Approach to Vibrational to Axially Rotational Shape Phase Transition Along the Yrast Line

With the energy surface of the nucleus in U(5) symmetry being analyzed in the framework of thermodynamics, the vibration and rotation phase diagram in terms of the angular momentum and deformation parameter is given. Together with examining the energy spectrum, we propose a theoretical approach to describe the vibrational to axially rotational phase transition along the yrast line. By analyzing the available experimental data we show that the vibrational to rotational shape phase transition along the yrast line takes place in many nuclei.