dealing with heavy nuclei fission and with investigation in properties of fission fragments

  18. Toxicity of 144Ce inhaled in a relatively insoluble form by immature Beagle dogs. XII

    Immature Beagle dogs (3 months old) were exposed once by inhalation to an aerosol of 144Ce incorporated in fused aluminosilicate particles. The influence of this age on the dose-response relationships is being compared to that of 13-mo-old and 8 to 10.5-yr-old dogs. This study involves 49 dogs that received graded initial lung burdens from 0.004 to 140 μCi 144Ce/kg body weight and five control dogs. To date, 19 of the 144Ce-exposed dogs and one of the controls have died. Dogs with the highest initial lung burdens of 144Ce died during the first 4 months with radiation pneumonitis, pulmonary fibrosis, and congestive heart failure. Pulmonary hemangiosarcoma was the primary finding in dogs that died at 1.5 to 2 years after exposure. Deaths beyond that time have been due primarily to extrapulmonary hemangiosarcomas. Observations are continued on the surviving 30 144Ce-exposed and four control dogs at 7.0 to 11.2 years after exposure

  19. Toxicity of 144Ce inhaled in a relatively insoluble form by aged Beagle dogs. XII

    The toxicity of relatively insoluble 144Ce inhaled by 8- to 10.5-year-old Beagle dogs is being investigated to determine possible age-related differences in long-term biological responses. Forty-two dogs were exposed to aerosols of 144Ce in fused aluminosilicate particles to yield initial lung burdens of 2.2 to 75 μCi 144Ce/kg body weight, and 12 control dogs were exposed to non-radioactive fused aluminosilicate particles. All 144Ce-exposed and control dogs have died or were euthanized between 197 and 2726 days after the inhalation exposure. Prominent findings in the 144Ce-exposed dogs were radiation pneumonitis in 19 of the 23 dogs that died during the first 943 days after exposure, and neoplastic disease in 13 of the 20 dogs that died beyond 904 days after exposure. Pulmonary tumors were found in five of these dogs. In contrast to the study with young adult dogs, in which pulmonary hemangiosarcomas were one of the prominent findings, all of these tumors were carcinomas

  20. Fission fragment orientation and gamma ray emission anisotropy

    Barabanov, A. L.

    1994-01-01

    Experimental data on angular distributions of gamma rays emitted from binary and ternary spontaneous fission of $^{252}{\\rm Cf}$ are analyzed. Their difference indicates that the alignment of fragments is higher in ternary fission than in binary one. The consequences of possible relation between the mechanism of ternary fission and the excitation of collective modes during the saddle-to-scission stage are discussed.

  1. New fission-fragment detector for experiments at DANCE

    Rusev, G.; Roman, A. R.; Daum, J. K.; Springs, R. K.; Bond, E. M.; Jandel, M.; Baramsai, B.; Bredeweg, T. A.; Couture, A.; Favalli, A.; Ianakiev, K. D.; Iliev, M. L.; Mosby, S.; Ullmann, J. L.; Walker, C. L.

    2015-10-01

    A fission-fragment detector based on thin scintillating films has been built to serve as a veto/trigger detector in neutron-induced fission measurements at DANCE. The fissile material is surrounded by scintillating films providing a 4 π detection of the fission fragments. The scintillation events caused by the fission fragment interactions in the films are registered with silicon photomultipliers. Design of the detector and test measurements are described. Work supported by the U.S. Department of Energy through the LANL/LDRD Program and the U.S. Department of Energy, Office of Science, Nuclear Physics under the Early Career Award No. LANL20135009.

  2. The fission fragment yields at the photofission of actinide nuclei

    The fission fragment yields of isotopes 101Mo, 135I, 135mCs were measured at the photo-fission of actinide nuclei 232Th, 238U, 237Np. These fission fragments have some peculiarities in nuclear structure or in practical using. The measurements were performed on the microtron bremsstrahlung at the Flerov Laboratory of Nuclear Reactions, JINR, at the electron energy 22 MeV. The activation method with an HPGe detector was used in these measurements of the yields

  3. Fission fragment mass distributions via prompt -ray spectroscopy

    L S Danu; D C Biswas; B K Nayak; R K Choudhury

    2015-09-01

    The distribution of fragment masses formed in nuclear fission is one of the most striking features of the process. Such measurements are very important to understand the shape evolution of the nucleus from ground state to scission through intermediate saddle points. The fission fragment mass distributions, generally obtained via conventional methods (i.e., by measuring the energy and/or the velocity of the correlated fission fragments) are limited to a mass resolution of 4–5 units. On the other hand, by employing the -ray spectroscopy, it is possible to estimate the yield of individual fission fragments. In this work, determination of the fission fragment mass distribution by employing prompt -ray spectroscopy is described along with the recent results on 238U(18O, f) and 238U(32S, f) systems.

  4. Characterization of the scission point from fission-fragment velocities

    Caamaño, M; Delaune, O; Schmidt, K -H; Schmitt, C; Audouin, L; Bacri, C -O; Benlliure, J; Casarejos, E; Derkx, X; Fernández-Domínguez, B; Gaudefroy, L; Golabek, C; Jurado, B; Lemasson, A; Ramos, D; Rodríguez-Tajes, C; Roger, T; Shrivastava, A

    2015-01-01

    The isotopic-yield distributions and kinematic properties of fragments produced in transfer-induced fission of 240Pu and fusion-induced fission of 250Cf, with 9 MeV and 45 MeV of excitation energy respectively, were measured in inverse kinematics with the spectrometer VAMOS. The kinematic properties of identified fission fragments allow to derive properties of the scission configuration such as the distance between fragments, the total kinetic energy, the neutron multiplicity, the total excitation energy, and, for the first time, the proton- and neutron-number sharing during the emergence of the fragments. These properties of the scission point are studied as functions of the fragment atomic number. The correlation between these observables, gathered in one single experiment and for two different fissioning systems at different excitation energies, give valuable information for the understanding and modeling of the fission process.

  5. Toxicity of inhaled 144Ce in fused aluminosilicate particles in aged beagle dogs. V

    The toxicity of 144Ce in fused aluminosilicate particles inhaled by 8- to 10.5-yr-old dogs is being investigated to provide information on age-related differences in the response of older members of the human population to accidental inhalation of radioactive aerosols. These data on aged dogs will be compared to the results of similar studies of dogs exposed at approximately 3 mo or 12 to 14 mo of age. Six blocks of five female dogs each have been divided into four exposure levels with mean initial lung burdens of 7.2, 14, 28 and 57 μCi 144Ce/kg body weight. Six blocks of four male dogs have been divided into three exposure levels with mean initial lung burdens of 7.2, 14 and 28 μCi 144Ce/kg body weight. Controls in each block were exposed to fused aluminosilicate particles containing stable cerium. Fifteen dogs with initial lung burdens ranging from 20 to 75 μCi 144Ce/kg body weight and cumulative doses to lung of from 22,000 to 74,000 rads have died or were euthanized 197 to 1207 days after exposure with clinicopathologic findings of radiation pneumonitis and pulmonary fibrosis.Pulmonary retention of the inhaled 144Ce was similar to that observed previously in dogs exposed at 18 to 22 mo of age in a radiation dose pattern study. Serial observations are continuing on the 19 surviving 144Ce-exposed and eight control dogs

  6. Toxicity of 144Ce fused clay particles inhaled by aged dogs. III

    The toxicity of 144Ce fused clay particles inhaled by 8- to 10.5-year-old dogs is being investigated to provide information on age-related differences in the response of older members of the human population to accidental inhalation of radioactive aerosols. These data on aged dogs will be compared to the results of similar studies using dogs exposed at approximately 3 months or 12 to 14 months of age. To date, 7 blocks of 5 dogs each, divided into 4 exposure levels with mean initial lung burdens of 7.5, 14, 24, and 57 μCi/kg body weight and control dogs exposed to non-labeled fused clay particles have been entered into a longevity study. Twelve dogs with initial lung burdens ranging from 20 to 75 μCi 144Ce/kg body weight and cumulative doses to lung of from 22,000 to 74,000 rads have died at 197 to 943 days post-inhalation with clinico-pathologic findings of radiation pneumonitis and pulmonary fibrosis. Two of these also had congestive heart failure. In addition, 4 dogs with ILBs of 8 to 14 μCi 144Ce/kg body weight have died of mammary neoplasms or congestive heart failure but without radiation pneumonitis. One dog with an ILB of 9 μCi 144Ce/kg body weight died with a chronic interstitial foreign body pneumonia. Two control dogs have died, one with a mammary carcinoma and one with pyometra. Pulmonary retention of the inhaled 144Ce was similar to that observed previously in dogs exposed at 18 to 22 months of age in a radiation dose pattern study. Serial observations are continuing on the 11 surviving 144Ce-exposed dogs and 5 controls. (U.S.)

  7. Toxicity of 144Ce inhaled in a relatively insoluble form by immature Beagle dogs. VIII

    The influence of age at exposure on the resulting patterns of deposition, retention, dosimetry and biological effects from a single inhalation exposure to a relatively insoluble form of a beta-emitting radionuclide with a relatively long physical half-life is being investigated. Immature Beagle dogs (3 months of age) have been exposed once, by inhalation, to an aerosol of 144Ce incorporated in fused aluminosilicate particles. Eighteen of these dogs were serially sacrificed to study the patterns of deposition, retention and dosimetry and the remaining 49 dogs received graded initial lung burdens that ranged from 0.004 to 140 μCi 144Ce/kg body weight and are being observed over their life span for study of the resulting long-term biological effects. Five control dogs are also included in this study. To date, 13 of the 144Ce-exposed dogs in the longevity study and none of the controls have died. Dogs with the highest initial lung burdens of 144Ce died first (during the first 4 months) with radiation pneumonitis, pulmonary fibrosis and congestive heart failure. Pulmonary hemangiosarcoma was the primary finding in dogs that died at 1.5 to 2 years after exposure. Deaths beyond that time have primarily involved extrapulmonary hemangiosarcomas. One dog, 627B, with an initial lung burden of 24 μCi 144Ce/kg body weight died during the past year at 2341 days after exposure with a widely disseminated hemangiosarcoma showing heavy involvement of the liver and skin. Observations are continuing on the surviving 36 144Ce-exposed and five control dogs

  8. Conservation of Isospin in Neutron-Rich Fission Fragments

    Jain, Ashok Kumar; Choudhury, Deepika; Maheshwari, Bhoomika

    2014-01-01

    On the occasion of the $75^{th}$ anniversary of the fission phenomenon, we present a surprisingly simple result which highlights the important role of isospin and its conservation in neutron rich fission fragments. We have analysed the fission fragment mass distribution from two recent heavy-ion reactions $^{238}$U($^{18}$O,f) and $^{208}$Pb($^{18}$O,f) as well as a thermal neutron fission reaction $^{245}$Cm(n$^{th}$,f). We find that the conservation of the total isospin explains the overall...

  9. Fusion – fission dynamics: fragment mass distribution studies

    Bhattacharya S.

    2015-01-01

    Full Text Available Using the major accelerator facilities available in India, detailed experimental studies have been made to understand the mechanism of quasi-fission and role of nuclear shell effect in heavy nuclei. Fission fragment mass distribution has been used as the probe to explore the role of entrance channel effects on fusion-fission and quasifission dynamics. Fission fragment mass distribution has also been demonstrated to be useful to identify the phenomenon of ‘washing out’ of nuclear shell effect with excitation energy.

  10. Study of the fission fragments angular momenta

    The work represents the results of angular distribution measurements performed for prompt gamma-rays in the range of 1.1. ... 1.2. MeV due to the 233U (n,f) and 239Pu (n,f) reactions. The measurements yielded anisotropy values found to be consistent with values previously measured and using the same technique at different gamma energy bands. Such consistency, also found to exist between anisotropy values previously measured for the 235U (n,f) reaction, is a strong evidence about the energy independence of the anisotropy and indicates that the gamma spectra (at 180deg and 90deg to the fission direction) are essentially the same. The average values of the fragment angular momentum were calculated according to Strutinsky and Nix-Swiatecki theories. It was found that the values of the average angular momentum calculated for 234U, 236U and 240Pu according to Strutinsky's formula (at different gamma energy bands) are consistent and yield average values which are in good agreement with those obtained from direct measurements. (orig.)

  11. Thermal annealing of fission fragment radiation damage in CR-39

    The annealing behavior of fission fragment tracks in CR-39 has been studied at different temperatures for various time intervals. Experimental data, obtained in isothermal and isochronal annealing experiments carried out on CR-39 irradiated with fission fragments of 252Cf, has been analyzed on the basis of different annealing models. It has been attempted to find out the validity of these models, developed on the basis of annealing data in minerals and other detectors, to the annealing data of fission fragment tracks in CR-39

  12. A new method to identify nuclear charges of fission fragments

    For a mass and velocity selected beam of fission fragments, the elemental components of the beam have been determined by measuring the difference between the time the fragments enter an axial ionization chamber (with the electrical field lines parallel to the particle trajectory) and the time the anode pulse crosses a given level. The nuclear charge resolution achieved for typical fission fragments out of the light mass group in thermal neutron induced fission of 235U is Z/δZ = 43 for a nuclear charge Z = 39. (orig.)

  13. Spectroscopy of fission fragments using prompt-delayed coincidence technique

    R Palit; S Biswas

    2015-09-01

    The time-stamp structure of the digital data acquisition system of the Indian National Gamma Array (INGA) has been utilized to carry out prompt-delayed coincidence technique for the spectroscopic study of fission fragments. This technique was found to be useful to determine the states above the long-lived isomer (with half-life up to ∼5 s), present in the fission fragments. The angular correlation of -rays, emitted by the fission fragments, has also been used in the present INGA geometry to determine the spins of the de-exciting states.

  14. Toxicity of 144Ce inhaled in a relatively insoluble form by aged beagle dogs. VI

    The toxicity of 144Ce inhaled in fused aluminosilicate particles by 8 to 10.5-year-old dogs is being investigated to provide information on age-related differences in the response of older members of the human population to accidental inhalation of radioactive aerosols. These data on aged dogs will be compared to the results of similar studies of dogs exposed at approximately 3 months or 12 to 14 months of age. Six blocks of five female dogs each have been divided into four exposure levels with mean initial lung burdens of 7.2, 14, 28 and 57 μCi 144Ce/kg body weight. Six blocks of four male dogs each have been divided into three exposure levels with mean initial lung burdens of 7.2, 14 and 28 μCi 144Ce/kg body weight. Controls in each block were exposed to fused aluminosilicate particles containing stable cerium. Eighteen dogs with initial lung burdens ranging from 14 to 75 μCi 144Ce/kg body weight and cumulative doses to lung of from 22,000 to 74,000 rads have died or were euthanized 197 to 1207 days after exposure with clinicopathologic findings of radiation pneumonitis and pulmonary fibrosis

  15. Evolution of isotopic fission-fragment yields with excitation energy

    Two fission experiments have been performed at GANIL using 238U beams at different energies and light targets. Different fissioning systems were produced with excitation energies from 10 to 230 MeV and their decay by fission was investigated with GANIL spectrometers. Preliminary fission-fragment isotopic distributions have been obtained. The evolution with impinging energy of their properties, the neutron excess and the width of the neutron-number distributions, gives important insights into the dynamics of fusion-fission mechanism. (authors)

  16. Evolution of isotopic fission-fragment yields with excitation energy

    Bazin D.

    2012-07-01

    Full Text Available Two fission experiments have been performed at GANIL using 238U beams at different energies and light targets. Different fissioning systems were produced with excitation energies from 10 to 230 MeV and their decay by fission was investigated with GANIL spectrometers. Preliminary fission-fragment isotopic distributions have been obtained. The evolution with impinging energy of their properties, the neutron excess and the width of the neutron-number distributions, gives important insights into the dynamics of fusion-fission mechanism.

  17. The SPIDER fission fragment spectrometer for fission product yield measurements

    The SPectrometer for Ion DEtermination in fission Research (SPIDER) has been developed for measuring mass yield distributions of fission products from spontaneous and neutron-induced fission. The 2E–2v method of measuring the kinetic energy (E) and velocity (v) of both outgoing fission products has been utilized, with the goal of measuring the mass of the fission products with an average resolution of 1 atomic mass unit (amu). The SPIDER instrument, consisting of detector components for time-of-flight, trajectory, and energy measurements, has been assembled and tested using 229Th and 252Cf radioactive decay sources. For commissioning, the fully assembled system measured fission products from spontaneous fission of 252Cf. Individual measurement resolutions were met for time-of-flight (250 ps FWHM), spacial resolution (2 mm FHWM), and energy (92 keV FWHM for 8.376 MeV). Mass yield results measured from 252Cf spontaneous fission products are reported from an E–v measurement

  18. The SPIDER fission fragment spectrometer for fission product yield measurements

    Meierbachtol, K.; Tovesson, F. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Shields, D. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Colorado School of Mines, Golden, CO 80401 (United States); Arnold, C. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Blakeley, R. [University of New Mexico, Albuquerque, NM 87131 (United States); Bredeweg, T.; Devlin, M. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Hecht, A.A.; Heffern, L.E. [University of New Mexico, Albuquerque, NM 87131 (United States); Jorgenson, J.; Laptev, A. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Mader, D. [University of New Mexico, Albuquerque, NM 87131 (United States); O' Donnell, J.M.; Sierk, A.; White, M. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

    2015-07-11

    The SPectrometer for Ion DEtermination in fission Research (SPIDER) has been developed for measuring mass yield distributions of fission products from spontaneous and neutron-induced fission. The 2E–2v method of measuring the kinetic energy (E) and velocity (v) of both outgoing fission products has been utilized, with the goal of measuring the mass of the fission products with an average resolution of 1 atomic mass unit (amu). The SPIDER instrument, consisting of detector components for time-of-flight, trajectory, and energy measurements, has been assembled and tested using {sup 229}Th and {sup 252}Cf radioactive decay sources. For commissioning, the fully assembled system measured fission products from spontaneous fission of {sup 252}Cf. Individual measurement resolutions were met for time-of-flight (250 ps FWHM), spacial resolution (2 mm FHWM), and energy (92 keV FWHM for 8.376 MeV). Mass yield results measured from {sup 252}Cf spontaneous fission products are reported from an E–v measurement.

  19. Effect of 144Ce inhaled in fused clay particles on the tracheobronchial lymph nodes

    Tracheobronchial lymph node changes and lymphopenia are sequelae to inhalation of relatively insoluble radioactive aerosols by Beagle dogs. To assess the development of these lesions, tracheobronchial lymph nodes from dogs that inhaled 144Ce in fused clay particles were examined at intervals from 2 to 730 days after exposure. Initial lung burdens in the dogs studied ranged from 33 to 63 μCi/kg body weight. The concentration of radioisotope in the tracheobronchial lymph nodes increased during the first year after exposure and exceeded that in the lung about 100 days after exposure. Autoradiographs of the lymph nodes showed that 144Ce particles were present in macrophages in the paracortical zone two days after exposure and that concentrations continued to increase in the paracortical zone and medullary cords. Histologic changes in the nodes included atrophy of the germinal centers and lymphocytic follicles, loss of lymphocytes and accumulation of macrophages in the paracortical zone, accumulation of pigment and isotope-laden macrophages in the medullary cords, occasional infiltrates of neutrophils in the medullary cords and, at later time periods, focal fibrosis of the medullary cords. Tracheobronchial lymph node weights of the dogs exposed to 144Ce in fused clay were not decreased until 512 days after exposure. These findings indicate that tracheobronchial lymph nodes accumulate relatively high burdens of 144Ce after inhalation of 144Ce in a relatively insoluble form and that the pathologic changes resulting from these burdens are basically atrophic in nature. Primary neoplasms in lymph nodes have not been observed in dogs with initial lung burdens from 0.0024 to over 30 μCi/kg body weight followed for up to 2000 days post-exposure. At the higher levels, however, a high incidence of primary pulmonary neoplasia has been observed. (U.S.)

  20. Fission fragment mass distributions in reactions populating 200Pb

    Chaudhuri, A; Ghosh, T K; Banerjee, K; Sadhukhan, Jhilam; Bhattacharya, S; Roy, P; Roy, T; Bhattacharya, C; Asgar, Md A; Dey, A; Kundu, S; Manna, S; Meena, J K; Mukherjee, G; Pandey, R; Rana, T K; Srivastava, V; Dubey, R; Kaur, Gurpreet; Saneesh, N; Sugathan, P; Bhattacharya, P

    2016-01-01

    The fission fragment mass distributions have been measured in the reactions 16O + 184W and 19F+ 181Ta populating the same compound nucleus 200Pb? at similar excitation energies. It is found that the widths of the mass distribution increases monotonically with excitation energy, indicating the absence of quasi-fission for both reactions. This is contrary to two recent claims of the presence of quasi-fission in the above mentioned reactions.

  1. Feasibility of an antiproton catalyzed fission fragment rocket

    Hidinger, David S.

    1992-03-01

    The purpose of this project was to investigate the feasibility of an antiproton catalyzed fission fragment rocket (FFR). The FFR is characterized by the extraction of fission fragments from the fuel, and the utilization of their kinetic energy for thrust generation. A significant drawback to previous FFR designs was the required critical nuclear pile as the fission fragment source. The author examined the possibility of replacing the critical pile with a sub-critical pile driven by antiprotons. Recent experiments have revealed that antiprotons stimulate highly energetic fissions in 238U, with a neutron multiplicity of 13.7 neutrons per fissions. This interaction was used as a throttled neutron source. The pile consisted of layers of fissile coated fibers which are designed to allow fission fragments to escape them, where the fragments collide with a fluid. The heated fluid is then ejected from the rocket to provide thrust. The calculations performed indicate that each antiproton injected into the pile can stimulate 8 or more fissions while maintaining a neutron multiplication of less than 0.4. Based on the results, the specific design presented was inadequate. Despite this, the concept of using the antiproton-U interaction as a source of thrust warrants further study.

  2. Investigation on 252Cf Fission Fragment Tracks in Polycarbonate Detectors

    A. Bhattacharyya

    1992-10-01

    Full Text Available Registration and development of fission fragments emitted from /sup 252/Cf source have been carried out in three different polycarbonate detectors. The detectors have been characterised in terms of bulk etch rate and its behaviour. Maximum etchable cone lengths have been compared with the theoretically computed values. Identification of the fission fragments in terms of their mass and charge has been done with the help of the computer programme 'FFR'.

  3. Prompt-Neutron Emission from U235 Fission Fragments

    A gadolinium-loaded large liquid scintillation counter is being used in conjunction with a neutron beam from the HERALD reactor at the Atomic Weapons Research Establishment, Aldermaston, to study neutron emission in the fission process. In particular, the neutron emission from individual fission fragments is observed. A fission-fragment detector comprising two gold-silicon suríace barrier counters operating in coincidence is situated at the edge of a 1-m-diam. spherical scintillation tank. The solid-state counters are placed on opposite sides of an evaporated fissile deposit on a thin nickel backing. A system of collimators selects for measurement only those fission events that have fragments travelling in the direction along the incident neutron beam and along the axis of the scintillator. Numbers of neutrons detected within 10 ps of a fission event are recorded. The angular correlation of neutron emission with fragment direction is used to associate the neutrons with the particular fission fragment that emitted them. Energies of both fragments are available from the solid-state counters, and identification of fragment mass and of the total kinetic energy of the fragment pair is made. The number of neutrons emitted by each fragment of the pair has been measured as a function of both the fragment mass and the total kinetic energy of the pair for thermal neutrons incident on U2'35. The usual asymmetry in the distribution of excitation energy between the heavy and light fragments is observed. The variation of the number of neutrons from the pair as a function of mass ratio is also determined. (author)

  4. Collection and collimation of fission fragments using electromagnetic fields

    Use of electromagnetic fields to collect and collimate energetic fission fragments into a charged particle beam has been proposed to either direct conversion to electrical power or, after neutralization, as a source of thrust for rocket propulsion systems. Highest efficiency for collection of the fragments produced in a fuel matrix is a very important requirement in this proposal. As Chapline and Matsuda of LLNL noted, the extraction of fission fragment power above way permits isotopic separation of fission fragments, leading to a convenient separation of more active radioisotopes from less active ones. However, it is also noted that there is no such thing as a quick trip to these high goals as this area of work is facing several inadequate methods and technologies. One of the major concerns is the stopping or energy degradation of fragments within the fuel matrix before they are collected

  5. Fission fragment mass distribution employing prompt γ-ray spectroscopy

    The present results provide important new insight into the understanding of the dynamical behavior fragment formation in the fission process. More systematic experimental data are required to clearly understand these experimental observations. The study of mass distribution as a function of ZPZT will be interesting where the fission dynamics is expected to affect the mass distribution. With this motivation, the fission fragment mass distribution studies have been carried out for 238U(32S,f) and 238U(12C,f) systems. Details of the measurement and result of the study are presented along with the review of the some of the work in the literature

  6. Toxicity of 144Ce inhaled in a relatively insoluble form by immature Beagle dogs. VII

    Immature Beagle dogs (approx. = 3 months of age at exposure) have been exposed by inhalation to a relatively insoluble form of 144Ce (in fused aluminosilicate particles) to compare the resulting patterns of metabolism, dosimetry and biological effects with those seen in dogs exposed at 12 and 14 months of age and at 8 to 10.5 years of age. Five blocks of longevity animals, each consisting of 10 exposed dogs and one control, are currently being studied. The initial lung burdens of the 144Ce-exposed dogs range from 0.004 to 140 μCi 144Ce/kg body weight. Three dogs with initial lung burdens of 73 to 120 μCi 144Ce/kg body weight died at 66 to 121 days after exposure with pulmonary injury and congestive heart failure. One dog with an initial lung burden of 140 μCi 144Ce/kg body weight died at 91 days after exposure with severe radiation pneumonitis and minimal pulmonary fibrosis and another dog whose initial lung burden was 70 μCi 144Ce/kg body weight died at 511 days after exposure with pulmonary injury that was mainly fibrotic in nature. Four dogs with initial lung burdens of 52 to 79 μCi/kg body weight had primary pulmonary hemangiosarcomas and died between 618 and 738 days, with cumulative average absorbed beta doses to lung of 23,000 to 31,000 rads. Two of these dogs, 1027S and 1024D, died within the past year. One dog with an initial lung burden of 28 μCi/kg body weight was euthanized at 1227 days after exposure with an hemangiosarcoma of the mediastinum. Within the past year, Dog 627S, with an initial lung burden of 48 μCi/kg body weight, died 1732 days after exposure with hemangiosarcoma primary in the liver or spleen. A dog with an initial lung burden of 12 μCi/kg body weight died from epilepsy at 1520 days after exposure. Serial observations are continuing on the surviving 37 exposed and five control dogs

  7. Toxicity of inhaled 144Ce fused clay particles in beagle dogs. VII

    The metabolism, dosimetry, and effects of inhaled 144Ce in fused clay particles are being investigated in the Beagle dog to aid in assessing the biological consequences of release of 144Ce in a relatively insoluble form such as might occur in certain types of nuclear accidents. The toxicity of inhaled 144Ce fused clay is also of general interest since it is representative of intermediate-lived beta-emitting radionuclides. Two major studies with young adult dogs (12 to 14 months of age at exposure) are involved: (1) a metabolism and dosimetry study in which 24 dogs were serially sacrificed over an extended period of time, and (2) a longevity study with 2 series of dogs; Series I with 15 dogs exposed to aerosols of 144Ce in fused clay particles to yield initial lung burdens of 11 to 210 μCi/kg body weight and 3 control dogs exposed to nonradioactive fused clay particles and Series II with 96 dogs exposed to aerosols of 144Ce in fused clay particles to yield initial lung burdens of 0.0024 to 66 μCi/kg body weight and 12 control dogs exposed to nonradioactive fused clay particles. Twenty-eight dogs died or were euthanized at 143 to 2396 days after inhalation of 144Ce. The prominent findings were radiation pneumonitis in 17 dogs that died or were euthanized at early time periods and neoplastic disease in 10 of the 11 dogs that died or were euthanized at 750 days or later; 5 with hemangiosarcoma of the lung, 1 with both a hemangiosarcoma and a fibrosarcoma of the lung, 1 with both a bronchiolo-alveolar carcinoma and a hemangiosarcoma of lung, 1 with a hemangiosarcoma of lung, bronchiolo-alveolar carcinoma, and a bronchiogenic adenocarcinoma, and 1 each with a hemangiosarcoma of the mediastinum and of the spleen. The cumulative radiation dose to the lung at time of death has ranged from 22,000 to 140,000 rads. Serial observations are continuing on the 83 survivors and 15 controls. (U.S.)

  8. Double treeing phenomenon of fission fragment tracks in plastic detectors

    Several possible theories that explain the formation of double tree observed while detecting 235U fission fragments in plastic detectors have been presented. Two likely explanations have been given: First, 235U fission and the emission of long range alpha 8Be particles, and the second is the spontaneous emission of 4.4 MeV alpha particles from 235U. The assumption backed with appropriate range calculations in Lexan. three less likely causes of the double tree phenomenon are : the recoil of the detector atoms as a result of the collision with fission fragments, the fission fragments themselves being reflected off the stainless-steel sample holder, and some mechanical and physical defects in the detectors at the production or utilization stage. We have made some suggestions related to experimental design that might prove these theories. (Author)

  9. Angular Anisotropy and Mass Asymmetry of Thorium-232 Fission Fragments

    A large number of experimental and theoretical papers on the angular distribution of the fission fragments of nuclei indicate that it is satisfactorily described by the parameters of the fissioning nucleus at the saddle point. The problem of the effect of these parameters on the distribution of the fragments according to mass has as yet found no generally accepted solution. It remains unclear to what extent the 'good' quantum numbers characteristic of the nucleus at the saddle point remain equally ''good'' when the nucleus passes from the saddle point to the moment of breakdown. If at the saddle point the nucleus has a set of different configurations, this must be apparent in some way in the distribution of the fragments by mass and in their angular distribution (via the moment of inertia of the nucleus). The paper investigates the angular anisotropy of fragments with different masses in the fission of thorium-232 by fast neutrons. The masses of the fragments were determined by simultaneous recording of the kinetic energy of paired fragments in a double ionization chamber with grids. The direction of flight of the fragments was determined using a mechanical collimator. The neutrons causing fission had an extended spectrum, but the contribution of fissions via the (n, n'f) reaction did not exceed a few per cent. The fragments were sorted out according to energy by a two-dimensional 128 x 128 channel analyser with a memory on ferrite. The dependence of angular anisotropy on the mass of the fragments and on their kinetic energy with fixed mass is discussed. The first dependence makes it possible to judge the degree to which the saddle point affects the distribution of the fragments according to mass, while the second gives information about the degree to which the configuration of the nucleus at the moment of breakdown affects the angular anisotropy of the fragments. (author)

  10. Fine structure in the fission fragment yields

    Discussed are the most interesting experiments on the fine structure of fission product yields of U, Pu, Th, Cf, Es, Cm, Fr, Np isotopes. Modern comprehension of the fine structure nature in connection with other problems of fission dynamics is considered. It is noted, that the fine structure results from pairing correlations in a nucleus. The conclusion is drawn, that the available set of experimental data is not sufficient to elucidate the fine structure nature

  11. Extraction of carrier-free 144Ce with acetylacetone and 8-hydroxyquinoline

    The extraction of carrier-free 144Ce with 3.25 to 0.65 M solutions of acetylacetone in carbon tetrachloride and with 1.0 to 0.01 M solutions of 8-hydroxyquinoline in chloroform at a constant as well as variable pH was investigated. On the basis of the analysis of distribution curves it may be presumed that in both extraction systems the oxidation of cerium(III) to cerium(IV) microamounts takes place. The distribution curves of extraction and reextraction in the systems with 8-hydroxyquinoline show a considerable complexity. In the extraction system with acetylacetone constants were found which satisfactorily express the distribution of 144Ce in this system. (author)

  12. Angular momenta of near-spherical fission fragments

    Angular momenta of fission fragments are sometimes exceeding 10 ℏ for thermal neutron induced and spontaneous fission. This is surprising since in the latter case the mother nucleus may have zero spin (e.g. 252Cf). In theory fragment spins are explained as a quantum mechanical effect. It is argued that they are due to zero-point oscillations of fragments being deformed at scission. In contrast to current theory it is shown that, for the specific case of near-magic 132Te, a large spin is generated by thermal excitation of single-particle states. (author)

  13. Biological effects of repeated exposure of beagle dogs to relatively insoluble aerosols of 144Ce. IV

    This experiment is being conducted to study the behavior and long-term biological effects in Beagle dogs of 144Ce inhaled in fused aluminosilicate particles in repeated inhalation exposures for comparison with similar data from dogs that were exposed only once to a similar aerosol. Four groups of nine dogs each were exposed once every eight weeks for two years (13 exposures) to achieve specified exposure goals. The 144Ce-exposed dogs received increasing or relatively constant beta radiation dose rates in contrast to the steadily decreasing dose rate seen after a single inhalation exposure. Exposures in the first and second groups were planned to yield a cumulative absorbed dose to lung of approximately equal to 35,000 rads and those in the third group approximately equal to 17,000 rads within two years after the first exposure. Singly exposed dogs that had died with pulmonary tumors when this experiment was initiated had cumulative doses to death of 29,000 to 61,000 rads. All 13 exposures have been completed. One dog in the 4.5-μCi 144Ce/kg body weight group died at 771 days after first exposure with emaciation, adrenal cortical degeneration and bone marrow aplasia. One control dog died accidentally during anesthesia. During the past year, two additional dogs have died. One dog in the repeated 2.5-μCi 144Ce/kg body weight group died at 1256 days after the first exposure with radiation pneumonitis and pulmonary fibrosis and a control dog died at 1052 days with autoimmune hemolytic anemia. The remaining 32 dogs appear to be in good physical condition except for a persistent lymphopenia at approximately equal to 4 years after the first exposure. They are being maintained for life span observations

  14. Distribution of Prompt Neutron Emission Probability for Fission Fragments in Spontaneous Fission of 252Cf and 244,248Cm

    Vorobyev, A. S.; Dushin, V. N.; Hambsch, F.-J.; Jakovlev, V. A.; Kalinin, V. A.; Laptev, A. B.; Petrov, B. F.; Shcherbakov, O. A.

    2005-05-01

    Neutrons emitted in fission events were measured separately for each complementary fragment in correlation with fission fragment energies. Two high-efficiency Gd-loaded liquid scintillator tanks were used for neutron registration. Fission fragment energies were measured using a twin Frisch gridded ionization chamber with a pinhole collimator. The neutron multiplicity distributions were obtained for each value of the fission fragment mass and energy and corrected for neutron registration efficiency, background, and pile-up. The dependency of these distributions on fragment mass and energy for different energy and mass bins as well as mass and energy distribution of fission fragments are presented and discussed.

  15. Simultaneous Measurements of Flight Times and Energies of Fission Fragments

    In a companion paper the results of measuring the prompt neutron emission from individual fission fragments arising in thermal fission are reported. In that experiment a large volume liquid scintillation counter was .used to. record the fission neutrons, and fragment mass was identified by a gold silicon surface barrier counter.- arrangement. An alternative Way of measuring the prompt neutron emission is described here. Fragment time-of- flight apparatus is mounted in an evacuated tube that passes laterally through the thermal column of the 5-MW research reactor HERALD. A centrally positioned thin source produces 3 x 105 fissions s-1. Fragments travel distances of 180 cm and 300 cm respectively to the terminal detectors, and in passing through a VYNS film, positioned 180 cm from the source along the longer flight path, eject electrons that are used to form a reference time-signal. Essentially the times of flight of both fission fragments are measured simultaneously with the kinetic energy of one of the pair. This is achieved by using a surface barrier counter for the 300-cm detector. The difficulty of maintaining good timing and energy resolutions simultaneously is overcome by routing the pulse to the charge sensitive preamplifier through a delay line amplifier from which a fast timing pulse is derived. The collected data enables the fragment mass to be determined both before and after prompt neutrons have been emitted. Hence the experiment provides a means for studying the behaviour of neutron emission from individual fragments. The experimental uncertainties are those associated with the measurement of small differences, and an appraisal is made of the errors and calibrations that enter into the measurements. Of particular importance, the response of the surface barrier counter to fission fragments is obtained directly, from the collected data from events in which the neutron emission is low. These calibrations are used in the measurements of postneutron mass

  16. Entrance channel dependence of fission fragment anisotropies - a direct experimental signature of fission before equilibration

    In several cases of heavy ion induced fusion-fission reactions, the fission fragment angular distributions exhibit much larger anisotropies than predicted by the standard Halpern-Strutinsky theory. Several explanations have been put forward to interpret these anomalous angular distributions. One of them is that a characteristic signature of fission before full K-equilibration will be an entrance channel dependence of the fragment anisotropies for target-projectile combinations across the Businaro-Gallone ridge in the mass/charge asymmetry degree of freedom. To look for any such entrance channel dependence of fragment anisotropies, we have carried out measurements of fragment angular distributions in fission induced by boron, carbon, oxygen ions on thorium and neptunium targets and by fluorine ions on neptunium target at above barrier energies. (author). 7 refs., 1 fig

  17. Isotopic fission fragment distributions as a deep probe to fusion-fission dynamics

    Farget, F.; Caamano, M.; Delaune, O.; Tarasov, O.B.; Derkx, X.; Schmidt, K. -H.; Amthor, A.M.; Audouin, L.; Bacri, C.-O.; Barreau, G.; Bastin, B.; Bazin, D.; Blank, B.; Benlliure, J.; Caceres, L.

    2012-01-01

    During the fission process, the nucleus deforms and elongates up to the two fragments inception and their final separation at scission deformation. The evolution of the nucleus energy with deformation is determined by the macroscopic properties of the nucleus, and is also strongly influenced by the single-particle structure of the nucleus. The fission fragment distribution is a direct consequence of the deformation path the nucleus has encountered, and therefore is the most genuine experiment...

  18. Calculation of fission fragment angular anisotropy in heavy-ion induced fission

    Fission fragment angular anisotropies from 16O + 232Th, 12C + 236U, 11B + 237Np, 14N + 232Th, 11B + 235U and 12C + 232Th systems were calculated by means of the standard saddle point statistical model (SSPSM). The results were obtained with and without neutron emission correction in the reactions, and comparisons were made with the corresponding experimental data. The normal and anomalous behaviors of fission fragment anisotropies are extensively discussed. (author)

  19. A fission fragment detector for correlated fission output studies

    Mosby, S., E-mail: smosby@lanl.gov [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Tovesson, F.; Couture, A. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Duke, D.L. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Colorado School of Mines, Golden, CO 80401 (United States); Kleinrath, V. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Idaho State University, Pocatello, ID 83201 (United States); Meharchand, R.; Meierbachtol, K.; O' Donnell, J.M.; Perdue, B.; Richman, D. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Shields, D. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Colorado School of Mines, Golden, CO 80401 (United States)

    2014-09-01

    A digital data acquisition system has been combined with a double Frisch gridded ionization chamber for use at both moderated and unmoderated neutron sources at the Los Alamos Neutron Science (LANSCE) facility. The high efficiency of the instrument combined with intense LANSCE beams and new acquisition system permits fission output measurements across 11 orders of magnitude incident neutron energy. The acquisition and analysis system is presented along with the first in-beam performance tests of the setup.

  20. A fission fragment detector for correlated fission output studies

    A digital data acquisition system has been combined with a double Frisch gridded ionization chamber for use at both moderated and unmoderated neutron sources at the Los Alamos Neutron Science (LANSCE) facility. The high efficiency of the instrument combined with intense LANSCE beams and new acquisition system permits fission output measurements across 11 orders of magnitude incident neutron energy. The acquisition and analysis system is presented along with the first in-beam performance tests of the setup

  1. A fission-fragment-sensitive target for X-ray spectroscopy in neutron-induced fission

    A fission-fragment-sensitive detector built for low-energy photon spectroscopy applications at the WNR 'white' neutron source at Los Alamos is described. The detector consists of eight layers of thin photovoltaic cells, onto which 1 mg/cm2 of pure 238U is deposited. The detector serves as an active target to select fission events from background and other reaction channels. The fairly small thickness of the detector with respect to transmission of 20-50 keV photons permits the measurement of prompt fission-fragment X-rays. Results with the GEANIE photon spectrometer are presented

  2. A fission-fragment-sensitive target for X-ray spectroscopy in neutron-induced fission

    Ethvignot, T; Giot, L; Casoli, P; Nelson, R O

    2002-01-01

    A fission-fragment-sensitive detector built for low-energy photon spectroscopy applications at the WNR 'white' neutron source at Los Alamos is described. The detector consists of eight layers of thin photovoltaic cells, onto which 1 mg/cm sup 2 of pure sup 2 sup 3 sup 8 U is deposited. The detector serves as an active target to select fission events from background and other reaction channels. The fairly small thickness of the detector with respect to transmission of 20-50 keV photons permits the measurement of prompt fission-fragment X-rays. Results with the GEANIE photon spectrometer are presented.

  3. Study of fission fragment trapping detector used in neutron detection

    To detect the absolute neutron flux in a weak neutron field and restricted space, the fission fragment trapping detector was fabricated and the properties of the detector were studied. In this paper, the detector and shielding chamber used in neutron detection were described and the experimental measurements of the fission rate in specific condition were performed with the detection system and the result has been compared with that obtained by fission chamber. The influence of the shielding chamber on the measured results was analyzed. (authors)

  4. Multi-Parameter Investigations of Fast Fission Fragments

    A number of investigators have noted the peculiar dependence of kinetic energy on the mass of the fragments. This dependence differs considerably for the fission of nuclei by thermal neutrons, neutrons with an energy of 14 MeV and a-particles. It may be that this is a result of the difference not only in excitation energy, but also in the moment introduced by the particle causing fission. It is obviously difficult to deny the part played by nuclear shells in the formation of fragments according to mass, and in this connection the study of the kinetic energy of fragments as a function of their mass is of great interest, as are the corresponding investigations of the widths of distribution of the kinetic energy. Particular attention is given to the characteristics of symmetrical fission of U235 , and it is found that when tails appear in the apparatus spectra of the fission fragments, there occur in the symmetrical mass-region pulses with a most probable total energy of ∼ 120 MeV. Actual symmetrical fission events correspond to a total mean energy of ∼ 155 MeV. The kinetic energy of paired fragments was measured using two surface-barrier silicon counters. The impulses are analysed for amplitude by a two-dimensional 128 x 128 channel ánalyser with a memory on ferrite. The neutron source used was the BR-5 fast neutron reactor, the mean energy of the fast neutron spectrum being ∼250 keV. Layers ofjfissile isotopes with a thickness of 20-30 μg/cm2 were used. The fission of Ù235 by thermal neutrons gave an experimental curve for the mass yield with a 250:1 ratio between peak and vailey. Comparison of the characteristics of the fragments (kinetic energy and mass distribution) showed no noticeable difference in the fission of U235 by thermal and fast neutrons. The total kinetic energy of the fragments in the symmetrical fission of U235 by thermal and fast neutrons proved to be identical, equalling ∼155 MeV, which agrees, within the limits of experimental error

  5. Hard error generation by neutron-induced fission fragments

    The authors observed that neutron-induced fission of uranium contaminants present in alumina ceramic package lids results in the release of fission fragments that can cause hard errors in metal-nitride-oxide nonvolatile RAMs (MNOS NVRAMs). Hard error generation requires the simultaneous presence of (1) a fission fragment with a linear energy transfer (LET) greater than 20 MeV/mg/cm/sup **2/ moving at an angle of 30 degrees or less from the electric field in the high-field, gate region of the memory transistor, and (2) a WRITE or ERASE voltage on the oxide-nitride transistor gate. In reactor experiments, they observe these hard errors when a ceramic lid is used on both MNOS NVRAMs and polysilicon-nitride-oxide (SNOS) capacitors, but hard errors are not observed when a gold-plated kovar lid is used on the package containing these die. They mapped the tracks of the fission fragments released from the ceramic lids with a mica track detector and used a Monte Carlo model of fission fragment transport through the ceramic lid to measure the concentration of uranium present in the lids. The authors' concentration measurements are in excellent agreement with other's measurement of uranium concentration in ceramic lids. The authors' Monte Carlo analyses also agree closely with their measurements of hard error probability in MNOS NVRAMs

  6. Fission fragments spectrometer based on ionization chamber and waveform digitizer

    The method for fission process investigation which allows to get full information on fission fragments properties is suggested. The method is based on using the fission fragment spectrometer with the twin ionization chamber having the Frisch grid and the waveform digitizer. The new design of the twin ionization chamber is described in details. The main and very important difference is the distances between the cathode and the grid and the anode. These values are 40 and 2 mm correspondingly, so the ratio is equal to 20 instead of 3 - 5 as usual. The diameter of the electrodes is 120 mm. The working gas is the mixture of argon plus 10% of methane under the pressure of 0.65 atm. High voltage of 3.5 kV is applied to the cathode. The scheme of the spectrometer electronic circuit is given. The method of simultaneous measurements of the signal amplitudes from the ionization chamber electrodes is applied, but the shape of the signals is processed by means of the waveform digitizer which gives an opportunity to obtain much more information on the fission fragments properties. It is shown that the described spectrometer can be successfully used for fission fragment energy, mass and charge distribution measurements

  7. The uptake of 90Sr, 137Cs and 144Ce by leaves of spring wheat and rape

    The distribution and accumulation of 90Sr, 137Cs, 144Ce through the leaf surface into the plant have been studied. The results show that the uptake rate of 137Cs by crop plant is about 53%, while the uptake rate for 90Sr and 144Ce is about 0.4%. However 90Sr is absorbed in significant amount from soil whereas 137Cs is absorbed in negligible amount

  8. Effects of fissioning nuclei distributions on fragment mass distributions for high energy fission

    Rossi P C R

    2012-02-01

    Full Text Available We study the effects of fissioning nuclei mass- and energy-distributions on the formation of fragments for fission induced by high energy probes. A Monte Carlo code called CRISP was used for obtaining mass distributions and spectra of the fissioning nuclei for reactions induced by 660 MeV protons on 241Am and on 239Np, by 500 MeV protons on 208Pb, and by Bremsstrahlung photons with end-point energies at 50 MeV and 3500 MeV on 238U. The results show that even at high excitation energies, asymmetric fission may still contribute significantly to the fission cross section of actinide nuclei, while it is the dominante mode in the case of lead. However, more precise data for high energy fission on actinide are necessary in order to allow definite conclusions.

  9. Sensitivity studies of spin cut-off models on fission fragment observables

    Thulliez L.; Litaize O.; Serot O.

    2016-01-01

    A fission fragment de-excitation code, FIFRELIN, is being developed at CEA Cadarache. It allows probing the characteristics of the prompt emitted particles, neutrons and gammas, during the de-excitation process of fully accelerated fission fragments. The knowledge of the initial states of the fragments is important to accurately reproduce the fission fragment observables. In this paper a sensitivity study of various spin cut-off models, completely defining the initial fission fragment angular...

  10. Coincident measurements of prompt fission γ rays and fission fragments at DANCE

    Walker, C. L.; Baramsai, B.; Jandel, M.; Rusev, G.; Couture, A.; Mosby, S.; Ullmann, J.; Kawano, T.; Stetcu, I.; Talou, P.

    2015-10-01

    Modern statistical approaches to modeling fission involve the calculation of not only average quantities but also fully correlated distributions of all fission products. Applications such as those involving the detection of special nuclear materials also rely on fully correlated data of fission products. Experimental measurements of correlated data are thus critical to the validation of theory and the development of important applications. The goal of this experiment was to measure properties of prompt fission gamma-ray emission as a function of fission fragments' total kinetic energy in the spontaneous fission of 252Cf. The measurement was carried out at the Detector for Advanced Neutron Capture Experiments (DANCE), a 4 π γ-ray calorimeter. A prototype design consisting of two silicon detectors was installed in the center of DANCE, allowing simultaneous measurement of fission fragments and γ rays. Effort has been taken to simulate fragment kinetic energy losses as well as γ-ray attenuation in DANCE using such tools as GEANT4 and SRIM. Theoretical predictions generated by the code CGMF were also incorporated as input for these simulations. Results from the experiment and simulations will be presented, along with plans for future measurements.

  11. Liver tumors in Beagle dogs exposed by inhalation to 144CeCl3

    Primary malignant hepatic neoplasms developed in 9 of 55 Beagle dogs (16 percent) exposed to 144CeCl3 in CsCl aerosol (seven primary hepatic hemangiosarcomas, one hepatocellular carcinoma and one intrahepatic bile duct carcinoma). Cerium-144 was rapidly translocated from the lung to the liver and skeleton; the liver received the highest cumulative beta dose. The latent periods of hepatic hemangiosarcomas appeared to be dose-related; death from hepatic hemangiosarcoma occurred earlier in dogs which received higher beta doses

  12. Effectiveness in detecting fission fragments with ionization chambers

    Detection of fission fragments is important in nuclear measurements. When a high detection accuracy is required it is necessary to take in account the detection losses due to the absorption of fragments in the fissionable material. The losses corrections might change the final results in 2-3%. The traditional expression used in the calculation of the detection efficiency does not consider neither the density variation of the fissionable substance with its width, because it depends on the target material. That's why actually in many labs it is being searched new methods that allow to find the efficiency for each target. In this work a new method for determination of absorption efficiency is presented. The obtained results are analyzed

  13. Fragment Deexcitation of Fission Induced by High Energy Nucleons

    Yavshits S.; Grudzevich O.

    2010-01-01

    The KRIF library of the neutron-, proton- and gamma-spectra emitted by the nuclei excited up to 500 MeV is presented. The KRIF contains information for about 2000 emitters which are the fragments of the ten targets fission induced by the nucleons with the energies up to 3 GeV.

  14. Fragment Deexcitation of Fission Induced by High Energy Nucleons

    Yavshits S.

    2010-03-01

    Full Text Available The KRIF library of the neutron-, proton- and gamma-spectra emitted by the nuclei excited up to 500 MeV is presented. The KRIF contains information for about 2000 emitters which are the fragments of the ten targets fission induced by the nucleons with the energies up to 3 GeV.

  15. Fission fragment formation and fission yields in the model of octupole neutron-proton oscillations

    Yavshits S.

    2010-03-01

    Full Text Available The fission fragment formation is considered as a result of neck instability in the process of octupole oscillations of neutrons and protons near the scission point. To describe such a phenomenon the potential surface of fissionning nucleus with neck radius about 1 fm was calculated with shell correction approach. The new version of smooth liquid drop part of deformation energy is proposed. The liquid drop part is formulated in a double folding model with n-n, p-p, and n-p Yukawa interaction potential. Fission fragment mass and charge distributions correspond approximately to isoscalar and isovector modes of vibrations and are defined by wave functions of oscillations. The preliminary calculation results have shown a rather good description of main integral fission yield observables.

  16. Fission fragment angular momentum in the neutron induced fission of 232Th and 232U

    High spin fractions (HSF) of 130,132Sb and 131,133Te have been determined in the neutron induced fission of 232Th and 232U using off-line gamma ray spectrometric technique. From the HSF, fragment angular momenta (Jrms) were deduced using statistical model analysis. From the Jrms values, deformation parameter (β) were deduced and compared with the same in the even-even and odd-even fissioning systems to examine the effect of nuclear structure and the role of odd neutron spin. In all the fissioning systems the effect of shell closure proximity and odd-even effect on Jrms was clearly observed. However, the role of odd neutron spin was not seen in even-odd fissioning systems like the odd-proton spin effect in odd-odd fissioning systems. (author)

  17. The SOFIA experiment: Measurement of 236U fission fragment yields in inverse kinematics

    Grente L.

