A first test of the E(5/4) Bose-Fermi symmetry: Ba-135

Abstract

There has been intense recent interest in equilibrium shape / phase transitions in nuclei and the concept of critical point symmetries to describe them. The first critical point symmetry for an odd-mass nucleus has been recently proposed, namely, the E(5/4) Bose-Fermi critical point symmetry, it corresponds to coupling between an odd particle in a j = 3/2 orbit and the E(5) critical point symmetry, at the transition between the O(6) gamma-soft and the U(5) vibrator symmetries. Since Ba-134 is a candidate for the E(5) critical point symmetry, we carried out a beta-decay experiment on Ba-135 whose last neutron can occupy a 2d(3/2) orbit as a first test of E(5/4). The experimental results were compared to E(5/4) and also with the Interacting Boson-Fermion Approximation Model (IBFA) and Shell Model calculations. We see fair agreement with E(5/4) for B(E2) values but not for all energies. The IBFA shows better agreement with data than E(5/4) and the Shell model shows the best agreement.