Evaluation of the calibration factors of neutron dose rate meters in a ²⁴¹Am–Be neutron field

Abstract

Calibrations were performed for three types of neutron ambient dose equivalent rate meters, i.e., Aloka TPS-451C (Hitachi), KSAR1U.06 (Baltic Scientific Instruments), and Model 12-4 (Ludlum), using a standard field of a ²⁴¹Am–Be source. The measured total neutron ambient dose equivalent rates, $H^*(10)_{\text{tot}}'$, were analyzed to obtain the direct neutron ambient dose equivalent rates, $H^*(10)_{\text{dir}}'$, using the ISO 8529-2-recommended generalized-fit method, semiempirical fit method, and reduced-fitting method (RFM) fit methods. The calibration factor (CF), defined as the ratio between the conventional true value of the neutron ambient dose equivalent rates in a free field, $H^*(10)_{\text{FF}}'$, and $H^*(10)_{\text{dir}}'$, was evaluated as one of the important characteristics of the neutron meters in the present work. The fitting results show that the $H^*(10)_{\text{dir}}'$ values of the meters are in good agreement within the theoretical data within 4%. The averaged CFs of the three neutron meters were evaluated as $0.99 \pm 0.01$, $1.00 \pm 0.03,$ and $0.99 \pm 0.08$, respectively. The largest standard uncertainty of these values was determined to be approximately 18.47% ($k=1$). The standard uncertainty of the CFs obtained using the RFM method was less than 4.23% ($k=1$), which is the smallest uncertainty among the three methods.