Abstract: A system includes a stage for supporting a sample having at least first and second atomic elements. The first atomic element has a first characteristic x-ray line with a first energy and the second atomic element has a second characteristic x-ray line with a second energy, the first and second energies lower than 8 keV and separated from one another by less than 1 keV. The system further includes an x-ray source of x-rays having a third energy between the first and second energies and at least one x-ray optic configured to receive and focus at least some of the x-rays as an x-ray beam to illuminate the sample. The system further includes at least one x-ray detector configured to detect fluorescence x-rays produced by the sample in response to being irradiated by the x-ray beam.