Hyperfine resonance of atomic deuterium at 1 K

Atomic-deuterium gas has been studied at temperatures just above 1 K. A short rf discharge was used to dissociate solid D 2 on the surface of a sealed pyrex bulb lined with a saturated helium film. Pulsed magnetic resonance on the β-δ transition at its minimum frequency (309 MHz in a magnetic field of 3.9 mT) was used to observe the resulting D. The free induction decays were shortened by spin-exchange collisions with impurity H atoms present in the sample. The H density, inferred using calculated spin-exchange cross sections, was typically higher than the D density. In addition, the samples of D were short-lived, decaying exponentially in time with a strongly temperature-dependent lifetime. We were able to show that recombination with the H impurity was not the cause of the sample decay, and we propose that the decay is due to the thermally activated process wherein D atoms penetrate the liquid helium film that coats the cell walls. Analysis of the lifetime data yields the value 13.6 (6) K for the rest energy of a D atom dissolved in liquid helium, the first measurement of this quantity for any hydrogen isotope.