In the second edition, new material on characteristic X-ray production has been added in Chapter 3. During the intervening period the study of X-ray production by proton bombardment has been actively pursued, and this has merited the inclusion of a new chapter (Chapter 6). Chapter 8 has been extended and up-dated.

The S.I. units are now in very widespread use, and this has justified the conversion of the whole book into this system of units. Occasionally, in topics where the old system of units is particularly entrenched, older units have been retained.

Although many aspects of X-ray physics have expanded very considerably since the first edition of this book appeared, I have attempted to keep the book within reasonable proportions, and hope that not too much of the work of recent years has been omitted.

I am indebted to Mrs Erica Gaize, Mrs Pauline Goddard and Mrs Eileen Shinn for re-typing the whole work, and to many friends and colleagues over the years for discussion of X-ray processes. I am especially indebted to Dr R. Sokhi, Dr R.G. Harris, and Dr M. Church for reading Chapters 6, 7, and parts of Chapter 8 respectively, and for their valuable comments. My thanks are due also to Longman Group UK Limited, publishers of the first edition of this work, for permission to reproduce here a substantial number of line diagrams which appeared originally in that edition.