Cylindrical Detector and Preamplifier Design for Detecting Neutrons

摘要

Tissue equivalent proportional counters are frequently used to measure dose anddose equivalent in mixed radiation fields that include neutrons; however, detectorssimulating sites 1?m in diameter underestimate the quality factor, Q, for low energyneutrons because the recoil protons do not cross the detectors. Proportional counterssimulating different site-sizes can be used to get a better neutron dose equivalentmeasurement since the range and stopping power of protons generated by neutrons in thetissue-equivalent walls depend on the energy of the primary neutrons. The differences inthe spectra measured by different size detectors will provide additional information onthe incident neutron energy.Monte Carlo N-particle extended (MCNPX) code was used to simulate neutrontransportation in proportional counters of different simulated tissue diameter. TheseMonte Carlo results were tested using two solid walled tissue equivalent proportionalcounters, 2mm and 10mm in diameter, simulating tissue volumes 0.1?m and 0.5?m indiameter, housed in a single vacuum chamber. Both detectors are built with 3mm thicktissue equivalent plastic (A-150) walls and propane gas inside for dose measurement. Using these two detectors, the spectra were compared to determine the underestimationof y for large detector, and thereby obtain more information of the incident neutronparticles.Based on the MCNPX simulation and experimental results, we can see that thesmaller detector produces a larger average lineal energy than the larger detector, whichmeans the larger detector (0.5?m diameter tissue equivalent size) underestimates the Qvalue for the low energy neutron, therefore underestimates the effective dose. Theseresults confirm the results of the typical analysis of lineal energy as a function of sitesize.