3.5

LoadMuonNexus v1

../_images/LoadMuonNexus-v1_dlg.png

LoadMuonNexus dialog.

Summary

The LoadMuonNexus algorithm will read the given NeXus Muon data file Version 1 and use the results to populate the named workspace. LoadMuonNexus may be invoked by LoadNexus if it is given a NeXus file of this type.

Properties

Name Direction Type Default Description
Filename Input string Mandatory The name of the Nexus file to load. Allowed extensions: [‘.nxs’]
OutputWorkspace Output Workspace Mandatory The name of the workspace to be created as the output of the algorithm. For multiperiod files, one workspace will be generated for each period
SpectrumMin Input number Optional Index number of the first spectrum to read (default 1)
SpectrumMax Input number Optional Index of last spectrum to read (default the last spectrum)
SpectrumList Input int list   Array, or comma separated list, of indexes of spectra to load
AutoGroup Input boolean False Determines whether the spectra are automatically grouped together based on the groupings in the NeXus file, only for single period data (default no)
EntryNumber Input number 0 0 indicates that every entry is loaded, into a separate workspace within a group. A positive number identifies one entry to be loaded, into one worskspace
MainFieldDirection Output string   Output the main field direction if specified in Nexus file (default Transverse). Allowed values: [‘Transverse’, ‘Longitudinal’]
TimeZero Output number   Time zero in units of micro-seconds (default to 0.0)
FirstGoodData Output number   First good data in units of micro-seconds (default to 0.0)
DeadTimeTable Output Workspace   Table or a group of tables containing detector dead times
DetectorGroupingTable Output Workspace   Table or a group of tables with information about the detector grouping stored in the file (if any)

Description

The algorithm LoadMuonNexus will read a Muon Nexus data file (original format) and place the data into the named workspace. The file name can be an absolute or relative path and should have the extension .nxs or .NXS. If the file contains data for more than one period, a separate workspace will be generated for each. After the first period the workspace names will have “_2”, “_3”, and so on, appended to the given workspace name. The optional parameters can be used to control which spectra are loaded into the workspace. If SpectrumMin and SpectrumMax are given, then only that range of data will be loaded. If a SpectrumList is given, then those values will be loaded. If a range and a list are supplied, the algorithm will load all the specified spectra.

  • TODO get XML descriptions of Muon instruments. This data is not in existing Muon Nexus files.
  • TODO load the spectra detector mapping. This may be very simple for Muon instruments.

Time series data

The log data in the Nexus file (NX_LOG sections) will be loaded as TimeSeriesProperty data within the workspace. Time is stored as seconds from the Unix epoch.

Errors

The error for each histogram count is set as the square root of the number of counts.

Time bin data

The corrected_times field of the Nexus file is used to provide time bin data and the bin edge values are calculated from these bin centre times.

Multiperiod data

To determine if a file contains data from more than one period the field switching_states is read from the Nexus file. If this value is greater than one it is taken to be the number of periods, N_p of the data. In this case the N_s spectra in the histogram_data field are split with N_s/N_p assigned to each period.

Dead times and detector grouping

Muon Nexus v1 files might contain dead time and detector grouping informationl. These are loaded as TableWorkspaces of the format accepted by ApplyDeadTimeCorr and MuonGroupDetectors accordingly. These are returned if and only if names are specified for the properties. For multi-period data workspace groups might be returned, if information in the Nexus files contains this information for each period.

ChildAlgorithms used

The ChildAlgorithms used by LoadMuonNexus are:

  • LoadMuonLog - this reads log information from the Nexus file and uses it to create TimeSeriesProperty entries in the workspace.
  • LoadInstrument - this algorithm looks for an XML description of the instrument and if found reads it.
  • LoadIntstrumentFromNexus - this is called if the normal LoadInstrument fails. As the Nexus file has limited instrument data, this only populates a few fields.

Usage

Note

To run these usage examples please first download the usage data, and add these to your path. In MantidPlot this is done using Manage User Directories.

Example - Load ISIS muon MUSR dataset:

# Load MUSR dataset
ws = LoadMuonNexus(Filename="MUSR00015189.nxs",EntryNumber=1)
print "Workspace has ",  ws[0].getNumberHistograms(), " spectra"

Output:

Workspace has  64  spectra

Example - Load event nexus file with time filtering:

# Load some spectra
ws = LoadMuonNexus(Filename="MUSR00015189.nxs",SpectrumMin=5,SpectrumMax=10,EntryNumber=1)
print "Workspace has ",  ws[0].getNumberHistograms(), " spectra"

Output:

Workspace has  6  spectra

Example - Load dead times into table:

# Load some spectra
ws = LoadMuonNexus(Filename="emu00006473.nxs",SpectrumMin=5,SpectrumMax=10,DeadTimeTable="deadTimeTable")
tab = mtd['deadTimeTable']
for i in range(0,tab.rowCount()):
    print tab.cell(i,0), tab.cell(i,1)

Output:

5 0.00161112251226
6 0.00215016817674
7 0.0102171599865
8 0.00431686220691
9 0.00743605662137
10 0.00421147653833

Example - Load detector grouping into table:

# Load some spectra
ws = LoadMuonNexus(Filename="emu00006473.nxs",SpectrumList="1,16,17,32",DetectorGroupingTable="detectorTable")
tab = mtd['detectorTable']
for i in range(0,tab.rowCount()):
    print tab.cell(i,0)

Output:

[ 1 16]
[17 32]

Categories: Algorithms | DataHandling | Nexus | Muon

Source

C++ source: LoadMuonNexus.cpp

C++ header: LoadMuonNexus.h