Abstract
Prompt-fission-neutron spectra from Pu239 (n,f) were measured with respect to Cf252 spontaneous fission for incident neutron energies from 0.7 to 700MeV at the Weapons Neutron Research facility (WNR) of the Los Alamos Neutron Science Center. A newly designed high-efficiency fission chamber was coupled to the highly segmented Chi-Nu neutron liquid scintillator array to detect neutrons emitted in fission events. The double time-of-flight technique was used to deduce the incident neutron energies from the spallation target and the outgoing-neutron energies from the fission chamber. Prompt-fission-neutron spectra (PFNS) were measured with respect to Cf252 spontaneous fission down to 200keV and up to about 12MeV for all the incident neutron energies with typical total uncertainties well below 2% up to about 7-MeV outgoing-neutron energy. The general trend of PFNS is well reproduced by JEFF3.3 and ENDF evaluations, although a better agreement is found with JEFF3.3. Discrepancies were observed for the low-energy part of the spectra, especially around the opening of the second-, third- and fourth-chance fission. Neutron average kinetic energies as a function of incident neutron energy are obtained experimentally with reported total uncertainties below 0.5%. The measured values agree with the most recent data. The trend is fairly well reproduced by the JEFF3.3 evaluation, although it fails to reproduce the experimental values within their uncertainties.
| Original language | English |
|---|---|
| Article number | 044614 |
| Journal | Physical Review C |
| Volume | 101 |
| Issue number | 4 |
| DOIs | |
| State | Published - Apr 2020 |
| Externally published | Yes |
Funding
We wish to acknowledge A. Moens, G. Sibbens, and D. Vanleeuw from the JRC-Geel target preparation laboratory for providing samples and assisting with their mounting in the fission chamber. We also wish to acknowledge the support of E. Bond from LANL C-NR for providing the sample. This work was performed under the auspices of a cooperation agreement between CEA/DAM and DOE/NNSA on fundamental sciences and benefited from the use of the LANSCE accelerator facility. The work at Los Alamos National Laboratory was performed under the auspices of the US Department of Energy under Contract No. 89233218CNA000001.