Decay ofNd8914960

The level structure of ${}_{61}{}^{}{}_{}{}^{}\mathrm{Pm}_{88}^{}{}_{}{}^{149}$ has been studied from the decay of 1.7-h ${\mathrm{Nd}}^{149}$. Studies were made of the internal-conversion electron spectrum with magnetic spectrographs, and of the gamma-ray spectrum with NaI(Tl) and Ge(Li) detectors. Gamma-gamma coincidence experiments were carried out with NaI(Tl) and Ge(Li) detectors. Beta-gamma coincidence measurements were made with combinations of proportional counters and anthracene, NaI(Tl), and Ge(Li) detectors. The half-life of ${\mathrm{Nd}}^{149}$ was found to be (1.73±0.01) h. About seventy gamma-ray transitions from 30 to 1456 keV were observed. The transitions with intensities greater than 1% of the decays have the following energies, transition intensities, and multipolarities: $30.0 (\sim 6\%, E2)$, 59.0 (∼2), 74.4 (∼2), $97.0 (\sim 3,M1)$, $114.3 \mathrm{}(38,M1)\mathrm{}$, $155.9 \mathrm{}(6.2,E1)\mathrm{}$, 188.8 (2.0), 198.9 (1.4), 208.2 (2.6), $211.3 \mathrm{}(24,M1)\mathrm{}$, $240.3 \mathrm{}(6.5,M2)\mathrm{}$, 267.7 (7), $270.3 \mathrm{}(10,E1)\mathrm{}$, 326.6 (4.5), 349.1 (1.5), 423.6 (7), 443.5 (1.1), 540.5 (6.5), 556.4 (1.1), and 654.7 (8.4). The 240-keV transition has a half-life of 41 μsec which agrees with the $M2\mathrm{}$ assignment based on the internal-conversion coefficients. From previous lifetime measurements for states at 114 and 270 keV, hindrance factors were computed for the following gamma-ray transitions: 114 keV ($M1,350\mathrm{}$), 270 keV ($E1,\sim 5\times {10}^5$), 155 keV ($E1,\sim 5\times {10}^5$), and 59 keV ($E1,\sim 5\times {10}^4$). The 30-keV transition between the 270- and 240-keV levels appears to be enhanced by a factor of about 80. A level scheme is proposed which includes about sixty transitions. There are well-established excited states at 114.3, 188.8, 211.4, 240.3, 270.2, 387.6, 538.0, 654.8, and 768 keV.