Distribution of absorbed beta energy in solid media

Abstract

Distributions of absorbed beta energy around a point source in Al and C19H21 plastic have been measured, with an extrapolation chamber, for seven emitters with endpoint energies from 0.16 to 3.55 MeV. In contrast with previous measurements made with plane solid absorbers, the shapes of the distributions at short distances are quite different for low- and high-energy emitters and the distributions for low-energy emitters are in agreement with those measured in gases. Dose distributions in Al and C19H21 have the same shapes. The distance scaling factors relating these distributions to that in air are 1.04 ±.01 for C19H21 and 1.00 ±.01 for Al, and are independent of beta energy to within 1%. All of these results agree with calculations based on the theory of Spencer.