Cascade production of secondary electrons and photons and energy absorption mechanisms in liquid nitrogen irradiated by photons in the energy range of 0.027–17.4 keV

Abstract

Mechanisms of absorption and redistribution of energy in liquid nitrogen irradiated by 0.027–17.4 keV photons are studied by Monte Carlo simulation, accurately accounting for the cascade relaxation of inner-shell vacancies and tracking all secondary electrons and photons. Densities of energy absorbed near the sites of initial photoionization due to inelastic processes caused by secondary electrons and photons and their spectra are calculated. The absorption of energy by the sample’s atoms that underwent initial ionization by incident photons is only important on a rather narrow incident photon energy interval in the UV range. With growing incident photon energy, the energy absorbed in primary photoionization acts decreases and becomes negligible in comparison with energy absorbed via other mechanisms. The main mechanism of energy transfer to the sample (average of 56% over the whole incident photon energy interval) is through secondary electrons causing ionization and excitation of atoms of the medium. The second most important energy absorption mechanism (22%) is by low-energy photons that do not produce ionization or excitation of the sample’s atoms. Low-energy secondary electrons are responsible for the absorption of 14% of energy, and 7% of the absorbed energy is transferred to the medium through photoionization by secondary photons. Low-energy electrons are produced in great quantities in liquid nitrogen after each primary photoionization act, and their number grows linearly against incident photon energy. The results of this study are in line with earlier reported results on energy absorption in photon-irradiated disordered solid neon, amorphous carbon, and water.