Neutron yield measurements by use of foil activation at JT-60U

To study the 14 MeV neutron emission, the neutron yield measurements have been complemented by a recently installed neutron activation system. By using threshold reactions (Si, Al, and Cu foils), it is possible to distinguish between the 2.5 and 14 MeV neutron emission. Neutron transport calculations have been performed using Monte Carlo trajectory sampling methods (MCNP code) in order to determine the neutron fluency and energy distribution at the irradiation position. The results from the MCNP calculations together with the known cross sections of the foils, make it possible to calculate a calibration factor, which relates the fluency at the irradiation position to the total fluency from the JT-60U plasma. The accuracy of these calculations have been confirmed (∼20%) by comparing the total 2.5 MeV neutron yields obtained from foil activation, with those obtained from the fission chambers, which were calibrated using a 252Cf source. The efficiency calibration of the HP-Ge detector have been performed using a set of calibration sources. However, due to sum-coincidence effects, the efficiency is expected to have large errors (∼10%).