Air-kerma cavity standards

This paper reviews the current status of air-kerma cavity standards for gamma rays from Co-60, Cs-137 and Ir-192 sources. It describes the basic principles and the theories to determine the air-kerma rate from the ionization current of graphite-walled cavity ionization chambers. A typical design of a cavity chamber is shown and described. The various correction factors to be applied to the standards and their determination by experimental and Monte Carlo methods are discussed. A typical uncertainty budget for a cavity standard is presented and the results of comparisons between primary standards are summarized and discussed. Finally, conclusions are drawn and proposals made for topics to be addressed in future studies.