Lelievre-Berna, E.; Bentley, P.; Bourgeat-Lami, E.; Thomas, M.; Pappas, C.; Kischnik, R.; Moskvin E.: Spherical neutron polarimetry applied to spin-echo and time-of-flight spectroscopy. Physica B 404 (2009), p. 2624-2628
10.1016/j.physb.2009.06.047
Abstract:
The changes in direction of the neutron spin that take place on scattering by a magnetic interaction vector are highly dependent on their relative directions. When the magnetic interaction vector is complex and/or when there are nuclear-magnetic interferences, the rotation of the incident polarisation can be of any angle around or toward a specific direction. In such circumstances, without zero-field polarimeter, it is impossible to distinguish between a simple depolarisation and a rotation of the polarisation vector. Motivated by the investigation of chiral magnetic fluctuations, we have implemented the third-generation zero-field polarimeter Cryopad on the Neutron Spin-Echo spectrometer SPAN at the HCB. We present the method and the limitations of this novel technique that is now available on IN15 at the ILL. The huge progress accomplished with 3 He neutron spin filters/flippers are going to facilitate the exploitation of polarised beams at spallation sources. Zero-field polarimeters like Cryopad are used routinely at several steady-state sources but their design would be inefficient at a pulse source. We have investigated the possibility to implement a zero-field polarimeter on a time-of-flight spectrometer. We propose a design that would lead to a better efficiency and present the finite element calculations.