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Microdosimetric characterization of energy-deposition patterns near the ends of alpha tracks
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The purpose of this study was the characterization of energy-deposition patterns in short segments near the ends of alpha particle tracks. Energy-deposition patterns in structures having dimensions on the order of nanometers were observed. Near the end of a particle's track, the average energy deposition goes through a maximum then rapidly drops to zero as the particle is stopped. However, due to the wide variations in energy imparted in individual atomic interactions, there is also a substantial fluctuation in the damage done within small regions when they are crossed by charged particles. For small sites, corresponding to short track segments, the change of LET can be ignored and energy-loss straggling predominates. Past studies have shown that Tissue Equivalent Proportional Counters (TEPC), which simulate small sites in tissue, are well suited for many studies including use in dosimetry, radiation protection and radiation therapy. Most commonly, measurements have been performed and data published for higher energy particles using solid-walled instruments simulating biological sites with diameters on the order of micrometers. Little was known, however, of the variance in lineal energy in sites with diameters smaller than 300 nanometers, as reliable methods for measuring the microdosimetric spectra in these small sites had not been developed. Thus, a detector was constructed to simulate smaller volumes, comparable to the constituents within biological cells, or sensitive components of microelectronics, in order to study single radiation interactions therein. Where the LET of the particle is rapidly approaching zero, near the end of the particle's track, continuous slowing down approximation (CSDA) methods do not predict the variability of energy deposition events observed. Although the average values of the measurements (the frequency mean lineal energy (y)) correlate closely with CSDA predictions, there was a dramatic increase in the variance for measurements near the end of the alpha track. Even though the LET and y are low at points near the end of the track, there was a significant frequency of very large energy deposition events not accounted for when CSDA averaged values are used to predict processes occurring.
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Includes bibliographical references (leaves 51-52).
Issued also on microfiche from Lange Micrographics.
Guetersloh, Stephen Brant (2000). Microdosimetric characterization of energy-deposition patterns near the ends of alpha tracks. Master's thesis, Texas A&M University. Available electronically from
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