ALCOHOL-SOLUTIONS OF TRIPHENYL-TETRAZOLIUM CHLORIDE AS HIGH-DOSE RADIOCHROMIC DOSIMETER

The radiolytic reduction of colorless tetrazolium salts in aqueous solution to the highly colored formazan dye is a well-known acid-forming radiation chemical reaction. Radiochromic thin films and three-dimensional hydrocolloid gels have been used for imaging and mapping absorbed dose distributions. The high solubility of 2,3,5-triphenyl-tetrazolium chloride (TTC) in alcohols provides a useful liquid dosimeter (45 mM TTC in aerated ethanol) and shows a linear response of absorbance increase (lambda(max) = 480 nm) with dose over the range 1-16 kGy. The linear molar absorption coefficient (epsilon(m)) for the formazan at the absorption peak is 1.5 x 10(3) m(2) mol(-1), and the radiation chemical yield for the above solution is G (formazan) = 0.014 mu mol J(-1) The irradiation temperature coefficient is about 0.8 percent per degree Celsius rise in temperature over the temperature range 0-30 degrees C but is much larger between 30 degrees and 60 degrees C. The unirradiated and irradiated solutions are stable over at least five days storage at normal laboratory temperature in the dark, but when stored in daylight at elevated temperature, the unirradiated solution in sealed amber glass ampoules undergoes slow photolytic dye formation, and the irradiated solution experiences initial fading and subsequent reversal (photochromism) when exposed to direct sunlight.