Table of Contents
Corrects the time of flight of an indirect geometry instrument by a time offset that is linearly dependent on the wavelength of the neutron after passing through the moderator.
Name | Direction | Type | Default | Description |
---|---|---|---|---|
InputWorkspace | Input | MatrixWorkspace | Mandatory | The name of the input workspace, containing events and/or histogram data, in units of time-of-flight |
Gradient | Input | number | Optional | Wavelength dependent TOF shift, units in microsec/Angstrom. Overrides the value stored in the instrument object |
Intercept | Input | number | Optional | TOF shift, units in microseconds. Overrides the valuestored in the instrument object |
OutputWorkspace | Output | MatrixWorkspace | Mandatory | The name of the output workspace |
This algorithm Corrects the time of flight (TOF) of an indirect geometry instrument by substracting a time offset t0 linearly dependent on the wavelength of the neutron when emitted through the moderator. This algorithm is suitable to data reduction of indirect instruments featuring a neutron flux with a narrow distribution of wavelengths. A empirical formula for the correction, stored in the instrument definition file, is taken as linear on the initial neutron wavelength λi: t0=a∗λi+b. Gradient a is in units of microsec/Angstrom and Intercept b is in units of microsec. Below is the example XML code included in BASIS beamline parameters file.
<!-- Moderator Tzero/LambdaZero Parameters -->
<parameter name="Moderator.TimeZero.Gradient">
<value val="11.967"/>
</parameter>
<parameter name="Moderator.TimeZero.Intercept">
<value val="-5.0"/>
</parameter>
The recorded TOF: TOF=t0+ti+tf, with
This algorithm will replace TOF with TOF′=TOF−t0=ti+tf
For an indirect geometry instrument, λi is not known but the final energy, Ef, selected by the analyzers is known. For this geometry:
and b′=b with b′ in units of microseconds.
Putting all together: TOF′=LiLi+a′⋅(TOF−tf−b′)+tf, with [TOF’]=microsec
If the detector is a monitor, then we can treat it as both sample and detector. Thus, we use the previous formula inserting the time from sample to detector tf=0 and with the initial fligh path Li as the distance from source to monitor.
Categories: AlgorithmIndex | CorrectionFunctions\InstrumentCorrections