Nuclear Polarization and Heat Conduction Changes in Gaseous 3 He

Although it is a dilute nondegenerate system, a gas of 3 He ↑ (spin-polarized 3 He) can exhibit interesting quantum effects due to particle indistinguishability. One of these effects is a variation of the heat conduction coefficient as a function of the nuclear polarization. An experiment is described where this change has been observed and measured. The nuclear polarization is obtained by optical pumping at a wave-length λ = 1.08 μm with a LNA crystal laser. The experimental results are in reasonable agreement with theoretical predictions, but the discrepancies are sufficiently clear to suggest that calculations should be slightly revised (including, possibly, a new fit of the He-He interatomic potential).