Measurement of the neutron spectrum at the pneumatic irradiation facility in JRR-4 reactor

A neutron spectrum from thermal to about 18 MeV at the irradiation position of the pneumatic facility in Japan Research Reactor (JRR-4 reactor) of JAERI was measured using the activation method with the SAND-II unfolding code. In the measurement, 6 kinds of resonance detectors and 12 kinds of threshold detectors were used. The intensity of gamma rays from the activation detectors was measured with a Ge detector within an error of about 5 %. The reaction rates were measured with an accuracy less than 12.6 %. Further, a P-I-N neutron dosimeter and a LiF thermoluminescent dosimeter (TLD) covered with a boron carbide neutron absorber were applied to enhance the accuracy of the unfolded spectrum in the energy range from intermediate to 1 MeV, and it was made clear that the dosimeters were effective. (author)