A Thin, Composite Sodium Chloride Dosimeter with Diffuse Reflected Light Spectrophotometric Read Out

Abstract

Optical absorption by electrons trapped in natural anionic vacancies in NaCl has been used for the construction of a dosimeter for radiation processing. To meet the demands of electron beam processing, characterised by congestion 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 from 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 the wavelength λ_max = 465 nm, i.e., the maximum absorption of the F band, is measured by diffuse reflected light spectrophotometry (DRS). The measurement is performed against the unirradiated film as reference, thus increasing the accuracy, by self-compensation of signals not belonging to the absorption of F-centres. The spectrum obtained in such a way is identical with that of F-centres in irradiated single NaCl crystals. The calibration curve of the height of the band is almost linear versus the dose in the range of several tens of kilograys. As ordinary grades of sodium chloride may be used, the dosimeter developed is cheap and enables to map the irradiation field in objects of complicated geometry.