Experience of using TLD's at the research reactor in the University of Tokyo

The experiences of using TLD's for the study of therapeutical irradiation field and fast neutron shielding experiment carried out with the fast neutron source reactor ''Yayoi'' in the University of Tokyo and for the Streaming experiment in the experimental hole of the NSRR (Nuclear Safety Research Reactor) of Japan Atomic Energy Research Institute are described. In the irradiation field of ''O'' system, it was necessary to obtain epithermal neutrons as many as possible, and to suppress γ-ray as far as possible by moderating the neutrons from the reactor with iron, graphite, polyethylene, lead and bismuth to obtain a therapeutical irradiation field. γ-ray was measured by using BeO and CaSO4 (Matsushita Electric Industrial Co.), and Mg2SiO4 powder (Dai Nippon Toryo Co.) filled in 2 mm diameter polyethylene tube (devised by Kyoto University). There was great difference between the measurements with the former two and Mg2SiO4, and the influence of glass on the BeO and CaSO4 sealed in the glass tube was supposed in the system with many thermal neutrons such as in water. The similar measurements were performed in three fields called ''Q'', ''R'' and ''I'' systems. When the luminescence of Mg2SiO4 powder is read with a TLD reader UD502A, there are difficulties because the background is hundreds of mR, the measuring range is small, and the error is large. Next, the measured results of the γ dose distribution in vertical direction in the central experimental hole for fuel irradiation of the NSRR is described. Since the amount of irradiation to Mg2SiO4 was small, its result was larger than others due to background effect. (Wakatsuki, Y.)