Evolution of the one-phonon 21,ms+ mixed-symmetry state in N=80 isotones as a local measure for the proton-neutron quadrupole interaction

An inverse kinematics Coulomb excitation experiment was performed to obtain absolute E2 and M1 transition strengths in Xe-134. The measured transition strengths indicate that the 2(3)(+) state of Xe-134 is the dominant fragment of the one-phonon 2(1,ms)(+) mixed-symmetry state. Comparing the energy of the 2(1,ms)(+) mixed-symmetry state in Xe-134 to that of the 2(1,ms)(+) levels in the N = 80 isotonic chain indicates that the separation in energy between the fully-symmetric 2(1)(+) state and the 2(1,ms)(+) level increases as a function of the number of proton pairs Outside the Z = 50 shell closure. This behavior call be understood as resulting from the mixing of the basic components of a two-fluid quantum system. A phenomenological fit based on this concept was performed. It provides the first experimental estimate of the strength of the proton-neutron quadrupole interaction derived from nuclear collective states with symmetric and antisymmetric nature. (C) 2009 Elsevier B.V. All rights reserved.