Optimization of a simple X-ray diffraction instrument for portable and planetary applications

The constraints placed on the design of portable and planetary X-ray diffraction (XRD) instruments by the limited mass, power and volume budgets are very different, in general, to the constraints applicable to laboratory equipment. A relatively simple angle-dispersive, reflection-mode instrument design with no moving parts is used to illustrate some optimization methods using Monte Carlo ray-trace modeling and theoretical calculations. Utilization of parafocusing is an important aspect of the optimization. An 55Fe radioisotope X-ray source is assumed, and it is shown that commercial, off-the-shelf sources are not optimal in their design for XRD applications. The geometrical parameters relating to the source and to a simple collimating aperture are subjected to an optimization process, which keeps both the flux incident on the sample and the size of the parafocusing circle constant.