Energy deposition spectra of simultaneous electron emissions from low energy protons

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references (leaves ).The biological effect of a heavy charged particle that ics. stops within a cell nucleus cannot be predicted from particles of similar stopping power that pass through the entire cell (Raju et al. 1991). The biological effect at the end of a particle track is more complicated than the normal LET/RBE relationship. Recent measurements of atomic cross-section indicate that interactions of low energy protons with target atoms sometimes produce two or more electrons simultaneously. However, these cross-sections are difficult to measure, and the available data suggests only that they are significant. In order to evaluate their potential biological consequences, a Monte Carlo track structure simulation was performed utilizing values that may be representative of the cross-sections for the production of simultaneous electron emissions. The Positive Ion Track Structure (PITS) code was modified to extend its useful energy range down to 0.10 Mev/nucleon. Another modification to PITS allowed the program to be used to examine the effects of simultaneous electron emissions on the energy deposition by protons ranging in energy from 100-250 kev. The resulting spectra of energy imparted (s) were calculated in spherical volumes with diameters of 0.5-50 nm. The frequency-mean lineal energy and the dose-mean lineal energy increased with increasing detector diameter regardless of the energy of the proton being simulated. These mean values also increased as the fraction of charge exchange events that lead to simultaneous electron emissions was increased for 100, 150, and 200 kev protons. The magnitude of the increase in these mean values is in the range of 5-15%. This is potentially significant for biology, but probably too small to observe with current detector technology. No increase in these mean values occurred with 250 kev protons. The changes in the mean values indicate that the dose-distribution in lineal energy shifted toward higher lineal energies. The smaller sites, 0.5 nm and 1 nm, display peaks in the dose distribution that are due to a single ionization within the site. As the diameter of the site increases, these peaks disappear because the probability of a single ionization occurring in the site decreases rapidly