Calculation of Photon Mass Energy-Transfer and Mass Energy-Absorption Coefficients

TLDR

The authors compute photon mass energy‑transfer and absorption coefficients by combining NIST cross‑section data with detailed modeling of electron binding effects, fluorescence cascades, and radiative losses of secondary electrons and positrons, including bremsstrahlung, characteristic X‑rays, annihilation quanta, and energy‑loss straggling. The resulting mass energy‑absorption coefficients agree with recent tabulations.

Abstract

Calculations of mass energy-transfer and mass energy-absorption coefficients for photon energies from 1 keV to 100 MeV have been developed, based on a re-examination of the processes involved after the initial photon interaction. The probabilities for the initial interaction are from the current photon interaction cross-section database at the National Institute of Standards and Technology. The calculations then take into account (1) electron binding effects on the Compton-scattered photon distribution; (2) the complete cascade of fluorescence emission after ionization events in any atomic subshell, including those associated with incoherent scattering and triplet production; and (3) the radiative energy losses of the secondary electrons and positrons slowing down in the medium, including the emission of bremsstrahlung, characteristic X rays from impact ionization, and positron in-flight as well as at-rest annihilation quanta. Consideration of the processes in (3) goes beyond the continuous-slowing-down approximation and includes the effects of energy-loss straggling. Results for the mass energy-absorption coefficient are compared with those from recent tabulations.