Magnet-Based Tabletop Detector Identifies Single Electrons- MIT Research

A team of physicists from Massachusetts Institute of Technology (MIT) has built a revolutionary tabletop particle detector that can observe and identify individual electrons in a radioactive gas. In the experiment called ‘Project 8’, the detector is basically developed on a phenomenon known as cyclotron radiation. In this phenomenon, the charged moving particles such as electrons emit electromagnetic radiation (radio waves) at a frequency of about 26 gigahertz in a magnetic field. However, the long-term goal of the team is to measure the mass of neutrinos that are subatomic particles produced by the decay of radioactive elements and they are electrically neutral. The researchers have set theoretical limits on their mass but they are difficult to detect.


As the gas decays, it produces and discharges electrons. The compact detector employs a magnet for trapping these electrons in a magnetic bottle. The main job of a radio antenna inside the detector is to catch weak signals released by the electrons. These signals can be used for mapping the electrons’ precise activity over several milliseconds without any ambiguity. MIT physicists also worked with researchers at Pacific Northwest National Laboratory, the University of Washington, the University of California at Santa Barbara (UCSB), and others in order to track and record the activity of 100,000+ single electrons in radioactive krypton gas. They noticed that most of the electrons behaved in a characteristic pattern. The electrons are emitted when the krypton gas decays and these electrons move to and fro at a baseline frequency before petering out. In the course of time, the frequency spikes again when electron hits an atom of the radioactive gas. Moreover, a step-like pattern of the energy of electron appears when it hits several atoms in the detector.

Benjamin Monreal, an assistant professor of physics at UCSB, proposed that if the team could tune into baseline frequency (as it changes a bit if the electron has energy) then it will be able to catch electrons and measure their energy in a magnetic field. After turning the detector on, the physicists were able to identify single electrons in the first 100 milliseconds of the experiment. However, the analysis took quite a long time owing to the software’s slow processing speed.

Joe Formaggio, an associate professor of physics at MIT, stated that the results obtained in case of krypton gas have encouraged the team to move on to tritium (a radioactive isotope of hydrogen) as it is relatively easy to observe electron byproducts of the decaying tritium gas. The team might later be able to measure the mass of a neutrino after making several improvements in the detector. The results of the research were published in Physical Review Letters.

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