The Extension of the X-Ray Spectrum to the Ultraviolet

Characteristic X-Radiation Due to Slow Electrons, 1,000 to 12 Volts.—By using the methods of modern high-vacuum technique, the difficulties experienced by previous investigators have been largely overcome. The radiation was measured in terms of the photo-electric current excited from a Pt dish. The effect was made large by utilizing a hot tungsten helix as a source of electrons, and all disturbances due to gas ions formed by the electrons were eliminated by maintaining a very high vacuum and by interposing an electrostatic field across the path of the radiation. The deflections thus obtained were large and perfectly reproducible. When the deflections per unit thermionic current were plotted as a function of the accelerating potential, sharp breaks appeared which each indicate the minimum energy necessary to excite the corresponding characteristic radiation. From these energy determinations the corresponding wave-lengths were computed using the quantum relation. Thus the following values have been obtained for the convergence wave-lengths in Angstroms: $K$-series of carbon 42.6, oxygen 23.8; $L$-series of carbon 375, oxygen 248, aluminum 100, silicon 82.5, titanium 24.5, iron 16.3, copper 12.3; M-series of aluminium 326, titanium 85.3, iron 54.3, copper 41.6; N-series of iron 247, copper 116. The relation of these results to those obtained by crystal analysis and by spectrum analysis is discussed. It is suggested that the radiation from solid targets may differ from the radiation from gaseous atoms, especially for the lighter elements.