The energy angle dependence of response of the NRPB CR39 fast neutron dosemeter

The National Radiological Protection Board (NRPB) has developed a fast neutron personal dosemeter which employs a CR39 detector. The detector consists of a flat piece of CR39 plastic, approximately 25 mm x 40 mm and of thickness 600 μm. Before issue detectors are hermetically sealed inside polyethylene/aluminium laminate pouches. The pouch fits inside a simple polypropylene holder. Proton tracks in the CR39 detector are revealed by a combination of chemical etching and electrochemical etching. A set of etching parameters has been arrived at which gives adequate sensitivity and energy dependence of response, at acceptable levels of, and variation in, background pit density. The minimum detectable dose equivalent, taken as 2 σ on background, varies between CR39 batches but is generally about 2.10-4 Sv