Comments on the Simulation of the Passage of Fast Electrons in Water

Abstract

A recent paper in this journal by Kaplan and Sukhonosov (1) uses a Monte Carlo method to simulate the passage of fast electrons in water and the subsequent radiation chemistry. In that paper the authors find a serious discrepancy between our work (2-4) and theirs regarding the dependence of the stopping of low-energy electrons on the phase of water. Figure 1 shows the stopping powers of water vapor and liquid as determined by ourselves (2-4), by Kaplan and Sukhonosov (1), and by Paretzke et al. (5). The differences between the stopping powers of Kaplan and Sukhonosov and our work are readily apparent and were attributed by them to our alleged use of the Bethe formula. This allegation is due to a misunderstanding of our procedure. We follow a method originated by Ashley' (6) for constructing the inelastic cross section for low-energy electrons which gives a significantly different result from that of Bethe even though both methods are based on the dipole oscillator strength distribution (DOSD). Ashley's method approximates the generalized oscillator strength distribution (GOSD) by a quadratic extension of the dielectric response function in the energy-momentum plane. One obtains for the imaginary part of the dielectric response function, e(q,w),