How to accept & reject in PMI Test. 

The principle of XRF (PLZ SUSCRIBE MY RU-vid CHANNEL)
A primary X-ray, typically generated in an X-ray tube, hits an inner shell electron of the atom and ejects the election from the atom. The open position is filled by an electron from a further outer shell and fluorescence radiation is emitted.
What is XRF and how does it work?
XRF is an acronym for X-ray fluorescence spectroscopy. ... Handheld XRF analyzers work by measuring the fluorescent (or secondary) X-rays emitted from a sample when excited by a primary X-ray source. Each of the elements present in a sample produces a set of characteristic fluorescent X-rays, or “unique fingerprints”.