The process by which high energy photons, x-rays, interact with atomic electrons and produce lower-energy photons with energies characteristic of the difference in electron binding energies is called x-ray fluorescence.
What it measures
X-ray energies are required in order to eject bound electrons from their orbital. the subsequent characteristic energy x-ray emission identifies the element.
Most common uses in conservation
elemental analysis of paintings and artifacts
XRF units are portable and can be placed in front of a painting or other art object. XRF units are popular in museum applications because they allow for analysis without destructive sampling.