Hoshio Eguchi

Deterioration of photo-stimulated luminescence signals from materials by radiation

AbstractA photo-stimulated luminescent (PSL) material, BaFBr 0:85 I 0:15 :Eu 2⁄ , was irradiated by 1 and 2 MeV He ⁄ ions. Thedeterioration of PSL signals caused by heavy irradiation was found quite stable for a long time. In situ measurements ofscintillation were also made during He ⁄ ion irradiation. A broad 400 nm peak and a decreasing continuum tail wereobserved for spectra of the scintillation. An afterglow e•ect was also observed as a function of time up to 10 s afterstopping the He ⁄ ion beam. Results are discussed relating with the incomplete erasing and the self generation of PSLsignals which were reported in our previous study. O 2000 Elsevier Science B.V. All rights reserved.PACS: 78.45; 78.90Keywords: Photo-stimulated luminescence (PSL); Scintillation; Radiation deterioration; He ⁄ ions; Incomplete erasing;Self generation of PSL signals; Afterglow e•ect 1. IntroductionSince photo-stimulated luminescent (PSL) ma-terials have been developed for X-ray imaging [1],many studies have been reported on their charac-teristics and responses to various radiation irra-diations [2–5]. Besides those basic studies, excellentperformances of the PSL materials have also beenreported such as wide linearity, simplicity of PSLstatistics and high confidence of stored image in-formation in practical use [6,7].Among varieties of studies, an elucidation ofthe radiation e•ect of the material in PSL andscintillation is the main interest in this study. De-terioration of PSL signals produced by 1 and 2MeV He

Gamma irradiation system with variable effective half-life function and its characteristics on spatial dose distribution.

The gamma irradiation system with variable effective half-life function has been developed, which provides the low dose rate gamma irradiation field by two 137Cs sources (3.7×1010 Bq and 7.4×1011 Bq) . This apparatus was designed to give an exposure at varying low dose rate in accordance with a biological half life of radioactivity in organisms by selecting one of two irradiation methods. The first irradiation mode uses the spatial attenuation by four movable irradiation tables and the other uses the radiation attenuation by an iron filter. Both of these are driven by pulse motors using the personal computer control. The characteristics on spatial gamma-ray irradiation field were measured using calibrated ionization chambers for gamma dose and NaI (Tl) scintillation ionization chambers for gamma dose and Nal (Tl) scintillation counter for gamma spectra. The irradiation field covers the dose rate between 2.5×10-3C kg-1 min-1 and 1.2×10-7 C kg-1 min-1. The energy spectrum information including scattered radiations are also obtained. The apparatus was proved to be useful in the experiments for the irradiation of mice at varying dose rate to simulate tritium in internal irradiation.