Nuclear Polarization of Spin-Polarized Hydrogen

The nuclear relaxation rate has been measured in spin-polarized hydrogen. The rate is so low that a gas composed of atoms initially in the two nuclear spin states spontaneously acquires a high nuclear polarization as one of the states recombines. The remaining state is stable against recombination, but decays slowly by nuclear relaxation. Nuclear polarization greater than 99% has been achieved. The absorption energy and the recombination rate of hydrogen have also been measured on liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$.