Gamma-Ray Absorption Coefficients at 6.13 Mev

Narrow-beam geometry attenuation measurements have been made with 6.13-Mev gamma rays which follow the beta decay of N¹⁶ using a NaI scintillation spectrometer detector. The measured absorption coefficients in cm²/g are: 0.0244 (C), 0.0264 (Al), 0.0309 (Cu), 0.0359 (Sn), 0.0359 (Cd), 0.0436 (Pb), 0.0459 (U), 0.0284 (H₂O), 0.0350 (NaI). The statistical standard deviations range from 0.2 percent to 0.4 percent. These results are in good agreement with previous experimental work in those cases for which earlier data exist. "Experimental" pair-production cross sections are derived from the data and compared with the calculated values from the Born approximation to the Bethe-Heitler theory. A discrepancy of 7 to 8 percent is observed for high atomic number elements (Pb and U).