Post-neutron fragment distributions of 233U(nth,f) and how they are influenced by model ingredients and pre-neutron fragment distributions

Abstract

The series of investigations focused on post-neutron fragment distributions, i.e. fractional and total independent yields (Y(Z,A_p), Y(A_p)), isotonic yields of post neutron fragments (Y(N_p)), kinetic energy distributions of secondary fragments (KE_p), and the various influences on them as well as of different correlations between pre- and post-neutron fragment quantities (performed for ²³⁵U(n_th,f), ²³⁹Pu(n_th,f) and ²⁵²Cf(SF)) is ending now with a deeper investigation devoted to ²³³U(n_th,f). This has involved comprehensive prompt emission calculations (performed with the DSE model code) by using reliable pre-neutron fragment distributions Y(A,TKE) (5 sets of experimental data and a calculated one) and two fragmentation ranges (deterministically constructed by using reliable sets of the charge polarization ΔZ(A) and rms(A) of the isobaric charge distribution). As TXE partitions, beside that based on modeling at scission, another one based this time on the so-called “experimental temperature ratio R_T” provided by a new method (without resorting to prompt emission model calculations for the fit of ν(A) data as other codes do) was employed. This study not only confirmed and strengthened the previously observed features of how the structures of Y(A_p) and Y(N_p) are influenced by model ingredients and Y(A,TKE) but also has revealed that the most significant influence on prompt emission and all post-neutron fragment distributions is that of the TXE partition. The good description of existing experimental data of Y(Z,A_p), Y(A_p), KE_p(Z), KE_p(A_p) for ²³³U(n_th,f) by the DSE results obtained with the TXE partition based on modeling at scission and several Y(A,TKE) can be considered as an indirect validation of these Y(A,TKE) distributions of pre-neutron fragments. The sawtooth shape of the nice correlation between the excitation energy E* of fully accelerated pre-neutron fragments and KE_p of post neutron fragments (looking as a reflection in mirror of the sawtooth shape of ν(A)) is maintained regardless of the employed fragmentation range, TXE partition and Y(A,TKE). The almost perfect overlap of E*(KE_p) in the case of ^{235, 233}U(n_th,f) (which might seem intuitive because the even-even compound nuclei ^{236, 234}U undergoing fission are close neighbors with similar nuclear properties) is explained in detail by investigating the beahviours of all physical quantities and distributions which are involved in this correlation.