Perspex dosimetry

Whatever the source of radiation used, the dose delivered to the biological samples is determined by the time of exposure to radiations. Thus the dose delivered by the radiation source must be measured with precision. Dosimetry can be performed with a ferrous sulfate solution (Fricke and Morse, 1927), thermoluminescent dosimeters, bleaching of films (Hart and Fricke, 1967), Perspex dosimetry (Berry and Marshall, 1969), or calibration with standard enzymes (Beauregard et al., 1980 Beauregard and Potier, 1982 Lo et al., 1982). In many laboratories, control enzymes with known D37 are added to protein preparations as internal standards so that any variation between experiments could be corrected for. Because of the better precision of dose rate in Gammacell irradiators, this precaution is not necessary. 

Resin-impregnated samples were irradiated for 40 h at a dose rate of 1 kGy/h (total dose, 40 kGy). Monomer-impregnated samples were cured in two batches, one at a dose rate of 0.6 kGy/h and the other at 1 kGy/h, also for 40 h (total doses of 24 kGy and 40 kGy, respectively). Dosimetry was carried out by using a Red Perspex dosimeter, based on the radiation coloration of commercial red-dyed Perspex type Red 4034 and a calibration curve relating the induced absorption coefficient to dose. 

Dyed polymethylmethacrylate (PMMA) dosimeter. Polymethylmethacrylate dosimeters containing different types of dyes have been developed for routine dosimetry mainly in radiation sterilization and have been used extensively for many decades (Whitakker 1970 ISO/ASTM 2002e). Various types of the PMMA dosimeters are known, but the most popular are the red Perspex, the amber Perspex, and the Gammachrome YR. 

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