Anisotropy in fission fragment and prompt neutron angular distributions

Abstract

Several physics mechanisms can lead to the deviation from an isotropic angular distribution for both fission fragments and the neutrons that are emitted during the fission event. Two of these effects have recently been implemented into CGMF, the Monte Carlo fission event generator developed at Los Alamos National Laboratory: angular distribution sampling for fission fragments and pre-equilibrium neutrons (those emitted before the compound nucleus forms). Using these new developments, we show that the anisotropy of the neutrons reflects the anisotropy of the fission fragments, in particular as the outgoing energy of neutrons increases. Correlations between the fission fragment and neutron anisotropies could be used to extract the fission fragment anisotropy from the neutron angular distributions.

Energy-Dependent Fission-Product Yields in the Region of Second-Chance Fission

“…The new FPY data in the mid-energy or second-chance fission region show a steady decrease as a function of incident neutron energy for all three actinides. This trend is consistent with the fission models implemented in GEF [14] and BeoH [15] codes. Considering FPYs near the valley of the mass distribution, described by the so-called superlong mode, we observe a steady increase in the measured fission yield with neutron energy.…”

“…All the GEF results have been obtained with the same default parameter set -no local parameter adjustment has been made. Our current results are also in very good agreement with the yields predicted by the BeoH multi-chance fission model as well [15]. The BeoH calculations are presented only for 239 Pu and 235 U neutron-induced fission [15,16].…”

“…Our current results are also in very good agreement with the yields predicted by the BeoH multi-chance fission model as well [15]. The BeoH calculations are presented only for 239 Pu and 235 U neutron-induced fission [15,16]. Both codes calculate a wide range of pre-and post-neutron fission observables in neutron-induced fission.…”

“…Both present and literature data are presented with their total uncertainty. comparison to the available literature data [10][11][12][13] and GEF and BeoH calculations [14][15][16]. Both present and literature data are presented with their total uncertainty.…”

“…2. Fission product yields of 95 Zr (left), 97 Zr (center), and 99 Mo (right) as a function of monoenergetic neutrons for fission of 239 Pu (top row), 235 U (middle row), and 238 U (bottom row) in comparison to the available literature data [10][11][12][13] and GEF and BeoH calculations [14][15][16]. Both present and literature data are presented with their total uncertainty.…”