The Study of Gamma-Rays Produced in the Inelastic Scattering of Neutrons

Abstract

A gamma-ray spectrometer employing a sodium iodide scintillation detector, has been constructed to observe the gamma-rays produced in -14.2 MeV neutron interactions with elemental samples. The predominant gamma-ray production mechanism is inelastic neutron scattering; the source neutrons being produced by the 3H(d,n)4He reaction. The main problem in the design of such a spectrometer is to overcome the large background owing to the sensitivity of sodium iodide to neutrons. This was overcome by using a gamma-ray detector neutron shield and a particle time-of-flight discrimination system. The associated particle time-of-flight method was used. The instant of production of a source neutron is defined by detecting the associated alpha-particle, enabling the subsequent neutron-gamma-ray time-of-flight discrimination. The different particle flight times over the sample to detector flight path are measured electronically and the system used is described. Three elements for which there have been few or no previous measurements were studied: silicon, sulphur and titanium. Gamma-ray spectra have been observed for each element under 14.2 MeV neutron bombardment, at several scattering com in the 0° to 90° angular interval. The spectra enabled absolute differential gamma-ray production cross-sections and angular distributions of the resolved gamma-ray lines to be measured. The differential gamma-ray production cross-section, angular distribution and integrated cross-section measurements are compared with the published data where available. The angular distribution measurements, of the gamma-rays produced in neutron inelastic scattering, for each element are compared with Hauser-Feshbach=Satchler compound nucleus model calculations.