Gamma-Gamma Directional Correlations inPm149

The directional correlations of six $\gamma -\gamma$ cascades in ${\mathrm{Pm}}^{149}$ from the decay of ${\mathrm{Nd}}^{149}$ have been studied. The results are as follows: $W\left({\theta }_{440-210}\right)=1-(0.026\mathrm{}\pm 0.011)P_2\left(cos\theta \right)+(0.033\mathrm{}\pm 0.018)P_4\left(cos\theta \right),$ $W\left({\theta }_{536-114}\right)=1+(0.042\mathrm{}\pm 0.006)P_2\left(cos\theta \right)-(0.009\mathrm{}\pm 0.010)P_4\left(cos\theta \right),$ $W\left({\theta }_{328-210}\right)=1+(0.109\mathrm{}\pm 0.006)P_2\left(cos\theta \right)-(0.020\mathrm{}\pm 0.010)P_4\left(cos\theta \right),$ $W\left({\theta }_{424-114}\right)=1-(0.102\mathrm{}\pm 0.006)P_2\left(cos\theta \right)-(0.027\mathrm{}\pm 0.010)P_4\left(cos\theta \right),$ $W\left({\theta }_{266-272}\right)=1-(0.227\mathrm{}\pm 0.008)P_2\left(cos\theta \right)+(0.013\mathrm{}\pm 0.013)P_4\left(cos\theta \right),$ $W\left({\theta }_{158-114}\right)=1+(0.074\mathrm{}\pm 0.026)P_2\left(cos\theta \right)+(0.026\mathrm{}\pm 0.040)P_4\left(cos\theta \right).\mathrm{}$ From the measured spin of the ground state of ${\mathrm{Pm}}^{149}$ as $\frac{7}{2}$ the excited states of ${\mathrm{Pm}}^{149}$ are assigned spins as follows: 114 keV, $\frac{5}{2}$; 210 keV, $\frac{5}{2}$ ($\frac{7}{2}$); 272 keV, $\frac{7}{2}$ or $\frac{5}{2}$; 538 keV, $\frac{5}{2}$; and 650 keV, $\frac{3}{2}$ ($\frac{7}{2}$). The half-lives of the 114- and 272-keV levels are found to be 2.4±0.2 and 2.6±0.2 nsec, respectively. The $M1\mathrm{}$ retardation and $E2\mathrm{}$ enhancement of the 114-keV transition in ${\mathrm{Pm}}^{149}$ are estimated to be 608 and 15, respectively, and these values are compared with those for similar transitions in the neighboring nuclei. The 272- and 158-keV $E1\mathrm{}$ transitions from the 272-keV level are retarded by factors of 3.0×${10}^5$ and 1.7×${10}^5$, respectively.