SESANS by modulation

With minor modification of the SESANS-instrument we obtained a modulated beam.  This was achieved by carefully tuning the strength of the effectively triangular precession regions to the distances between them and to the detector. In the graph you can see the modulation with a modulation period of 0.9 mm.  We expect that we can go down to periods of 20 micron (but we have not got a detector with such a good spatial resolution).

By inserting a sample scattering over small angles in the beam, the amplitude of the modulation will be decreased.  The decrease of the amplitude as a function of the modulation period is exactly equivalent to SESANS.  The advantage is that all the polarisation manipulation is performed before the sample.  The drawback is that a very good detector with a high spatial resolution is needed.

Spatial modulation of a neutron beam by Larmor precession
W.G. Bouwman, C.P. Duif, R. Gähler
Physica B in press (2009)
http://dx.doi.org/10.1016/j.physb.2009.06.052