An ionization method for the absolute measurement of γ-ray energy

Abstract

In the course of an attempt to determine in absolute measure the rate of emission of γ-ray energy by radioactive bodies, it became necessary to consider whether there existed any accurately ascertainable relation between the γ-ray energy absorbed per unit volume of a solid medium and the ionization produced in a small air-filled cavity in that medium. It was found that a very simple relation could be derived by theoretical reasoning from certain experiment facts concerning the loss of energy by swiftly moving electrons. The derivations was published, but no new experimental evidence was brought forward bearing specifically on the validity of this relation. Essentially the same relation had been enunicated in slightly different terms as long ago as 1912 by Sir William Bragg, but this treatment of the problem has unfortunately only recently been brought to my notice. I deeply regret having overlooked Sir William Bragg's admirable treatment, and I am glad of this opportunity of apologizing to him for having published a discussion of the problem without any reference to his work. Since a knowledge of the relation between the ionization in an enclosed volume of air the flux of γ-ray energy through that volume has important applications in the field of radiology as well as in nuclear physics, and since, in certain circumstances, an analogous relation may be obtained for the ionization produced by neutrons, the validity of the relation has been tested experimentally as thoroughly as possible.