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In situ polarized 3He system for the Magnetism Reflectometer at the Spallation Neutron Source
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View: Figures


Image of FIG. 1.
FIG. 1.

A typical cylindrical 3He cell. The cell is filled with 3He and N2 gas, as well as alkali metal, usually rubidium (Rb) and potassium (K). The cell described above is not the same but analogous to the cell we used in the present study.

Image of FIG. 2.
FIG. 2.

The scheme of the in situ 3He pumping system.

Image of FIG. 3.
FIG. 3.

Results for vs. neutron wavelength along with a fit (solid line) to . The fit yields nσ0 lP He = 0.965 ± 0.003 Å−1. The error bars shown in all figures are determined by statistical error.

Image of FIG. 4.
FIG. 4.

as a function of neutron wavelength along with a fit (solid line) to . Based on fitting over different wavelength bands a cell thickness of 1.270 ± 0.013 Å−1 is obtained. Combining with the fit result from Figure 3, we obtain the 3He polarization to be 76% ± 1%.

Image of FIG. 5.
FIG. 5.

The measured flipping ratio F vs. neutron wavelength. This is a combined flipping ratio, which takes into account the efficiency of the supermirror polarizer, the spin-flipper, the 3He analyzer, and spin transport efficiency (guide fields) as described in the text.

Image of FIG. 6.
FIG. 6.

Experimental neutron polarization plots as functions of neutron wavelength. The blue curve (“polarization-cell”) is obtained from the unpolarized neutron transmission measurement and corresponds to the analyzing efficiency P 2(λ) of the 3He analyzer. The red curve (“polarization-FR”) shows the polarizer and 3He analyzer polarizing efficiency product , as described in the text. The green curve (“polarization-supermirror”) shows the polarizing efficiency of the supermirror polarizer P 1(λ) determined from the ratio of the red and blue curves.

Image of FIG. 7.
FIG. 7.

The schematic view of the reflectometry experiment, showing sample (S), incident, reflected, and transmitted polarized neutron beams. Incoming neutron beam is polarized by supermirror bender polarizer followed by an adiabatic RF-gradient neutron spin flipper (not shown in the figure). The 3He cell covers the cross sections of both the reflected and transmitted beams. The intensity is recorded by a position sensitive detector and presented in three-dimensional coordinates. The dashed line indicates the area being analyzed by the cell.

Image of FIG. 8.
FIG. 8.

Experimental data from the Fe/Cr multilayer measured in the external magnetic field of 30 mT. The left panel shows the wavelength dependence of the specularly reflected, off-specularly scattered, and transmitted intensities for the four spin-states. The right panel represents the same data, shown in the coordinates of the position sensitive detector (PSD) and being integrated over the TOF.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: In situ polarized 3He system for the Magnetism Reflectometer at the Spallation Neutron Source