Dose dependence and uncertainty evaluation of calibration factors for active neutron personal dosimeters

Active neutron personal dosimeters are now widely used to monitor the neutron personal dose equivalent. They are calibrated periodically in the standard neutron fields such as Cf, D2O-moderated Cf, and Am-Be sources. Type B uncertainty of calibration factors should be determined if they are not offered by the manufacturer. DMC 2000 GN and EPD-N2 dosimeters were chosen to evaluate Type B uncertainties. Dose dependence of calibration factors and minimum dose to the dose indication were also investigated with Cf source neutrons in the neutron irradiation room at Korea Research Institute of Standards and Science. The neutron dose was irradiated up to around 10 mSv for studying dose dependence. The calibration factor of EPD-N2 was stable above neutron dose around 2 mSv and that of DMC 2000 GN was stable above around 1 mSv. Type B uncertainties of DMC 2000 GN and EPD-N2 were evaluated to be 6 % and 12 % from the serial measurements. Type B uncertainty of EPD-N2 was also evaluated by fitting the normalized normal distribution of calibration factors with Gaussian function from 153 dosimeters. The result was in good agreement with the result from the serial measurement. Study of minimum dose to the dose indication showed that DMC 2000 GN is more sensitive than EPD-N2.