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An innovative technique to measure the isotope distributions from fission of 238U

J.N. Wilson, M. Lebois, L. Qi, et al.

Measurements of the mass and charge distributions of isotopes, produced when a heavy nucleus fissions into two lighter fragments, are important for several reasons. These include understanding the complex phenomenon of fission itself, the functioning of nuclear reactors, and the study of very neutron-rich nuclei, the precursors of the stable nuclei here on earth. In our recent article we report an innovative technique to measure the isotope distributions from fission of 238U induced by fast neutrons, by detecting the unique gamma-ray signature of each nucleus. The results mostly show reasonable agreement with theoretical models but also some very large discrepancies for certain isotopes, indicating that the fragments prefer to adopt a deformed rather than a spherical shape when the 238U nucleus splits in two.
Our results also impact on a recent unsolved problem in physics, "the reactor antineutrino anomaly", where around 5% fewer antineutrinos than expected are detected near nuclear reactors. Our results appear to rule out one of the mundane explanations for the anomaly : a poor understanding of 238U fission yields, which could possibly underproduce anti-neutrinos during fragment decay. One possible remaining explanation of the effect is short-range neutrino oscillations and a potential new flavour of neutrino.

See online : Anomalies in the Charge Yields of Fission Fragments from the 238U(n,f) Reaction - Phys. Rev. Lett. 118, 222501 (2017)


 

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