Evaluation of the results

The results derived from beta dosimetry measurements with a set of beta-ray secondary standard sources of a type used by many laboratories are presented in the form of factors F(0;β) and F(0.07;β). The factors F(0.07;β) derived for a set of commercially available extended area sources are also presented. The data provided should facilitate the evaluation of absorbed dose to tissue for beta radiation incident at various angles on a phantom and investigations of the angular dependence of the response of dosemeters that are to be employed in practical radiation fields or for those that might be developed. A note of caution, however, is that whereas the data presented here are adequate for the specified type and construction of source, the measurement geometry and the filtration, they may not be readily applicable in a different set of circumstances because beta-ray spectra are in general sensitive to changes in any of these conditions. The results obtained with the three types of TL detectors used here show marked differences from those obtained with extrapolation chambers. The closest agreement was obtained with a detector that is effectively thin. This helps to reinforce he view that very thin detectors are needed to measure absorbed dose from beta radiation especially from low-energy sources. It is also important to note that when relatively thick TL detectors are used to measure the absorbed dose in tissue from beta radiation, they suffer not only from angular dependence of response, but also from energy dependence of response. The under-estimation of dose due to the energy dependence may be more significant than that due to angular dependence for thick detectors. Therefore caution should e exercised when such detectors, having been calibrated from a 90Sr/90y source or photons from a 60Co source, are used for monitoring absorbed dose to tissue in an environment with significant degree of low-energy beta radiation