4.2

NRCalculateSlitResolution v1

../_images/NRCalculateSlitResolution-v1_dlg.png

NRCalculateSlitResolution dialog.

Summary

Calculates the reflectometry resolution (dQ/Q) for a given workspace.

Properties

Name Direction Type Default Description
Workspace Input MatrixWorkspace Mandatory Workspace to calculate the instrument resolution of.
TwoTheta Input number Optional Two theta scattering angle in degrees.
FirstSlitName Input string slit1 Component name of the first slit.
SecondSlitName Input string slit2 Component name of the second slit.
VerticalGapParameter Input string vertical gap Parameter the vertical gap of each slit can be found in.
ThetaLogName Input string Theta Name theta can be found in the run log as.
Resolution Output number   Calculated resolution (dq/q).

Description

This algorithm takes a workspace and a value for two theta, and attempts to calculate the reflectometry resolution (dQ/Q) from them. If no value is provided for two theta then NRCalculateSlitResolution will attempt to fetch a value from the workspace’s log using the theta log name provided.

The effective inverse of this algorithm is CalculateSlits v1.

Beam Divergence

collimation_diagram.png

Schematic showing beam divergence using two slits (Slit1 and Slit2)

Proof

\frac{d1}{x} \equiv \frac{d2}{l - x} \equiv \tan(\alpha) \therefore \frac{d1}{x} = \frac{d1 + d2}{l} \therefore \alpha = \arctan\left(\frac{d1 + d2}{l}\right)

where \alpha gives is the beam divergence in radians. Parameter d1 is the vertical distance of Slit1 opening, d2 is the same for Slit2. parameter l is the distance between the slits in the beam direction. See figure above for reference.

The resolution is then calculated from:

resolution = \frac{\alpha}{2 \tan(\theta)}

Usage

ws = Load('INTER00013460')
res = NRCalculateSlitResolution(Workspace = ws, TwoTheta = 0.7 * 2)
print("Resolution: {:.4f}".format(res))

Resolution: 0.0340

Categories: AlgorithmIndex | Reflectometry\ISIS

Source

C++ source: NRCalculateSlitResolution.cpp (last modified: 2019-06-04)

C++ header: NRCalculateSlitResolution.h (last modified: 2018-10-05)