Absorption and Scattering of 90Sr/90Y Beta Particles Transmitted Through Aluminium and Plastic Filters

Absorption and scattering of 90Sr/90Y beta particles transmitted through aluminium and plastic filters have been studied. From measurements 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 build-up thickness corresponded to a d particle energy of 150 keV. The attenuation at large thickness followed an exponential function which predicted a half-value thickness of (112 mg.cm-2 and a range (99% attenuation) of (1000 mg.cm-2. Angular distributions of the absorbed dose rate for 90Sr/90Y beta particles transmitted through aluminium and plastic filters have also been measured. These distributions followed the multiple scattering Gaussian curves for small projected angles and the single scattering tails for large projected angles. The mean square angle of the Gaussian distributions was approximately a linear function of the filter thickness. The peak height, however, dropped rapidly with increasing filter thickness at small thicknesses but slowly at large thicknesses. Both the mean square angle and the peak height were slightly dependent on the filter material.