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Mars-XRD is an X-ray diffractometer developed for the in situ mineralogical analysis of the Martian
soil. The main components of the Mars-XRD experiment are: a Fe55 radioactive source, a collimator
and a CCD-based detector system. For spectroscopic requirements and quality of the machined micrograin
of the sample, the beam section should not be larger then 1 × 10 mm2 at sample distance. The
current collimator baseline is based on a two-windows system that uses about 20% of the total source
emitting surface. To improve the X-ray flux, we are studying a collimator with converging blades which
permits to use the entire source emission and tune the beam section. In order to better estimate the
efficiency of this collimator and because of the high number of variables, a C++ program has been written
that look for the best blades configuration among billion of combinations. In addition to the collimator
configuration, this software simulator gives the sample photons distribution for different angles of the tilt
of the source and for each couple of blades. The optimized collimator transmits a flux 30% higher than
a system with blades with the same angular aperture and 5 times higher than a two windows collimator.
Moreover the target photon distribution is a triangle function well focused on the sample surface instead
of an irregular function obtained with the previous system. Higher performances arise with the source
perpendicular to the source-sample direction. Thanks to this optimization we expect to strongly improve
the resolution of the diffraction pattern which is the main goal of the current activities of the instrument
development. This software simulator could be used also for the optimization of collimator system for
the other wavelength and applications (e.g. radiotherapy).
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