Longitudinal nuclear relaxation measurements in hcp H 2

Abstract

Measurements of T 1 in the hep phase of H 2, over the temperature range 2°–12°K and the ortho concentration range between 0.5 and 0.97 are presented. At temperatures below 10°K, the thermally activated self-diffusion is negligible and the mechanism for nuclear relaxation is that attributed by Moryia and Motizuki and by Harris to intramolecular dipolar interaction, modulated by intennolecular electric quadrupole-quadrupole (EQQ) interaction. The gaussian approximation for the correlation function was used by these authors to predict T 1. From the comparison between experiment and theory, we determine the EQQ parameter Γ k B to be 0.67°K. Above 10°K the effect of diffusion influences T 1, and the experimental results for an 88 per cent ortho H 2 sample up to the melting point suggest that the relaxation mechanisms resulting from EQQ interaction and diffusion are not independent of one another.