Charles Glover Barkla
1877–1944, Widnes, Lancashire, England, Edinburgh, Scotland
British physicist who discovered the characteristic X-rays of the elements, winning the Nobel Prize in Physics for 1917.
Barkla studied physics at Liverpool and Cambridge, then returned to Liverpool before holding chairs in London and Edinburgh. He devoted his career to the study of X-rays — their scattering, absorption, and the secondary radiations they produce — and at Edinburgh built a lasting school of radiation research. He received the Nobel Prize for discovering that each element emits its own X-ray 'fingerprint', a finding that paved the way to understanding the electron-shell structure of the atom.
Nobel-winning work
The 1917 Nobel Prize (presented at the 1918 ceremony) honoured 'his discovery of the characteristic Röntgen radiation of the elements'. When X-rays were shone on materials, Barkla observed that they produced secondary radiation; from about 1906 to 1911 he proved that, besides ordinary scattered radiation, each element also emitted X-rays of characteristic penetrating power, unchanged by experimental conditions and depending only on the element itself. He grouped these into series he called K (harder) and L (softer).
He also showed that the intensity of X-ray scattering was proportional to the number of electrons in the scattering atoms — an early clue to the atom's inner structure. Characteristic X-rays were later identified as spectral lines produced by electron transitions between inner shells; they related directly to shell structure and to the ordering of the periodic table by atomic number (Moseley's work), turning X-rays into a probe of atomic structure.
Workplaces: University of Liverpool, University of Edinburgh
United Kingdom