    2016-01-01

    Full Text Available The SOFIA (Studies On FIssion with Aladin experiment aims at measuring fission-fragments isotopic yields with high accuracy using inverse kinematics at relativistic energies. This experimental technique allows to fully identify the fission fragments in nuclear charge and mass number, thus providing very accurate isotopic yields for low energy fission of a large variety of fissioning systems. This report focuses on the latest results obtained with this set-up concerning electromagnetic-induced fission of 236U.

  18. Ejection of Uranium Atoms from UO2 by Fission Fragments

    The numbers of uranium atoms ejected from the surface of sintered plates of UO2 by fission fragments have been measured over the fission density range 5x1015 to 7x1016 fissions/cm3. The number of uranium atoms ejected per escaping fragment was about 9. The measurements were performed by irradiating the plates in vacuum and collecting a fraction of the uranium atoms ejected on catcher foils. The amount collected was determined by fission counting. Saturation of the amount collected, as reported by Rogers and Adam, was not observed. The numbers of uranium atoms ejected as knock-ons under the same experimental conditions have been calculated. The reasonably close agreement between the experimental and theoretical values indicates that, under the prevailing experimental conditions, mainly knock-ons are ejected. Other ejection mechanisms, e. g. evaporation of material in thermal spikes, are probably insignificant; this is in contrast to the usual interpretation of the ejection process. The mean range in UO2, of fission products of mass number 140 was found to be 7.37 ± 0. 05 mg/cm2 by direct gamma spectrometric, determination of the fraction of 140La escaping from the surface of the plates

  19. Prompt Neutron Emission from Fragments in Spontaneous Fission of 244, 248Cm and 252Cf

    Vorobyev, A. S.; Dushin, V. N.; Hambsch, F.-J.; Jakovlev, V. A.; Kalinin, V. A.; Laptev, A. B.; Petrov, B. F.; Shcherbakov, O. A.

    2005-11-01

    Neutrons emitted in fission were measured separately for each complementary fragment in correlation with fission fragment energies. Two high efficient Gd-loaded liquid scintillator tanks were used for neutron registration. Fission fragment energies were measured using a twin Frisch gridded ionization chamber with a pin-hole collimator. The neutron multiplicity distributions were obtained for each value of the fission fragment mass and energy and corrected for neutron registration efficiency, background and pile-up. The dependencies of these distributions on fragment mass and energy for different energy and mass bins, as well as the mass and energy distribution of the fission fragments are presented and discussed.

  20. Electron distribution function in a plasma generated by fission fragments

    Hassan, H. A.; Deese, J. E.

    1976-01-01

    A Boltzmann equation formulation is presented for the determination of the electron distribution function in a plasma generated by fission fragments. The formulation takes into consideration ambipolar diffusion, elastic and inelastic collisions, recombination and ionization, and allows for the fact that the primary electrons are not monoenergetic. Calculations for He in a tube coated with fissionable material shows that, over a wide pressure and neutron flux range, the distribution function is non-Maxwellian, but the electrons are essentially thermal. Moreover, about a third of the energy of the primary electrons is transferred into the inelastic levels of He. This fraction of energy transfer is almost independent of pressure and neutron flux.

  1. Study of the production of fission fragments from neutron induced fission on uranium 238

    This work is devoted to the study of the mass and charge distributions of fission fragments from the fission induced on uranium 238 by neutrons from 1 to 150 MeV. An experimental program allowed us to gather and analyse new data. The obtained results were interpreted by an original model, based on a microscopic description of the reaction. Data were taken at the LANSCE laboratory of Los Alamos (USA) where we used the neutron source WNR and the germanium array GEANIE. The aim was to measure secondary fission fragment production yields from a spectroscopic analysis of the prompt gamma and x-rays. A device with photovoltaic cells used as fission fragment detectors was developed. The trigger created with this device allowed us to reduce the background from the other neutron induced reactions. Close to one hundred fragments were identified and excitation functions were extracted for about thirty of them. Mass and charge distributions at different incident energies were extracted from these measurements. These results were then compared to evaluated reference data (Wahl systematics). It showed that the calculations are consistent with the measurements at low energies (below 20 MeV) but partially fail to reproduce the data at higher energy. To go into more detail about the obtained results, the reaction was studied using an original model. It provided a dynamic and totally microscopic description of the fission from constrained self-consistent Hartree-Fock-Bogoliubov calculations. This work was completed in two parts. First, a potential energy surface of the fissioning system was calculated in a deformation plane defined by the elongation and asymmetry variables. The second part was to use the resolution of the dynamic Schroedinger equation on this surface giving us a fragment mass distribution which we then compared to the low energy data. (author)

  2. FALSTAFF: a novel apparatus for fission fragment characterization

    Panebianco Stefano

    2014-04-01

    Full Text Available The study of nuclear fission and in particular the correlation between the produced fragments and the associated neutrons is encountering renewed interest since new models are available on the market and a large set of applications show a rather stringent demand on high quality nuclear data. The future Neutrons For Science installation, being presently built at GANIL (Caen, France in the framework of the SPIRAL2 project, will produce high intensity neutron beams from hundreds of keV up to 40 MeV. In view of this opportunity, the development of an experimental setup called FALSTAFF (Four Arm cLover for the Study of Actinide Fission Fragments has been undertaken since 2011. This novel apparatus is meant to provide a full characterization of fission fragments in terms of mass, nuclear charge and kinetic energy. Moreover, it will provide a measurement of the mass before and after neutron evaporation, leading to the determination of the neutron multiplicity as a function of the fragmentation. The FALSTAFF setup is presently in its R&D phase in order to achieve the required specifications, especially in terms of time, space and energy resolution of the different detectors.

  3. FALSTAFF: a novel apparatus for fission fragment characterization

    The study of nuclear fission and in particular the correlation between the produced fragments and the associated neutrons is encountering renewed interest since new models are available on the market and a large set of applications show a rather stringent demand on high quality nuclear data. The future Neutrons For Science installation, being presently built at GANIL (Caen, France) in the framework of the SPIRAL2 project, will produce high intensity neutron beams from hundreds of keV up to 40 MeV. In view of this opportunity, the development of an experimental setup called FALSTAFF (Four Arm cLover for the Study of Actinide Fission Fragments) has been undertaken since 2011. This novel apparatus is meant to provide a full characterization of fission fragments in terms of mass, nuclear charge and kinetic energy. Moreover, it will provide a measurement of the mass before and after neutron evaporation, leading to the determination of the neutron multiplicity as a function of the fragmentation. The FALSTAFF setup is presently in its R and D phase in order to achieve the required specifications, especially in terms of time, space and energy resolution of the different detectors. (author)

  4. A hybrid detector telescope for fission fragments and charged particles

    Measurement of light charged particle (LCP) multiplicities in coincidence with fission fragments (FFs) during the fusion-fission process is a very useful probe to understand the fission dynamics. In this type of measurement, the LCP's are indented to be measured in a wide range of relative angles (θrel) from 0° to 180° with respect to the FF direction. The conventional method of using two separate detectors one for the FF's and another for the LCPs does not allow to direct the LCPs along the direction of FF (in particular, θrel gas and Egas) and two CsI(Tl)-Si(PIN) detectors mounted at the end of the gas-section. In this paper, the results of in-beam usage of the HDT are presented

  5. Fission-fragment nuclear lasing of Ar/He/-Xe

    De Young, R. J.; Shiu, Y. J.; Williams, M. D.

    1980-01-01

    Nuclear-pumped lasing of Ar-Xe and He-Xe has been demonstrated using (U-235)F6 fission-fragment excitation. Fission fragments were created by absorption of thermal neutrons in a combination of gaseous (U-235)F6 and laser-tube wall coatings formed from UF6 chemical reaction products. At a pressure of 600 torr Ar-(3%)Xe, lasing occurred at 2.65 microns in Xe. Up to 3 torr of gaseous (U-235)F6 was added to 600 torr Ar-Xe before serious laser quenching occurred. With 3 torr of (U-235)F6 added, 38% of the energy deposition came from gaseous UF6 and the remainder from the uranium wall coating. The neutron flux at lasing threshold was found to be 4 x 10 to the 15th n/sq cm sec.

  6. Fission fragment detector by thin film capacitors. Pt. 1

    Heavy ion detection by solid dielectrics has been so far obtained by chemical etching. In this paper the detection of fission fragments is based on the counting of breakdowns in thin films of solid dielectries. These films are used as dielectric materials in capacitors with one electrode usually less than 1000 A thick. Breakdowns in such capacitors are non-shorting and can be sometimes repeated up to millions of times per cm2 of the capacitor area. The property that makes these capacitors suited for detection is that fission fragments induce breakdowns at fields distinctly lower than those due to the application of field only. The characteristics of these new detecting systems are described and compared with those of the damage track detectors. (orig.)

  7. Fission fragment mass distribution from combined dynamical and statistical model of fission including evaporation

    An appropriate theoretical model for fission fragment mass distribution (FFMD) of a highly excited heavy nucleus involves multidimensional Langevin dynamical calculations. Though a full Langevin simulation provides a more accurate description of fission dynamics, it is often replaced by a combined dynamical and statistical model (CDSM). This is essentially done because the demand on computer time for a full Langevin calculation is very large. In CDSM, the Langevin dynamical computation is pursued for a time interval during which the initial transients are settled and the fission width has reached a stationary value. The decay of the compound nucleus in subsequent times is followed treating fission at par with other decay channels, such as particle and γ emission channels which are already included in the calculation from the beginning, and using statistical methods. Evidently, CDSM takes less computer time than full dynamical model simulation

  8. Fission fragment passage in a small-size single crystal

    Using a method of mathematical simulation the passage of a 100 MeV fission fragment with the mass 140 amu and charge 20 through an insulated solid hydrogen single crystal is investigated. The problem is reduced to the consideration of multiple scattering in a Coulomb field in terms of classical mechanics. It was found that for the time of the fragment flight through the microcrystallite 17% of electrons left the latter. Among the remaining electrons only 40 % of them have the energy lower than 10 eV (the work function for the given microcrystallite). Thus, the concept of the ''ion burst'' is confirmed with a greater probability

  9. Detection efficiencies of solid state nuclear track detectors for fission fragments

    Detection efficiencies of solid state nuclear track detectors (SSNTDs) for fission fragments have been calibrated with the help of Au-Si surface barrier detector and fission chamber. The results obtained for thin fission source are given for muscovite mica; polycarbonate foil; polyester; phosphate glass; silicate glass; and quartz. Corrections have been made for the effect of backscattering of fission fragments by Au-Si surface barrier detector on the detection efficiencies with a special designed arrangement using SSNTD. The effects of backscattering of fission fragments on detection efficiencies range from 0 for silicate glass to 2.6% for polycarbonate foil (Chaoyan) for using Au-Si as backing material. A discussion was given to the effect of critical angles of SSNTDs on the correction for self absorption of fission fragments in thick fission sources. A formula is given to calculate the detection efficiency of SSNTDs for fission fragments from fission sources of various thickness. (author)

  10. Biological effects of repeated inhalation exposure of Beagle dogs to relatively insoluble aerosols of 144Ce. V

    The behavior and long-term biological effects in Beagle dogs of 144Ce inhaled in fused aluminosilicate particles in repeated inhalation exposures are being studied for comparison with data from dogs that were exposed only once to a similar aerosol. Four groups of nine dogs each were exposed once every 8 weeks for 2 years (13 exposures) to achieve specified exposure goals. These goals were: to increase the lung burden by 2.5 μCi 144Ce/kg body weight with each exposure in the first group; to reestablish lung burdens of 9 or 4.5 μCi 144Ce/kg body weight in the second and third groups, respectively; and to expose controls (fourth group) to fused aluminosilicate particles containing stable cerium. With these exposure sequences, the 144Ce-exposed dogs received increasing or relatively constant beta radiation dose rates in contrast to the steadily decreasing dose rate seen after a single inhalation exposure. Exposures in the first and second groups were planned to yield a cumulative absorbed dose to lung of approx. = 35,000 rads and those in the third group approx. = 17,000 rads within two years after the first exposure. All 13 exposures have been completed. During the past year, one dog in the 9.0 μCi 144Ce/kg body weight group died at 1558 days after the first exposure with autoimmune hemolytic anemia. The remaining 24 144Ce-exposed and seven control dogs generally appear to be in good physical condition with exception of a persistent lymphopenia at approx. = 5 years after the first exposure. They are continuing to be maintained for life span observations

  11. Dependence of Fission-Fragment Properties On Excitation Energy For Neutron-Rich Actinides

    Ramos D; Rodríguez-Tajes C.; Caamaño M.; Farget F.; Audouin L.; Benlliure J.; Casarejos E.; Clement E.; Cortina D.; Delaune O.; Derkx X.; Dijon A.; Doré D.; Fernández-Domínguez B.; France G. de

    2015-01-01

    Experimental access to full isotopic fragment distributions is very important to determine the features of the fission process. However, the isotopic identification of fission fragments has been, in the past, partial and scarce. A solution based on the use of inverse kinematics to study transfer-induced fission of exotic actinides was carried out at GANIL, resulting in the first experiment accessing the full identification of a collection of fissioning systems and their corresponding fission ...

  12. Effects of inhaled 144Ce on cardiopulmonary function and histopathology of the dog

    Twelve dogs inhaled single doses of relatively insoluble particles containing 144Ce and six dogs inhaled particles containing stable cerium as controls. Pulmonary function, clinical, and radiographic evaluations were performed serially. The dogs developed progressive radiation pneumonitis and pulmonary fibrosis similar to that previously reported for whole-lung irradiation from internal or external sources. Focal histologic changes in bronchioles and alveoli were detected functionally during treadmill and tube-breathing stresses at a time when the dogs' clinical and radiographic appearances were normal. Moderate functional impairment was associated with more severe inflammatory and proliferative changes in airways and alveoli. Severe impairment resulted from progressive fibrosis and scarring. These were several strong correlations between functional indices and histological scores. There was a nonlinear relationship between cumulative radiation dose and effects, and once the functional alterations became clinically evident, the disease progressed with little further increase in dose

  13. Simultaneous Velocity and Energy Measurement of Fission Fragments

    Semi-conductor detectors have been used in a double-velocity apparatus for a simultaneous measurement of fragment velocities and detector pulse heights. The purposes of this measurement were (1) to obtain the pulse-height-to-energy calibration of these detectors for fission fragments and (2) to evaluate a technique for the simultaneous determination of pre- and post neutron emission parameters of the fission process from a coincident measurement of fragment velocities and energies. Fast and slow output signals were obtained from the detectors for use in the time-of-flight and pulse-height measurements respectively. The recorded data were the flight times of both fragments and the pulse height from one of the detectors for a total of 46 000 Cf252 fission events. Fragment velocities, initial masses and initial energies were obtained in the usual manner from the time-of- flight data. The detector calibration function was determined from the correlation between the recorded pulse heights and the final parameters of the corresponding fragments. The latter values were obtained from the initial mass, initial energy and the published values of v(m, EK) for californium fragments. Finally, the calibration function was corrected for instrumental dispersions and the dependence of the average energy on fragment mass. The post-neutron-emission parameters were obtained from the recorded data and available detector calibration procedures including the one given above. The average number of neutrons emitted as.a function of fragment mass was obtained from the event-by-event differences of the initial and final masses. This result provided a sensitive test of the validity of this proposed technique and the various calibration procedures. Agreement with published data was found for the calibration procedure based on these data and one derived from the response of semi-conductor detectors to accelerated bromine and iodine ions. In each case the root mean square deviation from the

  14. Fission fragment mass and angular distributions: probes to study non-equilibrium fission

    It is found that the experimental observables in non-equilibrium fission are found to crucially depend on the interaction time (sticking time) of the di-nuclear complex with respect to the characteristic relaxation time of various degrees of freedom, before it decays into binary fission like fragments. This interaction time in turn depends on the entrance channel parameters of the colliding nuclei. Recent results on mass-angle correlations and mass distributions in fissile and less fissile systems will be presented. The importance of the sticking time of the dinuclear complex with respect to the equilibration times of various degrees of freedom is emphasized

  15. Fission fragment formation and fission yields in the model of octupole neutron-proton oscillations

    Yavshits S.

    2010-01-01

    The fission fragment formation is considered as a result of neck instability in the process of octupole oscillations of neutrons and protons near the scission point. To describe such a phenomenon the potential surface of fissionning nucleus with neck radius about 1 fm was calculated with shell correction approach. The new version of smooth liquid drop part of deformation energy is proposed. The liquid drop part is formulated in a double folding model with n-n, p-p, and n-p Yukawa interac...

  16. Apoptosis in immune cells induced by fission fragment 147Pm

    ZhuShou-Peng; ZhangLan-Sheng; 等

    1997-01-01

    Apoptosis in human acute lymphoblastic leukemia cell line Molt-4 cell and macrophage cell line Ana-1 cell could be induced by fission fragment 147Pm,The cumulative absorption dose of 147Pm in cultural cells through different periods were estimated.By using fluorescence microscopy and microautoradiographic tracing it can be found that Molt-4 and Anal-1 cells internally irradiated by 147Pm,displayed an obvious nuclear fragmentation and a marked phknosis in immune cell nucei,as well as DNA chain fragmentation and apoptotic bodies formation.The microautoradiographic study showed that 147Pm could infiltrate thourgh cell membrane and displayed membrane-seeking condensation in cells.At the same time.the membrane-bounded apoptotic bodies were observed.Experimental results in recent study provide evidence that Molt-4 and Ano-1 immune cells undergo apoptosis while internally irradiated with 147Pm.

  17. Methodology of a study of correlations between neutron multiplicity, mass and kinetic energy of fission fragments

    The description of an experimental set-up for the study of the excitation energy distribution of fission fragments by means of coincident measurement of fission neutrons is presented. For every fission event the kinetic energy and mass of both fragments are registered simultaneously with the number of prompt neutrons emitted by each of the complementary fission fragments. With this set-up, the fission fragments are detected by a twin ionization chamber and the neutrons - by two large Gd-loaded liquid scintillator tanks. (author)

  18. Biological effects of repeated inhalation exposure of beagle dogs to aerosols of 144Ce in fused clay particles I

    This experiment was initiated to study the biological behavior and long-term effects of repeated inhalation exposures to 144Ce in fused clay particles compared with those seen in Beagle dogs that received a single exposure as young adults. The 36 dogs, divided into four equal groups, are exposed every 8 weeks to achieve the following: to maintain lung burdens of 9 and 4.5 μCi 144Ce/kg body weight in the first and second groups, respectively; to increase the lung burden by 2.5 μCi 144Ce/kg body weight in the third group with each exposure and to expose controls (fourth group) to fused clay containing stable cerium. With these exposure sequences, the 144Ce-exposed dogs will receive increasing or maintained β dose rates in contrast to the steadily decreasing dose rate seen after a single inhalation exposure. Exposures to the first and third groups will produce a cumulative absorbed dose to lung of approximately equal to 35,000 rads and those to the second group will yield approximately equal to 17,000 rads within 2 yr after the first exposure. Single exposure dogs that had died with pulmonary neoplasia when this experiment was initiated had cumulative doses to death of 29,000 to 61,000 rads. Six of the planned 13 exposures have been completed to date. All exposed dogs are surviving and will be maintained for lifespan observation. (U.S.)

  19. Langevin description of fission fragment charge distribution from excited nuclei

    Karpov, A V

    2002-01-01

    A stochastic approach to fission dynamics based on a set of three-dimensional Langevin equations was applied to calculate fission-fragment charge distribution of compound nucleus sup 2 sup 3 sup 6 U. The following collective coordinates have been chosen - elongation coordinate, neck-thickness coordinate, and charge-asymmetry coordinate. The friction coefficient of charge mode has been calculated in the framework of one-body and two-body dissipation mechanisms. Analysis of the results has shown that Langevin approach is appropriate for investigation of isobaric distribution. Moreover, the dependences of the variance of the charge distribution on excitation energy and on the two-body viscosity coefficient has been studied

  20. Sensitivity studies of spin cut-off models on fission fragment observables

    Thulliez L.

    2016-01-01

    Full Text Available A fission fragment de-excitation code, FIFRELIN, is being developed at CEA Cadarache. It allows probing the characteristics of the prompt emitted particles, neutrons and gammas, during the de-excitation process of fully accelerated fission fragments. The knowledge of the initial states of the fragments is important to accurately reproduce the fission fragment observables. In this paper a sensitivity study of various spin cut-off models, completely defining the initial fission fragment angular momentum distribution has been performed. This study shows that the choice of the model has a significant impact on gamma observables such as spectrum and multiplicity and almost none on the neutron observables.

  1. Sensitivity studies of spin cut-off models on fission fragment observables

    Thulliez, L.; Litaize, O.; Serot, O.

    2016-03-01

    A fission fragment de-excitation code, FIFRELIN, is being developed at CEA Cadarache. It allows probing the characteristics of the prompt emitted particles, neutrons and gammas, during the de-excitation process of fully accelerated fission fragments. The knowledge of the initial states of the fragments is important to accurately reproduce the fission fragment observables. In this paper a sensitivity study of various spin cut-off models, completely defining the initial fission fragment angular momentum distribution has been performed. This study shows that the choice of the model has a significant impact on gamma observables such as spectrum and multiplicity and almost none on the neutron observables.

  2. Direct nuclear pumping by a volume source of fission fragments

    Deese, J. E.; Hassan, H. A.

    1978-01-01

    A detailed kinetic model is presented for the analysis of nuclear pumped lasers when the pumping is a result of a volume source of fission fragments. The results of the model are employed to study a He-3 - Xe laser. For the range of pressures, neutron fluxes and mixtures considered, the gain and power calculations are in good agreement with experiment. Moreover, based on these calculations, it appears that the collisional recombination is the dominant pumping mechanism for 7p-7s transitions while direct excitation is the dominant pumping mechanism for the 5d-6p transitions.

  3. Fission fragment mass reconstruction from Si surface barrier detector measurement

    Velkovska, J.; McGrath, R. L.

    1998-01-01

    A method for plasma delay and pulse-height defect corrections for Si surface barrier detectors (SBD) is presented. Based on known empirical formulae, simple approximations involving the measured time-of-flight (TOF) and energy of the ions were found and a mass reconstruction procedure was developed. The procedure was applied for obtaining the fission fragment mass and angular distributions from the $^{64}$ Ni+$^{197}$Au reaction at 418 MeV and 383 MeV incident energy using an array of eight S...

  4. Measurement techniques for analysis of fission fragment excited gases

    Schneider, R. T.; Carroll, E. E.; Davis, J. F.; Davie, R. N.; Maguire, T. C.; Shipman, R. G.

    1976-01-01

    Spectroscopic analysis of fission fragment excited He, Ar, Xe, N2, Ne, Ar-N2, and Ne-N2 have been conducted. Boltzmann plot analysis of He, Ar and Xe have indicated a nonequilibrium, recombining plasma, and population inversions have been found in these gases. The observed radiating species in helium have been adequately described by a simple kinetic model. A more extensive model for argon, nitrogen and Ar-N2 mixtures was developed which adequately describes the energy flow in the system and compares favorably with experimental measurements. The kinetic processes involved in these systems are discussed.

  5. Nuclear model calculation on neutron induced fission fragment mass yields of 238U

    The fission fragment mass yield is one of the most important characteristics of the fission process in both applications and basic nuclear physics. In nuclear energy applications, the configuration of fission products must be known because they are accumulated during the operation of a nuclear reactor. In theoretical physics, the ability to describe and predict fission yields is required for an effective nuclear fission model. Since the nuclear fission process is described by a great number of parameters, and the existing theoretical models fail to describe the fission process completely, the fission yields are amongst the most important consequences to benchmark the validity of fission models. In the present study, two different approaches to predict the neutron-induced fission fragment mass distribution of 238U has been applied. The first approach is temperature dependent Brosa model, and the other based on GEF model. The model-based predicted results are in good agreement with the experimental data

  6. Measurement of energy dependence of fission fragment angular anisotropy for resonance neutron induced fission of 235U aligned target

    The results of the experiment on measuring the energy dependence of fission fragment angular anisotropy in resonance neutron induced fission of 235U aligned target in energy region up to 42 eV are presented. The agreement with the data of Pattenden and Postma in resonances is good enough, while the theoretical curve, calculated using the R-matrix multilevel two fission channel approach, does not seem to describe the energy dependence of fission fragment angular anisotropy property. The necessity of taking into account the interference between levels with different spins is discussed. 11 refs., 2 figs

  7. Application of pulse shape discrimination in Si detector for fission fragment angular distribution measurements

    B K Nayak; E T Mirgule; R K Choudhury

    2005-12-01

    Pulse shape discrimination (PSD) with totally depleted transmission type Si surface barrier detector in reverse mount has been investigated to identify fission fragments in the presence of elastic background in heavy ion-induced fission reactions by both numerical simulation and experimental studies. The PSD method is compared with the other conventional methods adopted to identify fission fragments with solid-state detectors such as - telescope and single thin detector and the data for the 10B + 232Th fission reaction are presented. Results demonstrate the usefulness of a single transmission-type surface barrier detector for the identification of fission fragments and projectiles like heavy ions.

  8. Target conception for the Munich fission fragment accelerator

    For the new high-flux reactor FRM II, the fission fragment accelerator MAFF is under design. MAFF will supply intense mass-separated radioactive ion beams of very neutron-rich nuclei with energies around the Coulomb barrier. A central part of this accelerator is the ion source with the fission target, which is operated at a neutron flux of 1.5x1014 cm-2 s-1. The target consists of typically 1 g of 235U dispersed in a cylindrical graphite matrix, which is encapsulated in a Re container. To enable diffusion and extraction of the fission products, the target has to be maintained at a temperature of up to 2400 deg. C during operation. It has to stand this temperature for at least one reactor cycle of 1250 h. Comprehensive tests are required to study the long-term behaviour of the involved materials at these conditions prior to operation in the reactor. The present paper gives details of the target conception and the projected tests

  9. Studies of Fission Fragment Rocket Engine Propelled Spacecraft

    Werka, Robert O.; Clark, Rodney; Sheldon, Rob; Percy, Thomas K.

    2014-01-01

    The NASA Office of Chief Technologist has funded from FY11 through FY14 successive studies of the physics, design, and spacecraft integration of a Fission Fragment Rocket Engine (FFRE) that directly converts the momentum of fission fragments continuously into spacecraft momentum at a theoretical specific impulse above one million seconds. While others have promised future propulsion advances if only you have the patience, the FFRE requires no waiting, no advances in physics and no advances in manufacturing processes. Such an engine unequivocally can create a new era of space exploration that can change spacecraft operation. The NIAC (NASA Institute for Advanced Concepts) Program Phase 1 study of FY11 first investigated how the revolutionary FFRE technology could be integrated into an advanced spacecraft. The FFRE combines existent technologies of low density fissioning dust trapped electrostatically and high field strength superconducting magnets for beam management. By organizing the nuclear core material to permit sufficient mean free path for escape of the fission fragments and by collimating the beam, this study showed the FFRE could convert nuclear power to thrust directly and efficiently at a delivered specific impulse of 527,000 seconds. The FY13 study showed that, without increasing the reactor power, adding a neutral gas to the fission fragment beam significantly increased the FFRE thrust through in a manner analogous to a jet engine afterburner. This frictional interaction of gas and beam resulted in an engine that continuously produced 1000 pound force of thrust at a delivered impulse of 32,000 seconds, thereby reducing the currently studied DRM 5 round trip mission to Mars from 3 years to 260 days. By decreasing the gas addition, this same engine can be tailored for much lower thrust at much higher impulse to match missions to more distant destinations. These studies created host spacecraft concepts configured for manned round trip journeys. While the

  10. Fission fragment assisted reactor concept for space propulsion: Foil reactor

    Wright, Steven A.

    1991-01-01

    The concept is to fabricate a reactor using thin films or foils of uranium, uranium oxide and then to coat them on substrates. These coatings would be made so thin as to allow the escaping fission fragments to directly heat a hydrogen propellant. The idea was studied of direct gas heating and direct gas pumping in a nuclear pumped laser program. Fission fragments were used to pump lasers. In this concept two substrates are placed opposite each other. The internal faces are coated with thin foil of uranium oxide. A few of the advantages of this technology are listed. In general, however, it is felt that if one look at all solid core nuclear thermal rockets or nuclear thermal propulsion methods, one is going to find that they all pretty much look the same. It is felt that this reactor has higher potential reliability. It has low structural operating temperatures, very short burn times, with graceful failure modes, and it has reduced potential for energetic accidents. Going to a design like this would take the NTP community part way to some of the very advanced engine designs, such as the gas core reactor, but with reduced risk because of the much lower temperatures.

  11. Fission fragment assisted reactor concept for space propulsion: Foil reactor

    The concept is to fabricate a reactor using thin films or foils of uranium, uranium oxide and then to coat them on substrates. These coatings would be made so thin as to allow the escaping fission fragments to directly heat a hydrogen propellant. The idea was studied of direct gas heating and direct gas pumping in a nuclear pumped laser program. Fission fragments were used to pump lasers. In this concept two substrates are placed opposite each other. The internal faces are coated with thin foil of uranium oxide. A few of the advantages of this technology are listed. In general, however, it is felt that if one look at all solid core nuclear thermal rockets or nuclear thermal propulsion methods, one is going to find that they all pretty much look the same. It is felt that this reactor has higher potential reliability. It has low structural operating temperatures, very short burn times, with graceful failure modes, and it has reduced potential for energetic accidents. Going to a design like this would take the NTP community part way to some of the very advanced engine designs, such as the gas core reactor, but with reduced risk because of the much lower temperatures

  12. Scope of isomer spectroscopy of fission fragments using INGA

    Large array of Compton suppressed high purity germanium detectors continues to provide new insights on the novel quantal rotations of atomic nuclei. The Indian National Gamma Detector Array (INGA) is set up at TIFR-BARC accelerator facility at Mumbai, as a part of a collaboration between BARC, IUAC, SINP, TIFR, UGC-CSR-KC, VECC and different Universities. The array is designed for 24 Compton suppressed clover detectors providing around 5% photopeak efficiency. Recently, a digital data acquisition system with 96 channels (based on Pixie-16 modules developed by XIA LLC) has been implemented for this Compton suppressed clover array. The timing properties of fast scintillator detectors with the existing DDAQ have also been investigated. This facilitates the lifetime measurements of isomeric states from 1 nsec to few microsec during the usual gamma-gamma coincidence measurement. The scope of isomer spectroscopy of fission fragments using INGA will be discussed. In one of the in-beam experiments, 7Li + 232Th reaction at 38 MeV has been used to populate the fission fragments in mass 130 region. The prompt-delayed coincidence analysis was carried to establish the isomers in Te and Xe isotopes. A typical spectrum showing the delayed gamma rays with 197, 381, and 1313 keV energies emitted from the 6+ isomeric state of 136Xe with T1/2 = 2.95 micro sec is shown. The spectrum is generated with gate on 370 keV transition present above the isomer

  13. Effect of fasting on the transit time of 144Ce in the mouse gut

    Our work with G.I. absorption of actinide elements indicates greater absorption by fasted animals than by animals on regular diets (Weiss and Walburg, undated). Residence time of a metallic compound in the gut may be an important factor influencing G.I. absorption. Cerium-144 (III) chloride was administered by gavage to fasted mice and to mice on regular feed. The G.I. tract was excised, cut into sections, and the activity of each section determined as a function of time after dosing. Our results indicate rapid transit of 144CeCl3 along the empty mouse gut. One hour after dosing, about half the Ce is in the cecal contents; about 40% remains in stomach contents. Twelve hours after dosing, only about 2% remains in the cecum; by 16 hours, almost the entire dose has been cleared from the intestine. Transit times in mice with stomach and intestines containing food were 12 hours longer than in fasted mice. These results lead to the conclusion that factors other than G.I. residence time determine G.I. absorption of actinides in mice

  14. Effect on canine lymphocyte function of 144Ce inhaled in fused clay particles

    Beagle dogs exposed by inhalation to 144Ce in fused clay particles develop a persistent lymphopenia and the remaining peripheral lymphocytes in these dogs show a depressed in vitro response to plant mitogens. These studies were designed to evaluate the cellular basis for this defect. The survival and growth of lymphocytes from irradiated and control dogs were evaluated through 96 hours of culture. Many irradiated lymphocytes that were viable in vivo died within 24 hours in vitro. The remaining lymphocytes appeared to grow normally indicating that the early in vitro death was responsible for at least a portion of the difference between irradiated and control lymphocyte cultures. A second experiment was designed to determine if any humoral factors in plasma of irradiated dogs were responsible for the poor response of the lymphocytes. Lymphocytes from irradiated and control dogs were grown with plasma from both types of animals. Heterologous plasma had no apparent effect on lymphocyte growth, indicating that humoral factors were not involved. (U.S.)

  15. Compact multiwire proportional counters for the detection of fission fragments

    Two large area multistep position sensitive (two dimensional) multiwire proportional counters have been developed for experiments involving study of fission dynamics using general purpose scattering chamber facility at IUAC. Both detectors have an active area of 20x10 cm2 and provide position signals in horizontal (X) and vertical (Y) planes, timing signal for time of flight measurements and energy signal giving the differential energy loss in the active volume. The design features are optimized for the detection of low energy heavy ions at very low gas pressures. Special care was taken in setting up the readout electronics, constant fraction discriminators for position signals in particular, to get optimum position and timing resolutions along with high count rate handling capability of low energy heavy ions. A custom made charge sensitive preamplifier, having lower gain and shorter decay time, has been developed for extracting the differential energy loss signal. The position and time resolutions of the detectors were determined to be 1.1 mm full width at half maximum (FWHM) and 1.7 ns FWHM, respectively. The detector could handle heavy ion count rates exceeding 20 kHz without any breakdown. Time of flight signal in combination with differential energy loss signal gives a clean separation of fission fragments from projectile and target like particles. The timing and position signals of the detectors are used for fission coincidence measurements and subsequent extraction of their mass, angular, and total kinetic energy distributions. This article describes systematic study of these fission counters in terms of efficiency, time resolution, count rate handling capability, position resolution, and the readout electronics. The detector has been operated with both five electrode geometry and four electrode geometry, and a comparison has been made in their performances.

  16. Nuclear isomerism in fission fragments produced by the spontaneous fission of 252Cf

    This thesis is devoted to the study of the nuclear structure of neutron-rich nuclei, via the search of isomeric nuclear states. Neutron-rich nuclei were produced in the spontaneous fission of 252Cf. The experimental study of isomeric states in these nuclei was performed with the γ-array EUROGAM II, coupled to an additional and original fission fragment detector composed by photovoltaic cells, SAPhIR. The photovoltaic cells are well adapted to detect low energy heavy ions and have good energy and time resolutions to obtain a good fission fragment detection. This experiment led to the discovery of new isomeric states in 135Xe, 104Mo, 146,147,148Ce and 152,154,156Nd, with lifetimes between 60 ns and 2 μs. Level schemes of these nuclei have been completed. An interpretation of the isomeric states in the nuclei 154,156Nd and 156,158Sm was performed by Hartree-Fock-Bogolyubov calculations using the DIS Gogny force with two quasi-particles excitations. The confrontation with the experimental results led to an interpretation of these isomeric states as K-isomers. (author)

  17. Fission-fragment and neutron data traced back to the macroscopic and microscopic properties of the fissioning systems

    Schmidt K.-H; Jurado B.

    2010-01-01

    A new model description of fission-fragment yields and prompt neutron emission is developed. The yields of the different fission channels and their properties are attributed to the number of relevant states above the potential-energy landscape on the fission path at the moment of dynamical freeze-out, which is specific to the collective coordinate considered. The model combines well established ideas with novel concepts. The separability principle of macroscopic properties of the compound nuc...

  18. Description of Induced Nuclear Fission with Skyrme Energy Functionals: I. Static Potential Energy Surfaces and Fission Fragment Properties

    Schunck, N.; Duke, DJ; Carr, H.; Knoll, A

    2013-01-01

    Eighty years after its experimental discovery, a description of induced nuclear fission based solely on the interactions between neutrons and protons and quantum many-body methods still poses formidable challenges. The goal of this paper is to contribute to the development of a predictive microscopic framework for the accurate calculation of static properties of fission fragments for hot fission and thermal or slow neutrons. To this end, we focus on the Pu239(n,f) reaction and employ nuclear ...

  19. Dependence of Fission-Fragment Primary Charge on Nuclear Structure

    Assuming a quasi-static scission configuration the potential energy of this configuration has been calculated. The energy release between saddle point and scission point has been maximized using the liquid drop model and taking into account the mass dependence of the deform ability of the fission fragments. The leading terms that determine the charge distribution depend on the Coulomb and the asymmetry energy of the scission configuration. The deformability of the fragments shows dependence from nuclear structure. A term proportional to the difference of the deformation energies of the two fragments gives rise to a strong influence from this nuclear structure effect. In the region of closed shells the difference in the deformation energies is much the same as the total deformation energy. A term comparable to the Coulomb energy term has to be taken into account in these mass regions. The calculated Zp-values have been compared to experimental results for U235. Calculated Zp-values for Cf252 are given. (author)

  20. The temperature of fission fragments from spontaneous fission of 252Cf measured by time-of-flight spectrometer

    The detection system MONA (Modular Neutron Array) consisting of eight large BC-501A liquid scintillators, was applied to determine the temperature of fission fragments emitted in spontaneous fission of 252Cf. The determination of the temperature was based on the measurement of the neutron spectra

  1. Biological effects of repeated inhalation exposure of Beagle dogs to relatively insoluble aerosols of 144Ce. VI

    Beagle dogs were exposed repeatedly to a relatively insoluble form of 144Ce (in fused aluminosilicate particles) to study the deposition, retention and long-term biological effects for comparison with data from dogs that were exposed only once to a similar aerosol. Four groups of nine dogs each were exposed once every 8 weeks for 2 years (13 exposures) to achieve specified exposure goals. These goals were: to increase the lung burden by 2.5 μCi 144Ce/kg body weight with each exposure; to reestablish lung burdens of 9 or 4.5 μCi 144Ce/kg body weight and to expose controls to fused aluminosilicate particles containing nonradioactive cerium. With these exposure sequences, the 144Ce-exposed dogs received increasing or relatively constant beta radiation dose rates in contrast to the steadily decreasing dose rate seen after a single inhalation exposure. Following completion of the exposure series, the dogs are being observed for the development of long-term biological effects. To date, 11 dogs have died or were euthanized, nine exposed dogs and two controls. Although pulmonary hemangiosarcomas were a prominent finding in dogs exposed once to the same aerosol at a level that led to cumulative doses to lung similar to these repeatedly exposed dogs, only one has been observed in the repeatedly exposed dogs. Other effects of note to date include three pulmonary carcinomas, two hemangiosarcomas of the tracheobronchial lymph nodes and one splenic hemangiosarcoma. Observations are continuing on the surviving 18 exposed and seven control dogs

  2. Kinetic study of the deposition of 144Ce, 143Pr and 147Nd on a platinum anode

    Investigation of the electrodeposition of radioactive rare earth metal isotopes confirm that, depending on the conditions of electrolysis, they can be deposited on the platinum either cathodically or anodically. The anodic deposition of these isotopes can take place with electrochemical oxidation or electrosorption without electron-transfer, depending on the lanthanide(III-IV) oxidation potentials. The present paper reports the results of the investigation connected with the anodic deposition of 144Ce, 143Pr and 147Nd. (author)

  3. Dependence of Fission-Fragment Properties On Excitation Energy For Neutron-Rich Actinides

    Ramos, D.; Rodríguez-Tajes, C.; Caamaño, M.; Farget, F.; Audouin, L.; Benlliure, J.; Casarejos, E.; Clement, E.; Cortina, D.; Delaune, O.; Derkx, X.; Dijon, A.; Doré, D.; Fernández-Domínguez, B.; de France, G.; Heinz, A.; Jacquot, B.; Navin, A.; Paradela, C.; Rejmund, M.; Roger, T.; Salsac, M. D.; Schmitt, C.

    2016-03-01

    Experimental access to full isotopic fragment distributions is very important to determine the features of the fission process. However, the isotopic identification of fission fragments has been, in the past, partial and scarce. A solution based on the use of inverse kinematics to study transfer-induced fission of exotic actinides was carried out at GANIL, resulting in the first experiment accessing the full identification of a collection of fissioning systems and their corresponding fission fragment distribution. In these experiments, a 238U beam at 6.14 AMeV impinged on a carbon target to produce fissioning systems from U to Am by transfer reactions, and Cf by fusion reactions. Isotopic fission yields of 250Cf, 244Cm, 240Pu, 239Np and 238U are presented in this work. With this information, the average number of neutrons as a function of the atomic number of the fragments is calculated, which reflects the impact of nuclear structure around Z=50, N=80 on the production of fission fragments. The characteristics of the Super Long, Standard I, Standard II, and Standard III fission channels were extracted from fits of the fragment yields for different ranges of excitation energy. The position and contribution of the fission channels as function of excitation energy are presented.

  4. Revealing of the structure peculiarities of the fission fragments two-dimensional distributions

    Methods and results of the structure peculiarities revealing of different scales in two-dimensional distributions of experimental observables are discussed. The mass-energy distributions of fission fragments in the 252Cf and 234U nuclei are considered as an example. The approach elaborated opens up new possibilities for investigating the mechanism of nuclear fission and, in particular, the manifestation of fission modes

  5. A fission fragment reactor concept for nuclear space propulsion

    Suo-Anttila, A. J.; Parma, E. J.; Wright, S. A.; Vernon, M. E.; Pickard, P. S.

    1991-10-01

    Sandia National Laboratory (SNL) has proposed a new nuclear thermal propulsion concept that uses fission fragments to directly heat the propellant up to 1000 K or higher above the material temperatures. The concept offers significant advantages over traditional solid core nuclear rocket concepts because of higher propellant exit temperatures while at the same time providing for more reliable operation due to lower structure temperatures and lower power densities. The concept can be operated in either steady state or pulsed modes. The engine consists of tubular modules, each with its own pressure boundary and rocket nozzle. The steady state mode requires a large engine with a reflector for criticality, provides high thrust and high ISP. The pulse mode utilizes a driver reactor for criticality and can be considerably smaller with lower but scaleable thrust. The pulse mode does require an external heat radiator for reactor cooling, which limits its duty cycle.

  6. Orientations of fragments emitted in binary cold fission of 252Cf

    The dependence of the driving potential on the orientation of fragments at scission is investigated for the case of cold fission of 252Cf. It is shown that in the case of cold fission the fragments exclusively emerge at scission in the pole-pole configuration. However, quantum fluctuations enable small deviations from this configuration during the tunnelling process. The mass yields of fission fragment pairs in the cold fission of 252Cf are computed for pole-pole and equator-equator orientations and are compared to the experimental data

  7. Dependence of Fission-Fragment Properties On Excitation Energy For Neutron-Rich Actinides

    Ramos D.

    2016-01-01

    Isotopic fission yields of 250Cf, 244Cm, 240Pu, 239Np and 238U are presented in this work. With this information, the average number of neutrons as a function of the atomic number of the fragments is calculated, which reflects the impact of nuclear structure around Z=50, N=80 on the production of fission fragments. The characteristics of the Super Long, Standard I, Standard II, and Standard III fission channels were extracted from fits of the fragment yields for different ranges of excitation energy. The position and contribution of the fission channels as function of excitation energy are presented.

  8. Isotopic resolution of fission fragments from 238U + 12C transfer and fusion reactions

    Recent results from an experiment at GANIL, performed to investigate the main properties of fission-fragment yields and energy distributions in different fissioning nuclei as a function of the excitation energy, in a neutron-rich region of actinides, are presented. Transfer reactions in inverse kinematics between a 238U beam and a 12C target produced different actinides, within a range of excitation energy below 30 MeV. These fissioning nuclei are identified by detecting the target-like recoil, and their kinetic and excitation energy are determined from the reconstruction of the transfer reaction. The large-acceptance spectrometer VAMOS was used to identify the mass, atomic number and charge state of the fission fragments in flight. As a result, the characteristics of the fission-fragment isotopic distributions of a variety of neutron-rich actinides are observed for the first time over the complete range of fission fragments. (authors)

  9. Fission fragment angular distribution measurements in 18O+194Pt reaction

    Fission fragment angular distributions were measured for 18O + 194Pt in energy range 78.2 - 87.3 MeV. The normal nature of angular anisotropy suggests that the reaction proceeded through true CN formation. The present results are consistent with result obtained from fission fragment mass distribution measurements carried out for reaction using other isotopes of platinum

  10. Kinetic and experimental study of argon and argon--nitrogen mixtures excited by fission fragments

    Optical emission from argon and argon-nitrogen mixtures excited by fission fragments are studied in an effort to better understand the fission fragment energy deposition into the gas. A model of the energy flow in the gas is developed and compared with the experimental results

  11. Fission fragment mass yield deduced from density distribution in the pre-scission configuration

    Warda, M.; Zdeb, A.

    2015-01-01

    Static self-consistent methods usually allow to determine the most probable fission fragments mass asymmetry. We have applied random neck rupture mechanism to the nuclei in the configuration at the end of fission paths. Fission fragment mass distributions have been deduced from the pre-scission nuclear density distribution obtained from the self-consistent calculations. Potential energy surfaces as well as nuclear shapes have been calculated in the fully microscopic theory, namely the constra...

  12. Development Of A Digital Technique For The Determination Of Fission Fragments And Emitted Prompt Neutron Characteristics

    Varapai, N.; Hambsch, F.-J.; Oberstedt, S.; Serot, O.; Barreau, G.; Kornilov, N.; Zeinalov, Sh.

    2005-11-01

    The present work demonstrates the application of the digital technique for nuclear measurements. This method has been implemented for measurements of promptly emitted fission neutrons in coincidence with fission fragments from 252Cf(sf). A double Frisch-grid ionization chamber is used as fission fragment detector. The promptly emitted neutrons are detected by a NE213 liquid scintillation detector. The experimental set-up is installed at the Institute for Reference Materials and Measurements. Preliminary results are presented.

  13. SPIDER: A new instrument for fission fragment research at the Los Alamos Neutron Science Center

    Tovesson Fredrik; Arnold Charles; Blakeley Rick; Hecht Adam; Laptev Alexander; Mader Drew; Meierbachtol Krista; Snyder Lucas; White Morgan

    2013-01-01

    The study of fission fragment yields and how they behave as a function of excitation energy provides insight into the process in which they are formed. Fission yields are also important for nuclear applications, as they can be used as a diagnostic tool. A new instrument, SPIDER (Spectrometer for Ion DEtermination in fission Research), is being developed for measuring fission yields as a function of incident neutron energy at the Los Alamos Neutron Science Center. The instrument employs a time...

  14. Prompt neutron multiplicity in correlation with fragments from spontaneous fission of 252Cf

    GÖÖK Alf; Hambsch, Franz-Josef; Vidali, Marzio

    2014-01-01

    The spontaneous fission of 252Cf serves as an excellent benchmark of prompt emission in fission since experimental data can be obtained without the need of an incident beam. With the purpose of providing experimental data on the prompt fission neutron properties in correlation with fission fragment characteristics an experiment on 252Cf(SF) has been performed. In addition, the experiment serves as benchmark of setup and analysis procedures for measurements of fluctuations in the prompt neutro...

  15. A multiple parallel-plate avalanche counter for fission-fragment detection

    Wu, C.Y., E-mail: wu24@llnl.gov [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); Henderson, R.A. [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); Haight, R.C.; Lee, H.Y.; Taddeucci, T.N. [Los Alamos National Laboratory, Los Alamos, MN 87545 (United States); Bucher, B.; Chyzh, A. [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); Devlin, M.; Fotiades, N. [Los Alamos National Laboratory, Los Alamos, MN 87545 (United States); Kwan, E. [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); National Superconducting Cyclotron Laboratory, East Lansing, MI 48824 (United States); O’Donnell, J.M.; Perdue, B.A.; Ullmann, J.L. [Los Alamos National Laboratory, Los Alamos, MN 87545 (United States)

    2015-09-11

    A new low-mass multiple gas-filled parallel-plate avalanche counter for the fission-fragment detection has been developed to mark the fission occurrence in measurements of the prompt fission neutron energy spectrum as a function of incident neutron energy. It was used successfully for the neutron-induced fission of {sup 235}U and {sup 239}Pu with a total mass near 100 mg each and the spontaneous fission of {sup 252}Cf. Both the incident neutron energy and the prompt fission neutron energy are measured by using the time-of-flight method. The design and performance of this avalanche counter are described.

  16. A multiple parallel-plate avalanche counter for fission-fragment detection

    A new low-mass multiple gas-filled parallel-plate avalanche counter for the fission-fragment detection has been developed to mark the fission occurrence in measurements of the prompt fission neutron energy spectrum as a function of incident neutron energy. It was used successfully for the neutron-induced fission of 235U and 239Pu with a total mass near 100 mg each and the spontaneous fission of 252Cf. Both the incident neutron energy and the prompt fission neutron energy are measured by using the time-of-flight method. The design and performance of this avalanche counter are described

  17. Yield-Energy Dependence for 147Nd and 144Ce Under Strong Neutron Field

    QIAN; Jing; LIU; Ting-jin; SUN; Zheng-jun; SHU; Neng-chuan

    2012-01-01

    <正>The data of the fission product yield play an important role in the nuclear science technology and nuclear engineering because they are the key data in the calculation of the decay heat, shield design, nuclear verification, radiochemistry reprocessing and nuclear safety, etc. Especially, it is the essential data in fission power estimation for a fission device. It is well known that there exists a consecutive neutron spectrum with the energy from 1 keV to 15 MeV for a fission-fusion device. So in order to estimate the

  18. Decontamination of 60Co and 144Ce. low-activity liquid wastes with the Fe3+ /OH- /Ca2+ /PO-4-3- system

    The influence of reaction time, concentrations of Fe3+ and PO-4-3+, temperature and agitation velocity in the efficiency of decontamination of 60Co and 144Ce low-activity liquid wastes using the Fe3+ /OH-/Ca2+ /PO-4-3+ precipitator system was stud ied in this paper. The mathematical models of this process were obtained for 60Co and 144Ce. The best conditions for the decontamination we re calculated using the optimization program

  19. Properties of fission fragments for Z =112 -116 superheavy nuclei

    Kaur, Gurjit; Sandhu, Kirandeep; Sharma, Manoj K.

    2016-07-01

    The dynamical cluster decay model (DCM) is applied to understand the dynamics of 48Ca+238U,244Pu,248Cm reactions at comparable excitation energies across the barrier. To understand the capture stage of *286112 ,*292114 , and *296116 nuclei, the compound nucleus formation probability is calculated. The indication of PC Nprocess such as quasifission may occur at the capture stage of the 48Ca induced reactions. To understand this further, the comparative decay analysis of *286112 ,*292114 and *296116 , nuclei is carried out using β2 i deformations within hot optimum orientation criteria, and the calculated fission cross sections find nice agreement with available data. The fission mass distribution shows a double humped structure where a symmetric peak observed around the Sn region appears to find its genesis in a symmetric quasifission component. On the other hand, the emergence of peaks around Pb in the decay of Z =112 , 114, and 116 nuclei signify the possible presence of asymmetric quasifission. Higher and broader asymmetric quasifission peaks are observed for *296116 and *292114 nuclei as compared to *286112 nucleus. Beside this, the total kinetic energy (TKE) distribution of the decay fragments is also explored by using different proximity potentials, such as Prox-77, Prox-88, and Prox-00. Prox-88 seems to perform better and the calculated TKE values find relatively better comparison at lower angular momentum states. The possible role of different radii of the decaying nuclei is also exercised to understand the TKE ¯ dynamics of 48Ca+238U,244Pu,248Cm reactions.

