The Spin Polarised Hot Neutron Beam Facility

Spherical polarimetry with CRYOPAD

These movies show the adventures of neutron polarization during the passage through CRYOPAD and the sample. CRYOPAD is the acronym for “CRYOgenic Polarization Analysis Device”. The sample is in its center, in a magnetic field free zone created by a superconducting enclosure. Two sets of fixed and mobile coils make it possible to manipulate the direction of the neutron polarization vector at will, before and after the sample.

In the first video the scattered beam polarization vector is antiparrallel to the input polarization which means that the polarization rotates inside the sample by 180º around the magnetic interaction vector, which is true for collinear antiferromagnetic samples. Other kinds of magnetic samples modifies the beam polarization in a much complex way and this rotation is accurately measured by suitable precessions in the coils and rotations of the nutators.

In the second video the polarization axis of the incoming neutrons is set along the local x-axis, which is parallel to the scattering vector. In this example the rotation around the magnetic interaction vector creates a y-component (shown in green). In order to analyze this y-component it is guided along the neutron path until it reaches the He3 cell where the analysis axis is parallel to the direction of travel.


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