Highly deformed band in 136Pm and the anomalous dynamical moment of inertia behavior in the A~135 superdeformed region.

The dynamical moments of inertia (Jisl) of superdeformed bands in the A 150 Gd-Dy and A ~190 Hg-Pb regions are fairly well reproduced by standard cranking calculations [1, 2]. However, for the superdeformed or highly deformed A~135 Ce-Nd-Sm region, this is not true at all, and has presented a theoretical problem for some time. Several solutions in terms of quenched proton pairing [3] and a strong residual proton-neutron interaction [4, 5 have been proposed. The present Rapid Communication reports on the observation of a rotational band in 3 Pm possessing an enhanced moment of inertia consistent with other highly deformed structures in this latter region. The behavior of this band sheds new light on the alignment processes taking place in neighboring highly deformed nuclei and represents an important step forward in the understanding of the so-called anomalous J( l behavior found in this region. Up to the present time in the A 135 region highly deformed bands have been observed almost exclusively in even-Z nuclei, i.e. , Ce [6—8]» s s Nd [9—12], ~ss s s Sm [3, 13—16], and Gd [17 18] Only in ~soLa [19] has a highly deformed band been observed in an odd-Z nucleus. Unfortunately this band, due to its very irregular behavior below h~ = 0.5 MeV and