source: sasview/src/sas/sasgui/perspectives/calculator/media/resolution_calculator_help.copy @ 65dfa99

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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
6.. |pi| unicode:: U+03C0
7.. |lambda| unicode:: U+03BB
8.. |Ang| unicode:: U+212B
9
10Q Resolution Estimator Tool
11===========================
12
13Description
14-----------
15
16This tool is approximately estimates the resolution of Q from SAS instrumental
17parameter values assuming that the detector is flat and normal to the
18incident beam.
19
20.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
21
22Using the tool
23--------------
24
251) Select *SAS Resolution Estimator* from the *Tool* menu on the SasView toolbar.
26
272) Select the source (Neutron or Photon) and source type (Monochromatic or TOF).
28
29   *NOTE! The computational difference between the sources is only the
30   gravitational contribution due to the mass of the particles.*
31
323) Change the default values of the instrumental parameters as required. Be
33   careful to note that distances are specified in cm!
34
354) Enter values for the source wavelength(s), |lambda|\ , and its spread (= FWHM/|lambda|\ ).
36   
37   For monochromatic sources, the inputs are just one value. For TOF sources,
38   the minimum and maximum values should be separated by a '-' to specify a
39   range.
40   
41   Optionally, the wavelength (BUT NOT of the wavelength spread) can be extended
42   by adding '; nn' where the 'nn' specifies the number of the bins for the
43   numerical integration. The default value is nn = 10. The same number of bins
44   will be used for the corresponding wavelength spread.
45
465) For TOF, the default wavelength spectrum is flat. A custom spectral
47   distribution file (2-column text: wavelength (|Ang|\) vs Intensity) can also
48   be loaded by selecting *Add new* in the combo box.
49
506) When ready, click the *Compute* button. Depending on the computation the
51   calculation time will vary.
52
537) 1D and 2D dQ values will be displayed at the bottom of the panel, and a 2D
54   resolution weight distribution (a 2D elliptical Gaussian function) will also
55   be displayed in the plot panel even if the Q inputs are outside of the
56   detector limit (the red lines indicate the limits of the detector).
57   
58   TOF only: green lines indicate the limits of the maximum Q range accessible
59   for the longest wavelength due to the size of the detector.
60   
61   Note that the effect from the beam block/stop is ignored, so in the small Q
62   region near the beam block/stop
63
64   [ie., Q < 2. |pi|\ .(beam block diameter) / (sample-to-detector distance) / |lambda|\_min]
65
66   the variance is slightly under estimated.
67
688) A summary of the calculation is written to the SasView *Console* at the
69   bottom of the main SasView window.
70
71.. image:: resolution_tutor.gif
72
73.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
74
75Theory
76------
77
78The scattering wave transfer vector is by definition
79
80.. image:: q.gif
81
82In the small-angle limit, the variance of Q is to a first-order
83approximation
84
85.. image:: sigma_q.gif
86
87The geometric and gravitational contributions can then be summarised as
88
89.. image:: sigma_table.gif
90
91Finally, a Gaussian function is used to describe the 2D weighting distribution
92of the uncertainty in Q.
93
94.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
95
96References
97----------
98
99D.F.R. Mildner and J.M. Carpenter
100*J. Appl. Cryst.* 17 (1984) 249-256
101
102D.F.R. Mildner, J.M. Carpenter and D.L. Worcester
103*J. Appl. Cryst.* 19 (1986) 311-319
104
105.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
106
107.. note::  This help document was last changed by Steve King, 01May2015
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