The 235U(n,2n(gamma)) Yrast Partial Gamma-Ray Cross Sections: A Report on the 1998 -- 1999 GEANIE Data and Analysis Techniques

Abstract

Measurements of partial 235U(n,2ny) y-ray cross sections have been carried out as a function of incident neutron energy using the GEANIE spectrometer at LANSCE/WNR+ The yields of y rays resulting from the population of discrete levels in the residual nucleus 234U have been measured at incident neutron energies in the 1-20-MeV range. These data provide, with the aid of nuclear reaction modeling, a measurement of the 235U(n,2n) reaction cross section and serve as a proof of principle of the y-ray technique for the parallel 23gPu(n,2n) measurement [l]. This paper presents the analysis of the y-ray data and the extraction of partial y-ray cross sections as a function of incident neutron energy, Uncertainties associated with the spectroscopic analysis of the data and validation of the results are discussed in detail.

(n,xnγ) reaction cross section measurements for (n,xn) reaction studies

“…[3] and references inside). In the data base only two (n,xn γ) cross section references are available [11,10]. For the (n,n' γ) transition, our data agree with those of Younes et al at high neutron energies but the three TALYS-1.2 calculations under-estimate the cross section especially for neutron energy above 1 MeV.…”

Preliminary Report on the Population of the 235U T1/2=25-Minute Isomer by the (Nu,Nu'Gamma)Reaction

“…Detailed descriptions of the experimental setup can be found in references [7-91. In particular the experimental configuration is similar to the one described in reference [9] for the data set labeled "99Thin". The same 0.4820(27) g/cm2, 93.2%-isotopically enriched 235U sample was used and housed in the same Pu-blank container as in the 99Thin run.…”

Uncertainty Budget and Efficiency Analysis for the 239Pu (n,2ny) Partial Reaction Cross-Section Measurements

“…The software and hardware conditions that determine the resulting spectrum are discussed in [You00]. The γ-ray line shapes must be characterized for each spectrum in order to distinguish background from photopeak counts.…”

“…Depending on background and the local density of γ-ray lines, determining the counts in a particular transition can range from a simple sum of counts to a sophisticated maximum likelihood analysis. The details of this analysis varies from experiment to experiment, and is discussed for the 239 Pu(n,2nγ) measurement in [Ber00] and for the 235 U(n,2nγ) measurement in [You00].…”

“…The uncertainties quoted in Equations 10 and 11 include the statistical uncertainty in determining ρ f and the systematic uncertainty in determining N f . Additional uncertainty in σ f (1-4%) and in N f statistics (< 2%) are included in the work done by [Ber00] and [You00]. As discussed above, N f is the number of counts above threshold minus the number of random pulse heights.…”