High Proton Polarization Achieved with a (Yb, Y)(C2H5SO4)3· 9H2O Spin Refrigerator in a Nonuniform Magnetic Field

Proton polarization of approximately 65% has been achieved with the University of Massachusetts "spin refrigerator" in a nonuniform 1.07-T field at 1.25 K. The free protons in (Yb, Y) ${\left({\mathrm{C}}_2{\mathrm{H}}_5\mathrm{S}{\mathrm{O}}_4\right)}_3$ · 9${\mathrm{H}}_2$O are polarized through sample rotation at 100-200 rps. Results represent the first confirmation of high polarization predicted by a single-Yb-ion interaction model since the original proposals of Jeffries and Abragam. The polarized-proton target, with length equivalent to 9 cm of liquid hydrogen, will be utilized in studies of strange particles.