Nuclear shape properties of the even-even neutron-rich rare-earth nuclei

The physical properties of the nuclear shape have been investigated through the charge square radius (< r(2)>) and the quadrupole (Q(2)) and hexadecapole (Q(4)) moments of the even-even neutron-rich rare-earth nuclei. The single-particle energies used are those of a deformed Woods-Saxon mean-field. The pairing effects have been included by means of an exact projection method. The model has been tested for the "ordinary" nuclei near the shell closure N = 82 and has correctly reproduced the experimental data and particularly the "Kink" effect. The study has then been extended to the neutron-rich nuclei and has shown a stability of the < r(2)> and Q(2) results for N similar or equal to 100 which may be attributed to the existence of a new magic number. On the other hand, a saturation of the prolate shape appears around N = 108 for the elements Nd, Sm and Gd and near N = 102 for the Dy, Er and Yb. These observations could not be confirmed by the investigation of the hexadecapole moment.