The precession of the plane of polarization of $\gamma$ radiation in an external magnetic field was observed time differentially. As this experiment is in full analogy to that done by Hanle in 1925 on atoms, we called this behavior nuclear Hanle effect. The measurement was performed with a pulsed proton beam of 5.5 MeV, which defined the moment of excitation of the 197 keV level in the ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ nucleus. The result is well described by a simple theory in accordance with the theory of perturbed angular distributions.

NUCLEAR REACTIONS ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}(p,p^{\prime })$, $E=5.5\mathrm{}$ MeV; measured nuclear Hanle effect of ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ (197 keV level), deduced $g$.

• Received 1 September 1977

DOI:https://doi.org/10.1103/PhysRevC.17.2006