PMMA dosimeter

Whittaker, B Watts, M.F. Inlluenee of dose rate, ambient temperature and time on the radiation response of Harwell PMMA dosimeter. Radiat. Phys. Chem. 60, 101-110 (2001)... 

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. 

Table 23 Post-irradiation response of some dyed PMMA dosimeters (EB exposure, electron energy 2.2 MeV). The data were taken from [04F1].

Fig. 29 Variation in normalized absorbance for PMMA dosimeter (7 ( Co)-irradiation dose rate 5 kGy.h ). The data were taken from [09S1].

These analyses require that the 10) values for normal incidence be modified for irradiation geometries where the field is incident other than perpendicular to the surface of the personal monitor. The methods used in developing these modifications to fl pdO) for nonnormal incidence included extensive Monte Carlo calculations of photon interactions in anthropomorphic phantoms (Xu, 1994) or in PMMA and tissue slabs and the ICRU sphere (Grosswendt, 1991 Grosswendt and Hohlfeld, 1982), and thermoluminescent dosimeter measurements in water cubes (Lakshmanan et al., 1991). Some of these modifications for /fp(lO) are presented in ICRU (1992). 

The quality control checks whether the product has been irradiated homogeneously and received the correct dose. The controllable variables are the source intensity and the exposure time. The process control is performed with a dosimeter, for example plates of polymethylmethacrylate (PMMA) that discolours under the influence of gamma radiation. The extent of discolouration is dependent on the absorbed dose. In one container several dosimeters are placed, which are analysed in the quality control laboratory afterwards in a spectrophotometer. 

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