Manifestations Scientifiques

What nuclear physics can bring to reactor antineutrino physics?

by Magali Estienne (SUBATECH)


Reactor antineutrino energy spectra are the subject of active experimental researches nowadays, either through large reactor neutrino experiments, short baseline neutrino experiments at research reactors or through dedicated nuclear physics measurements of the properties of the fission products. Part of those researches were first motivated by the observation in 2011 of a deficit in the reactor antineutrino flux with respect to the conversion model which relies on measurements of integral beta spectra and a subsequent conversion approach to predict the antineutrino energy spectra: the reactor antineutrino anomaly (RAA).
In the meantime, in 2017, the Daya Bay experiment has measured the evolution of the antineutrino flux with the fuel content of the reactor core. The observed deficit of the detected flux compared with the predictions of the conversion model was almost totally explained by the data arising from the fissions of 235U while the part dominated by the fission of 239Pu was in good agreement with the conversion model. Furthermore, a distortion of the measured antineutrino energy spectra by Double Chooz, Daya Bay and Reno has been observed with respect to the conversion model between 5 and 7 MeV (the “shape anomaly”) and remains unexplained up to now.
Summation calculations are a unique alternative to the converted spectra which present in addition the advantage of being predictive for innovative fuels but also of giving access to the main nuclei contributing to the spectra in the various ranges of energy. The TAGS measurements allow one to overcome the systematic error known as Pandemonium effect which can affect high resolution data coming from experiments with HPGe detectors. Due to the low efficiency of HPGe detectors, high energy gamma-rays may be missed, leading to a wrong determination of the beta intensity probabilities obtained via gamma-intensity balance. One of the direct consequences being then to bias the predictions of antineutrino energy spectra. The TAGS collaboration has carried out two experimental campaigns during the last decade at the JYFLTRAP of Jyväskylä (Finland) measuring a large set of data in order to improve the quality of the predictions of our summation method. The impact of these ten years of measurement from the TAGS collaboration on the predicted antineutrino energy spectrum and flux using our summation calculations will be presented and discussed in the frame of reactor antineutrino experiments.