Spherical neutron polarimetry with Cryopad-II

Abstract Neutron polarimetry (NP), the observation of changes in the neutron spin polarisation vector induced by scattering processes is making progress. In a Spherical version of this method (SNP), routinely available at ILL, the measurement of the final polarisation vector is made totally independent of the incident polarisation direction by working in zero field. The zero-field polarimeter Cryopad-II is usually mounted on the IN20 3-axis spectrometer for inelastic as well as elastic measurements at moderate Q but it was also used very recently on the hot neutron diffractometer D3 in an attempt to do elastic measurements up to large momentum transfer. The most interesting results are obtained when measuring the transverse components of the scattered polarisation, a completely new possibility. Progress in neutron-scattering theory, triggered by the observation of such components in the inelastic mode, suggests that they are a unique signature of spin–lattice excitations.