Kinetic theory calculation of the NMR relaxation time of dilute 3He gas

The spin‐lattice relaxation time T₁ of ³He gas is calculated with the kinetic theory formulation due to Chen and Snider. The temperature dependence of T₁ is evaluated for the Beck and the McLaughlin and Schaeffer He–He isotropic potential functions with a dipolar interaction assumed to be responsible for the relaxation of the nuclear spin. A sharp minimum in T₁ near 1°K is obtained for both potentials and it appears that the minimum value of T₁ is sensitive to the form of the interatomic potential, particularly to the form of the potential in the region of the well. For temperatures above approximately 2°K, T₁ ρ varies approximately as T^1/2. The calculated values of T₁ at 4.2°K and a density of ${\text{0.7× 10}}^{\text{−2}}\mathrm{gm/cc}$ are 181.2 and 176.7 min for the Beck and the McLaughlin and Schaeffer potential functions, respectively. Chapman and Richards, in a preliminary set of experiments have measured T₁ and the longest relaxation time for this density and temperature was found to be 113 min.