Dynamics of Sorption—Desorption of ²²³Ra Therapeutic α-Emitter on Granulated Hydroxyapatite

The dynamics of the 223Ra distribution in the volume of spherical hydroxyapatite (HAP) granules in the course of the 223Ra sorption from aqueous solutions onto sorbent particles and desorption was studied by α-track radiography. The optimum time of contact of the sample with a detector (exposure) was found, and a procedure for preparing experimental samples was suggested. Taking into account the density of the porous sorbent, the ranges of the α-particles emitted by 223Ra and its daughter products and of the recoil nuclei were estimated. The averaged effective range of the α-particles in HAP is ∼35 μm. A mathematical model of the Ra diffusion into the depth of the porous sorbent, taking into account the sorption, was developed on the basis of the parameters obtained. The effective diffusion coefficient was estimated at ∼3 × 10–5 cm2 s–1. Correlation be¬tween the sorbent particle size, radionuclide sorption time, and the absorbed dose produced by the particle in a biological tissue was demonstrated.