RESUMEN
A nested neutron spectrometer was used to measure the stray neutron fluence and ambient dose equivalent produced by protons from a 4 MV tandem accelerator on various target materials at the Reactor Materials Testing Laboratory (RMTL), Queen's University, Kingston, Ontario. The nested neutron spectrometer utilizes a Helium-3 proportional counter and measures the thermal neutron count rate as a function of moderator shell-thickness. Using custom unfolding software, neutron spectra and neutron dosimetric quantities were derived at various locations within the RMTL. The nested neutron spectrometer can be operated in both a pulse mode and current mode allowing for measurements over a wide range of accelerator beam currents. All measurements conducted at the facility were within the main accelerator chamber and experimental target rooms. Target room measurements were conducted with a variety of target materials representative of those to be used for research planned at the RMTL.
RESUMEN
The response of a multi-element tissue equivalent proportional counter (METEPC) was investigated at the high energy neutron facility EU-CERF, in Prevessin, France. This facility was established specifically to provide reference neutron fields typical of those found at high altitude. The METEPC measurements were conducted along with a commercially available spherical tissue equivalent proportional counter (TEPC) used for comparison. The measured microdosimetric spectra were analyzed and compared for various measurement locations, with substantially different neutron energy distributions resulting from the use of iron or concrete shielding. The absorbed dose rate measured by the two counters in the dominant lower-energy neutron field locations from the iron-shielded target was <27%. A significant difference in the range of 32-58% was observed between the two counters in the higher-energy neutron field produced by the concrete-shielded target. Interestingly, due to a combination of factors, including the geometry and structure of the METEPC, values of dose-equivalent derived from the METEPC and the TEPC were in closer agreement (within 30%) and are well within acceptable limits for neutron monitoring.