Evaluation of delayed neutron yields and time spectra from photofission of ²³⁸U induced by Bremsstrahlung photons below 9 MeV

Université Paris-Saclay, CEA, List, F-91120 Palaiseau, France

^* Corresponding author: adrien.sari@cea.fr

Published online: 26 May 2023

Abstract

Few data exist regarding the yields and time spectra of delayed neutrons from the photofission reaction on actinides. In this paper, we report the characteristics of both six-group and eight-group delayed neutron time models for the photofission of ²³⁸U induced by a Bremsstrahlung photon spectrum with an end-point energy at 9 MeV. This study was conducted using a 9 MeV linear electron accelerator housed at the SAPHIR platform located at CEA Paris-Saclay, France. A reference sample of depleted uranium was positioned inside a neutron detection block, previously designed and optimized by Monte Carlo simulation, made of high-density polyethylene covered by cadmium and including ten one meter-long ³He proportional counters. Based on the consistent set of half-lives proposed by Spriggs et al. as early as 1999 for neutroninduced fission, our description in eight delayed neutron groups for ²³⁸U at 9 MeV is the first published for photofission. These new results bring valuable information to the scarce data available in the literature and represent useful inputs for the development of photofission-based nuclear measurement systems as they meet a significant interest in the fields of nuclear data, radioactive waste package characterization and for security-related applications.