Nuclear Instruments and Methods in Physics Research A 513 (2003) 300–303 Deterioration and recovery effects in energy responses of semiconductor X-ray detectors due to nuclear-fusion produced neutron irradiation J. Kohagura a, *, T. Cho a , M. Hirata a , T. Numakura a , R. Minami a , M. Yoshida a , H. Watanabe a , H. Ito a , N. Yokoyama a , K. Yatsu a , S. Miyoshi a , K. Hirano b , H. Maezawa b , T. Kondoh c , J. Hori c , T. Nishitani c a Plasma Research Centre, University of Tsukuba, Ibaraki 305-8577, Japan b High Energy Accelerator Research Organization, Ibaraki 305-0801, Japan c Japan Atomic Energy Research Institute, Ibaraki 319-1195, Japan Abstract Effects of neutron irradiation on X-ray energy responses of silicon semiconductor detectors have been investigated. Neutron irradiation experiments were carried out for n-type photodiode arrays utilized in the Joint European Torus (JET) using deuterium (D) beam-injection into a tritium (T) target for a well-calibrated deuterium–tritium (D–T) fusion neutron production at the Fusion Neutronics Source (FNS) facility of Japan Atomic Energy Research Institute. X-ray energy responses of these detectors are characterized before and after irradiation 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). A recovery of the degraded X-ray energy response after the neutron irradiation has been found at fluences beyond around 10 13 neutrons/cm 2 . A further novel finding is followed as a ‘‘re-degradation’’ by a neutron irradiation level over about 10 14 neutrons/cm 2 . This ‘‘non-linear response’’ may be physically interpreted in terms of a type inversion from n- to p-type silicon in the detectors. Long-term observations of X-ray energy responses of the detectors after neutron irradiation have also been made in order to clarify the ‘‘annealing effect’’. r 2003 Elsevier B.V. All rights reserved. PACS: 52.70.La; 61.80.Hg; 61.82.Fk Keywords: Semiconductor detector; Neutron damage; X-ray energy response 1. Introduction Two- or three-dimensional X-ray tomographi- cally reconstructed data analyses using silicon semiconductor detector arrays play an impor- tant role in controlled thermonuclear fusion research in order to investigate plasma elec- tron behaviour both temporally and spatially [1–4]. However, recent harsh radiation environ- ments in fusion experiments by using deuterium– tritium (D–T) and/or deuterium–deuterium (D–D) reactions [1,5] pose the serious problem of radiation-induced degradation in X-ray ARTICLE IN PRESS *Corresponding author. Tel.: +81-298-53-6228; fax: +81- 298-53-6202. E-mail address: kohagura@prc.tsukuba.ac.jp (J. Kohagura). 0168-9002/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2003.08.151