AbstractThe self-absorption alpha range for the 5.5-MeV alpha emission in238PuO2was determined to be 11.7±0.2μm by measurement of the effective activity on microspkerical sources of from 150 to 250μm diameter. A function was derived and experimentally tested which related the fractional escape of the total alpha emission to the range-radius ratio of the microspherical source. An energy distribution function was also derived for the alpha emission from a microspherical source which agreed quite well with the experimentally determined spectrum above 1 MeV. It is suggested that the derwed function provides a more accurate description of the energy region below 1 MeV than the experimental data.