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Abstract

An absolute calibration of the analysing powers of hydrogen and helium-4 has been performed at 24° and 15° lab, respectively, for protons between 200 and 520 MeV with a typical uncertainty of ±2%. In a double scattering experiment, the TRIUMF polarized proton beam was scattered, first at 15° on a liquid helium target, then a second time at 24° on a polyethylene target. The method combines the advantages of the very high analysing power of helium and the small difference in incident energies on both scatters. The analysing power of helium-4 was measured to be 0.964 ± .012, 0.792 ± .011 and 0.476 ± .018 at energies of 222, 325 and 518 MeV, respectively. The analysing power of hydrogen was found to be 0.294 ± 0.003, 0.354 ± 0.005 and 0.412 ± 0.013 at proton energies of 205, 308 and 499 MeV, respectively. This represents a great improvement over previous p-p data which was not known to better than ±6%, and so will permit a more accurate determination of nucleon-nucleon phase shifts.