NEW EXPRESSIONS FOR THE COLLECTIVE EXCITATION SPECTRA IN EVEN-EVEN NUCLEI

The collective spectra of the well-deformed nuclei with small axial asymmetry and the nuclei with large axial asymmetry are investigated separately in the frame of the Bohr Namiltonian. The collective spectra of well-deformed nuclei manifest the vibrational-rotational band structure and each of these bands can be expressed as a 2-parameter closed expression.The agreement between the calculated results and the observed data is very good.From this expression the radius of convergence for the energy expansion in terms of I(I+1) can be estimated and the em- pirical fact that the expansion in powers of rotational frequency converges much more rapidly than that in powers of I(I+1)can be understood. Similarly, the ground state quasi-band of the nuclei with large axial asymmetry can be expressed as a 3-parameter closed expression.