Gas samples with a mixture of hydrogen isotopes and $^3$He for NMR spectroscopy and estimation of the magnetic moment of the $^3$He nucleus

We describe the technique for preparing high-pressure glass ampoules for NMR spectroscopy, which contain hydrogen isotopes (deuterium and protium) as well as the light helium isotope ($^3$He). Using these ampoules, we succeeded in measuring the spin precession frequencies for $^3$He nuclei and the molecular deuterium nuclei and in calculating one of the fundamental physical constants, viz., the ratio of the magnetic moments of the helion and the proton $\mu_h/\mu_p$ = -0.761 812 215(3).