Variation of Beta Dose Attenuation in Different Media

Abstract

The dose distribution around a point source of β-particles in any homogeneous low-Z medium is related to that in air by a distance scaling factor and a closely related renormalization factor. A simple method is described for calculating this scaling factor (or relative attenuation), which is given approximately by the expression 0·818(1+0·0284 Z) (S/Sair), where S is the stopping power, and Z is an effective value of Z for the medium The values of relative attenuation obtained agree to within 1·5% with those calculated from Spencer's theory, or measured in aluminium, polystyrene and ethane, and to within 2% with that measured in argon. A similar linear expression, with a slope 2% smaller, gives agreement with values of relative attenuation measured for 13<Z<80.