The nuclear alinement of promethium isotopes and the decay scheme of 149Pm

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Nuclear alinement of the isotopes 149Pm and 151Pm has been obtained in the ethyl sulphate and double nitrate lattices by the low-temperature alinement method. The anisotropic γ-ray angular distributions were used to detect this alinement. The results suggest that in the double-nitrate lattice the lowest ionic state of Pm3+ is a singlet and that alinement arises through a ‘pseudo-quadrupole’ mechanism. Beta and γ-spectroscopy measurementsshow that the 285 keV γ-ray in the decay of 149Pm is associated with a weak (1.8 ± 0.3 %) β-group of maximum energy 0.77 ± 0.05 MeV. The alinement measurements are consistent with this 285 keV γ-ray being principally M 1 with the spin of the excited state being 5/2 or 9/2.