The secondary and tertiary cathode rays produced by external and internal absorption of homogeneous X-rays

Abstract

This paper deals with the results of further measurements made with an improved form of the Robinson-Rawlinson apparatus ('Phil. Mag.,’ vol. 28, p. 280 (1914)). Results already obtained with the same or similar apparatus have been described in two papers which will be referred to as R1 and R2 respectively. Full details of the apparatus and method are given in these papers. In the present work, molybdenum K rays have been used as primary X-radiation. In some of the experiments, the rays were passed through a thin filter of zirconium oxide to cut down the Kβ doublet. This filtration is less effective than the filtration of copper K rays by nickel (used in R1 and R2), as the K absorption discontinuity is notoriously less marked with heavier elements. We found eventually that we got better photographs, with approximately the same exposures (1½ to 3 hours), by using the full unfiltered X-ray beam and slower photographic plates. The energy difference between the Mo K x 1 and Mo Kβ 1 quanta is fairly large (about 2125 electron-volts); hence the magnetic spectra of a particular group of levels, produced by the action of K x1 and Kβ 1 respectively, do not cause any serious inconvenience by overlapping. Indeed, the presence of the spectra due to Kβ 1 often affords a valuable control of the results. Further, it will be seen that the presence in the unfiltered beam of a greater proportion of “white” radiation has led to the observation of specially interesting results from fluorescent effects in the target.