Neutron spectroscopy is a spectroscopic method of measuring atomic and magnetic motions by measuring the kinetic energy of emitted neutrons. The measured neutrons may be emitted directly (for example, by nuclear reactions), or they may scatter off cold matter before reaching the detector. Inelastic neutron scattering observes the change in the energy of the neutron as it scatters from a sample and can be used to probe a wide variety of different physical phenomena such as the motions of atoms (diffusional or hopping), the rotational modes of molecules, sound modes and molecular vibrations, recoil in quantum fluids, magnetic and quantum excitations or even electronic transitions.
Since its discovery, neutron spectroscopy has become useful in medicine as it has been applied to radiation protection and radiation therapy.
It is also used in nuclear fusion experiments, where the neutron spectrum can be used to infer the plasma temperature, density, and composition, in addition to the total fusion power.
Although neutron spectroscopy is currently capable of operating on many orders of neutron energy, much research focuses on expanding these capabilities to higher energies. In 2001, US researchers were able to measure neutrons with energies up to 100 gigaelectronvolts