1 | .. resolution_calculator_help.rst |
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2 | |
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3 | .. This is a port of the original SasView html help file to ReSTructured text |
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4 | .. by S King, ISIS, during SasView CodeCamp-III in Feb 2015. |
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5 | |
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6 | .. |pi| unicode:: U+03C0 |
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7 | .. |lambda| unicode:: U+03BB |
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8 | .. |Ang| unicode:: U+212B |
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9 | |
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10 | Q Resolution Estimator Tool |
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11 | =========================== |
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12 | |
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13 | Description |
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14 | ----------- |
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15 | |
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16 | This tool is approximately estimates the resolution of Q from SAS instrumental |
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17 | parameter values assuming that the detector is flat and normal to the |
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18 | incident beam. |
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19 | |
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20 | .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ |
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21 | |
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22 | Using the tool |
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23 | -------------- |
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24 | |
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25 | 1) Select *SAS Resolution Estimator* from the *Tool* menu on the SasView toolbar. |
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26 | |
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27 | 2) Select the source (Neutron or Photon) and source type (Monochromatic or TOF). |
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28 | |
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29 | *NOTE! The computational difference between the sources is only the |
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30 | gravitational contribution due to the mass of the particles.* |
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31 | |
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32 | 3) Change the default values of the instrumental parameters as required. Be |
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33 | careful to note that distances are specified in cm! |
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34 | |
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35 | 4) Enter values for the source wavelength(s), |lambda|\ , and its spread (= FWHM/|lambda|\ ). |
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36 | |
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37 | For monochromatic sources, the inputs are just one value. For TOF sources, |
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38 | the minimum and maximum values should be separated by a '-' to specify a |
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39 | range. |
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40 | |
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41 | Optionally, the wavelength (BUT NOT of the wavelength spread) can be extended |
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42 | by adding '; nn' where the 'nn' specifies the number of the bins for the |
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43 | numerical integration. The default value is nn = 10. The same number of bins |
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44 | will be used for the corresponding wavelength spread. |
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45 | |
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46 | 5) For TOF, the default wavelength spectrum is flat. A custom spectral |
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47 | distribution file (2-column text: wavelength (|Ang|\) vs Intensity) can also |
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48 | be loaded by selecting *Add new* in the combo box. |
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49 | |
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50 | 6) When ready, click the *Compute* button. Depending on the computation the |
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51 | calculation time will vary. |
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52 | |
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53 | 7) 1D and 2D dQ values will be displayed at the bottom of the panel, and a 2D |
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54 | resolution weight distribution (a 2D elliptical Gaussian function) will also |
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55 | be displayed in the plot panel even if the Q inputs are outside of the |
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56 | detector limit (the red lines indicate the limits of the detector). |
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57 | |
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58 | TOF only: green lines indicate the limits of the maximum Q range accessible |
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59 | for the longest wavelength due to the size of the detector. |
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60 | |
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61 | Note that the effect from the beam block/stop is ignored, so in the small Q |
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62 | region near the beam block/stop |
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63 | |
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64 | [ie., Q < 2. |pi|\ .(beam block diameter) / (sample-to-detector distance) / |lambda|\_min] |
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65 | |
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66 | the variance is slightly under estimated. |
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67 | |
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68 | 8) A summary of the calculation is written to the SasView *Console* at the |
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69 | bottom of the main SasView window. |
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70 | |
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71 | .. image:: resolution_tutor.gif |
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72 | |
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73 | .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ |
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74 | |
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75 | Theory |
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76 | ------ |
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77 | |
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78 | The scattering wave transfer vector is by definition |
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79 | |
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80 | .. image:: q.gif |
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81 | |
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82 | In the small-angle limit, the variance of Q is to a first-order |
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83 | approximation |
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84 | |
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85 | .. image:: sigma_q.gif |
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86 | |
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87 | The geometric and gravitational contributions can then be summarised as |
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88 | |
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89 | .. image:: sigma_table.gif |
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90 | |
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91 | Finally, a Gaussian function is used to describe the 2D weighting distribution |
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92 | of the uncertainty in Q. |
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93 | |
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94 | .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ |
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95 | |
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96 | References |
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97 | ---------- |
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98 | |
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99 | D.F.R. Mildner and J.M. Carpenter |
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100 | *J. Appl. Cryst.* 17 (1984) 249-256 |
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101 | |
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102 | D.F.R. Mildner, J.M. Carpenter and D.L. Worcester |
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103 | *J. Appl. Cryst.* 19 (1986) 311-319 |
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104 | |
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105 | .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ |
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106 | |
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107 | .. note:: This help document was last changed by Steve King, 01May2015 |
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