CalculateGammaBackground dialog.
Table of Contents
Calculates the background due to gamma rays produced when neutrons are absorbed by shielding.
| Name | Direction | Type | Default | Description |
|---|---|---|---|---|
| InputWorkspace | Input | MatrixWorkspace | Mandatory | An input workspace containing TOF data |
| ComptonFunction | InOut | Function | Mandatory | Function that is able to compute the mass spectrum for the input dataThis will usually be the output from the Fitting |
| WorkspaceIndexList | Input | int list | Indices of the spectra to include in the correction. If provided, the output only include these spectra (Default: all spectra from input) | |
| BackgroundWorkspace | Output | MatrixWorkspace | Mandatory | A new workspace containing the calculated background. |
| CorrectedWorkspace | Output | MatrixWorkspace | Mandatory | A new workspace containing the calculated background subtracted from the input. |
This algorithm is currently designed to be used by the Vesuvio spectrometer at ISIS to correct for background produced by photons that are created when the neutrons are absorbed by the shielding on the instrument. It only corrects the forward scattering detector banks - spectrum numbers 135-198.
Two workspaces are produced: the calculated background and a corrected
workspace where the input workspace has been corrected by the
background. The background is computed by a simple simulation of the
expected count across all of the foils. The corrected workspace counts
are computed by calculating a ratio of the expected counts at the
detector to the integrated foil counts (
) and then the
final corrected count rate 
is defined as
.
Example: Correcting the first spectrum
###### Simulates LoadVesuvio with spectrum number 135-136 #################
tof_ws = CreateSimulationWorkspace(Instrument='Vesuvio',BinParams=[50,0.5,562],UnitX='TOF')
tof_ws = CropWorkspace(tof_ws,StartWorkspaceIndex=134,EndWorkspaceIndex=135) # index one less than spectrum number
tof_ws = ConvertToPointData(tof_ws)
SetInstrumentParameter(tof_ws, ParameterName='t0',ParameterType='Number',Value='0.5')
SetInstrumentParameter(tof_ws, ParameterName='sigma_l1', ParameterType='Number', Value='0.021')
SetInstrumentParameter(tof_ws, ParameterName='sigma_l2', ParameterType='Number', Value='0.023')
SetInstrumentParameter(tof_ws, ParameterName='sigma_tof', ParameterType='Number', Value='0.3')
SetInstrumentParameter(tof_ws, ParameterName='sigma_theta', ParameterType='Number', Value='0.028')
SetInstrumentParameter(tof_ws, ParameterName='hwhm_lorentz', ParameterType='Number', Value='24.0')
SetInstrumentParameter(tof_ws, ParameterName='sigma_gauss', ParameterType='Number', Value='73.0')
# Algorithm allows separate parameters for the foils
SetInstrumentParameter(tof_ws, ComponentName='foil-pos0', ParameterName='hwhm_lorentz',
ParameterType='Number', Value='144.0')
SetInstrumentParameter(tof_ws, ComponentName='foil-pos0', ParameterName='sigma_gauss',
ParameterType='Number', Value='20.0')
SetInstrumentParameter(tof_ws, ComponentName='foil-pos1', ParameterName='hwhm_lorentz',
ParameterType='Number', Value='144.0')
SetInstrumentParameter(tof_ws, ComponentName='foil-pos1', ParameterName='sigma_gauss',
ParameterType='Number', Value='20.0')
###########################################################################
mass_function = "name=GaussianComptonProfile,Mass=1.0079,Width=0.4,Intensity=1.1"
corrected, background = CalculateGammaBackground(tof_ws, ComptonFunction=mass_function,
WorkspaceIndexList=0)
print "First 5 values of input:", tof_ws.readY(0)[0:4]
print "First 5 values of background:", background.readY(0)[0:4]
print "First 5 values of corrected:", corrected.readY(0)[0:4]
Output:
First 5 values of input: [ 1. 1. 1. 1.]
First 5 values of background: [ 1.00053361 1.00054704 1.00056072 1.00057468]
First 5 values of corrected: [-0.00053361 -0.00054704 -0.00056072 -0.00057468]
Example: Correcting all spectra
###### Simulates LoadVesuvio with spectrum number 135-136 #################
tof_ws = CreateSimulationWorkspace(Instrument='Vesuvio',BinParams=[50,0.5,562],UnitX='TOF')
tof_ws = CropWorkspace(tof_ws,StartWorkspaceIndex=134,EndWorkspaceIndex=135) # index one less than spectrum number5
tof_ws = ConvertToPointData(tof_ws)
SetInstrumentParameter(tof_ws, ParameterName='t0',ParameterType='Number',Value='0.5')
SetInstrumentParameter(tof_ws, ParameterName='sigma_l1', ParameterType='Number', Value='0.021')
SetInstrumentParameter(tof_ws, ParameterName='sigma_l2', ParameterType='Number', Value='0.023')
SetInstrumentParameter(tof_ws, ParameterName='sigma_tof', ParameterType='Number', Value='0.3')
SetInstrumentParameter(tof_ws, ParameterName='sigma_theta', ParameterType='Number', Value='0.028')
SetInstrumentParameter(tof_ws, ParameterName='hwhm_lorentz', ParameterType='Number', Value='73.0')
SetInstrumentParameter(tof_ws, ParameterName='sigma_gauss', ParameterType='Number', Value='24.0')
###########################################################################
mass_function = "name=GaussianComptonProfile,Mass=1.0079,Width=0.4,Intensity=1.1"
corrected, background = CalculateGammaBackground(tof_ws, ComptonFunction=mass_function)
print "Number of background spectra:", background.getNumberHistograms()
print "Number of corrected spectra:", corrected.getNumberHistograms()
Output:
Number of background spectra: 2
Number of corrected spectra: 2
Categories: Algorithms | CorrectionFunctions\BackgroundCorrections