The objective of this study is to investigate the emission mechanism of radiophotoluminescence(RPL)from Ag+-activated phosphate glass(glass dosemeter), which is now used as the individual radiation dosemeter, because the emission mechanism of RPL from glass dosemeter has not clearly been understood. The optical properties such as optical absorption spectra, RPL emission and excitation spectra of the Ag+-activated phosphate glass were analyzed. It was found that the optical absorption spectra of X-ray irradiated glass consisted of three dominant absorption bands peaked at about 255nm, 315nm and 370nm. It was also found that typical RPL spectrum of X-ray irradiated glass excited with 315 nm UV light has two emission bands peaked at about 460nm and 570nm. We also found that RPL intensity gradually increased after X-ray irradiation with elapsed time. It was also confirmed that 570nm RPL peak intensity increased with time, while the band around 460nm unchanged. This result strongly suggests that the 570nm RPL emission band is ascribed to Ag2+ ions. On the other hand, Ag+ activated phosphate glass irradiated with the femtosecond LASER-light exhibits photoluminescence emission peaked between 430 and 460nm, which strongly suggest that the 460nm RPL peak is ascribed to Ag0 ions because of valence change from Ag+ to Ag0.
Observation was made with rhyolitic volcanic rocks erupted from Kozu-shima, Niijima and Higashi-Izu monogenetic volcano group for activity ratios of 230Th/238U and 226Ra/230Th. While the activity ratios of basaltic products from Izu arc volcanoes showed disequilibria of 230Th/238U<1 and 226Ra/230Th>1, the majority of rhyolitic products was considered to be almost in equilibrium of 238U=230Th=226Ra. The observation that 238U-230Th and 230Th-226Ra for the rhyolite are in radioactive equilibrium is consistent with the recent petrological suggestions that the rhyolitic magma from Izu arc was generated in the partial melting of the crust, where 238U-230Th and 230Th-226Ra are in equilibrium, by the basaltic magma of high temperature. Some of the rhyolite samples showed the enrichment of 230Th over 238U, indicating that the young marine sediments with 230Th>238U may possibly take part in the generation of the rhyolitic magmas.
The radiation doses measured by Electric Personal Dosimeter (EPD) were compared with those by Radio-Photoluminescence Dosimeter (RPLD) in natural radiation environment. These two values were almost agreed and have a linear relationship with high correlation. However, the dose by EPD was higher than that by RPLD. The regression expression shows that the slope is a little higher than one, and this line does not pass through the zero dose point. In order to investigate the cause, the gamma ray irradiation was conducted. The result shows that the sensitivity of the EPDs were 4-11% higher than the expected dose. On the other hand, the dose rates varied from 0.019μSv/h to 0.028μSv/h in the lead box which has 10cm thickness. As a result, it would be necessary that the sensitivity of each EPD is calibrated in order to obtain an accurate dose.
We have developed a method to produce microbeams of ions focused by tapered glass capillaries. Glass capillary introduced here has been used as glass pipette in biological experiments, which is low-cost and easily manufactured. The beams can transmit through the capillaries, even if the capillary axis is not exactly parallel to the beam direction (guiding effect). Because the beam can be reflected by a self-organized charge-up potential of the inner wall for keV-energy ions, and by a small angle scattering at the inner wall for MeV-energy ions. The capillary is about 5 cm long, whose inlet and outlet diameters are 0.8 mm and about 1μm, respectively. Due to the taper and the reflection inside the capillary, the transmitted beam is focused (focusing effect). We report on (1) focusing and guiding effects for highly charged ion beams with keV-energy based on the charge-up process of insulator (glass) surfaces, (2) focusing of MeV-energy proton or He ion beams with the glass capillaries with end windows for biological application of “cell surgery” involving selective inactivation or disruption of cellular structures with a spatial resolution of μm3. The other applications to elementary particle beams of muon and positron, which are used for material analysis, are also described.
Recent comparative studies have demonstrated that 18F-sodium fluoride PET is more accurate than 99mTc-Methylenediphosphonate(MDP) bone scintigraphy for identifying both malignant and benign lesions of the skeleton. The favorable imaging performance and clinical utility of 18F-sodium fluoride PET support the consideration of 18F-fluoride as a routine bone imaging agent.