  20. Neutron and fragment yields in proton-induced fission of 238U at intermediate energies

    The primary fission fragment mass and kinetic energy distributions, and neutron multiplicities as function of fragment mass have been measured in the proton-induced fission of 238U at energies Ep=20, 35, 50 and 60 MeV using time-of-flight technique. Pre-scission and post-scission neutron multiplicities have been extracted from double differential distributions. The fragment mass dependence of the post-scission neutron multiplicities reveals the gross nuclear shell structure effect even at the higher proton energies we measured. The yields of neutron-rich fission products in the fission of 238U by 25 MeV protons were measured using an ion guide-based isotope separator technique. The results indicate enhancement for superasymmetric mass division at intermediate excitation energy of the fissioning nucleus. The experimental results have been analysed in the framework of a time-dependent statistical model with inclusion of nuclear friction effects in the fission process

  1. Fragment-mass distributions in fission of heavy nuclei by intermediate and high-energy probes

    Deppman, Airton; Andrade-II, E. [Universidade de Sao Paulo (IF/USP), SP (Brazil). Inst. de Fisica; Menezes, J.C.M.; Garcia, F. [Universidade Estadual de Santa Cruz (UESC), Ilheus, BA (Brazil); Duarte, S.B.; Tavares, O.A.P. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil); Rossi, P.C.R. [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

    2011-07-01

    Full text: Recent experiments have shown that the multimode approach for describing the fission process leads to some compatibility with the observed results. A systematic analysis of the parameters obtained by fitting the fission-fragment mass distribution to the spontaneous and low-energy data has shown that the values for those parameters present a smooth dependence upon the nuclear mass number. In the present work it is shown that the same parameter-values obtained for low- energy fission can be used to describe high-energy fission results of fragment-mass distributions if one takes into account the appropriate distribution of the fissioning system. To calculate the fission-fragment mass distributions, Monte Carlo simulations are used. This simulation considers a two-step reaction mechanism, namely, an intranuclear cascade providing the compound nucleus followed by a mechanism of competition between particle evaporation and fission. The fission-fragment masses are obtained according to the multimode approach following the Statistical Scission Model. Simulations for fission induced by 660 MeV protons on 241Am and 237Np, and for fission of 238U induced by photons from Bremsstrahlung with end-point energies of 50 MeV and 3500 MeV have been performed, and the results have been compared with recent experimental data. (author)

  2. SPY: A new scission point model based on microscopic ingredients to predict fission fragments properties

    Lemaître J.-F.

    2013-12-01

    Full Text Available Our purpose is to determine fission fragments characteristics in a framework of a scission point model named SPY for Scission Point Yields. This approach can be considered as a theoretical laboratory to study fission mechanism since it gives access to the correlation between the fragments properties and their nuclear structure, such as shell correction, pairing, collective degrees of freedom, odd-even effects. Which ones are dominant in final state? What is the impact of compound nucleus structure? The SPY model consists in a statistical description of the fission process at the scission point where fragments are completely formed and well separated with fixed properties. The most important property of the model relies on the nuclear structure of the fragments which is derived from full quantum microscopic calculations. This approach allows computing the fission final state of extremely exotic nuclei which are inaccessible by most of the fission model available on the market.

  3. SPY: A new scission point model based on microscopic ingredients to predict fission fragments properties

    Our purpose is to determine fission fragments characteristics in a framework of a scission point model named SPY for Scission Point Yields. This approach can be considered as a theoretical laboratory to study fission mechanism since it gives access to the correlation between the fragments properties and their nuclear structure, such as shell correction, pairing, collective degrees of freedom, odd-even effects. Which ones are dominant in final state? What is the impact of compound nucleus structure? The SPY model consists in a statistical description of the fission process at the scission point where fragments are completely formed and well separated with fixed properties. The most important property of the model relies on the nuclear structure of the fragments which is derived from full quantum microscopic calculations. This approach allows computing the fission final state of extremely exotic nuclei which are inaccessible by most of the fission model available on the market. (authors)

  4. Measurement of fission cross sections and fragment angular distributions using solid state track detectors

    Fission cross sections and angular distributions of fission fragments from fissions induced by 14.1 and 15.8 MeV neutrons, respectively, in 232Th, 231Pa, 233U, 235U, 238U, 237Np, 239Pu and 241Am have been studied using Lexan plastic track detectors. A novel experimental set-up evolved from considerations of neutron economy allows simultaneous measurement of angular distribution of fission fragments from five independently fissioning nuclides at a time. The data on angular anistropy were analysed in the perspective of different chances of fissions taking place simultaneously in this energy region. Third-chance fission thresholds for 231Pa and 241Am were estimated from the measured anisotropy values to be 13.2 and 11.1 MeV, respectively. (author)

  5. Thermal annealing effect on fission fragment track recording properties of polycarbonate

    Polycarbonate Track Detector is a commonly used Solid State Nuclear Track Detector (SSNTD) to identify the fission fragment. The phenomenon of spontaneous fission was discussed in papers. The most useful polycarbonate track detector Makrofol-N for recording fission tracks was used. This detector is insensitive to detect the light particles background such as alpha particle, proton etc. The present paper deals with the study of thermal annealing and the mass distribution of 252Cf fission fragments using unannealed and annealed Makrofol-N detectors

  6. Revisiting the even-odd staggering in fission-fragment yields

    The even-odd staggering observed in the experimental fission-fragment nuclear-charge yields is investigated over a wide systematics of fission fragments measured at Lohengrin in direct kinematics and at GSI in inverse kinematics. The general increase of the even-odd staggering in the fission-fragment charge yields towards asymmetric charge splits is explained by the absorption of the unpaired nucleons by the heavy fragment. As a consequence, the well established trend of even-odd staggering in the fission fragment charge yields to decrease with the fissility is attributed in part to the asymmetry evolution of the charge distribution. This interpretation is strongly supported by the data measured at GSI, which cover the complete charge distribution and include precise yields at symmetry. They reveal that the even-odd effect around symmetry remains constant over a large range of fissility. (authors)

  7. A fission fragment reactor concept for nuclear thermal propulsion

    Suo-Anttila, Ahti J.; Parma, Edward J.; Pickard, Paul S.; Wright, Steven A.; Vernon, Milton E.

    1992-01-01

    The Space Exploration Initiative requires the development of nuclear thermal and nuclear electric technologies for space propulsion for future Luna and Mars missions. Sandia National Laboratories has proposed a new nuclear thermal propulsion concept that uses fission fragments to directly heat the propellant up to 1000 K or higher above the material temperatures. The concept offers significant advantages over traditional solid-core nuclear rocket concepts because of higher propellent exit temperatures, while at the same time providing for more reliable operation due to lower structure temperatures and lower power densities. The reactor can be operated in either a steady-state or pulsed mode. The steady-state mode provides a high thrust and relatively high specific impulse, as compared to other nuclear thermal concepts. The pulsed mode requires an auxillary radiator for cooling, but has the possibility of achieving very high specific impulses and thrust scaleable to the radiator size. The propellant temperatures are limited only by thermal radiation and transient heat conduction back to the substrate walls.

  8. Systematic study of anomalous fragment anisotropies in near- and sub-barrier fusion-fission reactions

    The fusion cross sections and fragment angular distributions for the complete fusion-fission reactions of 11B+238U, 237Np, 12C+237Np, 16O+232Th, 238U, and 19F+23Th at near- and sub-barrier energies have been measured by the fragment folding angle technique. It is revealed that the anomalous anisotropies of fission fragments in latter three systems are existence. Based on the experimental observations and Dressing and Randrup's theory, a new version model of preequilibrium fission is put forward to explain the anomaly. (author)

  9. Varying Track Etch Rates along the Fission Fragments' Trajectories in CR-39 Detectors

    We determine the behavior of track etch rate VT along the tracks in CR-39 detectors exposed to fission fragments from 252Cf source. CR-39 detectors are etched at 70°C in different concentrations of Na2CO3-mixed 6M NaOH solutions for different etching time intervals of 5–10 min starting from 15 min up to 210 min. Two values of track etch rate are determined along the fission fragment trajectories. The variation in VT is correlated with the energy loss rate of the fission fragment in the detector material

  10. Angular Anisotropy of the Fission Fragments in the Dinuclear System Mo del

    T. M. Shneidman; A. V. Andreev; C. Massimi; M. T. Pigni; G. Vannini; A. Ventura; S. G. Zhou

    2015-01-01

    A theoretical evaluation of the collective excitation spectra of nucleus at large deformations is possible within the framework of the dinuclear system (DNS) model, which treats the wave function of the fissioning nucleus as a superposition of a mononucleus configuration and two-cluster configurations in a dynamical way, permitting exchange of nucleons between clusters. In this work the method of calculation of the potential energy and the collective spectrum of fissioning nucleus at scission point is presented. Combining the DNS model calculations and the statistical model of fission we calculate the angular distribution of fission fragments for the neutron–induced fission of 239Pu.

  11. Prompt Gamma Radiation from Fragments in the Thermal Fission of 235U

    Measurements were made on the gamma radiation emitted from fission fragments in slow neutron induced fission of 235U. The fragments were detected with solid state detectors of the surface barrier type and the gamma radiation with a Nal(Tl) scintillator. Mass selection was used so that the gamma radiation could be measured as a function of fragment mass. Time discrimination between the fission gammas and the prompt neutrons released in the fission process was employed to reduce the background. The gamma radiation emitted during different time intervals after the fission event was studied with the help of a collimator, the position of which was changed along the path of the fission fragments. In this way a decay curve was obtained from which the life-time of one of the gamma-emitting states could be estimated. The relative yield of the gamma-rays was determined as a function of mass for different gamma-ray energy portions and two specific time intervals after the fission events. Comparisons were made with data obtained from 252 Cf-fission. Attention is drawn to some features which seem to be the same in 235U and 252 Cf-fission

  12. Simultaneous measurement of fission fragments and prompt neutrons for thermal neutron-induced fission of U-235

    Nishio, Katsuhisa; Yamamoto, Hideki; Kimura, Itsuro; Nakagome, Yoshihiro [Kyoto Univ. (Japan)

    1997-03-01

    Simultaneous measurement of fission fragments and prompt neutrons following the thermal neutron induced fission of U-235 has been performed in order to obtain the neutron multiplicity (v) and its emission energy ({eta}) against the specified mass (m{sup *}) and the total kinetic energy (TKE). The obtained value of -dv/dTKE(m{sup *}) showed a saw-tooth distribution. The average neutron energy <{eta}>(m{sup *}) had a distribution with a reflection symmetry around the half mass division. The measurement also gave the level density parameters of the specified fragment, a(m{sup *}), and this parameters showed a saw-tooth trend too. The analysis by a phenomenological description of this parameters including the shell and collective effects suggested the existence of a collective motion of the fission fragments. (author)

  13. Library of prompt neutron and γ-emission spectra from fission fragments

    The statistical model of nuclear reactions is applied to describe the fission fragment neutron and gamma emission characteristics for spontaneous fission of 252Cf and for fission of 233,235U, 239Pu by thermal neutrons. The calculations of neutron and gamma-spectra are carried out for the fragments with A=70-160, excited up to 100 MeV. After testing of the model and input data library, calculations of neutron and γ-emission spectra for nuclei with A=70-170 excited up to 100 MeV were done to produce the Fission Fragments Emission Spectra Library (FFESL). FFESL contains the data of 1000 nuclei and will be used in calculations of neutron and γ-spectra for fission of heavy nuclei by intermediate energy nucleons. (author)

  14. Odd–even effect in fragment angular momentum in low-energy fission of actinides

    B S Tomar; R Tripathi; A Goswami

    2007-01-01

    Quantitative explanation for the odd–even effect on fragment angular momenta in the low-energy fission of actinides have been provided by taking into account the single particle spin of the odd proton at the fragment's scission point deformation in the case of odd- fragments along with the contribution from the population of angular momentum bearing collective vibrations of the fissioning nucleus at scission point. The calculated fragment angular momenta have been found to be in very good agreement with the experimental data for fragments in the mass number region of 130–140. The odd–even effect observed in the fragment angular momenta in the low-energy fission of actinides has been explained quantitatively for the first time.

  15. Absolute Energy Calibration of Solid-State Detectors for Fission Fragments and Heavy Ions

    Detailed measurements of the pulse-height response of silicon solid-state detectors to energetic heavy ions and fission fragments have been made. These studies have now led to a reliable method of absolute energy calibration of solid-state detectors for fission fragments, as well as to a better understanding of the somewhat peculiar response characteristics of the detectors to fission fragments and heavy ions. The use of silicon solid-state detectors in fragment kinetic energy measurements in recent years has been widespread; at the same time, questions have been raised about the detailed interpretation of such measurements because of the increasing evidence for anomalous behaviour in charge production, charge collection and charge multiplication in the case of densely ionizing particles. The present report discusses systematics and possible origins of these effects. Application of the absolute energy calibration method, which takes into account the mass and energy dependence of the response, is based simply on a Cf252 or U235 fragment pulse- height spectrum. Our studies were carried out with mono-energetic Br71, Br81 and I127 ions of energies from 30 to 120 MeV, and with fission fragments from spontaneous fission of Cf252 and neutron-induced fission of U235 and Pu239. It is shown that for a given fragment mass, over a wide energy range, the fragment energy versus pulse-height relationship is of the form E = ax + b, where E is the fragment energy and x is the measured pulse height. A dependence of pulse height on fragment mass has also been established, which leads to an energy versus pulse-height relationship, for the range of fission-fragment masses and energies, of the form E = (a + a'm)x + b + b'M, where M is the fragment mass. The effect of detector window and of detector type, resistivity and electric field have been studied. Guides to the selection of detectors and to their use with fission fragments are given. The effect of the more exact calibration

  16. Fission fragment mass distribution in the 13C+182W and 176Yb reactions

    Ramachandran K.; Hinde D.J.; Dasgupta M.; Williams E.; Wakhle A.; Luong D. H.; Evers M.; Carter I. P.; Das S.

    2013-01-01

    Shell effects can play a prominent role in fission fragment mass distributions. For lighter systems in the region of A~180-200, mass distributions were generally expected to be symmetric. However, a recent experiment showed that fission of 180Hg following electron capture of 180Tl leads to an asymmetric mass split. Recent calculations by various groups indicate that the mechanism of asymmetric fission could be very different in this mass region compared to the actinide region. To investigate ...

  17. Development of gridded ionization chamber for measuring atomic number of fission fragments

    In order to investigate the mechanism of asymmetric mass division in low energy fission of actinides, the detector for measuring an atomic number (Z) for fission fragments has been developed. Because the atomic number is closely related to energy losses of fragments, the gridded ionization chamber with divided anode is useful for this purpose. The detector was designed and optical conditions such as the distance and electric potential between electrodes were searched using alpha particles from 252Cf. The total energy and energy losses of fission fragments from 252Cf were measured under the obtained conditions. It was found that fission fragments lost most of the kinetic energy in the beginning of their range. This behavior agrees qualitatively with results of simulation by TRIM code. In the presentation, the results of energy measurements under various conditions will be shown and discussed. (author)

  18. Super-heavy nuclei with Z = 118 and their mass and charge spectrum of fission fragments

    Maslyuk, V. T.; Smolyanyuk, A. V.

    2015-12-01

    The first results of the calculation of the mass and charge yields of fission fragments for over 60 isotopes which have Z = 118 are presented. The results were obtained from the condition of thermodynamic ordering of the ensemble of fission fragments. The role of neutrons shells with N = 82 or N = 126 and protons shells with Z = 50 in the realization of symmetric (or one-humped) and asymmetric (2- or 3-humped) shapes of the fission-fragment yields with the transition from neutron-proficient to neutron-deficient isotopes was investigated. The data of fragments yields had been analyzed under the conditions of a “cold” and “hot” fission. The calculations show the possibility to identify super-heavy nuclei with Z ≥ 118 produced synthetically by heavy-ion reaction on their mass/charge spectrum division.

  19. Proposal for a Concept Assessment of a Fission Fragment Rocket Engine (FFRE) Propelled Spacecraft Project

    National Aeronautics and Space Administration — A new technology, the Fission Fragment Rocket Engine (FFRE), requires small amounts of readily available, energy dense, long lasting fuel, significant thrust at...

  20. Impact of prompt-neutron corrections on final fission-fragment distributions

    Al-Adili, A.; Hambsch, F.-J.; Pomp, S.; Oberstedt, S.

    2012-11-01

    Background: One important quantity in nuclear fission is the average number of prompt neutrons emitted from the fission fragments, the prompt neutron multiplicity, ν¯. The total number of prompt fission neutrons, ν¯tot, increases with increasing incident neutron energy. The prompt-neutron multiplicity is also a function of the fragment mass and the total kinetic energy of the fragmentation. Those data are only known in sufficient detail for a few thermal-neutron-induced fission reactions on, for example, 233,235U and 239Pu. The enthralling question has always been asked how the additional excitation energy is shared between the fission fragments. The answer to this question is important in the analysis of fission-fragment data taken with the double-energy technique. Although in the traditional approach the excess neutrons are distributed equally across the mass distribution, a few experiments showed that those neutrons are predominantly emitted by the heavy fragments.Purpose: We investigated the consequences of the ν(A,TKE,En) distribution on the fission fragment observables.Methods: Experimental data obtained for the 234U(n,f) reaction with a Twin Frisch Grid Ionization Chamber, were analyzed assuming two different methods for the neutron evaporation correction. The effect of the two different methods on the resulting fragment mass and energy distributions is studied.Results: We found that the preneutron mass distributions obtained via the double-energy technique become slightly more symmetric, and that the impact is larger for postneutron fission-fragment distributions. In the most severe cases, a relative yield change up to 20-30% was observed.Conclusions: We conclude that the choice of the prompt-neutron correction method has strong implications on the understanding and modeling of the fission process and encourages new experiments to measure fission fragments in coincidence with prompt fission neutrons. Even more, the correct determination of postneutron

  1. New data on the fragment angular momentum in spontaneous fission of 252 Cf

    Though a considerable progress has been made in understanding the process of low-energy fission still only a little is known about the energy balance occurring at the scission point. Regarding the value of the energy that is released at the descent of the nucleus from saddle to scission only theory estimates exist. For the case of 252 Cf spontaneous fission a value of 30 MeV could be assumed for this energy release. However, the partition of this free energy remains so far the least-understood aspect of nuclear fission. Evidently, the fragment pre-scission collective motion and internal excitation degrees of freedom share a part of this energy release resulting in the pre-scission kinetic energy and pre-scission excitation of fragments. It is generally recognized that the angular momentum that fission fragments acquire in the low-energy fission is a probe for the states of excitation for some of the orthogonal angular-momentum bearing modes at the scission point. In this work the average angular momentum for primary fission fragments as a function of neutron multiplicity and neutron-to-proton ratio of the primary fission fragments was extracted for the first time for the Mo-Ba and Zr-Ce charge splits of 252 Cf. The data are discussed in terms of the energy balance occurring at the scission point. (authors)

  2. Discrimination between roles of fissioning nucleus and asymmetry degree of freedom on the even-odd structure in fission-fragment yields

    Caamano, M.; Rejmund, F.; Schmidt, K. -H.

    2009-01-01

    Based on a wide systematics of fission-fragment distributions measured in low-energy fission, the even-odd staggering in the fission-fragment element yields is investigated. The well-established evolution of the global even-odd effect with the fissioning system is found to be only a partial aspect of the even-odd structure. Indeed, it is shown that the global even-odd effect is varying systematically with the mean asymmetry of the fission-fragment distribution, and that the general increase o...

  3. First use of single-crystal diamonds as fission-fragment detector

    FREGEAU MARC OLIVIER; Oberstedt, Stephan; BRYS TOMASZ; GAMBONI Thierry; GEERTS Wouter; Hambsch, Franz-Josef; Oberstedt, A.; Vidali, Marzio

    2015-01-01

    Single-crystal chemical vapor-deposited diamond (sCVD) was investigated for its ability to act as fission-fragment detector. In particular we investigated timing and energy resolution for application in a simultaneous time-of-flight and energy measurement to determe the mass of the detected fission fragment. Previous tests have shown that poly-crystalline chemical vapor deposited (pCVD) diamonds provide sufficient timing resolution, but their poor energy resolution did not allow complete sepa...

  4. Research on fission fragment excitation of gases and nuclear pumping of lasers

    Schneider, R. T.; Davie, R. N.; Davis, J. F.; Fuller, J. L.; Paternoster, R. R.; Shipman, G. R.; Sterritt, D. E.; Helmick, H. H.

    1974-01-01

    Experimental investigations of fission fragment excited gases are reported along with a theoretical analysis of population inversions in fission fragment excited helium. Other studies reported include: nuclear augmentation of gas lasers, direct nuclear pumping of a helium-xenon laser, measurements of a repetitively pulsed high-power CO2 laser, thermodynamic properties of UF6 and UF6/He mixtures, and nuclear waste disposal utilizing a gaseous core reactor.

  5. SOFIA: An innovative setup to measure complete isotopic yield of fission fragments

    We performed an experiment dedicated to the accurate isotopic yield measurement of fission fragments over the whole range. SOFIA exploits the inverse kinematics technique: using heavy ion beams at relativistic energies, fission is induced by Coulomb excitation in a high-Z target. The fragments are emitted forward and both of them are identified in charge and mass. The setup will be presented, as well as preliminary spectra. (authors)

  6. On the use of Makrofol KG to study fission fragment angular distributions

    Makrofol KG nuclear track detector processing and analysis is carefully regulated and assessed to reveal fission fragments' tracks and their angular distributions. For this purpose, foils of this detector are irradiated by a thin 252Cf source and are subjected to chemical etching followed by a two-step sparking process. The detector efficiency as a function of fission fragment incidence angle and different etching parameters is carried out with a good reproducibility

  7. Ionization chamber with fast timing properties and good energy resolution for fission fragment detection

    A twin ionization chamber for fission fragment detection is described. The chamber allows to extract both, fast timing- and energy proportional signals. A time resolution of 1.62 ns FWHM was obtained between two fission fragments detected in the two halves of the chamber. For 241Am α-particles the chamber gave an energy resolution of 1.3 percent. As counting gas methane NTP was used

  8. SOFIA: An innovative setup to measure complete isotopic yield of fission fragments

    Pellereau E.

    2013-12-01

    Full Text Available We performed an experiment dedicated to the accurate isotopic yield measurement of fission fragments over the whole range. SOFIA exploits the inverse kinematics technique: using heavy ion beams at relativistic energies, fission is induced by Coulomb excitation in a high-Z target. The fragments are emitted forward and both of them are identified in charge and mass. The setup will be presented, as well as preliminary spectra.

  9. The hole overlap correction and fission fragment detection efficiency in Makrofol

    Efficiency measurements for an SSNTD fission fragment detector have been analysed using the hole overlap correction of James et al. It is found that the measured efficiencies can be corrected, as required, to constant values which are independent of the fragment density. In the analysis the hole overlap probability is treated as a free parameter. Its dependence on fragment angle is established and examined in terms of increasing hole area with decreasing angle between the fragment and the foil. (author)

  10. Neutrons and Kinetic Energy of Fragments in Fission of Heavy Nuclei

    The distribution of excitation energy and kinetic energy depending on the mass of the fragment formed in heavy- isotope fission by thermal neutrons is experimentally investigated. The excitation energy is shown to have a low minimum in the region of the double-magic fragment (M ∼132), to increase in the symmetrical fission area and to be at its maximum for fragments complementary to magic. The kinetic energy of the fragments measured for U235 correlates with the excitation energy. The total energy release according to the experimental data is in good agreement with calculations according to Milton's mass tables in every case except that of strongly asymmetric fission. In the measurements conducted, the ratio of the maximum of the fragment yield curve to the minimum (after neutron escape) was 500 : 1. (author)

  11. Fission-fragment and neutron data traced back to the macroscopic and microscopic properties of the fissioning systems

    Schmidt K.-H.

    2010-10-01

    Full Text Available A new model description of fission-fragment yields and prompt neutron emission is developed. The yields of the different fission channels and their properties are attributed to the number of relevant states above the potential-energy landscape on the fission path at the moment of dynamical freeze-out, which is specific to the collective coordinate considered. The model combines well established ideas with novel concepts. The separability principle of macroscopic properties of the compound nucleus and microscopic properties of the fragments strongly reduces the number of model parameters and assures a high predictive power. The recently discovered energy-sorting mechanism in superfluid nuclear dynamics determines the sharing of intrinsic excitation energy at scission and the enhancement of even-odd structure in asymmetric splits.

  12. Distribution functions in plasmas generated by a volume source of fission fragments. [in nuclear pumped lasers

    Deese, J. E.; Hassan, H. A.

    1979-01-01

    The role played by fission fragments and electron distribution functions in nuclear pumped lasers is considered and procedures for their calculations are outlined. The calculations are illustrated for a He-3/Xe mixture where fission is provided by the He-3(n,p)H-3 reaction. Because the dominant ion in the system depends on the Xe fraction, the distribution functions cannot be determined without the simultaneous consideration of a detailed kinetic model. As is the case for wall sources of fission fragments, the resulting plasmas are essentially thermal but the electron distribution functions are non-Maxwellian.

  13. Fission fragment properties and the problem of the pulse height defect

    The pulse height defect (PHD) has been investigated for three different counting gases commonly used in ionization chambers. The PHD introduces an underestimation of the kinetic energy of a charged particle detected with an ionization chamber. Thus, in some cases it is of crucial importance to correct for this effect, e.g. when studying fission fragment properties. A new method was used, applying a waveform digitizer, to study the PHD. The fission fragment properties from spontaneous fission of 252Cf where determined using different counting gases and different ways of correcting for the PHD were evaluated. (author)

  14. Influence of asymmetry and fissility on even-odd effect in fission-fragment yields

    Rejmund F.; Caamaño M.; Schmidt K.-H

    2010-01-01

    Based on a wide systematics of fragment distributions measured in thermal-neutron induced fission, the even-odd staggering in the fission-fragment element yields is investigated. The asymmetry evolution of the element yield distribution with the fissility of the fissioning nucleus is shown to be for an important part responsible for the decrease of the even-odd staggering with the fissility. The even-odd staggering close to symmetry is shown to be a small contribution to the global even-odd e...

  15. Neutron emission as a function of fragment energy in the spontaneous fission of 260Md

    The authors have made the first measurement of the number of neutrons emitted in the spontaneous fission of a nuclide in which very high fragment energies dominate the fission process. In bombardments of 254Es, they produced 28-d 260Md, which was neutron-counted in a 1-m-diam spherical tank containing a Gd-doped scintillator solution. The average number of neutrons emitted per fission is only 2.58 ± 0.11, substantially less than for other actinides. A direct correlation of neutron multiplicity with fragment excitation energy is clearly demonstrated

  16. Fission-fragment detector for DANCE based on thin scintillating films

    Rusev, G.; Roman, A. R.; Daum, J. K.; Springs, R. K.; Bond, E. M.; Jandel, M.; Baramsai, B.; Bredeweg, T. A.; Couture, A.; Favalli, A.; Ianakiev, K. D.; Iliev, M. L.; Mosby, S.; Ullmann, J. L.; Walker, C. L.

    2015-12-01

    A fission-fragment detector based on thin scintillating films has been built to serve as a trigger/veto detector in neutron-induced fission measurements at DANCE. The fissile material is surrounded by scintillating films providing 4 π detection of the fission fragments. The scintillation photons were registered with silicon photomultipliers. A measurement of the 235U (n , f) reaction with this detector at DANCE revealed a correct time-of-flight spectrum and provided an estimate for the efficiency of the prototype detector of 11.6(7)%. Design and test measurements with the detector are described.

  17. Evolution of fission-fragment mass distributions in the neutron-deficient lead region

    Ghys, Lars; Andreyev, A.N.; Huyse, Mark; Van Duppen, Piet; Sels, Simon; Andel, B.; Antalic, S; Barzakh, A; Capponi, L.; Cocolios, Thomas Elias; Derkx, X.; De Witte, Hilde; J. Elseviers; Fedorov, D. V.; Fedosseev, V. N.

    2014-01-01

    Low-energy β-delayed fission of 194,196At and 200,202Fr was studied in detail at the mass separator ISOLDE at CERN. The fission-fragment mass distributions of daughter nuclei 194,196Po and 202Rn indicate a triple-humped structure, marking the transition between asymmetric fission of 178,180Hg and symmetric fission in the light Ra-Rn nuclei. Comparison with the macroscopic-microscopic finite-range liquid-drop model and the self-consistent approach employing the Gogny D1S energy den...

  18. Asymmetry of fission fragment mass distribution for Po and Ir isotopes

    Andreev, A. V.; Adamian, G. G.; Antonenko, N. V.

    2016-03-01

    Using the improved scission-point model, the mass distributions are calculated for induced fission of several Po and Ir isotopes. The calculated mass distributions and mean total kinetic energies of fission fragments are compared with the existing experimental data. The revealed coexistence of both symmetric and asymmetric modes in the β -delayed fission of At,196194 is in agreement with the experimental observations. The change of the shape of mass distribution with increasing A of fissioning AIr nucleus from asymmetric for 185Ir to symmetric for 193Ir is found.

  19. Fission of heavy nuclei: microscopic study of fission barriers and fragments angular momentum; Fission des noyaux lourds: etude microscopique des barrieres de fission et du moment angulaire des fragments

    Bonneau, L

    2003-11-01

    A lot of experimental data on nuclear fission has been being collected for the last 65 years, allowing theoreticians to confront their models with reality. The first part of this work is dedicated to the computation of fission barriers. We have extended the HF + BCS (Hartree Fock + Bandeen-Cooper-Schrieffer) method in order to include a new set of polynomials on which wave functions can be broken to, more accurately than on Hermite's polynomials in the 2 fragment configuration. The fission barriers of 26 heavy nuclei from Thorium-230 to Nobelium-256 have been assessed and compared to experimental data, it appears that differences are no greater than 1 MeV. We have discovered a neat correlation between the variation of the experimental fission lifetimes of even Fermium isotopes and the computed heights of second barriers. Moreover our model reproduces the hyper-deformed well of Thorium-230 with a good agreement on the well depth. The second part deals with the scission region. We have performed Hartree-Fock calculations in order to explore different ways of fragmentation. We have shown that the harmonic oscillator gives a valid description of such ways. In order to compute the mean value of J{sup 2} in the fragments we have been driven to propose an adequate definition of that quantity consistent with the non-locality property of the J{sup 2} operator. (A.C.)

  20. Primary fragment mass-yield distributions for asymmetric fission path of heavy nuclei

    The primary fragment mass-yield distribution for the asymmetric fission path in heavy nuclei, 233Pa, 239Np, 245Am and 249Bk at the excitation energy of ∼20 MeV are experimentally constructed based on the intensities of total kinetic energies for individual mass splits. The results revealed an interesting phenomenon: in all the studied fissioning systems, the inner wings of the mass-yield distributions in the asymmetric fission path appear along the same mass-wall of A = 130 fragment mass. The asymmetric mass-yield distribution indicates the strong effect of structural shells in fragments on the final mass division process of the asymmetric fission path. (author)

  1. Total kinetic energy distribution of fission fragments in 6,7Li + 238U reactions

    The shape and width of fission-fragment (FF) mass and kinetic energy distribution provides a lot of information on the fission reaction mechanism and the structure of the compound nucleus (CN), the fragments as well as the interacting nuclei. The shape of the mass distribution of the fission fragments for the actinides induced by the proton or neutron is known to change with the incident energy. At low energies, it shows a double humped distribution which changes slowly to a single humped distribution as energy increases. However, for a reaction involving a weakly bound projectile (i.e., 6Li + 232Th), a sharp change in the shape of the mass distribution with energy was observed. The sharp increase in the peak to valley ratio (P:V) in the fission-fragment mass distribution in 6Li + 232Th reaction by Itkis et al. and in 6,7Li + 238U reactions by Santra et al. was concluded to be due to the reduced energy transfer to the composite system caused by incomplete fusion (ICF) of alpha or deuteron/triton followed by fissions. Total Kinetic Energy (TKE) distribution of fission fragments is another important observable on which the effect of projectile breakup is not explored yet. In this contribution, the study of breakup/transfer effect on average TKE distribution for 6,7Li + 238U reactions is presented

  2. Dynamical approach to isotopic-distribution of fission fragments from actinide nuclei

    Ishizuka, Chikako; Chiba, Satoshi; Karpov, Alexander V.; Aritomo, Yoshihiro

    2016-06-01

    Measurements of the isotope distribution of fission fragments, often denoted as the primary fission yield (pre-neutron yield) or independent fission yield (post-neutron yield) are still challenging at low excitation energies, so that it is important to investigate it within a theory. Such quantities are vital for applications as well. In this study, fragment distributions from the fission of U isotopes at low excitation energies are studied using a dynamical model. The potential energy surface is derived from the two center shell model including the shell and pairing corrections. In order to calculate the charge distribution of fission fragments, we introduce a new parameter ηZ as the charge asymmetry, in addition to three parameters describing a nuclear shape, z as the distance between two centers of mass, δ as fragment deformation, and ηA as the mass asymmetry. Using this model, we calculated the isotopic distribution of 236U for the n-induced process 235U + n → 236U at low excitation energies. As a result, we found that the current model can well reproduce isotopic fission-fragment distribution which can be compared favorably with major libraries.

  3. Study of heavy ion induced fission fragment angular and mass distribution at near and sub-coulomb barrier energies

    Ghosh, T.K.

    2005-01-01

    The thesis presents investigations on the angular and mass distribution of fission fragments on heavy ion induced fission reactions. The present investigations address current issues in heavy ion induced fission reactions like finding the optimum entrance channel for the synthesis of super heavy elements (SHE). A double arm time of flight spectrometer over long flight path was used to measure the precise masses of complementary fission fragments. Necessary large area position sensitive gas de...

  4. Fission fragment charge and mass distributions in 239Pu(n,f) in the adiabatic nuclear energy density functional theory

    Regnier, D.; Dubray, N.; Schunck, N.; Verriere, M.

    2016-01-01

    Accurate knowledge of fission fragment yields is an essential ingredient of numerous applications ranging from the formation of elements in the r-process to fuel cycle optimization for nuclear energy. The need for a predictive theory applicable where no data is available is an incentive to develop a fully microscopic approach to fission dynamics. In this work, we calculate the pre-neutron emission charge and mass distributions of the fission fragments formed in the neutron-induced fission of ...

  5. Influence of complete energy sorting on the characteristics of the odd-even effect in fission-fragment element distributions

    Jurado, Beatriz; Schmidt, Karl-Heinz

    2014-01-01

    The characteristics of the odd-even effect in fission-fragment Z distributions are compared to a model based on statistical mechanics. Special care is taken for using a consistent description for the influence of pairing correlations on the nuclear level density. The variation of the odd-even effect with the mass of the fissioning nucleus and with fission asymmetry is explained by the important statistical weight of configurations where the light nascent fission fragment populates the lowest ...

  6. Fission fragment mass and angular distributions: Probes to study non-equilibrium fission

    R G Thomas

    2015-08-01

    Synthesis of heavy and superheavy elements is severely hindered by fission and fission-like processes. The probability of these fission-like, non-equilibrium processes strongly depends on the entrance channel parameters. This article attempts to summarize the recent experimental findings and classify the signatures of these non-equilibrium processes based on macroscopic variables. The importance of the sticking time of the dinuclear complex with respect to the equilibration times of various degrees of freedom is emphasized.

  7. A position-sensitive twin ionization chamber for fission fragment and prompt neutron correlation experiments

    Göök, A.; Geerts, W.; Hambsch, F.-J.; Oberstedt, S.; Vidali, M.; Zeynalov, Sh.

    2016-09-01

    A twin position-sensitive Frisch grid ionization chamber, intended as a fission fragment detector in experiments to study prompt fission neutron correlations with fission fragment properties, is presented. Fission fragment mass and energies are determined by means of the double kinetic energy technique, based on conservation of mass and linear momentum. The position sensitivity is achieved by replacing each anode plate in the standard twin ionization chamber by a wire plane and a strip anode, both readout by means of resistive charge division. This provides information about the fission axis orientation, which is necessary to reconstruct the neutron emission process in the fully accelerated fragment rest-frame. The energy resolution compared to the standard twin ionization chamber is found not to be affected by the modification. The angular resolution of the detector relative to an arbitrarily oriented axis is better than 7° FWHM. Results on prompt fission neutron angular distributions in 235U(n,f) obtained with the detector in combination with an array of neutron scintillation detectors is presented as a proof of principle.

  8. Kinetic energies of cluster fragments in ternary fission of 252 Cf

    Vijayaraghavan, K. R.; von Oertzen, W.; Balasubramaniam, M.

    2012-03-01

    The kinetic energy distribution and potential energies of fragments from the collinear cluster tripartition (CCT), the "true" ternary fission of 252Cf, have been calculated. It is assumed that the breakup of the nucleus into three fragments happens sequentially in two steps from a hyper-deformed shape. In the first step a first neck rupture occurs of the parent radioactive nucleus, forming two fragments (one of them is usually 132Sn) and, in the second step, one of the two fragments breaks into two other fragments, resulting finally in three fragments (the experiment is based on a binary coincidence where a missing mass is determined). We show the result for the principal combination of the three spherical fragments (semi-magic isotopes of Sn, Ca, Ni) observed recently experimentally. These isotopes are clusters with high Q -values, which produce the highest yields in the ternary fission bump. It is shown that the kinetic energies of the middle fragments have very low values, making their experimental detection quite difficult. This fact explains why the direct detection of true ternary fission with three fragments heavier than A > 40 has escaped experimental observation.

  9. Evidence for the predominant influence of the asymmetry degree of freedom on the evenodd structure in fission-fragment yields

    Caamaño, Manuel; Rejmund, Fanny; Schmidt, Karl-Heinz

    2011-01-01

    Abstract Based on a comprehensive set of fission-fragment distributions measured in low-energy fission, the even-odd staggering in the fission-fragment element yields is investigated. The well-established evolution of the global even-odd effect with the fissioning system is found to be only a partial aspect of the even-odd structure. Indeed, it is shown that the global even-odd effect varies systematically with the mean asymmetry of the fission-fragment distribution, and that the general i...

  10. A Brief Review of Past INL Work Assessing Radionuclide Content in TMI-2 Melted Fuel Debris: The Use of 144Ce as a Surrogate for Pu Accountancy

    D. L. Chichester; S. J. Thompson

    2013-09-01

    This report serves as a literature review of prior work performed at Idaho National Laboratory, and its predecessor organizations Idaho National Engineering Laboratory (INEL) and Idaho National Engineering and Environmental Laboratory (INEEL), studying radionuclide partitioning within the melted fuel debris of the reactor of the Three Mile Island 2 (TMI-2) nuclear power plant. The purpose of this review is to document prior published work that provides supporting evidence of the utility of using 144Ce as a surrogate for plutonium within melted fuel debris. When the TMI-2 accident occurred no quantitative nondestructive analysis (NDA) techniques existed that could assay plutonium in the unconventional wastes from the reactor. However, unpublished work performed at INL by D. W. Akers in the late 1980s through the 1990s demonstrated that passive gamma-ray spectrometry of 144Ce could potentially be used to develop a semi-quantitative correlation for estimating plutonium content in these materials. The fate and transport of radioisotopes in fuel from different regions of the core, including uranium, fission products, and actinides, appear to be well characterized based on the maximum temperature reached by fuel in different parts of the core and the melting point, boiling point, and volatility of those radioisotopes. Also, the chemical interactions between fuel, fuel cladding, control elements, and core structural components appears to have played a large role in determining when and how fuel relocation occurred in the core; perhaps the most important of these reaction appears to be related to the formation of mixed-material alloys, eutectics, in the fuel cladding. Because of its high melting point, low volatility, and similar chemical behavior to plutonium, the element cerium appears to have behaved similarly to plutonium during the evolution of the TMI-2 accident. Anecdotal evidence extrapolated from open-source literature strengthens this logical feasibility for

  11. Prompt neutron multiplicity in correlation with fragments from spontaneous fission of 252Cf

    Göök, A.; Hambsch, F.-J.; Vidali, M.

    2014-12-01

    The spontaneous fission of 252Cf serves as an excellent benchmark of prompt emission in fission since experimental data can be obtained without the need of an incident beam. With the purpose of providing experimental data on the prompt fission neutron properties in correlation with fission-fragment characteristics, an experiment on 252Cf(SF) has been performed. In addition, the experiment serves as a benchmark of setup and analysis procedures for measurements of fluctuations in the prompt-neutron properties as a function of incident neutron energy in fission of the major actinides 235U and 239Pu. The experiment employs a twin Frisch grid ionization chamber as fission-fragment detector while neutrons were counted by using a liquid scintillator placed along the symmetry axis of the ionization chamber. Average neutron multiplicity has been obtained as a function of fission-fragment mass and total kinetic energy (TKE). The average multiplicity as a function of mass agrees well with available data in the literature in the mass range from 80 to 170 u. The existence of additional sawtooth structures in the far asymmetric mass region could not be confirmed, although the statistical accuracy of the present experiment is as good as the previous study where such structures have been reported [Nucl. Phys. A 490, 307 (1988)., 10.1016/0375-9474(88)90508-8]. The available data in the literature on the TKE dependence of the multiplicity show strong deviations. Therefore, effort was focused on investigating experimental factors in low-efficiency neutron-counting experiments that may lead to faulty determination of this dependence. Taking these factors into account, a result that agrees well with data from high-efficiency neutron-counting experiments is obtained. The experimental arrangement allows determination of the angle between the detected neutron and the fission axis, which permits the neutron properties to be transformed into the fission-fragment rest frame. Fission neutron

  12. Dynamic approach to description of entrance channel effects in angular distributions of fission fragments

    Eremenko, D. O.; Drozdov, V. A.; Fotina, O. V.; Platonov, S. Yu.; Yuminov, O. A.

    2016-07-01

    Background: It is well known that the anomalous behavior of angular anisotropies of fission fragments at sub- and near-barrier energies is associated with a memory of conditions in the entrance channel of the heavy-ion reactions, particularly, deformations and spins of colliding nuclei that determine the initial distributions for the components of the total angular momentum over the symmetry axis of the fissioning system and the beam axis. Purpose: We develop a new dynamic approach, which allows the description of the memory effects in the fission fragment angular distributions and provides new information on fusion and fission dynamics. Methods: The approach is based on the dynamic model of the fission fragment angular distributions which takes into account stochastic aspects of nuclear fission and thermal fluctuations for the tilting mode that is characterized by the projection of the total angular momentum onto the symmetry axis of the fissioning system. Another base of our approach is the quantum mechanical method to calculate the initial distributions over the components of the total angular momentum of the nuclear system immediately following complete fusion. Results: A method is suggested for calculating the initial distributions of the total angular momentum projection onto the symmetry axis for the nuclear systems formed in the reactions of complete fusion of deformed nuclei with spins. The angular distributions of fission fragments for the 16O+232Th,12C+235,236,238, and 13C+235U reactions have been analyzed within the dynamic approach over a range of sub- and above-barrier energies. The analysis allowed us to determine the relaxation time for the tilting mode and the fraction of fission events occurring in times not larger than the relaxation time for the tilting mode. Conclusions: It is shown that the memory effects play an important role in the formation of the angular distributions of fission fragments for the reactions induced by heavy ions. The

  13. Fission and nuclear fragmentation of silver and bromine nuclei by photons of 1-6 GeV

    The studies of fission and fragmentation of silver and bromine nuclei by Bremsstrahlung photons of 1.6 GeV energy range are presented. The Il ford-KO nuclear emulsion submitted to Bremsstrahlung beams in Deutsches Elektronen Synchrotron (DESY) with total doses of 10'' equivalent photons, was used for nuclear fragment detection. The discrimination of fission and fragmentation events was done analysing angular distribution, range and angles between fragments. The results of fragment range distributions, angular distributions, distributions of angles between fragments, distributions of ratio between range, velocity distributions forward/backward ratio, cross sections of fission and fragmentation, nuclear fissionability and ternary fission frequency are presented and discussed. (M.C.K.)

  14. Fission fragment mass yield deduced from density distribution in the pre-scission configuration

    Warda, M

    2015-01-01

    Static self-consistent methods usually allow to determine the most probable fission fragments mass asymmetry. We have applied random neck rupture mechanism to the nuclei in the configuration at the end of fission paths. Fission fragment mass distributions have been deduced from the pre-scission nuclear density distribution obtained from the self-consistent calculations. Potential energy surfaces as well as nuclear shapes have been calculated in the fully microscopic theory, namely the constrained Hartree-Fock-Bogolubov model with the effective Gogny D1S density-dependent interaction. The method has been applied for analysis of fission of Fm-256,258, Cf-252 and Hg-180 and compared with the experimental data.

  15. Fission fragment mass yield deduced from density distribution in the pre-scission configuration

    Warda, M.; Zdeb, A.

    2015-11-01

    Static self-consistent methods usually allow one to determine the most probable fission fragments mass asymmetry. We have applied random neck rupture mechanism to the nuclei in the configuration at the end of fission paths. Fission fragment mass distributions have been deduced from the pre-scission nuclear density distribution obtained from the self-consistent calculations. Potential energy surfaces as well as nuclear shapes have been calculated in the fully microscopic theory, namely the constrained Hartree-Fock-Bogoliubov model with the effective Gogny D1S density-dependent interaction. The method has been applied for analysis of fission of {}{256,258}Fm, 252Cf and 180Hg and compared with the experimental data.

  16. Fission fragment mass distribution in the 13C+182W and 176Yb reactions

    Fission fragment mass distributions have been measured for many systems and found to be asymmetric in the fission of nuclei with nucleon number A in the range 228-258 and proton number Z in the range 90-100. For lighter systems, it has been observed that fission fragment mass distributions are usually symmetric. At high excitation energies the shell effects are expected to vanish and the nuclei are expected to behave like a charged liquid drop; hence, only symmetric fission is expected for all the nuclei. Even after much experimental and theoretical work in this field, the rate of damping of shell effects with excitation energy is not well known. This abstract reports our measurements with 13C beams on 182W and 176Yb targets

  17. Experimental evidence for the separability of compound-nucleus and fragment properties in fission

    Schmidt, Karl-Heinz; Kelic, Aleksandra; Ricciardi, Maria Valentina

    2007-01-01

    The large body of experimental data on nuclear fission is analyzed with a semi-empirical ordering scheme based on the macro-microscopic approach and the separability of compound-nucleus and fragment properties on the fission path. We apply the statistical model to the non-equilibrium descent from saddle to scission, taking the influence of dynamics into account by an early freeze out. The present approach reveals a large portion of common features behind the variety of the complex observation...

  18. A Monte Carlo Simulation of Prompt Gamma Emission from Fission Fragments

    Litaize O.; Regnier D.; Serot O.

    2013-01-01

    The prompt fission gamma spectra and multiplicities are investigated through the Monte Carlo code FIFRELIN which is developed at the Cadarache CEA research center. Knowing the fully accelerated fragment properties, their de-excitation is simulated through a cascade of neutron, gamma and/or electron emissions. This paper presents the recent developments in the FIFRELIN code and the results obtained on the spontaneous fission of 252Cf. Concerning the decay cascades simulation, a fully Hauser-Fe...

  19. New Fission Fragment Distributions and r-Process Origin of the Rare-Earth Elements

    Goriely, Stéphane; Sida, Jean-Luc; Lemaitre, Jean-François; Panebianco, Stefano; Dubray, Noel; Hilaire, Stéphane; Bauswein, Andreas; Janka, Hans-Thomas

    2013-01-01

    International audience Neutron star (NS) merger ejecta offer a viable site for the production of heavy r-process elements with nuclear mass numbers A * 140. The crucial role of fission recycling is responsible for the robustness of this site against many astrophysical uncertainties, but calculations sensitively depend on nuclear physics. In particular, the fission fragment yields determine the creation of 110 & A & 170 nuclei. Here, we apply a new scission-point model, called SPY, to deriv...

  20. Observed mass distribution of spontaneous fission fragments from samples of lime - an SSNTD study

    SSNTD is one of the most commonly used detectors in the studies involving nuclear phenomena. The ease of registration of the presence of alpha particles and fission fragments has made it particularly suitable in studies where stable long exposures are needed to extract reliable information. Studies on the presence of alpha emitting nuclides in the environment assume importance since they are found to be carcinogenic. Lime samples from Silchar in Assam of Eastern India have shown the presence of spontaneous fission fragments besides alphas. In the present study we look at the ratio of the average mass distribution of these fission fragments, that gives us an indication of the presence of the traces of transuranic elements

  1. Performance of the low pressure MWPCs for fission fragments under a high background

    Two couples of low pressure multi-wire proportional chambers (MWPC) were located in the target chamber to detect fission fragments in a hypernuclei producing experiment at Thomas Jefferson National Laboratory (Jlab). In the experiment, a continuous wave (CW) electron beam was applied to form hypernuclei by electromagnetic interaction. In the target chamber, the high energy (1.853 GeV) and high intensity (500 nA) primary electron beam caused a high particle background, which influenced the detection of the fission fragments. This report described the design of the MWPCs and studied the fission-fragment detecting performance of them under such a high background. The efficiency of the MWPCs was given with the help of a high resolution kaon spectrometer. At the same time, the background particles were discussed with a Monte Carlo code based on GEANT4. (authors)

  2. Isotopic yield distribution of neutron-rich fragment nuclei produced in thermal neutron induced fission

    Nuclear fission allows us to produce and study the properties of the nuclei with a higher neutron to proton ratio. Spectroscopic studies of such neutron-rich fragment nuclei provide direct information on the nuclear excited states. Such studies help to explore the new regions of nuclear deformations, and to extend the theoretical model(s) to regions which have hitherto been inaccessible. A lot of work has already been done on these set of nuclei by means of spontaneous fission of 252Cf and 248Cm sources, heavy-ion induced fusion-fission reactions, and also using deep-inelastic reactions. More recently, spectroscopic studies were performed using thermal neutron induced fission of 235U using CIRUS reactor facility. Here we report the yield distribution of the isotopes, produced in thermal neutron induced fission of 235U, using prompt γ-γ coincidence measurement technique

  3. Effect of Fission Fragments on the Properties of UO2 Fuel of Pressurized Water Reactors

    The effect of Xenon (Xe) and (Sr) Strontium fission fragments on the properties of UO2 fuel of pressurized water reactors has been evaluated us ing SRIM-2010 program. The released fission products being highly energetic with different masses, different phase states, and carry different charges cause ionization of the fuel from the surface up to the maximum range with the formation of electron-hole pairs. When the kinetic energy falls below the displacement energy of U and O atoms phonon production takes place. The collision of energetic fission products with the fuel results in the creation of recoil-vacancy pairs. The uranium and oxygen recoils re leased during the collision process changes the oxygen to uranium ratio of the UO2 matrix. The fission fragments as well as the recoils reside in interstitial positions in the structure of UO2 fuel with the result in increasing the internal stresses. The magnitude of damage introduced in the fuel is calculated on the bases of the fission rate of 4% enriched UO2. The released fission fragments and recoils as well as the increase in the fuel temperatures cause swelling of the fuel, increase fuel-clad interaction

  4. Development of a thin scintillation films fission-fragment detector and a novel neutron source

    Rusev, G.; Jandel, M.; Baramsai, B.; Bond, E. M.; Bredeweg, T. A.; Couture, A.; Daum, J. K.; Favalli, A.; Ianakiev, K. D.; Iliev, M. L.; Mosby, S.; Roman, A. R.; Springs, R. K.; Ullmann, J. L.; Walker, C. L.

