A THIN-FILM RADIATION MONITORING LABEL AND DOSIMETRY SYSTEM

A thin plastic film was fabricated by casting on a polyester base a thin layer of poly(vinyl alcohol) (PVA) in aqueous solution with a mixture of dissolved sodium salt of 2,6-dichlorophenolindophenol (DPIP-Na) (a blue dye) and Sandolan Yellow N-3GL dye (SYN-3GL). This flexible, coated plastic film dosimeter undergoes a color change from green to yellow, with a sensitivity depending on DPIP-Na concentration. By changing the concentration of DPIP-Na in the film, one can predict the dose region at which the film will change its color from green to yellow. The response range of this dosimeter depends, in fact, on the DPIP-Na concentration and, in the case of 0.2 phr (by weight), it can be used up to absorbed doses of about 25 kGy, with a minimum useful dose of about 2 kGy. The effects of variation in concentration of DPIP-Na and thickness of film on response have been studied. The effects of absorbed dose, dose rate, temperature and relative humidity during irradiation and post-irradiation storage and exposure to daylight on dosimeter performance are also discussed. The usefulness of this dyed-film detector depends on its application. Using different concentrations of DPIP-Na, it can be applied as a green-to-yellow visual go-no-go monitor in the absorbed dose region 8-32 kGy. For dosimetry by spectrophotometry at 641 nm, the films show a linear response from 1 to 12 kGy.