Evaluation of a microdosimetric-based neutron instrument

The commercially available REM500 neutron survey meter is a microdosimetric instrument based on the use of a low-pressure tissue-equivalent proportional counter. The neutron spectrometry capability, as well as the dose equivalent response, of the REM500 was evaluated with five radioisotopic neutron sources (238PuLi, 238PuF, 238PuB, 238PuBe and 252Cf) and the mono-energetic 14-MeV neutrons. The response (counts/mSv) and sensitivity (counts/neutron) as a function of neutron energy were determined. From the measured pulse height spectra, the frequency-mean and dose-mean lineal energy values, as well as the mean quality factors, were derived for all sources. The neutron dose equivalent determined from the dose and mean quality factor measured by the REM500 agreed well with the reference values of ICRP21 maximum dose equivalent. However, for the REM500 to measure proper lineal spectra, the low sensitivity and inaccurate measurements for high-energy neutrons are areas that may need improvements