NIST GRANTED PATENT FOR A COMPACT COMPRESSOR FOR POLARIZED [He.sup.3] GAS.

By using optical methods, it is possible to align the magnetic moments of 3He nuclei with an applied magnetic field producing "polarized [He.sup.3] gas." Since its first production about 40 years ago, polarized [He.sup.3] gas has been employed for many applications such as low temperature physics, studies of nucleon structure, and, more recently, for neutron spin filters and imaging of the human lung. Work on the latter two applications has been pursued by NIST scientists, and has resulted in a patent entitled "Method and apparatus for the compression of a polarized gas" being recently issued to NIST.

Magnetic resonance imaging (MRI), which traditionally relies on the signal derived from the small equilibrium polarization of protons in water in a strong magnetic field, can be more effectively performed for lungs by using the large non-equilibrium polarization produced by optical pumping of [He.sup.3] gas. To produce the polarized gas, two optical pumping methods are being employed at NISTspin--exchange and metastability-exchange. The latter method can rapidly produce highly polarized gas but the process is best performed at low pressures of only a few mbar. For the intended applications, pressures on the order of 1 bar are required, necessitating compression of the gas with as little loss of polarization as possible. Accordingly, NIST researchers modified a commercial diaphragm pump and tested it for use with polarized [He.sup.3] gas. The loss of polarization was found to be acceptable, and can be minimized by increasing the flow rate through the compressor. To maximize the achievable polarization at high flow rates, a new scheme to optimize the efficiency of the optical pumping is being employed. The NIST compressor can produce values of [He.sup.3] polarization as high as 50 %, which is competitive for application to neutron spin filters and polarized gas MRI.