The Thermoluminescence of X-Ray Irradiated Alkali Halides

Abstract

This thesis describes an investigation of the thermoluminescent properties of five alkali halides. The colouring of sodium chloride by x-rays had been observed by Goldstein in 1896 but the first thorough investigation of colour centres in alkali halides was undertaken by Pohl in 1937, using additively coloured crystals. Colour centres provide a ready means for studying radiation damage in ionic crystals, and for this reason they are being widely studied. Thermoluminescence may provide one method for studying the various centres produced. The construction of the thesis is as follows: Chapter I is a brief introduction to the band theory of allowed electron energies in solids. Chapter II discusses the imperfections found in crystals and their effect on the band structure. Chapter III is a review of the production and properties of the various colour centres found in the alkali halides. Chapter IV gives a more specific account of the proposed mechanisms for the production of colour centres by x-rays. Chapter V presents two models for luminescent centres, together with a discussion of thermoluminescence. Chapter VI is the first experimental chapter and here the main pieces of experimental equipment are described. Chapter VII continues the discussion of the experimental equipment and the additional equipment constructed. Chapter VIII describes the preparation of the samples and the methods used for investigating the thermal properties of the colour centres. Chapter IX is a presentation of the main experimental results. Chapter X is in two parts. In the first part the experimental results are compared with those of previous experimenters, while in the second section a model for the thermoluminescence is presented, together with experimental evidence for this model. Throughout the thesis the aim has been to emphasise the physical models and the physical processes involved rather than to give a detailed theoretical discussion of each point. A clear presentation of the physical model proposed, to explain the observed experimental results is, "prima facie", the main objective of the thesis.