One hundred years of moseley's law: An undergraduate experiment with relativistic effects

As the centenary of H. G. H. Moseley's untimely passing approached, the authors undertook an evaluation of Moseley's work as the basis for an undergraduate laboratory experiment. Using a modern solid-state detector and low activity sources, characteristic K X-rays were excited and detected without the use of a vacuum chamber, from a selection of elemental metal foil samples from Ti to Er. The authors introduce first order relativistic corrections into the experimental analysis to obtain better fits for K X-ray energies that deviate substantially from Moseley's original law for elements beyond the first row transition metals. The experimental set up is described in detail, and the data and conclusions are readily reproducible by undergraduate students in the span of a couple of typical lab sessions.