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Precise Measurement and Analysis of Neutron Transmission Through Uranium-238

D. K. Olsen, G. de Saussure, R. B. Perez, E. G. Silver, F. C. Difilippo, R. W. Ingle, H. Weaver

Nuclear Science and Engineering / Volume 62 / Number 3 / Pages 479-501

March 1977

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The transmissions of 0.52- to 4000-eV neutrons through 3.62-, 1.08-, 0.254-, 0.0762-, 0.0254-, 0.0127-, and 0.0036-cm-thick samples of uranium, enriched in the 238U isotope, have been measured at 42 m with a 1.0-mm-thick 6Li glass detector using the Oak Ridge Electron Linear Accelerator pulsed neutron source. To obtain resonance parameters, the seven transmissions of neutrons having energies ranging from 0.52 to 1086.8 eV have been shape-fitted by least-squares analysis to a multilevel Breit-Wigner cross-section formalism with “picket-fence” terms to account for truncation effects. This simultaneous fit yielded a χ2 per degree of freedom near unity. Averaged over this energy range, an s-wave strength function of (0.968 ± 0.036) × 10-4 cm and an effective radius of (0.944 ± 0.005) × 10-12 cm were obtained. In addition, these transmission data yielded an average radiation width of 23.1 ±1.0 meV for the 12 lowest energy s-wave resonances with radiation widths of 23.0 ± 0.8, 22.8 ± 0.8, and 22.9 ± 0.8 meV for the 6.67-, 20.9-, and 36.8-eV resonances, respectively. The derived radiation widths for these three resonances are shown to depend on the cross-section formalism employed. This work suggests that a multilevel formalism with truncation compensation is required to adequately represent the 238U total cross section.

 
 
 
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