A thin, composite sodium chloride dosimeter with diffuse reflected light spectrophotometric read out

Optical absorption by electrons trapped in natural anionic vacancies in NaC l has been used for the construction of a dosimeter for radiation processin g. To meet the demands of electron beam processing, characterised by conges tion of isodoses, the active part of the dosimeter, i.e., the microcrystals of NaCl are embedded in a 0.3 mm thick polyethylene film, in which doses f rom 10 MeV electrons do not exceed +/-2% difference in extreme parts of the dosimeter body. The dosimetric film is opaque and the optical density at t he wavelength lambda(max) = 465 nm, i.e., the maximum absorption of the F b and, is measured by diffuse reflected light spectrophotometry (DRS). The me asurement is performed against the unirradiated film as reference, thus inc reasing the accuracy, by self-compensation of signals not belonging to the absorption of F-centres. The spectrum obtained in such a way is identical w ith that of F-centres in irradiated single NaCl crystals. The calibration c urve of the height of the band is almost linear versus the dose in the rang e of several tens of kilograys. As ordinary grades of sodium chloride may b e used, the dosimeter developed is cheap and enables to map the: irradiatio n field in objects of complicated geometry.