Gamma-rigid solution of the Bohr Hamiltonian for gamma = 30 degrees   compared to the E(5) critical point symmetry
  A gamma-rigid solution of the Bohr Hamiltonian for gamma = 30 degrees is derived, its ground state band being related to the second order Casimir operator of the Euclidean algebra E(4). Parameter-free (up to overall scale factors) predictions for spectra and B(E2) transition rates are in close agreement to the E(5) critical point symmetry, as well as to experimental data in the Xe region around A=130. 
Dennis Bonatsos, D. Lenis, D. Petrellis, P. A. Terziev, I. Yigitoglu