Polarization, production and handling of hyperpolarized gases

Applications of hyperpolarized (HP) gases are various: from basic research to magnetic resonance imaging in medicine.

In our group HP gases are used or prepared for use in tests of fundamental symmetries by means of ultrasensitive magnetometry based on free precession of nuclear spins, for the measurement of the electric form factor of the neutron and for the accurate determination of the magnetic field strength by measurement of the precession frequency of nuclear spins in high magnetic fields.

Since HP gases were applied as contrast agents for magnetic resonance lung imaging our group developed methods, techniques and devices for polarization, storage, transport, application and recycling of the spin polarized 3He gas also for medical research.

 

Please do not hesitate to contact us if we can be of any further assistance for your experiments with the HP 3He!

 

 

Additionally techniques for the production of HP 129Xe are being developed. 

Both gases, 3He and 129Xe are spinpolarized by optical pumping technigues.

 

Optical Pumping

Polarization of ³He by optical pumping (OP) techniques is well known since the early 1960ies with first applications in fundamental physics experiments. Optical pumping transfers polarization from photons to atoms by resonant absorption of circularly polarized light in homogeneous magnetic field B0, which serves as a holding field and as quantization axis for the polarized nuclei (Fig.1).  

 

 

Fig.1: Optical Pumping    

 

It is possible to polarize 3He-nuclei by spin-exchange with optically-pumped alkali-vapour (SEOP) or by Metastability Exchange Optical Pumping (MEOP). By MEOP the atoms from the ground state are excited into the metastable 23S1 state by a discharge and then the 3He gas can be pumped by a circularly polarized laser light at 1083 nm. After the several cycles of absorption/emission of photons, the angular momentum of the photons is transferred to the electron shell of the atoms. For the 3He isotope in the excited metastable state, an efficient coupling between the nucleus and the electrons (the hyperfine interaction) results in a strong entanglement of electronic and nuclear spins. The resulting nuclear polarization is transferred to the ground state by metastability exchange collisions (Fig.2).

 

   

 

 Fig.2: Metastability Exchange Optical Pumping of 3He   

 

Our polarization apparatus for a preparation of 3He is based on the method of MEOP.

For the polarization of 129Xe the efficiency SEOP scheme is used. By alkali-SEOP, for instance Rubidium-SEOP, the unpaired spin of the valence electron of Rb is polarized by OP via the strong resonance line at 795 nm. Rb electron spins transfer then their polarization through magnetic hyperfine coupling to the nuclear spins of a noble gas.