  The capability of performing accurate measurements of neutron beam
polarization opens a number of exciting opportunities in fundamental neutron
physics and in neutron scattering. At the LANSCE pulsed neutron source we have
measured the neutron beam polarization with absolute accuracy of 0.3% in the
neutron energy range from 40 meV to 10 eV using an optically-pumped polarized
3He spin filter and a relative transmission measurement technique. 3He was
polarized using the Rb spin-exchange method. We describe the measurement
technique, present our results, and discuss some of the systematic effects
associated with the method.
