Other than generating power and creating catastrophic bombs, nuclear reactions are also used by humans to understand fundamental particle physics at the subatomic level, to further our knowledge of the elementary building blocks of the universe and everything that exists within it. Among the many mysteries that we have encountered in the process are those concerning the neutrino and its associated particles, especially the antineutrino.
The unofficially named “reactor antineutrino anomaly” refers to the phenomenon wherein scientists routinely detect fewer antineutrinos from nuclear reactors than predicted by theoretical models. A leading theory to explain the mismatch between theory and practice is that some of the neutrinos created during the process of nuclear fission are converted into sterile neutrinos.
Sterile neutrinos themselves are theoretical particles that could be a possible source of dark matter, which makes up about 27 percent of the universe. Numerous attempts to detect sterile neutrinos have failed, however. And now, a study published Thursday in the journal Physical Review D suggests sterile neutrinos may have no role to play in the case of the missing antineutrinos either. Rather, the anomaly could be caused by a modeling error in the theory.
Titled “Measurement of electron antineutrino oscillation based on 1230 days of operation of the Daya Bay experiment,” the study was carried out at the Daya Bay reactor neutrino experiment, located at a nuclear power complex in China.
According to a statement by the Chinese Academy of Sciences, antineutrinos remove about 5 percent of the total energy produced by the uranium and plutonium atoms during the nuclear fission process. As the reactor continues functioning, the composition of the different isotopes of the two elements keeps changing, as do the number and energy ranges of antineutrinos produced.
After measuring over two million antineutrinos from six reactors, the researchers — who come from 41 institutions across China, the Czech Republic, Russia and the United States — “found that antineutrinos produced by nuclear reactions that result from the fission of uranium-235, a fissile isotope of uranium common in nuclear fuel, were inconsistent with predictions. A popular model for uranium-235 predicts about 8 percent more antineutrinos coming from decays of uranium-235 than what was actually measured,” the statement said.
A less precise measurement of the antineutrinos produced from plutonium-239, the second-most common nuclear fuel, was consistent with theoretical predictions.