ROESCH, W. C. Microdosimetry of Internal Sources. Radiat. Res. 70, 494-510 (1977). Microdosimetry has been limited to irradiations characterized by uniform probabilities of charged-particle production. New methods are presented here for dealing with particles emitted by radionuclides embedded in the irradiated medium; these particles seldom emerge uniformly, because the radionuclides are not dispersed uniformly. In particular, emission from radionuclides that are agglomerated into particulates is extremely nonuniform. Microdosimetric distributions for these internal emitters can be calculated by: (1) determining the probability density in specific energy due to single energy deposition events by charged particles from a point source, (2) combining these densities by Fourier-transform methods, and (3) using existing numerical methods to evaluate the Fourier result. Examples are given calculated for 23"Pu a particles from point sources (particulates) and from particulates uniformly distributed through all space, a half space, and a sphere.