CHARACTERIZATION OF A THERMAL NEUTRON FIELD AT THE HEAVY WATER NEUTRON IRRADIATION FACILITY OF THE KYOTO UNIVERSITY REACTOR

In this work, the thermal neutron field at the Heavy Water Neutron Irradiation Facility of the Kyoto University Reactor, which had been used for boron neutron capture therapies for several years, was characterized. The spatial distributions of the thermal neutrons were measured with a small thermal neutron probe that was put on a tip of an optical fiber with a diameter of 1 mm. The probe consisted of ZnS(Ag) and LiF as a neutron converter. The probe was very small so that the detector could measure the spatial distribution with an excellent spatial resolution and without disturbing the thermal neutron field. The results were compared with that obtained with a conventional gold wire activation method and Monte Carlo calculations.