ABSORPTION AND SCATTERING OF SR-90 Y-90 BETA-PARTICLES TRANSMITTED THROUGH ALUMINUM AND PLASTIC FILTERS/

Absorption and scattering of Sr-90/Y-90 beta particles transmitted thr ough aluminium and plastic filters have been studied. From measurement s of the ionisation current by the extrapolation chamber, it was shown that a build-up in absorbed dose rate occurred over the first 0.1 mm of aluminium thickness before attenuation started to dominate. This bu ild-up thickness corresponded to a delta particle energy of 150 keV. T he attenuation at large thicknesses followed an exponential function w hich predicted a half-value thickness of similar to 112 mg.cm(-2) and a range (99% attenuation) of similar to 1000 mg.cm(-2). Angular distri butions of the absorbed dose rate for Sr-90/Y-90 beta particles transm itted through aluminium and plastic filters have also been measured. T hese distributions followed the multiple scattering Gaussian curves fo r small projected angles and the single scattering tails for large pro jected angles. The mean square angle of the Gaussian distribution was approximately a linear function of the filter thickness. The peak heig ht, however, dropped rapidly with increasing filter thickness at small thicknesses but slowly at large thicknesses. Both the mean square ang le and the peak height were slightly dependent on the filter material.