@misc{oai:niigata-u.repo.nii.ac.jp:00004783,
 author = {Fujita, Hiroki},
 month = {Mar},
 note = {It is very important to have a method of estimating radiation-dose received by people or irradiated in environmental space, without having or setting conventional dosemeters. However, dose evaluation method is not always established in the case of emergency situation. The purpose of this study was to confirm whether thermoluminescence (TL) and optically stimulated luminescence (OSL) from naturally occurring quartz could be used to estimate such accidental radiation doses or not. When ionizing radiation is interacted with a dielectric material, some parts of concerned radiation energies will be converted into luminescence such as TL, OSL and so on. Luminescence intensity contains information of total radiation-dose received in the past. Therefore, TL- and OSL-phenomena from natural minerals have been utilized for dating in the geological and archaeological fields, and for retrospective dosimetry. However, details of such luminescence mechanisms have not yet been clear, including difference of dose response in each sample and sensitivity change after annealing treatment. First of all, the existence of atomic hydrogens besides intense Al-hole centers was ascertained in electron spin resonance (ESR) spectrum measurements of various natural quartz grains after irradiation at -196℃. Remarkable decrease of Al-hole center signals, coincident with the complete disappearance of ESR-signal due to atomic hydrogens, was observed during heating up to room temperature. A positive correlation was established between the atomic hydrogen signals and the reduced proportion of the Al-hole centers. Additionally, the thermal annealing treatments of the quartz samples beyond 800℃ before irradiation induced the significant decrease of H0 as well as the removal of OH absorbance in IR-spectra around 3500 cm-1. On the basis of these experiments, it was presumed that atomic hydrogens derived from radiolysis of OH-related impurities could operate as "killers" of radiation-induced Al-hole centers. This quenching mechanism due to atomic hydrogen was also found in RTL quartz. The existence of atomic hydrogen plays an important role in the phase-transition temperature of β-quartz / tridymite on the TL-property changes. The ESR spectra of Ti-centers and Al-hole centers were measured in RTL quartz irradiated at -196℃, before and after warming up to room temperature. Only three kinds of Ti-centers were observed as electron-trapping centers in the samples: [TiO4/H+]0, [TiO4/Li+]0 and [TiO4/Na+]0 centers. They were affected by annealing treatments. The [TiO4/H+]0 center behaved just like atomic hydrogens. Tendency of the [TiO4/Na+]0 center resembled to the RTL-intensity change associated with increasing annealing temperature. The phenomena were supported by both results of RTL glowcurves broadened and kinetic parameters, which were influenced by the annealing temperatures. Secondary, mechanism of the different OSL sensitivities for quartz aliquots from different origins was investigated in terms of radioluminescence (RL) during artificial irradiation. RL spectra of RTL-quartz consisted of two broad RL emission peaks, assignable to a violet region (V-RL, 400 nm) and a red one (R-RL, 630 nm)., OSL sensitivity changed with the total amounts of V-RL emissions during irradiation of 20 Gy at different dose rates. Additionally, bleaching effects of RL with shorter wavelength light than OSL-illuminating light (470nm) were assured from another experiment with a combination of quartz slices and optical filter. Conclusively, it was confirmed that V-RL emissions appreciably affect the residual or naturally accumulated doses when the OSL / SAR protocol was applied. To develop retrospective dosimetry of unexpected radiation accident, the basic studies on VTL phenomena were conducted using natural quartz grains extracted from surface soils. All VTL glowcurves of as-received samples exhibited no peaks below 250℃, although there remain VTL peaks with their intrinsic mean lives in the temperature region below 250℃ for artificially irradiated quartz samples. Therefore, accident doses would be estimated without interference of naturally accumulated doses if VTL measurement was applied to soil samples collected from ancient site. The mean lives of VTL were evaluated by the various heating rates method and then the range of values was between some days and ten thousands of years depending on each peak. Especially, the mean life of VTL peak at 200℃ was years order, supporting the results of natural VTL glowcurve measurements. Furthermore, since the VTL intensity was proportional to the irradiation doses, the lower detection limit were calculated to be tens of mGy from the response curve. This value was lower than that of other methods such as ESR dosimetry. From these results, VTL dosimetry would be preferable for accidental evaluation. Finally, nine kinds of luminescence, including TL, OSL and infrared stimulated luminescence (IRSL) measurements were applied to determination of residual doses in atomic bomb-explosion suffered roof-tiles collected near epicenter areas in Hiroshima and Nagasaki, Japan. RTL-measurements of quartz extracts showed the highest residual doses in both tiles, which were consistent with the previous dose-evaluations. However, in addition to dose estimation with BTL and OSL for the same quartz fractions, all of the estimations for, including five kinds of TL and IRSL for feldspar extracts showed lower values than the RTL-dose value in quartz extracts. The lower residual-doses in the quartz and feldspar extracts would reflect unstability of their luminescence-centers and/or well-known anomalous fading effects. Conclusively, the highest residual doses of RTL from atomic bomb-suffered roof tiles are considered to be an evidence of the most stable property of RTL-centers in quartz., 新大院博（理）甲第247号, 新大院博（理）甲第247号},
 title = {Basic Studies on Radiation-Induced Luminescence from Natural Quartz and Its Application to Retrospective Dosimetry},
 year = {2006}
}