Nav: Home

Spinning electrons yield positrons for research

June 01, 2016

Researchers use accelerators to coax the electron into performing a wide range of tricks to enable medical tests and treatments, improve product manufacturing, and power breakthrough scientific research. Now, they're learning how to coax the same tricks out of the electron's antimatter twin - the positron - to open up a whole new vista of research and applications.

Using the Continuous Electron Beam Accelerator Facility (CEBAF) at the Department of Energy's Jefferson Lab, a team of researchers has, for the first time, demonstrated a new technique for producing polarized positrons. The method could enable new research in advanced materials and offers a new avenue for producing polarized positron beams for a proposed International Linear Collider and an envisioned Electron-Ion Collider.

Jefferson Lab Injector Scientist Joe Grames says the idea for the method grew out of the many advances that have been made in understanding and controlling the electron beams used for research in CEBAF.

"We have a lot of experience here at Jefferson Lab in operating a world-leading electron accelerator," Grames said. "We are constantly improving the electron beam for the experiments, pushing the limits of what we can get the electrons to do."

The CEBAF accelerator gathers up free electrons, sets the electrons to spinning like tops, packs them full of additional energy ("accelerating" the particles to up to 12 billion electron-volts), and directs them along a tightly controlled path into experimental targets. Grames and his colleagues would like to take that finesse a step further and transform CEBAF's well-controlled polarized electron beams into well-controlled beams of polarized positrons to offer researchers at Jefferson Lab an additional probe of nuclear matter. They named the endeavor the Polarized Electrons for Polarized Positrons experiment, or PEPPo.

Positrons are the anti-particles of electrons. Where the electron has a negative charge, the positron has a positive one. Producing positrons that are spinning in the same direction, like the electrons in CEBAF, is very challenging. Before PEPPo, researchers had successfully managed to coax polarized positrons into existence using very high-energy electron beams and sophisticated technologies. The PEPPo method, however, puts a new twist on things.

"From the beginning, our aim was to show that we could use the polarized electron beam we produce every day at CEBAF to create the positrons. But we wanted to do that using a low-energy and small-footprint electron beam, so that a university or company may also benefit from our proof of principle," Grames explained.

The PEPPo system was placed inside the CEBAF accelerator's injector, which is the part of the accelerator that generates electrons. The system consists mainly of small magnets for managing the particle beams, targets for transforming them, and detectors for measuring the particles.

In it, a new beam of electrons from CEBAF is directed into a slice of tungsten. The electrons rapidly decelerate as they pass through the tungsten atoms, giving off gamma rays. These gamma rays then interact with other atoms in the tungsten target to produce lower-energy pairs of positrons and electrons. Throughout the process, the polarization of the original electron beam is passed along. The researchers use a magnet to siphon the positrons away from the other particles and direct them into a detector system that measures their energy and polarization.

"We showed that there's a very efficient transfer of polarization from electrons to the positrons," said Grames.

Further, the researchers found that it is also possible to dial up the degree of polarization that they are interested in by selecting positrons of the right energy. While the more abundant lower-energy positrons are less polarized, the positrons with highest-energy retain nearly all of the polarization of the original electron beam. In PEPPo, the electron beam was 85 percent polarized and accelerated to 8 million electron-volts (MeV).

"Nuclear physicists typically want the highest polarization possible for their experiments," he explained. "Positrons collected at half the original electron energy were about 50 percent polarized, which is still quite high. But, as we approached the maximum energy, we measured 82 percent, showing that a very large portion of the original electron polarization is transferred."

The PEPPo experiment ran for four weeks in the spring of 2012. The result has just been published in Physical Review Letters, and it is featured as an Editors' Suggestion.

Grames and his colleagues say now that they have their proof of principle, they want to design a source that is capable of producing a beam of polarized positrons for research.

"With this result in hand, we are now asking ourselves what's the best way to collect these positrons into a beam that may be used by nuclear physicists in experiments at Jefferson Lab and that may be useful for other facilities. That's the next step."
-end-
This work was supported in part by the U.S. Department of Energy's Office of Science, the French Centre National de la Recherche Scientifique, and the International Linear Collider project.

Jefferson Science Associates, LLC, a joint venture of the Southeastern Universities Research Association, Inc. and PAE Applied Technologies, manages and operates the Thomas Jefferson National Accelerator Facility, or Jefferson Lab, for the U.S. Department of Energy's Office of Science.

DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, visit science.energy.gov.

DOE/Thomas Jefferson National Accelerator Facility

Related Electrons Articles:

Self-imaging of a molecule by its own electrons
Researchers at the Max Born Institute (MBI) have shown that high-resolution movies of molecular dynamics can be recorded using electrons ejected from the molecule by an intense laser field.
Electrons in the fast lane
Microscopic structures could further improve perovskite solar cells
Laser takes pictures of electrons in crystals
Microscopes of visible light allow to see tiny objects as living cells and their interior.
Plasma electrons can be used to produce metallic films
Computers, mobile phones and all other electronic devices contain thousands of transistors, linked together by thin films of metal.
Flatter graphene, faster electrons
Scientists from the Swiss Nanoscience Institute and the Department of Physics at the University of Basel developed a technique to flatten corrugations in graphene layers.
Researchers develop one-way street for electrons
The work has shown that these electron ratchets create geometric diodes that operate at room temperature and may unlock unprecedented abilities in the illusive terahertz regime.
Photons and electrons one on one
The dynamics of electrons changes ever so slightly on each interaction with a photon.
Using light to put a twist on electrons
Method with polarized light can create and measure nonsymmetrical states in a layered material.
What if we could teach photons to behave like electrons?
The researchers tricked photons - which are intrinsically non-magnetic - into behaving like charged electrons.
Electrons in rapid motion
Researchers observe quantum interferences in real-time using a new extreme ultra-violet light spectroscopy technique.
More Electrons News and Electrons Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: The Power Of Spaces
How do spaces shape the human experience? In what ways do our rooms, homes, and buildings give us meaning and purpose? This hour, TED speakers explore the power of the spaces we make and inhabit. Guests include architect Michael Murphy, musician David Byrne, artist Es Devlin, and architect Siamak Hariri.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

What If?
There's plenty of speculation about what Donald Trump might do in the wake of the election. Would he dispute the results if he loses? Would he simply refuse to leave office, or even try to use the military to maintain control? Last summer, Rosa Brooks got together a team of experts and political operatives from both sides of the aisle to ask a slightly different question. Rather than arguing about whether he'd do those things, they dug into what exactly would happen if he did. Part war game part choose your own adventure, Rosa's Transition Integrity Project doesn't give us any predictions, and it isn't a referendum on Trump. Instead, it's a deeply illuminating stress test on our laws, our institutions, and on the commitment to democracy written into the constitution. This episode was reported by Bethel Habte, with help from Tracie Hunte, and produced by Bethel Habte. Jeremy Bloom provided original music. Support Radiolab by becoming a member today at Radiolab.org/donate.     You can read The Transition Integrity Project's report here.