The crossed geometry of two super mirror polarisers—a new method for neutron beam polarisation and polarisation analysis

We propose a new arrangement of super mirror polarisers to polarise a white cold or thermal neutron beam. With this method, the dependence of the neutron polarisation on angle and wavelength is suppressed efficiently. For such a neutron beam, the average polarisation can be measured with a precision of better than 10 - 3 using opaque spin filters. Average polarisation values of 0.997 for a cold neutron beam can be obtained. Furthermore, the method can be used for efficient polarisation analysis. Here, however, the precision is limited to a few times 10 - 3 by depolarisation effects. We present the method and results of experimental tests.