Speaker
Description
Photofission and photoneutron reactions on $^{238}$U and $^{232}$Th were investigated in the energy range of 5.86 MeV – 20.12 MeV by quasi-monochromatic $\gamma$-ray beams produced in laser Compton-scattering at the NewSUBARU synchrotron radiation facility. Direct neutron-multiplicity sorting was performed with a flat-efficiency neutron detector [1]. Following Terrell’s prescription [2], a normal distribution was used to describe the prompt-fission-neutron (PFN) multiplicity and thus separate the photofission and photoneutron contributions. We provide novel experimental ($\gamma$,n), ($\gamma$,2n) and ($\gamma$,f) cross sections, average energies of PFN and of photoneutrons emitted in ($\gamma$,n) and ($\gamma$,2n) reactions, as well as the mean number of PFN per fission act. The new cross sections and average energies of ($\gamma$,n) and ($\gamma$,2n) neutrons are evaluated with statistical-model calculations performed with the EMPIRE code [3] in comparison with preceding data.
[1] H. Utsunomiya et al., Nucl. Instrum. Meth. A 871, 135 (2017).
[2] J. Terrell, Phys. Rev. 108, 783 (1957).
[3] M. Herman et al., Nuclear Data Sheets 108, 2655 - 2715 (2007).