Nuclear structure of 187W studied with [formula omitted] and [formula omitted] reactions

Abstract

The level structure of 187W has been studied using prompt and delayed gamma–gamma coincidences from thermal neutron capture in 186W and also measuring the ( d , p ) reaction. From these data and those of previous studies a total of 170 levels (121 connected by γ transitions) have been established for energies below 2.35 MeV. Some of these levels have been grouped into rotational bands built on 14 intrinsic states of quasi-particle and quasi-particle plus phonon character. Of particular interest has been the identification of “quasi bands” with inverse spin sequence based on the newly established isomeric 11 / 2 + state at 410.1 keV. Although the DWBA analysis permitted definite spin–parity assignments for most states a large number of particle transitions have “anomalous” angular distribution shapes with respect to the DWBA which indicate an influence of strong mixing between particle and probably hole states. The exchange of phonons across the Fermi surface leads to a fine structure in the extra fragmentation of most single particle strengths and, at the same time, it produces the effect of breakdown of individual properties of Nilsson states. The total extracted l = 1 , 2 and 3 ( d , p ) strengths below 2 MeV have about the same magnitudes as in 185W that comprise a rather small fraction of the expected strengths. The observed states below 2 MeV are compared with predictions of the quasi particle phonon model. The discussion focuses on transition aspects from rigid rotors of light W to γ-soft nuclei in the Os, Pt region.