PIN DIODE FOR REAL-TIME DOSIMETRY IN A MIXED FIELD OF NEUTRONS AND GAMMA-RAYS

The dose equivalent of neutrons and gamma rays in a mixed field was measured with a single small PIN diode implanted with boron atoms. The pulse height of the signals was discriminated against thermal, fast neutrons and gamma rays. The sensitivities corresponding to 1 cps of the detector in the mixed field were found to be 130-mu-Sv.h-1 and 280-mu-Sv.h-1 for photons and thermal neutrons, respectively. The directional dependence in free air irradiation for photons was almost isotropic with angle of incidence while the response for neutrons fell above an incident angle of 45-degrees. The energy response to neutrons was measured as a function of polyethylene thickness. The results obtained using a 4 cm thickness were in good agreement with the ICRP dose equivalent values for thermal, 144 keV and fast neutrons.