DEVELOPMENT OF REAL TIME PERSONAL NEUTRON DOSIMETER WITH TWO SILICON DETECTORS

摘要

Recently, two types of direct-reading personal neutron dosimeters have been developed. The first is a bubble-damage polymer detector which uses tiny, superheated droplets of a detector liquid uniformly dispersed in a firm elastic polymer developed separately by Apfel et al. (1985) and Ing et al. (1984) and the second a silicon dosimeter developed by (Nakamura et al., 1989) which uses two types of silicon p-n junction detectors fabricated by Fuji Electric Co. Ltd. The latter had low neutron sensitivity which we improved by using a larger silicon detector (30mm x 30mm). Our dosimeter has two neutron sensors and one gamma-ray sensor, enabling simultaneous measurements of neutron and gamma-ray doses. The slow neutron sensor is an n-type silicon crystalon which a 1mm thick p~+ layer of boron enriched to 94% by ~(10)B is deposited. The fast neutron sensor, is an p-type silicon crystal without boron coating. Both crystals are contacted with 0.08 mm thick polyethylene radiators and in some cases only theslow neutron sensor is covered with thermal neutron filter of 0.5mm thick cadmium to improve its energy response. The gamma-ray sensor is the p-type silicon detector of 3mm x 3mm without any radiator. These three sensors are encapsulated together with the charge sensitive preamplifier and the linear amplifier circuits.