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Measurement of the 241Am Neutron Fission Cross Section

J. W. T. Dabbs, C. H. Johnson, C. E. Bemis, Jr.

Nuclear Science and Engineering

Volume 83 / Number 1 / January 1983 / Pages 22-36


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The fission cross section of 241Am has been measured from 0.02 eV to 20 MeV using time-of-flight techniques at the Oak Ridge Electron Linear Accelerator. A “honeycomb” fission ionization chamber that contained six deposits totaling 14.3 mg of 241Am, six deposits totaling 116 mg of 235U, and a single deposit of 252Cf, which served as a monitor for the chamber performance, was used. The 235U fission served as the cross-section standard for energies above 101 keV while 6Li(n, α), normalized to 235U fission in the 7.8- to 11.0-eV interval, served as a shape standard below 101 keV. Approximately 700 h of data were obtained at a flight path distance of 9.1 m, primarily with 40-ns bursts. Because the fission cross section of 241Am is very small in the midrange of neutron energies, particular attention was paid to correction of backgrounds, particularly inscattered neutron-induced events. The fission resonance integral was found to be 14.1 ± 0.9 b.

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