Gaseous 3He-3He magnetic dipolar spin relaxation

We derive the nuclear-spin relaxation rate of gaseous 3He due to the magnetic-dipole interaction between the 3He nuclear spins. This dipolar relaxation rate is numerically evaluated for temperatures from 0.1 K to 550 K. At room temperature, the relaxation time for a 3He density of 10 amagats is 74.4 h. We have made a series of high-density (4--12 amagat) 3He samples for which nulcear relaxation is limited by the magnetic-dipole interaction. Both our theoretical and experimental results are particularly important for the growing use of 3He, polarized through spin exchange with optically pumped Rb vapor