Configuration assignment and decay of 126La high-spin bands

Complete text of publication follows. It has been shown recently that the πh11/2νh11/2 bands in the light Cs isotopes systematically exhibit signature inversion at relatively low spins. This phenomenon is expected when one of the valence nucleons lies in a low-Ω orbital of a high-J shell while the other nucleon is placed on a high- or medium-Ω orbital of a high-J shell. In the light La nuclei similarly to the Cs case the proton Fermi level lies just below the [550]1/2- low-Ω Nilsson orbital while the neutron Fermi level is close to the [523]7/2- orbital at the middle of the h11/2 subshell. On the basis of this fact one can expect signature inversion for the πh11/2νh11/2 bands in the light La isotopes, too. These bands are known in the La isotopes, however there is no unambiguous spin-parity assignment for them until now, and therefore the signatures are not known either. High spin states of 126La have been populated using the reaction 116Sn + 14N at 68 MeV. γ-rays and conversion electrons were detected with the GAREL array. Multipolarities of the lowest-lying in-band dipole transitions have been determined from the deduced internal conversion coefficients. Experimental B(M1)/B(E2) ratios have been derived for the bands and compared with calculated values using the Doenau-Frauendorf geometrical model. Configurations are proposed for the bands comparing them with cranked shell model calculations and on the basis of the measured B(M1)/B(E2) ratios. The β-decay of 126La has also been revisited. The population of the 126Ba levels gives a tentative spin value of five for the decaying high-spin 126La state with T1/2 ∼ 64 s which may indicate a signature inversion in the πh11/2νh11/2 band. (author)