Effect of Finite Size of Ionization Chambers on Measurements of Small Photon Sources

Abstract

The surface integral correlations developed and those obtained from the generalized Spiers formulas both account for the experimental deviations of ion chamber readings from the inverse-square law with a precision better than plus or minus 3% under very severe conditions. They are satisfactory improvements over the volume integral corrections. Although the theoretical basis for the correction factors is more rigorous than that for Spiers' work, conclusive experimental demonstration of a choice between the theories requires further, more-precise measurements. The simple, albeit tedious, theory resembles a thermodynamic theory that satisfactorily describes the over-all behavior of a system but is inadequate to describe the detailed mechanism, which in this case is secondary-electron behavior. (auth)