Experimental Studies of Neutron-Deficient Gadolinium Isotopes. I. The Electron-Capture Decay ofGd149

Abstract

$\gamma$ rays emitted in 9.4-day ${\mathrm{Gd}}^{149}$ have been studied with Ge(Li) and NaI(Tl) detectors. $25\gamma$ rays have been attributed to the decay of ${\mathrm{Gd}}^{149}$ with energies and relative intensities of 149.6 (233), 214.5 (0.81), 252.3 (1.1), 260.5 (5.8), 272.0 (15), 298.5 (127), $346.5\left(\equiv 100\right)$, 405.5 (3.7), 430 (0.33), 459.9 (2.4), 478.7 (0.95), 496.4 (7.2), 516.4 (11), 534.2 (13), 645.2 (5.9), 663.3 (1.1), 666.2 (3.9), 748.2 (35), 788.6 (30), 812.4 (0.55), 863 (0.32), 875.8 (0.90), 933.3 (2.2), 939.1 (9.0), and 947.7 keV (3.7). On the basis of coincidence and anticoincidence experiments, relative intensities, and energy sums, states in ${\mathrm{Eu}}^{149}$ have been placed at 0, 149.6, 459.9, 496.2, 534.2, 666.0, 748.2, 794.8, 812.4, 875.8, 933.3, 939.1, and 1097.3 keV. The ${\mathrm{Eu}}^{149}$ x-ray intensity has also been measured. From our $\gamma$-transition intensities and published conversion-electron intensities, conversion coefficients were obtained for most of the electromagnetic transitions, thus allowing multipolarity assignments to be made for these transitions. These assignments, together with the $log\mathrm{ft}$ values, were then used for the placement of limits on the spins of the deduced levels. Our proposed decay scheme is compared with previously published decay schemes and is discussed in terms of current models.