Abstract
The absorption and scattering of gamma-rays from radium filtered through 23 mm. of lead have been measured in magnesium, aluminium, zinc, tin and lead.
On the assumption that the mean effective wave-length of the radiation employed is0.021 Å, the experimental results are consistent with the following statements:-
When gamma-rays traverse matter, the characteristic radiations of the absorbing medium are excited.
The atomic fluorescent absorption coefficient of gamma-rays depends upon the wavelength of the incident radiation and the atomic number of the absorber according to the law τ/ρ·ω=Kλ3N4, which holds for X-rays.
The radiations which accompany this fluorescent absorption are the characteristic radiations of the K, L, M,... series of the absorbing elements.
The absorption of gamma-rays in light elements is due almost entirely to scattering.
The pure atomic scattering absorption coefficient is proportional to the atomic number of the absorber.
In addition to fluorescent and scattering absorption, a true absorption exists, the atomic coefficient of which is proportional to the atomic number.
Compton's formulae, deduced from his Quantum Theory of Scattering, would account for the experimental results if the wave-length of the incident radiation were 0.020 Å. Jauncey's formulae would require the wave-length to be 0.029 Å.