source: sasview/src/sas/qtgui/Calculators/media/resolution_calculator_help.rst @ 417c03f

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[ec392464]1.. resolution_calculator_help.rst
2
3.. This is a port of the original SasView html help file to ReSTructured text
4.. by S King, ISIS, during SasView CodeCamp-III in Feb 2015.
5
[a9dc4eb]6Q Resolution Estimator Tool
7===========================
[ec392464]8
9Description
10-----------
11
[5ed76f8]12This tool is approximately estimates the resolution of $Q$ from SAS instrumental
13parameter values assuming that the detector is flat and normal to the
[bc9a0e1]14incident beam.
[ec392464]15
16.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
17
[a9dc4eb]18Using the tool
19--------------
[ec392464]20
[850c753]211) Select *SAS Resolution Estimator* from the *Tool* menu on the SasView toolbar.
[bc9a0e1]22
232) Select the source (Neutron or Photon) and source type (Monochromatic or TOF).
[ec392464]24
[5ed76f8]25   *NOTE! The computational difference between the sources is only the
[bc9a0e1]26   gravitational contribution due to the mass of the particles.*
[ec392464]27
[5ed76f8]283) Change the default values of the instrumental parameters as required. Be
[bc9a0e1]29   careful to note that distances are specified in cm!
[ec392464]30
[5ed76f8]314) Enter values for the source wavelength(s), $\lambda$, and its spread (= $\text{FWHM}/\lambda$).
32
33   For monochromatic sources, the inputs are just one value. For TOF sources,
34   the minimum and maximum values should be separated by a '-' to specify a
[bc9a0e1]35   range.
[5ed76f8]36
37   Optionally, the wavelength (BUT NOT of the wavelength spread) can be extended
38   by adding '; nn' where the 'nn' specifies the number of the bins for the
39   numerical integration. The default value is nn = 10. The same number of bins
[bc9a0e1]40   will be used for the corresponding wavelength spread.
[ec392464]41
[5ed76f8]425) For TOF, the default wavelength spectrum is flat. A custom spectral
43   distribution file (2-column text: wavelength (|Ang|\) vs Intensity) can also
[bc9a0e1]44   be loaded by selecting *Add new* in the combo box.
[ec392464]45
[5ed76f8]466) When ready, click the *Compute* button. Depending on the computation the
[bc9a0e1]47   calculation time will vary.
[ec392464]48
[5ed76f8]497) 1D and 2D $dQ$ values will be displayed at the bottom of the panel, and a 2D
50   resolution weight distribution (a 2D elliptical Gaussian function) will also
51   be displayed in the plot panel even if the $Q$ inputs are outside of the
[bc9a0e1]52   detector limit (the red lines indicate the limits of the detector).
[5ed76f8]53
54   TOF only: green lines indicate the limits of the maximum $Q$ range accessible
[bc9a0e1]55   for the longest wavelength due to the size of the detector.
[ec392464]56
[5ed76f8]57   Note that the effect from the beam block/stop is ignored, so in the small $Q$
58   region near the beam block/stop
59
60   [i.e., $Q < (2 \pi \cdot \text{beam block diameter}) / (\text{sample-to-detector distance} \cdot \lambda_\text{min})$]
[ec392464]61
[bc9a0e1]62   the variance is slightly under estimated.
63
[5ed76f8]648) A summary of the calculation is written to the SasView *Console* at the
[bc9a0e1]65   bottom of the main SasView window.
[ec392464]66
[6aad2e8]67.. image:: resolution_tutor.png
[ec392464]68
69.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
70
71Theory
72------
73
74The scattering wave transfer vector is by definition
75
[6aad2e8]76.. image:: q.png
[ec392464]77
[5ed76f8]78In the small-angle limit, the variance of $Q$ is to a first-order
[bc9a0e1]79approximation
[ec392464]80
[6aad2e8]81.. image:: sigma_q.png
[ec392464]82
[bc9a0e1]83The geometric and gravitational contributions can then be summarised as
[ec392464]84
[6aad2e8]85.. image:: sigma_table.png
[ec392464]86
[5ed76f8]87Finally, a Gaussian function is used to describe the 2D weighting distribution
88of the uncertainty in $Q$.
[ec392464]89
90.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
91
92References
93----------
94
[5ed76f8]95D.F.R. Mildner and J.M. Carpenter
[bc9a0e1]96*J. Appl. Cryst.* 17 (1984) 249-256
97
[5ed76f8]98D.F.R. Mildner, J.M. Carpenter and D.L. Worcester
[bc9a0e1]99*J. Appl. Cryst.* 19 (1986) 311-319
100
101.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
102
[a9dc4eb]103.. note::  This help document was last changed by Steve King, 01May2015
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