The Compound Photoelectric Effect of X-rays in Light Elements

Abstract

The $K$ fluorescence yields of oxygen, neon, and argon have been found from the numbers of double photoelectron tracks (produced by auto-ionization), and the numbers of single tracks, on 1950 stereopictures made in a Wilson cloud chamber, with atmospheres containing small amounts of the gases under investigation. From the data of this experiment and the $K$ absorption data collected by Wien and Harms, the yields are: oxygen 8.2 percent, neon 8.3 percent, and argon 14.9 percent, for 0.709A x-rays. The $K$ yields previously found for heavier elements by A. H. Compton, M. I. Harms, and L. H. Martin, and those given here, mostly lie on a smooth curve. Auger's value for krypton seems to be 13 percent to low, and that for argon, at least 45 percent too low. The most probable values of the $K$ yields of 47 elements are considered to be, at present, as follows: O 8.2, F 8.5, Ne 8.8, Na 9.3, Mg 9.9, Al 10.5, Si 11.2, P 12.0, S 12.8, Cl 13.8, A 14.9, K 16.0, Ca 17.2, Sc 18.5, Ti 20.0, Va 21.7, Cr 23.6, Mn 25.5, Fe 28.4, Co 31.2, Ni 34.4, Cu 37.8, Zn 41.2, Ga 44.3, Ge 47.4, As 50 5, Se 55.3, Br 55.8, Kr 58.2, Rb 60.2, Sr 62.2, Y 64.0, Zr 65.5, Nb 67.0, Mo 68.0, Ma 69.1, Ru 70.0, Rh 70.8, Pa 71.7, Ag 72.5, Cd 73.0, In 73.5, Sn 74.0, Sb 74.5, Te 74.8, I 75.0, Xe 75.3, expressed as percentages of the $K$ quanta that escape from $K$ ionized atoms. The $L$ yield of argon is estimated to be between zero and 20 percent, on the basis of the numbers of tracks counted. A new type of double track has been observed; its components are of similar energy, but produce very unequal ionization. They are believed to be due to krypton atoms with metastable lives of the order of 0.01 second. The cloud method can be used for detecting heavy gases in light ones. It is shown that 15 parts of krypton in ${10}^{5}$ of oxygen, or 50 parts of xenon in ${10}^{6}$ of oxygen, will give 2 percent of characteristic double tracks due to the heavy element.