    2015-08-01

    Investigation of prompt fission and neutron-capture Υ rays from fissile actinide samples at the Detector for Advanced Neutron Capture Experiments (DANCE) requires use of a fission-fragment detector to provide a trigger or a veto signal. A fission-fragment detector based on thin scintillating films and silicon photomultipliers has been built to serve as a trigger/veto detector in neutron-induced fission measurements at DANCE. The fissile material is surrounded by scintillating films providing a 4π detection of the fission fragments. The scintillations were registered with silicon photomultipliers. A measurement of the 235U(n,f) reaction with this detector at DANCE revealed a correct time-of-flight spectrum and provided an estimate for the efficiency of the prototype detector of 11.6(7)%. Design and test measurements with the detector are described. A neutron source with fast timing has been built to help with detector-response measurements. The source is based on the neutron emission from the spontaneous fission of 252Cf and the same type of scintillating films and silicon photomultipliers. Overall time resolution of the source is 0.3 ns. Design of the source and test measurements with it are described. An example application of the source for determining the neutron/gamma pulse-shape discrimination by a stilbene crystal is given.

  5. Prompt Gamma Rays Emitted from Individual Fragments in Neutron-Induced Fission

    Prompt gamma rays associated with moving fission fragments of specific masses have been observed in thermal neutron-induced fission of 235U. The geometrical layout of the apparatus prevents detection of photons emitted from stopped fragments and determines the effective time resolution to about 1 ns after fission. Spectra are measured by means of a high-resolution Ge(Li) detector with 3.5% photopeak efficiency for 60Co. An 8'' ∅ x 9'' Nal(Tl) anti-Compton shield suppresses the Compton distribution in the spectra and the recording of events produced by fast fission neutrons. The coincident fission-fragment masses are deduced from their correlated kinetic energies as measured by two Si solid-state detectors. The observed Doppler shift in gamma ray energy allows the assignment of lines to single members of fragment pairs. Data are processed in a 256 x 256 x 2048 channel matrix. The main objective of these experiments is a study of the properties of individual neutron-rich nuclei far off the stability line. (author)

  6. Development of position-sensitive time-of-flight spectrometer for fission fragment research

    A position-sensitive, high-resolution time-of-flight detector for fission fragments has been developed. The SPectrometer for Ion DEtermination in fission Research (SPIDER) is a 2E–2v spectrometer designed to measure the mass of light fission fragments to a single mass unit. The time pick-off detector pairs to be used in SPIDER have been tested with α-particles from 229Th and its decay chain and α-particles and spontaneous fission fragments from 252Cf. Each detector module is comprised of thin electron conversion foil, electrostatic mirror, microchannel plates, and delay-line anodes. Particle trajectories on the order of 700 mm are determined accurately to within 0.7 mm. Flight times were measured with 250 ps resolution FWHM. Computed particle velocities are accurate to within 0.06 mm/ns corresponding to a precision of 0.5%. An ionization chamber capable of 400 keV energy resolution coupled with the velocity measurements described here will pave the way for modestly efficient measurements of light fission fragments with unit mass resolution

  7. Measurements of fission fragment properties using RPI's lead slowing down spectrometer

    A double sided Frisch-gridded fission chamber for use in the Rennselaer Polytechnic Institute (RPI) lead slowing-down neutron spectrometer (LSDS) is being developed at RPI. Placing this fission chamber in the high neutron flux of the LSDS allows the measurement of the energy dependent, neutron induced fission cross sections, as well as the mass and kinetic energy of the fission fragments of various small samples. The fission chamber consists of two anodes shielded by Frisch grids on either side of a single cathode. The sample is located in the center of the cathode and is made by depositing small amounts of actinides dissolved in solution on very thin films. The chamber was successfully tested and calibrated using 0.4 ng of 252Cf and mass distributions were compared to previous work. As a proof of concept, the chamber was then placed in the LSDS to measure, simultaneously, the neutron induced fission cross section and fragment mass and energy distributions of 24.9 μg of 235U. The mass distribution as a function of neutron energy was examined and it may be possible to see changes in the mass distribution as a function of neutron energy. This process will enable the measurement of isotopes that are not available in large enough quantities (sub-micrograms) or with small fission cross sections (μbarns). (authors)

  8. Heavy neutron-deficient radioactive beams: fission studies and fragment distributions

    The secondary-beam facility of GSI Darmstadt was used to study the fission process of short-lived radioactive nuclei. Relativistic secondary projectiles were produced by fragmentation of a 1 A GeV 238U primary beam and identified in nuclear charge and mass number. Their production cross sections were determined, and the fission competition in the statistical deexcitation was deduced for long isotopical chains. New results on the enhancement of the nuclear level density in spherical and deformed nuclei due to collective rotational and vibrational excitations were obtained. Using these reaction products as secondary beams, the dipole giant resonance was excited by electromagnetic interactions in a secondary lead target, and fission from excitation energies around 11 MeV was induced. The fission fragments were identified in nuclear charge, and their velocity vectors were determined. Elemental yields and total kinetic energies have been determined for a number of neutron-deficient actinides and preactinides which were not accessible with conventional techniques. The characteristics of multimodal fission of nuclei around 226Th were systematically investigated and related to the influence of shell effects on the potential energy and on the level density between fission barrier and scission. A systematic view on the large number of elemental yields measured gave rise to a new interpretation of the enhanced production of even elements in nuclear fission and allowed for a new understanding of pair breaking in large-scale collective motion. (orig.)

  9. Biological alterations resulting from chronic lung irradiation. I. The pulmonary lipid composition, physiology, and pathology after inhalation by beagle dogs of 144Ce-labeled fused clay aerosols

    Three groups of four beagle dogs inhaled a 144Ce-labeled fused clay aerosol; two additional dogs per group, exposed to a stable cerium-labeled fused clay aerosol, were used as controls. At monthly intervals, one diaphragmatic lobe of each of two dogs exposed to 144Ce and one control animal from each group was lavaged with isotonic saline. The recovered lavage solutions were centrifuged to isolate lung cells (mostly macrophages) and surfactant for lipid analyses. The groups were sacrificed at 2, 4, and 6 mo after exposure, when the lungs of the dogs exposed to 144Ce had average cumulative radiation doses of 23, 36, and 59 krad, respectively. Chronic irradiation of the lung resulted in a progressive radiation pneumonitis which was assessed clinically and pathologically at various intervals. At sacrifice, the lungs were analyzed for 144Ce and the right apical and diaphragmatic lobes were minced and lyophilized and the lipids were extracted. Total lipids from all lung samples were determined gravimetrically and individual compounds were identified, isolated, and quantitated. The quantities of lipid in lung tissue, in pulmonary cells, and in surfactant increased as a function of time and radiation dose. Neutral lipids (sterol esters and triglycerides) accounted for most of the increase. (U.S.)

  10. Preliminary Remarks on Some Correlations of Prompt-Neutron Multiplicities with Properties of the Fission Fragments

    The differential behaviour of prompt-neutron multiplicities in the system 235U(nth,f) as a function of the total kinetic energy of the fission fragments and as a function of the emission angle relative to the direction of the light fragment are calculated with the GEF code. The results deviate from previous calculations by Nikolay Kornilov and are closer to the experimental data. The possible role of approximations and the neglect of correlations in the multi-dimensional coordinate space that characterizes the fission process are discussed. (author)

  11. Gamma Radiation from Fission Fragments Experimental Apparatus-Mass Spectrum Resolution

    The gamma-radiation from fission fragments was studied as a function of the fragment mass. The mass was determined from the fragment energies using solid state detectors. The mass resolution which can be achieved by this method is treated in detail. The average initial fragment mass and the initial mass resolution is calculated as a function of the measured (apparent) mass yield for three different thicknesses of the fissile material deposit. This treatment gives a clear indication of those factors most important for good mass resolution work. A detailed description of the experimental apparatus is given in the appendices

  12. Fission Fragment Angular Distributions measured with a Time Projection Chamber

    Kleinrath, Verena [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2015-04-28

    The subject is presented in a series of slides with the following organization: Introduction (What is anisotropy? Relevance (Theory and ratio cross section), Previous measurements); Experiment (Particle tracking in the fissionTPC, Neutron time of flight, Data analysis & uncertainty calculation, Preliminary result for 235U); and Future Work (Refine 235U result, Process 239Pu data).

  13. Sub-barrier resonance fission and its effects on fission fragment properties, exemplified on 234,238U(n,f)

    The correlation between the sub-barrier resonant behaviour of fission cross-section of non-fissile actinides (pre-scission stage) and the visible fluctuations of their fission fragment and prompt neutron data (post-scission stage) around the incident energies of sub-barrier resonances is outlined and supported by quantitative results for two fissioning systems 234,238U(n,f). These quantitative results refer to both stages of the fission process: a) the pre-scission stage including the calculation of neutron induced cross-sections with focus on fission. Calculations are done in the frame of the refined statistical model for fission with sub-barrier effects also extended to take into account the multi-modal fission; b) the post-scission stage including the prompt neutron emission treated in the frame of the Point-by-Point model. Total quantities characterizing the fission fragments and the prompt neutrons obtained by averaging the Point-by-Point results as a function of fragment over the fission fragment distributions reveal variations around the energies of sub-barrier resonances in the fission cross-section. (authors)

  14. Sub-barrier resonance fission and its effects on fission fragment properties, exemplified on 234,238U(n,f

    Oberstedt S.

    2013-03-01

    Full Text Available The correlation between the sub-barrier resonant behaviour of fission crosssection of non-fissile actinides (pre-scission stage and the visible fluctuations of their fission fragment and prompt neutron data (post-scission stage around the incident energies of sub-barrier resonances is outlined and supported by quantitative results for two fissioning systems 234,238U(n,f. These quantitative results refer to both stages of the fission process: a The pre-scission stage including the calculation of neutron induced cross-sections with focus on fission. Calculations are done in the frame of the refined statistical model for fission with sub-barrier effects also extended to take into account the multi-modal fission. b The post-scission stage including the prompt neutron emission treated in the frame of the Point-by-Point model. Total quantities characterizing the fission fragments and the prompt neutrons obtained by averaging the Point-by-Point results as a function of fragment over the fission fragment distributions reveal variations around the energies of sub-barrier resonances in the fission crosssection.

  15. First use of single-crystal diamonds as fission-fragment detector

    Frégeau, M.O.; Oberstedt, S.; Brys, T.; Gamboni, Th.; Geerts, W.; Hambsch, F.-J. [European Commission, DG Joint Research Centre (IRMM), B-2440 Geel (Belgium); Oberstedt, A. [OSSOLUTIONS Consulting, S-70353 Örebro (Sweden); Fundamental Physics, Chalmers University of Technology, S-41296 Göteborg (Sweden); Vidali, M. [European Commission, DG Joint Research Centre (IRMM), B-2440 Geel (Belgium)

    2015-08-11

    Single-crystal chemical vapor-deposited diamond (sCVD) was investigated for its ability to act as fission-fragment detector. In particular we investigated timing and energy resolution for application in a simultaneous time-of-flight and energy measurement to determine the mass of the detected fission fragment. Previous tests have shown that poly-crystalline chemical vapor deposited (pCVD) diamonds provide sufficient timing resolution, but their poor energy resolution did not allow complete separation between very low-energy fission fragments, α-particles and noise. Our present investigations prove artificial sCVD diamonds to show similar timing resolution as pCVD diamonds close to 100 ps. Improved pulse-height resolution allows the unequivocal separation of fission fragments, and the detection efficiency reaches 100%, but remains with about a few percent behind requirements for fragment-mass identification. With high-speed digital electronics a timing resolution well below 100 ps is possible. However, the strongly varying quality of the presently available diamond material does not allow application on a sufficiently large scale within reasonable investments.

  16. First use of single-crystal diamonds as fission-fragment detector

    Single-crystal chemical vapor-deposited diamond (sCVD) was investigated for its ability to act as fission-fragment detector. In particular we investigated timing and energy resolution for application in a simultaneous time-of-flight and energy measurement to determine the mass of the detected fission fragment. Previous tests have shown that poly-crystalline chemical vapor deposited (pCVD) diamonds provide sufficient timing resolution, but their poor energy resolution did not allow complete separation between very low-energy fission fragments, α-particles and noise. Our present investigations prove artificial sCVD diamonds to show similar timing resolution as pCVD diamonds close to 100 ps. Improved pulse-height resolution allows the unequivocal separation of fission fragments, and the detection efficiency reaches 100%, but remains with about a few percent behind requirements for fragment-mass identification. With high-speed digital electronics a timing resolution well below 100 ps is possible. However, the strongly varying quality of the presently available diamond material does not allow application on a sufficiently large scale within reasonable investments

  17. Nuclear isomerism in fission fragments produced by the spontaneous fission of {sup 252}Cf; Isomerisme nucleaire dans les fragments de fission produits dans la fission spontanee du {sup 252}Cf

    Gautherin, C

    1997-09-01

    This thesis is devoted to the study of the nuclear structure of neutron-rich nuclei, via the search of isomeric nuclear states. Neutron-rich nuclei were produced in the spontaneous fission of {sup 252}Cf. The experimental study of isomeric states in these nuclei was performed with the {gamma}-array EUROGAM II, coupled to an additional and original fission fragment detector composed by photovoltaic cells, SAPhIR. The photovoltaic cells are well adapted to detect low energy heavy ions and have good energy and time resolutions to obtain a good fission fragment detection. This experiment led to the discovery of new isomeric states in {sup 135}Xe, {sup 104}Mo, {sup 146,147,148}Ce and {sup 152,154,156}Nd, with lifetimes between 60 ns and 2 {mu}s. Level schemes of these nuclei have been completed. An interpretation of the isomeric states in the nuclei {sup 154,156}Nd and {sup 156,158}Sm was performed by Hartree-Fock-Bogolyubov calculations using the DIS Gogny force with two quasi-particles excitations. The confrontation with the experimental results led to an interpretation of these isomeric states as K-isomers. (author)

  18. Evaluation of excitation energy and spin in fission fragments using the statistical model, and the FIPPS project

    Sage C.

    2013-03-01

    Full Text Available We review the statistical model and its application for the process of nuclear fission. The expressions for excitation energy and spin distributions for the individual fission fragments are given. We will finally emphasize the importance of measuring prompt gamma decay to further test the statistical model in nuclear fission with the FIPPS project.

  19. Evaluation of excitation energy and spin in fission fragments using the statistical model, and the FIPPS project

    We review the statistical model and its application for the process of nuclear fission. The expressions for excitation energy and spin distributions for the individual fission fragments are given. We will finally emphasize the importance of measuring prompt gamma decay to further test the statistical model in nuclear fission with the FIPPS project. (authors)

  20. Measurement of fragment mass distributions in neutron-induced fission reactions at intermediate energies

    Simutkin, V. D.; Ryzhov, I. V.; Tutin, G. A.; Vaishnene, L. A.; Blomgren, J.; Pomp, S.; Österlund, M.; Andersson, P.; Bevilacqua, R.; Meulders, J. P.; Prieels, R.

    2009-10-01

    Fragment mass distributions from neutron-induced fission of 232Th and 238U have been measured at quasi-monoenergetic neutron beam of the Louvain-la-Neuve cyclotron facility CYCLONE. The measurements have been carried out making use of a multi-section Frisch-gridded ionization chamber. The measurement technique as well as the data processing is described. Preliminary data on primary fragment mass yields are given for an incident neutron energy of 32.8 MeV.

  1. Prompt gamma ray-spectroscopy of N = 50 fission fragments

    Excited states in the nuclei 83As and 84,86Se have been studied via prompt γ-ray spectroscopy. The nuclei were produced by the proton-induced fission of a 238U target, at the accelerator of the University of Jyvaeskylae. The JUROGAM-II array was used to detect prompt γ-rays and a triple- coincidence analysis performed. A comparison of the N = 50 nuclei with shell-model calculations reproduces the low-lying states in 83As and 84Se well. The inclusion of particle-hole excitations is necessary to correctly describe the states above ∼3.5 MeV. (authors)

  2. Fragment properties from fission of 234,238U induced by 6 -10 MeV bremsstrahlung

    Experiments to investigate the photon-induced fission of actinide nuclei at excitation energies in the vicinity of the fission barrier are carried out at the super conducting Darmstadt linear electron accelerator S-DALINAC. A twin Frisch grid ionization chamber is used to deduce mass, total kinetic energy, and angular distributions of the fission fragments. In this contribution results on fission fragment mass and total kinetic energy distributions from 234,238U are presented along with the currently on-going investigation of 234U and 232Th fragment angular distributions.

  3. SPIDER: A new instrument for fission fragment research at the Los Alamos Neutron Science Center

    The study of fission fragment yields and how they behave as a function of excitation energy provides insight into the process in which they are formed. Fission yields are also important for nuclear applications, as they can be used as a diagnostic tool. A new instrument, SPIDER (Spectrometer for Ion Determination in fission Research), is being developed for measuring fission yields as a function of incident neutron energy at the Los Alamos Neutron Science Center. The instrument employs a time-of-flight mass spectrometry method in which the velocity and kinetic energy of the fragments are measured in order to determine their mass. Additionally, by using Bragg peak spectroscopy, the charge of the fragments can be identified. A prototype instrument has been developed and preliminary results indicate that ∼ 1 mass unit resolution is feasible using this approach. A larger detector array is currently being designed, and will be used at study fission yields from thermal neutron energies up to at least 20 MeV. (authors)

  4. SPIDER: A new instrument for fission fragment research at the Los Alamos Neutron Science Center

    Tovesson Fredrik

    2013-12-01

    Full Text Available The study of fission fragment yields and how they behave as a function of excitation energy provides insight into the process in which they are formed. Fission yields are also important for nuclear applications, as they can be used as a diagnostic tool. A new instrument, SPIDER (Spectrometer for Ion DEtermination in fission Research, is being developed for measuring fission yields as a function of incident neutron energy at the Los Alamos Neutron Science Center. The instrument employs a time-of-flight mass spectrometry method in which the velocity and kinetic energy of the fragments are measured in order to determine their mass. Additionally, by using Bragg peak spectroscopy, the charge of the fragments can be identified. A prototype instrument has been developed and preliminary results indicate that ∼ 1 mass unit resolution is feasible using this approach. A larger detector array is currently being designed, and will be used at study fission yields from thermal neutron energies up to at least 20 MeV.

  5. True ternary fission of 252Cf(sf), the collinear decay into fragments of similar size

    The ternary decay in 252Cf(sf, fff), with three cluster fragments of different masses (e.g.132Sn,52-48Ca,68-72Ni), has been observed by the FOBOS group in JINR. This work has established a new decay mode of heavy nuclei, the collinear cluster tripartition, (CCT). This ''true ternary fission'' of heavy nuclei has been predicted many times in theoretical works during the last decades. In the present report we discuss true ternary fission (FFF) into three nuclei of almost equal size (e.g. Z=98 → Zi = 32, 34, 32) and other fission modes in the same system. The possible fission channels for 252 Cf(sf) are predicted from potential-energy (PES) calculations. These PES's show pronounced minima for several ternary fragmentation decays, suggesting a variety of collinear ternary fission modes. The FFF-decays have very similar dynamical features as the previously observed collinear CCT-decays, the central fragment has very small kinetic energy. The data of the cited experiment allow the extraction of the yield for some FFF-decays, by using specific gates on the measured parameters

  6. SPIDER: A new instrument for fission fragment research at the Los Alamos Neutron Science Center

    Tovesson, Fredrik; Arnold, Charles; Blakeley, Rick; Hecht, Adam; Laptev, Alexander; Mader, Drew; Meierbachtol, Krista; Snyder, Lucas; White, Morgan

    2013-12-01

    The study of fission fragment yields and how they behave as a function of excitation energy provides insight into the process in which they are formed. Fission yields are also important for nuclear applications, as they can be used as a diagnostic tool. A new instrument, SPIDER (Spectrometer for Ion DEtermination in fission Research), is being developed for measuring fission yields as a function of incident neutron energy at the Los Alamos Neutron Science Center. The instrument employs a time-of-flight mass spectrometry method in which the velocity and kinetic energy of the fragments are measured in order to determine their mass. Additionally, by using Bragg peak spectroscopy, the charge of the fragments can be identified. A prototype instrument has been developed and preliminary results indicate that ˜ 1 mass unit resolution is feasible using this approach. A larger detector array is currently being designed, and will be used at study fission yields from thermal neutron energies up to at least 20 MeV.

  7. Some important aspects of fragment angular momentum in medium energy fission of 238U

    Independent isomeric yield ratios of 131Te, 133Te and 134I have been determined at five different energies in the range of 25-44 MeV alpha particle induced fission of 238U using radiochemical and gamma spectrometric techniques. From the independent isomeric yield ratios, fragment angular momenta (Jrms) have been deduced using a statistical model analysis. The Jrms were also calculated theoretically based on thermal equilibration of various collective modes after considering the occurrence of multichance fission. These data and the literature data for various fragments in the mass region 126-136 in 238U (α,f), 238U (p,f) and 238U (γ,f) show the following important features: (i) Both the entrance channel excitation energy and input angular momentum affect the fragment angular momentum in the exit channel. (ii) There are two groups of fission products from the point of view of change of fragment angular momentum with increase in excitation energy and input angular momentum. (iii) Fragment angular momentum depends on nuclear structure effect such as shell closure proximity and odd-even effect. (iv) The fragment angular momentum calculated theoretically based on statistical equilibration of various collective modes are in good agreement with the experimental values indicating the validity of such an assumption

  8. Analysis of plasmas generated by fission fragments. [nuclear pumped lasers and helium plasma

    Deese, J. E.; Hassan, H. A.

    1977-01-01

    A kinetic model is developed for a plasma generated by fission fragments and the results are employed to study helium plasma generated in a tube coated with fissionable material. Because both the heavy particles and electrons play important roles in creating the plasma, their effects are considered simultaneously. The calculations are carried out for a range of neutron fluxes and pressures. In general, the predictions of the theory are in good agreement with available intensity measurements. Moreover, the theory predicts the experimentally measured inversions. However, the calculated gain coefficients are such that lasing is not expected to take place in a helium plasma generated by fission fragments. The effects of an externally applied electric field are also considered.

  9. Time-zero fission-fragment detector based on low-pressure multiwire proportional chambers

    A time-zero fission fragment (FF) detector, based on the technique of low-pressure multiwire proportional chambers (LPMWPC), has been designed and constructed for the heavy hypernuclear lifetime experiment (E95-002) at Thomas Jefferson National Accelerator Facility. Its characteristics and the method of time-zero reconstruction were investigated using fission fragments from a 252Cf spontaneous fission source. The influence of the ionization energy loss was also studied. It is shown that Heptane, Hexane, and Isobutane gases at a pressure of 1-2 Torr are all suitable for such a FF detector. As desired by experiment, a timing resolution of about 200 ps (FWHM) for a chamber size of 21x21 cm2 was achieved

  10. Influence of asymmetry and fissility on even-odd effect in fission-fragment yields

    Rejmund F.

    2010-10-01

    Full Text Available Based on a wide systematics of fragment distributions measured in thermal-neutron induced fission, the even-odd staggering in the fission-fragment element yields is investigated. The asymmetry evolution of the element yield distribution with the fissility of the fissioning nucleus is shown to be for an important part responsible for the decrease of the even-odd staggering with the fissility. The even-odd staggering close to symmetry is shown to be a small contribution to the global even-odd effect, and seems to vary little with the fissility of the nucleus. These experimental observations show that the established interpretation in which the intrinsic excitation energy at scission is accountable for the even-odd staggering amplitude has to be reconsidered.

  11. High-resolution spectroscopy of fission fragments, neutrons, and γ-rays

    This volume contains most of the contributions presented at the 'International Workshop on High-Resolution Spectroscopy of Fission Fragments, Neutrons, and γ-Rays' held at Technische Universitaet Dresden. The scientific aim of the workshop was to obtain a presentation of the current knowledge of the methodology of high-resolution fission experiments. The main topics discussed at the workshop were: Concepts for high-resolution fission-fragment detectors (systems). Minimization of experimental uncertainties. Detector simulation including all secondary processes. Experimental determination of correlation coefficients (e.g. pulse height defect, efficiencies). Precise data analysis. Correction procedures (e.g. primary-mass determination) and consequences of approximations. Error estimation. Special requirements in correlation experiments, e.g. neutron and γ-ray spectroscopy/counting in 4 π. See hints under the relevant topics. (orig./HSI)

  12. Time-zero fission-fragment detector based on low-pressure multiwire proportional chambers

    Assamagan, Ketevi A; Bayatyan, G L; Carlini, R; Danagulyan, S; Eden, T; Egiyan, K; Ent, R; Fenker, H; Gan, L; Gasparian, A; Grigoryan, N K; Greenwood, Z; Gueye, P; Hashimoto, O; Johnston, K; Keppel, C; Knyazyan, S; Majewski, S; Margaryan, A; Margaryan, Yu L; Marikian, G G; Martoff, J; Mkrtchyan, H G; Parlakyan, L; Sato, Y; Sawafta, R; Simicevic, N; Tadevosyan, V; Takahashi, T; Tang, L; Vartanian, G S; Vulcan, W; Wells, S; Wood, S

    1999-01-01

    A time-zero fission fragment (FF) detector, based on the technique of low-pressure multiwire proportional chambers (LPMWPC), has been designed and constructed for the heavy hypernuclear lifetime experiment (E95-002) at Thomas Jefferson National Accelerator Facility. Its characteristics and the method of time-zero reconstruction were investigated using fission fragments from a sup 2 sup 5 sup 2 Cf spontaneous fission source. The influence of the ionization energy loss was also studied. It is shown that Heptane, Hexane, and Isobutane gases at a pressure of 1-2 Torr are all suitable for such a FF detector. As desired by experiment, a timing resolution of about 200 ps (FWHM) for a chamber size of 21x21 cm sup 2 was achieved.

  13. On the origin of high- spin states in nuclear fission fragments

    Mouze, G.; Ythier, C.; Hachem, S.

    2011-01-01

    In the "nucleon-phase" model of binary fission, the transfer of nucleons between an A =126 {\\guillemotleft} nucleon core {\\guillemotright} and the primordial "cluster" can explain both the formation of high- spin states and the saw-tooth behavior of the variation, as a function of fragment mass, of the average angular momentum.

  14. The magnetic properties of collective states in A ∼ 100 fission fragments

    The magnetic moments of Iπ = 2+1 states in even-even A ∼ 100 fission fragments have been measured using the Gammasphere array, using the technique of time-integral perturbed angular correlations. The collective (core) g factors of several odd nuclei have also been determined. The data are interpreted within the context of the interacting boson model (IBA2)

  15. Measurement of prompt neutrons from fission fragments for {sup 235}U(n{sub th}, f)

    Nishio, Katsuhisa; Yamamoto, Hideki; Jinno, Ikuo; Kimura, Itsuro; Nakagome, Yoshihiro [Kyoto Univ. (Japan)

    1997-03-01

    When the level density parameter is obtained from neutron resonance experiment and so forth, its value depends upon its model. In particular, the value forms 1.5 times difference by if the level increase due to collective motion is considered or not. The measuring method shown in this report has a characteristics capable of obtain an absolute value of the level density parameter. Then, in this paper, a consideration using Iljinov`s empirical equation on shell effect and collective motion of the fission fragment was conducted and a investigation on shell effect and collective motion of the fission fragment was executed. as a result, the level density parameter of the fission fragment obtained by the {sup 235}U(n{sub th},f) showed a distribution of a sawtooth wave shape, which is resemble to that of {sup 252}Cf(sf). And, it was found that this distribution can be explained by an empirical equation considering shell effect of fission fragment dependency and collective motion, and so forth. (G.K.)

  16. The even-odd effect in fission-fragment Z yields – a new kind of nuclear clock

    Jurado Beatriz; Schmidt Karl-Heinz

    2013-01-01

    A model for the even-odd effect in fission based on statistical mechanics is presented. It reveals that the variation of the even-odd effect with the mass of the fissioning nucleus and the increase towards asymmetric splits is due to the important statistical weight of configurations where the light fission fragment populates the ground state of an even-even nucleus. This implies that excitation energy and unpaired nucleons are predominantly transferred to the heavy fragment. Our results indi...

  17. Further evidence for energy sorting from the even-odd effect in fission-fragment element distributions

    Schmidt, Karl-Heinz; Jurado, Beatriz

    2010-01-01

    The even-odd effect in fission is explained by a model based on statistical mechanics. It reveals that the variation of the even-odd effect with the mass of the fissioning nucleus and the increase towards asymmetric splits is due to the important statistical weight of configurations where the light fission fragment populates the ground state of an even-even nucleus. This implies that entropy drives excitation energy and unpaired nucleons predominantly to the heavy fragment. Therefore, the eve...

  18. 252Cf spontaneous prompt fission neutron spectrum measured at 0 degree and 180 degree relative to the fragment motion

    The 252Cf spontaneous prompt fission neutron spectrum at 0 degree and 180 degree relative to the motion direction of corresponding fission fragments was measured. High angular resolution for fragment measurements and high energy resolution for neutron measurements were obtained using multi-parameter TOF spectrometer. The results showed that there is a symmetric distribution of 'forward' and 'backward' for low energy in C.M.S. neutrons, which was an evidence of nonequilibrium neutrons existed in fission process

  19. Fission fragment mass distribution studies for 28Si + 197Au, 209Bi, 235U reactions

    In reactions with heavy ions, complete fusion and quasi-fission are the competing processes at energies above the Coulomb barrier. The quasi-fission process, in which the system reseparates before reaching a compact compound nucleus, is a major hurdle in forming heavy and superheavy evaporation residues (ER) in heavy-ion reactions. Fission fragment mass distribution for the fully equilibrated compound nucleus is decided at the scission point due to a long descent from saddle to scission. At higher excitation energies, the shell effects are washed out and the mass distribution is expected to be symmetric. The width of the distribution strongly depends on the entrance channel properties, such as mass asymmetry, deformation of interacting nuclei, collision energy, and the Coulomb factor Z1 Z2. Any sudden change in the width of the mass distribution would indicate departure from full equilibration, while onset of mass asymmetry or a sudden increase in width would be a strong signal of quasi fission

  20. Artificial diamonds as radiation-hard detectors for ultra-fast fission-fragment timing

    In the framework of the construction of the double time-of-flight spectrometer VERDI, where we aim at measuring pre- and post-neutron masses directly and simultaneously, ultra-fast time pick-up detectors based on artificial diamond material were investigated for the first time with fission fragments from 252Cf (0.5MeV/u9 fission-fragments/cm2 together with more than 3.5×109 neutrons/cm2 and 3×1010α-particles/cm2. This fluence is characteristic for fission experiments. The pre-requisite for the observed signal stability is the application of priming of the diamond material with a strong β-source for about 48 h. The intrinsic timing resolution of a 100μm thick polycrystalline CVD diamond detector with a size of 1×1 cm2 was determined to σint=(283±41)ps by comparison with Monte-Carlo simulations. Using broadband pre-amplifiers, 4-fold segmented detectors of same total size and with a thickness of 180μm show an intrinsic timing resolution of σint=(106±21)ps. This is highly competitive with the best micro-channel plate detectors. Due to the limited and batch-dependent charge collection efficiency of poly-crystalline diamond material, the detection efficiency for fission fragments may be smaller than 100%. -- Highlights: ► First use of chemical vapor deposited diamond for heavy ions with kinetic energies below 2 MeV per nucleon. ► Fission-fragment time-of-flight measurements with a timing resolution better than 150 ps. ► Radiation-hard fission event trigger to be used in an intense neutron field

  1. Two parameter studies of TFD response to fission fragments for measurements of fragment mass and energy distributions

    A new technique involving detection of the pair fragments associated with each fission event by two thin film scintillators is investigated to determine its applicability for the determination of fragment mass and energy distributions. The thin film scintillation detectors (thickness 14 microns) were positioned on opposite sides of a VYNS backed 235U source of thickness 60/cm2 placed in a thermal neutron beam of flux 5 x 107 neutrons/cm2/sec. The coincident pulses from the two detectors were recorded event by event on a multi-parameter data acquisition system. The functional behaviour of the film response to fission fragments of specified E/M and Z was obtained by combining the specific luminescence and specific energy loss data for heavy ions. Using the mass and momentum conservation conditions and an iterative procedure it was possible to analyse the data event by event to obtain the fragment mass and kinetic energies. The mass and energy distributions and mass energy correlations so obtained are in good agreement with the published data based on solid state detector measurements. This technique can therefore be a good substitute for solid state detector based methods especially in those cases where radiation damage on solid state detectors is a serious problem. (author)

  2. Multi-mode fission mechanisms correlated to deformation of the fragments and transition of the characteristics in relation to excitation energy of the fissioning system

    Aiming to conduct a measurement under further higher resolution, a TOF measurement of the fission fragment of 235U(nth,f) was conducted by using a thin-film scintillator excellent in time responsibility. By TOF measurement, the fission fragment mass after emitting the prompt neutron and the numbers of the prompt neutron could be obtained. And, double energy measurement at the different incident proton energy was conducted for 238U(p,f) to investigate the to investigate the energy dependency of the nuclear fission. As a result of investigating the nuclear fission mechanism in multi face and due to the obtained data, it was found that degree of deformation of the fission fragment played an important role. However, as data on the prompt neutron numbers was not obtained this time, more detailed investigation could not be conducted. (G.K.)

  3. Multi-mode fission mechanisms correlated to deformation of the fragments and transition of the characteristics in relation to excitation energy of the fissioning system

    Takamiya, Koichi; Inoue, Takakazu; Nakanishi, Kiyoshi [Osaka Univ., Toyonaka (Japan). Faculty of Science] [and others

    1997-03-01

    Aiming to conduct a measurement under further higher resolution, a TOF measurement of the fission fragment of {sup 235}U(n{sub th},f) was conducted by using a thin-film scintillator excellent in time responsibility. By TOF measurement, the fission fragment mass after emitting the prompt neutron and the numbers of the prompt neutron could be obtained. And, double energy measurement at the different incident proton energy was conducted for {sup 238}U(p,f) to investigate the to investigate the energy dependency of the nuclear fission. As a result of investigating the nuclear fission mechanism in multi face and due to the obtained data, it was found that degree of deformation of the fission fragment played an important role. However, as data on the prompt neutron numbers was not obtained this time, more detailed investigation could not be conducted. (G.K.)

  4. Search for extremely deformed fission fragment in ^{28}Si+^{28}Si with Eurogam Phase II

    C. BeckUniversity of Sao Paulo; Nouicer, R.; Sanders, S J; Szanto de Toledo, A.; Sl. Cavallaro(INFN Catania)

    2015-01-01

    A high-resolution study of fragment-fragment-$\\gamma$ triple coincident measurements of the symmetric-mass fission exit-channel from the ^{28}Si+^{28}Si reaction has been performed at the VIVITRON Tandem facility by using the EUROGAM Phase II $\\gamma$-ray spectrometer. The bombarding energy E_{lab}(^{28}Si) = 111.6 MeV has been chosen to populate a well known quasi-molecular resonance in ^{56}Ni. Evidence is presented for a selective population of states in ^{28}Si fragments arising from the ...

  5. Measurements of charge distributions of the fragments in the low energy fission reaction

    The measurement for charge distributions of fragments in spontaneous fission 252Cf has been performed by using a unique style of detector setup consisting of a typical grid ionization chamber and a ΔΕ−Ε particle telescope, in which a thin grid ionization chamber served as the ΔΕ-section and the E-section was an Au–Si surface barrier detector. The typical physical quantities of fragments, such as mass number and kinetic energies as well as the deposition in the gas ΔΕ detector and E detector were derived from the coincident measurement data. The charge distributions of the light fragments for the fixed mass number A2⁎ and total kinetic energy (TKE) were obtained by the least-squares fits for the response functions of the ΔΕ detector with multi-Gaussian functions representing the different elements. The results of the charge distributions for some typical fragments are shown in this article which indicates that this detection setup has the charge distribution capability of Ζ:ΔΖ>40:1. The experimental method developed in this work for determining the charge distributions of fragments is expected to be employed in the neutron induced fissions of 232Th and 238U or other low energy fission reactions.

  6. Fission fragment angular distributions in proton-induced fission of 209 Bi(p,t) and 197 Au(p,f)

    De, S S; N H; M. L.

    2001-01-01

      The fission fragment angular distributions have been measured for proton-induced fission of 209Bi and 197Au nuclei using surface barrier detectors at several energies between 25 MeV and 30 MeV. The experimental anisotropies are found to be in agreement with the predictions of the Standard Saddle-Point Statistical Model (SSPSM). The fission cross sections of 209Bi 197Au nuclei were also measured and compared with the previous works.

  7. Fission fragment angular distributions in proton-induced fission of 209 Bi(p,t and 197 Au(p,f

    S. S.

    2001-12-01

    Full Text Available   The fission fragment angular distributions have been measured for proton-induced fission of 209Bi and 197Au nuclei using surface barrier detectors at several energies between 25 MeV and 30 MeV. The experimental anisotropies are found to be in agreement with the predictions of the Standard Saddle-Point Statistical Model (SSPSM. The fission cross sections of 209Bi 197Au nuclei were also measured and compared with the previous works.

  8. Feasibility of Traveling Wave Direct Energy Conversion of Fission Reaction Fragments

    Tarditi, A. G.; George, J. A.; Miley, G. H.; Scott, J. H.

    2013-01-01

    Fission fragment direct energy conversion has been considered in the past for the purpose of increasing nuclear power plant efficiency and for advanced space propulsion. Since the fragments carry electric charge (typically in the order of 20 e) and have 100 MeV-range kinetic energy, techniques utilizing very high-voltage DC electrodes have been considered. This study is focused on a different approach: the kinetic energy of the charged fission fragments is converted into alternating current by means of a traveling wave coupling scheme (Traveling Wave Direct Energy Converter, TWDEC), thereby not requiring the utilization of high voltage technology. A preliminary feasibility analysis of the concept is introduced based on a conceptual level study and on a particle simulation model of the beam dynamics.

  9. Channel Effects in the Kinetic Energy of Fragments of Fission Induced by Low-Energy Resonance Neutrons

    Recently, Blyumkina et al. have noted tfte existence ot fission channel ettects in the total kinetic energy of fragments of fission induced by s- and p-wave neutrons. Effects of this nature can also be expected in the variation of the fragment kinetic energies from resonance to resonance in low-energy (s-wave) neutron-induced fission. A fission-fragment detector whose efficiency is dependent on the kinetic energy of the fragments was used in the study of the slow-neutron-induced fission of U235. Comparing the counting-rate of this detector with a conventional fission detector, whose efficiency is independent of the fragment kinetic energy, shows that there exists a variation in the kinetic energy of certain fragments with neutron energy in the neutron energy region from 0.025 to 1 eV. In order to determine the response of the kinetic-energy-sensitive detector, it was necessary to measure the rangè-energy relations of fission fragments in various media, including noble gases and metallic foils. It was estimated from these data that the variation in the fragment kinetic energy release is ∼500 keV, for those fission events that give the lightest and most energetic of the heavy fragments. The variation in fragment kinetic energy is strongly asymmetric about the 0.28-eV resonance in U235, and suggests that the fragment kinetic energy sensitively reflects the presence of interference effects among resonances in fission. A multi-level multi-channel analysis of the data has been made, based on the parameters of Vogt and under the assumption that different fission channels lead to different configurations at scission, such that the kinetic energy release is also different. Previously a major objection to multi-level multi-channel analysis in fission has been that the parameters obtained are not unique. However, the possibility of observing partial fission cross-sections (fission occurring by way of one channel only) removes one of the ambiguities inherent in the multi

  10. Double-energy double-velocity measurement system for fission fragments and its application

    A new system of double-energy double-velocity (DEDV) measurement for fission fragments has been developed. In this system, the energies of fission fragments are measured by silicon surface barrier detectors (SSB) and the velocities by the time-of-flight (TOF) method utilizing thin film detectors (TFD) as start detectors and SSBs as stop detectors of TOF. Theoretical and experimental studies on TFDs and SSBs have been performed before the construction of the DEDV measurement system. The TFD consists of a thin plastic scintillator film and light guide. The author proposes a new model of the luminescence production in a scintillator film. This model takes into account the thickness of the scintillator film and uses only one parameter. The calculated TFD response to charged particles shows good agreement with other experiments. The dependence of the TFD response to the thickness of the scintillator film has been studied experimentally and analyzed by the luminescence production model. The results of this analysis shows the validity of the luminescence production model. The time resolution of the DEDV measurement system using TFDs and SSBs was 133 ps. As an application of this system, the DEDV measurement for the thermal neutron-induced fission of 233U has been carried out at the super mirror neutron guide tube facility of Kyoto University Reactor (KUR). The energy and velocity of each fission fragment have been stored on magnetic disk event by event in a list mode. The analyzed results of masses, energies and velocities of light and heavy fragments agree well with other authors' works. The value of the total neutron emission number is 2.53 and shows good agreement within experimental error, with the JENDL-2 value, 2.49. The light fragment shows a slightly greater number of neutrons emitted than the other works. This suggests the possibility of larger deformation of light fragments at the scission point. (author)

  11. Production and study of fission fragments, from Lohengrin to Alto

    The study of nuclei far from stability is constitutive of the history of nuclear physics at its very beginning and has been making considerable great strides since then. The study of these nuclei give the opportunity to reach new information on the nuclear structure and thus to measure the solidity of our knowledge on nuclear matter and its validity when it is pushed to its limits. The reaction selected for the production of exotic nuclei in the framework of the PARRNe program is the fission of uranium 238. The nuclei produced have an intermediate mass and are very rich in neutrons. The technique to recover them in order to accelerate them is the thick target method called also the Isol technique. The installation of the ancient Lep injector at the Tandem line in Orsay (IPN) is expected to increase by a factor 100 the production rate of exotic nuclei in the PARRNe program, it is the Alto project. The work presented here concerns studies carried out at the Lohengrin spectrometer installed at the ILL in Grenoble, and at the Tandem installation in Orsay. This document is divided into 4 parts: 1) in flight techniques at Lohengrin, 2) the Isol technique, 3) magic numbers in the domain N=50, and 4) the Alto project

  12. New fission fragment distributions and r-process origin of the rare-earth elements.

    Goriely, S; Sida, J-L; Lemaître, J-F; Panebianco, S; Dubray, N; Hilaire, S; Bauswein, A; Janka, H-T

    2013-12-13

    Neutron star (NS) merger ejecta offer a viable site for the production of heavy r-process elements with nuclear mass numbers A≳140. The crucial role of fission recycling is responsible for the robustness of this site against many astrophysical uncertainties, but calculations sensitively depend on nuclear physics. In particular, the fission fragment yields determine the creation of 110≲A≲170 nuclei. Here, we apply a new scission-point model, called SPY, to derive the fission fragment distribution (FFD) of all relevant neutron-rich, fissioning nuclei. The model predicts a doubly asymmetric FFD in the abundant A≃278 mass region that is responsible for the final recycling of the fissioning material. Using ejecta conditions based on relativistic NS merger calculations, we show that this specific FFD leads to a production of the A≃165 rare-earth peak that is nicely compatible with the abundance patterns in the Sun and metal-poor stars. This new finding further strengthens the case of NS mergers as possible dominant origin of r nuclei with A≳140. PMID:24483647

  13. Fission fragment charge and mass distributions in 239Pu(n,f) in the adiabatic nuclear energy density functional theory

    Regnier, D; Schunck, N; Verriere, M

    2016-01-01

    Accurate knowledge of fission fragment yields is an essential ingredient of numerous applications ranging from the formation of elements in the r-process to fuel cycle optimization for nuclear energy. The need for a predictive theory applicable where no data is available is an incentive to develop a fully microscopic approach to fission dynamics. In this work, we calculate the pre-neutron emission charge and mass distributions of the fission fragments formed in the neutron-induced fission of 239Pu using a microscopic method based on nuclear energy density functional (EDF) method, where large amplitude collective motion is treated adiabatically using the time dependent generator coordinate method (TDGCM) under the Gaussian overlap approximation (GOA). Fission fragment distributions are extracted from the flux of the collective wave packet through the scission line. We find that the main characteristics of the fission charge and mass distributions can be well reproduced by existing energy functionals even in tw...

  14. A Study of the Mass Spectra of Fission Fragments after Prompt Neutron Emission

    The distribution of the masses of fission fragments, following neutron emission, was obtained by simultaneously measuring the velocity and energy of each particle. The special feature of this method is that it is essentially independent of the initial energy of the fragments, so that we were able to use relatively thick targets of fissionable material (0.1 mg/cm2). The energy measurement is made by a gold-silicon surface barrier detector: the velocity measurement was made on a flight path of 130 cm, with a total resolving power of 1.5 ns; The ''starting'' detector consisted of a windowless photomultiplier that detected directly the secondary electrons emitted by a thin metallic sheet during the passage of the fission fragments. The ''stop'' signal is picked up directly, by means of a transformer, on the semi-conductor detector. The results given in the paper relate to the thermal fission of U235, and are compared with the results obtained by the radiochemical method. (author)

  15. Measurements of prompt neutron multiplicity distributions in correlation with mass-energy distribution of fission fragments in spontaneous fission of 252Cf, 244Cm and 248Cm

    The number of prompt neutrons emitted in the fission event have been measured separately for each complementary fragment in coincidence with fragment mass and kinetic energies in spontaneous fission of 252Cf, 244Cm and 248Cm. Two high efficient Gd-loaded liquid scintillator tanks were used for the neutron registration. Approximately 3x106 fission events coincident with prompt neutron emission have been accumulated for each isotope. The mean neutron multiplicity, the dispersion and the covariance of the multiplicity distributions have been obtained as a function of fission fragment mass and kinetic energy. The neutron multiplicity data have been corrected for neutron registration efficiency, background and pile-up. Dependencies of the moments of the multiplicity distributions on the fragment mass and total kinetic energy for different mass bins, as well as mass and total kinetic energy distributions of the fission fragments are presented, discussed and compared for the different isotopes investigated. The results showed a different behavior of the moments of the multiplicity distribution depending on the fragment mass asymmetry that reflects changes in the dynamical effects for different fission modes. (author)

  16. Fission and fragmentation of silver and bromine nuclei by 1-6 GeV energy photons

    Fission and fragmentation of silver and bromine nuclei induced by bremsstrahlung photons in the maximum energy range of 1-6 GeV are studied. A special technique of nuclear emulsion for the highly ionizing nuclear fragment detection is used in the discrimination between nuclear fission and fragmentation events. Films of Ilford-KO nuclear emulsion (approximatelly 1020 atoms/cm2 of Ag, Br) which had been exposed to bremsstrahlung beams in 'Deutsches Elektronen Synchrotron' (DESY, Hamburg) with total doses of approximatelly 1011 equivalent photons are used. Through a detailed analysis of range, angular and angle between fragment distributions, and empirical relations which permit to estimate nuclear fragment energy, range and velocity, the discrimination between fission and fragmentation events is made. Results related to fragment range distribution, angular distribution, distribution of angle between fragments, distribution of ratio between ranges, velocity distributions, forward/backward ratio, fission and fragmentation cross sections, nuclear fissionability and ternary fission frequency are presented and discussed. The results show that the mean photofragmentation cross section in the internal 1-6 GeV (0,09+-0,02mb) is significant when compared to the photofission (0,29+-0,05mb). It is also shown that the mean photofission cross section between 1 and 6 GeV is great by a factor of approximatelly 10 when compared to the foreseen by the cascade-evaporation nuclear model for monoenergetic photons of 0,6 GeV. (L.C.)

  17. Planetary Surface Power and Interstellar Propulsion Using Fission Fragment Magnetic Collimator Reactor

    Fission energy can be used directly if the kinetic energy of fission fragments is converted to electricity and/or thrust before turning into heat. The completed US DOE NERI Direct Energy Conversion (DEC) Power Production project indicates that viable DEC systems are possible. The US DOE NERI DEC Proof of Principle project began in October of 2002 with the goal to demonstrate performance principles of DEC systems. One of the emerging DEC concepts is represented by fission fragment magnetic collimator reactors (FFMCR). Safety, simplicity, and high conversion efficiency are the unique advantages offered by these systems. In the FFMCR, the basic energy source is the kinetic energy of fission fragments. Following escape from thin fuel layers, they are captured on magnetic field lines and are directed out of the core and through magnetic collimators to produce electricity and thrust. The exiting flow of energetic fission fragments has a very high specific impulse that allows efficient planetary surface power and interstellar propulsion without carrying any conventional propellant onboard. The objective of this work was to determine technological feasibility of the concept. This objective was accomplished by producing the FFMCR design and by analysis of its performance characteristics. The paper presents the FFMCR concept, describes its development to a technologically feasible level and discusses obtained results. Performed studies offer efficiencies up to 90% and velocities approaching speed of light as potentially achievable. The unmanned 10-tons probe with 1000 MW FFMCR propulsion unit would attain mission velocity of about 2% of the speed of light. If the unit is designed for 4000 MW, then in 10 years the unmanned 10-tons probe would attain mission velocity of about 10% of the speed of light

  18. Fission-Fragment Angular, Energy, and Mass Division Correlations for the U234 (d, Pf) Reaction

    The fission of the compound nucleus U235 in the neighbourhood of its fission threshold has been studied by means of the U234 (d.pf) reaction. A three-parameter analyser was used to record simultaneously the two fission-fragment kinetic energies and the proton energy for each coincident event. The excitation energy at which fission occurs is defined by the kinetic energy of the stripped.proton. The variation of angular anisotropy with excitation energy shows considerably more structure than that obtained by Lamphere for the same nucleus resulting from fast-neutron bombardment of U234. At least eight fission channels at the saddle point have been observed for the energy region between threshold and 2 MeV above threshold. Nilsson-type calculations of single particle energies for deformed nuclei have been made for the larger deformations more nearly describing the saddle-point configuration. The single particle states identified by Lamphere are consistent with those calculated to be close to the Fermi surface for reasonable saddle-point deformations. The primary motivation for this experiment was to search for a possible correlation between mass asymmetry and angular anisotropy. Mass yields obtained from the correlated fragment energies show no variation of the anisotropy with mass ratio, in contrast with experiments where the excitation energy at which fission is occurring is not fixed and where a dependence of anisotropy on mass ratio has been observed. There is therefore no evidence from anisotropy measurements that the properties of the saddle point influence the final mass division. The average total kinetic energy release in fission varies by less than 0.5% for the different saddle-point channels observed. The variation of total kinetic energy with mass ratio has also been investigated. (author)

  19. Fission Fragment Spectroscopy Using a Frisch-Gridded Chamber in RPI's Lead Slowing-Down Spectrometer

    Romano, Catherine

    2006-10-01

    A double sided Frisch-gridded fission chamber for use in RPI's Lead Slowing-Down Spectrometer (LSDS) is being developed at Rensselaer Polytechnic Institute. Placing this fission chamber in the high neutron flux of the LSDS allows measurements of neutron induced fission cross sections, as well as the mass and kinetic energy of the fission fragments of various isotopes. The fission chamber consists of two anodes shielded by Frisch grids on either side of a single cathode. The sample is deposited on a thin polyimide film located in the center of the cathode. Samples are made by dissolving small amounts of actinides in solution, placing the solution on the films and allowing the solution to evaporate. The anode signal and the sum of the anode and grid signals are collected by the data acquisition system. These values are used to calculate the angle of emission of the fission fragments which is then used to determine their energies and masses. RPI's LSDS is a 75 ton, 1.8m cube of lead. The RPI 60MeV Linac creates neutrons through a (γ,n) reaction when the electrons interact with a tantalum target inside the lead spectrometer. The resulting neutron flux is about 4 orders of magnitude larger than an equivalent resolution time-of-flight experiment. The high neutron flux allows for the measurement of isotopes that are not available in large quantities (sub-micrograms) or with small fission cross sections (microbarns). In collaboration with Ezekiel Blain, Zack Goldstein, Yaron Danon and Robert Block at Rensselaer Polytechnic Institute. Funded by Stewardship Science Academic Alliance, National Nuclear Security Agency.

