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Beta Backscatter — principle using
beta rays and diverting them at a plated samlple. Electrons will
penetrate plating material and reflect back (back scattered) toward
the source. George-Mueller tube collects electrons and is used
for conversion to coating thickness.
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Beta
rays are electrons emitted from unstable radio isotopes. If a
highly collimated beta source is directed at a plated sample (gold
over nickel on a printed circuit board, for instance), the electrons
will penetrate the plating material and be reflected back (back
scattered) toward the source. They can be collected and counted
with a Geiger-Mueller tube for subsequent conversion to coating
thickness. The atomic number of the coating material must be sufficiently
different (at least four atomic numbers) from the atomic number
of the base material to achieve accurate readings of coating thickness.
The beta backscatter method is also effective for measuring tin
and tin-lead thickness and composition, copper, chrome and anodize.
Beta Backscatter instruments are only available in the North American
Markets.
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