Speculations concerning the α-, β- and γ-Rays of Ra B, C, C.- Part I. A revised theory of the interval absorption coefficient

Abstract

1. Introduction .- It is well known that the γ-ray emitted by radioactive nuclei are often very strongly absorbed in a species of photoelectric effect by the planetary electrons of the parent atom, thus giving rise to the sharp lines of the β-ray spectrum. The recent work of Ellis and Aston provides numerical values of this “internal conversion coefficient” of the γ-rays from Ra BC and Ra CCD-data which bring out more clearly than hitherto the curiosities of this coefficient (see Table I below). The present paper is the outcome of repeated discussions between Dr. Ellis and the author about possible explanations of the data. All the preliminary work was carried out in collaboration, and it was our original intention to publish our results jointly. This has proved impossible, so that the responsibility for the corrections of the calculations of this paper rests entirely on me. But the work could not have been attempted without Dr. Ellis’s help. Ellis and Aston find that this coefficient behaves so differently for different classes of β-ray line that one is even sometimes tempted to suspect a different mechanism of emission. The rather soft γ-rays of Ra BC are converted by the K-level electrons in fractions of the surprising size of 10 percent. To 25 percent., varying in a normal manner with the frequency. The harder γ-rays of Ra CC’D fall, however, into three groups. The main γ-rays of energy from 6·12 X 10 5 to 12·48 X 10 5 volts have a practically constant conversion fraction of about 0·006; those from 13·90 X 105 to 22·19 X 10 5 volts a similar constant fraction now about 0·006; those from 13.90 X 10 5 to 22·19 X 10 5 volts a similar constant fraction now about 0·0015. All these γ-rays, though most easily studied via their derived natural β-ray lines undoubtedly can be studied as γ-rays outside their parent atom. But there is a third group containing one outstanding γ-ray of 14·26 X 10 5 volts energy whose existence has been inferred only from certain associated β-ray lines, among the strongest in the spectrum. (if is it a γ-ray) is so strongly converted in the parent atom that it is doubtful if it has ever been observed as a γ-ray at all. It would be consistent with (though not necessitated by) the evidence, to assert that it is a γ-ray with an internal conversion factor unity.