Development of a personal dosimeter applied for the photon and fast-neutron fields in high-energy accelerator facilities

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1. As a first step toward developing a personal dosimeter applicable for fast neutrons (energy > 10 MeV), we tested the feasibility of using two-layer CR-39 stacks (0.9 mm in thickness x 2) to make LET distribution measurements for secondary charged particles due to fast neutrons of 0.25, 0.55, 5 and 15 MeV. The front layers of the detectors act as a radiator and the back layers act as a neutron detector. The results indicated the following: chemical etching shorter than 5 um is needed to obtain the correct LET distribution and dose for sub MeV neutrons; the present CR-39 detector system and chemical etching condition (bulk etch ~15 μm) are appropriate for 5 MeV neutron dosimetry, and measured dose equivalents and averaged quality factors for LET > 10 keV/μm agreed with the ICRP 74 neutron-fluence-to-dose conversion factor and the ICRP 60 radiation weighting factor, respectively; a thick radiator of ~2 mm is required for 15 MeV neutron dosimetry. Although the present measurements partl … More y failed to obtain correct LET values for the low-energy and short-range charged particles induced by fast neutrons, we conclude that modifications of the CR-39 detector system and chemical etching condition should improve the accuracy of LET distribution measurement for fast neutron dosimetry in the sub MeV to tens MeV energy range.2. An automated scanning system was developed for measuring a large number of nuclear track-etch detectors. We investigated scanning performance using CR-39 plastic samples irradiated by high-energy heavy ions and fast neutrons. Overall scanning speed including sample transfer, sample ID recognition, image acquisition and image analysis was satisfactorily high. The system allowed the processing of 100 samples with scan areas of 4 cm2/sample in one day for neutron dosimetry.3. A new software "LETDose" was developed for personal dosimetry. The software combines absorbed doses measured by TLDs and the LET distributions measured by CR-39 track detectors for estimating absorbed doses and dose equivalents for radiation fields consisting of photons and fast neutrons. Less