Abstract
The frequency distributions of event size in the deposition of energy produced by the passage of protons in a pathlength of 6.99 x l0⁻⁵ g/cm² tissue equivalent gas have been measured after penetration of a 44 MeV monoenergetic proton beam through various amounts of bone and muscle equivalent plastic. Corresponding thicknesses of the absorbers of the two types were chosen such that the mean energy of the residual beam of protons entering the gaseous test volume was identical. Each pair of absorbers thus produced the same relative iontzation density as measured by the Bragg curve. The points of the Bragg curve where data has been taken are: (1) where the ionization density has not yet started to increase sharply toward peak values; (2) at a point where the ionization density was rising steeply; and (3) at the maximum ionization density. The resultant energy deposition distributions obtained for each pair of the two absorbing materials were identical. This indicates that both primary and forward scattered secondary particle spectra in a degraded beam of low energy protons are not significantly different after the primary beam passes through equivalent amounts of bone or soft tissue. The results obtained on a microscopic scale aremore » in agreement both with calculations of the absorbed dose and dose equivalent under similar conditions and with experimental measurements of absorbed dose. (auth)« less
Published Version
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