The article discusses the Spin Exchange Optical Pumping (SEOP) method for polarizing helium-3 (3He) nuclei. SEOP involves polarizing rubidium (Rb) or potassium (K) atoms using near-infrared laser light, then transferring this polarization to 3He nuclei through spin-exchange collisions between the polarized Rb/K atoms and 3He nuclei.
The process begins with generating an optically thick vapor of Rb/K in a cell filled with 3He and nitrogen gas. Circularly polarized laser light selectively excites Rb/K atoms in a specific spin state, which are then re-excited after decay, maintaining their polarization. The nitrogen gas suppresses photon emission that could depolarize other atoms.
During collisions between polarized Rb/K atoms and 3He nuclei, the hyperfine interaction transfers the Rb/K electron spin to the 3He nucleus, polarizing it. The polarization of 3He nuclei follows an exponential growth curve, approaching a maximum value determined by the ratio of spin-exchange rate to 3He spin relaxation rate.
Recent studies have revealed that the maximum achievable 3He polarization is limited by temperature-dependent relaxation processes, with the limiting factor (X) varying between 0.15 and 1 across different cells. To improve the maximum polarization, these relaxation processes need to be eliminated or reduced.
Source: https://www.nist.gov/ncnr/spin-filters/spin-filter-info/seop-method
Keywords: Spin Exchange, Optical Pumping, Hyperfine Interaction, Polarization, Relaxation Rate
