MEASUREMENT OF HUMAN EXPOSURE TO ULTRAVIOLET-B SOLAR RADIATION USING A CR-39 DOSIMETER C. F. Wong,* R. A. Fleming," S. J. Carter,* I. T. Ring,' and D. Vishvakarmad UVR wavelengths below 320 nm (UV-B in solar radiation), therefore, it can be used conveniently (Challenor et al. 1976; Holman and Armstrong 1984a, 1984b) to determine the erythemal dose defined in eqn (1). Recently, a new dosimeter based on the use of the plastic, allyl diglycol carbonate (CR-39), was investigated. The new UV-B dosimeter is similar to polysulphone and it also has a response (Wong et al. 1989) that approximates the average human action spectrum for erythema (Fig. 1). Both types of UV-B dosimeters are based on the use of the degradation in the polymer with the UVR exposure for determining the UV-B dose. Degradation in polysulphone causes changes in absorbance that can be measured accurately. To use CR-39 as a UV-B dosimeter, the dosimeter must be processed as follows. After exposure to UV-B, the dosimeter has to be etched in 6N KOH aqueous solution at an elevated temperature of 80°C for 3 h. The processed dosimeter should be rinsed in distilled water for 10 min and then dried in a desiccator (Wong et al. 1989; Wong 1991). The change in absorbance in the exposed dosimeter can then be measured using a spectrophotometer at a wavelength of 700 nm. Both types of dosimeters must be calibrated against a range of known doses that is determined using a spectroradiometer. The change in absorbance can then be used to determine an unknown dose. Unlike polysulphone films (0.04-mm thick), CR-39 comes in sheets with a thickness of about 0.5 mm. It can be used to fabricate self-supportingdosimeters. Furthermore, the sensitivity of CR-39 can be changed by varying the processing conditions. For example, it was observed that the sensitivity of the dosimeter in the low-dose region (