Properties of the excited states inTm171

Angular correlations of the 277.4-210.5 keV and the 371.9-277.4 keV $\gamma -\gamma$ cascades in ${}_{}{}^{171}{}_{}{}^{}\mathrm{Tm}$ populated in the decay of the 7.5 h ${}_{}{}^{171}{}_{}{}^{}\mathrm{Er}$ have been measured to be $W{\left(\theta \right)}_{277.4-210.5}=1+(0.124\mathrm{}\pm 0.005)P_2\left(cos\theta \right)$ and $W{\left(\theta \right)}_{371.9-277.4}=1+(0.018\mathrm{}\pm 0.012)P_2\left(cos\theta \right)$. The result for the first cascade, combined with the existing data on high resolution internal conversion measurements, establishes the spin of the 635.4 keV level to be $\frac{7}{2}$, corresponding to the ${\frac{7}{2}}^{+}\mathrm{}\left[404\right]\mathrm{}$ Nilsson state. The spins of the 912.8 keV ($\frac{5}{2}$) and the 1284.7 keV ($\frac{5}{2}$) levels are in agreement with the angular correlation measurements. The multipole mixing ratios of the transitions are deduced to be: 210.5 keV—$E1+(\lesssim 0.06)\%M2\mathrm{}$; 277.4 keV—$M1+(10\mathrm{}\pm 1)\%E2\mathrm{}$; and 371.9 keV—$M1+(9\mathrm{}\pm 3)\%E2\mathrm{}$. The half-life of the 635.4 keV level has been measured by the $\gamma -\gamma$ delayed coincidence method to be $T_{\frac{1}{2}}=1.26\mathrm{}\pm 0.06$ nsec. The identity of the delayed level has been confirmed by the delayed gating technique. The transition probability of the 210.5 keV $E1\mathrm{}$ transition has been evaluated and compared with the theoretical estimate and that of similar transitions in other nuclei in the region.