21-29 July 2022
US/Pacific timezone

Prompt fission neutron spectra in the $^{235}$U(n,f) reaction

28 Jul 2022, 06:00
Folsom ()



Benoit Mauss


Neutrons emitted in fission events can be detected with remarkable precision using the highly segmented Chi-Nu neutron liquid scintillator array at the Weapons Neutron Research facility of the Los Alamos Neutron Science Center. In two recent studies, prompt fission neutron spectra (PFNS) [1] and average prompt fission neutron multiplicities [2] from $^{238}$Pu(n,f) were measured with respect to $^{252}$Cf for incident neutron energies from about 1 MeV to 700 MeV. The setup consisted of a newly designed high efficiency and fast-timing fission chamber coupled to the Chi-Nu array. 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.

We will report on a follow-up study of PFNS from $^{235}$U(n,f) measured with respect to $^{252}$Cf using the same setup. The PFNS were measured down to 100 keV and up to 12 MeV for incident neutron energies from 0.3 to 700 MeV. Typical PFNS uncertainties obtained in the preliminary results are below 2% up to about 6 MeV at all incident energies. Neutron average kinetic energies as a function of incident neutron energy were obtained with uncertainties below 0.5%. These results along with average prompt fission neutron multiplicities as a function of incident energy will be shown and compared to existing data and evaluations.

[1] P. Marini et al. PRC 101, 044614 (2020)
[2] P. Marini et al. PRL, accepted

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