Effective Wave-lengths of -Rays


ONE of the difficulties in explaining the results of experiments on -rays is our lack of knowledge of the variation of intensity with wave-length in the spectrum of the -rays. This has led to the use of “effective” wave-lengths (two, in general, being needed because scattering and absorption coefficients vary with the wave-lengths in different manners), and values have been used, which, although incorrect, apparently help to explain the experimental results. For example, I have pointed out at two scientific meetings (American Physical Society, December 1922, and the British Association, Toronto, August 1924), that if we assume, as has been done by several physicists, that the effective wave-length of the -rays is about 0.02 Å.U., the secondary -rays produced in light elements by the hard -rays of radium-C possess far too much energy to be recoil electrons (for the properties of which see a paper by Compton and Hubbard, Physical Review, 4, p. 439, 1924). Experimental evidence indicates that these -rays are not photoelectrons. If they are recoil electrons, the effective wave-length of the -rays must be taken as about 0.008 Å.U. in order that we may account, on the quantum theory of scattering, for their observed energy. This result, which was first obtained by a comparison of the relative penetrating powers of the secondary -rays and the -rays of radium-E, has led, among other things, to a consideration of the following questions.

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GRAY, J. Effective Wave-lengths of -Rays. Nature 115, 13 (1925). https://doi.org/10.1038/115013a0

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