Neutron-Physical Characteristics of a Neutron Source for the Production of Radioactive Isotopes Based on the Interaction of Electrons with Liquid Gallium

Abstract

The nuclear-physical characteristics obtained for a gallium target in a series of experiments using the timeof-flight method, the method of threshold indicators and a spectrometer based on a 3 He proportional counter on the IREN setup (JINR, Dubna) are presented. The absolute values of the energy spectra of leakage neutrons in the energy range from 10 keV to 15 MeV were measured. The activation method was used to measure the neutron flux density on the surface of a gallium target: (2.882 ± 0.098)·10 8 sec ‐1 ·cm ‐2 . The integral yield of neutrons obtained from the gallium target on the basis of these data was 1.54·10 14 sec ‐1 with average current 4 mA. The time dependence of the activation level of the gallium target was measured. It was shown as a result of the analysis that the background level is reached on the surface of the irradiated gallium target in 5 days. The results of an experimental validation of a photoneutron source based on liquid gallium with no fissile materials, which is characterized by sufficient neutron yield for the production of radioactive isotopes for medical purposes, are present in this article. The method is based on a two-step process in which the reaction (γ, n) serves as the generator of the neutron flux, and the isotopes are produced by the neutron capture reaction (n, γ) or the neutron capture reaction (n, p) with the emission of a proton. For this reason, the database of neutron-physical constants for calculating the optimal configuration of the irradiation setup is expanded by including in it the cross sections of reactions induced by neutrons, as a result of which additional uncertainties in the computed quantities arise. Measurement of the Yield and the Angular and Energy Distributions of the Neutrons Generated in Gallium by 33.58 MeV Electrons. The IREN setup (Joint Institute for Nuclear Research, JINR, Dubna), operating in the pulsed regime with pulse repetition frequency 25 Hz, was used as the electron accelerator [1]. The average energy of the electrons incident on the gallium target was measured in a separate experiment and was equal to 33.58 MeV. The pulse width was 0.1 μsec and the current in a pulse was 1 A. The neutron flux monitor located in the experimental room showed high stability of the electron current. For this reason, the experimental data were processed assuming the intensity of the neutron source to be constant.