The spatial variation of dose-rate from Sr-90/Y-90 beta sources for use inluminescence dating

The spatial variation of dose-rate from a 1850 MBq (50 mCi) Sr-90/Y-90 Amer sham International SIF type ceramic-substrate beta particle source (5 mm di ameter active area) was measured and compared with that from a 1480 MBq (40 mCi) Sr-90/Y-90 Amersham International SIP type silver plaque type beta pa rticle source (12 mm diameter active area), for a variety of source-target spacings. The radiation field intensities were mapped using the intensity o f radioluminescence induced in a probe comprising an congruent to 1 mm diam eter calcium fluoride grain attached to the end of a glass fibre optic cabl e, and detected by a photomultiplier. Both sources were found to have radia lly symmetric dose distributions with no significant local irregularities, and dose-rate radial profiles indistinguishable at the closest source-probe spacing used (15 mm). At the largest source-probe spacing, 25 mm, the cera mic-substrate source exhibited slightly lower centre-periphery dose-rate de crease. Further measurements, using in addition a 3700 MBq (100 mCi) ceramic-substr ate source, found an apparently lower dose-rate/MBq from the ceramic-substr ate sources than from the silver plaque. This somewhat negates the practica l benefits arising from the increased source activity permissible on radiat ion safety grounds for ceramic-substrate sources for a given shielding conf iguration, as although a given shielding configuration can house a ceramic- substrate source delivering a greater dose-rate than can safely be achieved from a silver plaque source, a considerably higher source activity is requ ired to do so. It was concluded that the overall suitability of both types of sources for luminescence applications differs little in that both are suitable, and the choice between types is best governed by case-to-case considerations, such as practical constraints on shielding. (C) 2000 Elsevier Science Ltd. All rights reserved.