This section is dedicated to sharing materials that would aid in learning and understanding of principles and techniques applied at the BioXAS Imaging beamline. With the plain description of complex concepts, we aim to assist anyone who is interested in learning synchrotron techniques, regardless of their background and training. 

X-ray Fluorescence (XRF) imaging

In very simple terms, the beamline components will select, deliver and focus the monochromatic (single wavelength) X-ray light onto the sample mounted in the experimental hutch. The sample is moved either by point-by-point or in continuous fly-scanning mode relative to the incident X-ray light. In the former acquisition mode the sample is moved to a position, stops, then resumes moving; however, in the continuous fly scanning mode data are collected as the sample is moving in both directions. The dwell time for the fly scanning mode can also be set shorter (ms), therefore a collection of data with this mode can be a lot shorter in comparison to the point-by-point scan. The dwell time is how much time the X-ray light is allowed on the specific area or pixel. The size of a pixel is usually consistent with the beam size.

When the incident X-ray photon hits the sample, the inner shell electrons of atoms in the sample become excited, creating photon electrons and a core hole. The vacant inner shell of an atom is rapidly filled with an outer electron, subsequently releasing X-ray fluorescence photon. This emitted X-ray fluorescence photon's energy is unique for each atom, serving as a fingerprint to identify and study the distribution of elements in various types of samples. 

The images of elements' distribution in a scanned sample are built by a computer from a single-pixel X-ray fluorescence spectra collected by the X-ray detector. The peaks visible on the computer screen (see image below) would represent the energy of each photon specific to each element detected, the height of the peak indicates number of photons at different energies. 

Useful links to elements absorption edge/emission lines and more.