Particle- $\gamma$ γ coincidence spectroscopy of the N = 90 nucleus 154Gd by ( $p,t\gamma$ p , t γ )

A segmented Si-telescope and HPGe array, STARS-LIBERACE, was used to study the 156Gd(\(p,t\gamma\))154Gd direct reaction by particle- \( \gamma\) 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 \( K^{\pi}=0_{1}^{+},2_{1}^{+}\) and \(0_{2}^{+}\), \(2_{2}^{+}\) 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 \(2\Delta\). 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 \(0_{2}^{+}\) and \( 0_{3}^{+}\) states is provided.