Response of radiochromic film dosimeters to gamma rays in different atmospheres

Abstract

The high-dose gamma ray response (10 3 - 5×10 5 Gy) of radiochromic film dosimeters, with ten kinds of plastic matrices (polychlorostyrene containing 1 or 25% C ▪, polybromostyrene containing 2 or 43% Br, nylon, polyvinyl chloride, cellulose triacetate, and an aromatic polymide) were investigated when irradiated under certain conditions in vacuum and in different atmospheres (air, oxygen, nitrogen, and nitrous oxide). In addition, the stability of the films was studied for storage periods up to one month after irradiation under these conditions. The responses and stabilities of the polyhalostyrene and nylon films were only slightly affected by the different atmospheres of irradiation, but there were marked differences of response for the other film types. The dyed cellulose triacetate films and polyvinylchloride films are generally more sensitive in N 2O and O 2-deprived atmospheres than in air or in O 2, but the opposite is true for the dyed polyvinyl butyral and aromatic nylon films. The dyed cellulose triacetate and dyed polychlorostryrene with 1% C ▪ are the most stable films for all conditions or irradiation. For accurate routine radiation processing dosimetry, it is important to know the conditions of irradiation so that appropriate dosimetry systems and procedures may be used and so that suitable correction factors can be applied. Emphasis must be given to differences in atmospheric conditions encountered by dosimeters in practical industrial situations, which may cause marked differences in ultimate response factors.