Particle-Rotor Model Description of Doubly Odd Ta Isotopes

The doubly odd Ta isotopes are studied within the framework of the particle-rotor model. The main aim of this study is to obtain information on the neutron-proton interaction in deformed nuclei, with particular attention focused on the role of the tensor force. To this end, both zero-range and finite-range phenomenological interactions are considered. Comparison of the calculated results with experimental data provides evidence of the importance of the tensor-force effects. We have also performed calculations using a realistic two-body G matrix for the neutron-proton interaction. Some preliminary results are presented here. The neutron-proton interaction plays an important role in the description of doubly odd deformed nuclei. As is well known, the two most important effects associated with the residual interaction between the odd neutron and the odd proton are the Gallagher-Moszkowski (GM) splitting 1 and the Newby (N) shift. 2 Further information on the neutron-proton interaction may be obtained by studying the odd-even staggering in K 6 0 bands. In fact, this effect may be traced to direct Coriolis coupling of K 6 0 bands with one or more N-shifted K = 0 bands. Bands which exhibit odd-even staggering represent therefore a significant source of knowledge of the effective neutronproton interaction. In previous works, 3 5 we have studied the doubly odd isotopes 174,176 Lu within the framework of the particle-rotor model. Our aim was to assess the role of the effective neutron-proton interaction, with particular attention focused on the tensor force. The results of these calculations showed that the tensor force as well as the space-exchange and spin-spin space-exchange force play an important role in the description of K = 0 bands and of some K 6 0 bands. Motivated by these findings, we have extended our study to other doubly odd deformed nuclei in the rare-earth region. Here, we present some results concerning the two heavier nuclei 180,182 Ta. As we shall see in Sec. 3, the experimental data are very well reproduced when using the central plus tensor force proposed long ago by Boisson et al. 6 This is in complete agreement with