Precise determination of the 13C nuclear magnetic moment from 13C, 3He and 1H NMR measurements in the gas phase

► All NMR resonance frequencies of 13CH4 and 3He are linearly dependent on gas density. ► The magnetic moment of 13C nucleus is accurately determined by the NMR experiments. ► Experimental and theoretical shielding in 13CH4 give the similar 13C magnetic moment.