COLLECTIVE STRUCTURES AND SMOOTH BAND TERMINATION IN SN-109

Six rotational bands up to energies E(x) = 24.7 MeV and spins J(pi) =( 79/2(-)) have been identified in Sn-109 using the GAMMASPHERE gamma-de tector array. Four of the bands show smoothly decreasing dynamic momen ts of inertia at rotational frequencies HBAR omega > 0.6 MeV. The band s arise at medium spins from a coupling of a valence d(5/2), g(7/2) or h(11/2) neutron to the deformed 2p2h proton excitation of the Z=50 co re Sn-108. At very high HBAR omega these bands show the typical behavi our of smoothly terminating bands, i.e. a gradual alignment of the ang ular momenta of the valence particles and holes corresponding to a tra nsition from high collectivity to noncollective states.