[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 | |
---|
[bc9a0e1] | 6 | .. |pi| unicode:: U+03C0 |
---|
| 7 | .. |lambda| unicode:: U+03BB |
---|
| 8 | .. |Ang| unicode:: U+212B |
---|
| 9 | |
---|
[a9dc4eb] | 10 | Q Resolution Estimator Tool |
---|
| 11 | =========================== |
---|
[ec392464] | 12 | |
---|
| 13 | Description |
---|
| 14 | ----------- |
---|
| 15 | |
---|
[bc9a0e1] | 16 | This tool is approximately estimates the resolution of Q from SAS instrumental |
---|
| 17 | parameter values assuming that the detector is flat and normal to the |
---|
| 18 | incident beam. |
---|
[ec392464] | 19 | |
---|
| 20 | .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ |
---|
| 21 | |
---|
[a9dc4eb] | 22 | Using the tool |
---|
| 23 | -------------- |
---|
[ec392464] | 24 | |
---|
[850c753] | 25 | 1) Select *SAS Resolution Estimator* from the *Tool* menu on the SasView toolbar. |
---|
[bc9a0e1] | 26 | |
---|
| 27 | 2) Select the source (Neutron or Photon) and source type (Monochromatic or TOF). |
---|
[ec392464] | 28 | |
---|
[bc9a0e1] | 29 | *NOTE! The computational difference between the sources is only the |
---|
| 30 | gravitational contribution due to the mass of the particles.* |
---|
[ec392464] | 31 | |
---|
[bc9a0e1] | 32 | 3) Change the default values of the instrumental parameters as required. Be |
---|
| 33 | careful to note that distances are specified in cm! |
---|
[ec392464] | 34 | |
---|
[850c753] | 35 | 4) Enter values for the source wavelength(s), |lambda|\ , and its spread (= FWHM/|lambda|\ ). |
---|
[bc9a0e1] | 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. |
---|
[ec392464] | 45 | |
---|
[bc9a0e1] | 46 | 5) 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. |
---|
[ec392464] | 49 | |
---|
[bc9a0e1] | 50 | 6) When ready, click the *Compute* button. Depending on the computation the |
---|
| 51 | calculation time will vary. |
---|
[ec392464] | 52 | |
---|
[bc9a0e1] | 53 | 7) 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 |
---|
[ec392464] | 63 | |
---|
[850c753] | 64 | [ie., Q < 2. |pi|\ .(beam block diameter) / (sample-to-detector distance) / |lambda|\_min] |
---|
[ec392464] | 65 | |
---|
[bc9a0e1] | 66 | the variance is slightly under estimated. |
---|
| 67 | |
---|
| 68 | 8) A summary of the calculation is written to the SasView *Console* at the |
---|
| 69 | bottom of the main SasView window. |
---|
[ec392464] | 70 | |
---|
| 71 | .. image:: resolution_tutor.gif |
---|
| 72 | |
---|
| 73 | .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ |
---|
| 74 | |
---|
| 75 | Theory |
---|
| 76 | ------ |
---|
| 77 | |
---|
| 78 | The scattering wave transfer vector is by definition |
---|
| 79 | |
---|
| 80 | .. image:: q.gif |
---|
| 81 | |
---|
[bc9a0e1] | 82 | In the small-angle limit, the variance of Q is to a first-order |
---|
| 83 | approximation |
---|
[ec392464] | 84 | |
---|
| 85 | .. image:: sigma_q.gif |
---|
| 86 | |
---|
[bc9a0e1] | 87 | The geometric and gravitational contributions can then be summarised as |
---|
[ec392464] | 88 | |
---|
| 89 | .. image:: sigma_table.gif |
---|
| 90 | |
---|
[bc9a0e1] | 91 | Finally, a Gaussian function is used to describe the 2D weighting distribution |
---|
| 92 | of the uncertainty in Q. |
---|
[ec392464] | 93 | |
---|
| 94 | .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ |
---|
| 95 | |
---|
| 96 | References |
---|
| 97 | ---------- |
---|
| 98 | |
---|
[bc9a0e1] | 99 | D.F.R. Mildner and J.M. Carpenter |
---|
| 100 | *J. Appl. Cryst.* 17 (1984) 249-256 |
---|
| 101 | |
---|
| 102 | D.F.R. Mildner, J.M. Carpenter and D.L. Worcester |
---|
| 103 | *J. Appl. Cryst.* 19 (1986) 311-319 |
---|
| 104 | |
---|
| 105 | .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ |
---|
| 106 | |
---|
[a9dc4eb] | 107 | .. note:: This help document was last changed by Steve King, 01May2015 |
---|