3.12

PowderDiffILLDetEffCorr v1

../_images/PowderDiffILLDetEffCorr-v1_dlg.png

PowderDiffILLDetEffCorr dialog.

Summary

Performs detector efficiency correction calculation for powder diffraction instrument D20 at ILL.

Properties

Name Direction Type Default Description
CalibrationRun Input string Mandatory File path of calibration run. Must be a detector scan. Allowed values: [‘nxs’]
CalibrationFile Input string   Optional file containing previous calibration constants. Allowed values: [‘nxs’]
CalibrationMethod Input string Median The method of how the calibration constant of a pixel relative to the neighbouring one is derived. Allowed values: [‘Median’, ‘Mean’, ‘MostLikelyMean’]
InterpolateOverlappingAngles Input boolean False Wheter to interpolate 2theta values for overlapping regions between neighbouring cells.
NormaliseTo Input string None Normalise to time, monitor or ROI counts before deriving the calibration. Allowed values: [‘None’, ‘Monitor’, ‘ROI’]
ROI Input dbl list 0,100 Regions of interest for normalisation [in scattering angle in degrees].
ExcludedRange Input dbl list   2theta regions to exclude from the computation of relative calibration constants [in scattering angle in degrees].
PixelRange Input int list 1,3072 Range of the pixel numbers to compute the calibration factors for. For the other pixels outside the range, the factor will be set to 1.
OutputResponseWorkspace Output MatrixWorkspace   Output workspace containing the summed diffraction patterns of all the pixels.
OutputWorkspace Output MatrixWorkspace Mandatory Output workspace containing the detector efficiencies for each pixel.

Description

This algorithm calculates the detector efficiency corrections for the instrument D20 at the ILL.

It performs as follows:

  1. Takes the first cell response as a function of scattering angle as a reference
  2. Takes the second cell, and divides the reference to the second cell response in the overlapping region in terms of scattering angle. This results in the array of relative response ratios.
  3. Uses one of the 3 suggested options to compute the relative calibration factor from the array of relative response ratios. This factor is saved in the output as the calibration factor for the second cell.
  4. The response of the second cell is scaled up with that factor, and then merged (in the overlapping region) with the reference using WeightedMean.
  5. Repeat from Step 2 for the next cell and so on until the last cell.

For the zero-counting cells, the calibration factor cannot be computed, and it will be set to 1. Cells are treated as zero-counting, if they count zero more than 80% of time.

After the calibration factors are computed for all the cells, they are divided by the median of all the factors (excluding the zero counting cells), in order to absolutely normalise the calibration curve.

Input

The input must be a single detector-scan run in .nxs format produced for vanadium.

Optionally the previously derived calibration file can be seeded, and the algorithm will then compute the residual calibration factors on top of that.

Method

You can choose the method of how the relative calibration factor is extracted from the relative response ratios (Step 3). It can be the Median (default), Mean or MostLikelyMean.

Excluded range

Provide ranges in scattering angle in degrees, to exclude non-desired regions, e.g. the beam stop. Multiple regions can be set, -20,0,10,20 will exclude [-20,0] and [10,20]. This exclusion will happen at Step 3.

Pixel range

Provide the range of detector cells to compute the calibration factors for. For the rest of the cells, the factor will be set to 1.

Output

Output will be a single-column workspace containing the calibration factors for each cell. This should be normally saved with SaveNexusProcessed to be later used in PowderDiffILLReduction.

Optionally, the full absolute response resulted from the combination of the data for all the cells (see Step 4 above) can also be output.

Usage

Example - PowderDiffILLDetEffCorr

calib = PowderDiffILLDetEffCorr(CalibrationRun='967076', OutputWorkspace='constants')
print("Reduced workspace contains {0} constants, one for each cell.".format(calib.getNumberHistograms()))

Output:

Reduced workspace contains 3072 constants, one for each cell.

Categories: Algorithms | ILL\Diffraction | Diffraction\Reduction | Diffraction\Calibration

Source

Python: PowderDiffILLDetEffCorr.py (last modified: 2018-03-07)