Polarimetry

Cryopol-II is a cryogen-free cryostat able to host a large neutron spin filter cell in the stray field of a cryomagnet. The first experiment was carried out on D20 in July 2008: measurement of the magnetisation distributions of molecular and nano-scale samples.

As shown on the graph, the relaxation time of the 3He polarisation was better than 100 hours in the 1.9 litre cell (alias TetraPack) filled at 1.2 bar [more].

On a standard spin-echo spectrometer, the fact that the beam is essentially depolarised right before the sample is unimportant in systems where there is no spin-dependent scattering. But when investigating magnetic systems, it is necessary to analyse the change in direction of the polarisation vector. We have demonstrated that such an analysis is possible by using a zero-field polarimeter Cryopad and analysing the wavelength modulation of the spectrum. After this development phase at HCB on SPAN, the Polarimetric NSE technique has been commissioned at ILL on IN15 [more].

If you wish to better understand the behaviour of the polarisation vector upon scattering, we invite you to have a look at the simulations we have calculated for different incident polarisation directions and different types of nuclear and magnetic interactions [more].

We have written an external module (XOP) called "Neutron Scattering XOP" that adds functionality to IGOR Pro. It provides a set of functions which are useful for carrying out neutron scattering experiments, especially with polarised beams. This plug-in is free and may even be improved on request.