Abstract
The neutron Larmor diffraction technique has been implemented using superconducting magnetic Wollaston prisms in both single-arm and double-arm configurations. Successful measurements of the coefficient of thermal expansion of a single-crystal copper sample demonstrates that the method works as expected. The experiment involves a new method of tuning by varying the magnetic field configurations in the device and the tuning results agree well with previous measurements. The difference between single-arm and double-arm configurations has been investigated experimentally. We conclude that this measurement benchmarks the applications of magnetic Wollaston prisms in Larmor diffraction and shows in principle that the setup can be used for inelastic phonon line-width measurements. The achievable resolution for Larmor diffraction is comparable to that using Neutron Resonance Spin Echo (NRSE) coils. The use of superconducting materials in the prisms allows high neutron polarization and transmission efficiency to be achieved.
Highlights
The ability of conventional neutron diffraction to measure precise values of the d-spacings of crystalline materials is limited by factors such as the strength of the available neutron source and the practical length of neutron flight paths
For a crystal plane with a small diffraction angle, the RF flippers have to be tilted to a large angle, forcing the neutron beam to pass through regions of the flipper where achieving field homogeneity is difficult and introducing aberrations that cause the amplitude of the Larmor oscillations to be reduced
The experiment was conducted on the HB-1 polarized triple axis spectrometer (PTAX) at the High Flux Isotope Reactor (HFIR) at Oak
Summary
Tuning of the effective tilting angle using magnetic Wollaston prisms. The experiment was conducted on the HB-1 polarized triple axis spectrometer (PTAX) at the High Flux Isotope Reactor (HFIR) at Oak. To further demonstrate this effect experimentally, we rock the sample around the vertical axis to various small angles to mimic such misorientation For both configurations, the measured fringes are shown, where the left and right figures are for the single- and double-arm methods respectively. For the double-arm configuration, Fig. 8(c) shows that, the average intensity drops just as it does for the single-arm, the total Larmor phase and flipping ratio stay the same for different rocking angles. These uniform fringes again show the benefit of using the double-arm configuration to minimize the Larmor phase aberration due the crystal mosaic
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