SMOOTH TERMINATION OF INTRUDER BANDS IN SB-109(51)

Intruder rotational bands have been investigated to high frequency in Sb-109(51). Five decoupled (Delta I = 2) bands extending to rotational frequencies above 1.4 MeV/h have been observed. At the highest freque ncies, the J((2)) dynamic moments of inertia for four of these bands a re seen to decrease steadily to unexpectedly low values, J((2)) simila r to 10 h(2) MeV(-1). These four bands, which are interpreted as being based on deformed 2p-2h proton excitations across the Z = 50 closed-s hell gap, achieve the so-called ''smooth band termination'' following alignment of the valence nucleons outside of Sn-109. In addition, two strongly coupled (Delta I = 1) bands have been observed, which are rel ated to 1p-1h proton excitations across the gap.