The Absorption of Gamma-Radiation in Copper and Lead

The absorption coefficients for the gamma-rays emitted by certain activated elements have been accurately measured in copper and lead. The energies of the gamma-rays used, have all been determined by use of the beta-ray spectrometer. These gamma-rays are as follows: 1.14 Mev from zinc 65, 1.30 Mev from cobalt 60, and 1.38-2.85 Mev from sodium 24. The absorption coefficients for zinc and cobalt are in close agreement with the calculated values of Heitler. For the high energy component of the sodium radiation, values of 0.285 ${\mathrm{cm}}^{-1\mathrm{}}$ and 0.405 ${\mathrm{cm}}^{-1\mathrm{}}$ were obtained for the absorption coefficients in copper and lead, respectively. These values are more than ten percent less than the Heitler values. Since absorption in copper at this energy is due almost entirely to Compton scattering it is indicated that the Klein-Nishina formula is not completely valid.