Absorption of Gamma-Rays in Aluminum

The scattering cross section for gamma-rays in aluminum was measured by two independent methods at the three energies 1.11, 1.71, and 2.76 Mev. The results 0.156, 0.125, and 0.0996 ${\mathrm{cm}}^{-1\mathrm{}}$, respectively, for the three energies are in agreement with the predictions of theory within the experimental error of ±1 percent. The essential features of the measurements are: (1) Choice of gamma-ray energies and absorbing material such that Compton scattering is the only important process. (2) Use of a geometry which effectively eliminates single and multiple scattering and permits an accurate determination of the background. (3) Elimination of errors due to the other gamma-ray energies emitted by the source. (4) Determination of corrections for absorber impurities, counter deadtime, and random fluctuations in the counters and counter circuits. The two methods of measurement differ primarily in the way in which the errors due to the other gamma-rays emitted by the source are removed.