First experimental prompt γ-ray spectra in fast-neutron-induced fission of 238U

Abstract

The knowledge of prompt fission gamma-ray emission has been of major interest in reactor physics for a few years. Since no experimental spectra were ever published until now for fast neutron-induced fission, measurements would be also valuable to improve our understanding of the fission process. A simple experimental method was used to measure the prompt fission gamma-ray spectrum up to 10 MeV. In this approach, the gamma-rays are measured with a bismuth germanate (BGO) detector which offers two significant advantages with respect to other gamma-ray detectors: a high peak-to-total ratio and a high efficiency. The prompt fission neutrons are rejected by the time-of-flight technique between the BGO detector and a fission trigger given by a fission chamber. Prompt fission gamma-ray spectra were measured for 1.7, 5.2 and 15.6 MeV neutron-induced fission on 238U at the CEA, DAM, DIF Van de Graaff accelerator; average multiplicity and mean photon energy per fission were deduced from the spectra.