Touring the Planet’s Most Powerful Gamma Ray Source

By Erin Weeks

When students pass by its unassuming building along Circuit Drive, many have no idea the world’s most intense gamma ray laser lies tucked away in the heart of Duke’s campus.

The Duke Free Electron Laser Laboratory, or DFELL, attracts physicists from across the country to study everything from nuclear security to the death of stars. Gamma rays are the most energetic members of the electromagnetic spectrum, and they can tell us a great deal about physics at the nuclear level. Cosmic events, like massive star collapse, produce high gamma radiation, but few natural sources exist on earth — so DFELL provides a window into the dense and infinitesimal world of the atomic nucleus. A group of students organized by Duke’s Society of Physics Students recently toured the lab to learn more. All photos were taken by Jonathan Lee.

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DFELL’s gamma rays are generated by the collision of electron beams with photons racing around a large, oval storage ring, like a race track. Here, half the group gathers next to the straight leg of the oval’s left side.

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Physics professor Ying Wu, the associate director for accelerators & light sources at DFELL, explains how electrons colliding with photons are like bowling balls crashing into an oncoming train. At left, you can see the red magnets that help guide the beams.

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Though hidden to onlookers, this room houses a cavity mirror that helps to steer the beam of electrons with incredible precision. Even minute vibrations can knock the laser beam out of alignment, so the mirror assembly sits on reinforced concrete with shock absorbers.

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Behold the Blowfish. This detector system boasts 88 “spines,” which can precisely measure what happens when intense gamma rays excite a nucleus, causing it to spit out particles. The spines are comprised of liquid-scintillator cells, which produce photons triggered by radiation, and photomultiplier tubes, which convert the photons to electrical signals.

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“Blowfish’s goal in life is to make precision measurements of photonuclear reaction cross-sections,” says Grayson Rich, a graduate student at UNC who studies nuclear and neutrino physics at DFELL with Duke professor Phil Barbeau. Blowfish’s proximity to DFELL’s gamma rays “allows for really rigorous evaluation of theories for how nuclear systems behave.”


This entry was posted on Wednesday, February 19th, 2014 at 2:52 pm and is filed under Engineering, Faculty, Physics, Students. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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