A longstanding mystery of particle physics may soon be solved, thanks to a surprisingly compact new particle detector developed at the Massachusetts Institute of Technology (MIT). Neutrinos, small, fast elementary particles created by radioactive decay and in certain nuclear reactions (namely, the intense process of hydrogen fusion that powers the Sun) have been shown to have mass, but what that precise mass is, scientists have been unable to say. Now, with this new detector and a little bit of tritium gas, that value might finally be measured.
The tabletop detector uses a magnet to trap electrons generated by krypton gas decay and then detects weak radio signals they emit to map their activity. The electrons generate a signal by vibrating madly on a precise frequency when they are emitted by the decaying krypton. The signal dies out quickly, but it is emitted again as the electron smacks into another atom.
By tracking this sequence of emissions, the researchers were able to track the individual electrons. Of course, the mass of an electron has been known for quite some time. Neutrinos, however, are a different story.
The Standard Model of particle physics assumes that neutrinos are massless. But in the early 1950s, before the particles had even been experimentally detected, there were already some hypotheses that called for neutrinos to have a mass value.
By the late 1990s, experiments had verified that the particles behaved in such a way that required they did, in fact, have mass. But they were so fast and so light that no available technology could precisely determine what that mass was, although it was established to exist within a certain range.
Electrons and neutrinos are both generated by the decay of tritium gas into helium. The detector won’t be able to detect the neutrinos emitted in that process, but just as with the krypton decay, electrons should still be able to be tracked and their energy level established. Since the total energy of the emitted particles must add up to the original energy of the neutron from which they were emitted, the neutrinos energy level — and thus, its mass — can be established by basic arithmetic.
Other efforts to obtain the mass value of the neutrino by measuring single electron energy levels have been undertaken, but the detectors in those cases involve the destruction of the electron, which can effect the results of the experiment. By using radio emissions, the MIT team believes that they can obtain a much more accurate result.
The project has taken five years and involved researchers not only from MIT but also the University of Washington, the University of California at Santa Barbara, and the Pacific Northwest National Laboratory.
The team hopes to began working with tritium and making measurements that will lead to an accurate neutrino mass measurement within the next two years.