Monte Carlo study of the relative role of energy absorption mechanisms in water under irradiation by photons in the energy range of 3–1000 Ry

Abstract

Mechanisms of energy absorption in liquid water under 3–1000 Ry photon irradiation are studied by Monte Carlo simulation with accounting for the cascade decays of vacancies in inner electron subshells created by primary and secondary ionization processes. At incident photon energies above O1s ionization threshold, most of the energy is transferred to the medium by secondary electrons and photons produced in the processes of photoionization, electron impact ionization, and cascade decay of inner-shell vacancies. On the average, on the whole considered incident photon energy interval, 49.8% of the absorbed energy is transferred to the medium by high-energy secondary electrons and photons in inelastic processes of interaction with the atoms of the medium. Low-energy electrons and photons incapable of ionizing/exciting the atoms of the medium are responsible for 48.8% of energy absorption. Energy absorption in the processes of primary ionization by incident photons are significant only at small incident photon energies of a few Rydbergs, their average contribution to energy absorption on the whole considered energy interval makes only 1.4%. At incident photon energies above O1s-ionization threshold low-energy electrons are produced in large quantities; this can be important in radiotherapy since in the tissues of organisms, low-energy electrons may cause the DNA strand breaks via the mechanism of dissociative electron attachment.