Dose response of natural-polymer-based gel dosimeter; Composition effects on white turbidity increase by irradiations

天然高分子を母材としたゲル線量計の線量応答; 照射に伴う白濁化における組成の影響

山下 真一; 廣木 章博; 長澤 尚胤; 村上 健*; 田口 光正

Yamashita, Shinichi; Hiroki, Akihiro; Nagasawa, Naotsugu; Murakami, Takeshi*; Taguchi, Mitsumasa

従来、放射線検出剤モノマとして使用されているアクリルアミドやアクリル酸よりも毒性の低いメタクリル酸2-ヒドロキシエチル(HEMA)及びポリエチレングリコールジメタクリレート(9G)を用いて新たにポリマーゲル線量計を開発した。ゲル母材にはセルロース誘導体であるヒドロキシプロピルセルロース(HPC)を電子線橋かけして用い、温度変化でも軟化や離水しにくいものを用いた。HPCゲルは透明度が高く、吸光分析が可能である。照射に伴う白濁化を濁度、吸光度として数値化し、放射線検出剤モノマ組成が感度に与える影響を調べた。Co線照射の場合、2Gy以下の低線量域では9Gが主成分の方が、10Gyを超える高線量域ではHEMAが主成分の方が高感度に白濁化することがわかった。また、C135MeV/uでも照射を行い、線質効果があることも確認された。

We developed a new polymer gel dosimeter. 2-Hydroxyethyl methacrylate (HEMA) and polyethylene glycol dimethacrylate (9G), which are less toxic than methacrylic acid or acrylamide, were used as constituents polymerizing after irradiations. A cellulose derivative, hydroxypropyl cellulose (HPC), was selected and crosslinked to form gel matrix by an irradiation of 2-MeV electron beam, which doesn't soften at higher temperature. Hydrogel of HPC is enough transparent to observe light scattering and absorption of products of radiation-induced polymerization. As a result of Co -ray irradiation of a few Gy, white turbidity arisen inside the gel, detailed behavior of which depended on composition of constituent monomers. It appeared at rather lower dose and its increase saturated at around 10 Gy of -irradiation when 9G was predominant. In order to quantify the degree of white turbidity, haze measurement and UV-vis absorption spectrometry were conducted. In addition, white turbidity evolution was also confirmed after irradiations of therapeutic C ion beam of 135 MeV/u although degree of white turbidity was less clear than that observed after -irradiation.