Progress Towards the Development of a Personal Neutron Dosimetry System Based on the Chemical Etch of CR39

摘要

A brief historical review of systems used for monitoring individual neutron dose underlines the significance of the discovery that the plastic CR39 can be used to detect protons, and hence form the basis of a great improvement in neutron dosimetry. Proton tracks are revealed by etching the CR39 plastic in a hot concentrated caustic solution. First studies at BNL into the fundamental etch characteristics of commercially available CR39 showed that dosimetry grade material would be required with a low density of spurious etch pits and reproducible etch characteristics. This is now commercially available. There was also a requirement for a simple system which would give a rapid estimate of the number of etch pits with diameters less than 6 mu m over areas of order one square centimetre. Many possible systems were studied. The one shown to be most effective is based on side illumination of the CR39 sample which is then viewed by a videcon tube through a low-power microscope. The etch pit images which are effectively magnified by the videcon tube are counted by an inexpensive automatic image analysis system in less than one second. The thermal neutron sensitive CR39 is ideal for use as the detecting element in an albedo dosimetry system. This implies that a single dosemeter, of size comparable with the present film badge can be used to detect thermal, intermediate, and fast neutrons, the measurement of which currently requires two separate dosemeters. (ERA citation 13:001600)