Impact of Different Theoretical Models in the Calculation of Compton Mass Energy-Transfer Coefficients

Basic photon interaction data such as mass energy-transfer and mass energy-absorption coefficients for dosimetric purposes require as a main component the incoherent scattering energy-transfer fractions. The simplest approach for calculating incoherent scattering cross sections is the Klein-Nishina (KN) model, in which the photon is scattered by a free electron initially at rest. As an improvement on KN, a well-known and frequently-used approximation is the Waller-Hartree (WH) model which accounts for binding effects approximately through the incoherent scattering function, but which neglects the spread in energy of photons scattered at a given angle. The relativistic impulse approximation (RIA) incorporates both binding effects and Doppler broadening and yields an expression for the DDCS differential in outgoing photon angle and energy. The key ingredient to the calculation of the RIA cross sections is the Compton profile (CP) of each atomic or molecular orbital, which is computed from the corresponding linear momentum distribution. The atomic CPs typically used are from the tabulation of Biggs et al.