Spin-exchange optically pumped polarized He 3 target for low-energy charged particle scattering experiments

We have constructed, tested, and calibrated a polarized He 3 target system which facilitates p - He 3 elastic scattering at proton energies as low as 2 MeV . This system consists of a target cell placed in a uniform B field inside a scattering chamber and an external optical pumping station utilizing Rb spin exchange. Computer-controlled valves allow polarized He 3 gas to be transferred quickly between the optical pumping station and the spherical Pyrex target cell, which has Kapton film covering apertures for the passing beam and the scattering particles. The magnetic field required to maintain He 3 polarization in the target cell is created with a compact, shielded sine-theta coil. Target gas polarimetry is accomplished using nuclear magnetic resonance and calibrated using the known analyzing power of α - He 3 scattering.