The radioactivity of fission products in a nuclear reactor releases a large amount of energy. Some of this energy escapes from the reactor with the antineutrinos. Understanding their number and energy has kept the physics community on tenterhooks for some years with the reactor anomaly, a deficit of antineutrinos detected at short distances from nuclear reactors compared to predictions that could be explained by the existence of sterile neutrinos. The way in which the nuclei produced in the reactor core decay could perhaps also provide the key to this enigma. The study of some of these fission products remained a challenge, but the combination of the most advanced production, detection and analysis techniques allowed the radioactive properties of two niobium isotopes with isomeric states to be measured. The results show a major impact on the prediction of reactor antineutrino spectra by the summation method.

Publication: Large Impact of the Decay of Niobium Isomers on the Reactor ¯νe Summation Calculations, V. Guadilla et al., Phys. Rev. Lett. 122, 042502 – Published 30 January 2019.

Contacts: V. Guadilla, M. Fallot (Subatech)

Beta decay of 100Nb isomers (left). Impact of the results on the energy spectrum of antineutrinos from 239Pu fission (right).