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A Measurement of the Thermal Neutron Capture Cross Section of 232Th

R. T. Jones, J. S. Merritt, A. Okazaki

Nuclear Science and Engineering

Volume 93 / Number 2 / June 1986 / Pages 171-180


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The thermal neutron capture cross section of 232Th has been measured relative to that of 197Au. Foils of gold, thorium metal, and thoria were irradiated together in the NRU reactor thermal column. The 198Au activity was assayed in a 4πγ ionization chamber, which had been previously calibrated with samples of 198Au standardized by the 4π Β-γ coincidence method. Protactinium-233 sources were also standardized by this method. Comparison of these sources with the irradiated thorium, by means of a Ge(Li) spectrometer, enabled the 233Pa activity in the thorium-bearing foils to be determined. Taking the 2200 m/s capture cross section of 197Au to be 98.8 b, that of 232Th is found to be 7.33 ± 0.06 b. The uncertainty is at the 95% confidence level and includes an estimate of the systematic uncertainties.

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