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An Introduction to Neutron Scattering - Spallation Neutron Source

An Introduction to Neutron Scattering - Spallation Neutron Source

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“Phonon Focusing”<br />

• For a single incident neutron wavevec<strong>to</strong>r, k I , neutrons are<br />

scattered <strong>to</strong> k F by a phonon of frequency ω o and <strong>to</strong> k f by<br />

neighboring phonons lying on the “scattering surface”.<br />

– The <strong>to</strong>pology of the scattering surface is related <strong>to</strong> that of the phonon dispersion<br />

surface and it is locally flat<br />

• Provided the edges of the NSE precession field region are<br />

parallel <strong>to</strong> the scattering surface, all neutrons with scattering<br />

wavevec<strong>to</strong>rs on the scattering surface will have equal spin-echo<br />

phase<br />

k I<br />

Q 0<br />

k F k f<br />

k f⊥<br />

scattering surface<br />

Precession field region

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