A Study of the Gamma-Rays Associated with the Inelastic Scattering of Neutrons in Extended Target Samples

Abstract

The gamma-rays produced’ in the inelastic scattering of 14 MeV neutrons have been studied using a gamma-ray spectrometer employing a sodium iodide scintillation detector. The source neutrons are produced by the T(d,n)"He reaction using the Radiation Centre Dynamitron and.the SAMES accelerator. In order to overcome the large gamma-ray background and large stray neutron signal due to the sensitivity of the sodium iodide detector to neutrons, heavy shielding around the gamma-ray detector is used together with a particle time of flight discrimination system based on the associated particle time of flight method. The instant of production of a source neutron is defined by detecting the associated alpha-particle which enables discrimination between the neutrons and gamma-rays because of their different time of flight times. The electronic system used for measuring the time of flight of the neutrons and gamma-rays over the fixed flight path is described. The materials studied in this work were iron and concrete because of their importance as structural and shielding materials in the construction of both fission and fusion reactors. Several sample thicknesses were studied to determine the multiple scattering effects in large sample. The observed gamma-ray spectra from each sample at several scattering angles in the angular range 0°-90° enabled absolute differential gamma-ray production cross-sections and angular distributions of the resolved gamma-rays from iron to be measured and compared with published data where available. For the concrete sample, the absolute differential gamma-ray production cross-sections for discrete 1 MeV ranges and the angular distributions were measured and compared with cross-sections synthesized from the published cross-section data for the elements constituting concrete. The number of gamma-rays produced from each sample in the angular range studied were compared with the predictions of a theoretical model based on the continuous slowing down model and Fermi-Age equation, Good agreement between experiment and theory is obtained and a single parameter found which describes the effects of multiple scattering in both materials.