CONSTANT-Q CONFIGURATION OF 3-AXIS SPECTROMETER

Abstract

CONSTANT-Q CONFIGURATION OF 3-AXIS SPECTROMETER. The constant-q method has
been widely used in the 3-axis spectrometer, which requires more angles to be setup as compared to those of
the diffractometer. Those angles are not natural variables in the physical quantities of interest for the dynamic
properties of materials. As the physical quantities of interests are the energy and momentum transfer, those
angles must be converted into the energy and momentum transfer. To the author’s knowledge, although this
method has been known since around 1960’s, no literature sufficiently describes the details to provide the
necessary equations. This paper elaborates the conversion by using the energy and momentum conservation
with the vector and trigonometric consideration of the scattering processes in the reciprocal space. The angle
values resulted from this conversion might be used to obtained the dispersion relation measurement by utilizing
the 3-axis spectromenter.