New polarizing guide for neutron wavelengths above 2.5 Å

Abstract

We present a new polarizing system built for the relocated wide angle Neutron Spin Echo instrument SPAN. The new instruments at the second Guide Hall of BENSC and the relocation of SPAN to this hall of BENSC required a new beam extraction system and a new polarizer for SPAN, which replaced the old beam splitter produced in 1994 with FeCo-Si supermirrors with m=2. The new polarizer uses Fe-Si supermirrors, which do not run the risk to become activated as the old FeCo-Si supermirrors and was designed to deliver a polarized beam for wavelengths above 2.5 Å. The final polarizing cavity has a length of 9 m with a cross section of 60 mm × 100 mm. Si wafers coated on both sides with m=2.5 Fe-Si polarizing supermirrors are glued into the guide at an angle of 0.38° to the walls. The guide was installed during the second half year of 2006 and the first tests in early 2007 revealed excellent polarization efficiency over the whole wavelength range of the spectrometer of 2.5 Å to 9 Å, amounting to above 95% at 4.5 Å. © 2010 IOP Publishing Ltd.