A TORSION BALANCE SEARCH FOR LONG-RANGE SPIN-DEPENDENT FORCES USING POLARIZED NUCLEI

We report here on progress in a series of experiments to search for lo ng-range spin-dependent gravitational forces, and to test the equivale nce principle, using polarized nuclei. Our method is to cool the test- bodies together with the torsion balance to 10-15 mK using a dilution refrigerator to maintain nuclear polarization. Our first test body is a H0Fe3 permanent magnet. The hyperfine splitting of the 100% stable i sotope Ho-165 is large that nuclear polarization is essentially 100% c orrelated with electron polarization at 10-15 mK.