Half-Lives of 4+ and 2+ Rotational States in Several Rare-Earth Nuclei

A fast coincidence system was used to measure half-lives of 2+ and 4+ rotational states for several nuclei. The results of measurements to determine the value of $\frac{B(E2:4\mathrm{}\to 2)}{B(E2:2\mathrm{}\to 0)}$ for the groundstate band of several nuclei are presented. Half-life measurements were made for the first 2+ and 4+ states of the following nuclei: ${\mathrm{Gd}}^{156}$, ${\mathrm{Gd}}^{158}$, ${\mathrm{Er}}^{166}$, and ${\mathrm{Er}}^{168}$. The respective half-lives (nsec) with errors in the last significant figures in parentheses are 2.21 (6), 2.52(8), 1.83(5), 1.88(5) for the 2+ states, and 0.118(7), 0.162(13), 0.117(7), 0.119(7) for the 4+ states. The respective $\frac{B(E2:4\mathrm{}\to 2)}{B(E2:2\mathrm{}\to 0)}$ values are 1.35(11), 1.32(11), 1.47(11), and 1.47(11). The half-lives of the 2+ states of ${\mathrm{Sm}}^{152}$, ${\mathrm{Gd}}^{154}$, and ${\mathrm{Dy}}^{160}$ were measured to be 1.41(4), 1.21(4), and 2.01(6) nsec. The measured $\frac{B(E2:4\mathrm{}\to 2)}{B(E2:2\mathrm{}\to 0)}$ values were found to agree within errors with the rotational estimate of 1.43. These results and the data in the literature indicate that the value of $\frac{B(E2:4\mathrm{}\to 2)}{B(E2:2\mathrm{}\to 0)}$ is smaller than the rotational estimate for nuclei of $180\le A\le 196$, but experimental uncertainties are still too large to permit a conclusion concerning any possible deviation at the low end of the rare-earth region.