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(PP005) Microdosimetry for two site sizes.
Rayadurgam, Sripriya 1, Liu, Haifeng 1, Wang, Xudong 1, Xia, Zhenghua1, Braby, Leslie*,1, 1 Nuclear Engineering, College Station, Texas, USA
ABSTRACT- The lineal energy distribution and number of events, measured by a tissue equivalent proportional counter, provide an accurate measure of the dose and an estimate of the radiation quality for mixed radiation fields, such as those found in space. However, a measurement for single simulated site size does not provide information that can be used to predict the dose at a different depth in tissue, or to estimate the fraction of the dose that is delivered by the delta rays produced by high energy heavy ions. The amount of information about delta ray range can be increased by making measurements in simulated sites of different sizes. For a given high energy heavy ion the mean lineal energy decreases with decreasing site size because a larger fraction of the delta ray energy is deposited outside the site. Simulations show that there will be measurable differences in the distribution of events in proportional counters simulating different size sites. We have developed techniques for building grid walled (nominally wall-less) detectors as small as 1 mm in diameter to compliment the conventional wall-less detectors which range from 10 to 50 mm in diameter. This makes it possible to measure lineal energy in sites ranging from a few nm to about 20,000 nm in diameter. By measuring lineal energy simultaneously in 3 different size sites we expect to be able to distinguish between high energy heavy ions and lower energy lighter ions that have the same stopping power. This will result in a better estimate of the expected biological effectiveness of the radiation.
Key words: microdosimetry, Space radiation, delta rays, radiation quality
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