Least squares analyses of experimental differential cross-section data for the U-235 nucleus have yielded single level Breit-Wigner resonance parameters that fit, simultaneously, three nuclear cross sections of capture, fission, and total

Drawbaugh, D. W.

Gibson, G.

Miller, M.

Page, S. L.

English

NASA Technical Reports Server

December 1970
	 Brief 70-10686 
icy e S 1	 AEC—NASA TECH BRIEF r:  
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UT, Washington, D.C. 20546. 
Single-Level Resonance Parameters Fit Nuclear Cross-Sections 
For the first time, least-squares analyses of 
experimental differential cross-section data for the 
nucleus U 235 have yielded single-level Breit-Wigner 
resonance parameters that fit, simultaneously, three 
nuclear cross-sections - capture, fission, and total. 
Previous measured values of the parameters yielded 
derived cross-sections that agreed at best with only 
one or two of the three measured cross-sections. 
The resonance-capture and fission integrals calcu-
lated from the resonance parameters obtained for 
neutron energies of less than 63 eV agree within 3% 
with the corresponding direct numerical integration of 
the cross-section data. Earlier simultaneous measure-
ments of the fission and capture cross-sections for 
U 235 (ref. 1) were used in the analyses, resolving 
the discrepancy between measured and calculated 
values of the quantity a (a = ratio of capture-
resonance integral to fission-resonance integral). 
Two sets of resonance parameters have been de-
rived. They differ only in that unit weighting was 
used in one analyses, while weighting inversely pro-
portional to the cross-section was used in the other. 
In addition, the effects of fitting only two of 
the three nuclear cross-sections - total and fis-
sion, and capture and fission - were studied. 
Two multigroup cross-section libraries for the re-
action (neutron + U 235) have been generated. Each 
library treats a different section of the energy 
range to which the two sets of resonance parameters 
were applied. The value, 0.51, calculated for the 
ratio a for either library agrees with the accepted
value, 0.50 ± 0.02, derived from reactor integral 
measurements. 
The two sets of resonance parameters and the 
cross-section libraries should be useful in reactor 
calculations for any nuclear reactor fueled with U235. 
Reference: 
de Saussure, G.; et al.: Measurement of the Neu-
tron-Capture and Fission Cross Sections and of Their 
Ratios a for U 233 , U 235 , and Pu 239 . Preprint 
CN23/48, Intern. At. Energy Agency Conference on 
Nuclear Data: Microscopic Cross Sections and 
Other Data Basic for Reactors, Paris, 1966. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
AEC-NASA Space Nuclear Propulsion Office 
U.S. Atomic Energy Commission 
Washington, D.C. 20545 
Reference: B70-10686 
Patent status: 
No patent action is contemplated by the AEC or 
NASA.
Source: G. Gibson, D. W. Drawbaugh,
M. Miller, and S. L. Page of

Westinghouse Astron uclear Laboratory

under contract to

Space Nuclear Propulsion Office

(NUC-10101) 
Category 03 
This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son acting on behalf of the United States Government assumes any
liability resulting from the use of the information contained in this 
document, or warrants that the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
vately owned rights.
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Single-level resonance parameters fit nuclear cross-sections

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