Present state of the art of a fast neutron dosimeter incorporating RPL detectors

The recently introduced radiophotoluminescent (RPL) detectors offer a unique combination of advantages for radiation monitoring that include rapid exploitation, stability to fading, reusability, and insensitivity to light, temperature and humidity. We look at the behavior of an RPL-based fast neutron dosimeter capable of measuring neutrons in an n-g field. The tested dosimeter consists of an ordered assembly of Al foil, RPL detector (I), Al foil, polyethylene converter, RPL detector (II) and Al foil encased in a polyethylene container. The difference between the two RPL configurationsrepresents the (n,p) protons and is related to the fast neutron dose. The dosimeter response is linear and shows an acceptable angular dependence. However the measured detection threshold for this dosimeter is too high for routine monitoring. This threshold could be lowered at to a more practicable value if next generation improvements in RPL detectors and the reader are applied. The main shortcomings we encountered are (i) a 1.7 µm thick dead layer at the front surface of the detectors that render them insensitive to a large fraction of the recoil protons and (ii) an intrinsic detector background that could be reduced if the reader were able to separate individual densely ionized zones created by the recoil protons from the gamma-ray signal.