  20. Upgrading DRACULA setup to be used for light products - fission fragments coincidence measurements

    At low bombarding energy (E/A 238 U give rise to a number of fission processes, all leading to very similar fission products. Therefore, in order to understand the fission processes in this energy domain it is of interest to determine the amount of fission occurring after a peripheral interaction relative to that originating from compound nucleus formation. Although the detection of a projectile residue (PLF) in coincidence with the fission fragments is a very promising probe for the macroscopic features of the mechanism of induced fission, at incident energies in the vicinity of the Coulomb barrier (E/A 2 cross section area uses the phoswich technique by coupling a thin fast NE102A plastic scintillator to a 10 cm long BaF2 crystal of hexagonal section. The BaF2 crystal detectors have been successfully used in modular multielement detector ARGOS in the context of GANCT and HOTCT researches at LNS. The light response of the phoswich configuration as a function of the plastic thickness and of the energy and charge of the incident ion has been studied at Tandem energies. Both arrays will be placed in separate vacuum chambers attached to the remaining large angular opening windows of the reaction chamber. By rotating the whole device the fission fragment detection arrays will cover a range of 96 angle in the horizontal plane. The main advantage of this setup is that it allows to perform continuous measurements in energy and angle of the reaction products. The geometry of the whole device has been tested by Monte Carlo calculations using the code ELPHIC. The coincidence condition is completely fulfilled for the first two positions of the setup and partially for the third one. Measurements are intended to be performed at the SMP Tandem from LNS-Catania using light beams (16 O, 19 F, 20 Ne, 32 S) at ∼ 6 MeV/A on high fissility parameter targets. (authors)

  1. No influence of a N =126 neutron-shell closure in fission-fragment mass distributions

    Chaudhuri, A.; Ghosh, T. K.; Banerjee, K.; Bhattacharya, S.; Sadhukhan, Jhilam; Kundu, S.; Bhattacharya, C.; Meena, J. K.; Mukherjee, G.; Saha, A. K.; Asgar, Md. A.; Dey, A.; Manna, S.; Pandey, R.; Rana, T. K.; Roy, P.; Roy, T.; Srivastava, V.; Bhattacharya, P.; Biswas, D. C.; Joshi, B. N.; Mahata, K.; Shrivastava, A.; Vind, R. P.; Pal, S.; Behera, B. R.; Singh, Varinderjit

    2015-10-01

    Mass distributions of the fragments in the fission of 206Po and the N =126 neutron shell closed nucleus 210Po have been measured. No significant deviation of mass distributions has been found between 206Po and 210Po, indicating the absence of shell correction at the saddle point in both the nuclei, contrary to the reported angular anisotropy and prescission neutron multiplicity results. This result provides benchmark data to test the new fission dynamical models to study the effect of shell correction on the potential energy surface at saddle point.

  2. Observed branching ratios of alpha to fission fragments of Cf252 using CR-39

    There has been a rapid growth in the application of SSNTD to the study of nuclear phenomena in the recent past. The considerable ease introduced in recording the signature of heavy ions in the presence of alpha particles has made them particularly suitable for the study of spontaneous fission of transuranic elements. It is the object of the present study to explore the response of CR-39 for the determination of the branching ratios of alpha to fission fragments of Cf252 at the end of almost one and four half-life periods for alpha decay. The results more or less confirm the expected values

  3. Fission fragment angular distribution in 24Mg induced reactions on 192Os and 197Au

    Angular distributions of fission fragments have been measured in 24Mg + 192Os and 24Mg + 197Au reactions at Elab = 128 MeV which is close to entrance channel Coulomb barrier. Experimental angular anisotropies were in reasonably good agreement with those calculated using the statistical theory. Analysis of the angular distribution data of the present study and of our earlier measurement in 19F + 197Au reaction has shown that contribution from non-compound nucleus fission in these systems is not significant. (author)

  4. Lifetime measurements on fission fragments in the A ∼ 100 region

    Lifetimes of first 4+ and 6+ states have been measured in neutron-rich isotopes of Zr, Mo, Ru and Pd using the recoil distance Doppler shift method at GANIL. The nuclei were produced through a fusion-fission reaction in inverse kinematics. The fission fragments were fully identified in the large-acceptance VAMOS spectrometer and γ-rays were detected in coincidence with the EXOGAM germanium array. Lifetimes of excited states in the range of 1-100 ps were measured with the Cologne plunger. Preliminary lifetime results are presented as well as a discussion on the evolution of the collectivity in this region. (authors)

  5. Lifetime measurements on fission fragments in the A ∼ 100 region

    Grente L.

    2013-12-01

    Full Text Available Lifetimes of first 4+ and 6+ states have been measured in neutron-rich isotopes of Zr, Mo, Ru and Pd using the recoil distance Doppler shift method at GANIL. The nuclei were produced through a fusion-fission reaction in inverse kinematics. The fission fragments were fully identified in the large-acceptance VAMOS spectrometer and γ-rays were detected in coincidence with the EXOGAM germanium array. Lifetimes of excited states in the range of 1–100 ps were measured with the Cologne plunger. Preliminary lifetime results are presented as well as a discussion on the evolution of the collectivity in this region.

  6. Fission-fragment kinetic-energy distributions from a two-dimensional Fokker-Planck equation

    We calculate the fission-fragment kinetic-energy distribution for the compound nucleus 213At by simultaneously taking into account spreading in a stretching degree of freedom and fluctuations in a fission degree of freedom. This is done in terms of an approximate solution of a two-dimensional Fokker-Planck equation obtained by propagating Gaussian bundles in momentum space. When compared as functions of nuclear temperature with experimental data, our calculated mean kinetic energies are in approximate agreement and our calculated variances are slightly too small

  7. Experimental evidence for the separability of compound-nucleus and fragment properties in fission

    Schmidt, Karl-Heinz; Ricciardi, Maria Valentina

    2007-01-01

    The large body of experimental data on nuclear fission is analyzed with a semi-empirical ordering scheme based on the macro-microscopic approach and the separability of compound-nucleus and fragment properties on the fission path. We apply the statistical model to the non-equilibrium descent from saddle to scission, taking the influence of dynamics into account by an early freeze out. The present approach reveals a large portion of common features behind the variety of the complex observations made for the different systems. General implications for out-of-equilibrium processes are mentioned.

  8. No influence of a N=126 Neutron Shell Closure in Fission Fragment Mass Distributions

    Chaudhuri, A; Banerjee, K; Bhattacharya, S; Sadhukhan, Jhilam; Kundu, S; Bhattacharya, C; Meena, J K; Mukherjee, G; Saha, A K; Asgar, Md A; Dey, A; Manna, S; Pandey, R; Rana, T K; Roy, P; Roy, T; Srivastava, V; Bhattacharya, P; Biswas, D C; Joshi, B N; Mahata, K; Shrivastava, A; Vind, R P; Pal, S; Behera, B R; Singh, Varinderjit

    2015-01-01

    Mass distributions of the fragments in the fission of $^{206}$Po and the N=126 neutron shell closed nucleus $^{210}$Po have been measured. No significant deviation of mass distributions has been found between $^{206}$Po and $^{210}$Po, indicating the absence of shell correction at the saddle point in both the nuclei, contrary to the reported angular anisotropy and pre-scission neutron multiplicity results. This new result provides benchmark data to test the new fission dynamical models to study the effect of shell correction on the potential energy surface at saddle point.

  9. Determination of the Primary Nuclear Charge of Fission Fragments from their Characteristic K-X-Ray Emission in Spontaneous Fission of Cf252

    The distribution of nuclear charge in the spontaneous fission of Cf252 has been determined directly by simultaneous measurement of the masses and characteristic K-X-ray energies associated with the primary fission products. The X-rays were detected by a thin Nal (Tl) crystal (or by an argon-filled proportional counter) in coincidence with a pair of solid-state detectors for the complementary fission fragments. Preliminary to the three-parameter study of the charge-mass distribution the gross characteristics of the K-X-rays were examined in some detail. The average yield of K-X-rays is 0.55 ± 0.1 pet fission (the heavy group accounting fot 70% of the total). From delayed-coincidence and fragment time-of-flight experiments it was.found that about 30% of the X-rays are emitted within 0.1 ns after fission, another 30% between 0.1 and 1 ns, 25% between 1 and 10 ns, the remainder appearing as two delayed components of equal intensity with half-lives of ∼30 ns and ∼100 ns. These characteristics indicate that the X-rays arise from internal conversion during de-excitation of the primary fission fragments, an interpretation supported by the observed yield 1 per fission) of 50 - 300 - keV electrons emitted within 2 ps of fission. In the three-parameter experiments the yield and energy of K-X-rays emitted in the first centimeter (ns) of fragment flight were determined as a function of fragment mass. The yield of K-X-rays per fragment is a pronounced saw-tooth function of mass, rising from p) function in better agreement with the empirical rule of equal charge displacement (ECD) than with other postulates for charge division in nuclear fission. (author)

  10. Neutron-fragment and Neutron-neutron Correlations in Low-energy Fission

    Lestone, J. P.

    2016-01-01

    A computational method has been developed to simulate neutron emission from thermal-neutron induced fission of 235U and from spontaneous fission of 252Cf. Measured pre-emission mass-yield curves, average total kinetic energies and their variances, both as functions of mass split, are used to obtain a representation of the distribution of fragment velocities. Measured average neutron multiplicities as a function of mass split and their dependence on total kinetic energy are used. Simulations can be made to reproduce measured factorial moments of neutron-multiplicity distributions with only minor empirical adjustments to some experimental inputs. The neutron-emission spectra in the rest-frame of the fragments are highly constrained by ENDF/B-VII.1 prompt-fission neutron-spectra evaluations. The n-f correlation measurements of Vorobyev et al. (2010) are consistent with predictions where all neutrons are assumed to be evaporated isotropically from the rest frame of fully accelerated fragments. Measured n-f and n-n correlations of others are a little weaker than the predictions presented here. These weaker correlations could be used to infer a weak scission-neutron source. However, the effect of neutron scattering on the experimental results must be studied in detail before moving away from a null hypothesis that all neutrons are evaporated from the fragments.

  11. Suppression of the pulmonary clearance of Staphylococcus aureus in mice that had inhaled either 144CeO2 or 239PuO2

    The rate of pulmonary clearance of inhaled Staphylococcus aureus in mice was determined at intervals after inhalation exposure to either 144CeO2 or 239PuO2. In mice with mean initial lung burdens between 0.6 and 4.7 μCi 144Ce the pulmonary clearance of S. aureus was suppressed up to 12 weeks after inhalation of 144CeO2. In mice with mean initial lung burdens between 1.3 and 29.0 μCi 239Pu the pulmonary clearance of S. aureus was suppressed up to 26 weeks after inhalation of 239PuO2. The suppressed pulmonary clearance of S. aureus appeared to correlate with the radiation dose rate to the lungs at the time of exposure to bacteria but not with the cumulative radiation dose to the lungs. The changes in bacterial clearance did not appear to be correlated with changes in body weight, hematological parameters, or radiation-induced histopathological changes. Altered bacterial clearance may be related to radiation damage to pulmonary macrophages. It was concluded that irradiation of the lung from radionuclides inhaled in relatively insoluble forms may result in increased bacterial invasion of the lungs

  12. Sub-barrier resonance fission and its effects on fission fragment properties, exemplified on 234,238U(n,f)

    Oberstedt S.; Hambsch F.-J.; Tudora A.

    2013-01-01

    The correlation between the sub-barrier resonant behaviour of fission crosssection of non-fissile actinides (pre-scission stage) and the visible fluctuations of their fission fragment and prompt neutron data (post-scission stage) around the incident energies of sub-barrier resonances is outlined and supported by quantitative results for two fissioning systems 234,238U(n,f). These quantitative results refer to both stages of the fission process: a) The pre-scission stage including the calculat...

  13. Energies and Yields of Prompt Gamma Rays from Fragments in Slow-Neutron Induced Fission of 235U

    Measurements were made on the gamma radiation emitted from fission fragments in slow-neutron induced fission of 235U. The fragments were detected with solid state detectors of the surface barrier type and the gamma radiation with a Nal(Tl) scintillator. Mass selection was used so that the gamma radiation could be measured as a function of fragment mass. Time discrimination between the fission gammas and the prompt neutrons released in the fission process was employed to reduce the background. The gamma radiation emitted during different time intervals after the fission event was studied with the help of a collimator, the position of which was changed along the path of the fission fragments. In this way it was possible to select various collimator settings and let gamma radiation of different half-lives be enhanced. Gamma-ray energy spectra from these time components were then recorded as function of mass. The spectrum shape differed greatly depending on the half-life of the radiation and the fragment from which it was emitted. The results of the present measurements were discussed in the light of existing fission models, and comparisons were made with prompt gamma-ray and neutron data from other fission experiments

  14. Parity nonconservation in nuclear fission: does it depend on fragment mass/energy?

    For fission of 233U induced by polarized cold neutrons the dependence of the PNC asymmetry coefficient αnf(mLF, TKE) on light fragment mass mLF and total kinetic energy TKE was studied. Concurrently the angular distribution predicted for PNC reactions was tested. Altogether more than 2x1010 fission events with high mass/energy resolution have been collected. This corresponds to an increase in the statistics compared to previous experiments (U. Graf, F. Goennenwein, P. Geltenbort, et al., Z. Phys. A 351 (1995) 281 and V.A. Vesna, V.A. Knyaz'kov, E.A. Kolomenskii et al., JETP. Lett. 31 (1980) 663) by a factor of about 20. The preliminary analysis of the PNC asymmetry shows no significant variation of αnf for different fragment masses/energies, whereas the prediction concerning the angular dependence was confirmed with a precision not obtained up to now

  15. Description of the mass and kinetic-energy distributions of fission fragments using an adiabatic potential

    The mass distributions of fission fragments from rotating composite nuclear systems with parameters Z2/A > 40 have been calculated in the framework of the diffusion model based on the Fokker-Planck equation for the distribution function of the collective variables. In this formalism the two-body nuclear viscosity coefficient describing the intensity of the dissipative forces is the only free parameter. It has been found that the consideration of the angular momenta of the fissile nuclei leads to a small increase in the calculated widths which slightly improves the agreement with the experimental data. In addition, the fission fragment kinetic-energy distributions have been calculated and compared with the measured ones

  16. Fission fragment mass distribution in the 13C+182W and 176Yb reactions

    Ramachandran K.

    2013-12-01

    Full Text Available Shell effects can play a prominent role in fission fragment mass distributions. For lighter systems in the region of A~180-200, mass distributions were generally expected to be symmetric. However, a recent experiment showed that fission of 180Hg following electron capture of 180Tl leads to an asymmetric mass split. Recent calculations by various groups indicate that the mechanism of asymmetric fission could be very different in this mass region compared to the actinide region. To investigate the role of shell effects in this mass region, we have measured the fission fragment mass distribution for the 13C+182W,176Yb reactions forming the compound nuclei 195Hg and 189Os respectively, at lab bombarding energies of 60, 63 and 66 MeV using the CUBE detector setup located at the ANU Heavy Ion Accelerator Facility. The experimental data were fitted with single and double Gaussian distributions. The results indicate an asymmetric mass split for 195Hg, whereas for 189Os, the mass distribution is well fitted with a single Gaussian distribution.

  17. Fission fragment mass distribution in the 13C+182W and 176Yb reactions

    Shell effects can play a prominent role in fission fragment mass distributions. For lighter systems in the region of A∼180-200, mass distributions were generally expected to be symmetric. However, a recent experiment showed that fission of 180Hg following electron capture of 180Tl leads to an asymmetric mass split. Recent calculations by various groups indicate that the mechanism of asymmetric fission could be very different in this mass region compared to the actinide region. To investigate the role of shell effects in this mass region, we have measured the fission fragment mass distribution for the 13C+182W, 176Yb reactions forming the compound nuclei 195Hg and 189Os respectively, at lab bombarding energies of 60, 63 and 66 MeV using the CUBE detector setup located at the ANU Heavy Ion Accelerator Facility. The experimental data were fitted with single and double Gaussian distributions. The results indicate an asymmetric mass split for 195Hg, whereas for 189Os, the mass distribution is well fitted with a single Gaussian distribution. (authors)

  18. Monte Carlo Simulation of Prompt Neutron Emission During Acceleration of Fission Fragments

    Possible reasons for apparent discrepancy in the prompt fission neutron spectra (PFNS) in the low-energy region, say <0.5 MeV, have been discussed. There are five possibilities: (1) uncertainty in the measured data in the low energy region, (2) neutron emission during acceleration (NEDA), instead of after full acceleration, (3) angular anisotropy in neutron emission in the CM-system of fission fragments (FF), (4) possible effect of 'yrast levels', and (5) possible existence of scission neutrons. In this report we examined the possibility (2) and (3) as well. It has been considered that the most of the prompt fission neutrons are emitted after full acceleration of fission fragments due to rapid acceleration by strong Coulomb repulsion working between them. On the other hand, however, there has also been a discussion on a possibility of neutron emission during acceleration. This phenomenon is interesting from physics point of view, as it provides knowledge on the timescale of de-excitation of excited nuclei and on possible competition with the Coulomb acceleration of FFs. It is also interesting from application point of view, since neutron emission from FFs before full acceleration implies an enhancement of low-energy component of the PFNS, because the NEDA neutrons receive smaller linear momentum from the FF. This possibility was examined by using Monte Carlo simulation

  19. Fission fragment distributions in resolved resonances of 235U(n,f)

    Fission fragment energies and emission angles with respect to the incident neutron beam were measured for 235U(n,f) using a twin Frisch-gridded ionization chamber. The neutron energy range from 0.006 eV to 0.5 MeV was covered in a time-of-flight experiment at the Geel Electron Linear Accelerator (GELINA). Fission fragment mass-, and total kinetic energy distributions were evaluated for thermal neutrons, for resolved resonances below 40 eV, and in certain energy bins at higher neutron energy. Fluctuations in the average total kinetic energy with respect to the thermal value of up to ∼450 keV are observed for resonances below 40 eV. The variations of from resonance to resonance can be related to changes in the population of the three fission exit channels. Also the symmetric fission yields or valley to peak ratios of the mass distributions fluctuate from resonance to resonance up to a factor 2. Both fluctuations are not correlated with the resonance spin of the compound nucleus. An explanation for the fluctuations is proposed. (author)

  20. Population of rotational states in the ground-band of fission fragments

    Misicu, Serban

    2013-01-01

    The population of rotational states in the ground-state band of neutron-rich fragments emitted in the spontaneous fission of $^{252}$Cf is described within a time-dependent quantum model similar to the one used for Coulomb excitation. The initial population probability of the states included in the selected basis is calculated according to the bending model at scission. Subsequently these initial amplitudes are feeding the coupled dynamical equations describing the population of rotational states in both fragments during the tunneling and post-barrier (pure Coulomb) motion. As application we consider the high yield Mo-Ba pair for different number of emitted neutrons.

  1. Microscopic approach of fission dynamics applied to fragment kinetic energy and mass distributions in 238U

    Goutte, H.; Berger, J.F.; Casoli, P.; Gogny, D.

    2005-01-01

    The collective dynamics of low energy fission in 238U is described within a time-dependent formalism based on the Gaussian Overlap Approximation of the time-dependent Generator Coordinate Method. The intrinsic deformed configurations of the nucleus are determined from the self-consistent Hartree-Fock-Bogoliubov procedure employing the effective force D1S with constraints on the quadrupole and octupole moments. Fragment kinetic energy and mass distributions are calculated and compared with exp...

  2. Measurement of the energy spectra of fission fragments using nuclear track detectors and digital image processing

    Energy spectra of fission fragments were determined using a Nuclear Track Methodology (NTM) supported by digital image analysis and numerical data processing using a standard personal computer. The analysis of a californium (252Cf) spectrum with this approach shows improvement compared with the values reported previously using the standard procedure, in terms of resolution and accuracy. This new method adds full automation to the technical advantages and cost effectiveness of an NTM.

  3. Burnout and gate rupture of power MOS transistors with fission fragments of 252Cf

    A study to determine the single event burnout (SEB) and single event gate rupture (SEGR) sensitivities of power MOSFET devices is carried out by exposure to fission fragments from 252Cf source. The test method, test results, a description of observed burnout current waveforms and a discussion of a possible failure mechanism are presented. The test results include the observed dependence upon applied drain or gate to source bias and effect of external capacitors and limited resistors

  4. Measurement of the angular distribution of fission fragments using a PPAC assembly at CERN nTOF

    A fission reaction chamber based on Parallel Plate Avalanche Counters (PPACs) was built for measuring angular distributions of fragments emitted in neutron-induced fission of actinides at the neutron beam available at the Neutron Time-Of-Flight (nTOF) facility at CERN. The detectors and the samples were tilted 45° with respect to the neutron beam direction to cover all the possible values of the emission angle of the fission fragments. The main features of this setup are discussed and results on the fission fragment angular distribution are provided for the 232Th(n,f) reaction around the fission threshold. The results are compared with the available data in the literature, demonstrating the good capabilities of this setup

  5. Measurement of the angular distribution of fission fragments using a PPAC assembly at CERN n_TOF

    Tarrío, D; Audouin, L; Duran, I; Paradela, C; Tassan-Got, L; Le Naour, C; Bacri, C O; Petitbon, V; Mottier, J; Caamano, M; Altstadt, S; Andrzejewski, J; Barbagallo, M; Bécares, V; Bečvář, F; Belloni, F; Berthoumieux, E; Billowes, J; Boccone, V; Bosnar, D; Brugger, M; Calviani, M; Calviño, F; Cano-Ott, D; Carrapiço, C; Cerutti, F; Chiaveri, E; Chin, M; Colonna, N; Cortés, G; Cértes-Giraldo, M A; Diakaki, M; Domingo-Pardo, C; Dzysiuk, N; Eleftheriadis, C; Ferrari, A; Fraval, K; Ganesan, S; García, A R; Giubrone, G; Gómez-Hornillos, M B; Gonçalves, I F; González-Romero, E; Griesmayer, E; Guerrero, C; Gunsing, F; Gurusamy, P; Jenkins, D G; Jericha, E; Kadi, Y; Käppeler, F; Karadimos, D; Koehler, P; Kokkoris, M; Krtička, M; Kroll, J; Langer, C; Lederer, C; Leeb, H; Losito, R; Manousos, A; Marganiec, J; Martínez, T; Massimi, C; Mastinu, P F; Mastromarco, M; Meaze, M; Mendoza, E; Mengoni, A; Milazzo, P M; Mingrone, F; Mirea, M; Mondalaers, W; Pavlik, A; Perkowski, J; Plompen, A; Praena, J; Quesada, J M; Rauscher, T; Reifarth, R; Riego, A; Roman, F; Rubbia, C; Sarmento, R; Schillebeeckx, P; Schmidt, S; Tagliente, G; Tain, J L; Tsinganis, A; Valenta, S; Vannini, G; Variale, V; Vaz, P; Ventura, A; Versaci, R; Vermeulen, M J; Vlachoudis, V; Vlastou, R; Wallner, A; Ware, T; Weigand, M; Weiß, C; Wright, T J; Žugec, P

    2014-01-01

    A fission reaction chamber based on Parallel Plate Avalanche Counters (PPACs) was built for measuring angular distributions of fragments emitted in neutron-induced fission of actinides at the neutron beam available at the Neutron Time-Of-Flight (n_TOF) facility at CERN. The detectors and the samples were tilted 45 1 with respect to the neutron beam direction to cover all the possible values of the emission angle of the fission fragments. The main features of this setup are discussed and results on the fission fragment angular distribution are provided for the 232 Th(n,f) reaction around the fission threshold. The results are compared with the available data in the literature, demonstrating the good capabilities of this setup

  6. Statistical and evaporation models for the neutron emission energy spectrum in the center-of-mass system from fission fragments

    The neutron emission energy spectra in the CMS (center-of-mass) frame from two compound nuclei produced by fission are studied. The neutron spectra calculated with the Hauser–Feshbach statistical model are compared with the evaporation theory, and the definition of the temperature is revisited. Using the Monte Carlo technique we average the CMS neutron spectra from many fission fragments to construct the representative CMS spectrum from both the light and heavy fragments. The CMS spectra for each fission fragment pair are also converted into the laboratory frame to calculate the total prompt fission neutron spectrum that can be observed experimentally. This is compared to measured laboratory data for thermal neutron induced fission on 235U. We show that the Hauser–Feshbach calculation gives a different spectrum shape than the Madland–Nix model calculation

  7. Influence of complete energy sorting on the characteristics of the odd-even effect in fission-fragment element distributions

    Jurado, Beatriz

    2014-01-01

    The characteristics of the odd-even effect in fission-fragment Z distributions are compared to a model based on statistical mechanics. Special care is taken for using a consistent description for the influence of pairing correlations on the nuclear level density. The variation of the odd-even effect with the mass of the fissioning nucleus and with fission asymmetry is explained by the important statistical weight of configurations where the light nascent fission fragment populates the lowest energy state of an even-even nucleus. This implies that entropy drives excitation energy and unpaired nucleons predominantly to the heavy fragment. Therefore, within our model, the odd-even effect appears as an additional signature of the recently discovered energy-sorting process in nuclear fission.

  8. Fission of highly excited fragments produced in collisions of 750 A.MeV ions of 238U with Pb target nuclei

    Fission of heavy fragments of U-projectiles produced in collisions with Pb target was investigated by analyzing fission fragments after many neutrons have been evaporated. The distributions of the fragments identified in A, Z and measured in momentum gives access to the distributions of intermediate excited fragments. (authors)

  9. Brownian shape motion on five-dimensional potential-energy surfaces: Nuclear fission-fragment mass distributions

    Randrup, Jorgen; Moller, Peter

    2011-01-01

    Although nuclear fission can be understood qualitatively as an evolution of the nuclear shape, a quantitative description has proven to be very elusive. In particular, until now, there exists no model with demonstrated predictive power for the fission fragment mass yields. Exploiting the expected strongly damped character of nuclear dynamics, we treat the nuclear shape evolution in analogy with Brownian motion and perform random walks on five-dimensional fission potential-energy surfaces whic...

  10. Multi-modal study of angular momentum distribution of fission fragments as a result of bending modes

    The average angular momentum of the primary fission fragments as a function of their masses was calculated using the wave function of the bending mode excitation at the scission point. The scission configuration was assumed to be determined by the prescission shapes of fissioning nucleus within the multimodal fission model. Results in 235U(nth, f) is in good agreement with the recent experimental data. (author)

  11. The Prompt Gamma-Ray, Prompt Electron and Prompt X-Ray Spectra Associated with Fission Fragments of Specific Mass

    Well-defined prompt gamma-rays, prompt-conversion elections and prompt K-X-rays have been observed in coincidence with moving fission fragments of Cf252. In a few cases, the masses and charges of the nuclei emitting the gamma-rays and conversion electrons have been identified. The gamma-ray, prompt-electron and prompt X-ray energies as well as the two fission fragments energies were measured with high-resolution solid-state detectors. The masses of the fragments were deduced from their energies, and the nuclear charges were determined by measuring the K-X - ray energies associated with different masses. The magnitude and sign of the Doppler shift in gamma-ray energy allowed assignment of the gamma-ray lines to single members of fragment pairs. The Doppler shift also provides an independent measure of the fragment velocity and hence the fragment mass after neutron emission. The results of the X-ray measurements are consistent with the view that the majority of the prompt X-rays emitted during the spontaneous fission of Cf252 are the result of internal conversion during the de-excitation of low-energy collective states of the primary fission fragments. Apart from the specific results discussed above, the most important consequence of these experiments has been the demonstration that it is possible to study the properties of individual fission fragments, as identified by their characteristic radiations, rather than studying the properties of an average fission fragment with an average mass and charge. The consequences of this advance in the technique of studying fission fragments ate being explored. (author)

  12. Even-odd effects and Coulomb effects on minimal excitation energy of fragments from low energy fission

    Montoya, Modesto

    2014-01-01

    This work is focused on even-odd effects on the minimal total fragment excitation energy in thermal neutron induced fission of 233U and 235U as well as in spontaneous fission of 252Cf. In a scission model, taking into account the fragment deformation properties and Coulomb interaction between fragments, the expression of the difference between Q-values referred to even/even and odd/odd charge splits, respectively, on the corresponding difference between the minimal total fragment excitation e...

  13. Even-odd effects and Coulomb effects on minimal excitation energy of fragments from low energy fission

    Montoya, Modesto

    2014-01-01

    This work is focused on even-odd effects on the minimal total fragment excitation energy in thermal neutron induced fission of 233U and 235U as well as in spontaneous fission of 252Cf. In a scission model, taking into account the fragment deformation properties and Coulomb interaction between fragments, the expression of the difference between Q-values referred to even/even and odd/odd charge splits, respectively, on the corresponding difference between the minimal total fragment excitation energy is studied.

  14. Fragment excitation, kinetic energy distributions and neutron evaporation in nuclear fission calculated from a random excitation model

    We present a model which allows for the calculation of fragment excitation energy, fragment kinetic energies and neutron evaporation in nuclear fission. The model is based on the assumption that, at the end of the fission process, fragments are excited to a temperature which is proportional to the reaction Q-value. Starting from this assumption the distribution functions of fragment excitation can be formulated and the distribution functions for the kinetic energies can be derived by a Monte Carlo method. From the distribution functions for the excitation energy neutron evaporation characteristics are calculated. (author)

  15. The most compact scission configuration of fragments from low energy fission of 234U and 236U

    Using a time of flight technique, the maximal values of the kinetic energy as a function of the primary mass of fragments from low energy fission of 234U and 236U were measured by Signarbieux et al. From calculations of scission configurations, one can conclude that, for those two fissioning systems, the maximal values of the total kinetic energy corresponding to fragmentations (42Mo62, 50Sn80) and (42Mo64, 50Sn80) respectively, are equal to the available energy, and that their scission configurations are composed of a spherical heavy fragment and a prolate light fragment, both in their ground state. (author).

  16. SSNTD study of the probable influence of alpha activity on the mass distribution of 252Cf fission fragments

    The SSNTD has come a long way in its application for the study of nuclear phenomena. Spontaneous fission of transuranic elements is one such phenomena wherein use of SSNTD offers easy registration of the signature of the fission fragments. The object of the present study is to explore whether any one of the track parameters such as the diameter can be used to estimate the atomic mass ratios of the spontaneous fission fragments. The spontaneous fission data from 252Cf recorded almost at the end of one and four half-life periods for alpha decay are analysed, taking a plot of the number of tracks versus the track diameter. From these plots it is seen that initially, when significant alpha activity of 252Cf persists, the fission fragments appear to cluster into two predominant groups as indicated by two peaks. The ratio of the diameters at these peak positions appear to be related to the ratio of average mass numbers of the light and heavy groups of fission fragments. However, absence of two peaks for similar plots at the end of about four half-life periods for alpha decay suggests that presumably the presence of alphas influence the mass distribution of the fission fragments

  17. Fragment angular momenta and descent dynamics in 252 Cf spontaneous fission

    Average angular momentum values of primary fission fragments as a function of neutron multiplicity and neutron-to-proton ratio were extracted for the first time for the Mo-Ba and Zr-Ce charge splittings of 252 Cf. The results are discussed in terms of the energy balance occurring at the scission point. For the first time we show that for large fragment elongation associated with larger numbers of evaporated neutrons (vtot ≥6), essentially only zero point bending oscillation takes places, i.e. T = 0 for this degree of freedom. For the major part of the fission events, with vtot = 2-5, the banding oscillation is excited to a temperature of 2-3 MeV. Such a high bending temperature implies that the coupling between the collective and internal degrees of freedom is weak at the descent of the even-even nucleus of 252 Cf to the scission point. The dipole oscillations occurring at the descent take away some 2.5 - 3.0 MeV from the release energy. A correlation between the fragment angular momentum and the mass asymmetry dependent yields of primary fragment pairs is reported. This correlation shows that the subtraction of 2.5 - 3.0 MeV from the total energy balance results in a remarkable reduction of the bending temperature. (authors)

  18. A high-resolution time-of-flight spectrometer for fission fragments and ion beams

    For the purpose of fission-fragment detection a double time-of-flight (TOF) spectrometer has been developed. The key component of the TOF spectrometer is a TOF detector consisting of multichannel-plate (MCP) detectors with a position-sensitive readout, a foil for secondary electron (SE) production and an electrostatic mirror. The fission fragments are detected by measuring the SEs impinging on the position-sensitive anode after emission from the foil, acceleration and deflection by the electrostatic mirror. The functionality of the different detector components is proven in detail. Optimised schemes for the high-voltage supplies of the MCP detectors have been implemented successfully. In order to process the multichannel-plate detector signals optimally, a new state-of-the-art constant-fraction discriminator based on the amplitude and rise time compensated technique with very low threshold capabilities and optimised walk properties has been developed and incorporated into the setup. In a setup consisting of two mirror MCP detectors, we could successfully observe the TOF spectrum of a mixed (226Ra,222Rn,210Po,218Po,214Po) α-source. Testing photo-fission experiments were performed at the bremsstrahlung facility at the ELBE accelerator. The setup consisted of two mirror detectors (first arm) and a 80 mm diameter MCP detector (second arm) with a 238U target positioned in between. TOF measurements with two bremsstrahlung end-point energies of 12.9 and 16.0 MeV were carried out. A clear cut separation of the TOF peaks for the medium-mass and heavy fission fragments was observed. (orig.)

  19. A high-resolution time-of-flight spectrometer for fission fragments and ion beams

    Kosev, Krasimir Milchev

    2007-07-01

    For the purpose of fission-fragment detection a double time-of-flight (TOF) spectrometer has been developed. The key component of the TOF spectrometer is a TOF detector consisting of multichannel-plate (MCP) detectors with a position-sensitive readout, a foil for secondary electron (SE) production and an electrostatic mirror. The fission fragments are detected by measuring the SEs impinging on the position-sensitive anode after emission from the foil, acceleration and deflection by the electrostatic mirror. The functionality of the different detector components is proven in detail. Optimised schemes for the high-voltage supplies of the MCP detectors have been implemented successfully. In order to process the multichannel-plate detector signals optimally, a new state-of-the-art constant-fraction discriminator based on the amplitude and rise time compensated technique with very low threshold capabilities and optimised walk properties has been developed and incorporated into the setup. In a setup consisting of two mirror MCP detectors, we could successfully observe the TOF spectrum of a mixed ({sup 226}Ra,{sup 222}Rn,{sup 210}Po,{sup 218}Po,{sup 214}Po) {alpha}-source. Testing photo-fission experiments were performed at the bremsstrahlung facility at the ELBE accelerator. The setup consisted of two mirror detectors (first arm) and a 80 mm diameter MCP detector (second arm) with a {sup 238}U target positioned in between. TOF measurements with two bremsstrahlung end-point energies of 12.9 and 16.0 MeV were carried out. A clear cut separation of the TOF peaks for the medium-mass and heavy fission fragments was observed. (orig.)

  20. On some uses of the recording op fission fragments occurring in insulators; Sur quelques utilisations de l'enregistrement des fragments de fission dans les isolants

    Mory, J. [Commissariat a l' Energie Atomique, Fontenay-aux-Roses (France). Centre d' Etudes Nucleaires

    1965-07-01

    The passage of fission fragments is manifested in insulators by the formation of damage lines which can easily be observed by transparence using the electron microscope after a suitable chemical attack. Since the recording efficiency is 100 per cent for mica and plastics this phenomenon has a certain number of applications. After briefly recalling the interaction processes between charged particles and matter, and giving a quantitative study of the relationships connecting the various parameters, the author considers here some of these applications: - thermal neutron dosimetry: it is possible to measure integrated fluxes of between lO{sup 3} and 10{sup 21} n/cm{sup 2}, according to the method used; - fast neutron dosimetry: by using fission fragment threshold sources it is easy to measure biological type doses of about 1 rem: - dosage of very low fissile impurity concentrations: atomic concentrations of about 10{sup -9}; can be measured; this limit has never been attained by conventional methods; - study of fissile elements occurring in atmospheric dusts. Results are then briefly given of an automated counting test for traces effected by measuring the electrical resistivity, of the irradiated membrane. Finally are given the advantages and disadvantages of these solid detectors, especially with respect to nuclear emulsions whose uses are approximately identical. (author) [French] Le passage des fragments de fission se materialise dans les isolants par des lignes de dommages que l'on peut facilement observer par transparence au microscope optique apres une attaque chimique appropriee. L'efficacite d'enregistrement etant de 100 pour cent dans le mica et les plastiques, ce phenomene peut avoir un certain nombre d'applications. Apres un bref rappel des processus d'interaction entre particules chargees et matiere, et une etude quantitative des relations unissant les differents parametres, on etudie ici quelques-unes de ces applications

  1. Studies of fragment spin as a function of fragment mass in heavy ion induced fission reactions

    Measurement on fragment spin as a function of its mass has been carried out over a wide range of bombarding energy in 12C, 16O + 209Bi and 12C, 16O + 232Th reactions. The mass dependence of fragment spin for 12C, 16O + 232Th reactions is observed to be in marked contrast to that for the 12C, 16O + 209Bi reactions. The present results have been analysed within the statistical model by taking into account the finite relaxation time for the equilibration of the collective spin modes. It is found that the observed feature in 12C, 16O + 232Th reactions are characteristic of incomplete equilibration of the collective spin modes where the mass relaxation process at extreme mass asymmetry terminates before full statistical equilibration of the collective spin modes are reached

  2. A Model for Fragment Mass-Versus-Energy Correlations in Fission

    A detailed investigation of the two-spheioid model of the scission configuration in fission, including the study of both the classical and quantum-mechanical properties of the system, is given. The most probable total fragment kinetic energy as a function of mass division is calculated from minimization of the total potential energy of the system. The root mean square width of the kinetic energy distribution is calculated from the quantum mechanical properties of the system. The local effective stiffness τ as a function of fragment mass m required for these calculations was obtained solely from correlated fragment kinetic energy measurements for thermal-neutron fission of 239Pu, 241Pu, and 235U, together with the minimum potential energy hypothesis. Strong shell effects in the function τ (m) were found to occur in the region of m ≅ 132, where Z ≅ 50, N ≅ 82; however, no shell effects seem to occur in the region of m es 83, where N ≅ 50. We may interpret this result to indicate that for N ≅ 50 proton-deficient nuclei, the ground-state well in the nuclear potential is relatively shallow, so that when these nuclei occur in fission they occur with distorted shapes outside the ground-state well, where the effective stiffness is reduced. Effective stiffnesses obtained for fragments of mass 82 ≤ m ≲ 112 are within ∼ 20% of the liquid-drop-model value. The stiffness parameters τ (m) are used together with minimization of the potential energy to calculate EK (m), the average total fragment kinetic energy as a function of mass. In all cases examined to date, the calculated and experimental energies agree to within about 3%. The root-mean-square width oEK; (m) of the total kinetic energy distribution as a function of fragment mass is determined from quantum-mechanical properties of the system. Normal modes of the system are derived, and a harmonic approximation to the potential is used. Calculated and measured widths agree within about 20% for a wide range

  3. A model for fragment mass-versus-energy correlations in fission

    A detailed investigation of the two-spheroid model of the scission configuration in fission, including the study of both the classical and quantum-mechanical properties of the system, is given. The most probable total fragment kinetic energy as a function of mass division is calculated from minimization of the total potential energy of the system. The root mean square width of the kinetic energy distribution is calculated from the quantum mechanical properties of the system. The local effective stiffness τ as a function of fragment mass m required for these calculations was obtained solely from correlated fragment kinetic energy measurements for thermal-neutron fission of 239Pu, 241Pu, and 235U, together with the minimum potential energy hypothesis. Strong shell effects in the function τ (m) were found to occur in the region of m ≅ 132, where Z ≅ 50, N ≅ 82; however, no shell effects seem to occur in the region of m ≅ 83, where N ≅ 50. We may interpret this result to indicate that for N = 50 proton-deficient nuclei, the ground-state well in the nuclear potential is relatively shallow, so that when these nuclei occur in fission they occur with distorted shapes outside the ground-state well, where the effective stiffness is reduced. Effective stiffnesses obtained for fragments of mass 82 ≤ m K (m), the average total fragment kinetic energy as a function of mass. In all cases examined to date, the calculated and experimental energies agree to within about 3%. The root-mean-square width σEK (m) of the total kinetic energy distribution as a function of fragment mass is determined from quantum-mechanical properties of the system. Normal modes of the system are derived, and a harmonic approximation to the potential is used. Calculated and measured widths agree within about 20% for a wide range of fissioning nuclei. Discussions of the sensitivity of these results to the stiffness parameters, to the nuclear vibrational mass parameter, and to nuclear

  4. Fission fragment properties from a microscopic approach with the Gogny force

    Potential energy surfaces are calculated in the elongation-asymmetry plane, with nuclear shapes ranging from sphericity to very large deformations, using the Hartree-Fock-Bogoliubov method and the Gogny nucleon-nucleon effective interaction (parameterization D1S), for the 226Th and 256,258,260Fm Fissioning systems. In order to discriminate between pre- and post-scission configurations, we define a criterion based on the nuclear density. Using this criterion, a big number of scission configurations are identified, and several fragment properties are extracted from them, namely fragment deformations, deformation energies, energy partitioning, neutron binding energies at scission, charge polarization, total fragment kinetic energies and neutron emission multiplicities. (authors)

  5. Accurate measurements of fission-fragment yields in 234,235,236,238U(γ,f) with the SOFIA set-up

    Chatillon, A.; Taïeb, J.; Martin, J.-F.; Pellereau, E.; Boutoux, G.; Gorbinet, T.; Grente, L.; Bélier, G.; Laurent, B.; Alvarez-Pol, H.; Ayyad, Y.; Benlliure, J.; Caamaño, M.; Audouin, L.; Casarejos, E.; Cortina-Gil, D.; Farget, F.; Fernández-Domínguez, B.; Heinz, A.; Jurado, B.; Kelić-Heil, A.; Kurz, N.; Lindberg, S.; Löher, B.; Nociforo, C.; Paradela, C.; Pietri, S.; Ramos, D.; Rodriguez-Sanchez, J.-L.; Rodrìguez-Tajes, C.; Rossi, D.; Schmidt, K.-H.; Simon, H.; Tassan-Got, L.; Törnqvist, H.; Vargas, J.; Voss, B.; Weick, H.; Yan, Y.

    2016-03-01

    SOFIA (Studies On Fission with Aladin) is a new experimental set-up dedicated to accurate measurement of fission-fragments isotopic yields. It is located at GSI, the only place to use inverse kinematics at relativistic energies in order to study the (γ,f) electromagnetic-induced fission. The SOFIA set-up is a large-acceptance magnetic spectrometer, which allows to fully identify both fission fragments in coincidence on the whole fission-fragment range. This paper will report on fission yields obtained in 234,235,236,238U(γ,f) reactions.

  6. Accurate measurements of fission-fragment yields in $^{234,235,236,238}$U(γ,f) with the SOFIA set-up

    Chatillon A.; Taïeb J.; MARTIN J. - F.; Pellereau E.; Boutoux G.; Gorbinet T.; Grente L.; Bélier G.; Laurent B.; Alvarez-Pol H.; Ayyad Y.; Benlliure J.; Caamaño M.; Audouin L.; Casarejos E.

    2015-01-01

    SOFIA (Studies On Fission with Aladin) is a new experimental set-up dedicated to accurate measurement of fission-fragments isotopic yields. It is located at GSI, the only place to use inverse kinematics at relativistic energies in order to study the (γ,f) electromagnetic-induced fission. The SOFIA set-up is a large-acceptance magnetic spectrometer, which allows to fully identify both fission fragments in coincidence on the whole fission-fragment range. This paper will report on fission yields...

  7. Accurate measurements of fission-fragment yields in 234,235,236,238U(γ,f with the SOFIA set-up

    Chatillon A.

    2016-01-01

    Full Text Available SOFIA (Studies On Fission with Aladin is a new experimental set-up dedicated to accurate measurement of fission-fragments isotopic yields. It is located at GSI, the only place to use inverse kinematics at relativistic energies in order to study the (γ,f electromagnetic-induced fission. The SOFIA set-up is a large-acceptance magnetic spectrometer, which allows to fully identify both fission fragments in coincidence on the whole fission-fragment range. This paper will report on fission yields obtained in 234,235,236,238U(γ,f reactions.

  8. Fragmentation of spherical radioactive heavy nuclei as a novel probe of transient effects in fission

    Peripheral collisions with radioactive heavy-ion beams at relativistic energies are discussed as an innovative approach for probing the transient regime experienced by fissile systems evolving toward quasiequilibrium and thereby studying the viscous nature of nuclear matter. A dedicated experiment using the advanced technical installations of GSI, Darmstadt, made it possible to realize ideal conditions for the investigation of relaxation effects in a metastable well. Combined with a highly sensitive experimental signature, it provides a measure of the transient effects with respect to the flux over the fission barrier. Within a two-step reaction process, 45 proton-rich unstable spherical isotopes between At and Th produced by projectile-fragmentation of a stable 238U beam have been used as secondary projectiles which impinge on lead target nuclei. The fragmentation of the radioactive projectiles results in nearly spherical compound nuclei that span a wide range in excitation energy and fissility. The decay of these excited systems by fission is studied with a dedicated setup which, together with the inverse kinematics of the reaction, permits the detection of both fission products in coincidence and the determination of their atomic numbers with high resolution. The information on the nuclear charges of the two fragments is used to sort the data according to the initial excitation energy and fissility of the compound nucleus. The width of the fission-fragment nuclear charge distribution is shown to be specifically sensitive to presaddle transient effects and is used to establish a clock for the passage of the saddle point. The comparison of the experimental results with model calculations points to a fission delay τtrans of (3.3±0.7)x10-21 s for initially spherical compound nuclei, independent of excitation energy and fissility. This value suggests a nuclear dissipation strength β at small deformation of (4.5±0.5)x1021 s-1. The very specific combination of the

  9. Timing characteristics of a two-dimensional multi-wire cathode strip detector for fission fragments

    In the recent past, a gas filled two-dimensional multi-wire cathode strip detector (MCSD) was developed for the detection of fission fragments (FFs). The position resolution was found to be about 1.0 and 1.5 mm in X and Y directions respectively. The detector has three electrode planes consisting of cathode strip (X-plane), anode wires and split-cathode wires (Y-plane). Each thin wire of the anode plane placed between the two cathode planes is essentially independent and behaves like a proportional counter. The construction of the detector in detail has been given in our earlier paper. The position information has been obtained by employing high impedance discrete delay line read out method for extracting position information in X and Y-directions. In this work, the timing characteristics of MCSD detector are reported to explore the possible use of this detector for the measurement of the mass of the fission fragments produced in heavy ion induced fission reactions

  10. The even-odd effect in fission-fragment Z yields – a new kind of nuclear clock

    Jurado Beatriz

    2013-12-01

    Full Text Available A model for the even-odd effect in fission based on statistical mechanics is presented. It reveals that the variation of the even-odd effect with the mass of the fissioning nucleus and the increase towards asymmetric splits is due to the important statistical weight of configurations where the light fission fragment populates the ground state of an even-even nucleus. This implies that excitation energy and unpaired nucleons are predominantly transferred to the heavy fragment. Our results indicate that the time for transfer of excitation energy and nucleons is shorter than the saddle-to-scission time.

  11. The even-odd effect in fission-fragment Z yields - A new kind of nuclear clock

    A model for the even-odd effect in fission based on statistical mechanics is presented. It reveals that the variation of the even-odd effect with the mass of the fissioning nucleus and the increase towards asymmetric splits is due to the important statistical weight of configurations where the light fission fragment populates the ground state of an even-even nucleus. This implies that excitation energy and unpaired nucleons are predominantly transferred to the heavy fragment. Our results indicate that the time for transfer of excitation energy and nucleons is shorter than the saddle-to-scission time. (authors)

  12. Fission Fragment Angular Distribution of 232Th(n,f) at the CERN n_TOF Facility

    Tarrío, D; Audouin, L; Duran, I.; Paradela, C.; Tassan-Got, L; Altstadt, S; Andrzejewski, J; Barbagallo, M; Bécares, V; Bečvář, F; Belloni, F; Berthoumieux, E; Billowes, J; Boccone, V; Bosnar, D; Brugger, M; Calviani, M; Calviño, F; Cano-Ott, D; Carrapiço, C; Cerutti, F; Chiaveri, E; Chin, M; Colonna, N; Cortés, G; Cortés-Giraldo, M A; Diakaki, M; Domingo-Pardo, C; Dzysiuk, N; Eleftheriadis, C; Ferrari, A; Fraval, K; Ganesan, S; García, A R; Giubrone, G; Gómez-Hornillos, M B; Gonçalves, I F; González-Romero, E; Griesmayer, E; Guerrero, C; Gunsing, F; Gurusamy, P; Jenkins, D G; Jericha, E; Kadi, Y; Käppeler, F; Karadimos, D; Koehler, P; Kokkoris, M; Krtička, M; Kroll, J; Langer, C; Lederer, C; Leeb, H; Losito, R; Manousos, A; Marganiec, J; Martínez, T; Massimi, C; Mastinu, P F; Mastromarco, M; Meaze, M; Mendoza, E; Mengoni, A; Milazzo, P M; Mingrone, F; Mirea, M; Mondalaers, W; Pavlik, A; Perkowski, J; Plompen, A; Praena, J; Quesada, J M; Rauscher, T; Reifarth, R; Riego, A; Roman, F; Rubbia, C; Sarmento, R; Schillebeeckx, P; Schmidt, S; Tagliente, G; Tain, J L; Tsinganis, A; Valenta, S; Vannini, G; Variale, V; Vaz, P; Ventura, A; Versaci, R; Vermeulen, M J; Vlachoudis, V; Vlastou, R; Wallner, A; Ware, T; Weigand, M; Weiß, C; Wright, T J; Žugec, P

    2014-01-01

    The angular distribution of fragments emitted in neutron-induced fission of Th-232 was measured in the white spectrum neutron beam at the n\\_TOF facility at CERN. A reaction chamber based on Parallel Plate Avalanche Counters (PPAC) was used, where the detectors and the targets have been tilted 45 degrees with respect to the neutron beam direction in order to cover the full angular range of the fission fragments. A GEANT4 simulation has been developed to study the setup efficiency. The data analysis and the preliminary results obtained for the Th-232(n,f) between fission threshold and 100 MeV are presented here.

