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<p>[QUOTE=&quot;calcol, post: 26332704, member: 77639&quot;]There are multiple ways to do XRF.&nbsp; There are handheld instruments that shoot a quick pulse of high energy x-rays at the coin.&nbsp; The impinging x-rays will displace some orbital electrons in the metal atoms.&nbsp; When the orbitals refill from lower energy orbitals or the circulating crowd of electrons passing among metal atoms, characteristic (i.e. specific energy), x-rays will be emitted.&nbsp; These are detected, and their energy evaluated as they hit the detector in the instrument.&nbsp; The sum of these evaluations constitutes a spectrum of return intensity versus energy with peaks representing the characteristic energy of the orbitals of different elements (i.e. different metals).&nbsp; The software in the instrument analyzes the peaks and produces a readout of the percent of various metals.</p><p><br /></p><p>Another way to displace inner electrons from their orbits is with a beam of subatomic particles.&nbsp; For XRF, this is usually done with a scanning electron microscope (SEM) which shoots a beam of electrons at the metal in a vacuum and then evaluates the spectrum of emitted x-rays.&nbsp; One advantage of SEM compared to handheld x-ray devices is the electron beam can be focused on a very small (submicron) area.&nbsp; This allows multiple sites on the surface of a coin to be analyzed.&nbsp; So, for example, if a coin was suspected of being gilt but there appeared to be a few small spots of exposed underlying metal, these could be analyzed.&nbsp; The one time PCGS had a coin analyzed for me, it was done by SEM with 5 different sites on each side analyzed.&nbsp; And yeah, the original slab label was wrong, which is another story.</p><p><br /></p><p>XRF is primarily a surface analysis tool.&nbsp; Usually, gilt coins will return the same spectrum as solid gold coins.&nbsp; Very powerful x-ray-emitting lab instruments or SEMs can digger deeper, but it’s still pretty shallow.&nbsp; The problem is not the ability of high energy x-rays or electrons to penetrate, it’s the ability of the characteristic x-rays, which are of lower energy, to get out and be detected.</p><p><br /></p><p>Cal[/QUOTE]</p><p><br /></p>

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