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Title: Gamma-Ray Emission Spectra as a Constraint on Calculations of 234,236,238U Neutron-Capture Cross Sections

Neutron capture cross sections in the “continuum” region (>≈1 keV) and gamma-emission spectra are of importance to basic science and many applied fields. Careful measurements have been made on most common stable nuclides, but physicists must rely on calculations (or “surrogate” reactions) for rare or unstable nuclides. Calculations must be benchmarked against measurements (cross sections, gamma-ray spectra, and <Γγ>). Gamma-ray spectrum measurements from resolved resonances were made with 1 - 2 mg/cm2 thick targets; cross sections at >1 keV were measured using thicker targets. The results show that the shape of capture cross section vs neutron energy is not sensitive to the form of the strength function (although the magnitude is); the generalized Lorentzian E1 strength function is not sufficient to describe the shape of observed gamma-ray spectra; MGLO + “Oslo M1” parameters produces quantitative agreement with the measured 238U(n,γ) cross section; additional strength at low energies (~ 3 MeV) -- likely M1-- is required; and careful study of complementary results on low-lying giant resonance strength is needed to consistently describe observations.
Authors:
 [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [2] ;  [3]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Charles Univ., Prague (Czech Republic)
Publication Date:
OSTI Identifier:
1183397
Report Number(s):
LA-UR--15-23962
TRN: US1600156
DOE Contract Number:
AC52-06NA25396
Resource Type:
Conference
Resource Relation:
Conference: 5. Workshop on Nuclear Level Density and Gamma Strength, Oslo (Norway), 18-22 May 2015; Related Information: PowerPoint presentation
Research Org:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE/LANL
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; URANIUM 238 TARGET; URANIUM 236 TARGET; URANIUM 234 TARGET; NEUTRON REACTIONS; CROSS SECTIONS; EMISSION SPECTRA; GAMMA RADIATION; GAMMA SPECTRA; KEV RANGE; INTERMEDIATE NEUTRONS; STRENGTH FUNCTIONS; CAPTURE; GIANT RESONANCE; LIMITING VALUES; MEV RANGE; SHAPE; E1-TRANSITIONS; M1-TRANSITIONS; LEVEL WIDTHS; EXCITATION FUNCTIONS; URANIUM 235; URANIUM 237; URANIUM 239