Study of237Np Photonuclear Reactions Near Threshold Induced by Gamma Rays from Thermal Neutron Capture

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Abstract
The photodisintegration of 237Np has been studied using monochromatic photons produced by thermal neutron capture in several materials. The partial cross sections σγ, f and σγ, n were measured in the energy interval from 5.43 to 10.83 MeV. Analyzing the photofission data according to the liquid drop model, the height (Ef) and the curvature (ℏω) of the simple fission barrier were determined: Ef = (5.9 ± 0.2) MeV and ℏ;ω = (0.8 ± 0.4) MeV. For the competition between photoneutron emission and fission (Γn/Γf), a constant value was found (1.28 ± 0.15) in the 6.73- to 10.83-MeV energy range. From this result the following nuclear temperatures for 237Np were extracted on bases of some models of level density: T = 0.84 ± 0.06 MeV (Fujimoto-Yamaguchi model) and T = 0.60 ± 0.04 MeV (constant nuclear temperature model).