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National Advisory Committee for Aeronautics, Technical Notes - Tables for Determining Reduction of Energy and Intensity of X-Rays and Gamma Rays at Various Scattering Angles in Small Thickness of Matter

Tables are presented for determining the total—absorption
coefficients, as well as the intensities and spectral distribution
of gamma-rays at any given scattering angle. Only thin scatterers
are treated and secondary effects are neglected.

Included are both experimental and computed data on gamma-rays
of quantum energies up to 20 million electron volts for all elements
for which significant data are available. Published, experimentally
verified data on total-absorption coefficients have been used wher-
ever possible. In those energy regions for which such data are still
lacking, values of photoelectric, Compton, and pair-formation coeffi-
cients were computed using the formulas of Hall and Klein-Nishina and
interpolating from the Bethe-Heitler formula, respectively. Examples
are included to illustrate the use of the tables.

A determination of the absorption characteristics of gamma-rays
in thick absorbers is complicated by secondary factors, such as
multiple scattering and angular distribution of annihilation radi-
ation. As a first approximation to the problem of gamma-ray scat-
tering in thick absorbers, a consideration of single scattering in
thin absorbers is warranted, The problem of scattering by thin
absorbers is much simpler than the corresponding one for thick
absorbers because the aforementioned secondary effects may be neg-
lected without serious loss of accuracy.

The computed values supplement the experimental ones and are
included only for those cases in which the theory has been checked
by published experimental data. The tables contain values of absorp-
tion coefficients for gamma-rays extending from the soft X—ray region
of 0.01 Mev (million electron volts) to the hard gamma-ray region of
20.0 Mev. Auxiliary tables are included for all chemical elements
that are solids or liquids at room temperature and for which pub-
lished data on densities are available.