Measurements of Gamma-Ray Absorption Coefficients

Abstract

The absorption of $\gamma$-rays in Al, Cu, Sn, Ta, and Pb was measured using $\gamma$-rays from ${\mathrm{I}}^{131}$, ${\mathrm{Cu}}^{64}$, ${\mathrm{Mn}}^{54}$, ${\mathrm{Co}}^{60}$, ${\mathrm{Zn}}^{65}$, and ${\mathrm{Na}}^{24}$. Tests showed that scattering from nearby objects and from the absorber were negligible. Tests of the absorption of radium $\gamma$-rays in Pb showed good agreement with other workers and with theory. The absorption curves of ${\mathrm{I}}^{131}$ showed the presence of a 0.65-Mev $\gamma$-ray about 15 percent as abundant as the 0.367-Mev $\gamma$-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 ($Z=73\mathrm{}$) and ${\mathrm{Zn}}^{65}$ and ${\mathrm{Co}}^{60}$ sources ($h\nu \sim 1.2$ Mev) needs reinvestigation.