Optical and electrical analysis of blue polymethyl methacrylate for high-dose dosimetry

The response to gamma radiation of polymethyl methacrylate ('blue PMMA') containing a blue dye was investigated, with the aim of providing a high-dose dosimeter based on either spectrophotometry or electrical-conductivity measurements. It is found that the 3-mm thick pieces of blue PMMA can be used for dosimetry in a range of absorbed doses from about 5 to 50 kGy, for which the changes in optical transmission density (absorbance) at different wavelengths in the visible region (402, 596, 612 and 643 nm) are linear functions of dose. Results also show that irradiation of thin 0.1 mm films of blue PMMA produces two components of radiation-induced conductivity: a transient component which can be used to determine the absorbed dose rate and a steady-state component which registers the total absorbed dose in the range 20 to 80 kGy as based on a suitable calibration. The effects of post-irradiation storage time, day light, and storage temperature on the radiation-induced visible spectrum were investigated. The storage-temperature effect on post-irradiation conductivity measurement was also evaluated. (author)