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common geometries through the graphical user interface.
More complex geometries can be simulated using the script-
ing interface.
Monte Carlo modeling is based on simulating the trajec-
tories of thousands of electrons and X-rays. The simulated
electrons are given an initial energy and trajectory which
models the initial energy and trajectory of electrons from an
SEM gun. The simulated electrons scatter and lose energy as
their trajectories take them through the sample. Occasionally,
an electron may ionize an atom and generate a characteristic
X-ray. Occasionally, an electron may decelerate and gener-
ate a bremsstrahlung photon. The X-rays can be tracked
from the point of generation to a simulated detector. A
simulated spectrum can be accumulated. If care is taken
modeling the electron transport and the X-ray interactions,
the simulated spectrum can mimic a measured spectrum.
Other data such as emitted intensities, emission images, tra-
jectory images and excitation volumes can be accumulated.
Multi-element materials are modeled as mass-fraction
averaged mixtures of elements. Complex sample geometries
can be constructed out of discrete sample shapes that include
blocks, spheres, cylinders, regions bounded by planar sur-
faces, and sums and differences of the basic shapes. In this way,
it is possible to model arbitrarily complex sample geometries.. Fig. 17.13 To assist the user, DTSA-II maintains a database of
materials. Each time the user enters a new material or redefines an
old material, the database is updated. The database is indexed by
“Name”
. Fig. 17.14 Albite (“NaAlSi 3 O 8 ”) and anorthite (“CaAl 2 Si 2 O 8 ”)
represent end members of the plagioclase solid solution series. To
calculate a admixture of 50 % by mass albite and 50 % by mass anorthite,
you can enter the formula “0.5NaAlSi3O8 + 0.5CaAl2Si2O8”. Other
admixtures of stoichiometric compounds can be calculated in a similar
manner. Remember to provide a user friendly name for the database
. Fig. 17.12 It is possible to enter the chemical formula directly into
the “Name” edit box. When the search button is pressed the chemical
formula will be parsed and the appropriate mass and atomic fractions
entered into the table. Capitalization of the element abbreviations is
important as “CO” is very different from “Co”—one is a gas and the other
a metal. More complex formulas like fluorapatite (“Ca 5 (PO 4 ) 3 F”) can be
entered using parenthesis to group terms. It is important that the for-
mula is unambiguous. Once the formula has been parsed you may
specify a new operator friendly name for the material like “Albite” of “Flu-
orapatite” in the “Name” edit box
Chapter 17 · DTSA-II EDS Software