14.33  The Collimator_ROC McStas Component

Radial Oscillationg Collimator (ROC)

Identification

• Author: <a href="mailto:hansen@ill.fr">Thomas C Hansen</a>

• Origin: <a href="http://www.ill.fr">ILL</a> (Dif/<a href="http://www.ill.fr/YellowBook/D20">D20</a>)

• Date: 15 May 2000

Description

ESCRIPTION

This is an implementation of an Ideal radial oscillating collimator, which is usually placed between a polycrystalline sample and a linear curved position sensitive detector on a 2-axis diffractometer like D20. The transfer function has been implemented analytically, as this is much more efficient than doing Monte-Caqrlo (MC) choices and to absorb many neutrons on the absorbing blades. The function is basically triangular (except for rather ’exotic’ focuss apertures) and depends on the distance from the projection of the focus centre to the plane perpendicular to the collimator planes to the intersection of the same projection of the velocity vector of the neutron with a line that is perpendicular to it and containing the same projection of the focus centre. The oscillation is assumed to be absolutely regular and so shading each angle the same way. All neutrons not hitting the collimator core will be absorbed.

Example: Collimator_ROC( ROC_pitch=5, ROC_ri=0.15, ROC_ro=0.3, ROC_h=0.15, ROC_ttmin=-25, ROC_ttmax=135, ROC_sign=-1)

Input parameters

Parameters in boldface are required; the others are optional.

Links

• Component source code found in file Collimator_ROC.comp.

• D20 diffractometer at the ILL