The decay of ${\mathrm{Au}}^{195}$ has been re-examined by gamma-ray spectroscopy techniques in order to obtain a more reliable value of the internal conversion coefficient $\alpha$ of the 99-keV ground-state transition. ${\mathrm{Au}}^{195}$ decays by electron capture to the ground state of ${\mathrm{Pt}}^{195}$ and to the first three excited states at 99, 130, and 210 keV. The relative-decay branching ratios to these states are (13±10)%, (47±6)%, (40±6)%, and <0.04%, respectively. The decay energy $W_0=(222\mathrm{}\pm 5)$ keV was determined from the observed $\frac{L}{K}$ capture ratios. Four gamma rays are present in the decay with energy and relative intensity: 31 keV (12%), 99 keV (100%), 130 keV (7.7%), and 210 keV (0.25%). The $K$ internal conversion coefficient ${\alpha }_K$ of the 99-keV ground-state transition is ${\alpha }_K=5.9\mathrm{}\pm 0.6$ which, together with the experimental result $\frac{{\alpha }_K}{({\alpha }_L+{\alpha }_M)}=4.7\mathrm{}$ of de-Shalit et al., yields a value for the total internal-conversion coefficient $\alpha =7.2\mathrm{}\pm 0.7$. Finally, the half-life of the 99-keV state was determined from the measurement of the linewidth in the recoilless-absorption spectrum of the 99-keV radiation: ${\tau }_{\frac{1}{2}}=(1.7\mathrm{}\pm 0.2)\times {10}^{-10\mathrm{}}$ sec.

• Received 16 December 1964

DOI:https://doi.org/10.1103/PhysRev.138.B554