Figure 1.

(a) Typical scattering triangle showing incoming neutrons with incident energy E_i, wavelength λ_i, and wave vector $\overrightarrow{k_i}$ interacting with the sample and assuming final energy E_f, wavelength λ_f, and wave vector $\overrightarrow{k_f}$. The momentum transfer $\overrightarrow{Q}$ is defined as the change in wave vector ($\overrightarrow{Q}$= $\overrightarrow{k_i}$− $\overrightarrow{k_f}$); (b) summary of the main features of the QENS technique. These are explained in detail in the text.