Direct And Indirect Characteristic X-rays Their Ratio As A Function Of Cathode-ray Energy

330 PHYSICS: D. L.. WEBSTER PRtoc N. A. S. thLat several modes of vibration are excited at once, we have no experience available to aid us in setting up an expression for the probability of a double emission from the nucleus. In conclusion, the experiment suggested above is critical in one direction only, and previous experiments point strongly to the conclusion that the principles of energy and momentum are valid in each atomic process. Such experiments are a sheet anchor of faith when we seek to apply exact laws to occurrences within the nucleus. Z. Physik, 38, 803 (1926) and 40, 167 (1926). 2Proc. Roy. Soc., Al17, 258 (1927). ' Z. Physik, 43, 172 (1927). See also the preceding paper. ' Ellis and Skinner, Proc. Roy. Soc., A105, pp. 165 and 185 (1924). ' Phil. Mag., 27, 854 and 28, 263 (1914). 6 Phys. Rev., 13, 272 (1919); 14, 179 (1919); Proc. Nat. Acad. Sci., 6, 105 (1920); Phys. Rev., 23, 559 (1924). 7 Phil. Mag., 50, 521 (1925). 8 Phys. Rev., 26, 290 (1925). DIRECT AND INDIRECT CHARACTERISTIC X-RAYS: THEIR RATIO AS A FUNCTION OF CATHODE-RAY ENERGY BY DAVID L. WEBSTER STANORD UNIVERSITY, CAUjORNIA Communicated March 10, 1928 I. Introduction.-In the June, 1927, issue of these PROCEEDINGS an account was given of some preliminary experiments on the ratio of the intensities of characteristic x-rays produced by the two processes that occur in any ordinary x-ray target and have been called the direct and indirect processes. The direct process may be defined as the ejection of K electrons from atoms by impact of the cathode rays on those atoms and their resulting reorganization; the indirect process is the ejection of K electrons by photo-electric effect of continuous-spectrum x-rays excited by cathode rays in other atoms. Two questions arise here: one is whether these processes both occur to any noticeable extent; and the other is on the nature of the dir