3.6

LoadVulcanCalFile v1

../_images/LoadVulcanCalFile-v1_dlg.png

LoadVulcanCalFile dialog.

Summary

Loads set of VULCAN’s offset files into up to 3 workspaces: a GroupingWorkspace, OffsetsWorkspace and/or MaskWorkspace.

Properties

Name Direction Type Default Description
OffsetFilename Input string Mandatory Path to the VULCAN offset file. Allowed extensions: [‘.dat’]
Grouping Input string 6Modules Choices to output group workspace for 1 bank, 2 banks or 6 modules. Allowed values: [‘6Modules’, ‘2Banks’, ‘1Bank’]
BadPixelFilename Input string   Path to the VULCAN bad pixel file. Allowed extensions: [‘.dat’]
WorkspaceName Input string   The base of the output workspace names. Names will have ‘_group’, ‘_offsets’, ‘_mask’ appended to them.
BankIDs Input int list   Bank IDs for the effective detectors. Must cover all banks in the definition.
EffectiveDIFCs Input dbl list   DIFCs for effective detectors.
Effective2Thetas Input dbl list   2 thetas for effective detectors.
EventWorkspace InOut EventWorkspace   Optional input/output EventWorkspace to get aligned by offset file. It serves as a verifying tool, and will be removed after test.

Description

This algorithm loads a set of VULCAN’s calibration files, including detector offset file and bad pixel file, and convert VULCAN’s offset on time-of-flight to Mantid’s offset on d-spacing.

By this algorithm, Vulcan’s calibration file can be converted to the standard calibration file for SNSPowderReduction.

Detector offset file

There are 62500 (50\times 1250) rows in the offset file. In each row, the first value is the pixel ID; and the second is inner-module offset.

For each module, it starts from row 1250\times M_{i}, where M_{i} is the module ID starting from 0.

  • Line 1250\times M_i + 0: pixel ID, offset (first detector in module)
  • Line 1250\times M_i + 1: pixel ID, offset
  • ... ...
  • Line 1250\times M_i + 1231: pixle ID, offset (last detector in module)
  • Line 1250\times M_i + 1232: pixel ID, offset (detector is not used)
  • ... ...
  • Line 1250\times M_i + 1248: pixel ID, inter module correction
  • Line 1250\times M_i + 1249: pixel ID, inter bank correction

Bad pixel file

In bad pixel file, each line contains one and only one integer corresponding to the detector ID of a bad pixel. The bad pixels will be masked in the output MaskWorkspace.

Conversion from offset in TOF to d-spacing

With VULCAN’s offsets in TOF, the calibration is done as the following.

  • Total offset is the product of innter-bank offset, inner-module offset and inter-module offset

\log_{10}(\xi) = \log_{10}(\xi_0) + \log_{10}(\xi_1) + \log_{10}(\xi_2)

  • Time-of-flight value of each neutron is obtained by division of total offset.

\log_{10}(T') = \log_{10}(T) - \log_{10}(\xi)

T' = \frac{T}{\xi}`

where (1) \xi_0 is the inner-bank correction, (2) \xi_1 is the inner module (inter-bank) correction, and (3) \xi_2 is the inter-module (inner-pack) correction.

Be noticed that the correction factor recorded in VULCAN’s offset file is \log(\xi). Thus if we define \Xi = \log(\xi), then time focussing formula used by VUCLAN’s IDL code is T^{(f)} = \frac{T}{10^{\Xi}}

Therefore, by defining \xi^{(v)} as the VULCAN’s offset, and \xi^{(m)} as the Mantid’s offset, then we can convert VULCAN’s offset to Mantid’s as

\xi^{(m)} = \frac{L\cdot\sin\theta}{L'\cdot\sin\theta'}\cdot\frac{1}{\xi^{(m)}} - 1

VULCAN uses effective DIFC and 2\theta for the effective detector to be focussed on. It follows the Bragg rule for time-of-flight, i.e.,

T = DIFC \cdot d = (252.777\cdot L\cdot 2\cdot\sin\theta)\cdot d

Usage

# Load Vulcan calibration files
LoadVulcanCalFile(OffsetFilename='pid_offset_vulcan_new.dat',
  BadPixelFilename='bad_pids_vulcan_new_6867_7323.dat',
  WorkspaceName='Vulcan_idl', BankIDs='21,22,23,26,27,28',
  EffectiveDIFCs='16372.6,16377,16372.1,16336.6,16340.8,16338.8',
  Effective2Thetas='90.091,90.122,90.089,89.837,89.867,89.852')

# Print
offsetws = mtd["Vulcan_idl_offsets"]
groupws = mtd["Vulcan_idl_group"]
for iws in [0, 100, 1000, 3500, 7000]:
  print "Spectrum %-5d Offset = %.5f of Group %d" % (iws, offsetws.readY(iws)[0], groupws.readY(iws)[0])
maskws = mtd["Vulcan_idl_mask"]
print "Size of mask workspace = %d" % (maskws.getNumberHistograms())

Output:

Spectrum 0     Offset = -0.00047 of Group 1
Spectrum 100   Offset = -0.00096 of Group 1
Spectrum 1000  Offset = -0.00060 of Group 1
Spectrum 3500  Offset = -0.00036 of Group 3
Spectrum 7000  Offset = 0.00058 of Group 6
Size of mask workspace = 7392

Categories: Algorithms | DataHandling\Text | Diffraction\DataHandling