Electron chirp: Cyclotron radiation from single electrons measured directly for first time

Electron chirp: Cyclotron radiation from single electrons measured directly for first time
This spectrogram shows the first electron detected by the Project 8 collaboration. The horizontal axis is time, the vertical axis is frequency, and the color is power. Multiple separate "tracks" are seen because the electron scatters off of gas molecules and ends up emitting cyclotron radiation at slightly different frequencies; the slope of each track indicates that the electron is losing energy to the cyclotron radiation.

A year before Albert Einstein came up with the special theory of relativity, or E=mc2, physicists predicted the existence of something else: cyclotron radiation. Scientists predicted this radiation to be given off by electrons whirling around in a circle while trapped in a magnetic field. Over the last century, scientists have observed this radiation from large ensembles of electrons but never from individual ones.

Until now.

A group of almost 30 scientists and engineers from six research institutions reported the direct detection of cyclotron radiation from individual April 20 in Physical Review Letters. They used a specially developed spectroscopic method that allowed them to measure the energy of electrons, one single electron at a time.

Besides the excitement of actually detecting this radiation from a single fundamental charged particle—the electron—the method provides a new way to potentially measure the of the neutrino, a subatomic particle that weighs at most two-billionths of a proton.

"One of the biggest problems in physics today is the unknown mass of the neutrino," said physicist Brent VanDevender, lead scientist from the Department of Energy's Pacific Northwest National Laboratory. "The universe is full of . There are so many of them that it matters how much they weigh. Even at two-billionths of a proton mass they would outweigh all of the other normal matter in the universe like stars, planets and dust, and affect the formation of large-scale structures like galaxy clusters."

Within the atom

Physicists are trying to understand some of the smallest parts of the universe. Typical atoms—which make up all matter—contain a nucleus surrounded by a cloud of electrons. The nucleus holds positively charged particles called protons and inert particles called neutrons, which give the atom heft. Electrons are negatively charged and zip around the nucleus.

These particles might appear unrelated, but the inert neutrons sometimes turn into protons in what is called beta decay. The proton stays behind while an electron and a neutral bit called a neutrino zip away into the universe.

Because they are so small and carry no charge, neutrinos are hard to measure. Currently, scientists have determined the heaviest a neutrino can be. Comparing the mass of a neutrino to a neutron would be like comparing a toddler to the Great Pyramid of Giza.

There are several efforts currently under way to detect and measure the neutrino mass directly, such as the KATRIN nuclear physics experiment in Germany. These efforts are huge, enlisting hundreds of researchers and building analytical instruments the size of a large house. Even so, there's a chance that the neutrino will be too small to be detected by such experiments.

About five years ago, two of the co-authors on this study proposed that perhaps instead of detecting neutrinos, or even electrons directly, they could come at the problem sideways by measuring electrons' cyclotron radiation, which can reveal an electron's energy.

If they measure, with enough precision, electrons emitted when a hydrogen carrying two extra neutrons—a tritium atom—beta decays to helium-3, they could infer the mass of a neutrino by adding up the energies of the helium-3 and an electron, and comparing that to a tritium atom. If they don't add up to a whole tritium atom, the difference must be the neutrino mass.

Measuring mass with energy? Yes, thanks to Einstein and special relativity. Because mass and energy are related, the team can measure the energy of electrons and get at mass that way. Gathering a few dozen collaborators into Project 8, the team developed a new method called Cyclotron Radiation Emission Spectroscopy to do so, and demonstrated it in this study.

CRES to impress

The instrument the team developed stands about as tall as a few wine barrels stacked on top of each other, much smaller than a house. To maximize their odds of success, they started with the best possible conditions. They chose an atom that would give them clean and easy to read spectroscopic information. That atom, a form of krypton called metastable krypton-83 (or 83mKr), would decay and give them lots of electrons that they could capture in their .

As they trapped single electrons in the field, they measured how fast they zipped around in a circle, which led them to the electron energy. The energy they measured for the krypton electrons came in at the expected 30.4 kilo-electron-volts. Their precision was within 0.05 percent of the target—not tight enough to infer neutrinos, but a very good start.

"Neutrino mass is tiny so the spectroscopy has to be exquisite. We have to do about 10 times better in the end," said VanDevender.

They didn't expect enough precision to measure the neutrino in this prototype experiment, he said, so the most exciting result for now was detecting cyclotron radiation.

