Triple-axis spectrometry (TAS, three axis spectroscopy) is a technique used in conjunction with inelastic neutron scattering.
The instrument is referred to as triple-axis spectrometer (also called TAS).
It allows measurement of the scattering function at any point in energy and momentum space physically accessible by the spectrometer.
The triple-axis spectrometry method was first developed by Bertram Brockhouse at the National Research Experimental NRX reactor at the Chalk River Laboratories in Canada.
Bertram Brockhouse shared the 1994 Nobel Prize for Physics for this development, which allowed elementary excitations, such as phonons and magnons, to be observed directly.