Nuclear Resonance Fluorescence inRe185

The resonant scattering of $\gamma$ rays from the 646-, 718-, and 874-keV excited states of ${\mathrm{Re}}^{185}$ has been observed with NaI as well as with Ge(Li) detectors. An ${\mathrm{Os}}^{185}$ source, moving on the periphery of a fast rotor at speeds of up to 1.3×${10}^5$ cm/sec, provided the resonant $\gamma$ rays. From the magnitude of the scattering effects, values of $\frac{g{{\Gamma }_0}^2}{\Gamma }=(2.37\mathrm{}\pm 0.15)\times {10}^{-5\mathrm{}}, (4.8\mathrm{}\pm 1.0)\times {10}^{-5\mathrm{}}, \mathrm{and} (2.7\mathrm{}\pm 0.3)\times {10}^{-4\mathrm{}}$ eV were obtained for the widths of these levels, respectively. The angular distributions of the resonance radiations were found to be consistent with the previously accepted spin assignments of ½ to the 646-keV level, $\frac{3}{2}$ to the 718-keV level, and ½ or $\frac{3}{2}$ to the 874-keV level. A comparison of resonance scattering and Coulomb-excitation cross sections made it possible to eliminate spin ½ for the 874-keV level. A value 1.18±0.06 was measured for the ratio of the intensities of the 874- and 879-keV $\gamma$ rays emitted in the disintegration of ${\mathrm{Os}}^{185}$. Evidence for the existence of a level in ${\mathrm{Re}}^{185}$ at 929±2 keV was obtained, and upper limits of 0.2% of the ground-state transitions were established for the branchings from the 874- and 879-keV levels to the ${\frac{7}{2}}^{+}$ first excited state.