4.2

PDConvertReciprocalSpace v1

../_images/PDConvertReciprocalSpace-v1_dlg.png

PDConvertReciprocalSpace dialog.

Summary

Transforms a Workspace2D between different reciprocal space functions.

Properties

Name Direction Type Default Description
InputWorkspace Input MatrixWorkspace Mandatory Input workspace with units of momentum transfer
From Input string S(Q) Function type in the input workspace. Allowed values: [‘S(Q)’, ‘F(Q)’, ‘FK(Q)’, ‘DCS(Q)’]
To Input string S(Q) Function type in the output workspace. Allowed values: [‘S(Q)’, ‘F(Q)’, ‘FK(Q)’, ‘DCS(Q)’]
OutputWorkspace Output Workspace Mandatory Output workspace

Description

The neutron diffraction is measuring the differential scattering cross section (DCS(Q) in the algorithm)

(1)\frac{d\sigma}{d\Omega} = \frac{N}{\phi d\Omega}

Here the N is the number of scattered neutrons in unit time in a solid angle d\Omega, and \phi is the incident neutron flux. The algorithm supports the following conversions:

(2)S(Q) = \frac{1}{N_{s} \langle b_{coh} \rangle^2}\frac{d\sigma}{d\Omega}(Q) - \frac{\langle b_{tot}^2 \rangle - \langle b_{coh} \rangle^2}{\langle b_{coh} \rangle^2}

(3)F(Q) = Q [S(Q) - 1]

(4)F_K(Q) = \langle b_{coh} \rangle^2 [S(Q) - 1] = \frac{\langle b_{coh} \rangle^2}{Q} F(Q)

where N_s is the number of scatters in the sample and both \langle b_{tot}^2 \rangle and \langle b_{coh} \rangle^2 are defined in the Materials concept page.

NOTE: This algorithm requires that SetSampleMaterial v1 is called prior in order to determine the \langle b_{tot}^2 \rangle and \langle b_{coh} \rangle^2 terms.

PyStoG

This algorithm uses the external project PyStoG and specifically uses the pystog.converter.Converter object. To modify the underlying algorithms, the following functions are used for the conversions.

Usage

import wget
import numpy as np
import matplotlib.pyplot as plt
from mantid.simpleapi import CreateWorkspace, SetSampleMaterial, PDConvertReciprocalSpace
from mantid import plots

# Grab the reciprocal data for argon
url = "https://raw.githubusercontent.com/marshallmcdonnell/pystog/master/tests/test_data/argon.reciprocal_space.dat"
filename = wget.download(url)
q, sq, fq_, fk_, dcs_ = np.loadtxt(filename, skiprows=2, unpack=True)

# Convert S(Q) to Mantid wksp
s_of_q = CreateWorkspace(DataX=q, DataY=sq,
                       UnitX="MomentumTransfer",
                       Distribution=True)
SetSampleMaterial(InputWorkspace=s_of_q, ChemicalFormula='Ar')
f_of_q=PDConvertReciprocalSpace(InputWorkspace=s_of_q, From='S(Q)', To='F(Q)')
fk_of_q=PDConvertReciprocalSpace(InputWorkspace=s_of_q, From='S(Q)', To='FK(Q)')
dcs_of_q=PDConvertReciprocalSpace(InputWorkspace=s_of_q, From='S(Q)', To='DCS(Q)')

fig, ax = plt.subplots(subplot_kw={'projection':'mantid'})
ax.plot(s_of_q,'k-', label='$S(Q)$')
ax.plot(f_of_q,'r-', label='$F(Q)$')
ax.plot(fk_of_q,'b-', label='$F_K(Q)$')
ax.plot(dcs_of_q,'g-', label='$d\sigma / d\Omega(Q)$')
ax.legend() # show the legend
fig.show()

The output should look like:

../_images/PDConvertReciprocalSpace.png

Categories: AlgorithmIndex | Diffraction\Utility

Source

Python: PDConvertReciprocalSpace.py (last modified: 2019-03-06)