Changeset 78f02c3 in sasview for src/sas/calculator/media/sas_calculator_help.rst
- Timestamp:
- Feb 14, 2015 10:12:40 AM (9 years ago)
- Branches:
- master, ESS_GUI, ESS_GUI_Docs, ESS_GUI_batch_fitting, ESS_GUI_bumps_abstraction, ESS_GUI_iss1116, ESS_GUI_iss879, ESS_GUI_iss959, ESS_GUI_opencl, ESS_GUI_ordering, ESS_GUI_sync_sascalc, costrafo411, magnetic_scatt, release-4.1.1, release-4.1.2, release-4.2.2, release_4.0.1, ticket-1009, ticket-1094-headless, ticket-1242-2d-resolution, ticket-1243, ticket-1249, ticket885, unittest-saveload
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- 898a8b9
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- 3e2ebbb
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src/sas/calculator/media/sas_calculator_help.rst
r37bbd5f r78f02c3 1 1 ..sas_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 .. |beta| unicode:: U+03B2 7 .. |gamma| unicode:: U+03B3 8 .. |theta| unicode:: U+03B8 9 .. |mu| unicode:: U+03BC 10 .. |sigma| unicode:: U+03C3 11 .. |phi| unicode:: U+03C6 12 13 .. |equiv| unicode:: U+2261 14 .. |noteql| unicode:: U+2260 2 15 3 16 Generic Scattering Calculator Tool 4 17 ================================== 5 18 6 Placeholder for generic SAS calculator help 19 Polarization and Magnetic Scattering 20 21 Theory_ 22 GUI_ 23 PDB_Data_ 24 25 .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ 26 27 .. _Theory: 28 29 Theory 30 ------ 31 32 In general, a particle with a volume V can be described by an ensemble 33 containing N 3-dimensional rectangular pixels where each pixels are much 34 smaller than V. Assuming that all the pixel sizes are same, the elastic 35 scattering intensity by the particle 36 37 .. image:: gen_i.gif 38 39 where /beta/jand rj are the scattering length density and the position of the 40 j'th pixel respectively. And the total volume 41 42 .. image:: v_j.gif 43 44 for /beta/j/noteql/0 where vj is the volume of the j'th pixel (or the j'th 45 natural atomic volume (= atomic mass/natural molar density/Avogadro number) for 46 the atomic structures). The total volume V can be corrected by users. This 47 correction is useful especially for an atomic structure (taken from a pdb file) 48 to get the right normalization. Note that the /beta/j displayed in GUI may be 49 incorrect but will not affect the scattering computation if the correction of 50 the total volume is made. The scattering length density (SLD) of each pixel 51 where the SLD is uniform, is a combination of the nuclear and magnetic SLDs and 52 depends on the spin states of the neutrons as follows:For magnetic scattering, 53 only the magnetization component, *M*perp, perpendicular to the scattering 54 vector *Q* contributes to the the magnetic scattering length. (Figure below). 55 56 .. image:: mag_vector.bmp 57 58 The magnetic scattering length density is then 59 60 .. image:: dm_eq.gif 61 62 where /gamma/= -1.913 the gyromagnetic ratio, /mu/B is the Bohr magneton, r0 is 63 the classical radius of electron, and */sigma/* is the Pauli spin. 64 65 For polarized neutron, the magnetic scattering is depending on the spin states. 66 67 Let's consider that the incident neutrons are polarised parallel (+)/ 68 anti-parallel (-) to the x' axis (See both Figures above). The possible 69 out-coming states then are + and - states for both incident states, where 70 71 - Non-spin flips: (+ +) and (- -) 72 - Spin flips: (+ -) and (- +) 73 74 .. image:: gen_mag_pic.bmp 75 76 Now, let's assume that the angles of the *Q* vector and the spin-axis (x') 77 from x-axis are /phi/ and /theta/up respectively (See Figure above). Then, 78 depending upon the polarization (spin) state of neutrons, the scattering 79 length densities, including the nuclear scattering length density (/beta/N) 80 are given as, for non-spin-flips 81 82 .. image:: sld1.gif 83 84 and for spin-flips 85 86 .. image:: sld2.gif 87 88 where 89 90 .. image:: mxp.gif 91 92 .. image:: myp.gif 93 94 .. image:: mzp.gif 95 96 .. image:: mqx.gif 97 98 .. image:: mqy.gif 99 100 Here, the M0x, M0yand M0zare the x, y and z components of the magnetisation 101 vector given in the xyz lab frame. 102 103 .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ 104 105 .. _GUI: 106 107 GUI 108 --- 109 110 .. image:: gen_gui_help.bmp 111 112 After the computation, the result will be listed in the 'Theory' box in the 113 data explorer panel on the main window.The 'Up_frac_in' and 'Up_frac_out' are 114 the ratio, (spin up) /(spin up + spin down) neutrons before the sample and at 115 the analyzer, respectively. 116 117 *Note I: The values of 'Up_frac_in' and 'Up_frac_out' must be in the range 118 between 0 and 1. For example, both values are 0.5 for unpolarized neutrons.* 119 120 *Note II: This computation is totally based on the pixel (or atomic) data 121 fixed in the xyz coordinates. Thus no angular orientational averaging is 122 considered.* 123 124 *Note III: For the nuclear scattering length density, only the real component 125 is taken account.* 126 127 .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ 128 129 .. _PDB_Data: 130 131 PDB Data 132 -------- 133 134 This Generic scattering calculator also supports some pdb files without 135 considering polarized/magnetic scattering so that the related parameters 136 such as Up_*** will be ignored (see the Picture below). The calculation for 137 fixed orientation uses (the first) Equation above resulting in a 2D output, 138 whileas the scattering calculation averaged over all the orientations uses 139 the Debye equation providing a 1D output 140 141 .. image:: gen_debye_eq.gif 142 143 where vj /beta/j /equiv/ bj the scattering length of the j'th atom. The resultant outputs 144 will be displayed in the DataExplorer for further uses. 145 146 .. image:: pdb_combo.jpg
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