A Investigation Into the Use of Beta-Particle Transmission and Backscatter for the Measurement of Elemental Composition and Thickness of Metallic Foils.

Available from UMI in association with The British Library. The theories and experimental laws describing the interactions of radiation with matter have been examined in detail and models are proposed from which relations for the backscattered and transmitted response have been derived in terms of the composition and thickness of foils. The constants in the relations have been derived statistically by fitting experimental data for foils of known composition. Computer software has been developed for this calibration and for the calculation of weight fraction and thickness of composite foils. Experimental verification has been carried out for high and low energy sources (^{90 }Sr and ^{147}Pm) and comparison made with other methods of foil assessment. In the course of this investigation optimal conditions were determined for geometry and detection of the particles, spectrum stripping techniques being used when required to minimise the response to bremsstrahlung. An investigation was also carried out into the scattering and lateral spread of the initial beta-particle beam in order to evaluate the spatial resolution that can be obtained with foils of different thickness and atomic number. Expressions have been derived for the accuracy and minimum detectable change in composition, thickness and spatial resolution attainable, these being found to be strongly dependent on atomic number. Predictions using the theoretical models are compared with the experimental results.