Speaker
Dr
Junko Kohagura
(Plasma Research Centre, University of Tsukuba)
Description
Two- or three-dimensional X-ray tomographically reconstructed data
analyses by the use of multichannel silicon semiconductor detectors
play an important role in investigating plasma electron behaviour in
controlled thermonuclear fusion research. However, recent harsh
radiation environments in fusion experiments with deuterium-tritium
(D-T) and/or deuterium-deuterium (D-D) reactions pose the serious
problem of radiation-induced degradation in X-ray detection
characteristics of silicon semiconductor detectors.
In order to clarify the effects of fusion-produced neutrons on
silicon semiconductor x-ray detectors, the characterization
experiments for both n-type and p-type multichannel silicon x-ray-
tomography detectors used in the Joint European Torus (JET) and the
GAMMA 10 tandem-mirror are carried out by utilizing D-T fusion
neutron production at the Fusion Neutronics Source (FNS) facility of
Japan Atomic Energy Research Institute (JAERI). These detectors are
characterized before and after the fusion-produced neutron exposure
by the use of synchrotron radiation from a 2.5-GeV positron storage
ring at the Photon Factory of High Energy Accelerator Research
Organization (KEK). Different fluence dependence is found between
these two types of detectors; (i) for the n-type detector, the
recovery of the degraded response is found after the neutron
exposure beyond around 1013 neutrons/cm2 onto the detector. A
further finding is followed as a “re-degradation” by a neutron
irradiation level over about 1014 neutrons/cm2. On the other hand,
(ii) the energy response of the p-type detector shows only a gradual
decrease with increasing neutron fluences. Similar characterization
experiments for p-type detectors with different effective doping
concentrations are also carried out. These properties are
interpreted by our proposed theory on semiconductor x-ray responses
in terms of the effects of neutrons on the effective doping
concentration and the diffusion length of a semiconductor detector.
Primary author
Dr
Junko Kohagura
(Plasma Research Centre, University of Tsukuba)
