Confirmation of the Shears Mechanism in Near-Spherical Tin Nuclei

Lifetimes of states of a magnetic dipole band in each of the nuclei ${}^{106,108}\mathrm{Sn}$ have been obtained using the Doppler shift attenuation method. The deduced $B\left(M1\mathrm{}\right)$ transition rates show the characteristic behavior associated with the shears mechanism. A simplified semiclassical analysis yields $B\left(M1\mathrm{}\right)$ values in qualitative agreement with those expected for previously assigned configurations. The results suggest extremely low deformations for these dipole structures. In particular, the ${}^{106}\mathrm{Sn}$ band appears to be the first example of almost pure magnetic rotation in a spherical nucleus.