Intercalibration and testing of blue cellophane- and cellulosetriacetate films for the megarad dose range

The γ-radiation response of blue cellophane films is dependent in a rather complex way upon dose rate as well as on the relative humidity of the air to which the films are under equilibrium. Generally, the response decreases with increasing humidity. Up to about 25% r.h. an increase in dose rate from 0.23 to 2.3 Gy/s results in a response increase by 10-15%. Above 66% r.h. there is no dose rate effect and at intermediate humidities a distinct negative dose rate effect was observed. Gamma irradiation of CTA films in air results in an absorbance change in the UV region which is higher than for electron irradiation and which is - contrary to the latter - dependent on the water content of the films. Replacing air by argon removes that humidity dependence and additionally, the γ-response in argon becomes almost identical to that found for electron irradiations. It may be concluded from this, that the dose rate - as well as the humidity effect are in fact oxygen effects. Post-irradiation coloration proceeds after irradiation under argon as well as under air. It is caused mainly by the reaction with some reactive intermediates of oxygen diffusing into the films after irradiation. (author)