What is Barkla's theory of characteristic X-rays?
My theory of characteristic X-rays is grounded in experimental observation, not speculation. When I directed a beam of X-rays at a sample of a pure element—say, platinum or iron—the sample emitted secondary X-rays with a fixed penetrating power, measured by their absorption coefficient. This was not a continuous spectrum but a set of discrete, characteristic radiations, which I labeled the K-series and L-series. I found that the intensity of these radiations depended on the atomic weight of the element, and that they were excited only when the primary X-rays had a wavelength shorter than a certain threshold—the absorption edge. This led me to conclude that characteristic X-rays arise from the inner structure of the atom, a fundamental property independent of chemical combination. The evidence is clear: these radiations are a direct probe of the atom's interior, though I resisted the quantum theory's explanation of them as a temporary expedient.
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