Low-spin mixed particle–hole structures in 185W Original Research Article

The level structure of 185W has been studied using the prompt and delayed gamma–gamma coincidences from thermal neutron capture in 184W accompanied with the one-nucleon transfer reactions (d,p) and (d,t) with polarized beams. From these data and those of previous studies a total of 183 levels has been established for energies below 3 MeV. Many of these states have been grouped into rotational bands built on 28 intrinsic states of quasiparticle and quasiparticle-plus-phonon character. Although the DWBA analysis permitted definite spin–parity assignments for most of states a large number of particle transitions have ‘anomalous’ angular and asymmetry shapes with respect to the DWBA which indicate an influence of strong mixing between particle and hole states. The extra exchange of phonons and the significance of configurational ΔN=±2 mixing across the Fermi surface lead to a fine structure in the fragmentation of most single-particle strengths and at the same time has the effect of breakdown of the individual properties of Nilsson states. The accumulated l=1(d,p) sum is about a factor two smaller than the equivalent (d,t) strength. Thus, the previously observed loss of the (d,p) strength in the W nuclei with A=184,185 is presumably because of their redistribution amongst particle- and hole-type states. The observed states below 2 MeV are compared with predictions of the quasiparticle–phonon nuclear model.