The Need for Precise and Well-documented Experimental Data on Prompt Fission Neutron Spectra from Neutron-induced Fission of {sup 239}Pu

• Published in: Nuclear data sheets Vol. 131
• Main Authors: Neudecker, D., Taddeucci, T. N., Haight, R. C., Lee, H. Y., White, M. C., Rising, M. E.
• Format: Journal Article
• Language: English
• Published: United States 15.01.2016
• Subjects: CALIFORNIUM 252; EVALUATION; FISSION; FISSION NEUTRONS; MULTIPLE SCATTERING; MULTIPLICITY; NEUTRON SPECTRA; NUCLEAR PHYSICS AND RADIATION PHYSICS; PLUTONIUM 239; REACTOR PHYSICS; SECURITY; SIMULATION; URANIUM 235; ZERO POWER REACTORS
• DOI: 10.1016/j.nds.2015.12.005
• ISSN: 0090-3752

The spectrum of neutrons emitted promptly after {sup 239}Pu(n,f)—a so-called prompt fission neutron spectrum (PFNS)—is a quantity of high interest, for instance, for reactor physics and global security. However, there are only few experimental data sets available that are suitable for evaluations. In addition, some of those data sets differ by more than their 1-σ uncertainty boundaries. We present the results of MCNP studies indicating that these differences are partly caused by underestimated multiple scattering contributions, over-corrected background, and inconsistent deconvolution methods. A detailed uncertainty quantification for suitable experimental data was undertaken including these effects, and test-evaluations were performed with the improved uncertainty information. The test-evaluations illustrate that the inadequately estimated effects and detailed uncertainty quantification have an impact on the evaluated PFNS and associated uncertainties as well as the neutron multiplicity of selected critical assemblies. A summary of data and documentation needs to improve the quality of the experimental database is provided based on the results of simulations and test-evaluations. Given the possibly substantial distortion of the PFNS by multiple scattering and background effects, special care should be taken to reduce these effects in future measurements, e.g., by measuring the {sup 239}Pu PFNS as a ratio to either the {sup 235}U or {sup 252}Cf PFNS.