\(\renewcommand\AA{\unicode{x212B}}\)

Scripting SANS Reductions¶

Introduction ¶

SANS data from ISIS can be analysed using Python commands. Below is an example of a basic reduction on LOQ.

from ISISCommandInterface import *

LOQ()
MaskFile('MASK.094AA')

AssignSample('54431.raw')
TransmissionSample('54435.raw', '54433.raw')
AssignCan('54432.raw')
TransmissionCan('54434.raw', '54433.raw')

WavRangeReduction(3, 9)

To configure the reduction the following commands are available once the ISISCommandInterface module has been imported, using the following command:

from ISISCommandInterface import *

These commands are given here in the order they are likely to be found in a script file although, except were stated, the order does not matter:

`LOQ()` `SANS2D()`¶

This specifies which instrument the data was collected from. Either LOQ() or SANS2D(). The layout of the detector banks and detector efficiency files are stored here.

This line must be included and before the MaskFile() line.

`UserPath(path)`¶

Sets the directory in which Mantid should look for user settings file if a full path was not specified.

This must be specified before the MaskFile() line to have any effect.

This can be used to specify an extra directory in which Mantid will look for run files. The directories that have been set in the Manage User Directories dialog, or equivalently the Mantid.user.properties file, are also checked.

`MaskFile(file_name)`¶

This settings file can be either a full path or a filename found in the UserPath(). The settings here are overridden by the commands listed below.

UserPath("C:/SANS/masks")
MaskFile("MASK.09A") # or MaskFile("C:/SANS/masks/MASK.09A")

`AssignSample(sample_run, reload=True, period)`¶

Specifies the run to analyse using the format InstRun#.extension, e.g. SANS2D7777.nxs. This is one of the few commands that executes Mantid algorithms when called, the effects of most commands are only felt after the reduction starts. On calling this function the experimental run is loaded and component positions are changed (normally the detector bank and sample). Currently only reload=true is supported.

`TransmissionSample(sample, direct, reload=True, period_t, period_d)`¶

Specifies the runs that will be used to calculate the transmission fraction for the sample run. sample contains transmission monitor counts data for the sample when the sample is present, direct contains similar counts data when the sample position is empty (direct beam). The workspaces are loaded and the transmission IDF, if one exists for the instrument, is loaded into the workspaces when this command is encountered. The transmission fraction is calculated later. The period_t and period_d are used when there are multi-period files and specify the period to use for the sample and direct run respectively.

`AssignCan(can_run, reload=True, period)`¶

The can is a scattering run made under the same conditions as the experimental run but only the sample container is in the sample position. Hence allowing the effect of the container to be removed. The run is specified using instrumentrunnumber.extension, e.g. SANS2D7777.nxs. On calling this function the run is loaded to a workspace and the detector banks and other components are moved as applicable. Currently only reload=true is supported.

`TransmissionCan(can, direct, reload=True, period_t, period_d)`¶

Specify the transmission and direct beam runs that will be used for the analysis of the can run. The runs are loaded and with transmission IDF, if applicable, when Python encounters this command.

`SetMonitorSpectrum(specNum, interp=False)`¶

Specifies the number of the TOF spectrum that will be used to for monitor normalisation. This value will be used in the next reduction that is called (e.g. with WavRangeReduction()).

`TransFit(mode, lambdamin, lambdamax)`¶

Sets the method and range over which to calculate a fit for the variation of transmission fraction with wavelength. These arguments are passed to the algorithm CalculateTransmission v1. There is an extra fit mode Off which causes the unfitted workspace produced by CalculateTransmission v1 to be used and lambdamin or lambdamax then have no effect.

`Detector(det_name)`¶

Sets the detector bank to use for the reduction e.g. front-detector. The lowest angle detector is assumed if this line is not given.

`SetPhiLimit(phimin, phimax, use_mirror=True)`¶

Call this function to restrict the analysis to sectors of the detector. Phimin and phimax define the limits of the sector where phi=0 is the x-axis and phi=90 is the y-axis. Setting use_mirror to true causes the mirror sector to be included.

`WavRangeReduction(wav_start, wav_end, full_trans_wav, name_suffix)`¶

Assuming the mask file contains the correct analysis details one can proceed to calculate \(I(Q)\) using the WavRangeReduction() function, which can be executed with no arguments. The return value of WavRangeReduction() is the name of the final reduced workspace. This function calls many algorithms ending with a call to Q1D v2 or Qxy v1.

wav_start: the first wavelength to be in the output data.
wav_end: the last wavelength in the output data.

`BatchReduce(filename, format, plotresults=False, saveAlgs={'SaveRKH':'txt'},verbose=False, centreit=False)`¶

This analyses a list of files to analyse from a file, it calls WavRangeReduction. The function is available after the following import:

from SANSBatchMode import *

The first argument is the name of a CSV file, where each line specifies the data for a single reduction (in this format). The format argument is used to specify whether to load raw or nexus files and saveAlgs is a Python dictionary that contains the name of the save algorithm to use and the extension that it should have. If two algorithms in the dictionary use the same extension the first file will be overwritten!

`AddRuns(runs, instrument ='sans2d', saveAsEvent=False, binning = "Monitors", isOverlay = False, time_shifts = None, defType='.nxs', rawTypes=('.raw', '.s*', 'add','.RAW'), lowMem=False)`¶

This file adds a list of run files. The runs variable holds a list of runs which are to be added. The variable instrument specifies which instrument is currently being used. The variable saveAsEvent allows the user to add multiple event files in a combined event file. The isOverlay flag determines if the times of the events and sample logs should be placed on top of each other. This is only applied if saveAsEvent was selected. The time_shifts variable is a list of additional time shifts which will be applied if isOverlay is selected. Note that there has to be exactly one less time time shift than files to be added.

Category: Techniques