Index: src/sas/calculator/media/sas_calculator_help.rst
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 ..sas_calculator_help.rst
+
+.. This is a port of the original SasView html help file to ReSTructured text
+.. by S King, ISIS, during SasView CodeCamp-III in Feb 2015.
+
+.. |beta| unicode:: U+03B2
+.. |gamma| unicode:: U+03B3
+.. |theta| unicode:: U+03B8
+.. |mu| unicode:: U+03BC
+.. |sigma| unicode:: U+03C3
+.. |phi| unicode:: U+03C6
+
+.. |equiv| unicode:: U+2261
+.. |noteql| unicode:: U+2260
 
 Generic Scattering Calculator Tool
 ==================================
 
-Placeholder for generic SAS calculator help
+Polarization and Magnetic Scattering
+
+Theory_ 
+GUI_ 
+PDB_Data_ 
+
+.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
+
+.. _Theory:
+
+Theory
+------
+
+In general, a particle with a volume V can be described by an ensemble 
+containing N 3-dimensional rectangular pixels where each pixels are much 
+smaller than V. Assuming that all the pixel sizes are same, the elastic 
+scattering intensity by the particle
+
+.. image:: gen_i.gif
+
+where /beta/jand rj are the scattering length density and the position of the 
+j'th pixel respectively. And the total volume
+
+.. image:: v_j.gif
+
+for /beta/j/noteql/0 where vj is the volume of the j'th pixel (or the j'th 
+natural atomic volume (= atomic mass/natural molar density/Avogadro number) for 
+the atomic structures). The total volume V can be corrected by users. This 
+correction is useful especially for an atomic structure (taken from a pdb file) 
+to get the right normalization. Note that the /beta/j displayed in GUI may be 
+incorrect but will not affect the scattering computation if the correction of 
+the total volume is made. The scattering length density (SLD) of each pixel 
+where the SLD is uniform, is a combination of the nuclear and magnetic SLDs and 
+depends on the spin states of the neutrons as follows:For magnetic scattering, 
+only the magnetization component, *M*perp, perpendicular to the scattering 
+vector *Q* contributes to the the magnetic scattering length. (Figure below).
+
+.. image:: mag_vector.bmp
+
+The magnetic scattering length density is then
+
+.. image:: dm_eq.gif
+
+where /gamma/= -1.913 the gyromagnetic ratio, /mu/B is the Bohr magneton, r0 is 
+the classical radius of electron, and */sigma/* is the Pauli spin.
+
+For polarized neutron, the magnetic scattering is depending on the spin states.
+
+Let's consider that the incident neutrons are polarised parallel (+)/ 
+anti-parallel (-) to the x' axis (See both Figures above). The possible 
+out-coming states then are + and - states for both incident states, where 
+
+- Non-spin flips: (+ +) and (- -)
+- Spin flips:     (+ -) and (- +)
+
+.. image:: gen_mag_pic.bmp
+
+Now, let's assume that the angles of the *Q*  vector and the spin-axis (x') 
+from x-axis are /phi/ and /theta/up respectively (See Figure above). Then, 
+depending upon the polarization (spin) state of neutrons, the scattering 
+length densities, including the nuclear scattering length density (/beta/N) 
+are given as, for non-spin-flips
+
+.. image:: sld1.gif
+
+and for spin-flips
+
+.. image:: sld2.gif
+
+where
+
+.. image:: mxp.gif
+
+.. image:: myp.gif
+
+.. image:: mzp.gif
+
+.. image:: mqx.gif
+
+.. image:: mqy.gif
+
+Here, the M0x, M0yand M0zare the x, y and z components of the magnetisation 
+vector given in the xyz lab frame. 
+
+.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
+
+.. _GUI:
+
+GUI
+---
+
+.. image:: gen_gui_help.bmp
+
+After the computation, the result will be listed in the 'Theory' box in the 
+data explorer panel on the main window.The 'Up_frac_in' and 'Up_frac_out' are 
+the ratio, (spin up) /(spin up + spin down) neutrons before the sample and at 
+the analyzer, respectively.
+
+*Note I: The values of 'Up_frac_in' and 'Up_frac_out' must be in the range 
+between 0 and 1. For example, both values are 0.5 for unpolarized neutrons.*
+
+*Note II: This computation is totally based on the pixel (or atomic) data 
+fixed in the xyz coordinates. Thus no angular orientational averaging is 
+considered.*
+
+*Note III: For the nuclear scattering length density, only the real component 
+is taken account.*
+
+.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
+
+.. _PDB_Data:
+
+PDB Data
+--------
+
+This Generic scattering calculator also supports some pdb files without 
+considering polarized/magnetic scattering so that the related parameters 
+such as Up_*** will be ignored (see the Picture below). The calculation for 
+fixed orientation uses (the first) Equation above resulting in a 2D output, 
+whileas the scattering calculation averaged over all the orientations uses 
+the Debye equation providing a 1D output
+
+.. image:: gen_debye_eq.gif
+
+where vj /beta/j /equiv/ bj the scattering length of the j'th atom. The resultant outputs 
+will be displayed in the DataExplorer for further uses.
+
+.. image:: pdb_combo.jpg
