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USJ-TAX  -  US-Japan Triple Axis Spectrometer

Niche for Cold Neutron Triple Axis Spectrometer

Cold neutrons (typical energies, <5 meV), in contrast to thermal neutrons (10-80 meV), provide higher energy resolution and momentum resolution for triple-axis spectrometers. One application exploiting this feature is measuring dispersion curves at low energy transfer. This higher resolution is needed to isolate peaks which are separated by small energy or are located near the incoherent elastic scattering peak centered at 0 meV. In addition, neutron-scattering experiments that exploit cold neutrons generally encounter fewer ‘spurions,’ which simplifies analysis. A smaller Ewald sphere contains fewer Bragg peaks to hit, so there would be less multiple scattering.

Cold neutrons also provide greater sensitivity to magnetic phenomena, due both to larger magnetic scattering intensities for smaller Q, and a matching energy scale to achievable magnetic fields at the sample. It is therefore optimized for studies on highly correlated electronic systems, quantum magnetism, molecular and nanocluster magnetic systems, and superconductivity.

There is considerable need for more capacity in cold neutron TAX’s. The only one currently available in the US is SPINS at the NIST Center for Neutron Research, which is oversubscribed.

The USJ-TAX will also function as an intermediate-energy neutron triple axis spectrometer, bridging the gap between cold and thermal TAX instruments. Intermediate-energy neutrons (5-20 meV), as compared to cold neutrons, provide a larger selection of Brillouin zones, increasing the chances of finding and appropriate experimental configuration at which to acquire good-quality data. Intermediate-energy neutrons also provide greater sensitivity to nuclear superlattice peaks (due to small displacements) than do cold neutrons.

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Last Modified: Tuesday, 04-Mar-2008 14:56:05 EST
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