source: sasview/docs/sphinx-docs/source/user/sasgui/perspectives/calculator/resolution_calculator_help.rst @ 49148bb

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[49148bb]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
6Q Resolution Estimator Tool
7===========================
8
9Description
10-----------
11
12This tool is approximately estimates the resolution of Q from SAS instrumental
13parameter values assuming that the detector is flat and normal to the
14incident beam.
15
16.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
17
18Using the tool
19--------------
20
211) Select *SAS Resolution Estimator* from the *Tool* menu on the SasView toolbar.
22
232) Select the source (Neutron or Photon) and source type (Monochromatic or TOF).
24
25   *NOTE! The computational difference between the sources is only the
26   gravitational contribution due to the mass of the particles.*
27
283) Change the default values of the instrumental parameters as required. Be
29   careful to note that distances are specified in cm!
30
314) Enter values for the source wavelength(s), |lambda|\ , and its spread (= 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
35   range.
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
40   will be used for the corresponding wavelength spread.
41
425) For TOF, the default wavelength spectrum is flat. A custom spectral
43   distribution file (2-column text: wavelength (|Ang|\) vs Intensity) can also
44   be loaded by selecting *Add new* in the combo box.
45
466) When ready, click the *Compute* button. Depending on the computation the
47   calculation time will vary.
48
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
52   detector limit (the red lines indicate the limits of the detector).
53   
54   TOF only: green lines indicate the limits of the maximum Q range accessible
55   for the longest wavelength due to the size of the detector.
56   
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   [ie., Q < 2. |pi|\ .(beam block diameter) / (sample-to-detector distance) / |lambda|\_min]
61
62   the variance is slightly under estimated.
63
648) A summary of the calculation is written to the SasView *Console* at the
65   bottom of the main SasView window.
66
67.. image:: resolution_tutor.gif
68
69.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
70
71Theory
72------
73
74The scattering wave transfer vector is by definition
75
76.. image:: q.gif
77
78In the small-angle limit, the variance of Q is to a first-order
79approximation
80
81.. image:: sigma_q.gif
82
83The geometric and gravitational contributions can then be summarised as
84
85.. image:: sigma_table.gif
86
87Finally, a Gaussian function is used to describe the 2D weighting distribution
88of the uncertainty in Q.
89
90.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
91
92References
93----------
94
95D.F.R. Mildner and J.M. Carpenter
96*J. Appl. Cryst.* 17 (1984) 249-256
97
98D.F.R. Mildner, J.M. Carpenter and D.L. Worcester
99*J. Appl. Cryst.* 19 (1986) 311-319
100
101.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
102
103.. note::  This help document was last changed by Steve King, 01May2015
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