Nuclear levels and spectroscopy of191Os

Thirty-nine states, all except two of which are new, have been observed up to 1535 keV in¹⁹¹Os using the reactions¹⁹⁰Os(d,p)¹⁹¹Os,¹⁹²Os(d, t)¹⁹¹Os with 12 MeV deuterons and magnetic analysis with photographic emulsions of the outgoing particles, and¹⁹⁰Os(n, γ)¹⁹¹Os with thermal neutrons and three modes of gamma detection in the energy range from 40 keV to ～6 MeV. The neutron separation energy was determined as 5758.5±2.0 keV in agreement with the value of the (d, p) reaction. TheQ value for the (d, t) reaction was determined as ?1265±15 keV. Spins and parities are assigned for most of the states below 800 keV. The states below 463 keV are shown to be qualitatively but not quantitatively consistent with the expectations of the Nilsson model. Nilsson systematics of the 1/2^?: ¦510¦ and 3/2^? ¦512¦ orbitals in odd-A Os isotopes with increasing neutron number can be understood in terms of decreasing deformation. Anomalously large (d, p) and (d, t) cross sections populating 5/2^? and 3/2^? states at 134 and 142 keV, respectively, are explained as a tendency to restore the cross sections expected for a spherical nucleus. Evidence for triaxiality in¹⁹¹Os is observed in the form of a 5/2^? state at 273 keV which appears to be a rotational state built on the 9/2^? ground state.