Precision manipulation of the neutron polarisation vector

The rotation of the neutron polarisation vector that takes place on scattering is determined with polarimeters which can measure the three components of the scattered polarisation for any chosen incident polarisation direction. Cryopad zero-field polarimeters are used on the D3/ILL diffractometer and the IN14/ILL, IN20/ILL, IN22/CEA and TAS-1/JAEA three-axis spectrometers. MuPAD zero-field polarimeters have also recently been built for use at the cold neutron beam MIRA/FRM-II and the three-axis spectrometer TASP/SINQ. We present the experimental strategy of this technique called spherical neutron polarimetry (SNP), develop the equations that relate the polarisation components to the CRYOPAD rotation angles, and explain the uncertainties that must be taken into account when carrying out SNP experiments.