At ISEF, fusion is hot

South Carolina teen makes finals with directed neutron source

PITTSBURGH — Ben Bartlett, a 17-year-old from Lexington, S.C., built a portable nuclear fusion reactor in his parents’ house and earned himself a trip to Pittsburgh where he has a chance to take home one of the top awards later this week at the world’s largest precollege science fair.

LEARNING FUSION Ben Bartlett discusses his tabletop fusion project at the 2012 Intel International Science & Engineering Fair in Pittsburgh. Devin Powell

Nevadan Taylor Wilson won a Young Scientist Award at last year’s Intel International Science and Engineering Fair for a similar reactor that detected radioactive materials by spraying out subatomic particles called neutrons. Bartlett’s project goes a step further by training the neutrons to move in one direction. That directionality could be useful for fashioning intense neutron beams used in treating some kinds of advanced cancers.

“One of the reasons why neutron therapy is only administered in a few locations is because it’s so hard to get the necessary concentration of neutrons in beams. The method of directionalization I’ve come up with … should have widespread applications in neutron therapy or any application requiring a high neutron flux,” says Bartlett, a junior at Lexington High School.

At this year’s fair, Bartlett and more than 1,500 other students are vying for over $3 million in awards, including a top award of $75,000 to be announced on May 18. The annual event is sponsored by the Intel Foundation and administered by the Society for Science & the Public, which publishes Science News.

Bartlett is not the first person to achieve fusion. He’s the 34th outside government and industry, he says. Neither is he the youngest. That record belongs to Wilson, who built his reactor at age 14. Would-be “fusioneers” — such as Mike Kovalchick of York, Pa., another competitor at the science fair — often start with plans posted online by the Open Source Fusor Research Consortium.

At the heart of Bartlett’s $2,800 machine, a long shiny windowed tube that emits a pink glow when switched on, is a suspended ball of deuterium plasma. Deuterium gas injected into the chamber and stripped of its electrons crashes into the plasma. Colliding particles don’t have enough energy to overcome their natural repulsion, but a quantum mechanical effect called tunneling kicks in and allows them to sometimes fuse into helium, spitting out neutrons in the process.

“Neutrons typically come out in all directions,” says Brenden Heidrich, a nuclear reactor physicist at Penn State. Guiding the particles in a single direction “would be very difficult to do,” he says, because neutrons are neutral — and thus ignore electromagnetic fields that can guide charged particles such as protons or electrons.

Forming a beam typically means using shielding to block most of the radiating particles. A small hole in the shielding allows only particles moving in the right direction to escape.

In search of a more efficient process, Bartlett figured out how to make neutrons that tend to travel in the right direction to begin with. A 140,000-volt difference from one end of the device to the other creates electric fields that change the speeds of the charged gas particles circulating within. Those moving toward the front of the tube accelerate, while those moving toward the back slow down.

That speed difference shapes the pattern of neutrons that emerges after collisions. Bartlett’s calculations suggest that about twice as many neutrons should emerge from the front of his device as from the back. Theoretically, stronger fields that can create a larger speed difference could send all of the neutrons toward a single point, in true beamlike fashion.

Vials of neutron-detecting fluid arrayed around the device bubbled in a pattern consistent with the math. To prove that that his device really works, though, the budding scientist will need to make some quantitative measurements, says Ronald Rogge, a physicist who works with neutrons at the National Research Council Canada’s Chalk River Laboratories in Ontario.

“People have suggested they could get this kind of direction preference before,” but such effects tend to be very small, says Rogge.

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