Single proton states in odd holmium isotopes

Abstract

The (3He,d) and (α,t) reactions have been used to study odd proton states in 157,159,161,163Ho. The beams were provided by tandem Van de Graaff accelerators and the light reaction products were analyzed with magnetic spectrographs and detected with photographic emulsions. Spectra were studied up to excitation energies of ~1.5 MeV for each nuclide with resolutions (FWHM) of ~14 keV for the (3He,d) reaction and ~12 keV for the (α,t) reaction. Information on the l-values was obtained from the ratios of (3He,d) and (α,t) cross sections and from (3He,d) angular distributions. The results are interpreted in terms of the Nilsson model with pairing and Coriolis mixing included. Nuclear structure factors were extracted from the experimental data with the aid of DWBA calculations. Nilsson assignments from previous gamma-ray studies have been confirmed for many low-lying rotational bands. In addition, many new assignments have been made, particularly in the lighter isotopes for which very little nuclear structure information existed previously. A relatively strong l = 0 transition is found in each nuclide and arguments are made to suggest these Iπ = 1/2+ states are gamma vibrations based on the 5/2+[402] states. Similarly, strong l = 2 transitions populate states which may be Iπ = 3/2+ gamma vibrations based on the 7/2+[404] orbitals. Some interesting systematics of the behaviour of single particle states in this region are presented and some anomalies in the populations of the 1/2+[411] and 3/2+[411] states are pointed out.