Peak shape at the axially focusing E9 powder diffractometer - theoretical and experimental description

Abstract

The high-resolution neutron powder diffractometer E9 at the Berlin Neutron Scattering Center, HMI, uses an axially focusing monochromator in combination with a wide detector opening in order to optimize the intensity. Common descriptions of the asymmetry for this type of instrument consider the effects of the heights of sample and detector only. However, with an axial convergence angle of about 7° from the monochromator the effects caused by the high inclination of parts of the incoming beam have to be considered. An improved peak-shape model was tested taking into account these and additional minor effects.