An exactly separable gamma-rigid version of the X(5) critical point symmetry

A gamma-rigid version (with gamma=0) of the X(5) critical point symmetry is constructed. The model, to be called X(3) since it is proved to cointain three degrees of freedom, utilizes an infinite well potential, is based on exact separation of variables, and leads to parameter free (up to overall scale factors) predictions for spectra and B(E2) transition rates, which are in good agreement with existing experimental data for Os and Pt. An unexpected similarity of the beta 1 bands of the X(5) nuclei Nd-150, Sm-152, Gd-154, and Dy-156 to the X(3) predictions is observed