Measurement of the specific radioactivity with respect to particle size for labeled aerosols

Abstract The relationship between labeled radioactivity and particle size is an important characteristic of a labeled aerosol. Measurements were made of the specific activity of labeled fused clay aerosols using the following methods: (1) dividing the aerosol into several narrow size groups using the Lovelace Aerosol Particle Separator (a spinning spiral spectrometer similar to that of Stober), (2) determining the radioactivity per particle by counting the number of particles and the radioactivity associated with a known area, (3) determining the relationship between relative radioactivity per particle and particle size, and (4) dividing the function thus obtained by the cube of the particle diameter. Fused clay aerosols labeled with 91 Y, 90 SrY, 144 CePr and 137 CsBa had the relative radioactivity proportional to the cube of the particle size, thus demonstrating that the specific activity is independent of particle size. Fused clay aerosol labeled with 106 RuRh had a relationship other than cubic, demonstrating particle size dependence of specific activity, probably because of the volatility of Ru under heat treatment. Adaptation of this method as a general method for characterizing labeled aerosols is discussed.