High-spin states in 187, 189Ir: : Coexistence of strong-coupling, rotation-alignment and weak-coupling

Abstract

The level schemes of the odd-proton nuclei 187Ir and 189Ir have been studied using in-beam spectroscopic methods. Energies, intensities, angular distributions and coincidences of the γ-rays following the 185, 187Re(α, 2n) 187, 189Ir reactions were determined at an α-particle energy of 27 MeV. Furthermore, conversion electrons and delayed singles and coincidence γ-ray spectra were recorded. From the 187Re(α, 4n) 187Ir reaction ( E α = 48 MeV) singles γ-ray spectra at different angles of emission and γ-γ coincidences were measured. A singles γ-ray spectrum was also taken from the 189Os(p, n) 189Ir reaction. About 45 new levels were found in each nucleus. Two positive parity bands are ascribed to the Nilsson configurations 3 2 +[402] and 1 2 +[400] . As much as 20 levels in 187Ir are related to excitations of the h 9 2 configuration. Most of them form the characteristic sequences predicted by the rotation-aligned coupling scheme. The levels connected with the 11 2 − isomer form separated multiplets rather than rotational bands. They are described as being an h 11 2 excitation weakly coupled to a Pt core. In 189Ir a 3.8 ms isomer found at 2332.3 MeV was assigned as I π = 25 2 + .