Smooth termination of intruder bands in ¹⁰⁹₅₁Sb

Intruder rotational bands have been investigated to high frequency in ¹⁰⁹₅₁Sb. Five decoupled (ΔI=2) bands extending to rotational frequencies above 1.4 MeV/ℏ have been observed. At the highest frequencies, the script J sign⁽²⁾ dynamic moments of inertia for four of these bands are seen to decrease steadily to unexpectedly low values, script J sign⁽²⁾ ∼ 10 ℏ² MeV^-1. These four bands, which are interpreted as being based on deformed 2p-2h proton excitations across the Z=50 closed-shell gap, achieve the so-called "smooth band termination" following alignment of the valence nucleons outside of ¹⁰⁰Sn. In addition, two strongly coupled (ΔI=1) bands have been observed, which are related to 1p-1h proton excitations across the gap.