After looking on the diffraction pattern one usually wants to determine its parameters. There is a variety of ways how to do it. One way can start with the background separation and corrections for different angular factors as well as Ka1 line elimination.
Corrections submenu
Background determination and subtraction
Data correction by GCS
Smoothing of the data
Alpha 2 elimination
Intensity - integrated intensity calculation for all peaks
Lorentz - correction for angle dependent factors
Background
There is no automatic procedure of background elimination in Version 1.5.
Global background:
Only left and right points are to be given. They are connected by
straight line and the background is determined by this manner
within the corresponding 2 q range. (The limits are given by graphic cursor THE LEFT
LIMIT MUST BE GIVEN FIRST !). This is used mainly for
determination of zero estimates for least-squares fitting
Segment calc:
Several segments of the diffraction pattern which do not contain
contributions from diffraction peaks must be given. Input of all
the limits is graphical - for each segment first left and then
right limit. By pressing <ESC> at left limit input the
definition of segments is finished. Then a polynom is fitted to
all the data lying within the segments. The order of polynom must
be given in the top input line (0-4). If zero is given,
then polynomials from the first to fourth orders are fitted and
that giving the smallest error is used. Finally, the user is
asked for acception of the background calculated. If the answer
is negative (<ESC>) another order of polynom is used,
otherwise the background within approapriate limits is
determined. It can be changes later.
Calculation:
The background is calculated in the same way like in the above
scale. In addition the background fitted is extended to the whole
X-scale range of the file.
Subtraction:
The background determined by one of the above methods is
subtracted from the Current pattern in the whole 2 q range (see File parameters for minimal and maximal values). After a single
application of the procedure with subtraction a variable BackgroundSubtracted
is set to TRUE (see Get info, Environment). This is only changed by loading a new file.
Smoothing
The diffraction pattern is smoothed within the current 2 q limits by the current method - linear or Savitzky-Golay (default). The method can be changed in Lines, Peak search.
First, the smoothing window (number of points) must be given in the top input line. Then the result is shown and if accepted (top line) it replaces the original data within the current limits. After a single application of the smoothing procedure with acception a variable DataSmoothed is set to TRUE. This is only changed by loading a new file.
Data correction
One data point can be corrected in Current file with the aid of graphic cursor . Select approapriate q position and then set a new value of intensity. Circles and crosses as labels for data point are useful in the correction procedure. By multiple application of the item more data points can be corrected.
Alpha 2 stripping
The elimination of Ka1 line by the algorithm of Ladell, Zagofsky and Pearlman (J.Appl.Cryst. 8(1975),499-506) in the whole range of the Current file. The range can be graphically changed, if TAB is pressed after the selection of the menu item. Number of histograms (see the reference) must be given (3, 5, or 7). The result of the elimination is displayed. The histograms are loaded each time from the file 'ALPHA2.PRF' for the corresponding radiation. The file can be updated and extended by the user. If the file is not found, the correction is not performed. After a single application of the procedure a variable Alpha2 Subtracted is set to TRUE (see Get info, Environment). This is only changed by loading of a new file.
Intensities
Integrated intensities of all the peaks which have been found (Peak search) are calculated. However, at first the background should be subtracted. The calculation is performed very simply from the left side of peak (or groups of peaks), where the intensity is zero to the right point with the same condition. There is no peak separation. The left and right limits can be changed and calculations carried out somewhat more precisely in Parameters item.
Lorentz correction
Some angle dependent factors can be corrected. The procedure includes different diffraction geometries and is applied to the whole 2 q range.
Lorentz -
correction for the Lorentz factor. After a single application of
the procedure a variable LorentzFactorCorrected is set
to TRUE (see Get info, Environment) and correction cannot be applied again. This is only
changed by loading of a new file.
Polarization -
correction for the polarization factor. After a single
application of the procedure a variable PolarizationCorrected
is set to TRUE and correction cannot be applied again. This
is only changed by loading of a new file.
Absorption -
correction for the absorption factor. After a single application
of the procedure a variable AbsorptionCorrected is set
to TRUE and correction cannot be applied again. This is only
changed by loading of a new file.
The above corrections need some Instrumental parameters (Main Menu). They should be checked before application of the corrections. They also can be changed either in program or in configuration file. The latter way is recommended if the pameters are not varied frequently. Different configuration files can be used (in Difpatan command line).
Because of control variables it is recommended to use the correction only to the Main file.