Quantum Tunneling of the Excited Rotational Bands in the Superdeformed Nucleus 143EU

The thermally excited rotational motion in the SD well of ¹⁴³Eu is studied experimentally in a EUROBALL experiment. The effective lifetime of the discrete rotational bands forming the ridge structures in γ-γ coincidence matrices is measured by a Doppler Shift Attenuation Method. The obtained results, consistent with a quadrupole deformation Q_t ≈ 10eb, support the superdeformed rotational character of the excited nuclear rotation. In addition, the number of superdeformed bands is extracted by a statistical analysis of the fluctuations in the number of counts of the ridges. It is found that the data are well reproduced by microscopic cranked shell model calculations including a two-body residual interaction and taking also into account the decay-out process to the lower deformation minimum. This gives evidence for a quantum tunneling of the excited superdeformed rotational bands into the normally deformed minimum.