Phenomenological Description of the Yrast Lines

Analysis of the collective structure of 0^{+} states in terms of phonon tations for great amount of nuclei is presented .It is shown that the rotational bands built on these states strongly depend on their structure. The spectrum of the bands is obtained by the application of the Nuclear Surface Oscillation /NSO/ model and assumption of "Kassini form" for the nuclear shape. The yrast lines energies can be successfully described by the crossing of the different rotational "beta - bands", if the collective structure of these band heads is properly taken into account