Spectrum-Averaged Cross-Section Measurement of ¹⁰³Rh(n, n′)^103mRh in the ²⁵²Cf Fission Neutron Spectrum

Because of the similarity in energy dependence of the ¹⁰³Rh(n,n′) differential cross section to the kerma muscle response function for neutrons, rhodium may be useful as a neutron kerma monitor. In support of its use as a neutron monitor, the spectrum-averaged cross section has been measured for a ²⁵²Cf fission neutron spectrum. Pairs of thin rhodium samples were irradiated on opposite sides of a thinly encapsulated ²⁵²Cf neutron source. The neutron emission rate of the ²⁵²Cf source was determined by the manganous sulfate (MnSO₄) bath technique. In this method, the californium source emission rate is determined by comparison to the known emission rate of NBS-I, a standard radium-beryllium neutron source. The neutron fluence incident on the rhodium samples is determined from the californium source strength, average sample-to-source distance, and the duration of the irradiation. Corrections are made for neutron scattering, saturation of activity, and attenuation of the X rays by the sample during counting. The X rays were detected with an intrinsic germanium detector designed specifically for low-energy X-ray detection. The activity was not determined by absolute counting so that the final results depend on the value of P_Kx, the total K X-ray emission probability. The results of five separate irradiations yield a value of . P_Kx = 62.3 ± 1.9 mb. Using the most recently published value of P_Kx gives a value of = 739 ± 22 mb. A discussion of systematic uncertainties is given.