A group of scientists from the Project 8 Collaboration has developed a new particle detector that is able to detect the frequency of cyclotron radiation emitted by single electrons in a radioactive gas.
The color indicates the electron’s detected power as a function of frequency and time. The sudden ‘jumps’ in frequency indicate an electron collision with the residual hydrogen gas in the cell. Image credit: Massachusetts Institute of Technology.
Although first proposed in 1904 by the English physicist Oliver Heaviside, cyclotron radiation from a single electron orbiting in a magnetic field has never been observed directly.
Now, the Project 8 team claims it has demonstrated single-electron detection in a novel radio-frequency spectrometer.
“We can literally image the frequency of the electron, and we see this electron suddenly pop into our radio antenna,” said Dr Joe Formaggio of Massachusetts Institute of Technology, a team member and a co-author of the paper published in the Physical Review Letters.
“Over time, the frequency changes, and actually chirps up. So these electrons are chirping in radio waves.”
As the gas decays and gives off electrons, the spectrometer uses a magnet to trap them in a magnetic bottle.
A radio antenna then picks up very weak signals emitted by the electrons, which can be used to map the electrons’ precise activity over several milliseconds.
A new radio-frequency spectrometer is able to identify single electrons. Image credit: Massachusetts Institute of Technology.
In their experiment, the physicists recorded the activity of more than 100,000 individual electrons in krypton gas (Kr-83m).
The majority of electrons observed behaved in a characteristic pattern: as the radioactive krypton gas decays, it emits electrons that vibrate at a baseline frequency before petering out; this frequency spikes again whenever an electron hits an atom of radioactive gas.
As an electron ping-pongs against multiple atoms in the detector, its energy appears to jump in a step-like pattern.
According to the scientists, their detector is a big step toward a more elusive goal – measuring the mass of a neutrino.
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D. M. Asner et al. 2015. Single-Electron Detection and Spectroscopy via Relativistic Cyclotron Radiation. Phys. Rev. Lett. 114, 162501; doi: 10.1103/PhysRevLett.114.162501
