gFactor of a Magnetic-Rotational Band Head in193Pb

The recently discovered regular bands of enhanced $M1$ $\ensuremath{\gamma}$-ray transitions in nearly spherical Pb nuclei have been explained in terms of magnetic rotation. However, the special angular momentum coupling of the nucleons that form magnetic-rotational states has never been tested experimentally. In this paper, we report on the measurement of the $g$ factor of the 2583-keV head of such a band in ${}^{193}\mathrm{Pb}$. The result, $g\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.68(3)$, is the first direct proof of the almost perpendicular coupling of the proton-particle and neutron-hole angular momentum vectors. This coupling results in a large component of the magnetic moment perpendicular to the total nuclear angular momentum, which is required for the occurrence of magnetic rotation.