Optimal scheme for stimulating photofission of shielded nuclear materials on the Microtron M-30: a combination of theoretical and experimental studies

Abstract

Relevance. The photofission of shielded nuclear materials is widely used to develop methods for non-destructive analysis of their isotopic composition. To stimulate the photofission reaction, bremsstrahlung beams obtained on electronic accelerators are used. Their parameters significantly depend on the design features of accelerators and sample activation schemes. Purpose. Theoretical modelling of parameters of an optimal scheme for stimulating the photofission of shielded nuclear materials on an electronic accelerator – Microtron M-30 for the analysis of their isotopic composition, considering its technical characteristics, and experimental verification of its parameters. Methodology. Theoretical calculations of the parameters of bremsstrahlung beams for the Microtron M-30 were carried out using the GEANT4 toolkit. For experimental studies of the influence of structural elements of the optimal stimulation scheme on the integral characteristics of inhibitory photons, secondary photoneutrons, the method of activation of detectors made of gold was used; for residual electrons – the transmission method based on a passage chamber and a Faraday cylinder. Results. As a result of the combination of theoretical and experimental studies, optimal parameters of the activation scheme of nuclear materials on the Microtron M-30 have been established. The scheme provides experimental conditions under which the losses of bremsstrahlung photon beams interacting with the test samples (with energies ≥6 MeV) do not exceed 35% of their initial values, with the practical absence of residual electrons (98% of electrons are absorbed) and secondary photoneutrons (no more than 1E-9 n/e). Conclusions. The parameters of the developed stimulation scheme for the Microtron M-30 can be applied to various types of accelerators, considering their design features, characteristics of the samples, and implemented activation schemes