Experimental examination of cavity ionisation theory applied to alpha-particle fields.

Abstract

The form of a general theory of cavity ionisation is outlined and its applications to alpha-particle fields considered. The attenuation of the alpha particles within the cavity, which gives rise to the weighting factor in general cavity theory, is considered in detail and an appropriate treatment for alpha-particle fields developed. Apparatus, consisting of an ionisation chamber composed of electrodes emitting alpha rays, was constructed in order to impose a rigorous test on the theory in the most critical region of cavity size. The general theory of cavity ionisation as applied to alpha-particle fields is shown to be in close agreement with the experimental results. As in the case of photon and electron fields, it is possible to characterise a cavity by a single chord length (path length) but the charged particle energy spectrum and the variation of stopping power with energy must be considered in detail.