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ComputeCalibrationCoefVan v1¶
Summary¶
Calculate coefficients for detector efficiency correction using the Vanadium data.
Properties¶
Name 
Direction 
Type 
Default 
Description 

VanadiumWorkspace 
Input 
Mandatory 
Input Vanadium workspace 

EPPTable 
Input 
Mandatory 
Input EPP table. May be produced by FindEPP algorithm. 

OutputWorkspace 
Output 
Mandatory 
Name the workspace that will contain the calibration coefficients 

Temperature 
Input 
number 
Optional 
Temperature during the experiment (in Kelvins) if temperature is not given in the sample logs or needs to be overriden. 
EnableDWF 
Input 
boolean 
True 
Enable or disable the DebyeWaller correction. 
Description¶
Algorithm creates a workspace with detector sensitivity correction coefficients using the given Vanadium workspace. The correction coefficients are calculated as follows.
Load the peak centre and sigma from the EPPTable. These values are used to calculate sum \(S_i\) as
\(S_i = \sum_{x = x_C  3\,\mathrm{fwhm}}^{x_C + 3\,\mathrm{fwhm}} Y_i(x)\)
where \(x_C\) is the peak centre position and \(Y_i(x)\) is the corresponding to \(x\) \(Y\) value for ith detector.
(If EnableDWF is true) Calculate the DebyeWaller factor according to [1]:
\(D_i = \exp\left[B_i\cdot\left(\frac{4\pi\sin\theta_i}{\lambda}\right)^2\right]\)
\(B_i = \frac{3\hbar^2\cdot 10^{20}}{2m_VkT_m}\cdot J(y)\)
where \(J(y) = 0.5\) if \(y < 10^{3}\), otherwise
\(J(y) = \int_0^1 x\cdot\mathrm{coth}\left(\frac{x}{2y}\right)\,\mathrm{d}x\)
where \(y=T/T_m\) is the ratio of the temperature during the experiment \(T\) to the Debye temperature \(T_m = 389K\), \(m_V\) is the Vanadium atomic mass (in kg) and \(\theta_i\) is the polar angle of the ith detector. By default, the temperature is read from the sample logs. The log entry can be given as the ‘temperature_sample_log’ in the IPF, otherwise ‘temperature’ entry is used. If the log is missing, or incorrect, the Temperature input property can be used instead.
Warning
If no temperature is available, or is set to an invalid value, \(T\) = 293K will be taken for the DebyeWaller factor calculation. The algorithm will log a warning in this case.
(If EnableDWF is true) Finally, the correction coefficients \(K_i\) are calculated as
\(K_i = \frac{S_i}{D_i}\)
Workspace containing these correction coefficients is created as an output and can be used as a RHS workspace in Divide v1 to apply correction to the LHS workspace.
Restrictions on the input workspaces¶
The valid input workspace:
must have an instrument set
must have a wavelength sample log
Restrictions for EPPTable:
number of rows of the table must match to the number of histograms of the input workspace.
table must have the PeakCentre and Sigma columns.
Note
The input EPPTable can be produced using the FindEPP v2 algorithm.
Usage¶
Note
To run these usage examples please first download the usage data, and add these to your path. In Mantid this is done using Manage User Directories.
Example
# load Vanadium data
wsVana = LoadMLZ(Filename='TOFTOFTestdata.nxs')
# find elastic peak positions
epptable = FindEPP(wsVana)
# calculate correction coefficients
wsCoefs = ComputeCalibrationCoefVan(wsVana, epptable)
print(f'Spectrum 4 of the output workspace is filled with: {wsCoefs.readY(999)[0]:.1f}')
# wsCoefs can be used as rhs with Divide algorithm to apply correction to the data
wsCorr = wsVana/wsCoefs
print(f'Spectrum 4 of the input workspace is filled with: {wsVana.readY(999)[0]:.1f}')
print(f'Spectrum 4 of the corrected workspace is filled with: {wsCorr.readY(999)[0]:.5f}')
Output:
Spectrum 4 of the output workspace is filled with: 6894.8
Spectrum 4 of the input workspace is filled with: 1.0
Spectrum 4 of the corrected workspace is filled with: 0.00015
References¶
Categories: AlgorithmIndex  CorrectionFunctions\EfficiencyCorrections
Source¶
Python: ComputeCalibrationCoefVan.py