Spin-Diffusion Measurements in Hydrogen between 20 and 55°K

The spin-diffusion coefficient $D$ of hydrogen has been measured as a function of the density $\rho$ up to a maximum density of 850 amagats for various ortho-para hydrogen concentrations in the range 20-75% of orthohydrogen between 20 and 55°K by the spin echo technique. Within the experimental error of ±10%, the absolute value of $D$ for the dilute gas is in agreement with the calculations of Buckingham et al. over this entire temperature range. Within this accuracy, no dependence on orthohydrogen concentration (at constant total density) is observed. The experimental results tend to confirm the conclusion of Emery, deduced from a detailed analysis of the Boltzmann diffusion equation, that symmetry effects cannot be observed in the diffusion process.