Design of tissue-equivalent proportional counters

This paper deals with those factors which are of importance in the design of tissue equivalent proportional counters. Basic physical processes in the transport of ions and electrons through gases are discussed, as well as electron avalanche, but only from simple classical approximations. Monte Carlo techniques are dealt with elsewhere in this volume. Emphasis is on practical design considerations, and therefore the importance of geometrical factors is considered in some detail, as is physical size. These design parameters are illustrated with some successful designs of both cylindrical and spherical types. Finally, some of the more exotic recent developments in proportional counters are illustrated.