Induced charges in X-ray proportional detectors.

A brief description is given of gas proportional detectors, with emphasis on the development and behaviour of multiwire proportional counters (MWPC's). In particular, the behaviour of MWPC's as position sensitive detectors is discussed and a description given of the various techniques employed in obtaining and processing positional information. A theoretical analysis of a recently discovered phenomenon, known as angular localisation of the electron avalanche, is presented and a study is made of induced charges, due to this avalanche, on nearby anodes and cathodes. Formulae are developed which allow the calculation of the induced charges, and theoretical predictions are given of how the effect may be used to provide position signals. An experimental system is described from which evidence has been obtained that a high degree of angular localisation does indeed exist. Comparisons are made between these experimental measurements and the predictions of the theoretical model. Various fundamental limitations are discussed which indicate the feasibility of using the localisation effect for positional interpolation between anode wires. The experimental work is extended to observe the effects of using several common counter gas mixtures and also of varying the chamber geometry. Finally some applications are discussed and suggestions are made for future research.