= Neutron spectroscopy
<Neutron spectroscopy> measures neutron <energies> or the <energy> changes caused by interactions with a sample. In inelastic scattering, comparing incident and outgoing <energy> and <momentum> probes excitations and motion in matter rather than only its static arrangement.
A pulsed or velocity-selected beam, a sample and detectors at known directions form a typical experiment. For a nonrelativistic outgoing neutron traveling known distance $L$ from the sample in time $t$, <time of flight> gives $E_f=m_nL^2/(2t^2)$. A known incident <energy> then determines the sample's <energy> transfer. Timing resolution, flight-path uncertainty and background limit the result. https://www.nist.gov/ncnr/neutron-instruments/spectroscopy[NIST Center for Neutron Research, Spectroscopy: accessible material dynamics and time-of-flight instruments]{ref}
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