  13. Fission fragment mass and angular distribution in 6,7Li+235,238U reactions

    Fission fragment (FF) angular distributions for 6,7Li+235,238U reactions and mass distributions for 6,7Li+ 238U reactions have been measured at energies near and above the Coulomb barrier. The angle integrated fission cross sections for 6Li induced reactions at sub-barrier energies are found to be higher than 7Li induced reactions possibly due to larger contribution of breakup induced fission in case of the former compared to the latter. The FF anisotropy for 6,7Li+235U was found to be smaller than 6,7Li+238U, manifesting the effect of target ground state spin. The statistical saddle point (SSP) model predictions were found to be consistent with the measured FF anisotropy for 6,7Li+235U, however they were under-estimated for 6,7Li+238U particularly at lower energies. Observation of larger FWHM of FF folding angle distribution and sharp increase in peak to valley ratio for FF mass distribution with the decrease in bombarding energy in 6,7Li+238U reactions confirms the presence of breakup induced fission. (authors)

  14. Fission fragment mass and angular distribution in 6,7Li+235,238U reactions

    Santra S.

    2013-12-01

    Full Text Available Fission fragment (FF angular distributions for 6,7Li+235,238U reactions and mass distributions for 6,7Li+238U reactions have been measured at energies near and above the Coulomb barrier. The angle integrated fission cross sections for 6Li induced reactions at sub-barrier energies are found to be higher than 7Li induced reactions possibly due to larger contribution of breakup induced fission in case of the former compared to the latter. The FF anisotropy for 6,7Li+235U was found to be smaller than 6,7Li+238U, manifesting the effect of target ground state spin. The statistical saddle point (SSP model predictions were found to be consistent with the measured FF anisotropy for 6,7Li+235U, however they were under-estimated for 6,7Li+238U particularly at lower energies. Observation of larger FWHM of FF folding angle distribution and sharp increase in peak to valley ratio for FF mass distribution with the decrease in bombarding energy in 6,7Li+238U reactions confirms the presence of breakup induced fission.

  15. Contribution to the design, fulfillment, and data analysis of fission fragment yields of the SOFIA experiment at GSI

    The isotopic fission yields of U 238 following the SOFIA experiment, conducted at the GSI facility (Darmstadt), are presented here. This experiment takes advantage of the inverse kinematics technique at relativistic energies. Benefits are several: fission fragments are highly focused (high geometrical efficiency) and are also completely stripped, which greatly simplifies their nuclear charge measurement. The first detector of the SOFIA setup is an active target in which fission occurs via electromagnetic excitation, followed by an ionization chamber to measure the nuclear charge and the horizontal angle of both fission fragments. The masses are deduced by the bending radius measurement of the fragments, deflected by a strong magnet (ALADIN), thanks to two position detectors (MWPC), and also by a highly resolved time-of-flight measurement (40 ps FWHM) so that heavy neighboring isotopes can be separated. The data analysis shows that the main goals are achieved since the isotopic separation is reached over the whole range of the fission fragments. A strong even-odd effect is seen in the charge spectrum, which also exhibits a mean heavy charge close to Z = 54. Surprisingly, the neutron even-odd effect of the light region is seen to be very close to the one in thermal neutron induced fission. The peak-to-valley ratio of the mass spectrum confirms that the mean excitation energy at fission is close to the expected one (14 MeV). The GEF code is used for comparison and always gives results very close to ours. (author)

  16. Fragment properties from fission of actinide nuclei induced by 6-10 MeV bremsstrahlungI

    Gook, A.; Eckardt, C.; Enders, J.; Freudenberger, M.; von Neumann-Cosel, P.; Oberstedt, A.; Oberstedt, S.; Richter, A.

    Experiments to investigate the photon-induced fission of actinide nuclei at excitation energies in the vicinity of the fission barrier are carried out at the superconducting Darmstadt linear electron accelerator S-DALINAC. A twin-Frisch-grid ionization chamber is used to deduce mass, total kinetic energy, and angular distributions of the fission fragments. First experiments on 238U and 234U have shown that the experimental setup provides excellent conditions for investigating low-energy bremsstrahlung induced fission. Further experiments on 234U and 232Th are currently in progress. In this contribution results from the first experiment on fission fragment mass and total kinetic energy distributions from 234,238U are presented along with preliminary data from an on-going investigation of angular distributions from 234U(γ, f)

  17. From ground state to fission fragments: A complex, multi-dimensional multi-path problem

    Experimental results on the fission properties of nuclei close to 264Fm show sudden and large changes with a change of only one or two neutrons or protons. The nucleus 258Fm, for instance, undergoes symmetric fission with a half-life of about 0.4 ms and a kinetic-energy distribution peaked at about 235 MeV whereas 256Fm undergoes asymmetric fission with a half-life of about 3 h and a kinetic-energy distribution peaked at about 200 MeV. Qualitatively, these sudden changes have been postulated to be due to the emergence of fragment shells in symmetric-fission products close to 132Sn. Here we present a quantitative calculation that shows where high-kinetic-energy symmetric fusion occurs and why it is associated with a sudden and large decrease in fission half-lives. We base our study on calculations of potential-energy surfaces in the macroscopic-microscopic model and a semi-empirical model for the nuclear inertia. We use the three-quadratic-surface parameterization to generate the shapes for which the potential-energy surfaces are calculated. The use of this parameterization and the use of the finite-range macroscopic model allows for the study of two touching spheres and similar shapes. Since these shapes are thought to correspond to the scission shapes for the high-kinetic-energy events it is of crucial importance that a continuous sequence of shapes leading from the nuclear ground state to these configurations can be studied within the framework of the model. We present the results of the calculations in terms of potential-energy surfaces and fission half-lives for heavy even nuclei. The surfaces are displayed in the form of contour diagrams as functions of two moments of the shape. They clearly show the appearance of a second fission valley, which leads to scission configurations close to tow touching spheres, for fissioning systems in the vicinity of 264Fm

  18. New features of the FIFRELIN code for the investigation of fission fragments characteristics

    The characteristics of the fission fragments (FF) as well as those of the prompt neutrons and gammas can be deduced using FIFRELIN Monte Carlo simulation code. The quality of the results obviously depends on the experimental entry data, the theoretical and phenomenological models, and the various assumptions done in the code. The goal of this paper is to highlight new features of the code and to present some selected new results focusing on the use of a temperature-dependent spin cut-off, the prompt gamma de-excitation capability, a ROOT-based tool for the analysis of the FF histories, the estimation of correlated quantities, and so on. The influence of some experimental data on the neutron multiplicity and the influence of the level density parameter models on fission observables are also presented. Finally a preliminary result concerning the neutron spectrum for the 238U(n,f) reaction at 1.8 MeV is shown. (authors)

  19. Angular Distributions of U238 Fission Fragments Produced by Mono-Energetic Gamma Rays

    The angular distribution of U238 fission fragments has been measured using mica plates as detectors. The fission process was induced by mono-energetic gamma rays of the following discrete energies: 6.07, 6.75, 6.80, 7.38, 7.64, 7.73 and 9.00 MeV. The sources of mono-energetic gamma-rays were (n, γ ) reactions on seven different target elements in the SAPHIR reactor of the E.T.H. in Zurich. The gamma-ray line absolute intensities were of the order of 106 photons/cm2s. The neutron and gamma-ray backgrounds were estimated with a bismuth target. (author)

  20. The electron Boltzmann equation in a plasma generated by fission fragments

    Hassan, H. A.; Deese, J. E.

    1976-01-01

    A Boltzmann equation formulation is presented for the determination of the electron distribution function in a plasma generated by fission fragments. The formulation takes into consideration ambipolar diffusion, elastic and inelastic collisions, recombination and ionization, and allows for the fact that the primary electrons are not monoenergetic. Calculations for He in a tube coated with fissionable material show that, over a wide pressure and neutron flux range, the distribution function is non-Maxwellian, but the electrons are essentially thermal. Moreover, about a third of the energy of the primary electrons is transferred into the inelastic levels of He. This fraction of energy transfer is almost independent of pressure and neutron flux but increases sharply in the presence of a sustainer electric field.

  1. Angular distribution of fission fragments from 236U(d,pf)

    Complete text of publication follows. 236U is the only isotope in the actinide region in which transmission fission resonances observed and at the same time a superdeformed fission isomer is well-established. We have been investigating these transmission resonances for several years. The aim of our latest experiment was to measure the angular distribution of the fission fragments in order to determine the spin and K-values of the resonances and to improve the statistics compared to the previous experiment. An experiment was performed to study the fission resonances of 236U at the Munich Tandem Laboratory using 235U(d,p) reaction at 13 MeV. A 235U2O3 target was used with a thickness of 90 μg/cm2. The outgoing proton energy was determined by a Q3D magnetic spectrometer at an angle 139.4 deg. An energy resolution of ΔE = 5keV was achieved. Fission fragments were detected by two position sensitive avalanche detectors (PSAD) consisting of two wire planes corresponding to horizontal and vertical directions. Thus, the spatial positions of the fragments and their angular correlation with respect to the recoil axis could be determined. High resolution measurement of the angular distribution allowed us to determine the spin and K-values of the observed resonances individually. The angular correlation was parametrized with coefficients a2 and a4 of even Legendre polynomials. Fig. 1b) shows the a2 coefficient belonging to the different resonances. The a2 values are agree with the values of Ref. [4], which were used to determine the K-values in the data analysis of the previous experiment. The most interesting energy region is around 5.1 MeV, where hyperdeformed resonances were identified recently in contrast to the superdeformed interpretation published so far. The high-resolution excitation energy spectrum, which was deduced from the proton kinetic energy is shown in Fig. 1a). A combined analysis of the energy spectrum and the angular distribution confirms that the

  2. Fission Fragment Mass Distributions and Total Kinetic Energy Release of 235-Uranium and 238-Uranium in Neutron-Induced Fission at Intermediate and Fast Neutron Energies

    Duke, Dana Lynn [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2015-11-12

    This Ph.D. dissertation describes a measurement of the change in mass distributions and average total kinetic energy (TKE) release with increasing incident neutron energy for fission of 235U and 238U. Although fission was discovered over seventy-five years ago, open questions remain about the physics of the fission process. The energy of the incident neutron, En, changes the division of energy release in the resulting fission fragments, however, the details of energy partitioning remain ambiguous because the nucleus is a many-body quantum system. Creating a full theoretical model is difficult and experimental data to validate existing models are lacking. Additional fission measurements will lead to higher-quality models of the fission process, therefore improving applications such as the development of next-generation nuclear reactors and defense. This work also paves the way for precision experiments such as the Time Projection Chamber (TPC) for fission cross section measurements and the Spectrometer for Ion Determination in Fission (SPIDER) for precision mass yields.

  3. Towards the high spin–isospin frontier using isotopically-identified fission fragments

    Measurements of prompt γ rays in coincidence with isotopically-identified fission fragments, produced in collisions of 238U on a 9Be target, at an energy around the Coulomb barrier are reported. This technique provides simultaneous access to the spectroscopy of many nuclei, extending to very neutron-rich isotopes and fairly high angular momenta. The structural evolution of the neutron-rich zirconium isotopes is discussed in the light of the present measurements in 105,106Zr and in the context of the interacting boson model with a global parameterization that includes triaxiality but no shape coexistence

  4. Atomic mass identification of CF-252 fission fragments using an NE-102 thin film detector

    The measurement of atomic number of low energy Cf-252 fission products using a three element thin film scintillation detector in conjunction with a residual energy solid state detector is described. Critical comparison of the separate spectra yielded by the three thin film elements is used to show both quantitative and qualitative consistency. Through the use of simple data handling techniques, increased resolution between peaks is easily obtained; the resultant spectrum for the distribution of both heavy and light fragments of Cf-252 is presented. The anticipated application of thin film scintillation techniques for event-by-event illucidation of decay schemes will also be discussed

  5. Fission fragment mass distribution studies in 30Si +180Hf reaction

    Shamlath, A.; Shareef, M.; Prasad, E.; Sugathan, P.; Thomas, R. G.; Jhingan, A.; Appannababu, S.; Nasirov, A. K.; Vinodkumar, A. M.; Varier, K. M.; Yadav, C.; Babu, B. R. S.; Nath, S.; Mohanto, G.; Mukul, Ish; Singh, D.; Kailas, S.

    2016-01-01

    Fission fragment mass-angle and mass ratio distributions have been measured for the 30Si + 180Hf reaction in the beam energy range 128-148 MeV. Quasifission signature is observed in this reaction, forming the compound system 210Rn. The results are compared with a very asymmetric reaction 16O + 194Pt, forming the same compound nucleus. Calculations assuming saddle point, scission point and DNS models have been performed to interpret the experimental results. The results strongly suggest the entrance channel dependence of quasifission in heavy ion collisions.

  6. Yield of Prompt Gamma Radiation in Slow-Neutron Induced Fission of 235U a a Function of the Total Fragment Kinetic Energy

    Fission gamma radiation yields as functions of the total fragment kinetic energy were obtained for 235U thermal-neutron induced fission. The fragments were detected with silicon surface-barrier detectors and the gamma radiation with a Nal(Tl) scintillator. In some of the measurements mass selection was used so that the gamma radiation could also be measured as a function of fragment mass. Time discrimination between the fission gammas and the prompt neutrons released in the fission process was employed to reduce the background. The gamma radiation emitted during different time intervals after the fission event was studied with the help of a collimator, the position of which was changed along the path of the fission fragments. Fission-neutron and gamma-ray data of previous experiments were used for comparisons of the yields, and estimates were made of the variation of the prompt gamma-ray energy with the total fragment kinetic energy

  7. Radiogenotoxicological effect of fission fragment 147Pm on BALB/C mice

    The purpose of the present study is to ascertain the radiogenotoxicological effect, such as chromosome aberration, sister chromatid exchange and micronucleus formation in bone marrow cells induced by fission fragment 147Pm. 42 male BALB/C strain mice were used. Results indicated that the chromosome aberration rates were elevated along with increasing doses of 147Pm. It showed a linear relationship between dose and effect: Y = -4.403 + 1.435 Ln X. Five aberrations in one cell could be induced. This phenomenon might be partly due to nonuniform irradiation of bone marrow cells by local deposition of 147Pm. Chromatid type of chromosome aberrations could also be observed. Chromatid breakages were predominatnt, accompanied by a few chromosome fragments and translocations. The micronucleus rates were also elevated with the increase of contamination dose of 147Pm

  8. Determination of Nuclear Charge Distributions of Fission Fragments from ^{235} U (n_th , f) with Calorimetric Low Temperature Detectors

    Grabitz, P.; Andrianov, V.; Bishop, S.; Blanc, A.; Dubey, S.; Echler, A.; Egelhof, P.; Faust, H.; Gönnenwein, F.; Gomez-Guzman, J. M.; Köster, U.; Kraft-Bermuth, S.; Mutterer, M.; Scholz, P.; Stolte, S.

    2016-03-01

    Calorimetric low temperature detectors (CLTD's) for heavy-ion detection have been combined with the LOHENGRIN recoil separator at the ILL Grenoble for the determination of nuclear charge distributions of fission fragments produced by thermal neutron-induced fission of ^{235} U. The LOHENGRIN spectrometer separates fission fragments according to their mass-to-ionic-charge ratio and their kinetic energy, but has no selectivity with respect to nuclear charges Z. For the separation of the nuclear charges, one can exploit the nuclear charge-dependent energy loss of the fragments passing through an energy degrader foil (absorber method). This separation requires detector systems with high energy resolution and negligible pulse height defect, as well as degrader foils which are optimized with respect to thickness, homogeneity, and energy loss straggling. In the present, contribution results of test measurements at the Maier Leibnitz tandem accelerator facility in Munich with ^{109} Ag and ^{127} I beams with the aim to determine the most suitable degrader material, as well as measurements at the Institut Laue-Langevin will be presented. These include a systematic study of the quality of Z-separation of fission fragments in the mass range 82≤ A ≤ 132 and a systematic measurement of ^{92} Rb fission yields, as well as investigations of fission yields toward the symmetry region.

  9. Determination of Nuclear Charge Distributions of Fission Fragments from ^{235}U (n_th, f) with Calorimetric Low Temperature Detectors

    Grabitz, P.; Andrianov, V.; Bishop, S.; Blanc, A.; Dubey, S.; Echler, A.; Egelhof, P.; Faust, H.; Gönnenwein, F.; Gomez-Guzman, J. M.; Köster, U.; Kraft-Bermuth, S.; Mutterer, M.; Scholz, P.; Stolte, S.

    2016-08-01

    Calorimetric low temperature detectors (CLTD's) for heavy-ion detection have been combined with the LOHENGRIN recoil separator at the ILL Grenoble for the determination of nuclear charge distributions of fission fragments produced by thermal neutron-induced fission of ^{235}U. The LOHENGRIN spectrometer separates fission fragments according to their mass-to-ionic-charge ratio and their kinetic energy, but has no selectivity with respect to nuclear charges Z. For the separation of the nuclear charges, one can exploit the nuclear charge-dependent energy loss of the fragments passing through an energy degrader foil (absorber method). This separation requires detector systems with high energy resolution and negligible pulse height defect, as well as degrader foils which are optimized with respect to thickness, homogeneity, and energy loss straggling. In the present, contribution results of test measurements at the Maier Leibnitz tandem accelerator facility in Munich with ^{109}Ag and ^{127}I beams with the aim to determine the most suitable degrader material, as well as measurements at the Institut Laue-Langevin will be presented. These include a systematic study of the quality of Z-separation of fission fragments in the mass range 82le A le 132 and a systematic measurement of ^{92}Rb fission yields, as well as investigations of fission yields toward the symmetry region.

  10. SPY: a new scission-point model based on microscopic inputs to predict fission fragment properties

    Panebianco Stefano

    2014-04-01

    Full Text Available Despite the difficulty in describing the whole fission dynamics, the main fragment characteristics can be determined in a static approach based on a so-called scission-point model. Within this framework, a new Scission-Point model for the calculations of fission fragment Yields (SPY has been developed. This model, initially based on the approach developed by Wilkins in the late seventies, consists in performing a static energy balance at scission, where the two fragments are supposed to be completely separated so that their macroscopic properties (mass and charge can be considered as fixed. Given the knowledge of the system state density, averaged quantities such as mass and charge yields, mean kinetic and excitation energy can then be extracted in the framework of a microcanonical statistical description. The main advantage of the SPY model is the introduction of one of the most up-to-date microscopic descriptions of the nucleus for the individual energy of each fragment and, in the future, for their state density. These quantities are obtained in the framework of HFB calculations using the Gogny nucleon-nucleon interaction, ensuring an overall coherence of the model. Starting from a description of the SPY model and its main features, a comparison between the SPY predictions and experimental data will be discussed for some specific cases, from light nuclei around mercury to major actinides. Moreover, extensive predictions over the whole chart of nuclides will be discussed, with particular attention to their implication in stellar nucleosynthesis. Finally, future developments, mainly concerning the introduction of microscopic state densities, will be briefly discussed.

  11. SPY: a new scission-point model based on microscopic inputs to predict fission fragment properties

    Despite the difficulty in describing the whole fission dynamics, the main fragment characteristics can be determined in a static approach based on a so-called scission-point model. Within this framework, a new Scission-Point model for the calculations of fission fragment Yields (SPY) has been developed. This model, initially based on the approach developed by Wilkins in the late seventies, consists in performing a static energy balance at scission, where the two fragments are supposed to be completely separated so that their macroscopic properties (mass and charge) can be considered as fixed. Given the knowledge of the system state density, averaged quantities such as mass and charge yields, mean kinetic and excitation energy can then be extracted in the framework of a microcanonical statistical description. The main advantage of the SPY model is the introduction of one of the most up-to-date microscopic descriptions of the nucleus for the individual energy of each fragment and, in the future, for their state density. These quantities are obtained in the framework of HFB calculations using the Gogny nucleon-nucleon interaction, ensuring an overall coherence of the model. Starting from a description of the SPY model and its main features, a comparison between the SPY predictions and experimental data will be discussed for some specific cases, from light nuclei around mercury to major actinides. Moreover, extensive predictions over the whole chart of nuclides will be discussed, with particular attention to their implication in stellar nucleosynthesis. Finally, future developments, mainly concerning the introduction of microscopic state densities, will be briefly discussed. (author)

  12. SPY: a new scission-point model based on microscopic inputs to predict fission fragment properties

    Panebianco, Stefano; Lemaître, Jean-Francois; Sida, Jean-Luc [CEA Centre de Saclay, Gif-sur-Ivette (France); Dubray, Noëel [CEA, DAM, DIF, Arpajon (France); Goriely, Stephane [Institut d' Astronomie et d' Astrophisique, Universite Libre de Bruxelles, Brussels (Belgium)

    2014-07-01

    Despite the difficulty in describing the whole fission dynamics, the main fragment characteristics can be determined in a static approach based on a so-called scission-point model. Within this framework, a new Scission-Point model for the calculations of fission fragment Yields (SPY) has been developed. This model, initially based on the approach developed by Wilkins in the late seventies, consists in performing a static energy balance at scission, where the two fragments are supposed to be completely separated so that their macroscopic properties (mass and charge) can be considered as fixed. Given the knowledge of the system state density, averaged quantities such as mass and charge yields, mean kinetic and excitation energy can then be extracted in the framework of a microcanonical statistical description. The main advantage of the SPY model is the introduction of one of the most up-to-date microscopic descriptions of the nucleus for the individual energy of each fragment and, in the future, for their state density. These quantities are obtained in the framework of HFB calculations using the Gogny nucleon-nucleon interaction, ensuring an overall coherence of the model. Starting from a description of the SPY model and its main features, a comparison between the SPY predictions and experimental data will be discussed for some specific cases, from light nuclei around mercury to major actinides. Moreover, extensive predictions over the whole chart of nuclides will be discussed, with particular attention to their implication in stellar nucleosynthesis. Finally, future developments, mainly concerning the introduction of microscopic state densities, will be briefly discussed. (author)

  13. On some uses of the recording op fission fragments occurring in insulators

    The passage of fission fragments is manifested in insulators by the formation of damage lines which can easily be observed by transparence using the electron microscope after a suitable chemical attack. Since the recording efficiency is 100 per cent for mica and plastics this phenomenon has a certain number of applications. After briefly recalling the interaction processes between charged particles and matter, and giving a quantitative study of the relationships connecting the various parameters, the author considers here some of these applications: - thermal neutron dosimetry: it is possible to measure integrated fluxes of between lO3 and 1021 n/cm2, according to the method used; - fast neutron dosimetry: by using fission fragment threshold sources it is easy to measure biological type doses of about 1 rem: - dosage of very low fissile impurity concentrations: atomic concentrations of about 10-9; can be measured; this limit has never been attained by conventional methods; - study of fissile elements occurring in atmospheric dusts. Results are then briefly given of an automated counting test for traces effected by measuring the electrical resistivity, of the irradiated membrane. Finally are given the advantages and disadvantages of these solid detectors, especially with respect to nuclear emulsions whose uses are approximately identical. (author)

  14. A Monte Carlo simulation of prompt gamma emission from fission fragments

    The prompt fission gamma spectra and multiplicities are investigated through the Monte Carlo code FIFRELIN which is developed at the Cadarache CEA research center. Knowing the fully accelerated fragment properties, their de-excitation is simulated through a cascade of neutron, gamma and/or electron emissions. This paper presents the recent developments in the FIFRELIN code and the results obtained on the spontaneous fission of 252Cf. Concerning the decay cascades simulation, a fully Hauser-Feshbach model is compared with a previous one using a Weisskopf spectrum for neutron emission. A particular attention is paid to the treatment of the neutron/gamma competition. Calculations carried out using different level density and gamma strength function models show significant discrepancies of the slope of the gamma spectra at high energy. The underestimation of the prompt gamma spectra obtained regardless our de-excitation cascade modeling choice is discussed. This discrepancy is probably linked to an underestimation of the post-neutron fragments spin in our calculation. (authors)

  15. A Monte Carlo Simulation of Prompt Gamma Emission from Fission Fragments

    Litaize O.

    2013-03-01

    Full Text Available The prompt fission gamma spectra and multiplicities are investigated through the Monte Carlo code FIFRELIN which is developed at the Cadarache CEA research center. Knowing the fully accelerated fragment properties, their de-excitation is simulated through a cascade of neutron, gamma and/or electron emissions. This paper presents the recent developments in the FIFRELIN code and the results obtained on the spontaneous fission of 252Cf. Concerning the decay cascades simulation, a fully Hauser-Feshbach model is compared with a previous one using a Weisskopf spectrum for neutron emission. A particular attention is paid to the treatment of the neutron/gamma competition. Calculations lead using different level density and gamma strength function models show significant discrepancies of the slope of the gamma spectra at high energy. The underestimation of the prompt gamma spectra obtained regardless our de-excitation cascade modeling choice is discussed. This discrepancy is probably linked to an underestimation of the post-neutron fragments spin in our calculation.

  16. A Monte Carlo Simulation of Prompt Gamma Emission from Fission Fragments

    Regnier, D.; Litaize, O.; Serot, O.

    2013-03-01

    The prompt fission gamma spectra and multiplicities are investigated through the Monte Carlo code FIFRELIN which is developed at the Cadarache CEA research center. Knowing the fully accelerated fragment properties, their de-excitation is simulated through a cascade of neutron, gamma and/or electron emissions. This paper presents the recent developments in the FIFRELIN code and the results obtained on the spontaneous fission of 252Cf. Concerning the decay cascades simulation, a fully Hauser-Feshbach model is compared with a previous one using a Weisskopf spectrum for neutron emission. A particular attention is paid to the treatment of the neutron/gamma competition. Calculations lead using different level density and gamma strength function models show significant discrepancies of the slope of the gamma spectra at high energy. The underestimation of the prompt gamma spectra obtained regardless our de-excitation cascade modeling choice is discussed. This discrepancy is probably linked to an underestimation of the post-neutron fragments spin in our calculation.

  17. Fragment angular momenta and descent dynamics in sup 2 sup 5 sup 2 Cf spontaneous fission

    Popeko, J S; Ter-Akopian, G M

    2002-01-01

    Average angular momentum values of primary fission fragments as a function of neutron multiplicity and neutron-to-proton ratio were extracted for the first time for the Mo-Ba and Zr-Ce charge splittings of sup 2 sup 5 sup 2 Cf. The results are discussed in terms of the energy balance occurring at the scission point. For the first time we show that for large fragment elongation associated with larger numbers of evaporated neutrons (v sub t sub o sub t >=6), essentially only zero point bending oscillation takes places, i.e. T = 0 for this degree of freedom. For the major part of the fission events, with v sub t sub o sub t = 2-5, the banding oscillation is excited to a temperature of 2-3 MeV. Such a high bending temperature implies that the coupling between the collective and internal degrees of freedom is weak at the descent of the even-even nucleus of sup 2 sup 5 sup 2 Cf to the scission point. The dipole oscillations occurring at the descent take away some 2.5 - 3.0 MeV from the release energy. A correlation...

  18. The detection of tracks of fission fragments on one-sided aluminized polyester

    The polymeric or solid state nuclear track detectors are able to detect and register the tracks of high energy charged particles such as alpha, proton and neutron, by chemical or electrochemical etching processes under particular conditions. In this paper, the tracks of fission fragments are studied on polyester film with six micron thickness which is coated by a thin Al. layer at one side. A chamber with two cells are used for chemical etching where the film is inserted as the wall between two isolated cells. The cell which faces to Al. side is filled with etchant and the other cell filled with liquid dielectric. The etchant reaches Al. layer whenever each track etching process completes, then traces of etched tracks on Al. layer may be counted even by naked eye. The optimum parameters of etching time, electric field, etchant and liquid dielectric are determined and the magnification of Al. layer in development of tracks of fission fragments are studied. It is also found that there is a linear relationship between counted tracks density and exposure time, until the saturation occurs

  19. Multiplicity and energy of neutrons from {sup 233}U(n{sub th},f) fission fragments

    Nishio, Katsuhisa; Kimura, Itsuro; Nakagome, Yoshihiro [Kyoto Univ. (Japan)

    1998-03-01

    The correlation between fission fragments and prompt neutrons from the reaction {sup 233}U(n{sub th},f) was measured with improved accuracy. The results determined the neutron multiplicity and emission energy as a function of fragment mass and total kinetic energy. The average energy as a function of fragment mass followed a nearly symmetric distribution centered about the equal mass-split and formed a remarkable contrast with the saw-tooth distribution of the average neutron multiplicity. The neutron multiplicity from the specified fragment decreases linearly with total kinetic energy, and the slope of multiplicity with kinetic energy had the minimum value at about 130 u. The level density parameter versus mass determined from the neutron data showed a saw-tooth structure with the pronounced minimum at about 128 and generally followed the formula by Gilbert and Cameron, suggesting that the neutron emission process was very much affected by the shell-effect of the fission fragment. (author)

  20. Partition between the fission fragments of the excitation energy and of the neutron multiplicity at scission in low-energy fission

    Carjan, N.; Hambsch, F.-J.; Rizea, M.; Serot, O.

    2012-04-01

    The partition between the light (L) and the heavy (H) fission fragments of the excitation energy available at scission is studied in the framework of the sudden approximation, i.e., under the assumption that the neck rupture and the absorption of the neck pieces by the fragments happen infinitely fast. We are dealing with a sudden transition between two different nuclear configurations (αi→αf) and we only need to know the two sets of neutron eigenstates involved. The accent in the present work is put on the dependence of this share of energy on the mass asymmetry AL/AH of the primary fission fragments during the low-energy fission of 236U. In particular, for every fragment mass A we estimate the scission neutron multiplicity νsc, the average energy cost for their release , the primary fragments' excitation energy Esc*, and the corresponding temperature Tsc. The results are analyzed separately for each value of Ω (the projection of the angular momentum on the symmetry axis). As general trends, a decrease of Esc* (Tsc) and an increase of νsc () with increasing A were observed.

  1. Measurement of isotopic cross sections of the fission fragments produced in 500 AMeV 208Pb + p reaction

    The aim of this work is the study of the fission fragments produced in the spallation reaction 208Pb + p at 500 AMeV. The fission fragments from Z=23 up to Z=59 have been detected and identified by using the inverse kinematics technique with the high-resolution spectrometer FRS. The production cross sections and the recoil velocities of 430 nuclei have been measured. The measured data have been compared with previous data. The isotopic distributions show a high precision. However, the absolute value of the fission cross section is higher than expected. From the experimental data the characteristics of the average fissioning system have been reconstructed (Zfis, Afis, E*fis). In addition, the number of post-fission neutrons emitted from the fission fragments, vpost, has been determined by using a new method. The experimental data have been compared to the two-steps models describing the spallation reaction. The impact of the model parameters on the observables has been analysed and the reasons Leading to the observed differences between the codes are also presented. This analyse shows a good agreement with the INCL4+ABLA code. (author)

  2. Study of binary fragmentation and compound nucleus sion in the fission reaction 50Ti + 208Pb

    The synthesis of super-heavy elements (She's) continues to be one of premiere frontiers of nuclear physics. There have been several reports on the production of super-heavy nuclei using different target-projectile combinations using cold fusion reactions by the observation of evaporation residues. However, the sion path in these reactions has not been investigated in full detail. The sion characteristics of the super-heavy nuclei can be studied through binary fragmentation reactions in the exit channel of suitably selected heavy ion reactions, provided that the binary fragmentations resulting from the f sion of compound nucleus can be separated from those resulting from non-compound processes. Further recent experimental data on cold fusion reactions leading to the formation of super-heavy nuclei with Z≤ 113 shows a strong dependence on coulomb parameter. In order to further investigate the dynamics of binary fragmentation and fusion-fission of super-heavy systems, we carried out detailed investigation of fragment mass vs total kinetic energy distribution and neutron emission in the 294 MeV 50Ti + 208Pb reaction, leading to the formation of the super-heavy nucleus 258Rf, for which residues have been experimentally observed. Two Time of Flight arms based on position sensitive MCP detectors were used to catch the two complementary fragments providing a full kinematics reconstruction of the event. The emitted neutrons were detected by using an array of BC501 liquid scintillators. The neutron energy was determined by measuring the time of flight (TOF) with respect to the MCP start signal. A custom digital acquisition system was used. Preliminary results will be presented and discussed

  3. Irradiation effects in fused quartz 'Suprasil' as a detector of fission fragments under high flux of reactor neutrons

    A systematic study about the registration characteristics of synthetic fused quartz 'Suprasil I' use as a detector of fission fragments under high flux of reactor neutrons and the effects of irradiation on it was performed. Fission fragments of 252Cf, gamma radiation doses of of 60Co up to 150 MGy, and integrated neutrons fluxes up to 1020 n/cm2 were used. A model to explain the effects on track registration and development characteristics of 'Suprasil I' irradiated on reactors were proposed, based on the obtained results for efficiency an for annealing. (C.G.C.)

  4. The etching property of the surface of CR-39 and the track core radius of fission fragment

    Mineyama, D; Yamauchi, T; Oda, K; El-Rahman, A

    2002-01-01

    The etch pits of fission fragments in CR-39 detector have been observed carefully using an atomic force microscope (AFM) after extremely short chemical etching in stirred 6N KOH solution kept at 70degC. It was found that there existed a thin layer where the bulk etch rate is relativity from large the etch-pit growth curve for the etching duration between 10 and 1800 seconds. The track core radius of fission fragment was evaluated to be about 6 nm from the extrapolation of the growth curve in a thinner region. (author)

  5. Primary Distributions of Nuclear Charge for Fission-Fragment Masses 132, 134, 136 and 137 from Thermal Fission of U235

    By a mass spectrometer fission fragments from thermal fission of U235 are exactly separated with respect to mass and kinetic energy within a time of 10-6 s after fission. The separated fragments are caught in a β-sensitive Ilford G 5 emulsion that is located in the focal plane of the spectrometer. Development of the irradiated emulsions is carried out, if possible, after a time long compared with the longest half-life of the regarded decay chain. Half-lives of days or longer are not taken into account, but corrections can be easily made for them. After development of the emulsions all beta tracks emerging from the end of every fission-fragment track can be seen under the microscope. The possibility of correlating every single β-track with a particular fission-fragment track allows the evaluation of the number n(x) of fission fragments possessing x β-tracks, thus giving not only the mean chain length but also the β-particle distribution. As the stable end product of each decay chain is known, this β-distribution is an exact image of the primary nuclear charge distribution. In the measurements done up to now only β-particles emitted into the half solid angle formed by the emulsion plate were registered, buta simple statistical calculation enables the desired 4π-distribution to be evaluated. By this method β-distributions at fixed kinetic energies near the mean kinetic energy of each fragment mass are given for the masses 132, 134, 136 and 137. For the lower masses 132 and 134 the neutron shell N = 82 is responsible for the most probable primary charges near 50 and 52 respectively. For M = 136 and 137 the primary charge is about 53 and 53.2. Additional approximative corrections in respect of conversion electrons (by omitting very short β-tracks corresponding to very low β-energies) and to delayed neutrons (for mass 137) were not very large. Similar measurements carried out directly in 4π—geometry to avoid the statistical error arising from the

  6. Study of near-stability nuclei populated as fission fragments in heavy-ion fusion reactions

    Examples are presented to illustrate the power of prompt γ-ray spectroscopy of fission fragments from compound nuclei with A ∼ 200 formed in fusion-evaporation reactions in experiments using the Gammasphere Ge-detector array. Complementary methods, such as Coulomb excitation and deep-inelastic processes, are also discussed. In other cases (n, xnγ) reactions on stable isotopes have been used to establish neutron excitation functions for γ-rays using a pulsed 'white'-neutron source, coupled to a high-energy-resolution germanium-detector array. The excitation functions can unambiguously assign γ-rays to a specific reaction product. Results from all these methods bridge the gaps in the systematics of high-spin states between the neutron-deficient and neutron-rich nuclei. Results near shell closures should motivate new shell model calculations.

  7. Fission fragment charge and mass distributions in 239Pu(n ,f ) in the adiabatic nuclear energy density functional theory

    Regnier, D.; Dubray, N.; Schunck, N.; Verrière, M.

    2016-05-01

    Background: Accurate knowledge of fission fragment yields is an essential ingredient of numerous applications ranging from the formation of elements in the r process to fuel cycle optimization for nuclear energy. The need for a predictive theory applicable where no data are available, together with the variety of potential applications, is an incentive to develop a fully microscopic approach to fission dynamics. Purpose: In this work, we calculate the pre-neutron emission charge and mass distributions of the fission fragments formed in the neutron-induced fission of 239Pu using a microscopic method based on nuclear density functional theory (DFT). Methods: Our theoretical framework is the nuclear energy density functional (EDF) method, where large-amplitude collective motion is treated adiabatically by using the time-dependent generator coordinate method (TDGCM) under the Gaussian overlap approximation (GOA). In practice, the TDGCM is implemented in two steps. First, a series of constrained EDF calculations map the configuration and potential-energy landscape of the fissioning system for a small set of collective variables (in this work, the axial quadrupole and octupole moments of the nucleus). Then, nuclear dynamics is modeled by propagating a collective wave packet on the potential-energy surface. Fission fragment distributions are extracted from the flux of the collective wave packet through the scission line. Results: We find that the main characteristics of the fission charge and mass distributions can be well reproduced by existing energy functionals even in two-dimensional collective spaces. Theory and experiment agree typically within two mass units for the position of the asymmetric peak. As expected, calculations are sensitive to the structure of the initial state and the prescription for the collective inertia. We emphasize that results are also sensitive to the continuity of the collective landscape near scission. Conclusions: Our analysis confirms

  8. Measurement of Absolute Cross-Sections of Fission Induced by 156-MeV Protons, Using Mica as a Fission Fragment Detector

    The fission of elements of medium Z induced by 156-MeV protons is difficult to demonstrate, owing to the particularly small cross-section of the reaction. The detection of fission fragments by means of sheets of mica seemed to be a technique well suited to this type of experiment. In the sheets of synthetic mica that we used it was only the fission fragments that left microscopically identifiable traces. Moreover, these samples contain very few impurities likely to undergo fission, so practically no parasitic traces are observed. The targets consisted of metals of not less than 99.999% purity. We determined the absolute cross-sections.of fission induced by 156-MeV protons in the case of lanthanum (5 μb) and praseodymium (6 μb), and estimated those of cadmium, indium, tin and antimony (≤ 0.1 μb). The sheets of mica were placed on each side of the metal sheet. The kinetics of the reaction explain why more traces were found on the mica sheets placed on the from face. As thick targets were used to take account of self-absorption, we determined (in the case of uranium and gold) the ratio of yields between a thin target and a thick target, and then extrapolated our results to the other elements. We made checks by comparing the absolute cross-sections for fission (induced by 156-MeV protons) in uranium, bismuth, gold and tantalum, as obtained by this method, with those obtained by counters at this energy. The observed agreement was very good. (author)

  9. Determination of 2> from fission fragment anisotropy for reactions involving weakly bound 6,7Li projectiles

    Fission fragment (FF) angular distributions for 6,7Li+235,238U reactions and FF mass distributions for 6,7Li+238U reactions have been measured at energies around the Coulomb barrier and reported in earlier symposia. The aim is to investigate the effect of projectile breakup on various observables in fission reactions. Due to low breakup threshold there is a probability of breakup of the projectiles which in turn may affect the compound nucleus (CN) formation cross section. In the present study it is proposed to determine the 2 > from the measured fission fragment anisotropy and compare them with the ones obtained from coupled channels calculations to investigate the effect of projectile breakup

  10. On the possibilities and accuracy of fission fragment characteristics measuring by the method of semiconductor gamma spectrometry

    A method for determining the semiconductor detector absolute efficiency, based on the application radioactive nuclide γ radiation in the decay chains of spontaneous fissionable 252Cf fragments is proposed. Proceeding from the values of half-lives of the nuclides used and choosing the irradiation regimes according to gamma spectrum measurement data, the absolute efficiency is calculated. 8 refs.; 1 fig.; 1 tab

  11. Study of the mass, nuclear charge and kinetic energy distribution of the fission fragments produced in the reaction 237 Np (2n th, f)

    In this work, we report fission fragment mass, energy and charge distributions measured for the fissioning nucleus: 239 Np 146, This odd Z nucleus is formed after double thermal neutron capture on to the 237 Np 144 target nucleus. These measurements were performed at the I.L.L. recoil mass spectrometer ''Lohengrin'' in Grenoble. The fission fragments were registered by an ionisation chamber placed at the focal plane of the spectrometer. The obtained distributions are compared to the 240 Pu 146 fragment mass, energy and charge distributions. They are discussed within the Wilkins' scission-point model. Cold fission has been studied while selecting fragmentations with final kinetic energies close to the maximum energy released in the reaction. These cold fission events are discussed according to a calculation based on the Wilkins' scission-point model extrapolated to the cold fragmentation case. 51 refs

  12. Determination of nuclear charge resolution of a thin film detector using a 252Cf fission fragment source

    Little quantitative information is available regarding the ability of a thin film detector (TFD) to determine the nuclear charge of a low energy heavy mass ion. To compare the nuclear charge resolving power Z/ΔZ of the TFD to other heavy ion detectors, an experiment was performed where the TFD luminescence response to 252Cf fission fragments was recorded in coincidence with the gamma de-excitation of the fragments. With this technique, the TFD nuclear charge resolving power Z/ΔZ was determined to be 25.2 for the light mass fragment group. (orig.)

  13. Determination of nuclear charge resolution of a thin film detector using a [sup 252]Cf fission fragment source

    Milosevich, Z.; Muga, M.L. (Florida Univ., Gainesville, FL (United States). Dept. of Chemistry); Coldwell, R.L. (Florida Univ., Gainesville, FL (United States). Dept. of Physics)

    1992-09-15

    Little quantitative information is available regarding the ability of a thin film detector (TFD) to determine the nuclear charge of a low energy heavy mass ion. To compare the nuclear charge resolving power Z/[Delta]Z of the TFD to other heavy ion detectors, an experiment was performed where the TFD luminescence response to [sup 252]Cf fission fragments was recorded in coincidence with the gamma de-excitation of the fragments. With this technique, the TFD nuclear charge resolving power Z/[Delta]Z was determined to be 25.2 for the light mass fragment group. (orig.).

  14. Monte-Carlo simulation for fragment mass and kinetic energy distributions from neutron induced fission of 235U

    Montoya, M; Rojas, J

    2007-01-01

    The mass and kinetic energy distribution of nuclear fragments from thermal neutron induced fission of 235U have been studied using a Monte-Carlo simulation. Besides reproducing the pronounced broadening on the standard deviation of the final fragment kinetic energy distribution $\\sigma_{e}(m)$ around the mass number m = 109, our simulation also produces a second broadening around m = 125, that is in agreement with the experimental data obtained by Belhafaf et al. These results are consequence of the characteristics of the neutron emission, the variation in the primary fragment mean kinetic energy and the yield as a function of the mass.

  15. Monte-Carlo simulation for fragment mass and kinetic energy distributions from neutron-induce fission of 235U

    The mass and kinetic energy distribution of nuclear fragments after neutron-induced fission of 235U have been studied using a Monte-Carlo simulation. Besides reproducing the pronounced peak in the standard deviation of the kinetic energy σE(m) at the fragment mass number around m=109, our simulation also produces a second peak at about m=126. These results are in good agreement with experimental data obtained by Belhafaf et.al. We conclude that the obtained results are consequence of the characteristics of the fragments' neutron evaporation and of the sharp variation on the primary mass yield curve. (orig.)

  16. Effect of transverse vibrations of fissile nuclei on the angular and spin distributions of low-energy fission fragments

    Bunakov, V. E.; Kadmensky, S. G.; Lyubashevsky, D. E.

    2016-05-01

    It is shown that A. Bohr's classic theory of angular distributions of fragments originating from low-energy fission should be supplemented with quantum corrections based on the involvement of a superposition of a very large number of angular momenta L m in the description of the relative motion of fragments flying apart along the straight line coincidentwith the symmetry axis. It is revealed that quantum zero-point wriggling-type vibrations of the fissile system in the vicinity of its scission point are a source of these angular momenta and of high fragment spins observed experimentally.

  17. Spectroscopy of correlated fragments from the fission of hot nuclei performed at the FOBOS 4π-array

    Investigations of the decay of hot nuclei with mass A∼200 at excitation energies of 200/600 AMeV are presently carried out at the 4π-facility FOBOS at JINR Dubna. Main efforts are directed to the spectroscopy of correlated fragments from fission accompanied with the emission of intermediate mass fragments and light charged particles. The low registration threshold of the detector array allows registration of masses up to heavy residues. From the independent measurement of the fragment momenta the transferred linear momentum can be determined. It is a considerable good measure for the excitation energy of the composite system after the incomplete fusion reaction. (orig.)

  18. Fission Fragment Angular Distribution measurements of 235U and 238U at CERN n_TOF facility

    Leal-Cidoncha, E.; Durán, I.; Paradela, C.; Tarrío, D.; Leong, L. S.; Tassan-Got, L.; Audouin, L.; Altstadt, S.; Andrzejewski, J.; Barbagallo, M.; Bécares, V.; Bečvář, F.; Belloni, F.; Berthoumieux, E.; Billowes, J.; Boccone, V.; Bosnar, D.; Brugger, M.; Calviani, M.; Calviño, F.; Cano-Ott, D.; Carrapiço, C.; Cerutti, F.; Chiaveri, E.; Chin, M.; Colonna, N.; Cortés, G.; Cortés-Giraldo, M. A.; Diakaki, M.; Domingo-Pardo, C.; Dressler, R.; Dzysiuk, N.; Eleftheriadis, C.; Ferrari, A.; Fraval, K.; Ganesan, S.; García, A. R.; Giubrone, G.; Gómez-Hornillos, M. B.; Gonçalves, I. F.; González-Romero, E.; Griesmayer, E.; Guerrero, C.; Gunsing, F.; Gurusamy, P.; Hernández-Prieto, A.; Jenkins, D. G.; Jericha, E.; Kadi, Y.; Käppeler, F.; Karadimos, D.; Kivel, N.; Koehler, P.; Kokkoris, M.; Krtička, M.; Kroll, J.; Lampoudis, C.; Langer, C.; Lederer, C.; Leeb, H.; Lo Meo, S.; Losito, R.; Mallick, A.; Manousos, A.; Marganiec, J.; Martínez, T.; Massimi, C.; Mastinu, P. F.; Mastromarco, M.; Meaze, M.; Mendoza, E.; Mengoni, A.; Milazzo, P. M.; Mingrone, F.; Mirea, M.; Mondelaers, W.; Pavlik, A.; Perkowski, J.; Plompen, A.; Praena, J.; Quesada, J. M.; Rauscher, T.; Reifarth, R.; Riego, A.; Robles, M. S.; Roman, F.; Rubbia, C.; Sabaté-Gilarte, M.; Sarmento, R.; Saxena, A.; Schillebeeckx, P.; Schmidt, S.; Schumann, D.; Tagliente, G.; Tain, J. L.; Tsinganis, A.; Valenta, S.; Vannini, G.; Variale, V.; Vaz, P.; Ventura, A.; Versaci, R.; Vermeulen, M. J.; Vlachoudis, V.; Vlastou, R.; Wallner, A.; Ware, T.; Weigand, M.; Weiß, C.; Wright, T.; Žugec, P.

    2016-03-01

    Neutron-induced fission cross sections of 238U and 235U are used as standards in the fast neutron region up to 200 MeV. A high accuracy of the standards is relevant to experimentally determine other neutron reaction cross sections. Therefore, the detection effciency should be corrected by using the angular distribution of the fission fragments (FFAD), which are barely known above 20 MeV. In addition, the angular distribution of the fragments produced in the fission of highly excited and deformed nuclei is an important observable to investigate the nuclear fission process. In order to measure the FFAD of neutron-induced reactions, a fission detection setup based on parallel-plate avalanche counters (PPACs) has been developed and successfully used at the CERN-n_TOF facility. In this work, we present the preliminary results on the analysis of new 235U(n,f) and 238U(n,f) data in the extended energy range up to 200 MeV compared to the existing experimental data.

  19. Additional evidence for fusion-fission in 32S+24Mg reactions: Division of excitation energy and spin in the fission fragments

    We have measured γ rays in coincidence with 12C fragments from the fission of 56Ni produced with the 32S+24Mg reaction at Elab=140 MeV. These data provide insight into the fission process in this light system by giving information about the energy and spin sharing between the 12C and 44Ti fragments, and the spin alignment of the lighter, 12C fragment. The spin transfer and the nuclear ''temperature'' at scission deduced from this measurement can be related to the compound-nucleus spin and potential energy at scission. The results indicate a statistical decay process consistent with the predictions of the transition-state model employing newer estimates of the spin- and mass-asymmetry-dependent saddle-point energies and corresponding shapes. No evidence is found for the spin alignment of the 12C fragments, contrary to what might be expected for a deep-inelastic scattering origin of the fully energy damped yields

  20. Mass and nuclear charge yields for sup 237 Np(2n sub th ,f) at different fission fragment kinetic energies

    Martinez, G.; Barreau, G.; Sicre, A.; Doan, T.P.; Audouard, P.; Leroux, B. (CEA Centre d' Etudes Nucleaires de Bordeaux-Gradignan, 33 - Gradignan (France)); Arafa, W.; Brissot, R.; Bocquet, J.P. (Grenoble-1 Univ., 38 (France). Inst. des Sciences Nucleaires); Faust, H. (Institut Max von Laue - Paul Langevin, 38 - Grenoble (France)); Koczon, P.; Mutterer, M. (Technische Hochschule Darmstadt (Germany, F.R.). Inst. fuer Kernphysik); Goennenwein, F. (Tuebingen Univ. (Germany, F.R.). Physikalisches Inst.); Asghar, M. (Universite des Sciences et de la Technologie Houari Boumediene, Algiers (Algeria). Inst. de Physique); Quade, U.; Rudolph, K. (Muenchen Univ. (Germany, F.R.)); Engelhardt, D. (Karlsruhe Univ. (T.H.) (Germany, F.R.)); Piasecki, E. (Warsaw Univ. (Poland))

    1990-09-03

    The recoil mass separator LOHENGRIN of the Laue-Langevin Institute Grenoble has been used to measure for the first time, the yields of light fission fragments from the fissioning system: {sub 93}{sup 239}Np; this odd-Z nucleus is formed after double thermal neutron capture in a {sub 93}{sup 237}Np target. The mass distributions were measured for different kinetic energies between 92 and 115.5 MeV, but the nuclear charge distributions were determined only up to 112 MeV. These distributions are compared to the distributions obtained for the even-even system {sub 94}{sup 240}Pu. At high kinetic energy, the mass distribution shows a prominent peak around mass number A{sub L}=106. These cold fragmentations are discussed in terms of a calculation based on a scission point model extrapolated to the cold fission case. As expected for an odd-Z fissioning nucleus, the nuclear charge distributions do not reveal any odd-even effect. The global neutron odd-even effect is found to be (8.1{plus minus}1.5)%. A simple model has been used to show that most of the neutron odd-even effect results from prompt neutron evaporation from the fragments. (orig.).

  1. Effect of the energy spectrum and angular momentum of pre-scission neutrons on the prediction of fission fragment angular anisotropy by the models

    Soheyli, Saeed; Khanlari, Marzieh Varasteh

    2016-04-01

    Effects of the various neutron emission energy spectra, as well as the influence of the angular momentum of pre-scission neutrons on theoretical predictions of fission fragment angular anisotropies for several heavy-ion induced fission systems are considered. Although theoretical calculations of angular anisotropy are very sensitive to neutron emission correction, the effects of the different values of kinetic energy of emitted neutrons derived from the various neutron emission energy spectra before reaching to the saddle point on the prediction of fission fragment angular distribution by the model are not significant and can be neglected, since these effects on angular anisotropies of fission fragments for a wide range of fissility parameters and excitation energies of compound nuclei are not more than 10%. Furthermore, the theoretical prediction of fission fragment angular anisotropy is not sensitive to the angular momentum of emitted neutrons.

