Coulomb excitation of 73Ge and quasiparticle-phonon coupling theories

Abstract

The excitation energies and γ-ray decay modes of several low-lying states in the nucleus 73Ge have been studied using Coulomb excitation with 2.6–4.0 MeV α-particles on an enriched 73Ge target to test the predictions of quasiparticle-phonon coupling theories, in particular to test if there are any high-spin states in the low-energy spectrum. Gamma-rays were observed with a 60 cm 3 Ge(Li) detector. Thick-target γ-ray yields were utilized to establish Coulomb excited levels, to clarify the γ-ray decay of 73Ge, and to obtain reduced upward transition probabilities, B(E2)↑, associated with the levels indicated as follows: 68.6 keV (0.073 ±0.007), 499.0 keV (0.0091±0.0005) and 825.6 keV (0.077±0.004). Angular distributions of the de-excitation γ-rays from the Coulomb excited levels were measured and various spin possibilities for each level were eliminated by the χ 2 technique. The following spinparity assignments are consistent with our γ-ray angular distribution measurements: 68.6 keV ( 5 2 + , 7 2 + , 9 2 + ), 499.0 keV ( 7 2 + ), and 825.6 ( 7 2 + , 13 2 + ). Branching ratios were extracted from the γ-ray angular distribution measurements. The εB(E2)↑ values for the first 2 + excited states of 72Ge(0.18), 74Ge(0.29), and 76Ge(0.27) were also obtained. The results for 73Ge are compared with the predictions of several quasiparticle-phonon coupling theories and some suggestions are made to improve agreement between experiment and theory.