Radioisotope Production by Irradiation Inside a Cylindrical Fuel Element

The neutron flux and energy distribution inside the cylindrical fuel of JRR-2 used for irradiation have been measured by activation method, and the results compared with those obtained by irradiation at the same position without the fuel.Threshold detectors such as nickel and sulphur were used to measure the fast neutron flux. Gold and cobalt metal foils were used as thermal neutron monitor. In order to measure the contribution of resonance neutrons to the effective activation cross section, elements possessing different resonance neutron absorption energies were irradiated along with the flux monitors.It was estimated that approximately 30% of the thermal neutrons were converted to fast neutrons inside the cylindrical fuel and that the fast neutron flux was 6 times as high as obtained in the absence of fuel material, but that the epithermal index was found unchanged.