Decay ofNd8914960

Abstract

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\ifmmode\pm\else\textpm\fi{}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: $30.0 (\ensuremath{\sim}6%, E2)$, 59.0 (\ensuremath{\sim}2), 74.4 (\ensuremath{\sim}2), $97.0 (\ensuremath{\sim}3,M1)$, $114.3 (38,M1)$, $155.9 (6.2,E1)$, 188.8 (2.0), 198.9 (1.4), 208.2 (2.6), $211.3 (24,M1)$, $240.3 (6.5,M2)$, 267.7 (7), $270.3 (10,E1)$, 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 \ensuremath{\mu}sec which agrees with the $M2$ 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 ($M1,350$), 270 keV ($E1,\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{5}$), 155 keV ($E1,\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{5}$), and 59 keV ($E1,\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{4}$). 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.