Photofission and photoneutron cross sections for ²³⁸U and ²³²Th

¹ Horia Hulubei National Institute of Physics and Nuclear Engineering (IFIN-HH), 30 Reactorului, 077125 Bucharest, Romania
² Shanghai Advanced Research Institute, Chinese Academy of Sciences, No.99 Haike Road, Zhangjiang Hi-Tech Park, 201210 Pudong Shanghai, China
³ Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 Japan
⁴ Institute for Integrated Radiation and Nuclear Science, Kyoto University, 2-1010 Asashiro-nishi, Kumatori, Sennan, Osaka 590-0494, Japan
⁵ Department of Physics, University Politehnica of Bucharest, Splaiul Independentei 313, 060042 Bucharest, Romania
⁶ Lomonosov Moscow State University, Skobeltsyn Institute of Nuclear Physics, 119991 Moscow, Russia
⁷ University of Bucharest, Bucharest, Romania
⁸ Department of Physics, University of Oslo, N-0316 Oslo, Norway
⁹ Cyclotron Institute, Texas A&M University, College Station, Texas 77843, USA
¹⁰ Konan University, Department of Physics, 8-9-1 Okamoto, Higashinada, Kobe 658-8501, Japan
¹¹ Laboratory of Advanced Science and Technology for Industry, University of Hyogo, 3-1-2 Kouto, Kamigori, Ako-gun, Hyogo 678-1205, Japan

^* e-mail: dan.filipescu@nipne.ro

Published online: 26 May 2023

Abstract

A specific objective of the recent IAEA Coordinated Research Project on Photonuclear Data and Photon Strength Functions (Code F41032; Duration 2016-2019) has been to measure photonuclear cross-section data where needed, for unexplored nuclei and cases of discrepant existing data. A dedicated experimental campaign has been conducted at the laser Compton-scattering γ-ray source of the NewSUBARU synchrotron radiation facility of SPring8, Japan, where photoneutron reactions for 11 nuclei from ⁹Be to ²⁰⁹Bi have been investigated in the Giant Dipole Resonance energy region. The measurements followed the development of a flat-effi ciency moderated neutron detection array and the associated neutron-multiplicity sorting techniques. The IAEA CRP campaign has been followed at NewSUBARU by new measurements of photofission and photoneutron reactions on ²³⁸U and ²³²Th in the energy range of 5.87 MeV – 20.14 MeV. 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, xn) and photofission (γ, fxn) reactions have been discriminated by considering a Gaussian distribution of prompt-fission-neutrons (PFN) multiplicities predicted by the evaporation theory. We here provide preliminary experimental (γ, n), (γ, 2n) and (γ, F) cross sections, average energies of PFN and of photoneutrons emitted in (γ, n) and (γ, 2n) reactions, as well as the mean number of PFN per fission act. The new ²³⁸U cross sections are compared with recent statistical-model calculations performed with the EMPIRE code on existing data.