Confirmation of the shears mechanism in near-spherical tin nuclei

Lifetimes of states of a magnetic dipole band in each of the nuclei Sn-106, Sn-108 have been obtained using the Doppler shift attenuation method. The d educed B(M1) transition rates show the characteristic behavior associated w ith the shears mechanism. A simplified semiclassical analysis yields B(M1) values in qualitative agreement with those expected for previously assigned configurations. The results suggest extremely low deformations for these d ipole structures. In particular, the Sn-106 band appears to be the first ex ample of almost pure magnetic rotation in a spherical nucleus.