23 research outputs found
The microscopic theory of fission
Fission-fragment properties have been calculated for thermal neutron-induced
fission on a target, using constrained
Hartree-Fock-Bogoliubov calculations with a finite-range effective interaction.
A quantitative criterion based on the interaction energy between the nascent
fragments is introduced to define the scission configurations. The validity of
this criterion is benchmarked against experimental measurements of the kinetic
energies and of multiplicities of neutrons emitted by the fragments.Comment: 8 page, 4 figures, to be published in Proceedings of the 4th
International Workshop on Fission and Fission Product Spectroscop
Astrophysical Implication of Low E(2^+_1) in Neutron-rich Sn Isotopes
The observation and prediction of unusually depressed first excited 2^+_1
states in even-A neutron - rich isotopes of semi-magic Sn above 132Sn provide
motivations for reviewing the problems related to the nuclear astrophysics in
general. In the present work, the beta-decay rates of the exotic even Sn
isotopes (134,136Sn) above the 132Sn core have been calculated as a function of
temperature (T). In order to get the necessary ft values, B(GT) values
corresponding to allowed Gamow Teller (GT-) beta-decay have been theoretically
calculated using shell model. The total decay rate shows decrease with
increasing temperature as the ground state population is depleted and
population of excited states with slower decay rates increases. The abundance
at each Z value is inversely proportional to the decay constant of the waiting
point nucleus for that particular Z. So the increase in half-life of isotopes
of Sn, like 136Sn, might have substantial impact on the r-process
nucleosynthesis.Comment: 4th International Workshop on Nuclear Fission and Fission Product
Spectroscopy, CEA Cadarache, May 13 - 16, 2009, 4 pages, 2 figure
Spectroscopie des transfermiums impairs en proton (la structure du noyau de 251 Md)
La structure des transfermiums impairs en proton est actuellement peu connue. Ces noyaux sont produits par réactions de fusion-évaporation avec une faible section efficace, de l'ordre de 1 b. Leur identification a nécessité ici l'emploi de la méthode de Recoil-Tagging. Afin d'identifier les orbitales présentes dans cette région de masse, les isotopes de 255Lr, 251Md et 247Es ont été étudiés par spectroscopie retardée a l'Université de Jyväskylä et au GANIL, grâce au spectromètre LISE et au détecteur a et électron BEST couplé à 4 clovers empruntés à EXOGAM. De nouveaux états ont été observés et leur configuration proposée. Les propriétés collectives du 251Md ont également été étudiées par spectroscopie prompte g en combinant le multidétecteur JUROGAM avec le séparateur RITU équipé à son plan focal du spectromètre GREAT. Pour la première fois une bande rotationelle a été observée dans un transfermium impair en proton. L'interprétation de cette structure est basée sur des calculs HFBLYON1-BU.Sciences (692662101) / SudocSudocFranceF
Prendre soin des services publics : le management en question
International audienc
New prompt fission neutron spectra measurements in the 238U(n,f) reaction with a dedicated setup at LANSCE/WNR
A new prompt fission neutron spectra (PFNS) measurement in the 238U(n,f) reaction was performed at LANSCE/WNR facility. Evaluated data show discrepancies on the low (below 1 MeV) and high (above 5 MeV) energy parts in the PFNS for different major and minor actinides. The goal is to improve these measurements in a wide range of incident energy. The energy of the incoming neutron, inducing the fission, and the prompt neutron energies, are measured by time-of-flight method. A dedicated fission chamber was developed, in order to improve alpha-fission discrimination, timing resolution, actinide mass, and to reduce the amount of neutron scattering. To detect prompt neutrons, the 54 Chi-Nu scintillator cells array were surrounding the fission chamber. High statistics were recorded during this experiment, allowing a precise study of PFNS behavior as a function of incident neutron energy, from 1 MeV to 200 MeV. This experiment also showed that all the new tools developed to improve PFNS measurements are performing. Therefore, measurements of PFNS with others actinides such as 239Pu are planned
First Results on 238U(n,f) Prompt Fission Neutron Spectra from 1 to 200 MeV incident neutron energy
A new 238U(n,f) prompt fission neutron spectra (PFNS) measurement has been recently performed at the WNR facility of the Los Alamos National Laboratory. The measurement allows one to explore the dependence of the prompt fission neutron energy spectra on the incident neutron energy. The experimental setup couples the Chi-Nu scintillator array to a newly developed fission chamber, characterized by an improved alphafission discrimination and time resolution, a reduced amount of matter in the neutron beam and a higher actinide mass. The dedicated setup and the high statistics collected allow us to obtain a good precision on the measured fission neutron energy, as well as to explore the low energy region, down to 650keV, and the high energy region, above 5 MeV, of the emitted neutron spectrum. These are indeed the regions where discrepancies in the evaluated PFNS data are found. We present here the first preliminary results of the experiment
New prompt fission neutron spectra measurements in the U(n,f) reaction with a dedicated setup at LANSCE/WNR
International audienceA new prompt fission neutron spectra (PFNS) measurement in the 238U(n,f) reaction was performed at LANSCE/WNR facility. Evaluated data show discrepancies on the low (below 1 MeV) and high (above 5 MeV) energy parts in the PFNS for different major and minor actinides. The goal is to improve these measurements in a wide range of incident energy. The energy of the incoming neutron, inducing the fission, and the prompt neutron energies, are measured by time-of-flight method. A dedicated fission chamber was developed, in order to improve alpha-fission discrimination, timing resolution, actinide mass, and to reduce the amount of neutron scattering. To detect prompt neutrons, the 54 Chi-Nu scintillator cells array were surrounding the fission chamber. High statistics were recorded during this experiment, allowing a precise study of PFNS behavior as a function of incident neutron energy, from 1 MeV to 200 MeV. This experiment also showed that all the new tools developed to improve PFNS measurements are performing. Therefore, measurements of PFNS with others actinides such as 239Pu are planned
First Results on
A new 238U(n,f) prompt fission neutron spectra (PFNS) measurement has been recently performed at the WNR facility of the Los Alamos National Laboratory. The measurement allows one to explore the dependence of the prompt fission neutron energy spectra on the incident neutron energy. The experimental setup couples the Chi-Nu scintillator array to a newly developed fission chamber, characterized by an improved alphafission discrimination and time resolution, a reduced amount of matter in the neutron beam and a higher actinide mass. The dedicated setup and the high statistics collected allow us to obtain a good precision on the measured fission neutron energy, as well as to explore the low energy region, down to 650keV, and the high energy region, above 5 MeV, of the emitted neutron spectrum. These are indeed the regions where discrepancies in the evaluated PFNS data are found. We present here the first preliminary results of the experiment
Mesure de très haute précision des neutrons de fission du plutonium 239
International audienc