"Nobody ever really doubted its existence, but it is still cool to be the first to observe a basic phenomenon of nature. This is a prediction that has been hanging out there since 1904 and it took 110 years for somebody to confirm at the level of individual fundamental particles," said VanDevender.

Beta test

VanDevender predicted it will take another decade to get a measurement for the neutrino mass, and it's possible KATRIN might weigh it first. The next step is to repeat the krypton experiments they did with tritium.

Once they've mastered that, they will have to figure out how to scale up to accommodate more tritium in much larger volumes to get the information they need to determine the .


Explore further

New tabletop detector 'sees' single electrons

More information: D. M. Asner, R. F. Bradley, L. de Viveiros, P. J. Doe, J. L. Fernandes, M. Fertl, E. C. Finn, J. A. Formaggio, D. Furse, A. M. Jones, J. N. Kofron, B. H. LaRoque, M. Leber, E. L. McBride, M. L. Miller, P. Mohanmurthy, B. Monreal, N. S. Oblath, R. G. H. Robertson, L. J Rosenberg, G. Rybka, D. Rysewyk, M. G. Sternberg, J. R. Tedeschi, T. Thummler, B. A. VanDevender, and N. L. Woods. Single electron detection and spectroscopy via relativistic cyclotron radiation, Phys. Rev. Lett. April 20, 2015, DOI: 10.1103/PhysRevLett.114.162501
Journal information: Physical Review Letters

Citation: Electron chirp: Cyclotron radiation from single electrons measured directly for first time (2015, April 28) retrieved 23 August 2019 from https://phys.org/news/2015-04-electron-chirp-cyclotron-electrons.html
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Apr 28, 2015
Is the neutrino generated from the spin and not motion around any other particle, the radiation, i.e. the neutrino period reflects the period of this spin. Consider any charge in circular motion about a point. This motion will produce a magnetic field as well as an e field as a function of time. The frequency define's the oscillatory rate. The Pole of this motion may also precess and be disturbed, etc.

With this understanding this would be all we can infer, not "mass" which is a multi-polar response based upon the stability of the whole and the motion of the charge-centers. Scale-able to describe these centers even if within an explosion, the motion is as the whole without outside disturbance. Given this quality to elemental particles, that most likely create this force is not the same as the conglomerate. The search for "mass" of the radiation is nonsense, for an elementary particle we get the description of the constituents of mass.

Apr 28, 2015
Mass is a function of the stability of multiple particles, not even demonstrable as a quality of the electron. I'd prefer a definition such as: an electron is anti-space and a proton is the hole left in space, sense the proton is mounted to the whole, then the electron has greater freedom, i.e. a different set of constraints, ~space-time. The field is the wrinkle in space and time and propagates at a constant relative speed to any particle, and the speed of the wave-front is a function of the relative velocity vectors. A tensor space is not needed to bend space, not even a push. You can express this as a four dimensional space in units of time or space using a simple definition, Lamda Nu = x/t of my emitted front. Depends on the media for actual speed.

Apr 28, 2015
Cause space is nothing, we only need the fields at any point in time and space, i.e. a four dimensional perspective. For your simulator, add a knob length or time, i.e. Lambda or Nu and scan space, i,e, initial conditions, from zero to infinity, you choose the scale, not Einstein! I would build my block-size based upon attributes fro bottom to top, for what I'm looking for, not from the poorly defined top-down. Don't forget to view from all quadrants. After that give the attribute a different name, with a record of it's attributes not predefined by someone's mind.

dubious rufus

Apr 28, 2015
You can say whatever fits Maxwell and let it be a description of charge. I like the hole idea, think about the radius of the spin, what happen's if it is collapsed to zero or is it fixed, i.e Dynamics? See idea and reality. You find verifiable limits based upon known physics. i.e. distribution and frequency response of multiple ways to create neutrinos scaled. Ya sure this is our first trip to the rodeo? I do this in EXCEL! How to create a neutron with an electron and a proton, forward and backward, simply based upon static proximity, the run the function, Maxwell forward and backward to fit the data. How many geometries are available?

Apr 28, 2015
@rufusgwarren; that is some weird stuff there dude. Where are the quarks, gluons, charmed, strange and colored things?

Apr 29, 2015
@rufusgwarren; that is some weird stuff there dude. Where are the quarks, gluons, charmed, strange and colored things?


same sketches from the 30's, or was it the 40's, anyway getting close to a hundred years, the only thing in science collecting "exotic" objects "before" the experiment! Go figure ...

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