We report on the in-situ polarized 3He neutron polarization analyzer developed for the time-of-flight Magnetism Reflectometer (MAGICS) at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). Using the spin exchange optical pumping (SEOP) method we achieved a 3He polarization of 76 % +/- 1% and maintained it for the entire 3 day duration of the test experiment. Based on transmission measurements with unpolarized neutrons, we show that the analyzing efficiency of the 3He system is >99 % for the neutron wavelength band from 3 A to 5 A . Using a highly polarized incident neutron beam produced by a supermirror bender polarizer, we obtained a flipping ratio >100 of with a transmission of 25 % for polarized neutrons, averaged over the wavelength band of 2 A to 5 A. After the cell was depolarized for transmission measurements, we re-polarized it and this performance was maintained for 3 weeks. A high quality polarization analysis experiment was performed on a reference sample of Fe/Cr multilayer with strong spin-flip off-specular scattering. Using a combination of the position sensitive detector, time-of-flight method and the excellent parameters of the 3He cell the polarization analysis of the 2-dimensional maps of reflected, refracted and offspecular scattered intensity above and below the horizon were obtained simultaneously.
Citation: Review of Scientific Instruments
Pub Type: Journals
Magnetism Reflectometer, unpolarized neutrons, time-of-flight