We derive the exact semiclassical expression for the second inertial parameter $\cal B$ for the superfluid and normal phases. Interpolation between these limiting values shows that the function ${ \cal B}(I)$ changes sign at the spin $I_c$, which is critical for a rotational spectrum. The quantity $\cal B$ turns out to be a sensitive measure of the change in static pairing correlations. The superfluid-to-normal transition reveals itself in the specific variation of the ratio ${ \cal B}/{ \cal A}$ versus spin $I$ with the plateau characteristic of the normal phase. We find this dependence to be universal for normal deformed and superdeformed bands. The long plateau with a small value ${ \cal B}/{ \cal A}\sim A^{ -8/3}$ explains the extreme regularity of superdeformed bands.
Categories: nucl-th nucl-ex