Spurions is a commonly used expression for parasitic signals, which can be easily mistaken as real signals from the studied sample. There are different origins of spurions. Most of them are linked to a specific instrumental set-up or the chosen sample environment. In the following we give a list of the most common spurions run across in classical TAS experiments:
Bragg peaks from Aluminium or Copper in the beam.
Harmonic wavelengths in ki and kf
Incoherent scattering of monochromator/analyzer:
A small part (10-5) of the incoming beam is always scattered incoherently by the monochromator or the analyzer. It is then possible to get a Bragg reflection from the sample or the sample container for this ki or kf
A scanning on A3 sample rotation will have the width of a Bragg peak; -) Moving the monochromator or analyzer will make the 'good' signal to disappear, but the incoherent contamonation will remain; -) Changing ki or kf will make that peak move.
For some spectrometer configurations, the detector can be in the axis of the incoming beam. Fast neutrons that may pass the protections will give an additional peak. Also, for small A4 angles, one can have an additional scattering from tubes lying in the incoming beam, that would 'deviate' the beam toward the analyzer and detector.
Phonon on monochromator or analyzer:
These phonons will not depend on temperature or A3!