A detailed re-evaluation of C$\lambda$ and CE with application to ferrous sulphate G-values

Abstract

The theoretical basis of C_lambda and C_E is re-examined and consistent expressions derived involving the quantity F_a^w which is a combination of a stopping-power ratio and an energy-absorption coefficient ratio, thereby taking into account the extent to which the ionisation chamber acts as an 'electron detector' and as a 'photon detector' for a particular radiation quality. An extension of the Spencer-Attix cavity ionisation theory is used to calculate values for F_a^w appropriate to the Baldwin-Farmer ionisation chamber assuming an air-equivalent inner wall, and new values of C_lambda and C_E are presented. The new set of C_lambda and C_E has been used to recalculate the experimental ferrous sulphate G-values of Law and Naylor (1972) with the result that the differences between G for high energy photons and electrons disappears.