THE RESPONSE OF A MULTI-ELEMENT TISSUE EQUIVALENT PROPORTIONAL COUNTER IN ACCELERATOR BASED HIGH-ALTITUDE NEUTRON FIELDS.

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.