An experimental setup for measuring neutron yield from nuclear materials under exposure to bremsstrahlung (a photonuclear method)

Abstract

An experimental setup developed on the basis of the У-28 electron accelerator for investigating the applicability of a photonuclear method to detection of nuclear materials is described. The photonuclear method is based on quantitative analysis of delayed and prompt neutron fluxes from a sample after its irradiation with bremsstrahlung. Using results of numerical simulation of electron-photon and γ-ray-neutron transport, the key elements of the setup—the converter, the beam filter, the bremsstrahlung collimator, and the multilayer neutron detector—are optimized. Electronic modules have been developed for the data acquisition system and for switching a high voltage applied to the neutron counter for the bremsstrahlung emission time. The yields of prompt and delayed neutrons from nuclear material simulators (natural uranium and beryllium) shielded with various materials have been measured. In our experiments, it is shown that the photonuclear method allows reliable detection of highly shielded nuclear materials with masses of tens or hundreds of grams at a distance of >1 m.