On the Absorption of Slow Neutrons by Rhodium

Abstract

The absorption of neutrons in rhodium as a function of their time of flight was studied with the Cornell slow neutron velocity spectrometer in the energy range of 0.0044 to 330 ev. A resonance was observed at an energy of 1.21±0.02 ev. No other resonances were observed. Values of the Breit-Wigner parameters, which best seem to fit the experimental results for a resonance energy of 1.21 ev, are 2750±200 barns for the cross section at resonance (${\sigma }_r$) and 0.21±0.01 ev for the level width ($\Gamma$). The Breit-Wigner formula fits the experimental data in the low energy region. The coefficient of the $\frac{1}{v}$ term is 0.295±0.005 barn/ μsec./m and the constant term (taken as the scattering cross section) is 6±2 barns. Values for the strength of the resonance (${\sigma }_r{\Gamma }^2$) were computed from the minimum cross section on the low energy side of the resonance, from the $\frac{1}{v}$ slope, from an activity plot, and from the chosen Breit-Wigner parameters. The average of these values of ${\sigma }_r{\Gamma }^2$ is 117±8 barn-${\mathrm{ev}}^2$. Self-absorption measurements were made to check the results of the time-of-flight measurements. The resonance cross section obtained from the self-absorption measurements is 3120±50 barns, which is in closer agreement with the results of the spectrometer measurements than with those of previous investigators.