  2. Measurement of the fission fragment angular distribution for 232Th(n,f) at the CERN n-TOF facility

    Tarrío, D; Audouin, L; Duran, I; Leong, L S; Paradela, C; Altstadt, S; Andrzejewski, J; Barbagallo, M; Bécares, V; Bečvář, F; Belloni, F; Berthoumieux, E; Billowes, J; Boccone, V; Bosnar, D; Brugger, M; Calviani, M; Calviño, F; Cano-Ott, D; Carrapiço, C; Cerutti, F; Chiaveri, E; Chin, M; Colonna, N; Cortés, G; Cortés-Giraldo, M A; Diakaki, M; Domingo-Pardo, C; Dzysiuk, N; Eleftheriadis, C; Ferrari, A; Fraval, K; Ganesan, S; Garcìa, A R; Giubrone, G; Gómez-Hornillos, M B; Gonçalves, I F; González-Romero, E; Griesmayer, E; Guerrero, C; Gunsing, F; Gurusamy, P; Jenkins, D G; Jericha, E; Kadi, Y; Käppeler, F; Karadimos, D; Koehler, P; Kokkoris, M; Krtička, M; Kroll, J; Langer, C; Lederer, C; Leeb, H; Losito, R; Manousos, A; Marganiec, J; Martìnez, T; Massimi, C; Mastinu, P F; Mastromarco, M; Meaze, M; Mendoza, E; Mengoni, A; Milazzo, P M; Mingrone, F; Mirea, M; Mondalaers, W; Pavlik, A; Perkowski, J; Plompen, A; Praena, J; Quesada, J M; Rauscher, T; Reifarth, R; Riego, A; Roman, F; Rubbia, C; Sarmento, R; Schillebeeckx, P; Schmidt, S; Tagliente, G; Tain, J L; Tsinganis, A; Valenta, S; Vannini, G; Variale, V; Vaz, P; Ventura, A; Versaci, R; Vermeulen, M J; Vlachoudis, V; Vlastou, R; Wallner, A; Ware, T; Weigand, M; Weiß, C; Wright, T J; Žugec, P

    2012-01-01

    A fission reaction chamber was designed to measure the angular distribution of the fragments emitted in neutron-induced fission reactions at n_TOF. Up to ten Parallel Plate Avalanche Counters can be included and kept at controlled low-pressure gas. Counters are tilted 45º with respect to the neutron beam direction and up to nine targets can be interleaved in between. A first measurement of the 232Th(n,f) was recently done and preliminary experimental results demonstrating the suitability of the setup are presented here.

  3. Mass-energy distribution of fragments in Langevin dynamics of fission induced by heavy ions

    Vanin D. V.

    2012-12-01

    Full Text Available Four-dimensional Langevin equation was employed to calculate mass-energy distributions of fission fragments of highly excited compound nuclei. The research took into account not only three shape collective coordinates introduced on the basis of {c,h,α}-parametrization but also orientation degree of freedom (K-state— spin about the symmetry axis. Overdamped Langevin equation was used to describe the evolution of the K-state. Friction tensor was calculated using the “wall+window” model of the modified one-body dissipation mechanism with a reduction coeffcient from the “wall” formula ks. The calculations have been performed with ks = 0:25 and ks = 1:0. To learn more about the role of the dissipation effects the calculations have also been done with use of the chaoticity measure of nucleon movements in the nuclear shape configuration as ks parameter. Calculations were performed for the large number of compound nuclei with Z2/A parameter in the range 21 ≤ Z2/A ≤ 44. The goal was to study the mass-energy distributions not only for heavy nuclei but also for light nuclei close to the Businaro-Gallone point. Mass-energy distributions and variances of the mass fragments are well reproduced in the applied calculations for all considered compound nuclei. It was shown that inclusion of the K-state in the dynamical model produces considerable increase of the mass and energy variances. Inclusion of the chaoticity measure to the friction tensor provides a better agreement with the experiment results on mass variances.

  4. Dependence of Fission-Fragment Total Kinetic-Energy and Mass Distributions on the Excitation Energy and Angular-Momentum Distribution of the Fissioning Nuclide 210Po

    The fission of 210Po, produced by three different nuclear reactions (209Bi + p, 206Pb + α and 198Pt + 12C), has been studied in detail in order to establish the dependence of various scission-point properties on the excitation energy and angular-momentum distribution of the fissioning nucleus. Excitation energies of 31, 44 and 57 MeV were chosen so as to give reasonable fission cross-sections, while avoiding a large contribution from second chance fission. The experiments were conducted on a beam line of the Harwell Variable Energy Cyclotron. The mean-fragment total-kinetic-energy release was found to be dependent on the 210Po excitation energy and angular-momentum distribution. The variances of the total-kinetic energy and mass distributions were found to be a strongly dependent on excitation energy but not on angular momentum. The experimental results of this work were found to be in good agreement with the theoretical liquid-drop-model calculations of Nix and Swiatecki. (author)

  5. Hybrid molecular ions emitted from CO-NH3 ice bombarded by fission fragments

    Martinez, R.; Ponciano, C. R.; Farenzena, L. S.; Iza, P.; Homem, M. G. Pe; Naves de Brito, A.; da Silveira, E. F.; Wien, K.

    2007-05-01

    CO-NH3 ice at 25 K is bombarded by 65 MeV fission fragments and the emitted secondary ions are analyzed by time-of-flight mass spectrometry. The yields of the specific ion species (those formed only from CO or from NH3 molecules) and of the hybrid ion species (formed from both CO and NH3 molecules) are determined as a function of the ice temperature. The time-temperature dependence of desorption yields has been used for secondary ion identification because its behavior characterizes the ion's origin around the sublimation temperature of CO ice (~30 K). The mass spectrum of positive ions measured before CO sublimation is decomposed into three spectra corresponding to CO specific ions, NH3 specific ions and hybrid molecular ions, respectively. The observed spectrum after CO sublimation is very similar to that of a pure NH3 specific spectrum. The total yield of all positive hybrid molecular ions over 600 u mass range is found to be about 2 ions/impact: 20% of this is attributed to N and NH3 containing ions and 80% are ions having the CnOmHl+ structure. The ions Cnindicates the formation of hydrogen cyanide.

  6. Brownian shape motion on five-dimensional potential-energy surfaces:nuclear fission-fragment mass distributions.

    Randrup, Jørgen; Möller, Peter

    2011-04-01

    Although nuclear fission can be understood qualitatively as an evolution of the nuclear shape, a quantitative description has proven to be very elusive. In particular, until now, there existed no model with demonstrated predictive power for the fission-fragment mass yields. Exploiting the expected strongly damped character of nuclear dynamics, we treat the nuclear shape evolution in analogy with Brownian motion and perform random walks on five-dimensional fission potential-energy surfaces which were calculated previously and are the most comprehensive available. Test applications give good reproduction of highly variable experimental mass yields. This novel general approach requires only a single new global parameter, namely, the critical neck size at which the mass split is frozen in, and the results are remarkably insensitive to its specific value. PMID:21517377

  7. Effects of Neutron Emission on Fragment Mass and Kinetic Energy Distribution from Thermal Neutron-Induced Fission of 235U

    The mass and kinetic energy distribution of nuclear fragments from thermal neutron-induced fission of 235U(nth,f) have been studied using a Monte-Carlo simulation. Besides reproducing the pronounced broadening in the standard deviation of the kinetic energy at the final fragment mass number around m = 109, our simulation also produces a second broadening around m = 125. These results are in good agreement with the experimental data obtained by Belhafaf et al. and other results on yield of mass. We conclude that the obtained results are a consequence of the characteristics of the neutron emission, the sharp variation in the primary fragment kinetic energy and mass yield curves. We show that because neutron emission is hazardous to make any conclusion on primary quantities distribution of fragments from experimental results on final quantities distributions

  8. A new fission-fragment detector to complement the CACTUS-SiRi setup at the Oslo Cyclotron Laboratory

    Tornyi, T.G., E-mail: tornyitom@atomki.hu [Department of Physics, University of Oslo (Norway); Institute of Nuclear Research of the Hungarian Academy of Sciences (MTA Atomki), Debrecen (Hungary); Görgen, A.; Guttormsen, M.; Larsen, A.C.; Siem, S. [Department of Physics, University of Oslo (Norway); Krasznahorkay, A. [Institute of Nuclear Research of the Hungarian Academy of Sciences (MTA Atomki), Debrecen (Hungary); Csige, L. [Institute of Nuclear Research of the Hungarian Academy of Sciences (MTA Atomki), Debrecen (Hungary); Max-Planck-Institute for Quantum Optics, D-85748 Garching (Germany)

    2014-02-21

    An array of Parallel Plate Avalanche Counters (PPAC) for the detection of heavy ions has been developed. The new device, NIFF (Nuclear Instrument for Fission Fragments), consists of four individual detectors and covers 60% of 2π. It was designed to be used in conjunction with the SiRi array of ΔE−E silicon telescopes for light charged particles and fits into the CACTUS array of 28 large-volume NaI scintillation detectors at the Oslo Cyclotron Laboratory. The low-pressure gas-filled PPACs are sensitive for the detection of fission fragments, but are insensitive to scattered beam particles of light ions or light-ion ejectiles. The PPAC detectors of NIFF have good time resolution and can be used either to select or to veto fission events in in-beam experiments with light-ion beams and actinide targets. The powerful combination of SiRi, CACTUS, and NIFF provides new research opportunities for the study of nuclear structure and nuclear reactions in the actinide region. The new setup is particularly well suited to study the competition of fission and γ decay as a function of excitation energy.

  9. A new fission-fragment detector to complement the CACTUS-SiRi setup at the Oslo Cyclotron Laboratory

    Tornyi, T. G.; Görgen, A.; Guttormsen, M.; Larsen, A. C.; Siem, S.; Krasznahorkay, A.; Csige, L.

    2014-02-01

    An array of Parallel Plate Avalanche Counters (PPAC) for the detection of heavy ions has been developed. The new device, NIFF (Nuclear Instrument for Fission Fragments), consists of four individual detectors and covers 60% of 2π. It was designed to be used in conjunction with the SiRi array of ΔE-E silicon telescopes for light charged particles and fits into the CACTUS array of 28 large-volume NaI scintillation detectors at the Oslo Cyclotron Laboratory. The low-pressure gas-filled PPACs are sensitive for the detection of fission fragments, but are insensitive to scattered beam particles of light ions or light-ion ejectiles. The PPAC detectors of NIFF have good time resolution and can be used either to select or to veto fission events in in-beam experiments with light-ion beams and actinide targets. The powerful combination of SiRi, CACTUS, and NIFF provides new research opportunities for the study of nuclear structure and nuclear reactions in the actinide region. The new setup is particularly well suited to study the competition of fission and γ decay as a function of excitation energy.

  10. A new fission-fragment detector to complement the CACTUS-SiRi setup at the Oslo Cyclotron Laboratory

    An array of Parallel Plate Avalanche Counters (PPAC) for the detection of heavy ions has been developed. The new device, NIFF (Nuclear Instrument for Fission Fragments), consists of four individual detectors and covers 60% of 2π. It was designed to be used in conjunction with the SiRi array of ΔE−E silicon telescopes for light charged particles and fits into the CACTUS array of 28 large-volume NaI scintillation detectors at the Oslo Cyclotron Laboratory. The low-pressure gas-filled PPACs are sensitive for the detection of fission fragments, but are insensitive to scattered beam particles of light ions or light-ion ejectiles. The PPAC detectors of NIFF have good time resolution and can be used either to select or to veto fission events in in-beam experiments with light-ion beams and actinide targets. The powerful combination of SiRi, CACTUS, and NIFF provides new research opportunities for the study of nuclear structure and nuclear reactions in the actinide region. The new setup is particularly well suited to study the competition of fission and γ decay as a function of excitation energy

  11. Monte-carlo simulation for fragment mass and kinetic energy distributions from neutron induced fission of 235U

    Mass and kinetic energy distribution of nuclear fragments after neutron induced fission of 235U have been studied using a Monte-Carlo simulation. Besides that the pronounced peak in the standard deviation of the kinetic energy σE(m) at the mass number around m = 110 was reproduced, a second peak was found at m = 126. These results are in good agreement with experimental data obtained by Belhafaf et. al. We have concluded that the obtained results are consequence of the characteristics of neutron evaporation for the fragments and sharp variation on primary mass yield curve. (authors)

  12. CeLAND: search for a 4th light neutrino state with a 3 PBq 144Ce-144Pr electron antineutrino generator in KamLAND

    Gando, A; Hayashida, S; Ikeda, H; Inoue, K; Ishidoshiro, K; Ishikawa, H; Koga, M; Matsuda, R; Matsuda, S; Mitsui, T; Motoki, D; Nakamura, K; Oki, Y; Otani, M; Shimizu, I; Shirai, J; Suekane, F; Suzuki, A; Takemoto, Y; Tamae, K; Ueshima, K; Watanabe, H; Xu, B D; Yamada, S; Yamauchi, Y; Yoshida, H; Cribier, M; Durero, M; Fischer, V; Gaffiot, J; Jonqueres, N; Kouchner, A; Lasserre, T; Leterme, D; Letourneau, A; Lhuillier, D; Mention, G; Rampal, G; Scola, L; Veyssiere, Ch; Vivier, M; Yala, P; Berger, B E; Kozlov, A; Banks, T; Dwyer, D; Fujikawa, B K; Han, K; Kolomensky, Yu G; Mei, Y; O'Donnell, T; Decowski, P; Markoff, D M; Yoshida, S; Kornoukhov, V N; Gelis, T V M; Tikhomirov, G V; Learned, J G; Maricic, J; Matsuno, S; Milincic, R; Karwowski, H J; Efremenko, Y; Detwiler, A; Enomoto, S

    2013-01-01

    The reactor neutrino and gallium anomalies can be tested with a 3-4 PBq (75-100 kCi scale) 144Ce-144Pr antineutrino beta-source deployed at the center or next to a large low-background liquid scintillator detector. The antineutrino generator will be produced by the Russian reprocessing plant PA Mayak as early as 2014, transported to Japan, and deployed in the Kamioka Liquid Scintillator Anti-Neutrino Detector (KamLAND) as early as 2015. KamLAND's 13 m diameter target volume provides a suitable environment to measure the energy and position dependence of the detected neutrino flux. A characteristic oscillation pattern would be visible for a baseline of about 10 m or less, providing a very clean signal of neutrino disappearance into a yet-unknown, sterile neutrino state. This will provide a comprehensive test of the electron dissaperance neutrino anomalies and could lead to the discovery of a 4th neutrino state for Delta_m^2 > 0.1 eV^2 and sin^2(2theta) > 0.05.

  13. An experimental study of the time dependence of uptake from soil of 137Cs, 106Ru, 144Ce and 99Tc into green vegetables, wheat and potatoes

    In this study the experimental data were analysed using the CEGB's dynamic foodchain model, and were used to validate the relevant part of the model structure, to produce model-specific input data and to identify possible future improvements to the model structure. The root uptake of the specified radionuclides was studied and the concentration levels measured. The data were analysed using a simplified version of the general model. The compartment system incorporated within the model was shown to be capable of reproducing the data for 137Cs, 106Ru and 144Ce to an extent sufficient to justify its use in ingestion radiological dose assessments, but to be less successful in fitting the 99Tc data. The analysis resulted in the production of a well validated set of model-specific input data relevant to UK conditions and agricultural practice differing significantly from values obtained from global literature surveys. Possible future improvements to the model structure were also identified, aimed at providing improved estimates of crop contamination levels for timescales in excess of those considered in this study. (U.K.)

  14. Position reconstruction in fission fragment detection using the low pressure MWPC technique for the JLab experiment E02-017

    Qiu, Xi-Yu; Tang, L.; Margaryan, A.; Hu, Bi-tao; Chen, Xi-Meng

    2013-01-01

    When a lambda hyperon was embedded in a nucleus, it can form a hypernucleus. The lifetime and its mass dependence of stable hypernuclei provide information about the weak decay of lambda hyperon inside nuclear medium. This work will introduce the Jefferson Lab experiment (E02-017) which aims to study the lifetime of the heavy hypernuclei using a specially developed fission fragment detection technique, a multi-wire proportional chamber operated under low gas pressure (LPMWPC). Presented here ...

  15. Fragment characteristics from fission of 238U and 234U induced by 6.5-9.0 MeV bremsstrahlung

    Göök, A.; Chernykh, M.; Eckardt, C.; Enders, J.; von Neumann-Cosel, P.; Oberstedt, A.; Oberstedt, S.; Richter, A.

    2011-02-01

    Fission of 238U and 234U induced by bremsstrahlung of 6.5-9.0 MeV endpoint energy has been investigated at the superconducting Darmstadt electron linear accelerator S-DALINAC. Using a twin Frisch grid ionization chamber, fission-fragment energy and mass distributions have been determined by means of the double kinetic-energy technique. Results on the fission-fragment characteristics from U238(γ,f) are in agreement with results from the literature. In addition fission-fragment mass and energy distributions from U234(γ,f) are presented for the first time in this energy region. An analysis of fission modes within the Brosa model has been performed. The relative yield of the S1 mode was found to be (13±3)% in 234U and (35±2)% in 238U.

  16. Analysis of neutron multiplicity and fission fragment mass distribution within the asymmetric two-center shell model

    The fission fragment mass distribution followed by neutron emission is studied for the 238U(18O,f) reaction using the asymmetric two-center shell model. Within the thermodynamic approach, excitation energy carried by the compound nucleus is dissipated in the emission of a pair of neutrons in several consecutive steps. Therefore, we have considered 2-12 (in step of 2) neutron emission channels in our formalism. The mass distribution corresponding to 8-neutron emission channel compares reasonably well with the experimental data. The observed fine structure dips corresponding to shell closure (Z = 50 and N = 82) of individual fission fragment arise mainly due to shell structure in the mass parameters. However, an exact location and magnitude of the dip at A = 124 in the mass distribution depends on how the temperature modifies masses and, also, on the precise information of pre- and post-neutron emission data. This suggests a possible importance of extending these calculations to get new insight into an understanding of the dynamical behaviour of fragment formation in the fission process. (orig.)

  17. Measurement of Fragment Mass Distributions in Neutron-induced Fission of 238U and 232Th at Intermediate Energies

    Conceptual analysis of accelerator-driven systems assumes extensive use of nuclear data on neutron-induced reactions at intermediate energies. In particular, information about the fission fragment yields from the 238U(n,f) and 232Th(n,f) reactions is of particular interest at neutron energies from 10 to 200 MeV. However, there is a lack of such data for both 238U and 232Th. Up to now, the intermediate energy measurements have been performed for 238U only, and there are no data for the 232Th(n,f) reaction. The aim of the work is to provide such data. Fission fragment mass distributions for the 232Th(n,f) and 238U(n,f) reactions have been measured for the incident neutron energies 32.8 MeV, 45.3 MeV and 59.9 MeV. The experiments have been performed at the neutron beam facility of the Universite Catholique de Louvain, Belgium. A multi-section Frisch-gridded ionization chamber has been used as a fission fragment detector. The data obtained have been interpreted in terms of the multimodal random neck-rupture model (MMRNRM). (authors)

  18. γ-ray spectroscopy of fission fragments from the cold-neutron 235U induced fission with EXILL

    A cold neutron induced fission experiment recently took place at the Institute Laue-Langevin (ILL) in Grenoble. The neutron beam was provided by the nuclear reactor facility at ILL and the detector setup that was used for the γ-spectroscopy of the fission products consisted mainly of the detectors of the EXOGAM array [1], thereby the name of the campaign is EXILL. The main purpose of our measurement was to investigate the nuclei in the region with N = 50 close to 78Ni as well as the nuclei close to the N = 82 shell closure. In this paper, the motivation of the experiment is described as well as the experimental setup and the status of the ongoing data analysis. (authors)

  19. γ-ray spectroscopy of fission fragments from the cold-neutron 235U induced fission with EXILL

    Konstantinopoulos T.

    2013-12-01

    Full Text Available A cold neutron induced fission experiment recently took place at the Institute Laue-Langevin (ILL in Grenoble. The neutron beam was provided by the nuclear reactor facility at ILL and the detector setup that was used for the γ-spectroscopy of the fission products consisted mainly of the detectors of the EXOGAM array [1], thereby the name of the campaign is EXILL. The main purpose of our measurement was to investigate the nuclei in the region with N = 50 close to 78Ni as well as the nuclei close to the N = 82 shell closure. In this paper, the motivation of the experiment is described as well as the experimental setup and the status of the ongoing data analysis.

  20. Local even-odd effect based on the number of configurations of pre-formed and formed fragmentations in a fissioning nucleus

    Tudora, A.; Hambsch, F.-J.; Giubega, G.

    2016-09-01

    The present paper proposes a modeling of the local even-odd effect based on the number of configurations in a nucleus undergoing fission at two stages along its fission path. One is the fissioning nucleus stage just after passing through the outer saddle point when the fragments are considered as pre-formed and the intrinsic energy is not yet shared. The other stage is at the end of the fission path when the scission is imminent. Then the intrinsic energy is already partitioned and the fragments are completely formed. The probability that a pre-formed fragmentation arrives at the end of the fission path (i.e. at scission) when the fragmentation is completely formed is expressed by the ratio of the number of configurations of the formed fragmentation to the one of pre-formed fragmentation. The local even-odd effect is defined as half of the difference between these normalized ratios corresponding to even-Z and odd-Z fragmentations. Both numbers of configurations in the fissioning nucleus, in which the fragments are pre-formed and completely formed, are calculated using level densities described by the constant temperature function (justified by the small values of the intrinsic energy before scission). The obtained local even-odd effect results describe well the experimental data, including the increase at asymmetry values corresponding to fragmentations in which one of the fragments is magic or double magic (i.e. fragmentations in which ZH = 50 and/or NH = 82 and very asymmetric fragmentations in which ZL = 28).

  1. Fission-fragment mass distribution and estimation of the cluster emission probability in the gamma+.SUP.232 Th and .SUP.181 Ta reactions

    Karamian, S. A.; Adam, Jindřich; Belov, A. G.; Čaloun, Pavel; Norseev, Yu. V.; Stegailov, V. I.

    Singapore: World scientific, 1997 - (von Egidy, T.; Hartmann, H.; Habs, D.; Lobner, K.; Nifenecker, H.), s. 199-204 [International Workshop on Research with Fission Fragment s. Benediktbeurn (DE), 28.10.1996-30.10.1996

  2. Automatic registration of fission fragment tracks with a spark gap counting system

    The theoretical aspects of fission track production in polycarbonate foils are briefly discussed. An automatic counting system for fission tracks based on a spark gap chamber is described. A linear response for low fission track density, typical of environmental and biological samples, was obtained with a 252Cf source using an electrode of 33.2 mm2. The system also functions with electrodes of larger and smaller areas without any major changes in the instrument. (author) 23 refs.; 6 figs

  3. Quantitative analysis of fission products by γ spectrography

    The activity of the fission products present in treated solutions of irradiated fuels is given as a function of the time of cooling and of the irradiation time. The variation of the ratio (144Ce + 144Pr activity)/ 137Cs activity) as a function of these same parameters is also given. From these results a method is deduced giving the 'age' of the solution analyzed. By γ-scintillation spectrography it was possible to estimate the following elements individually: 141Ce, 144Ce + 144Pr, 103Ru, 106Ru + 106Rh, 137Cs, 95Zr + 95Nb. Yield curves are given for the case of a single emitter. Of the various existing methods, that of the least squares was used for the quantitative analysis of the afore-mentioned fission products. The accuracy attained varies from 3 to 10%. (author)

  4. Neutron emission effects on fragment mass and kinetic energy distribution from fission of 239Pu induced by thermal neutrons

    The average of fragment kinetic energy () and the multiplicity of prompt neutrons (ν(bar sign)) as a function of fragment mass (m*), as well as the fragment mass yield (Y (m*)) from thermal neutron induced fission of 239Pu, have been measured by Tsuchiya et al.. In that work the mass and kinetic energy are calculated from the measured kinetic energy of one fragment and the difference of time of flight of the two complementary fragments. However they do not present their results about the standard deviation σE*(m*). In this work we have made a numerical simulation of that experiment, assuming an initial distribution of the primary fragment kinetic energy (E(A)) with a constant value of the standard deviation as function of fragment mass σE(A)). As a result of that simulation we obtain the dependence σE*(m*) which presents an enhancement between m* = 92 and m* 110, and a peak at m* = 121. (orig.)

  5. Neutron emission effects on fragment mass and kinetic energy distribution from fission of 239Pu induced by thermal neutrons

    The average of fragment kinetic energy (E-bar sign*) and the multiplicity of prompt neutrons (ν(bar sign)) as a function of fragment mass (m*), as well as the fragment mass yield (Y(m*)) from thermal neutron-induced fission of 239Pu have been measured by Tsuchiya et al.. In that work the mass and kinetic energy are calculated from the measured kinetic energy of one fragment and the difference of time of flight of the two complementary fragments. However they do not present their results about the standard deviation σE*(m*). In this work we have made a numerical simulation of that experiment which reproduces its results, assuming an initial distribution of the primary fragment kinetic energy (E(A)) with a constant value of the standard deviation as function of fragment mass (σE(A)). As a result of the simulation we obtain the dependence σE*(m*) which presents an enhancement between m* = 92 and m* = 110, and a peak at m* = 121.

  6. Fission of transactinide elements described in terms of generalized Cassinian ovals: Fragment mass and total kinetic energy distributions

    Carjan, N.; Ivanyuk, F. A.; Oganessian, Yu.; Ter-Akopian, G.

    2015-10-01

    The total deformation energy at scission for Z = 100, 102, 104 and 106 isotopes is calculated using the Strutinsky's procedure and nuclear shapes described in terms of Cassinian ovals generalized by the inclusion of three additional shape parameters: α1, α4 and α6. The corresponding fragment-mass distributions are estimated supposing they are due to thermal fluctuations in the mass asymmetry degree of freedom. For these four series of isotopes the experimentally observed transition from asymmetric to symmetric fission, that happens with increasing mass number A, is qualitatively reproduced. In lighter isotopes (e.g. 254Fm and 254Rf) two mass-asymmetric fission modes are predicted to occur with comparable yields: one having relatively compact and the other relatively elongated scission configurations. On the other hand, in heavier isotopes (e.g. 264Fm and 264Rf) the fragment-mass distributions are predicted to be narrow single-peaked around A / 2 corresponding to essentially one mass-symmetric fission mode. The mass distributions are estimated separately for each fission mode, in the case of Fm and Rf isotopes, in order to display their inversion when A increases. Finally the distributions of the total kinetic energy of the fragments are calculated, for the same isotopes, in the point-charge approximation. Non-Gaussian shapes are obtained. With increasing mass number A, a transition from a distribution tailing towards higher energies to a distribution tailing towards lower energies and an increase of the difference in the peak positions of the two modes were observed; again in qualitative agreement with experimental data.

  7. Ternary Fission

    The fission process in which heavy nuclei fragment into three large charged panicles, in place of the usual two, has been studied in the case of thermal-neutron-induced fission of U235 and the spontaneous fission of Cf252. Solid-state detectors, a fast triple coincidence system and a three-coincident-parameter analyser were used to measure the three fission fragment energies parallel with the detection of each ternary fission event. Experimental evidence is presented supporting the existence of ternary fission by specifically excluding recoil phenomena and accidental events as contributing to the observed three-fold coincidence events. Mass-energy-angular correlations of ternary fission have been determined and are summarized as follows: The total kinetic energy release in ternary fission appears to be slightly higher (by approximately 10 MeV) than that for binary fission. In the case of the spontaneous ternary fission of Cf252, the frequency of occurrence is observed to be greater than 2.2 x 10-6 ternary fission events per binary fission event. Tripartition of Cf252 results preferentially in division into two medium mass particle (one of which has a mass number near 56) and one larger mass. In the case of thermal-neutron-induced fission of U235, the frequency of occurrence is observed to be greater than 1.2 x 10-6 ternary fission events per binary fission event. Ternary fission of U236: results in the formation of one light fragment (near mass 36) and two large fragments or, as in the case of Cf252, two medium fragments and one large one. These results indicate that axially asymmetric distortion modes are possible in the pre-scission configurations of the fissioning nucleus. A description is given of experiments designed to radiochemically detect the light fragment resulting from ternary fission. (author)

  8. Preliminary Results of a Full Hauser-feshbach Simulation of the Prompt Neutron and Gamma Emission from Fission Fragments

    Regniera, D.; Litaizea, O.; Serota, O.

    The prompt neutron and gamma emission from fission fragments are investigated through the Monte Carlo code FIFRELIN which is developed at the CEA Cadarache research center. In a previous release of the code, the de-excitation of the fragments was treated in a two steps process. First the emission of all the prompt neutrons was simulated using a Weisskopf spectrum for the distribution of their kinetic energy. In a second step, the excitation energy still available was dissipated by the fragments as an electromagnetic decay cascade. This paper presents a new procedure for fragment de-excitation using an Hauser-Feshbach treatment of prompt particles emission. The neutron/gamma competition is then accounted for during the whole cascade. Moreover, the neutron emission is now ruled by the transmission coefficients directly coming from an optical model calculation performed with TALYS-1.4. The implementation of these models in the code FIFRELIN is quickly highlighted. The results in terms of neutrons and gamma multiplicities and spectra for one simulation of a 252Cf spontaneous fission are emphasized. The neutron multiplicity experimental data are used to constraint the parameters of our simulation. The prompt gamma spectrum calculated is then consistent with experimental data and the structures observed experimentally in the low energy range are well reproduced. However, the same simulation performed with several different nuclear models and parameters reveals high variation of these fission observables. For example, the average total gamma energy (Eγ,tot) is shown to vary up to 20% with changes in the level density or radiative strength function model.

  9. Calculation of the fission cross section for 233U and the interpretation of fragment anisotropy and fine structure in anti νsub(p) and anti Esub(k)

    The fission cross section of 233U has been calculated using a new version of the statistical model and recent data for inelastic scattering levels and fission barrier parameters. The calculation accurately reproduces the experimental fission cross section. The calculated partial cross section for fission through different saddle point states (JKπ) has been used in the explanation of structure in average number of fission prompt neutrons anti νsub(p) and average total fission fragment kinetic energy anti Esub(k) and the energy dependence of the fission fragment anisotropy

  10. A new fission-fragment detector to complement the CACTUS-SiRi setup at the Oslo Cyclotron Laboratory

    Tornyi, Tamás Gábor; Guttormsen, Magne; Larsen, Ann-Cecilie; Siem, Sunniva; Krasznahorkay, Attila; Csige, Lóránt

    2013-01-01

    An array of Parallel Plate Avalanche Counters (PPAC) for the detection of heavy ions has been developed. The new device, NIFF (Nuclear Instrument for Fission Fragments), consists of four individual detectors and covers $60\\%$ of 2$\\pi$. It was designed to be used in conjunction with the SiRi array of ${\\Delta}E-E$ silicon telescopes for light charged particles and fits into the CACTUS array of 28 large-volume NaI scintillation detectors at the Oslo Cyclotron Laboratory. The low-pressure gas-filled PPACs are sensitive for the detection of fission fragments, but are insensitive to scattered beam particles of light ions or light-ion ejectiles. The PPAC detectors of NIFF have good time resolution and can be used either to select or to veto fission events in in-beam experiments with light-ion beams and actinide targets. The powerful combination of SiRi, CACTUS, and NIFF provides new research opportunities for the study of nuclear structure and nuclear reactions in the actinide region. The new setup is particularly...

  11. The study of the effect of gamma radiation on the ionic and collodial solutions of 144Ce/III/ at trace concentration by the method of self-diffusion and centrifugation

    Gamma irradiation of a solution of trace concentration of 144Ce/III/ at pH 3.0 causes an increase in the self-diffusion coefficient of 144Ce/III/ and small decrease in its centrifugable fraction. The significant increase in the self-diffusion coefficient is observed after irradiation at pH 9.0 and 11.0 and on the centrifugation of these solutions an increased susceptibility of particles containing 144Ce/III/ to the coagulation accurs. The measurements were performed by a method of the open end capillary immersed into the excess of inactive solution and the self-diffusion coefficient calculated as described earlier. The solutions were irradiated either directly in the capillaries for the self-diffusion measurment fixed in the glass tubes or in borosilicate Sial glass sample tubes with subsequent pipetting into the capillaries. The dose rate of 60Co γ-radiation was about 0.4 Mrad. hour-1, the time of irradiation was 1.5 to 15 hours. The period between the end of the irradiation and the beginning of the self-diffusion measurement amounted to about 15 to 30 min. (F.G.)

  12. Reaction 48Ca+208Pb: the capture-fission cross-sections and the mass-energy distributions of fragments above and deep below the Coulomb barrier

    Prokhorova, E. V.; Cherepanov, E. A.; Itkis, M.G.; Kondratiev, N. A.; Kozulin, E. M.; Krupa, L.; Oganessian, Yu.Ts.; Pashkevich, V. V.; Pokrovsky, I. V.; Rusanov, A. Ya.

    2003-01-01

    The capture-fission cross-sections in an energy range of 206-242 MeV of 48Ca-projectiles and mass-energy distributions (MEDs) of reaction products in an energy range of 211-242 MeV have been measured in the 48Ca+208Pb reaction using the double-arm time-of-flight spectrometer CORSET. The MEDs of fragments for heated fission were shown to consist of two components. One component, which is due to classical fusion-fission, is associated with the symmetric fission of the 256No compound nucleus. Th...

  13. Fission fragment mass and energy distributions as a function of incident neutron energy measured in a lead slowing-down spectrometer

    Romano, C.; Danon, Y.; Block, R.; Thompson, J.; Blain, E.; Bond, E.

    2010-01-01

    A new method of measuring fission fragment mass and energy distributions as a function of incident neutron energy in the range from below 0.1 eV to 1 keV has been developed. The method involves placing a double-sided Frisch-gridded fission chamber in Rensselaer Polytechnic Institute’s lead slowing-down spectrometer (LSDS). The high neutron flux of the LSDS allows for the measurement of the energy-dependent, neutron-induced fission cross sections simultaneously with the mass and kinetic energy of the fission fragments of various small samples. The samples may be isotopes that are not available in large quantities (submicrograms) or with small fission cross sections (microbarns). The fission chamber consists of two anodes shielded by Frisch grids on either side of a single cathode. The sample is located in the center of the cathode and is made by depositing small amounts of actinides on very thin films. The chamber was successfully tested and calibrated using 0.41±0.04 ng of Cf252 and the resulting mass distributions were compared to those of previous work. As a proof of concept, the chamber was placed in the LSDS to measure the neutron-induced fission cross section and fragment mass and energy distributions of 25.3±0.5μg of U235. Changes in the mass distributions as a function of incident neutron energy are evident and are examined using the multimodal fission mode model.

  14. Fission fragment mass and energy distributions as a function of incident neutron energy measured in a lead slowing-down spectrometer

    A new method of measuring fission fragment mass and energy distributions as a function of incident neutron energy in the range from below 0.1 eV to 1 keV has been developed. The method involves placing a double-sided Frisch-gridded fission chamber in Rensselaer Polytechnic Institute's lead slowing-down spectrometer (LSDS). The high neutron flux of the LSDS allows for the measurement of the energy-dependent, neutron-induced fission cross sections simultaneously with the mass and kinetic energy of the fission fragments of various small samples. The samples may be isotopes that are not available in large quantities (submicrograms) or with small fission cross sections (microbarns). The fission chamber consists of two anodes shielded by Frisch grids on either side of a single cathode. The sample is located in the center of the cathode and is made by depositing small amounts of actinides on very thin films. The chamber was successfully tested and calibrated using 0.41±0.04 ng of 252Cf and the resulting mass distributions were compared to those of previous work. As a proof of concept, the chamber was placed in the LSDS to measure the neutron-induced fission cross section and fragment mass and energy distributions of 25.3±0.5 μg of 235U. Changes in the mass distributions as a function of incident neutron energy are evident and are examined using the multimodal fission mode model.

  15. Fission Fragment Angular Distributions in the $^{234}$U(n,f) and $^{236}$U(n,f) reactions

    We propose to measure the fission fragment angular distribution (FFAD) of the $^{234}$U(n,f) and $^{236}$U (n,f) reactions with the PPAC detection setup used in previous n_TOF-14 experiment. This experiment would take advantage of the high resolution of the n_TOF facility to investigate the FFAD behaviour in the pronounced vibrational resonances that have been observed between 0.1 and 2 MeV for the thorium cycle isotopes. In addition, the angular distribution of these isotopes will be measured for the first time beyond 14 MeV. Furthermore, the experiment will also provide the fission cross section with reduced statistical uncertainty, extending the $^{236}$U(n,f) data up to 1 GeV

  16. Evaluation of the damage resulting from fission fragments in the fuel elements of the ETRR-2 materials testing reactor

    The damage resulting from fission fragments in the fuel elements of the ETRR-2 Materials Testing Reactor (MTR) was evaluated using the TRIM-86 computer code. The effect of very low yield fission ions (Zn and Gd) and high yield ions (Mo and La) on the structural changes of the aluminum matrix for the enriched U3O8 dispersed fuel was studied. The kinetic energy of the highly ionized fission fragments Zn, Mo, La and Gd was evaluated to be 106. 93. 61 and 48 MeV respectively. The tracks and distributions of ions and recoils were recorded and the mean ranges were calculated. The recoil and vacancy distributions as a function of track depth was studied mainly for the high yield Mo and La fission ions. The results indicated that the average number of recoils and vacancies produced from one ion of Mo and/or La amounted to 367x104 for recoils and 3.61 x 104 and 6.55 x 104 for vacancies, respectively. The replacement collisions amounted to 4% and 1% for Mo and La ions. The Total energy to aluminum recoils resulting from Mo and La ions was 3.67 and 6.77 MeV. The corresponding energies per recoil are 82 eV and 100 eV. The displacement energy required to create vacancy-recoil pair was found to be 20 5 eV and and the minimum energies with recoils to create Frenkle pairs are 102.5 and 120.5 eV for Mo and La ions

  17. Automatic counting of fission fragments tracks using the gas permeation technique

    Yamazaki, I M

    1999-01-01

    An automatic counting system for fission tracks induced in a polycarbonate plastic Makrofol KG (10 mu m thickness) is described. The method is based on the gas transport mechanism proposed by Knudsen, where the gas permeability for a porous membrane is expected to be directly related to its track density. In this work, nitrogen permeabilities for several Makrofol films, with different fission track densities, have been measured using an adequate gas permeation system. The fission tracks were produced by irradiating Makrofol foils with a 252Cf calibrated source in a 2 pi geometry. A calibration curve fission track number versus nitrogen permeability has been obtained, for track densities higher than 1000/cm sup 2 , where the spark gap technique and the visual methods employing a microscope, are not appropriate for track counting.

  18. Automatic counting of fission fragments tracks using the gas permeation technique

    An automatic counting system for fission tracks induced in a polycarbonate plastic Makrofol KG (10 μm thickness) is described. The method is based on the gas transport mechanism proposed by Knudsen, where the gas permeability for a porous membrane is expected to be directly related to its track density. In this work, nitrogen permeabilities for several Makrofol films, with different fission track densities, have been measured using an adequate gas permeation system. The fission tracks were produced by irradiating Makrofol foils with a 252Cf calibrated source in a 2π geometry. A calibration curve fission track number versus nitrogen permeability has been obtained, for track densities higher than 1000/cm2, where the spark gap technique and the visual methods employing a microscope, are not appropriate for track counting

  19. Fission-Fragment Mass Distribution and Particle Evaporation at low Energies

    Schmitt, Ch.; Bartel, J.; Pomorski, K.; Surowiec, A.

    2002-01-01

    Fusion-fission dynamics is investigated with a special emphasis on fusion reactions at low energy for which shell effects and pairing correlations can play a crucial role leading in particular to multi-modal fission. To follow the dynamical evolution of an excited and rotating nucleus we solve a 2-dimensional Langevin equation taking explicitly light-particle evaporation into account. The confrontation theory-experiment is demonstrated to give interesting information on the model presented, i...

  20. The Effects of Nuclear Excitation of Prompt Fragments on the Independent Yields and Neutron Yields in Fission

    It has been found possible to account for the fine structure in the neutron yield versus mass distribution. The prediction is based on the assumption of a prompt independent curve obtained from the equal-charge-displacement (ECD) postulate and a linear dependence of fission-fragment excitation energy with mass. The method adopted for calculating neutron yields has been used to investigate the effect of neutron emission on independent yields. Independent yields after neutron emission have been calculated using ECD and a ''transition-state'' method to describe the prompt charge distribution. The calculated independent yields have been compared with some recent data. (author)

  1. Integral range, energy, residual range, and linear energy transfer distributions for Californium fission fragments in microelectronics materials

    This report discusses the advantages and limitations of using Cf-252 radiation sources for single event testing of microelectronics for space environments. Integral distributions for the range, energy, residual range, and linear energy transfer of Cf-252 fission fragments in absorber and microelectronic materials have been calculated. Techniques are suggested for determining when single event testing using Cf-252 is appropriate; also, techniques are given for estimating the saturation cross section and thresh old linear energy transfer from test data. 10 refs., 25 figs., 2 tabs

  2. Production and study of fission fragments, from Lohengrin to Alto; Production et etude des fragments de fission, de Lohengrin a Alto

    Ibrahim, F

    2005-06-15

    The study of nuclei far from stability is constitutive of the history of nuclear physics at its very beginning and has been making considerable great strides since then. The study of these nuclei give the opportunity to reach new information on the nuclear structure and thus to measure the solidity of our knowledge on nuclear matter and its validity when it is pushed to its limits. The reaction selected for the production of exotic nuclei in the framework of the PARRNe program is the fission of uranium 238. The nuclei produced have an intermediate mass and are very rich in neutrons. The technique to recover them in order to accelerate them is the thick target method called also the Isol technique. The installation of the ancient Lep injector at the Tandem line in Orsay (IPN) is expected to increase by a factor 100 the production rate of exotic nuclei in the PARRNe program, it is the Alto project. The work presented here concerns studies carried out at the Lohengrin spectrometer installed at the ILL in Grenoble, and at the Tandem installation in Orsay. This document is divided into 4 parts: 1) in flight techniques at Lohengrin, 2) the Isol technique, 3) magic numbers in the domain N=50, and 4) the Alto project.

  3. Percolation-fission model study of the fragment mass distribution for the 1 GeV proton induced reaction

    The 1 GeV proton induced reaction on 208Pb targets is analyzed by using the percolation model combined with the Atchison fission model. The fragment mass distribution and the isotopic production cross sections obtained from our model are compared with the experimental data. The trends of the fragment mass distribution for the 1 GeV proton induced reaction can be reproduced by our calculation in some degree. The order of magnitude for the calculated isotopic production cross sections at the calculated peak positions is similar to that of the experimental peak values. The calculated peak positions of the isotopic production cross sections are shifted to the heavier region than those of the experimental data. (author)

  4. Fission-fragment attachment to aerosols and their transport through capillary tubes

    The transport of radioactive aerosols was studied using equipment, collectively called the Helium jet, that has been constructed to provide basic nuclear physics data on fission product nuclides. The transport of the fission products in the system depends on their attachment to aerosol particles. The system consists of 1) a tube furnace which generates aerosols by the sublimation or evaporation of source material, 2) a helium stream used to transport the aerosols, 3) a 25 m settling tube to eliminate the larger aerosols and smaller aerosols that would deposit in the capillary, 4) a Californium-252 self-fissioning source of fission product nuclides, and 5) a small capillary to carry the radioactive aerosols from the hot cell to the laboratory. Different source materials were aerosolized but NaCl is generally used because it yielded the highest transport efficiencies through the capillary. Particle size measurments were made with NaCl aerosols by using a cascade impactor, an optical light scattering device, and the capillary itself as a diffusion battery by performing radiation measurements and/or electrical conductivity measurements. Both radioactive and nonradioactive aerosols were measured in order to investigate the possibility of a preferential size range for fission product attachment. The measured size distributions were then used to calculate attachment coefficients and finally an attachment time

  5. Evaluation of fission product yields from fission spectrum n+239Pu using a meta analysis of benchmark data

    Chadwick, Mark B.

    2009-10-01

    Los Alamos conducted a dual fission-chamber experiment in the 1970s in the Bigten critical assembly to determine fission product data in a fast (fission neutron spectrum) environment, and this defined the Laboratory's fission basis today. We describe how the data from this experiment are consistent with other benchmark fission product yield measurements for 95,97Zr, 140Ba, 143,144Ce, 137Cs from the NIST-led ILRR fission chamber experiments, and from Maeck's mass-spectrometry data. We perform a new evaluation of the fission product yields that is planned for ENDF/B-VII.1. Because the measurement database for some of the FPs is small—especially for 147Nd and 99Mo—we use a meta-analysis that incorporates insights from other accurately-measured benchmark FP data. The %-relative changes compared to ENDF/B-VI are small for some FPs (less than 1% for 95Zr, 140Ba, 144Ce), but are larger for 99Mo (3%) and 147Nd (5%). We suggest an incident neutron energy dependence to the 147Nd fission product yield that accounts for observed differences in the FPY at a few-hundred keV average energy in fast reactors versus measurements made at higher average energies.

  6. Combining random gene fission and rational gene fusion to discover near-infrared fluorescent protein fragments that report on protein-protein interactions.

    Pandey, Naresh; Nobles, Christopher L; Zechiedrich, Lynn; Maresso, Anthony W; Silberg, Jonathan J

    2015-05-15

    Gene fission can convert monomeric proteins into two-piece catalysts, reporters, and transcription factors for systems and synthetic biology. However, some proteins can be challenging to fragment without disrupting function, such as near-infrared fluorescent protein (IFP). We describe a directed evolution strategy that can overcome this challenge by randomly fragmenting proteins and concomitantly fusing the protein fragments to pairs of proteins or peptides that associate. We used this method to create libraries that express fragmented IFP as fusions to a pair of associating peptides (IAAL-E3 and IAAL-K3) and proteins (CheA and CheY) and screened for fragmented IFP with detectable near-infrared fluorescence. Thirteen novel fragmented IFPs were identified, all of which arose from backbone fission proximal to the interdomain linker. Either the IAAL-E3 and IAAL-K3 peptides or CheA and CheY proteins could assist with IFP fragment complementation, although the IAAL-E3 and IAAL-K3 peptides consistently yielded higher fluorescence. These results demonstrate how random gene fission can be coupled to rational gene fusion to create libraries enriched in fragmented proteins with AND gate logic that is dependent upon a protein-protein interaction, and they suggest that these near-infrared fluorescent protein fragments will be suitable as reporters for pairs of promoters and protein-protein interactions within whole animals. PMID:25265085

  7. Systematic experimental survey on projectile fragmentation and fission induced in collisions of 238U at 1 A GeV with lead

    Projectile fragmentation and fission, induced in collisions of 238U at 1 A GeV with lead, have systematically been studied. A complete survey on the isotopic production cross sections of all elements between vanadium (Z = 23) and rhenium (Z = 75) down to a cross section of 0.1 mb is given. About 600 isotopes produced in fragmentation and about 600 isotopes produced in fission were identified in the GSI fragment separator FRS from magnetic rigidities, time-of-flight values, and the energy loss in an ionisation chamber. In addition, the velocity distributions of all these reaction products have been mapped, and the products are unambiguously attributed to the different reaction mechanisms due to their kinematical properties. The results are compared with empirical systematics and previous data. The velocity of the fragments obtained in the fission process by the Coulomb repulsion allows to reconstruct the TKE-value of the break-up and to identify the atomic number of the fissioning nucleus in hot fission. The mean velocities of light projectile fragments were found to be higher than the beam velocity. (orig.)

  8. Systematic experimental survey on projectile fragmentation and fission induced in collisions of {sup 238}U at 1 A GeV with lead

    Enquist, T.; Benlliure, J.; Farget, F.; Schmidt, K.H.; Armbruster, P. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany); Bernas, M.; Tassan-Got, L. [Paris-11 Univ., 91 - Orsay (France). Inst. de Physique Nucleaire; Boudard, A.; Legrain, R.; Volant, C. [CEA Centre d`Etudes Nucleaires de Saclay, 91 - Gif-sur-Yvette (France). Dept. d`Astrophysique, de Physique des Particules, de Physique Nucleaire et de l`Instrumentation Associee (DAPNIA); Boeckstiegel, C.; Jong, M. de [Technische Univ. Darmstadt (Germany); Dufour, J.P. [CEA Centre d`Etudes Nucleaires de Bordeaux-Gradignan, 33 - Gradignan (France)

    1999-03-01

    Projectile fragmentation and fission, induced in collisions of {sup 238}U at 1 A GeV with lead, have systematically been studied. A complete survey on the isotopic production cross sections of all elements between vanadium (Z = 23) and rhenium (Z = 75) down to a cross section of 0.1 mb is given. About 600 isotopes produced in fragmentation and about 600 isotopes produced in fission were identified in the GSI fragment separator FRS from magnetic rigidities, time-of-flight values, and the energy loss in an ionisation chamber. In addition, the velocity distributions of all these reaction products have been mapped, and the products are unambiguously attributed to the different reaction mechanisms due to their kinematical properties. The results are compared with empirical systematics and previous data. The velocity of the fragments obtained in the fission process by the Coulomb repulsion allows to reconstruct the TKE-value of the break-up and to identify the atomic number of the fissioning nucleus in hot fission. The mean velocities of light projectile fragments were found to be higher than the beam velocity. (orig.) 41 refs.

  9. Decay heat and anti-neutrino energy spectra in fission fragments from total absorption spectroscopy

    Rykaczewski, Krzysztof

    2015-10-01

    Decay studies of over forty 238U fission products have been studied using ORNL's Modular Total Absorption Spectrometer. The results are showing increased decay heat values, by 10% to 50%, and the energy spectra of anti-neutrinos shifted towards lower energies. The latter effect is resulting in a reduced number of anti-neutrinos interacting with matter, often by tens of percent per fission product. The results for several studied nuclei will be presented and their impact on decay heat pattern in power reactors and reactor anti-neutrino physics will be discussed.

