3.5

DNSDetEffCorrVana v1

../_images/DNSDetEffCorrVana-v1_dlg.png

DNSDetEffCorrVana dialog.

Summary

Peforms detector efficiency correction on a given data workspace using the Vanadium data.

Properties

Name Direction Type Default Description
InputWorkspace Input MatrixWorkspace Mandatory A workspace with experimental data from sample.
OutputWorkspace Output MatrixWorkspace Mandatory A workspace to save the corrected data.
VanaWorkspace Input MatrixWorkspace Mandatory A workspace with Vanadium data.
BkgWorkspace Input MatrixWorkspace Mandatory A workspace with background for Vanadium data.
VanadiumMean Input string   A 2x1 matrix workspace with mean Vanadium counts (optional).

Description

Warning

This algorithm is being developed for a specific instrument. It might get changed or even removed without a notification, should instrument scientists decide to do so.

This algorithm applies detector efficiency correction to a given data Workspace2D. As a result, two workspaces will be created:

  • output workspace with corrected data. Sample logs will be copied from the data workspace.
  • if InputWorkspace has the normalization workspace (which contains monitor counts or experiment duration by user’s choice), the copy of it will be created with name OutputWorkspace_NORM.

Detector efficiency correction is performed using the measurements of vanadium standard sample (hereafter Vanadium). Background for Vanadium must be also measured and provided to the algorithm as an input BkgWorkspace. Vanadium and its background can be measured at several detector bank positions. This algorithm does the detector efficiency for a particular run in following steps:

  1. Normalize Vanadium workspace to a chosen normalization:

    (V_i)_{Norm} = \frac{(V_i)_{Raw}}{(C_i)_V}

    where (V_i)_{Raw} is the signal from the i th detector in the Vanadium workspace and (C_i)_V is the number in the corresponding bin of the normalization workspace. The Divide v1 algorithm is used for this step.

  2. Normalize Background workspace to a chosen normalization:

    (B_i)_{Norm} = \frac{(B_i)_{Raw}}{(C_i)_B}

    where (B_i)_{Raw} is the signal from the i th detector in the Background workspace and (C_i)_B is the number in the corresponding bin of the normalization workspace. The Divide v1 algorithm is used for this step.

Warning

Normalization workspaces are created by the LoadDNSLegacy v1 algorithm. It is responsibility of the user to take care about the same type of normalization (monitor counts or run duration) for Vanadium and Background.

  1. Subtract Background from Vanadium:

    V_i = (V_i)_{Norm} - (B_i)_{Norm}

    The Minus v1 algorithm is used for this step. In the case of negative result, the error message will be produced and the algorithm terminates.

  2. Calculate the correction coefficients:

    k_i = \frac{<V>}{V_i}

    where <V> is a mean value of Vanadium counts. The Divide v1 algorithm is used for this step.

Note

If no VanadiumMean workspace is given as an input, the <V> will be calculated as <V> = \frac{1}{n}\sum V_i. However, in the case if correction is applied to a group of runs, <V> must be calculated as for the whole group, saved to VanadiumMean workspace and provided to this algorithm as an input.

  1. Apply correction to the data:

    (I_i)_{corr} = k_i\times I_i

    where I_i are the neutron counts in the InputWorkspace.

Valid input workspaces

The input workspaces (InputWorkspace, VanaWorkspace, BkgWorkspace) have to have the following in order to be valid inputs for this algorithm.

  • The same number of dimensions
  • The same number of spectra
  • The same number of bins
  • VanaWorkspace and BkgWorkspace must have the corresponding normalization workspaces

For the physically meaningful correction it is also important that these workspaces have the same slits size, polarisation, detector bank rotation angle, flipper status and the neutron wavelength. If some of these parameters are different, algorithm produces warning. If these properties are not specified in the workspace sample logs, no comparison is performed.

The workspace VanadiumMean is an optional parameter. However, if it is specified, it must be a Workspace2D with 2 dimensions, 1 histogram and 1 bin.

Usage

Example - Apply correction to a single run:

# data, vanadium and background files.
datafile = 'oi196012pbi.d_dat'
vanafile = 'dn134011vana.d_dat'
bkgrfile = 'dn134031leer.d_dat'

# Load datasets, loader will create an additional normalization workspace
data_ws = LoadDNSLegacy(datafile, Polarisation='x', Normalization='monitor')
vana_ws = LoadDNSLegacy(vanafile, Polarisation='x', Normalization='monitor')
bkgr_ws = LoadDNSLegacy(bkgrfile, Polarisation='x', Normalization='monitor')

corrected = DNSDetEffCorrVana(data_ws, vana_ws, bkgr_ws)

for i in range(3):
 print round(corrected.readY(i), 2)

Output:

99180.91

77190.96

77265.61

Categories: Algorithms | PythonAlgorithms | MLZ | DNS | CorrectionFunctions | EfficiencyCorrections