AN EFFICIENT 14-MEV NEUTRON DETECTOR FOR USE IN MIXED 2.5-MEV AND 14-MEV NEUTRON BEAMS

A neutron detector capable of measuring the time-dependent yield of 14-MeV neutrons from a D-D plasma producing predominantly 2.5-MeV neutrons has been developed. The detector consists of a thick polythene recoil proton radiator backed by a graphite foil attached to a large area totally depleted ion-implanted diode. Protons scattered in the forward direction by 14-MeV neutrons pass through the graphite foil and are registered in the diode. Recoil protons from 2.5-MeV neutrons, however, are prevented from reaching the diode by the foil. When operated with a 1.5-MeV energy bias, the measured neutron detection efficiency for 15-MeV neutrons is 3.2 X 10(-3) per neutron. The corresponding figure for 3. 1-MeV neutrons is a factor of 540 lower. The neutron detector and its laboratory calibration are described, as is its deployment at the Joint European Torus where it serves as a triton burn-up monitor.