$$\renewcommand\AA{\unicode{x212B}}$$

## Summary¶

The LoadMuonNexus algorithm will read the given NeXus Muon data file Version 2 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

0

Index number of the first spectrum to read

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. If a range and a list of spectra are both supplied, all the specified spectra will be loaded.

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). Version 1 only.

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 workspace

MainFieldDirection

Output

string

Output the main field direction if specified in Nexus file (run/instrument/detector/orientation, default longitudinal). Version 1 only. 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)

LastGoodData

Output

number

Last good data in the OutputWorkspace’s spectra

TimeZeroList

Output

dbl list

A vector of time zero values

TimeZeroTable

Output

Workspace

TableWorkspace containing time zero values per spectra.

CorrectTime

Input

boolean

True

Boolean flag controlling whether time should be corrected by timezero.

Output

Workspace

Table or a group of tables containing detector dead times. Version 1 only.

DetectorGroupingTable

Output

Workspace

Table or a group of tables with information about the detector grouping stored in the file (if any). Version 1 only.

## 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. For single period data, the optional parameters can be used to control which spectra are loaded into the workspace. If spectrum_min and spectrum_max are given, then only that range to data will be loaded. If a spectrum_list is given than those values will be loaded.

• TODO get XML descriptions of Muon instruments. This data is not in existing Muon Nexus files.

### Version Identification¶

To be identified as a version 2 muon nexus file, the nexus file must have a IDF_version or idf_version item in its main group with an integer value of 2 and also a definition item with string value "muonTD" or "pulsedTD", else it will be identified as version 1.

The following properties apply only to Version 1:

• AutoGroup

• MainFieldDirection

• DetectorGroupingTable

### 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.

Here are more details of data loaded from the Nexus file:

Description of Data

Found in Nexus file (within the main entry)

Placed in Workspace (Workspace2D) or output

Detector Data

First group of class NXData (henceforth referred as [DET])

Histogram Data of workspace

Instrument

group Instrument

Spectrum of each workspace index

[DET]/spectrum_index

Spectra-Detector mapping of workspace (see below)

Title (optional)

title

title in workspace

Note orcomment (optional)

note

comment in workspace

Time Zero (optional)

instrument/detector_fb/time_zero if found

TimeZero property

First good time (optional)

instrument/detector_fb/first_good_time if found

FirstGoodData property

Run

various places as shown later on

Run object of workspace

Sample name

sample/name

name in Sample Object of workspace

Time series

sample/ groups of class NXLog

#### Run Object¶

Nexus

Workspace run object

title

run_title

(data)

nspectra

start_time

run_start

end_time

run_end

run/good_total_frames

goodfrm

run/number_periods

nperiods

(start & end times)

dur_secs

(data) indicates that the number is got from the histogram data in an appropriate manner.

#### Spectra-detector mapping¶

Unlike muon v1 NeXus files, v2 files have the possibility that one spectrum maps to multiple detectors. This mapping is handled as follows:

The spectrum numbers are in run/detector_fb/spectrum_index.

The spectrum spectrum_index[j] maps to detector_count[j] detectors. Their detector IDs are contained in detector_list, starting at the index detector_index[j].

If the above optional entries detector_count, detector_list and detector_index are not present in the file, it is assumed that the mapping is one-to-one (spectrum number = detector ID). This is the case for most ISIS data at the moment.

### Child Algorithms used¶

The ChildAlgorithms used by LoadMuonNexus are:

• LoadMuonNexus v1 - this loads the muon nexus file if not identified as version 2. It in turn uses the following child algorithm:

• LoadInstrument v1 - this algorithm looks for an XML description of the instrument and if found reads it.

• LoadInstrumentFromNexus v1 - this is called if the normal LoadInstrument fails. As the Nexus file has limited instrument data, this only populates a few fields.

## Previous Versions¶

### Version 1¶

Version 1 supports the loading version 1.0 of the muon nexus format. This is still in active use, if the current version of LoadMuonNexus detects that it has been asked to load a previous version muon nexus file it will call the previous version of the algorithm to perform the task.

Some algorithm properties apply to Version 1 only.

## Usage¶

Note

Example - Load ISIS muon MUSR dataset:

# Load MUSR dataset
print("Workspace has  {}  spectra".format(ws[0].getNumberHistograms()))


Output:

Workspace has  64  spectra


Example - Load event nexus file with time filtering:

# Load some spectra
print("Workspace has  {}  spectra".format(ws[0].getNumberHistograms()))


Output:

Workspace has  6  spectra


# Load some spectra
for i in range(0,tab.rowCount()):
print("{} {:.12f}".format(tab.cell(i,0), tab.cell(i,1)))


Output:

5 0.001611122512
6 0.002150168177
7 0.010217159986
8 0.004316862207
9 0.007436056621
10 0.004211476538


Categories: AlgorithmIndex | DataHandling\Nexus | Muon\DataHandling