Dose response of a natural-polymer-based gel dosimeter; Effects of composition on white turbidity increase after irradiations

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

A new polymer gel dosimeter was developed to overcome weakness of earlier polymer gel dosimeters. Hydroxyethyl 2-methacrylate (HEMA) and polyethylene glycol ester dimethacrylate (9G) were less toxic constituents, which polymerize with irradiations. One of cellulose derivatives, hydroxypropyl cellulose (HPC), was crosslinked by irradiations of electron beam and used as a gel matrix, which doesn't soften with increasing temperature. Hydrogel of HPC is very transparent, so light scattering and absorption of products of radiation-induced polymerization are easily observable. As a result of irradiation, white turbidity was observed inside the gel at around 1-2 Gy. Increasing behavior of white turbidity with irradiation depended on composition of constituent monomers. White turbidity appears at rather lower dose and its increase saturates at around 10 Gy of -irradiation when 9G is predominant. On the other hand, it becomes stronger even beyond 10 Gy when HEMA is 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 although degree of white turbidity was less clear than that observed after Co -irradiation.