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# NRCalculateSlitResolution v1¶

## Summary¶

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

CalculateSlits

## 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¶

Proof

\begin{align}\begin{aligned}\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)\end{aligned}\end{align}

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