Self-Bleaching Effects of Radioluminescence on OSL-Responses of Natural Quartz Samples

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藤田 博喜; 橋本 哲夫*

Fujita, Hiroki; Hashimoto, Tetsuo*

絶縁性白色鉱物と電離放射線との相互作用によって、様々なルミネッセンス現象が観測される。放射線照射中には、ラジオルミネッセンス(RL)が観測される。このRLには400nmと630nm付近にピークのある2つの発光波長があることをこれまでに明らかにした。このうち、400nmの波長領域のRLはOSLの励起光よりも波長が短いため、OSLによる積算線量測定に影響を及ぼすことが考えられる。そこで、RLとOSLとの関連性について研究を行った。RL挙動を調べたところ、(1)線量率に応じて発光強度が増加 (2)前もって照射された放射線量からの影響があった。既知線量を照射した複数の石英粒子について、照射線量率を変化させてOSL測定を行ったところ、得られた線量値が石英の起源毎に異なっていた。この積算線量の分散は、400nmの波長領域のRLと関係があることが示唆された。TLでは影響がほとんどなかった。これらのことからRL発光はOSLに大きく関与していることが考えられた。

Radioluminescence (RL) phenomena can be observed from many insulating minerals including quartz during radiation-irradiation. The RL attracts much attention to the purpose of both the alternative dosimetry and the elucidation of luminescence mechanism.RL spectrum consists of two RL emission regions assigned to emission peaks at 400 (violet region) and 630nm (Red region) on natural quartz by using an on-line spectrometric system. Increment of RL intensities was observed by increasing dose rate. When the sample was irradiated beforehand, the RL emission intensities depended on the predoses. The above phenomena will lead to a possibility to determine doses using RL measurement. The RL emission peak at 400nm was almost close to stimulated wavelength (470nm) on optically stimulated luminescence (OSL)-measurements. Therefore OSL source would be stimulated by the RL emission wavelength. Overestimated or underestimated OSL-doses were occurred by measuring conditions (high- and low-dose rate), and quartz origins, compared with applied dose. The OSL-doses was related to violet-RL (V-RL) emission intensity but red-RL (R-RL). This result suggested that OSL source would be stimulated by V-RL emission within quartz grain. However, estimated doses by red-TL (RTL) and blue-TL (BTL) measurements were less or not affected by dose rate. These results imply that RL emission is more effective to OSL measurement than TL measurement.