An analysis of the Z-dependence of photon and electron interactions.

A comprehensive analysis has been completed of the dependence of photon and electron interactions upon atomic number. The calculations were specifically biased towards the application of the data to biological tissues and their substitutes. The photon interactions considered in the survey included all the partial attenuation and energy absorption cross-sections. The electron interactions analysed were collision and radiation stopping powers and angular scattering powers. The derived Z-exponents are tabulated for different energies and elemental groupings and indicate the inadequacy of existing Z-exponents. In particular, the continued use of the single exponent 3.94 for photoelectric attenuation (per atom) is put in question.