Positrons from the Decay ofP32andY90

A magnetic focusing arrangement is combined with coincidence counting of the annihilation radiation to permit detection of very low positron intensities in the presence of other radiations. Sources of ${\mathrm{P}}^{32}$ yielded (7.5±2)×${10}^{-10\mathrm{}}$ positrons per beta decay. An experiment with a gold-covered source showed that secondary effects in the source material may contribute an important fraction of these positrons. One may conclude that the number of positrons per beta decay of ${\mathrm{P}}^{32}$ does not exceed by more than a factor two the value 5.5×${10}^{-10\mathrm{}}$ expected theoretically from electromagnetic effects and is probably close to the theoretical value.