A Monte Carlo calculation of subexcitation and vibrationally-relaxing electron spectra in irradiated liquid water

An energy spectrum of “subexcitation electrons” produced in liquid water by electrons with initial energies of a few keV is obtained by using a Monte Carlo transport simulation calculation. It is found that the introduction of vibrational-excitation cross sections leads to the appearance of a sharp peak in the probability density function near the electronic-excitation threshold. Electrons contributing to this peak are shown to be more naturally described if a novel energy spectrum, that we propose to name “vibrationally-relaxing electron” spectrum, is introduced. The corresponding distribution function is presented, and an empirical expression of it is given.