Resonance Absorption of Neutrons in Rhodium, Antimony, and Gold

The following experiments were performed on the resonance neutrons of Rh, ${\mathrm{Sb}}^{121}$, and Au: absorption in the element itself, absorption in boron, measurement of the total activation in an extended volume of hydrogenous material. The constants evaluated are the resonance energy $E_r$, the absorption coefficient for self-indication $K_r$, and the level width $\Gamma$. We found: for rhodium, $\Gamma =0.16\mathrm{}$ ev; for antimony, $E_r=14\mathrm{}$ ev, $K_r=4\mathrm{}$ ${\mathrm{cm}}^2$/g, $\Gamma =0.8\mathrm{}$ ev; for gold, $E_r=2.6\mathrm{}$ ev, $K_r=40\mathrm{}$ ${\mathrm{cm}}^2$/g, $\Gamma =0.11\mathrm{}$ ev. In antimony and gold, the measurements indicate that a small fraction of the resonance activity induced in thin detectors is due to levels of higher energy. The observed absorption coefficient for thermal neutrons $K_{\mathrm{th}}$ in rhodium and gold is found to agree with the one calculated from the Breit and Wigner formula, by taking into account only the resonance level observed. In Sb, the calculated $K_{\mathrm{th}}$ is about six times larger than the one observed, which suggests the interference effect of negative levels.