Published online by Cambridge University Press: 24 October 2008
No satisfactory formula has so far been derived theoretically for the photoelectric absorption of X-rays and γ-rays. The empirical law
has hitherto been generally accepted as giving approximately the variation of the photoelectric absorption coefficient per electron, with atomic number Z and wave length λ for X-rays of wave length greater than 100 X.U., and the validity of this law has often been assumed for γ-rays also.
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