The gamma-ray response of radiochromic dye films at different absorbed dose rates

Abstract

In leucotriphenylmethane radiochromic dye systems, using polymeric host materials, low-intensity rate dependence of gamma-ray response at doses >10 kGy and at dose rates <1 Gy·s −1 is observed in some dye-plastic combinations. This effect is prevalent under dry or anoxic conditions, and accompanies a shift in the optical absorption band. Whether or not the net dye yield becomes sublinear with dose and diminishes with decreasing dose rate is determined by environmental effects (e.g. relative humidity) and especially by the nature of the host material. Experiments at absorbed dose rates between 0.01 and 3 Gy·s −1 show that the apparent low-intensity dose rate dependence is due mainly to a moisture-controlled decrease in efficiency of radiation-induced dye formation at relatively low radiation intensities. For several hydrophilic dosimeters, the thinner the film, the greater the dose rate effect. With the exception of polyvinyl pyrrolidone and the very thin films, there is only slight rate dependence at intermediate relative humidity.