Use of gamma-ray spectroscopy for direct detection of thermal neutrons

Abstract

A neutron detector based on detection of the prompt gamma-radiation emitted as a result of neutron interaction with a suitable neutron absorber is described. Boron-10 loaded polyethylene is used as the neutron converter. Neutrons are thermalized in the polyethylene and are subsequently absorbed by ¹⁰B. The result of the neutron absorption is production of ⁷Li, in the excited state (⁷Li^*) and an alpha-particle. This occurs for 94% of the absorbed neutrons. The ⁷Li^* (T _1/2 = 10^-13 s) emits a 477.6 keV gamma-ray ("prompt" gamma-ray) after it is formed and may be detected in a gamma-ray spectroscopy system. Since the "prompt" gamma-ray peak is Doppler broadened – the recoiled ⁷Li^* emits the gamma-ray on "fly" – it is easily distinguishable from other non-capture gamma-ray peaks. The neutron converter, ¹⁰B loaded into a polyethylene end cap placed on the standard gamma-ray spectroscopy detector, adds the neutron detection capability without impeding the system's gamma-ray spectroscopy characteristics. Results for detection of neutrons from a moderated ²⁵²Cf source are presented.