Gamma-Ray Absorption Coefficients

In the early period of X-ray research, the radiation sources were discharge tubes with applied potentials well below 100 key. X rays from these sources interact with matter primarily through the photoelectric effect. Their penetration is then limited by photoelectric absorption and is adequately described by an exponential law.

Penetration and Diffusion of X Rays

Mathematical theory of radiation fields

Accurate airborne multichannel gamma‐ray surveys require accurate knowledge of the spectral shapes of the natural radioelements and their variation with height. Simple physical considerations suggest a model with two spectral components for each radioelement, in which the first component decays into the second with increasing height. The two spectral components are approximately identified with gamma rays that have been scattered and those that have not been scattered since entering the atmosphere, although this interpretation is irrelevant to the applications of the model. The model’s analytic representation of spectral dependence on height yields an explicit formula for the effective height of the detector as deduced from spectral shape. Atmospheric radon is shown to produce a negative effective height, which implies a possible method for estimating atmospheric radon directly rather than from spectral shape. An extension of this approach gives an approximate formula for estimating the spectral contribut...

The altitude dependence of terrestrial gamma‐ray spectra: A simple model

As the simplest problem involving the multiple scattering of gamma-rays, the case of perpendicular incidence on a plane slab has been studied by various simple theoretical methods. No exact solution is available as a test of these methods, but approximations of increasing accuracy, known to give too small a dose under the slab, have been combined with a theoretical upper limit for the dose, forming a zone in which the exact solution must lie. Most of the methods tested could be used even if pair-creation or the photoelectric effect gave an appreciable absorption, though for simplicity the computations have been carried out for pure Compton scattering and for quantum energies of a few MeV. Polarization by the Compton effect has been neglected. The best of the simple methods is a modification of the upper limit solution; in problems where this is too difficult to formulate, a good alternative is to calculate the dose from unscattered and once-scattered quanta, giving the latter the penetrating power of the incident quanta and the maximum possible energy-absorption cross-section.

L. Cave

Papers

The Scattering of Gamma-Rays in Extended Media. I. Perpendicular Incidence on a Plane Slab