Just What Is
In this experiment, we optically pump 5S(1/2)Rb with 795 nm,
circularly polarized light to a polarized state. Under radiative decays,
spin -(1/2) Rb is excited to this metastable 5P(1/2) state by the incoming
photons. As governed by the polarization ratio, one-third of which return
to their original state, the rest are sent to a spin +(1/2) state.
Most undergoe Non-Radiative Decay; they are first excited to the P(1/2)
state, exhibit collisional mixing, and return back to the S(1/2) state.
Eventually, a all end up in the S(1/2) (+1/2)-spin state.
Next, as governed by the hyperfine interaction of the Rb polarized
elctron's wavefunction and the He3 nuclear's wavefunction, the polarized Rb
electron interacts with the He3 nuclear via. spin-exchange. This means that
when encountered with a He3 nuclear, whoes spin is 'anitparallel' to that of
the Rb, the spin directions are exchanged....else nothing happens.
(/|\)Rb + (\|/)He -> (\|/)Rb + (/|\)He
The result: Polarized He3, which is used to polarize
the beam of neutrons. He3 strongly absorbs neutrons of opposite spin
through a broad resonance. Since neutrons of parallel spin with the He3
weakly interact with He3, what is left is a beam of neutrons polarized
parallel to that of the already polarized He3.