Study of doubly polarized atomic hydrogen by electron-spin resonance

An extensive description is given of a special ESR spectrometer designed to perform electron-spin resonance in the (160-200)-GHz frequency range in spin-polarized atomic hydrogen in high magnetic fields. Results obtained in this experiment clearly demonstrate how a state of nuclear polarization is established by recombination under conditions of slow nuclear relaxation. A new method to measure the ratio KₐₐKab of two-body recombination-rate constants is introduced, yielding the result 2<KₐₐKab<8 at $T=0.31$ K. ESR detection also allows a check on possible thermal non-equilibrium situations between H gas and container walls. No deviations from equilibrium were found at $T=0.3$ K up to densities n=6×10¹⁵ cm³. It is also demonstrated that resonant microwave power can be used to pump atoms out of the stabilization cell, providing an alternative method of creating nonequilibrium distributions in the hyperfine states.