A step forward in solving the reactor-neutrino flux problem

June 17, 2020

Joint effort of the nuclear theory group at the University of Jyvaskyla and the international collaborative EXO-200 experiment paves the way for solving the reactor antineutrino flux problems. The EXO-200 collaboration consists of researchers from 26 laboratories and the experiment is designed to measure the mass of the neutrino. As a by product of the calibration efforts of the experiment the electron spectral shape of the beta decay of Xe-137 could be measured. This particular decay is optimally well suited for testing a theoretical hypothesis to solve the long-standing and persistent reactor antineutrino anomaly. The results of measurements of the spectral shape were published in Physical Review Letters (June 2020)

Nuclear reactors are driven by fissioning uranium and plutonium fuel. The neutron-rich fission products decay by beta decay towards the beta-stability line by emitting electrons and electron antineutrinos. Each beta decay produces a continuous energy spectrum for the emitted electrons and antineutrinos up to a maximum energy (beta end-point energy).

The number of emitted electrons for each electron energy constitutes the electron spectral shape and the complement of it describes the antineutrino spectral shape.

Nuclear reactors emit antineutrinos with an energy distribution that is sum of the antineutrino spectral shapes of all the beta decays in the reactor. This energy distribution has been measured by large neutrino-oscillation experiments. On the other hand, this energy distribution of antineutrinos has been built by using the available nuclear data on beta decays of the fission products.

The established reference for this construction is the Huber-Mueller (HM) model. Comparison of the HM-predicted antineutrino energy spectrum with that measured by the oscillation experiments revealed a deficit in the number of measured antineutrinos and an additional "bump", an extra increase in the measured number of the antineutrinos between 4 and 7 MeV of antineutrino energy. The deficit was coined the reactor antineutrino anomaly or the flux anomaly and has been associated with the oscillation of the ordinary neutrinos to the so-called sterile neutrinos which do not interact with ordinary matter, and thus disappear from the antineutrino flux emitted by the reactors. Up to recently there has not been a convincing explanation for the appearance of the bump in the measured antineutrino flux.

Only recently a potential explanation for the flux anomaly and bump has been discussed quantitatively. The flux deficit and the bump could be associated to omission of accurate spectral shapes of the so-called first-fobidden non-unique beta decays taken into account for the first time in the so-called "HKSS" flux model (from the first letters of the surnames of the authors, L. Hayen, J. Kostensalo, N. Severijns, J. Suhonen, of the related article).

How to verify that the HKSS flux and bump predictions are reliable?

"One way is to measure the spectral shapes of the key transitions and compare with the HKSS predictions. These measurements are extremely hard but recently a perfect test case could be measured by the renowned EXO-200 collaboration and comparison with our theory group's predictions could be achieved in a joint publication [AlKharusi2020]. A perfect match of the measured and theory-predicted spectral shape was obtained, thus supporting the HKSS calculations and its conclusions. Further measurements of spectral shapes of other transitions could be anticipated in the (near) future", says Professor Jouni Suhonen from the Department of Physics at the University of Jyvaskyla.
Link to the spectral shape measurement in Physical Review Letters (June 2020):


Nuclear-theory group at the University of Jyvaskyla:


For further information:

Professor Jouni Suhonen, jouni.t.suhonen@jyu.fi, tel. +358408054118
Communications Specialist Tanja Heikkinen, tanja.s.heikkinen@jyu.fi, tel. 358 50 581 8351
The Faculty of Mathematics and Science:
FB: jyuscience Twitter: jyscience

University of Jyväskylä - Jyväskylän yliopisto

Related Antineutrinos Articles from Brightsurf:

Understanding ghost particle interactions
Argonne scientists were part of a team that constructed a nuclear physics model capturing the interactions between neutrinos and atomic nuclei.

A step forward in solving the reactor-neutrino flux problem
Joint effort of the nuclear theory group at the University of Jyvaskyla and the international collaborative EXO-200 experiment paves the way for solving the reactor antineutrino flux problems.

Scientists make step towards understanding the universe
Physicists from the University of Sheffield have taken a step towards understanding why the universe is made of mostly matter and not antimatter, by studying the difference between the two.

Strongest evidence yet that neutrinos explain how the universe exists
New data throws more support behind the theory that neutrinos are the reason the universe is dominated by matter.

T2K insight into the origin of the universe
Lancaster physicists working on the T2K major international experiment in Japan are closing in on the mystery of why there is so much matter in the universe, and so little antimatter.

Where did the antimatter go? Neutrinos shed promising new light
We live in a world of matter -- because matter overtook antimatter, though they were both created in equal amounts when our universe began.

Why didn't the universe annihilate itself? Neutrinos may hold the answer
New results from an experiment called T2K suggest that physicists are closer than ever before to answering a major mystery: Why didn't the universe annihilate itself in a humungous burst of energy not long after the Big Bang?

T2K results restrict possible values of neutrino CP phase
The T2K Collaboration has published new results showing the strongest constraint yet on the parameter that governs the breaking of the symmetry between matter and antimatter in neutrino oscillations.

Researchers detail how antineutrino detectors could aid nuclear nonproliferation
The article appears in the latest issue of Reviews of Modern Physics.

Closing in on elusive particles
In the quest to prove that matter can be produced without antimatter, the GERDA experiment at the Gran Sasso Underground Laboratory in Italy is looking for signs of neutrinoless double beta decay.

Read More: Antineutrinos News and Antineutrinos Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.