Direct evidence for mixing of two-quasiproton and two-quasineutron configurations in 172Yb

Abstract

The 175Lu(p,α)172Yb reaction has been studied using beams of 17 MeV protons from the McMaster University tandem Van de Graaff accelerator. The alpha particle reaction products were analyzed with a magnetic spectrograph and detected with photographic emulsions. Levels up to an excitation energy of 2.8 MeV were studied with a resolution of 20 keV FWHM. The spin 3, 4, 5, and 6 members of the Kπ = 3+ band at 1172 keV were populated appreciably, indicating the existence of a significant two-quasiproton admixture in this band. The measured angular distributions and relative intensities within the band are consistent only with a Kπ = 3+, {7/2+ [404] − 1/2+ [411]} configuration for this admixture, and the absolute intensities indicate that it makes up (27 ± 10)% of the state. This observation provides a quantitative explanation for the observed magnetic moment of the 1172 keV level and also for the observed E2–M1 mixing ratios within the band. It may also be important in the explanation of other anomalous properties of this band. The present measurements also show large Kπ = 3+, {7/2+ [404] − 1/2+ [411]} admixtures in the previously assigned Kπ = 2+ band at 1609 keV and the Kπ = 3+ band at 1663 keV. In addition, the assignment of the 2073 and 2192 keV levels as Iπ = 4+ and 5+ members of a Kπ = 4+, {7/2+ [404] + 1/2+[411]} band has been confirmed.