source: sasview/src/sas/sasgui/perspectives/fitting/media/mag_help.copy @ 65dfa99

ESS_GUIESS_GUI_DocsESS_GUI_batch_fittingESS_GUI_bumps_abstractionESS_GUI_iss1116ESS_GUI_iss879ESS_GUI_iss959ESS_GUI_openclESS_GUI_orderingESS_GUI_sync_sascalccostrafo411magnetic_scattrelease-4.1.1release-4.1.2release-4.2.2release_4.0.1ticket-1009ticket-1094-headlessticket-1242-2d-resolutionticket-1243ticket-1249ticket885unittest-saveload
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1.. mag_help.rst
2
3.. This is a port of text from 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.. |mu| unicode:: U+03BC
9.. |sigma| unicode:: U+03C3
10.. |phi| unicode:: U+03C6
11.. |theta| unicode:: U+03B8
12.. |chi| unicode:: U+03C7
13
14.. |inlineimage004| image:: sm_image004.gif
15.. |inlineimage005| image:: sm_image005.gif
16.. |inlineimage008| image:: sm_image008.gif
17.. |inlineimage009| image:: sm_image009.gif
18.. |inlineimage010| image:: sm_image010.gif
19.. |inlineimage011| image:: sm_image011.gif
20.. |inlineimage012| image:: sm_image012.gif
21.. |inlineimage018| image:: sm_image018.gif
22.. |inlineimage019| image:: sm_image019.gif
23
24
25.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
26
27Polarisation/Magnetic Scattering
28--------------------------------
29
30Magnetic scattering is implemented in five (2D) models
31
32*  *SphereModel*
33*  *CoreShellModel*
34*  *CoreMultiShellModel*
35*  *CylinderModel*
36*  *ParallelepipedModel*
37
38In general, the scattering length density (SLD, = |beta|) in each region where the
39SLD is uniform, is a combination of the nuclear and magnetic SLDs and, for polarised
40neutrons, also depends on the spin states of the neutrons.
41
42For magnetic scattering, only the magnetization component, *M*\ :sub:`perp`,
43perpendicular to the scattering vector *Q* contributes to the the magnetic
44scattering length.
45
46.. image:: mag_vector.bmp
47
48The magnetic scattering length density is then
49
50.. image:: dm_eq.gif
51
52where |gamma| = -1.913 is the gyromagnetic ratio, |mu|\ :sub:`B` is the
53Bohr magneton, *r*\ :sub:`0` is the classical radius of electron, and |sigma|
54is the Pauli spin.
55
56Assuming that incident neutrons are polarized parallel (+) and anti-parallel (-)
57to the *x'* axis, the possible spin states after the sample are then
58
59No spin-flips (+ +) and (- -)
60
61Spin-flips    (+ -) and (- +)
62
63.. image:: M_angles_pic.bmp
64
65If the angles of the *Q* vector and the spin-axis (*x'*) to the *x*-axis are |phi|
66and |theta|\ :sub:`up`, respectively, then, depending on the spin state of the
67neutrons, the scattering length densities, including the nuclear scattering
68length density (|beta|\ :sub:`N`) are
69
70.. image:: sld1.gif
71
72when there are no spin-flips, and
73
74.. image:: sld2.gif
75
76when there are, and
77
78.. image:: mxp.gif
79
80.. image:: myp.gif
81
82.. image:: mzp.gif
83
84.. image:: mqx.gif
85
86.. image:: mqy.gif
87
88Here, *M*\ :sub:`0x`, *M*\ :sub:`0y` and *M*\ :sub:`0z` are the x, y and z components
89of the magnetization vector given in the laboratory xyz frame given by
90
91.. image:: m0x_eq.gif
92
93.. image:: m0y_eq.gif
94
95.. image:: m0z_eq.gif
96
97and the magnetization angles |theta|\ :sub:`M` and |phi|\ :sub:`M` are defined in
98the figure above.
99
100The user input parameters are:
101
102===========   ================================================================
103 M0_sld        = *D*\ :sub:`M` *M*\ :sub:`0`
104 Up_theta      = |theta|\ :sub:`up`
105 M_theta       = |theta|\ :sub:`M`
106 M_phi         = |phi|\ :sub:`M`
107 Up_frac_i     = (spin up)/(spin up + spin down) neutrons *before* the sample
108 Up_frac_f     = (spin up)/(spin up + spin down) neutrons *after* the sample
109===========   ================================================================
110
111*Note:* The values of the 'Up_frac_i' and 'Up_frac_f' must be in the range 0 to 1.
112
113.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
114
115.. note::  This help document was last changed by Steve King, 02May2015
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