An efficient 14‐MeV neutron detector for use in mixed 2.5‐ 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 3.2×10−3 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.