Longitudinal Spin Relaxation inHe3Gas at 4.2 K

The first measurements of longitudinal spin relaxation due to binary atomic collisions in bulk ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ gas are reported. At 4.2 K the data are fitted by the expression $\rho T_1=61\mathrm{}\pm 2$ sec g ${\mathrm{cm}}^{-3\mathrm{}}$ for densities $\rho$ such that $0.01<\mathrm{}\rho <0.05\mathrm{}$ g ${\mathrm{cm}}^{-3\mathrm{}}$. At lower densities wall relaxation predominates and at higher densities a binary collision theory is inadequate. A model of wall relaxation is given which identifies the role of the absorbed phase of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ on the wall.