Experimental Prompt Fission Neutron Spectra Comparisons for the U-235,U-238(n,f) and Pu-239(n,f) Reactions

The Chi-Nu project to measure prompt fission neutron energy spectra for the major actinides has now completed two measurements, for neutron-induced fission of Pu-239 and U-235 for incident neutron energies from 1 to 20 MeV, and has almost completed the prompt fission neutron spectrum measurement for U-238. In addition, similar data have been taken for spontaneous fission in some other isotopes, and a measurement of fission neutron spectra from Pu-240(n,f) is in progress. These measurements are done at the same facility, with the same equipment and analyzed in a similar way. A useful way to look at such data is to examine ratios of the prompt fission neutron spectra among actinides, as some of the experimental uncertainties involved in these data are the same from isotope to isotope, making the ratios of fission neutron spectra less dependent on the experimental and analysis details. We discuss here the ratios of prompt fission neutron spectra between Pu-239(n,f) and U-235(n,f), as well as the evolution of the mean fission neutron energy for Pu-239(n,f) and U-235,U-238(n,f) with increasing incident neutron energy.

Automated summary

The Chi-Nu project has completed two measurements for prompt fission neutron energy spectra of Pu-239 and U-235, and is almost done with the measurement for U-238. Similar data have also been collected for spontaneous fission in other isotopes, and a measurement for fission neutron spectra from Pu-240(n,f) is currently underway.