Delayed neutron yields and spectra from photofission of actinides: data and calculations with Bremsstrahlung photons below 20 MeV

Abstract

Abstract. Photonuclear reactions, especially photofission delayed neutron emission, play an important role for applications involving nuclear material detection. In order to provide good quality data for evaluations and data libraries, an experimental program of delayed neutron measurements has been undertaken for actinides with Bremsstrahlung energy from 12 up to 20 MeV. In this paper, we report on delayed neutron yields and time spectra characteristics from the photofission of 238 U and 235 U for several endpoint energies between 12 and 18.5 MeV. The associated modelling efforts will be described including some calculations compared to experimental data.

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

“…Finally, the irradiation times chosen to "stimulate" preferentially groups two by two are: 300 s, 10 s and 1 s. Whatever the irradiation time, as soon as an irradiation sequence is completed, the neutron detection system is switched on and acquires the signal for a duration of 300 s. For statistics purposes, these measurements -based on 300 s, 10 s and 1 sirradiation times -were repeated respectively: 5, 50 and 100 times. Regarding groups 5 and 6, irradiation times below 1 s raise questions about beam stability and measurement reliability, which from the point of view of the authors of this paper is the case for experimental protocols followed in previous studies [6][7][8][9][10].…”

“…3 presents the results obtained. However, for this type of study, the delayed neutron groups are usually matched in pairs and three different irradiation times are chosen [6][7][8][9][10]. Fig.…”