Development of New Techniques for Thermal and Fast Neutron Dosimetry Based on Scintillator-Filled Etched-Track Counting

Abstract

The scintillation method of Harvey and Weeks (1982) has been extended to the counting of etched tracks in CR-39 made by thermal and fast neutrons. For thermal neutrons, CR-39 detectors placed in contact with both Li2B4O7 and BN1 converter screens have been exposed to neutrons from portable sources, with suitable moderation. For fast neutrons, beams of neutrons of different energies up to ~19 MeV from an accelerator have been used without moderation. The pits of the chemically etched 'intrinsic' tracks of fast neutrons, or the (n,a) tracks from the thermal neutrons, are filled with scintillator material, and the light pulses caused by a strong readout a source are detected by a photomultiplier. A number of new methods of producing convenient repositories for the scintillator paste (e.g. using electrochemical etching), and of readout (e.g. by using a separate scintillator screen underneath the etched-through holes produced by a spark counter, rather than filling the etch pits with a scintillator) have also been developed. The linearity of response by these methods has been tested for neutrons of different energies (thermal up to 19.2 MeV). The response (in terms of scintillation count rate) remains linear so long as serious overlapping of etch pits does not occur. The method promises to offer a quick and automatic technique for neutron dosimetry.