Nuclear Energy Levels ofOs188

The beta and gamma radiations of the 18-hour ${\mathrm{Re}}^{188}$ have been examined with scintillation and magnetic spectrometers. Of the total beta disintegrations, 79% lead to the ground state, 20% to the first excited state at 155 kev, and 1% to the other excited states of ${\mathrm{Os}}^{188}$. The beta-ray spectra leading to the ground state and the first two excited states of ${\mathrm{Os}}^{188}$ are first forbidden. Thirteen gamma rays have been detected. Extensive gamma-gamma coincidence studies were made. The $K$-shell conversion coefficient of the 155-kev gamma ray has been obtained which agrees quite well with the $E2\mathrm{}$ assignment for that gamma ray. The $\frac{K}{L}$ ratio also supports this assignment. No conversion electrons corresponding to the 478-kev gamma ray were found and it is concluded that it is primarily $E2\mathrm{}$ in nature with a small admixture of $M1\mathrm{}$ transition. A decay scheme is proposed on the basis of these data.