Proton hole states in 187, 189, 191Re investigated by the (t, α) reaction

Proton hole states in 187Re, 189Re and 191Re have been studied using the (t, α) reaction. Beams of 17 MeV tritons with a polarization of 0.75 were obtained from the tandem Van de Graaff accelerator at the Los Alamos Scientific Laboratory. The α-particles were detected in a Q3D magnetic spectrometer with a helical-cathode position-sensitive proportional counter. Spectra were recorded up to > 2 MeV excitation energy with a resolution (FWHM) of ≈ 20 keV. These measurements exhibit large analyzing powers for transitions to well-known states in the deformed nuclide 187Re. This is of interest because the only other single-nucleon transfer results on heavy deformed nuclei (in a (d, p) study of tungsten isotopes) showed “disappointingly small” analyzing powers. The (t,α) analyzing powers were reproduced by DWBA calculations very well. Thus other levels in 187Re and many states in 189Re and 191Re could be assigned spins and parities on the basis of angular distributions for the cross sections and analyzing powers. In particular, the present results have made it possible to determine which of the three possible interpretations suggested previously for the structure of 191Re is correct. The results have been interpreted within the framework of the Nilsson model, with pairing and Coriolis mixing corrections included. The energy systematics of single-quasiparticle states are well reproduced by the Nilsson model if a hexadecapole deformation is included in the nuclear potential. Finally, it has been demonstrated that the (t, α) reaction is an extremely useful spectroscopic tool for studies of heavy deformed nuclei.