Giant Dipole Resonance photofission and photoneutron reactions in ^238U and ^232Th
arxiv(2024)
Abstract
New measurements of photofission and photoneutron reactions on ^238U and
^232Th in the Giant Dipole Resonance (GDR) energy region have been
performed at the laser Compton-scattering γ-ray source of the NewSUBARU
synchrotron radiation facility using a high-and-flat efficiency moderated
^3He detection array. The neutron-multiplicity sorting of high-multiplicity
fission neutron coincidence events has been performed using a dedicated energy
dependent, multiple firing statistical treatment. The photoneutron
(γ, in) with i = 1 – 3 and photofission (γ, F) reactions
have been discriminated by considering a Gaussian distribution of
prompt-fission-neutron (PFN) multiplicities predicted by the theory of
evaporation in sequential neutron emission from excited fission fragments. We
report experimental (γ, n), (γ, 2n), (γ, 3n) and
(γ, F) cross sections, average energies of PFNs and of (γ, in)
photoneutrons, as well as the mean number of PFNs per fission act and the width
of the PFNs multiplicity distribution. Based on these primary experimental
results and combined with reasonable assumptions, we extract also the first-
and second-chance fission contributions. The new experimental results are
compared with statistical-model calculations performed with the EMPIRE-3.2
Malta and TALYS-1.964 codes on the present data and with prompt fission
emission calculations obtained with the Los Alamos model in the frame of the
most probable fragmentation approach with and without sequential emission.
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