Miniaturization of Polysulphone Dosimeters

Miniaturized polysulphone dosimeters were employed to take high density measurements on living and manikin subjects under various environmental conditions to facilitate detailed mapping of the erythemal UV exposure to unprotected skin (Downs and Parisi, 2007; 2008). These dosimeters are cost-effective and provide accurate short-term UV exposure measurements for personal and environmental applications that may require a large number of dosimeters. Such applications may include UV exposure measurements to humans, animals, and plants.

Polysulphone film employed in the manufacturing of miniaturized dosimeters is adhered to flexible cardboard frames measuring approximately 1.5 cm x 1 cm having a clear circular aperture of 6 mm. The smaller flexible, lightweight dosimeter can be placed along curved surfaces and attached to complex surface topography not readily accessible to conventionally sized dosimeters, including the eyes, ears, and fingers of life-sized manikin models. The miniaturized dosimeter can also be conveniently attached to human subjects with the use of medical tape. An example of the application of miniaturized dosimeters used to measure UV exposures on the hand is given in Fig. 7.2.

Figure 7.2 UV exposure measured by application of miniaturized polysulphone dosimeters placed on the hand of a life-sized manikin

Miniaturized polysulphone dosimeters undergo the same UV induced photodegradation as conventional polysulphone film dosimeters and can be calibrated on a horizontal plane in proximity to a calibrated spectroradiometer or radiometer. Typically this involves the measurement of pre- and post-exposure polysulphone film absorbance at 330 nm (AA330) taken at four different dosimeter film sites which are averaged to account for a variation in film absorbance and plotted with respect to the cumulative UV exposure measured by a spectroradiometer or radiometer. The change in absorbance is measured at 330 nm as this is approximately the wavelength at which the maximum change occurs (Davis et al., 1976a). Polysulphone film calibrated in this manner is typically weighted to the erythemally effective UV, but alternative action spectra, including the vitamin D action spectrum, can also be used. The dose response calibration of polysulphone dosimeters is related to the total atmospheric ozone amount and the solar zenith angle (Casale et al., 2006). This requires the calibration curve to be determined under the same atmospheric conditions of the field study.

The calibrated UV exposure measured using conventional polysulphone dosimeters is accurate to within 10% for a AA330 less than 0.3 and 30% for a AA330 less than 0.4 (Diffey, 1987). Comparative measurements made using miniaturized polysulphone dosimeters give the uncertainty in calibrated UV exposure at 24% for a AA330 less than 0.35 (Downs and Parisi, 2008), the approximate equivalent of 1,500 Jm-2 of erythemally effective UV. Increases in calibrated uncertainty with greater periods of exposure are due to the dynamic saturation of the polysulphone. Figure 7.3 illustrates the increasing calibrated uncertainty with increasing exposure. In this figure, sets of three miniaturized polysulphone dosimeters were removed at predetermined time intervals extending up to nine hours of exposure during a clear summer day, and measured at a subtropical latitude. Greater variability in the change of absorbance can be observed for dosimeters removed after longer periods of exposure.

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Figure 7.3 Calibration of miniaturized polysulphone dosimeters measured over a nine-hour period in summer

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Figure 7.3 Calibration of miniaturized polysulphone dosimeters measured over a nine-hour period in summer

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