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LoadVesuvio v1

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Summary

Loads raw data produced by the Vesuvio instrument at ISIS.

See Also

LoadEmptyVesuvio, LoadRaw

Properties

Name	Direction	Type	Default	Description
Filename	Input	string	Mandatory	The run numbers that should be loaded. E.g.14188 - for single run14188-14195 - for summed consecutive runs14188,14195 - for summed non-consecutive runs
SpectrumList	Input	string	Mandatory	The spectrum numbers to load. A dash will load a range and a semicolon delimits spectra to sum
Mode	Input	string	DoubleDifference	The difference option. Valid values: [‘SingleDifference’, ‘DoubleDifference’, ‘ThickDifference’, ‘FoilOut’, ‘FoilIn’, ‘FoilInOut’]. Allowed values: [‘SingleDifference’, ‘DoubleDifference’, ‘ThickDifference’, ‘FoilOut’, ‘FoilIn’, ‘FoilInOut’]
InstrumentParFile	Input	string		An optional IP file. If provided the values are used to correct the default instrument values and attach the t0 values to each detector. Allowed values: [‘dat’, ‘par’]
SumSpectra	Input	boolean	False	If true then the final output is a single spectrum containing the sum of all of the requested spectra. All detector angles/parameters are averaged over the individual inputs
LoadMonitors	Input	boolean	False	If true then the monitor data is loaded and will be output by the algorithm into a separate workspace.
LoadLogFiles	Input	boolean	True	If true, then the log files for the specified runs will be loaded.
OutputWorkspace	Output	Workspace	Mandatory	The name of the output workspace.

Description

The Vesuvio instrument at ISIS produces RAW files in the standard format. However, due to the unique design of the instrument the raw counts from the input files must be manipulated before they are considered useful.

This algorithm wraps calls to LoadRaw and computes the counts (\(\mu \text{s}^{-1}\)) using the foil-cycling method described here.

The output is point data and not a histogram.

IP File

There is an option to specify an ascii instrument parameter file to specify new detector positions along with a t0 delay time parameter for each detector.

Information on Vesuvio operation

Vesuvio as an instrument has the ability to analyse both forward and back scattering from the sample. In addition, when data is collected, foils are put in front of, or remove from, the detectors. The foils are different for forward and back scattering. In forward scattering, there are only 2 foils states, the foil is either in front of the detector (foil in) or not infront of the detector (foil out). In back scattering there are 3 foil states. Like in forward scattering there is both a foil in and foil out state, but in addition to this there is also a foil thick state which is where a thicker foil is placed in front of the detector.

Vesuvio allows for measurements to be taken in different periods:

• 2 period data is for only analysing forward scattering (2 foil states - foil out/foil in)

• 3 period data is for only analysing back scattering (3 foil states - foil out/foil in/ foil thick)

• 6 period data is for both backward and forward scattering (combination of forward and back scattering states)

When loading data from .RAW files using this algorithm, several differencing modes can be used:

• Single Difference: Foil In minus Foil Out (available in both forward and back scattering)

• Thick Difference : Foil Thick minus Foil Out (only available in back scattering - as forward scattering has no foil Thick)

• Double Difference: Foil In minus Foil Out combined with Foil Thick minus Foil Out (only available in back scattering - as forward scattering has no foil Thick)

From the above modes of operation on Vesuvio we can deduce a table of valid combinations of scattering and differencing for each period. This is shown in the tables below:

2 period

Gold foils only move in forward scattering, so only differencing in forward scattering is valid.

Scattering	Single Difference	Thick Difference	Double Difference
Forward	Valid	NEVER	NEVER
Back	Not Valid	Not Valid	Not Valid

3 period

Gold foils only move in back scattering, so only differencing in back scattering is valid.

Scattering	Single Difference	Thick Difference	Double Difference
Forward	Not Valid	NEVER	NEVER
Back	Valid	Valid	Valid

6 period

All are valid (with the exclusion of Thick Difference and Double difference in forward scattering - never valid)

Scattering	Single Difference	Thick Difference	Double Difference
Forward	Valid	NEVER	NEVER
Back	Valid	Valid	Valid

Usage

Load a single file & spectrum with default difference:

tof = LoadVesuvio("14188",SpectrumList=135)

print("Number of spectra: {}".format(tof.getNumberHistograms()))

Output:

Number of spectra: 1

Sum runs on single spectrum with default difference:

tof = LoadVesuvio("14188-14193",SpectrumList=135)

print("Number of spectra: {}".format(tof.getNumberHistograms()))

Output:

Number of spectra: 1

Sum runs on a range of spectra with default difference:

tof = LoadVesuvio("14188-14193",SpectrumList="135-142")

print("Number of spectra: {}".format(tof.getNumberHistograms()))

Output:

Number of spectra: 8

Sum runs and spectra on a range of spectra with default difference:

tof = LoadVesuvio("14188-14193",SpectrumList="135-142", SumSpectra=True)

print("Number of spectra: {}".format(tof.getNumberHistograms()))

Output:

Number of spectra: 1

Sum runs and spectra on a range of spectra using single difference method:

tof = LoadVesuvio("14188-14193",SpectrumList="135-142", SumSpectra=True,
                  Mode="SingleDifference")

print("Number of spectra: {}".format(tof.getNumberHistograms()))

Output:

Number of spectra: 1

Categories: AlgorithmIndex | DataHandling\Raw

Source

Python: LoadVesuvio.py