Gamma-Ray Spectrum of Polonium-209

A polonium sample was produced at Oak Ridge National Laboratory by the bombardment of bismuth targets with 20-Mev protons. The sample contained a mixture of the polonium isotopes of mass 208 and 209 with a negligible amount of the isotope of mass 210. Measurements were made of the isotopic ratio from the molecular spectrum and the alpha activity was determined by calorimetry. The spectrum obtained with a NaI(Tl) crystal and pulse-height analyzer showed the existence of gamma rays with energies of about 270, 570, and 865 kev. The 803-kev gamma ray of ${\mathrm{Po}}^{210}$ was not detected. This spectrum is attributed to ${\mathrm{Po}}^{209}$ since there is no gamma radiation from ${\mathrm{Po}}^{208}$. The intensity of the 865-kev gamma ray relative to the gamma ray of a calibrated ${\mathrm{Po}}^{210}$ sample was estimated to be about 7.5×${10}^{-3\mathrm{}}$ quanta per ${\mathrm{Po}}^{209}$ alpha particle. Coincidence measurements between various pairs of gamma rays indicated that only the 270- and 570-kev quanta were in cascade and existed with about the same relative intensity as the 865-kev gamma ray.