AlignDetectors v1


AlignDetectors dialog.


AlignDetectors is deprecated (on 2021-01-04). Use ConvertUnits instead.


Performs a unit change from TOF to dSpacing, correcting the X values to account for small errors in the detector positions.


Name Direction Type Default Description
InputWorkspace Input MatrixWorkspace Mandatory A workspace with units of TOF
OutputWorkspace Output MatrixWorkspace Mandatory The name to use for the output workspace
CalibrationFile Input string   Optional: The .cal file containing the position correction factors. Either this or OffsetsWorkspace needs to be specified. Allowed extensions: [‘.h5’, ‘.hd5’, ‘.hdf’, ‘.cal’]
CalibrationWorkspace Input TableWorkspace   Optional: A Workspace containing the calibration information. Either this or CalibrationFile needs to be specified.
OffsetsWorkspace Input OffsetsWorkspace   Optional: A OffsetsWorkspace containing the calibration offsets. Either this or CalibrationFile needs to be specified.


As of 2021-01-04, this algorithm is officially deprecated. As a result, developers and users are recommend to use ApplyDiffCal, followed by ConvertUnits, followed by ApplyDiffCal (ClearCalibration=true) to produce the equivalent results.


This algorithm applies a calibration table to convert a workspace from time-of-flight to dSpacing as described below. The equation in GSAS converts from d-spacing (\(d\)) to time-of-flight (\(TOF\)) by the equation:

\[TOF = DIFC * d + DIFA * d^2 + TZERO\]

The manual describes these terms in more detail. Roughly, \(TZERO\) is related to the difference between the measured and actual time-of-flight base on emission time from the moderator, \(DIFA\) is an empirical term (ideally zero), and \(DIFC\) is

\[DIFC = \frac{2m_N}{h} L_{tot} sin \theta\]

Measuring peak positions using a crystal with a very well known lattice constant will give a good value for converting the data. The d-spacing of the data will be calculated using whichever equation below is appropriate for solving the quadratic.

When \(DIFA = 0\) then the solution is just for a line and

\[d = \frac{TOF - TZERO}{DIFC}\]

For the case of needing to solve the actual quadratic equation

\[d = \frac{-DIFC}{2 DIFA} \pm \sqrt{\frac{TOF}{DIFA} + \left(\frac{DIFC}{2 DIFA}\right)^2 - \frac{TZERO}{DIFA}}\]

Here the positive root is used when \(DIFA > 0\) and the negative when \(DIFA < 0\).

This algorithm always uses a calibration table which it either reads from the CalibrationWorkspace property, or uses ConvertDiffCal to produce from the OffsetsWorkspace.


The workspace that this algorithms outputs is a ragged workspace.

Restrictions on the input workspace

The input workspace must contain histogram or event data where the X unit is time-of-flight and the Y data is raw counts. The instrument associated with the workspace must be fully defined because detector, source & sample position are needed if an OffsetsWorkspace is provided.


Example: Use offset to move peak in Dspace

ws = CreateSampleWorkspace("Event",NumBanks=1,BankPixelWidth=1)
ws = MoveInstrumentComponent(Workspace='ws', ComponentName='bank1', X=0.5, RelativePosition=False)
wsD = ConvertUnits(InputWorkspace='ws',  Target='dSpacing')
maxD = Max(wsD)
offset = GetDetectorOffsets(InputWorkspace='wsD', DReference=2.5, XMin=2, XMax=3)
wsA = AlignDetectors(InputWorkspace='ws', OutputWorkspace='wsA', OffsetsWorkspace='offset')
maxA = Max(wsA)
print("Peak in dSpace {:.11f}".format(maxD.readX(0)[0]))
print("Peak from calibration {:.10f}".format(maxA.readX(0)[0]))


Peak in dSpace 2.66413186052
Peak from calibration 2.5622683421

Categories: AlgorithmIndex | Diffraction\Calibration | Deprecated


C++ header: AlignDetectors.h

C++ source: AlignDetectors.cpp