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One-Dimensional Sans Employing Bent-Single Crystal Optics: Theory and Demonstration

  • B. J. Heuser (a1), M. Popovici (a2) and R. Berliner (a2)

Abstract

A recent small-angle neutron scattering (SANS) instrumentation development at the University of Missouri Research Reactor Center (MURR) using bent, double Si crystal diffraction is presented. Neutron rocking curves of flat single crystals are only a few seconds of arc with correspondingly low integrated intensities. The rocking curve can be significantly broadened if the crystals are bent. However, the phase-space acceptance and emergence windows of two bent crystals in parallel can be matched only if the reflecting planes have different d-spacing. We have used a combination of the Si (111) and (220) reflections in the work presented here. The peak intensity of the rocking curve with this configuration was approximately 2.5 x 105 neutrons per second over a 5 cm2 area of sample at 1.5 Å. The rocking curve wings fell sharply (approximately as Q"11), permitting accurate scattered intensity measurements down to a minimum Q value of 0.005 1/Å at a Q resolution of 0.003 1/Å. The technique also offers the possibility of variable resolution without too much difficulty; changes up to a factor of 2 can be made by adjusting the sample-to-analyzer crystal distance, while changes of a factor of 10 can be made by using different Si reflections. Since the incident neutron wavelength can be tuned to the peak of the leakage spectrum, this technique is ideal for low-flux reactors, which otherwise cannot be used for SANS research. The usefulness of one-dimensional SANS is demonstrated by measurements of Portland cement.

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References

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6 Popovici, M., Yelon, W.B., Berliner, R., and Stoica, A.D., 41st Annual Mid-West Solid State Conference, Columbia, MO (1993).
7 Worcester, D.L., 1994, private communication.

One-Dimensional Sans Employing Bent-Single Crystal Optics: Theory and Demonstration

  • B. J. Heuser (a1), M. Popovici (a2) and R. Berliner (a2)

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