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Neutron Cross-Section Measurements on Structural Materials at ORELA
K. H. Guber,P. E. Koehler,D. Wiarda,J. A. Harvey 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
Neutron capture experiments, using isotopically enriched and natural samples of chromium and titanium, were performed on flight paths 6 and 7 at the 40 m flight station of ORELA. The experimental data were acquired using a pair of deuterated benzene detectors employing the now well-established pulse-height-weighting technique. These data were complemented by new total cross-section measurements where no useful previous data were available.
Evaluation of the Chromium Resonance Parameters Including Resonance Parameter Covariance
L. Leal,H. Derrien,K. Guber,G. Arbanas,D. Wiarda 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
The intent of this work is to report the results and describe the procedures utilized to evaluate the chromium isotopes' cross sections, i.e., ^(50)Cr, ^(52)Cr, ^(53)Cr, and ^(54)Cr, for criticality safety applications. The evaluations were done in the resolved resonance region using the reduced Reich-Moore R-matrix formalism. The novel aspect of this evaluation is the inclusion of new transmission and capture cross-section measurements performed at the Oak Ridge Electron Linear Accelerator (ORELA) for energies below 100 keV and the extension of the ^(53)Cr energy region. The resonance analysis was performed with the multilevel R-matrix code, SAMMY, which utilizes the generalized least-squares technique based on the Bayes' theory. Complete sets of resonance parameters and resonance parameter covariance matrices (RPCMs) were obtained for each of the chromium isotopes from the SAMMY analysis of the experimental database.
P. E. Koehler,J. A. Harvey,F. Becvar,M. Krticka,K. H. Guber 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
We describe new techniques for determining spins and parities of neutron resonances which have resulted in large improvements over previous methods. These advances have made it possible, for the first time, to obtain reduced-neutron- and total-radiation-width distributions separately for resonances of different spin and parity in odd-A target nuclides. Using these new as well as previous data, we show that neutron distributions sometimes are significantly different from the Porter-Thomas distribution assumed by the nuclear statistical model. Furthermore, we show that the radiation-width distributions often are substantially different than predicted by the nuclear statistical model using standard level densities and photon strength functions. These differences could have significant impact on astrophysical reaction rates calculated using the statistical model.