Eur. Phys. J. A (2017) 53: 62
https://doi.org/10.1140/epja/i2017-12253-2

Regular Article - Experimental Physics

Particle- coincidence spectroscopy of the N = 90 nucleus ¹⁵⁴Gd by ()

¹ Physics Division, Oak Ridge National Laboratory, 37831, Oak Ridge, TN, USA
² Department of Physics, University of Richmond, 23173, Richmond, VA, USA
³ Department of Physics, University of Surrey, GU27XH, Guildford, Surrey, UK
⁴ Nuclear Science Division, Lawrence Berkeley National Laboratory, 94720, Berkeley, CA, USA
⁵ Department of Nuclear Engineering, University of California, 94720, Berkeley, CA, USA
⁶ Lawrence Livermore National Laboratory, 94551, Livermore, CA, USA
⁷ School of Physics, Georgia Institute of Technology, 30332, Atlanta, GA, USA
⁸ Department of Physics, Rhodes College, 38112, Memphis, TN, USA
⁹ Department of Physics, University of Wisconsin-La Crosse, 54601, La Crosse, WI, USA
¹⁰ TRIUMF, 4004 Wesbrook Mall, V6T 2A3, Vancouver, British Columbia, Canada
¹¹ Department of Nuclear Physics, iThemba LABS, P.O. Box 722, 7129, Somerset West, South Africa

^* e-mail: allmondjm@ornl.gov

Received: 19 January 2017
Accepted: 14 March 2017
Published online: 29 March 2017

Abstract

A segmented Si-telescope and HPGe array, STARS-LIBERACE, was used to study the ¹⁵⁶Gd()¹⁵⁴Gd direct reaction by particle- 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 and , 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 states below . This may account for a large number of the low-lying states observed in two-nucleon transfer reactions. A hypothesis for the origin of the and states is provided.