Angular calibration in energy dispersive X-Ray diffraction by using genetic algorithms

In Energy Dispersive X-Ray diffraction measurements, the estimate of momentum transfer q, on which the diffracted intensity depends, should be as accurate as possible. Since q, in turn, depends on both the energy and the scattering angle, an error on the latter due to an incorrect positioning of the sample, to the asymmetric angular spread induced by the collimation slits or, in general, to any uncertainty on the geometric setup, results in an uncertainty on the q value. Here, a new self calibration method to correct such errors, based on a genetic algorithm is presented. It is robust, fast and completely automatic. Results obtained by carrying out Energy Dispersive X-Ray Diffraction measurements on reference samples are reported and discussed. They show how the application of such genetic algorithm may provide a fast esteem of the two parameters required when multiple angle pattern collection is performed, namely the effective starting angle and the angular step. In this way, reliable q-values of all the diffraction pattern features (Bragg peaks for crystalline, and diffused bumps for non-crystalline samples) are obtained.