GetEiMonDet v3

../_images/GetEiMonDet-v3_dlg.png

GetEiMonDet dialog.

Summary

Calculates the kinetic energy of neutrons leaving the source based on the time it takes for them to travel between a monitor and a set of detectors.

Properties

Name Direction Type Default Description
DetectorWorkspace Input MatrixWorkspace Mandatory A workspace containing the detector spectra.
DetectorWorkspaceIndexType Input string   The type of indices in the optional index set; For optimal performance WorkspaceIndex should be preferred;. Allowed values: [‘WorkspaceIndex’, ‘SpectrumNumber’]
DetectorWorkspaceIndexSet Input int list   An optional set of spectra that will be processed by the algorithm; If not set, all spectra will be processed; The indices in this list can be workspace indices or possibly spectrum numbers, depending on the selection made for the index type; Indices are entered as a comma-separated list of values, and/or ranges; For example, ‘4,6,10-20,1000’;
MonitorWorkspace Input MatrixWorkspace   A Workspace containing the monitor spectrum; if empty, DetectorWorkspace will be used.
MonitorEPPTable Input TableWorkspace   An EPP table corresponding to MonitorWorkspace
MonitorIndex Input number Mandatory Usable monitor’s workspace index.
PulseInterval Input number Optional Interval between neutron pulses, in microseconds; taken from the sample logs, if not specified.
MaximumEnergy Input number Optional Multiple pulse intervals will be added to the flight time the until final energy is less than this value.
IncidentEnergy Output number   Calculated incident energy, in meV.

Description

This algorithm calculates the incident energy from the time-of-flight between one monitor and some detectors. The detector spectra are summed together using GroupDetectors and a Gaussian is fitted to both the monitor and summed detector data, the difference in the peak positions giving the time-of-flight. If the detector peak is before the monitor one, one pulse interval is added to the time-of-flight. The pulse interval can be given by the PulseInterval property or it is read from the sample logs under the entry pulse_interval (in seconds). It is also possible to specify a maximum expected neutron energy by MaximumEnergy. The pulse interval is added to the time-of-flight also if the calculated energy exceeds this value.

If the monitor peak has been previously fitted using FindEPP, one fitting step can be omitted by supplying the EPP table via MonitorEPPWorkspace.

If no MonitorWorkspace is specified, the monitor spectrum is expected to be in the detector workspace. DetectorWorkspaceIndexSet understands complex expression, for example 2,3,5-7,101 would use detectors 2, 3, 5, 6, 7, and 101 for the computation.

Usage

Example - simple incident energy calibration:

import numpy

spectrum = 'name = Gaussian, PeakCentre = 1000.0, Height = 500.0, Sigma = 30.0'
ws = CreateSampleWorkspace(WorkspaceType='Histogram', XUnit='TOF',
    XMin=100.0, XMax=1100.0, BinWidth=10.0,
    NumBanks=1, NumMonitors=1,
    Function='User Defined', UserDefinedFunction=spectrum, BankDistanceFromSample = 1.5)
# Shift monitor Y and E data
shift = -70
ws.setY(0, numpy.roll(ws.readY(0), shift))
ws.setE(0, numpy.roll(ws.readE(0), shift))
calibratedE_i = GetEiMonDet(DetectorWorkspace=ws,
    DetectorWorkspaceIndexSet="1-100", MonitorIndex=0)

print('Calibrated energy: {0:.3f}'.format(calibratedE_i))

Output:

Calibrated energy: 53.298

Example - using separate monitor workspace and monitor EPP table:

import numpy
from scipy.constants import elementary_charge, neutron_mass

spectrum = 'name = Gaussian, PeakCentre = 1000.0, Height = 500.0, Sigma = 30.0'
ws = CreateSampleWorkspace(WorkspaceType='Histogram', XUnit='TOF',
  XMin=100.0, XMax=1100.0, BinWidth=10.0,
  NumBanks=1, NumMonitors=1,
  Function='User Defined', UserDefinedFunction=spectrum, BankDistanceFromSample = 1.5)
# Shift monitor Y and E data
shift = -70
ws.setY(0, numpy.roll(ws.readY(0), shift))
ws.setE(0, numpy.roll(ws.readE(0), shift))
ExtractMonitors(ws, DetectorWorkspace='detectors', MonitorWorkspace='monitors')
monitorEPPs = FindEPP('monitors')
calibratedE_i = GetEiMonDet(DetectorWorkspace='detectors',
  DetectorWorkspaceIndexSet="0-99", MonitorWorkspace='monitors', MonitorEPPTable=monitorEPPs, MonitorIndex=0)

print('Calibrated energy: {0:.3f}'.format(calibratedE_i))

Output:

Calibrated energy: 53.298

Categories: AlgorithmIndex | Inelastic\Ei

Source

C++ source: GetEiMonDet3.cpp (last modified: 2019-06-04)

C++ header: GetEiMonDet3.h (last modified: 2019-01-10)