Development of a ¹³⁷Cs Scattering Gamma-ray Source for Nuclear Gauge

Abstract

An assembled radiation source device emitting a few hundred keV gamma-rays was developed for industrial radiation gauges by utilizing Compton scattering of ¹³⁷Cs gamma-rays with an appropriate scatterer. The effects of design parameters of the source device on the energy distribution of emitted photons and their intensities were investigated by computer aided Monte Carlo simulation in advance of experimental examinations. The investigation on the shape and material of the scatterer resulted in the choice of a cylindrical backscatterer made of iron for the source device. The backscatterer designed has an outer size of 140×70 mm, an inner hollow space of 100×50 mm, and a wall thickness of 20 mm. The source device fabricated consists of a tiny sealed ¹³⁷Cs gamma-ray source, the cylindrical iron backscatterer, and a lead shield against primary gamma-rays. The characteristics of the gamma-rays emitted from it were experimentally examined. The energy spectrum ranges from about 100 to 300 keV. The output intensity at a distance of 300 mm is 0.65 mR h^-1 mCi^-1 (¹³⁷Cs) and almost uniform within a circular plane of 40 mm radius vertical to the central axis of the source device. The gamma-ray absorption characteristics by iron plates shows that the source device has place just between ²⁴¹Am and ¹³⁷Cs sources for radiation gauging use.