Akihisa Kaihara

Silicon semiconductor detectors for various nuclear radiations

Silicon semiconductor detectors for a nuclear radiation monitor of various rays (/spl gamma/ rays, neutrons and charged particles) have been developed. These detectors are diffused p-n junction type devices with low leakage current. The /spl gamma/ ray detector is produced, using high resistivity p-type silicon (2-10 k /spl Omega//spl middot/cm), to increase thickness of the depletion layer. This detector has been applied as an area monitor and a computerized personal dosimeter with an IC card. For the neutron detector, proton radiators and boron convertors are coated on the surface of the detector element. Neutrons are detected as recoil protons by interaction of the proton radiator and, as /spl alpha/-particles generated by the nuclear reaction /sup 10/B(n,/spl alpha/)/sup 7/Li. The energy response of this detector meets the ICRP recommendation for a radiation monitor. The charged particles (/spl alpha/, /spl beta/ rays) detector having a large sensitive area (up to 6000 mm/sup 3/) is coated with double passivation layers (Si/sub 3/N/sub 4//SiO/sub 2/) on the surface of the detector element in order to reduce leakage current due to surface stress. The leakage current of less than 220 nA is achieved for the sensitive area by application of the double layers. The charged particles detector can be applied as a radioactive dust monitor and a contamination monitor, and the neutron detector is suited as an area monitor and a personal dosimeter.

Energy Response of Neutron Area Monitor with Silicon Semiconductor Detector.

Abstract A prototype neutron area monitor with a silicon semiconductor detector has been developed which has the energy response of 1 cm dose equivalent recommended by the 1CRP-26. Boron and proton radiators are coated on the surface of the silicon semiconductor detector. The detector is set at the center of a cylindrical polyethylene moderator. This moderator is covered by a porous cadmium board which serves as the thermal neutron absorber. Neutrons are detected as α-particles generated by the nuclear reaction 10B(n, α)7Li and as recoil protons generated by the interaction of fast neutrons with hydrogen. The neutron energy response of the monitor was measured using thermal neutrons and monoenergetic fast neutrons generated by an accelerator. The response was consistent with the 1cm dose equivalent response required for the monitor within ±34% in the range of 0.025–15 MeV.