Polarization of ³He, D₂ and (eventually) ¹²⁹Xe Using Low Temperatures and High Magnetic Fields

Abstract

The recent discovery that inhaling polarized ³ He or ¹²⁹ Xe allows high resolution MRI images of the lungs to be made is having a large impact among the medical and physics communities. In fact, this technique could become the first high resolution, harmless diagnostic tool for several lung diseases. Neutron–lean nuclear fusion would also benefit from the use of polarized fuel (D, ³ He) through an enhanced fusion cross–section. At present, laser techniques are being used for polarizing ³ He and ¹²⁹ Xe, but the yield is still quite low, at most a few tens of liters per day. Cryogenic techniques combining high magnetic fields and low temperatures could be used to produce much larger quantities of highly polarized ³ He through adiabatic compression. In a reasonable field of 15 T and 5 mK the polarization of the resulting solid is larger than 95%. Once polarized the solid is melted. The magnetization remains in the liquid for several minutes and the cell could be moved to a region at 6–7 K where the liquid would evaporate. The resulting gas could be removed and kept in a convenient vessel. Extraction could in principle be done in a time much shorter than the relaxation time T ₁ of the liquid, which has a minimum around 300 s at 1 bar pressure. This process could produce large quantities of gas in the range of 100 to 1000 l/day. We have also demonstrated that by condensing molecular deuterium (catalized to mostly J= 0) inside the ³ He cell it was possible to polarize the D ₂ molecules to 13%. Production of finely divided D ₂ should lead to quite larger polarizations. Using this technique one might consider the polarization of ¹²⁹ Xe.