Measurements of Gamma-Ray Absorption Coefficients

The absorption of γ-rays in Al, Cu, Sn, Ta, and Pb was measured using γ-rays from I¹³¹, Cu⁶⁴, Mn⁵⁴, Co⁶⁰, Zn⁶⁵, and Na²⁴. Tests showed that scattering from nearby objects and from the absorber were negligible. Tests of the absorption of radium γ-rays in Pb showed good agreement with other workers and with theory. The absorption curves of I¹³¹ showed the presence of a 0.65-Mev γ-ray about 15 percent as abundant as the 0.367-Mev γ-ray. Absorption coefficients measured with the other sources showed agreement within 0.5 percent to 2 percent with theory. An anomalous absorption coefficient (5 percent less than expected) with tantalum absorber ($Z=73$) and Zn⁶⁵ and Co⁶⁰ sources (hν~1.2 Mev) needs reinvestigation.