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

Background: One important quantity in nuclear fission is the average number of prompt neutrons emitted from the fission fragments, the prompt neutron multiplicity. The total number of prompt fission neutrons 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 fragment yields has an impact on the reliable assessment of the nuclear waste inventory, as well as on the correct prediction of delayed neutron precursor yields.

AL-ADILI A.;  HAMBSCH Franz-Josef;  POMP S.;  OBERSTEDT Stephan; 

2013-01-23

AMER PHYSICAL SOC

JRC74072

0556-2813,   

http://prc.aps.org/abstract/PRC/v86/i5/e054601,    https://publications.jrc.ec.europa.eu/repository/handle/JRC74072,   

10.1103/PhysRevC.86.054601,