High-Resolution Study ofCo58by (d,α) and (He3,d) Reactions

Abstract

We have investigated levels of ${\mathrm{Co}}^{58}$ up to 4.1-MeV excitation by studying ${\mathrm{Ni}}^{60}(d,\alpha ){\mathrm{Co}}^{58}$ at 17 MeV and the reactions ${\mathrm{Fe}}^{57}({\mathrm{He}}^3,d)$ and ${\mathrm{Co}}^{59}({\mathrm{He}}^3,\alpha )$ at 18-MeV bombarding energy using the University of Pittsburgh Van de Graaff accelerator. Angular distributions up to 80 and 45°, respectively, for the first two reactions were taken with position-sensitive counters and nuclear emulsions in the focal plane of the Enge split-pole spectrograph. Typical experimental resolutions were 9-14 keV. Angular distributions for over 110 levels were compared with distorted-wave Born-approximation calculations in order to extract orbital angular momentum transfers. Optical-model well parameters satisfying the "well-matching" condition gave improved agreement of ($d,\alpha$) calculations with experimental angular distributions. Spectroscopic factors were obtained for seventy ${\mathrm{Fe}}^{57}({\mathrm{He}}^3,d){\mathrm{Co}}^{58}$ transitions. We give $J^{\pi }$ assignments for nine levels and $J^{\pi }$ suggestions or limits for a total of 88 levels. Some low-lying ${\mathrm{Co}}^{58}$ levels can be described as ${\mathrm{Co}}^{56*}$ plus a "spectator" neutron pair. Comparison with shell-model calculations of McGrory suggests that noticeable ($\pi f_{\frac{7}{2}}^{}{}_{}{}^{-1\mathrm{}},\nu f_{\frac{7}{2}}^{}{}_{}{}^{-1\mathrm{}}$) strength appears in the ${\mathrm{Co}}^{58}$ spectrum for $4^{+}$ states at around 500 keV of excitation. About 11 states predicted by McGrory could be identified with those seen experimentally.