UC Berkeley

A segmented Si-telescope and HPGe array, STARS-LIBERACE, was used to study the ¹⁵⁶Gd(p, tγ)¹⁵⁴Gd direct reaction by particle- γ coincidence spectroscopy. New cross sections with a 25MeV proton beam are reported and compared to previous (p,t) and (t,p) studies. Furthermore, additional evidence for coexisting Kπ=01+,21+ and 02+, 22+ configurations at N = 90 is presented. Direct and indirect population patterns of the low-lying states are also explored. Review of the new and existing evidence favors an interpretation based on a configuration-dependent pairing interaction. The weakening of monopole pairing strength and an increase in quadrupole pairing strength could bring 2p-2h 0 ⁺ states below 2 Δ. This may account for a large number of the low-lying 0 ⁺ states observed in two-nucleon transfer reactions. A hypothesis for the origin of the 02+ and 03+ states is provided.