Tissue equivalent proportional counters are frequently used to measure dose and
dose equivalent in mixed radiation fields that include neutrons; however, detectors
simulating sites 1?m in diameter underestimate the quality factor, Q, for low energy
neutrons because the recoil protons do not cross the detectors. Proportional counters
simulating different site-sizes can be used to get a better neutron dose equivalent
measurement since the range and stopping power of protons generated by neutrons in the
tissue-equivalent walls depend on the energy of the primary neutrons. The differences in
the spectra measured by different size detectors will provide additional information on
the incident neutron energy.
Monte Carlo N-particle extended (MCNPX) code was used to simulate neutron
transportation in proportional counters of different simulated tissue diameter. These
Monte Carlo results were tested using two solid walled tissue equivalent proportional
counters, 2mm and 10mm in diameter, simulating tissue volumes 0.1?m and 0.5?m in
diameter, housed in a single vacuum chamber. Both detectors are built with 3mm thick
tissue equivalent plastic (A-150) walls and propane gas inside for dose measurement. Using these two detectors, the spectra were compared to determine the underestimation
of y for large detector, and thereby obtain more information of the incident neutron
particles.
Based on the MCNPX simulation and experimental results, we can see that the
smaller detector produces a larger average lineal energy than the larger detector, which
means the larger detector (0.5?m diameter tissue equivalent size) underestimates the Q
value for the low energy neutron, therefore underestimates the effective dose. These
results confirm the results of the typical analysis of lineal energy as a function of site
size.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2008-12-158 |
| Date | 14 January 2010 |
| Creators | Xia, Zhenghua |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation |
| Format | application/pdf |
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