Effects of neutrons on semiconductor x-ray detectors including n-type Joint European Torus and p-type GAMMA 10 tomography detectors

Characterization experiments have been carried out so as to investigate the effects of fusion-produced neutrons on the x-ray-energy responses of semic onductor detectors for x-ray tomography in the Joint European Torus (JET) t okamak (n-type silicon) and the GAMMA 10 tandem mirror (p-type silicon). Ne utron effects on the x-ray-energy responses of these detectors are studied using synchrotron radiation from a 2.5 GeV positron storage ring at the Pho ton Factory. Changes in the material properties of the detectors have been investigated using an impedance analyzer to estimate neutron effects on x-r ay-sensitive depletion thicknesses. A cyclotron accelerator is employed for well-calibrated neutron irradiation onto these plasma x-ray detectors; a f luence of 2-5X10(13) neutrons/cm(2) is utilized for simulating the effects of fusion-produced neutrons in JET. Modifications of the x-ray responses af ter neutron exposure due to fusion plasma shots in JET as well as cyclotron -produced neutron irradiations are found to have a functional dependence on x-ray energy. Also, recovery of the detector energy response is found when detector bias is applied. Our theory consistently interprets such properti es in terms of the neutron effects on the diffusion length and the resistiv ity of detectors. (C) 1999 American Institute of Physics. [S0034-6748(99)50 401-2].