WASHINGTON — The solution to the big issue of nuclear nonproliferation might be smaller than you think, so small it’s virtually invisible and massless.
Physicists at Virginia Tech have found a way to use these teeny subatomic particles, called neutrinos, to detect what’s going on at nuclear reactors, such as the Arak reactor in Iran. Neutrinos are ghostlike particles that move close to the speed of light and travel to Earth by the billions from space every day. They barely interact and can travel through planets; even through you.
Here on Earth, nuclear reactors produce large amounts of antineutrinos, the counterpart of neutrinos, which is handy for monitoring reactor use.
“You can’t shield neutrinos or antineutrinos. It’s impossible to shield. You can’t hide them,” said Bob Svoboda, a co-leader of the WATCHMAN Collaboration, a group of universities and laboratories that are experimenting with nuclear detection methods.
The researchers from Virginia Tech found a way to monitor plutonium or uranium use outside a reactor by using antineutrino detectors with surprising accuracy. This might provide information on whether Iran is honoring its commitment under the Treaty on the Non-Proliferation of Nuclear Weapons not to develop a nuclear weapons program.
“If Iran cheats, antineutrino monitoring could provide an early warning to the international community, prompting further investigations, diplomatic interventions or potentially military action,” said Thomas Shea, a nuclear scientist from TomSheaNuclear Consulting Services. Shea spent more than two decades with the International Atomic Energy Agency.
Essentially, scientists are inferring what’s going on inside a nuclear reactor from neutrino emissions without having to actually go in and check. If the amount of uranium or plutonium goes up _ and you need a lot of the former to produce the latter _ scientists can tell that the uranium likely isn’t being used for energy purposes.
“If you can carefully measure the energy of the outcome in the neutrinos, which is actually fairly simple, then you can sort of distinguish whether they’re making plutonium or uranium,” said Patrick Huber, an associate professor of physics at Virginia Tech and author of the neutrino research.
Physicists can detect the frequency of use and whether anyone is removing plutonium, and they can do it all by setting up detectors in the range of 10 kilometers – about 6.25 miles – from an installation.
Without this technology, “If they kick you out the day before they open the reactor, you have no idea what’s really in the reactor,” Huber said in a telephone interview. “And you also have no idea, if they let you back in two weeks later, what they did.”
Neutrinos, which get their name from an Italian diminutive meaning “little neutral one,” were discovered in the 1930s by a German physicist, Wolfgang Pauli. Despite physicists studying neutrinos for nearly a century, they still hold many mysteries and might help unlock the history of the universe.
“There’s not much in terms of practical application for neutrinos. So these detectors outside these nuclear reactors is sort of a concrete application of neutrino physics that hopefully leads to the benefit of society,” said David Latimer, an assistant professor of physics at the University of Puget Sound in Washington state.
In August, Iranian President Hassan Rouhani told the International Atomic Energy Agency he’d reject restraints imposed outside the framework of the nuclear treaty. However, there may be a benefit for Iran to allowing a detector to be set up outside the Arak, or IR-40, reactor.
It could offer a way for Iran to show it’s not cheating on the agreement, while satisfying the needs of some who may think negotiations can’t be trusted, said Stephen Zunes, a professor of politics at the University of San Francisco.
“I think this kind of helps the more moderate of voices, the voices that are interested in a diplomatic solution,” he said.
Huber and Shea think this could open the doors for scientific collaboration with neutrino experts in Iran, allowing for participation in research and development.
Science can build bridges, Huber said, because scientists tend to be less focused on politics and ”more on getting things done.”
The research conducted at the European Organization for Nuclear Research, known as CERN, was one of the first things European countries did together after fighting two world wars. Internationally, scientists such as the researchers at Virginia Tech are making strides in neutrino and antineutrino studies.
“The good news is that early this year, a Japanese group demonstrated detection of neutrinos actually out of the back of a van,” Huber said. That is, the scientists were mobile and using a detector aboveground. “That’s a huge breakthrough.”
The other good news is that the WATCHMAN group, which is planning experiments in Cleveland, will be making its own headway. The researchers are hoping to try a different form of detection using water instead of scintillator, a liquid that can be costly and isn’t great for the environment, Svoboda said.
“The hope is we can find a hidden reactor somewhere in the world. Is there a reactor around or is there not?” said Adam Bernstein, leader of the rare event detection group in the physics division of the Lawrence Livermore National Laboratory.
So what’s the bad news? Getting one of these antineutrino detectors set up and operating isn’t something that is happening tomorrow _ or maybe even a year from now. Technical feasibility isn’t ready yet. “In terms of politics, now, that’s everybody’s guess,” Huber said.
Shea said the next steps would be to create a group of antineutrino experts, such as the ones at Virginia Tech and WATCHMAN, to build, design and install a detector adjacent to the IR-40 reactor in Iran in order to experiment and analyze data.
“After a suitable period of time, the IAEA could then take over these functions, as the circumstances warrant,” he said.
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