Opacity and Stellar Structure


THE emission of the nuclear γ-rays from radioactive elements is accompanied by the photoelectrons emitted from the atom giving rise to the γ-radiation. This has been described by Ellis1 as the internal photoelectric effect. For a long time, the obvious explanation has been that the γ-ray is sometimes absorbed by the extranuclear electron which is emitted with the energy given by the Einstein equation. Calculations based on this view, made recently by Casimir, lead to the conclusion that the probability of emission of the photoelectron is about 1/10 to 1/30 of that experimentally observed. Thus, for RaC γ-ray of energy 6.12 × 105 volts, experiment shows that in 994 disintegrations out of 1000 the γ-ray escapes and in 6 it is absorbed. Therefore, the value for the probability of absorption is 6 × 10-3, while the calculated value for this case is only 0.46 × 10-3: that is, the experiment shows the atom to possess about ten times more opacity for its γ-radiation than is indicated by calculation.

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  1. 1

    Ellis: a very lucid account is given in Science Progress, April 31, p. 615.

  2. 2

    Fowler, Proc. Roy. Soc., vol. 129, p. 1.

  3. 3

    Milne, Mon. Not. Roy. Ast. Soc., vol. 91, p. 4.

  4. 4

    Observatory, Feb. 1931, p. 36.

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KOTHARI, D. Opacity and Stellar Structure. Nature 127, 740–741 (1931). https://doi.org/10.1038/127740b0

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