Two-quasineutron states in 168Er populated by the 167Er(d, p) and 167Er(t, d) reactions

Abstract

The nuclear structure of 168Er has been studied with the 167Er(d, p) 168Er and 167Er(t, d) 168Er reactions, using 12 MeV deuterons and 15 MeV tritons from the McMaster tandem Van de Graaff accelerator. The reaction products were analyzed with an Enge split-pole magnetic spectrograph and detected with photographic emulsions. Angular distributions were obtained for levels up to ∼2.5 MeV excitation, with typical resolutions of ∼9 keV and ∼11 keV (FHWM) for the (d, p) and (t, d) reactions, respectively. Since the I, K π values for all levels up to ∼2 MeV were known from previous ( n, γ) studies, the main contribution of this study was to determine the admixtures of specific two-quasineutron configurations to the various bands. Earlier {7/2 +[633]±1/2 −[521]} assignments for the 1094.0, K π = 4 − and 1541.5 keV, K π = 3 − bands have been confirmed, although the full {7/2 +[633]+1/2 −[521]} strength is not observed in the 1094.0 keV band. The K π = 1 − octupole band at 1358.8 keV has a dominant {7/2 +[633] − 5/2 −[512]} component, as predicted by the Soloviev model. The K π = 6 −, {7/2 +[633] + 5/2 −[512]} configuration has been assigned in this work to the 1773.2 keV level. The K π = 4 − band at 2059.9 keV is found to contain ∼35% of the {7/2 +[633] + 1/2 −[510]} strength, and a ∼25% admixture of the {7/2 +[633] − 1/2 −[510]} configuration is tentatively assigned in the K π = 3 − band at 1828.0 keV. Relative cross sections for members of the 168Er ground state band suggest the presence of a mixed wave function for the 167Er target ground state. The K π = 0 +, 1217.1 keV band exhausts the {7/2 +[633] − 7/2 +[633]} strength which does not go to the ground band, while the K π = 0 +, 1422.0 keV band was not observed. The Soloviev model is the only one which has made quantitative predictions that can be compared with the present results. In general, it is quite successful in explaining the experimental data.