CrystalDiffract provides a dedicated, Scattering Factors window, that lets you edit x-ray atomic scattering factors and neutron scattering lengths.
X-ray scattering factors are represented by a 9-coefficient polynomial, the values f1-f9 in the Scattering Factors table. CrystalDiffract uses the standard analytical approximation defined in the International Tables for Crystallography, Volume C:
f = Σi=1,4 ai exp( -bi sin2 θ / λ2 ) + c
Where f is the value of the atomic scattering factor for a particular sin θ / λ and ai bi, and c are coefficients. These are tabulated for different elements in the scattering factors table as the variables f1-f9 (to avoid confusion with the neutron scattering length, b):
Equation: | a1 | b1 | a2 | b2 | a3 | b3 | a4 | b4 | c |
CrystalDiffract: | f1 | f2 | f3 | f4 | f5 | f6 | f7 | f8 | f9 |
Neutron scattering lengths (denoted by the symbol b) are given in femto metres (1 fm = 1 x 10-15 m). Zero values indicate that no data are available for these elements. CrystalDiffract takes its default data from the tabulated values published in Neutron News in 1992.
You can compare the results for multiple elements graphically, and copy or export graphics.
Do one of the following:
Choose: Edit > Scattering Factors.
Click the Factors button in the toolbar.
Select the appropriate element row in the table (command-click to select multiple rows). The corresponding atomic scattering factor curve is displayed in the graphics pane above the table.
Do the following:
Click in the graph to display a vertical cursor.
Click-and-drag the cursor to measure different parts of the scattering factor curve.
To copy graphics to the clipboard:
Right-click on the graph and choose: Copy Graphics.
To save graphics to a graphics file:
Right-click on the graph and choose: Export Graphics.
Note: you can resize the graphics pane by dragging the horizontal divider between it and the table. You can also resize the scattering factors window by clicking-and-dragging its sides or corners.
To edit an existing element:
Locate the element you wish to edit in the table.
Edit the appropriate parameters for x-ray scattering factors (f1-9) or the neutron scattering length (b).
To add a new element:
Click the + button in the bottom left-hand corner of the window.
To delete an existing element:
Select the row(s) you wish to delete (shift-click to select multiple rows)
Click the - button in the bottom left-hand corner of the window.
See Also