  10. Structure of fission fragments of mass A = 100 - 110: lifetime measurements and mean field and beyond mean field analysis

    Neutron-rich nuclei of mass A=100-110 are of great interest for the study of nuclear structure far from stability. Previous experimental and theoretical studies suggest a complex evolution of deformation and collectivity in the isotopic chains of Zr, Mo, Ru and Pd. In order to extend information on the evolution of the collectivity towards higher spin states and more neutron-rich nuclei, lifetimes of excited states were measured in nuclei produced through a fusion-fission reaction in inverse kinematic at GANIL. Fission fragments were separated and identified in both A and Z with the high acceptance magnetic spectrometer VAMOS while the EXOGAM germanium detectors array was used for the coincident gamma-ray detection. Lifetimes of about twenty excited states were extracted using the plunger device of Cologne. This is the first RDDS measurement on fission fragments which are identified in A and Z on an event-by-event basis. The study of this mass region is completed by theoretical calculations using self consistent mean field and beyond mean field methods implemented with the Gogny force (D1S). The structure of the ground states and the excited states is described with Hartree-Fock-Bogoliubov calculations with constraints placed on the axial and triaxial deformations. Individual excitations are investigated through blocking calculations and the high spin states are studied through cranking calculations. Finally, an approximated generator coordinate method (GCM+GOA) using the 5DCH Hamiltonian is used to describe the low energy collective states and to interpret the experimental evolution of the collectivity. (author)

  11. Comments About the Partition of Excitation Energy Between Complementary Fission Fragments in Connection with 'A Chairman's Note' of T. Ohsawa

    The very interesting Chairman's Note of Mr. T. Ohsawa regarding the question of excitation energy partition pushed me to write some comments about this theme that maybe can give 'much food for thoughts'. Regarding the energy sorting mechanism proposed by K-H.Schmidt and B.Jurado, affirming that the nascent fragments cannot share the same temperature at scission. P.Talou and co-workers have written: this 'stems from one assumption and one observation: i) it is assumed that the nascent fragments near scission are already in their equilibrated ground- state shape and ii) a formula for the temperature of the fragments is inferred from observed level densities. The assumption of a constant temperature formula is best suited to low excitation energies and is part of the Gilbert-Cameron level density composite representation. However, the distribution of excitation energies in the fission fragments extends to higher energies for which the Fermi-gas formula might be a better representation, as it was considered by a great part of physicists, for instance research groups from Dresda (A.Ruben et al), Los Alamos (P.Talou et al.), CEA-Cadarache (O.Serot and O.Litaize), Bucharest (A.Tudora et al.) and so on. Concerning the energy sorting mechanism, as T.Ohsawa mentioned, K-H Schmidt discussed, on the base of Egidy's formula: T =A-2/3 (17.45-0.515S+0.51S2 that the temperature of heavy fragments (HF) is lower than that of light fragments (LF) unless the shell effect S is large, which can explain the behaviour of experimental ν(A) of Naqvi et al. at 0.8 MeV and 5.5 MeV, the increase in νtot is totally accounted for only by νH.' This experimental fact is 'interpreted by energy sorting in a superfluid system due to temperature difference TL>TH

  12. Measurement of Fragment Mass Yields in Neutron-Induced Fission of 232TH and 238U at 33, 45 and 60 Mev

    Simutkin, V. D.; Pomp, S.; Blomgren, J.; Österlund, M.; Andersson, P.; Bevilacqua, R.; Ryzhov, I. V.; Tutin, G. A.; Khlopin, V. G.; Onegin, M. S.; Vaishnene, L. A.; Meulders, J. P.; Prieels, R.

    2011-10-01

    Over the past years, a significant effort has been devoted to measurements of neutron-induced fission cross-sections at intermediate energies but there is a lack of experimental data on fission yields. Here we describe recent measurements of pre-neutron emission fragment mass distributions from intermediate energy neutron-induced fission of 232Th and 238U. The measurements have been done at the quasi-monoenergetic neutron beam of the Louvain-la-Neuve cyclotron facility CYCLONE and neutron peak energies at 32.8, 45.3 and 59.9 MeV. A multi-section Frisch-gridded ionization chamber was used as a fission fragment detector. The measurement results are compared with available experimental data. Some TALYS code modifications done to describe the experimental results are discussed.

  13. Spontaneous fission

    Recent experimental results for spontaneous fission half-lives and fission fragment mass and kinetic-energy distributions and other properties of the fragments are reviewed and compared with recent theoretical models. The experimental data lend support to the existence of the predicted deformed shells near Z = 108 and N = 162. Prospects for extending detailed studies of spontaneous fission properties to elements beyond hahnium (element 105) are considered. (orig.)

  14. Experimental Neutron-Induced Fission Fragment Mass Yields of 232Th and 238U at Energies from 10 to 33 MeV

    Simutkin, V. D.; Pomp, S.; Blomgren, J.; Österlund, M.; R. Bevilacqua; Ryzhov, I. V.; Tutin, G. A.; Yavshits, S. G.; Vaishnene, L. A.; Onegin, M S; Meulders, J.P.; Prieels, R.

    2013-01-01

    Development of nuclear energy applications requires data for neutron-induced reactions for actinides in a wide neutron energy range. Here we describe measurements of pre-neutron emission fission fragment mass yields of 232Th and 238U at incident neutron energies from 10 to 33 MeV. The measurements were done at the quasi-monoenergetic neutron beam of the Louvain-la-Neuve cyclotron facility CYCLONE; a multi-section twin Frisch-gridded ionization chamber was used to detect fission fragments. For...

  15. Extreme population inversion in the fragments formed by UV photoinduced S-H bond fission in 2-thiophenethiol.

    Ingle, Rebecca A; Karsili, Tolga N V; Dennis, Gregg J; Staniforth, Michael; Stavros, Vasilios G; Ashfold, Michael N R

    2016-04-20

    H atom loss following near ultraviolet photoexcitation of gas phase 2-thiophenethiol molecules has been studied experimentally, by photofragment translational spectroscopy (PTS) methods, and computationally, by ab initio electronic structure calculations. The long wavelength (277.5 ≥ λphot ≥ 240 nm) PTS data are consistent with S-H bond fission after population of the first (1)πσ* state. The partner thiophenethiyl (R) radicals are formed predominantly in their first excited Ã(2)A' state, but assignment of a weak signal attributable to H + R(X[combining tilde](2)A'') products allows determination of the S-H bond strength, D0 = 27 800 ± 100 cm(-1) and the Ã-X[combining tilde] state splitting in the thiophenethiyl radical (ΔE = 3580 ± 100 cm(-1)). The deduced population inversion between the à and X[combining tilde] states of the radical reflects the non-planar ground state geometry (wherein the S-H bond is directed near orthogonal to the ring plane) which, post-photoexcitation, is unable to planarise sufficiently prior to bond fission. This dictates that the dissociating molecules follow the adiabatic fragmentation pathway to electronically excited radical products. π* ← π absorption dominates at shorter excitation wavelengths. Coupling to the same (1)πσ* potential energy surface (PES) remains the dominant dissociation route, but a minor yield of H atoms attributable to a rival fragmentation pathway is identified. These products are deduced to arise via unimolecular decay following internal conversion to the ground (S0) state PES via a conical intersection accessed by intra-ring C-S bond extension. The measured translational energy disposal shows a more striking change once λphot ≤ 220 nm. Once again, however, the dominant decay pathway is deduced to be S-H bond fission following coupling to the (1)πσ* PES but, in this case, many of the evolving molecules are deduced to have sufficiently near-planar geometries to allow passage through the

  16. Development of a higher power fission-fragment-excited CO laser

    Mcarthur, D. A.

    1976-01-01

    Moderate dilution of the CO with Ar lowers the reactor excitation threshold for lasing. Fission coatings on ceramic substrates have been developed which minimize fouling of laser mirrors. A new laser apparatus was constructed which more closely resembles large electrically excited CO lasers. Measurements of the energy emerging from the foils indicate that excitation of the gas is still below optimum values. Laser action at room temperature has also been observed.

  17. Radiochemical methods used by the IAEA's laboratories at Siebersdorf for the determination of 90Sr, 144Ce and Pu radionuclides in environmental samples collected for the International Chernobyl Project

    During the IAEA's International Chernobyl Project to assess the radiological consequences of the nuclear reactor accident, the Agency's Laboratories at Seibersdorf participated in the collection and analyses of environmental samples from the Soviet Union. Under Task 2 of this effort, the determination of the activity concentrations of 90Sr and the alpha-emitting Pu radionuclides was important for the corroboration of the official USSR environmental contamination maps. The present paper describes in detail the sampling methods and radiochemical procedures used for the 90Sr, 144Ce, 238Pu and 239,240Pu analyses in these samples with emphasis on the grass and soil treatments. (Author)

  18. Variation of Kinetic Energy of Fragments in Fission of 235U with 0.006 - 20ev Neutrons

    Utilizing the LNF ONYal neutron spectrometer working in the energy range between 0.006 and 20 eV, the variation in fragments' kinetic energy (EK) was studied, applying the method of relative yields (W) measurements, in the thermal neutron region and at 11 resonances of 235U. It was found that the resonances at 0.29, 2.04, 3.14, 4.84, and 7.09 eV can be sorted in a group of resonances with small values of W and EK . The resonances at 1.14, 3.60, 6.40, 8.78, 12.4, and 19.3 eV form a group with big values of W and EK. Comparison of W with radiochemical data on fragments' yield at thermal and resonance region of 235U showed that EK is larger at more asymmetrical fission. From the values W ( I ) and W(II) for the two groups of resonances, the change in the average kinetic energy of fragments 2ΔEK = 0.74 ± 0. 32 MeV was determined. (author)

  19. Analysis of Intermediate-Energy Nucleus-Nucleus Spallation, Fission, and Fragmentation Reactions with the LAQGSM code

    Mashnik, S G; Prael, R E; Sierk, A J

    2003-01-01

    The LAQGSM code has been recently developed at Los Alamos National Laboratory to simulate nuclear reactions for proton radiography applications. We have benchmarked our code against most available measured data both for proton-nucleus and nucleus-nucleus interactions at incident energies from 10 MeV to 800 GeV and have compared our results with predictions of other current models used by the nuclear community. Here, we present a brief description of our code and show illustrative results obtained with LAQGSM for neutron spectra measured recently by Nakamura's groups for reactions induced by light and medium nuclei on targets from C to Pb at several incident energies from 95 to 600 MeV/nucleon and with the recent GSI measurements of spallation, fission, and fragmentation yields from A+p and A+A reactions at incident energies near and below 1 GeV/nucleon. Further necessary work is outlined.

  20. Effect of the fragment excitation energy distribution on the prompt fission neutron spectrum

    The effects of cascade emission of neutrons from a nucleus and of distribution of the initial excitation energy upon characteristics of the emission spectrum are studied. Calculations of the emission spectrum are made in the Weisskopf form in the constant temperature approximation. It has been elucidated that the cascade character of particle emission is not sufficient for the total spectrum to approach the maxwellian one. A dependence of the distorting function upon energy has been obtained. The calculation spectrum is compared with the experimental and with the Weisskopf spectra. A conclusion is drawn that the temperature dependence upon excitation energy is predominant in formation of a fission neutron spectrum

  1. Fragment-mass distributions in neutron-induced fission of Th232 and U238 at 33, 45, and 60 MeV

    Ryzhov, I. V.; Yavshits, S. G.; Tutin, G. A.; Kovalev, N. V.; Saulski, A. V.; Kudryashev, N. A.; Onegin, M. S.; Vaishnene, L. A.; Gavrikov, Yu. A.; Grudzevich, O. T.; Simutkin, V. D.; Pomp, S.; Blomgren, J.; Österlund, M.; Andersson, P.; Bevilacqua, R.; Meulders, J. P.; Prieels, R.

    2011-05-01

    We have measured fission fragment-mass yields for neutron-induced fission of Th232 and U238 at energies 32.8, 45.3, and 59.9 MeV. The experiments were done at quasimonoenergetic neutron beams of the Cyclotron Research Center at Louvain-la-Neuve. To detect the fission fragments, a multisection Frisch-gridded ionization chamber was used. The measurement and data analysis techniques are discussed in detail. The obtained mass yields are compared to model calculations with the intermediate-energy nuclear reaction code MCFX. The MCFX code is used to calculate the fraction of fissioning nuclei after cascade, preequilibrium, and statistical reaction stages. The formation of mass distributions is considered as a result of oscillations of the mass-asymmetry degree of freedom in the potential well calculated with the temperature-dependent shell correction method. The experimental results as well as the results of the model calculations demonstrate that the probability of symmetric fission increases with incident neutron energy for both nuclei. The comparison also shows that the symmetric fission is more enhanced for thorium than for uranium with increasing neutron energy. We also compare U238 results with available experimental data; the Th232 data were measured for the first time.

  2. Excitation energy dependence of fragment-mass distributions from fission of 180,190Hg formed in fusion reactions of 36Ar + 144,154Sm

    K. Nishio

    2015-09-01

    Full Text Available Mass distributions of fission fragments from the compound nuclei 180Hg and 190Hg formed in fusion reactions 36Ar + 144Sm and 36Ar + 154Sm, respectively, were measured at initial excitation energies of E⁎(Hg180=33–66 MeV and E⁎(Hg190=48–71 MeV. In the fission of 180Hg, the mass spectra were well reproduced by assuming only an asymmetric-mass division, with most probable light and heavy fragment masses A¯L/A¯H=79/101. The mass asymmetry for 180Hg agrees well with that obtained in the low-energy β+/EC-delayed fission of 180Tl, from our earlier ISOLDE(CERN experiment. Fission of 190Hg is found to proceed in a similar way, delivering the mass asymmetry of A¯L/A¯H=83/107, throughout the measured excitation energy range. The persistence as a function of excitation energy of the mass-asymmetric fission for both proton-rich Hg isotopes gives strong evidence for the survival of microscopic effects up to effective excitation energies of compound nuclei as high as 40 MeV. This behavior is different from fission of actinide nuclei and heavier mercury isotope 198Hg.

  3. Total Absorption Spectroscopy of Fission Fragments Relevant for Reactor Antineutrino Spectra and Decay Heat Calculations

    Porta A.

    2016-01-01

    Full Text Available Beta decay of fission products is at the origin of decay heat and antineutrino emission in nuclear reactors. Decay heat represents about 7% of the reactor power during operation and strongly impacts reactor safety. Reactor antineutrino detection is used in several fundamental neutrino physics experiments and it can also be used for reactor monitoring and non-proliferation purposes. 92,93Rb are two fission products of importance in reactor antineutrino spectra and decay heat, but their β-decay properties are not well known. New measurements of 92,93Rb β-decay properties have been performed at the IGISOL facility (Jyväskylä, Finland using Total Absorption Spectroscopy (TAS. TAS is complementary to techniques based on Germanium detectors. It implies the use of a calorimeter to measure the total gamma intensity de-exciting each level in the daughter nucleus providing a direct measurement of the beta feeding. In these proceedings we present preliminary results for 93Rb, our measured beta feedings for 92Rb and we show the impact of these results on reactor antineutrino spectra and decay heat calculations.

  4. Total Absorption Spectroscopy of Fission Fragments Relevant for Reactor Antineutrino Spectra and Decay Heat Calculations

    Porta, A.; Zakari-Issoufou, A.-A.; Fallot, M.; Algora, A.; Tain, J. L.; Valencia, E.; Rice, S.; Bui, V. M.; Cormon, S.; Estienne, M.; Agramunt, J.; Äystö, J.; Bowry, M.; Briz, J. A.; Caballero-Folch, R.; Cano-Ott, D.; Cucouanes, A.; Elomaa, V.-V.; Eronen, T.; Estévez, E.; Farrelly, G. F.; Garcia, A. R.; Gelletly, W.; Gomez-Hornillos, M. B.; Gorlychev, V.; Hakala, J.; Jokinen, A.; Jordan, M. D.; Kankainen, A.; Karvonen, P.; Kolhinen, V. S.; Kondev, F. G.; Martinez, T.; Mendoza, E.; Molina, F.; Moore, I.; Perez-Cerdán, A. B.; Podolyák, Zs.; Penttilä, H.; Regan, P. H.; Reponen, M.; Rissanen, J.; Rubio, B.; Shiba, T.; Sonzogni, A. A.; Weber, C.

    2016-03-01

    Beta decay of fission products is at the origin of decay heat and antineutrino emission in nuclear reactors. Decay heat represents about 7% of the reactor power during operation and strongly impacts reactor safety. Reactor antineutrino detection is used in several fundamental neutrino physics experiments and it can also be used for reactor monitoring and non-proliferation purposes. 92,93Rb are two fission products of importance in reactor antineutrino spectra and decay heat, but their β-decay properties are not well known. New measurements of 92,93Rb β-decay properties have been performed at the IGISOL facility (Jyväskylä, Finland) using Total Absorption Spectroscopy (TAS). TAS is complementary to techniques based on Germanium detectors. It implies the use of a calorimeter to measure the total gamma intensity de-exciting each level in the daughter nucleus providing a direct measurement of the beta feeding. In these proceedings we present preliminary results for 93Rb, our measured beta feedings for 92Rb and we show the impact of these results on reactor antineutrino spectra and decay heat calculations.

  5. A contribution to the study of mass-kinetic energy-nuclear charges correlations for fission fragments with the 'Cosi Fan Tutte' spectrometer

    The present work is devoted to the fragments produced in the neutrons induced fission of 235U, performed with the time of flight-energy spectrometer 'Cosi Fan Tutte' recently built at the neutron high flux reactor of the Laue-Langevin Institute at Grenoble. Mass-kinetic energy-nuclear charge correlations were measured for the light fission fragment group. Nuclear charges were identified for the first time on this spectrometer using the range difference of the fission fragments in an axial field ionisation chamber. The present results are in good agreement with the previous one obtained using the spectrometer 'Lohengrin', which proves the validity of the methods which we developed. In addition, we extend the measurements to higher kinetic energies. The structures which appear in the distributions are attributed to spherical and deformed shell effects in the nascent fragments and to even odd effects. The study of thermal neutron induced fission of 229Th, which is scarcely known, has been started. (author)

  6. Investigation of the fission fragment properties of the reaction 238U(n,f) at incident neutron energies up to 5.8 MeV

    The fission fragment properties of the reaction 238U(n,f) have been studied, at different incident neutron energies ranging from En=1.2 to 5.8 MeV. The pre-neutron emission mass, kinetic energy and fission fragment angular distributions have been investigated with a double Frisch-gridded ionization chamber. The influence of the subthreshold vibrational resonances and of the proton pairing effect on the fission fragment properties is clearly visible. The total kinetic energy averaged over all fission fragment masses TKEbar shows an increasing trend up to En=3.5 MeV with a sudden drop at roughly En=3.8 MeV which has been attributed to the onset of pair breaking at the barrier. Above En=3.8 MeV, the TKEbar is again continuously increasing. The changes in the mass yield and TKEbar(A) distributions have been studied as a function of the compound nuclear excitation energy and their contribution to the observed variations in the TKEbar have been determined. The two-dimensional mass-TKE distributions have been described in terms of fission modes and compared with theoretical calculations performed recently in the frame of the multi-modal random neck-rupture model. Although theoretically six asymmetric fission modes are predicted which all surpass individual outer barriers, an interpretation in terms of only two asymmetric modes has physical meaning. This points to an influence of shell structure effects to the observed distributions. In any case, the super-long symmetric mode has to be included, in order to explain the dip in TKEbar(A) distribution close to symmetry

  7. Investigation of the fission fragment properties of the reaction 238U(n,f) at incident neutron energies up to 5.8 MeV

    Vivès, F.; Hambsch, F.-J.; Bax, H.; Oberstedt, S.

    2000-01-01

    The fission fragment properties of the reaction 238U(n,f) have been studied, at different incident neutron energies ranging from En=1.2 to 5.8 MeV. The pre-neutron emission mass, kinetic energy and fission fragment angular distributions have been investigated with a double Frisch-gridded ionization chamber. The influence of the subthreshold vibrational resonances and of the proton pairing effect on the fission fragment properties is clearly visible. The total kinetic energy averaged over all fission fragment masses ( overlineTKE) shows an increasing trend up to En=3.5 MeV with a sudden drop at roughly En=3.8 MeV which has been attributed to the onset of pair breaking at the barrier. Above En=3.8 MeV, the overlineTKE is again continuously increasing. The changes in the mass yield and overlineTKE( A) distributions have been studied as a function of the compound nuclear excitation energy and their contribution to the observed variations in the overlineTKE have been determined. The two-dimensional mass-TKE distributions have been described in terms of fission modes and compared with theoretical calculations performed recently in the frame of the multi-modal random neck-rupture model. Although theoretically six asymmetric fission modes are predicted which all surpass individual outer barriers, an interpretation in terms of only two asymmetric modes has physical meaning. This points to an influence of shell structure effects to the observed distributions. In any case, the super-long symmetric mode has to be included, in order to explain the dip in overlineTKE( A) distribution close to symmetry.

  8. The Energies, Angular Distribution and Yields of the Prompt Neutrons from Individual Fragments in the Thermal-Neutron Fission of U233 and U235

    An apparatus for simultaneously recording the velocities of both fission fragments and the velocity of a neutron at any one of four angles to the fragment direction has been used to investigate the neutron-emission properties of individual fragments. Early results for U233 exhibit the saw-tooth variation of v, the neutron yield per fragment, observed in the spontaneous fission of Cf252 The yields in the vicinity of mass 130 are consistent with no neutrons being emitted from these fragments. Unlike the neutron yields, the average neutron kinetic energy is symmetric about the symmetric mass point, being high near this point and low at the most probable mass division. The paradox between very small yields and high apparent nuclear temperatures has been qualitatively explained on the basis of a model that takes account of shell structure in the level densities and assumes that at the time of scission the fragments are cold but in some cases highly deformed, in others nearly spherical. The model is supported by the fact that in fissions with more than the average total excitation energy, the fragments near mass 130 and 80 receive much less than half the increase in energy and the other fragment of the pair much more. The experiment is now being conducted with U235 under considerably improved conditions. The background per channel under the neutron spectrum has been reduced by nearly a factor of three, so that 0.39 of all recorded events in the 10° detector are useful neutron events with a corresponding increase in statistical accuracy. Better time resolution in the fragment system (1.5 ns, full width at half maximum) has allowed the. flight paths to be shortened to 125 and 100 cm (formerly 145-145 cm) with a concomitant higher countings rate. (author)

  9. New statistical scission-point model to predict fission fragment observables

    Lemaître, Jean-François; Panebianco, Stefano; Sida, Jean-Luc; Hilaire, Stéphane; Heinrich, Sophie

    2015-09-01

    The development of high performance computing facilities makes possible a massive production of nuclear data in a full microscopic framework. Taking advantage of the individual potential calculations of more than 7000 nuclei, a new statistical scission-point model, called SPY, has been developed. It gives access to the absolute available energy at the scission point, which allows the use of a parameter-free microcanonical statistical description to calculate the distributions and the mean values of all fission observables. SPY uses the richness of microscopy in a rather simple theoretical framework, without any parameter except the scission-point definition, to draw clear answers based on perfect knowledge of the ingredients involved in the model, with very limited computing cost.

  10. Final report: Accelerated beta decay for disposal of fission fragment wastes

    The fundamental theory of the interaction of intense, low-frequency electromagnetic fields with certain radioactive nuclei has been fully formulated. The nuclei are of the type that exists in high-level radioactive wastes that are end products of the production of energy from nuclear fission. The basic physical mechanisms that underlie the coupling of the applied field to the nucleus have been identified. Both the basic theory and numerical predictions that stem from it support the conclusion that high-level radioactive wastes can be disposed of by substantially accelerating the rate of radioactive decay. Some old experiments on the acceleration of this type of radioactivity, with results that were not understood at the time, have been re-examined. Their interpretation is now clear, and the experiments are found to be in agreement with the theory

  11. Fragment angular momentum and descent dynamics in 252Cf spontaneous fission

    Fragment angular momenta as a function of neutron multiplicity were extracted for the first time for the Mo-Ba and Zr-Ce charge splits of 252Cf by studying prompt coincident γ-rays. The obtained primary fragment angular momenta do not continuously rise with the increase in the number of neutrons evaporated. In frame of the scission point bending oscillation model such regularity is explained due the decrease of the bending temperature. Adiabatic bending oscillations (T=0) are obtained at large (νtot>5) and small (νtot=0) scission point elongation. These oscillations are excited to the temperature of 2-3 MeV for the most probable scission configurations indicating a weak coupling between collective and internal degrees of freedom. A strong coupling between the collective bending and dipole oscillations was found

  12. Fragment angular momentum and descent dynamics in 252Cf spontaneous fission

    Fragment angular momenta as a function of neutron multiplicity were extracted for the first time for the Mo-Ba and Zr-Ce charge splits of 252Cf by studying prompt coincident γ-rays. The obtained primary fragment angular momenta do not continuously rise with the increase in the number of neutrons evaporated. In frame of the scission point bending oscillation model such regularity is explained due the decrease of the bending temperature. Adiabatic bending oscillations (T=0) are obtained at large (νtot>5) and small (νtot=0) scission point elongation. These oscillations are excited to the temperature of 2 - 3 MeV for the most probable scission configurations indicating a weak coupling between collective and internal degrees of freedom. A strong coupling between the collective bending and dipole oscillations was found. copyright 1998 American Institute of Physics

  13. Multi-parameter spectroscopy of fission fragments and related emission products

    An exclusive measurement of the 252C f(sf) fragment distribution in mass and energy in coincidence with the related emission products by combining a twin ionization chamber with a 4π-neutron tank, a n-γ-detector, and a solid-state detector telescope is presented. The experimental set-up, data handling and acquisition is described followed by a discussion of the raw data evaluation. (orig.)

  14. Fission barrier determinations and fragment angular correlations for the 244Pu, 242Pu, 240U, 238U, 234Th, and 232Th compound nuclei from (t, pf) reactions

    Fission probabilities and the angular distribution of the fission fragments have been measured for six even-even compound nuclear systems using the (t, pf) reaction. Angular correlations of fission fragments obtained in these experiments provide information about the low-lying collective excitations or transition states at the fission barrier. The (t, p) reaction in particular leads to neutron-rich residual nuclei unobtainable by other methods. The absence of spin coupling for (t, p) reactions on even-even targets provides angular distributions with well defined structure in the region of the fission barrier. The experimental data were obtained using an 18-MeV triton beam on targets of 242Pu, 240Pu, 238U, 236U, 232Th and 230Th at Los Alamos Van-de-Graaff accelerator facility. Outgoing protons were detected at 140 deg relative to the incident triton beam. Excitation energies ranging from 3.0 to 9.0 MeV were obtained in these experiments. Fission fragment angular distributions were measured at 24 angles from 0 deg to 140 deg relative to the kinematic recoil angle. The data were fitted to a series of even Legendre polynomials W(θ) = A0 [1 + ΣL gL PL (cos θ)] and the coefficients g2 through g12 and A0 were determined as a function of excitation energy. The fission probability Pf was obtained from the ratio of A0 to the (t, p) cross-section for the target nucleus. The results exhibit well defined structure in the angular coefficients which correlates with structure in the fission probability for most of the nuclei studied. In an attempt to interpret this observed structure the experimentally determined fitting parameters Pf and g are compared with calculated results of a microscopic model. This model takes into consideration the penetrability and angular dependence of fission through each member of the various transition bands at the saddle point and appropriately sums the results for comparison with the data. The effects of barrier penetration through a two

  15. True ternary fission, the collinear decay into fragments of similar size in the 252Cf(sf) and 235U(nth, f) reactions

    The collinear cluster decay in 252Cf(sf, fff), with three cluster fragments of different masses (e.g. 132Sn, 52–48Ca, 68–72Ni), which has been observed by the FOBOS group in JINR, has established a new decay mode of heavy nuclei, the collinear cluster tripartition (CCT). The same type of ternary fission decay has been observed in the reaction 235U(nth, fff). This kind of “true ternary fission” of heavy nuclei has been predicted many times in theoretical works during the last decades. In the present note we discuss true ternary fission (TFFF) into three nuclei of almost equal size (e.g. Z=98→Zi=32, 34, 32) in the same systems. The possible fission channels are predicted from potential-energy (PES) calculations. These PES's show pronounced minima for several ternary fragmentation decays, e.g. for 252Cf(sf) and for 235U(nth, f). They suggest the existence of a variety of collinear ternary fission modes. The TFFF-decays chosen in this letter have very similar dynamical features as the previously observed collinear CCT-decays. The data obtained in the above mentioned experiments allow us to extract the yield for these TFFF-decays in both systems by using specific gates on the measured parameters. These yields are a few 1.0⋅10−6/(binary fission)

  16. Ternary fission

    M Balasubramaniam; K R Vijayaraghavan; C Karthikraj

    2015-09-01

    We present the ternary fission of 252Cf and 236U within a three-cluster model as well as in a level density approach. The competition between collinear and equatorial geometry is studied by calculating the ternary fragmentation potential as a function of the angle between the lines joining the stationary middle fragment and the two end fragments. The obtained results for the 16O accompanying ternary fission indicate that collinear configuration is preferred to equatorial configuration. Further, for all the possible third fragments, the potential energy surface (PES) is calculated corresponding to an arrangement in which the heaviest and the lightest fragments are considered at the end in a collinear configuration. The PES reveals several possible ternary modes including true ternary modes where the three fragments are of similar size. The complete mass distributions of Si and Ca which accompanied ternary fission of 236U is studied within a level density picture. The obtained results favour several possible ternary combinations.

  17. Measurement of isotopic cross sections of the fission fragments produced in 500 AMeV {sup 208}Pb + p reaction; Etude de la production des fragments de fission issus de la reaction {sup 208}Pb + p a 500 AMeV

    Fernandez-Dominguez, B

    2003-03-01

    The aim of this work is the study of the fission fragments produced in the spallation reaction {sup 208}Pb + p at 500 AMeV. The fission fragments from Z=23 up to Z=59 have been detected and identified by using the inverse kinematics technique with the high-resolution spectrometer FRS. The production cross sections and the recoil velocities of 430 nuclei have been measured. The measured data have been compared with previous data. The isotopic distributions show a high precision. However, the absolute value of the fission cross section is higher than expected. From the experimental data the characteristics of the average fissioning system have been reconstructed (Z{sub fis}, A{sub fis}, E*{sub fis}). In addition, the number of post-fission neutrons emitted from the fission fragments, v{sub post}, has been determined by using a new method. The experimental data have been compared to the two-steps models describing the spallation reaction. The impact of the model parameters on the observables has been analysed and the reasons Leading to the observed differences between the codes are also presented. This analyse shows a good agreement with the INCL4+ABLA code. (author)

  18. Time-odd effects and the spectroscopic properties of odd-mass fission fragments

    Adding an extra nucleon having a definite K-value to an axially symmetrical even-even core generates a breaking of the time-reversal symmetry. Within the Skyrme-Hartree-Fock approach the effects of the time-odd mean-field terms resulting from the presence of non-vanishing current and spin-vector densities are investigated. In this preliminary study, pairing correlations are not taken into account. The associated removal of the Kramers degeneracy is interpreted in terms of diamagnetic/paramagnetic types of polarization of the even-even core in the field of an odd particle. This general approach is illustrated here by calculations in the region of light fragments of heavy (e.g. actinide) nuclei. (authors)

  19. Calculation of Beta Decay Half-Lives and Delayed Neutron Branching Ratio of Fission Fragments with Skyrme-QRPA

    Minato Futoshi

    2016-01-01

    Full Text Available Nuclear β-decay and delayed neutron (DN emission is important for the r-process nucleosynthesis after the freeze-out, and stable and safe operation of nuclear reactors. Even though radioactive beam facilities have enabled us to measure β-decay and branching ratio of neutron-rich nuclei apart from the stability line in the nuclear chart, there are still a lot of nuclei which one cannot investigate experimentally. In particular, information on DN is rather scarce than that of T1/2. To predict T1/2 and the branching ratios of DN for next JENDL decay data, we have developed a method which comprises the quasiparticle-random-phase-approximation (QRPA and the Hauser-Feshbach statistical model (HFSM. In this work, we calculate fission fragments with T1/2 ≤ 50 sec. We obtain the rms deviation from experimental half-life of 3:71. Although the result is still worse than GT2 which has been adopted in JENDL decay data, DN spectra are newly calculated. We also discuss further subjects to be done in future for improving the present approach and making next generation of JENDL decay data.

  20. Calculation of Beta Decay Half-Lives and Delayed Neutron Branching Ratio of Fission Fragments with Skyrme-QRPA

    Minato, Futoshi

    2016-06-01

    Nuclear β-decay and delayed neutron (DN) emission is important for the r-process nucleosynthesis after the freeze-out, and stable and safe operation of nuclear reactors. Even though radioactive beam facilities have enabled us to measure β-decay and branching ratio of neutron-rich nuclei apart from the stability line in the nuclear chart, there are still a lot of nuclei which one cannot investigate experimentally. In particular, information on DN is rather scarce than that of T1/2. To predict T1/2 and the branching ratios of DN for next JENDL decay data, we have developed a method which comprises the quasiparticle-random-phase-approximation (QRPA) and the Hauser-Feshbach statistical model (HFSM). In this work, we calculate fission fragments with T1/2 ≤ 50 sec. We obtain the rms deviation from experimental half-life of 3:71. Although the result is still worse than GT2 which has been adopted in JENDL decay data, DN spectra are newly calculated. We also discuss further subjects to be done in future for improving the present approach and making next generation of JENDL decay data.

  1. Method of photo-etching and photogravure using fission fragment and/or alpha ray etch tracks from toned photographs

    The formation of images on non-photo-receptive surfaces is described. In the past the reproduction of images has involved the initial step of screening the image. The present method does not require such screening and the image produced bears a quantitative and positional relationship to the silver grains present in the photograph from which the image is being produced. The method consists of reproducing a photographic image on a normally non-photo-receptive surface comprising the steps of toning the photograph with substances which combine with or replace the silver grains so that the photograph emits either spontaneously or indirectly fission fragments or alpha particles in amounts related to the distribution of the silver grains in the photograph, and placing the toned photograph contiguous with the surface on which the image is to be reproduced, for sufficient time for the emissions from the photograph to reproduce the image as a radiation-damage image on the surface, the damage areas having a close positional relationship to the silver grains in the original photograph

  2. Variation of Fission-Fragment Kinetic Energy Distribution, Mass Distribution, and Yield of Long-Range Alpha Particles in the Resonance-Neutron-Induced Fission of U235 and Pu239

    These measurements were undertaken to obtain additional information on the fission process, and to investigate the application of this information to the assignment of J-values to resonance levels, as the usual methods of determining J-values are of limited applicability in the case of fissile isotopes. An earlier study of U235 showed that the fission-fragment kinetic energy and the alpha yield varied significantly from level to level, and fell into two groups suggestive of the two possible J-values. The present paper reports on measurements on Pu239. A study of 19 levels shows 15 levels with high average kinetic energy and 4 levels with low average kinetic energy, the former being assigned J -1 and the latter J = 0 on the basis of the expected ratio of population of the two spin states and also for maximum compatibility with other determinations. Some variation of relative alpha-particle yield was found. It is concluded that (1) there are definite variations of kinetic energy of the fragments from level to level; (2) the variation in the case of U235 is correlated with the relative yield of symmetric fission; (3) there is some indication in the case of Pu239 that the variation of fragment energy is correlated with the J-values; and (4) the relative yield of alpha particles varies in an expected fashion. (author)

  3. Experimental Neutron-Induced Fission Fragment Mass Yields of 232Th and 238U at Energies from 10 to 33 MeV

    Simutkin, V D; Blomgren, J; Österlund, M; Bevilacqua, R; Ryzhov, I V; Tutin, G A; Yavshits, S G; Vaishnene, L A; Onegin, M S; Meulders, J P; Prieels, R

    2013-01-01

    Development of nuclear energy applications requires data for neutron-induced reactions for actinides in a wide neutron energy range. Here we describe measurements of pre-neutron emission fission fragment mass yields of 232Th and 238U at incident neutron energies from 10 to 33 MeV. The measurements were done at the quasi-monoenergetic neutron beam of the Louvain-la-Neuve cyclotron facility CYCLONE; a multi-section twin Frisch-gridded ionization chamber was used to detect fission fragments. For the peak neutron energies at 33, 45 and 60 MeV, the details of the data analysis and the experimental results have been published before and in this work we present data analysis in the low-energy tail of the neutron energy spectra. The preliminary measurement results are compared with available experimental data and theoretical predictions.

  4. Coulomb and even-odd effects in cold and super-asymmetric fragmentation for thermal neutron induced fission of 235U

    Montoya, Modesto

    2015-01-01

    The Coulomb effects hypothesis is used to interpret even-odd effects of maximum total kinetic energy as a function of mass and charge of fragments from thermal neutron induced fission of 235U. Assuming spherical fragments at scission, the Coulomb interaction energy between fragments (C_sph) is higher than the Q-value, the available energy. Therefore at scission the fragments must be deformed, so that the Coulomb interaction energy does not exceed the Q-value. The fact that the even-odd effects in the maximum total kinetic energy as a function of the charge and mass, respectively, are lower than the even-odd effects of Q is consistent with the assumption that odd mass fragments are softer than the even-even fragments. Even-odd effects of charge distribution in super asymmetric fragmentation also are interpreted with the Coulomb effect hypothesis. Because the difference between C_sph and Q increases with asymmetry, fragmentations require higher total deformation energy to occur. Higher deformation energy of the...

  5. On the energy balance and on dynamical aspects of proton induced fission of 235,236,238U by coincident spectroscopy of neutrons and fragments

    An improved experimental set up has been developed and applied to the measurement of neutrons in coincidence with fragments originating in proton induced fission of heavy nuclei. The reaction systems studied were p+235,236,238U for Ep = 12.84 MeV and Ep = 20.4 MeV. Data interpretation focuses on the following aspects: 1. Neutron multiplicities and average kinetic energies were studied as a function of fragment mass and total kinetic energies of these fragments. 2. The isotropic (i.e. the prefission plus scission) neutrons reveal a dependence of their multiplicities on the primary excitation energy E*CN that indicates a preference of the neutron over the fission exit channel with increasing E*CN not found in statistical model calculations. 3. A consistent analysis of all existing data for p+235,236,238U covering the interval 18 MeV ≤ E*CN ≤ 30 MeV in terms of neutron multiplicities and nuclear temperatures yields that pre- and postfission neutrons carry away comparable fractions of the additional energy ΔE*CN. 4. The total energy released in neutron and fragment emission is shown for p+238U (Ep = 20.4 MeV) to compare with the energy expected from mass tables for the fragmentations selected to within 2-3%. (orig.)

  6. New results from isochronous mass measurements of neutron-rich uranium fission fragments with the FRS-ESR-facility at GSI

    Knöbel, R.; Diwisch, M.; Geissel, H.; Litvinov, Yu. A.; Patyk, Z.; Plaß, W. R.; Scheidenberger, C.; Sun, B.; Weick, H.; Bosch, F.; Boutin, D.; Chen, L.; Dimopoulou, C.; Dolinskii, A.; Franczak, B.; Franzke, B.; Hausmann, M.; Kozhuharov, C.; Kurcewicz, J.; Litvinov, S. A.; Matoš, M.; Mazzocco, M.; Münzenberg, G.; Nakajima, S.; Nociforo, C.; Nolden, F.; Ohtsubo, T.; Ozawa, A.; Stadlmann, J.; Steck, M.; Suzuki, T.; Walker, P. M.; Winkler, M.; Yamaguchi, T.

    2016-05-01

    Masses of uranium fission fragments have been measured with the FRagment Separator (FRS) combined with the Experimental Storage Ring (ESR) at GSI. A 410-415 MeV/u 238U projectile beam was fast extracted from the synchrotron SIS-18 with an average intensity of 109/spill. The projectiles were focused on a 1g/cm2 beryllium target at the entrance of the FRS to create neutron-rich isotopes via abrasion-fission. The fission fragments were spatially separated with the FRS and injected into the isochronous storage ring ESR for fast mass measurements without applying cooling. The Isochronous Mass Spectrometry (IMS) was performed under two different experimental conditions, with and without B ρ-tagging at the high-resolution dispersive central focal plane of the FRS. The evaluation has been done for the combined data sets from both experiments with a new method of data analysis. The use of a correlation matrix has provided experimental mass values for 23 different neutron-rich isotopes for the first time and 6 masses with improved values. The new masses were obtained for nuclides in the element range from Se to Ce. The applied analysis has given access even to rare isotopes detected with an intensity of a few atoms per week. The novel data analysis and systematic error determination are described and the results are compared with extrapolations of experimental values and theoretical models.

  7. Measurement of Fragment Mass Distributions in Neutron-induced Fission of {sup 238}U and {sup 232}Th at Intermediate Energies

    Simutkin, V.D. [Uppsala University, P.O Box 525, SE-751 20 Uppsala (Sweden)

    2008-07-01

    Conceptual analysis of accelerator-driven systems assumes extensive use of nuclear data on neutron-induced reactions at intermediate energies. In particular, information about the fission fragment yields from the {sup 238}U(n,f) and {sup 232}Th(n,f) reactions is of particular interest at neutron energies from 10 to 200 MeV. However, there is a lack of such data for both {sup 238}U and {sup 232}Th. Up to now, the intermediate energy measurements have been performed for {sup 238}U only, and there are no data for the {sup 232}Th(n,f) reaction. The aim of the work is to provide such data. Fission fragment mass distributions for the {sup 232}Th(n,f) and {sup 238}U(n,f) reactions have been measured for the incident neutron energies 32.8 MeV, 45.3 MeV and 59.9 MeV. The experiments have been performed at the neutron beam facility of the Universite Catholique de Louvain, Belgium. A multi-section Frisch-gridded ionization chamber has been used as a fission fragment detector. The data obtained have been interpreted in terms of the multimodal random neck-rupture model (MMRNRM). (authors)

  8. Fission Research at IRMM

    Al-Adili A.; Fabry I.; Borcea R.; Zeynalov S.; Kornilov N.; Hambsch F.-J.; Oberstedt S.

    2010-01-01

    Fission Research at JRC-IRMM has a longstanding tradition. The present paper is discussing recent investigations of fission fragment properties of 238 U(n,f), 234 U(n,f), prompt neutron emission in fission of 252 Cf(SF) as well as the prompt fission neutron spectrum of 235 U(n,f) and is presenting the most important results.

  9. Preparative electrophoresis of industrial fission product solutions

    The aim of this work is to contribute to the development of the continuous electrophoresis technique while studying its application in the preparative electrophoresis of industrial fission product solutions. The apparatus described is original. It was built for the purposes of the investigation and proved very reliable in operation. The experimental conditions necessary to maintain and supervise the apparatus in a state of equilibrium are examined in detail; their stability is an important factor, indispensable to the correct performance of an experiment. By subjecting an industrial solution of fission products to preparative electrophoresis it is possible, according to the experimental conditions, to prepare carrier-free radioelements of radiochemical purity (from 5 to 7 radioelements): 137Cs, 90Sr, 141+144Ce, 91Y, 95Nb, 95Zr, 103+106Ru. (author)

  10. Behaviour of solid fission products in the HTGR coated fuel particles

    Results of profile measurements for volume concentrations of 134,137Cs, 144Ce, 155Eu, 106Ru and fissionable material in the HTGR coated fuel particles which have been subjected to standard tests in the temperature range of 1273-2133 K and at burnup up to 17% fima are presented. Values of the effective coefficients of cesium diffusion in kern and protective coating of fuel particles which were subjected to standard in-pile tests in spherical fuel elements at the temperature of 1273 K and the burnup up to 15% fima as well as the value of relative release of solid fission products from the samples studied are given

  11. Fission Fragment Folding Angle Distributions for the Systems 11B+237Np, 12C+236U, and 16O+232Th in the Energy Range 1.1B<2.1

    Fission fragment folding angle distributions have been measured for the systems 11B+237Np, 12C+236U, and 16O+232Th, populating the same compound nucleus (248Cf) and at similar excitation energies (Ex 45-100 MeV). The full momentum transfer and incomplete momentum transfer fusion-fission components have been separated over the bombarding energy range 1.1c.m/VB 2.1. It is observed that the largest value of the ratio of the transfer fission to the total fission is around 10 to 15% at the highest energy investigated. Over the energy range mentioned above, it is found that the transfer fission corrected fission fragment anisotropies are not significantly different from the values already obtained from the analysis of the total fission data reported earlier and hence the conclusions reached from the inclusive data remain unchanged. The anisotropy data were analyzed for the two cases corresponding to fission events with sizable fission barriers (Bf>T) and with smaller fission barriers (Bf>T). It was interesting to find that the effective moment of inertia (Jeff) values deduced from the latter component were consistent with the values from Sierk prescription used in the former case

  12. Average Number and Energy of Gamma-Rays Emitted as a Function of Fragment Mass in U235 Thermal-Neutron-Induced Fission

    The average number and energy of gamma-rays emitted as a function of fragment mass in U235 thermal-neutron-induced fission have been measured. A three-parameter correlation experimeni was performed in which two silicon suríace barrier detectors were used to measure the fission product energies, and a 5-in-diam., 4-in-thick Nal(Tl) scintillation crystal was used to measure the gamma-ray energies. Extreme care was taken in the experimental arrangement to avoid counting direct fission neutrons, scattered gamma-rays and neutrons, and other false events. Data were recorded event-by-event in a system similar to that used in previous energy correlation experiments at Oak Ridge, and were analysed according to a ''weighting method'' proposed by Maier-Leibnitz. The total number and energy of the gamma- rays for both fragments as a function of mass ratio were obtained directly. The number and energy of gamma- rays for individual fragment masses were determined by making use of the variation in laboratory angular distribution and energy of the gamma-rays emitted from moving fragments. In particular, the 0° to 180° ratio of the number of gamma-rays from a moving source emitting isotropically in its centre-of-mass system is proportional to 1 + 2 x 2v/c; similarly the 0° to 180° ratio in total gamma energy is proportional to 1 + 2 x3v/c. Thus by comparing appropriate ratios in the analysis for light and heavy fragments moving towards or away from the gamma-ray derector, one obtains these quantities as a function of individual fragment mass. Results of preliminary analyses show interesting similarities in behaviour to those for neutrons. Both the total energy and average quantum energy of gamma-rays are essentially constant over most of the range of mass ratios; however a broad minimum is observed for the total energy in the region where Mh ∼ 130, i. e. where ZH ∼ 50 or NH ∼ 82. An increase is observed in the total energy as the mass ratio approaches unity. The number

  13. Storage ion trap of an 'In-Flight Capture' type for precise mass measurement of radioactive nuclear reaction products and fission fragments

    Data on nuclear masses provide a basis for creating and testing various nuclear models. A tandem system of FLNR comprised of the U-400M cyclotron, the COMBAS magnetic separator and the mass-spectrometric ion trap of an 'in-flight capture' type is considered as a possible complex for producing of the short-lived nuclei in fragmentation reactions by heavy ions and for precise mass measurement of these nuclei. The plan of scientific and technical FLNR research includes a project DRIBs for producing beams of accelerated radioactive nuclear reaction products and photofission fragments. This project proposes also precise mass measurements of the fission fragment with the help of the ion trap. The in-flight entrance of the ions and their capture in the mass-spectrometric ion trap using the monochromatizing degrader, the static electric and magnetic fields and a new invention, a magnetic unidirectional transporting ventil, is considered

  14. Assessment of selected fission products in the Savannah River Site environment

    Most of the radioactivity produced by the operation of a nuclear reactor results from the fission process, during which the nucleus of a fissionable atom (such as 235U) splits into two or more nuclei, which typically are radioactive. The Radionuclide Assessment Program (RAP) has reported on fission products cesium, strontium, iodine, and technetium. Many other radionuclides are produced by the fission process. Releases of several additional fission products that result in dose to the offsite population are discussed in this publication. They are 95Zr, 95Nb, 103Ru, 106Ru, 141Ce, and 144Ce. This document will discuss the production, release, migration, and dose to humans for each of these selected fission products

  15. Use of Angular-Distribution Measurements of Fission Fragments Emitted from Single Crystals for Determining the Lifetimes of Excited Compound Nuclei

    The angular distribution of fission fragments emitted from uranium oxide crystals bombarded with protons in the energy range 9-12 MeV has been measured by using plastic fission-track detectors. The protein energies, and with these the compound-nuclei excitation energies, were selected to give second-chance fission 238Np compound nuclei with life-times in the range detectable by this technique. An upper limit of ≤ 7 x 10-17s has been established for the ''effective lifetime'' of compound nuclei formed by 12-MeV proton bombardment of 238U. A value of 1.4 ± 0.6 x 10-16s has been measured for the total lifetime and 2. 5 ± 1.2 x 10-16s for the partial fission lifetime of 238Np compound nuclei at an average excitation energy of ∼7.3 MeV. The measurements were found to be sensitive to random scattering effects. Experimental determination and analytical treatment of such effects are discussed. (author)

  16. High resolution measurement of fragment mass-charge-kinetic energy correlations in the cold fragmentation region of thermal fission of 235U

    Signarbieux, C.; Simon, G.; Trochon, J.; Brisard, F.

    1985-01-01

    The performance of a back-to-back gridded ionization chamber containing an extremely thin fissile target has been investigated for studying the cold fragmentation phenomenon : primary fragment kinetic energy is measured with a resolution much better than 300 keV; mass separation is total and for each mass, a good charge separation is obtained. The evolution of the charge distribution as a function of the fragments' total kinetic energy is discussed for the mass-ratio 132/104.

  17. Fission fragment mass, kinetic energy and angular distribution for 235U(n,f) in the neutron energy range from thermal to 6 MeV

    A double Frisch gridded ionization chamber has been used for the measurements. For both fission fragments the mass, kinetic energy and emission angle is found. Data have been measured at different neutron energies, Esub(n), ranging from thermal to 6.0 MeV in steps of 0.5 MeV. The measured angular anisotropies will be shown. A fit, based on statistical theory, to earlier measurements of negative anisotropies for Esub(n)<=0.2 MeV will be discussed.The measured total kinetic energy averaged over all fragment masses, TKE-bar(Esub(n)), shows a sudden decrease at Esub(n)approx. 4.5 MeV in agreement with earlier measurements. This sudden decrease can not be explained by the measured change in the mass distribution. The present data of TKE-bar(Esub(n)) as function of mass-split reveal that TKE-bar(Esub(n)) decreases with Esub(n) for mass splits around the 104/132 split as predicted by calculations of B.D. Wilkins et al. It is also seen that TKE-bar(Esub(n)) increases with Esub(n) for the symmetric and the extreme asymmetric fissions. The very structured mass distribution from approximately cold fragmentation will be presented. (author)

  18. Experimental Neutron-induced Fission Fragment Mass Yields of 232Th and 238U at Energies from 10 to 33 Me

    Simutkin, V. D.; Pomp, S.; Blomgren, J.; Österlund, M.; Bevilacqua, R.; Andersson, P.; Ryzhov, I. V.; Tutin, G. A.; Yavshits, S. G.; Vaishnene, L. A.; Onegin, M. S.; Meulders, J. P.; Prieels, R.

    2014-05-01

    Development of nuclear energy applications requires data for neutron-induced reactions for actinides in a wide neutron energy range. Here we describe measurements of pre-neutron emission fission fragment mass yields of 232Th and 238U at incident neutron energies from 10 to 33 MeV. The measurements were done at the quasi-monoenergetic neutron beam of the Louvain-la-Neuve cyclotron facility CYCLONE; a multi-section twin Frisch-gridded ionization chamber was used to detect fission fragments. For the peak neutron energies at 33, 45 and 60 MeV, the details of the data analysis and the experimental results were published in Ref. [I.V. Ryzhov, S.G. Yavshits, G.A. Tutin et al., Phys. Rev. C 83, 054603 (2011)]. In this work we present data analysis in the low-energy tail of the neutron energy spectra. The preliminary measurement results are compared with available experimental data and theoretical predictions.

  19. Fission fragments and structural materials cross sections accuracy influence on main characteristics in fast neutron reactor physics

    This report is devoted to the exactingness in neutronic data to impose at the fission products and at the structural materials. To construct fast neutron power reactors it is necessary to know the accuracy in the calcul of multiplication factor, regeneration factor and reactivity losses. In this report the main error sources are examined

  20. Appendix to Health and Safety Laboratory environmental quarterly, March 1, 1976--June 1, 1976. [Tabulated data on content of lead in surface air and /sup 7/Be, /sup 95/Zr, /sup 137/Cs, /sup 144/Ce, and /sup 90/Sr in surface air, milk, drinking water, and foods sampled in USA

    Hardy, E.P. Jr.

    1976-07-01

    Tabulated data are presented on: the monthly deposition of /sup 89/Sr and /sup 90/Sr at some 100 world land sites; the content of lead and /sup 7/Be, /sup 95/Zr, /sup 137/Cs, and /sup 144/Ce in samples of surface air from various world sites; and the content of /sup 90/Sr in samples of milk, drinking water, and animal and human diets collected at various locations throughout the USA. (CH)