The neutron-rich N=93 isotones, 155Sm and 153Nd, have been studied by delayed gamma-ray and conversion-electron spectroscopy at the Lohengrin mass spectrometer of the Institut Laue-Langevin, Grenoble.
A half-life of 2.9(5) microseconds has been measured for the 5/2+[642] state at 16.5 keV in 155Sm.
The decay of a 1.17(7)-microsecond isomer in 153Nd, at 191.7 keV, has been remeasured and its spin has been reassigned as 5/2+. This state contains a strong component of the neutron 5/2+[642] Nilsson orbital.
In addition, a new 1.00(8)-microsecond isomeric state at 538.6 keV, with a probable neutron 11/2-[505] Nilsson configuration, has been observed in 155Sm. Triple gamma-ray coincidence data, from the spontaneous
fission of a 252Cf source placed inside the GAMMASPHERE array, were used to extend the collective band on top of the (5/2+) isomeric state of 153Nd and a new band, with the same band head spin has been observed in 151Ce. The observation of this new band and an additional new transition in the ground state band has led us to change the ground state spin of 151Ce to (3/2-). Quasiparticle-Rotor-Model calculations successfully reproduce the majority of the features of the gamma decays of these nuclei, including branching ratios and isomeric half-lives. As this model uses a reflection-symmetric core we conclude that the polarizing effect of the odd particle is responsible for the dipole moment present in the 5/2+[642] states of the three nuclei studied and the 11/2-[505] level of 155Sm.
A review of new and existing data in the A=150 region will also be presented.