Radiation chemistry of anionic disazo dyes in Cellophane films applications for high-dose dosimetry

Abstract Thin transparent Cellophane films containing anionic disazo “Direct” dyes, e.g. blue Cellophanes, have long been used as monitors of large absorbed doses of ionizing radiation (10–300 kGy) and especially for mapping electron-beam dose profiles. Examples of dyes for such purposes are variations on forms of the disazo dyes, Direct Orange, Direct Violet or Direct Blue. The films have a thickness of 25.6 μm (+0.1 μm) and are available in rolls of either 30 m×0.51 m or 60 m×0.76 m. Such dyed Cellophanes are typically lightfast but can readily be bleached irreversibly by ionizing radiation, as a means of dosimetry using spectrophotometry as the analytical tool. The radiation response is markedly dependent on temperature and relative humidity during irradiation. The reaction is initiated mainly by dehydrogenation and nitrosation upon electrophilic reductive attack on the dye molecule by the thermal electrons, at initial reaction rate constants in the range 10 5 –10 6  s −1 .