Radioactive decay of Eu¹⁵⁴

The radioactive decay of Eu154 (t 1/2=16y), obtained from thermal neutron irradiations of 95% enriched Eu153, has been studied by using the Seigbahn-Slätis intermediate image spectrometer, a thin lens magnetic spectrometer and a coincidence scintillation spectrometer. The following gamma-rays (energy in kev.) have been identified as belonging to this isotope: 123, 248, 585, 717, 759, 875, 998, 1007, 1285, 1600. Beta end points of Eu154 were measured at 275 (20%), 590 (45%), 890 (23%) and 1860 (12%). The K-conversion coefficient of 123 kev. gamma-ray has been experimentally determined to be ∼0·5. On the basis of gamma-gamma and beta-gamma coincidences, the decay scheme of Eu154 has been deduced: the resulting level-structure of Gd154 conforms well with the predictions of the unified nuclear model.