To evaluate the X-ray-induced afterglow phenomenon, we developed an ionizing-radiation-induced luminescence characterization system equipped with a pulse-width-tunable X-ray source. The system consists of a pulse X-ray tube and a detector system based on photon counting. The excitation pulse width was tunable from nano- to millisecond ranges, and the dynamic range of the X-ray-induced afterglow was 106. Conventional scintillators for X-ray CT or security systems, namely, Bi4Ge3O12, CdWO4, Tl-doped CsI, and Tb and Pr-codoped Gd2O2S, were evaluated for the performance test. Results show that the afterglow time profiles of these scintillators are consistent with generally known results with high accuracy.

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We have prepared single-crystalline films of BaFeO3, which may contain high valent Fe4+ ions, on (100) SrTiO3 substrates by pulsed laser-beam deposition. The reflection high-energy electron diffraction patterns for the films apparently show a C4 symmetry operation, suggesting that the sample had a pseudocubic perovskite structure rather than hexagonal unit cell. The films were found to be highly insulating, and showed a high value of dielectric constant of ε=59. At 300 K, the magnetization loop of the film apparently shows hysteresis, as well as small remanent magnetization. These characteristics are totally different from those of bulk BaFeO3.

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The temperature dependence (from 20 to +20 degrees C) of gamma-ray irradiated light outputs, energy resolutions, and decay time profiles of three YAG:Ce poly-ceramic scintillators are studied. The Ce concentrations are 0.5, 0.05, and 0.005 mol%. The relative light yield of the YAG:Ce with 0.5 mol% with a 2 s shaping time was measured as 1 : 1.08 : 1.14 at +20, 0, and 20 degrees C, respectively, including the temperature dependence of the phototube ( 0 2% degree). The energy resolution stays almost constant at 7.2% for 662 keV gamma-rays. The ceramic with 0.05 mol% shows the almost same properties, while the light yield of that with 0.005 mol% is 2-4 times lower (hence the energy resolution becomes 14-19%). All the scintillators exhibit good linearities within 1% between the light output and the irradiated gamma-ray energy from 59.5 keV to 662 keV. The decay time constants of the dominant decay components are about 80 ns and 300 ns at +20 degrees C. As the temperature increases from 20 to +20 degrees C, the effective decay of all the ceramics becomes faster, because the decay time constants and fractions of the slower components shorten and decrease, respectively. This result suggests that carriers which are captured in shallow traps before transferring excitation to Ce ions can escape the traps more easily at higher temperatures. Considering the decrease of the total light yield toward higher temperatures, it is thought that thermal quenching starts to dominate the temperature dependence of the ceramic YAG:Ce around the room temperature. The 0.5 mol% scintillator shows a lower quenching energy than the 0.05 mol% one. This can be explained in terms of self absorption of Ce emission.