The study of ‘ghost particles’ might benefit physics and nuclear nonproliferation

A nuclear reactor at an Illinois energy plant is assisting University of Chicago scientists in learning how to trap and interpret neutrinos, which are small, elusive particles.

The scientists used a small detector to monitor neutrinos coming from a nuclear reactor at Constellation’s (previously Exelon) Dresden Generating Station near Morris, Illinois. Because they interact with matter so seldom, these particles are incredibly difficult to capture, yet power reactors are one of the few sites on Earth with a large concentration of them.

“This was an amazing chance to profit from the large neutrino output from a reactor, but it was also a difficulty given the loud industrial environment directly next to a reactor,” said Prof. Juan Collar, the study’s lead author and particle physicist. “This is the closest neutrino physicists have come to a commercial reactor core.” Thanks to Constellation’s generosity in supporting our experiment, we obtained unique experience operating a detector under these circumstances.”

With this information, the group intends to do more measurements that may provide solutions to concerns regarding the underlying principles regulating particle and nuclear interactions.

The approach might also be beneficial in nuclear nonproliferation since neutrinos can inform scientists what’s going on within the reactor core. As a precaution, detectors might be put near reactors to monitor whether the reactor is being used to produce electricity or weapons.

 

‘Majority orders’

Neutrinos are commonly referred to as “ghost particles” since they travel through practically all matter unseen. (Billions have already gone past your body without your knowledge today, en way from someplace in outer space.) If you can capture them, they can inform you about what’s going on where they came from as well as the basic features of the cosmos.

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Scientists are particularly interested in learning about certain characteristics of neutrino activity, such as whether they have electromagnetic properties (for example, a “magnetic moment”) and if they interact with previously discovered particles or in novel ways with existing particles. Extensive measurements of as many neutrinos as feasible may aid in narrowing down these options.

Collar’s team was drawn to nuclear reactors by the necessity for a large number of neutrinos. “By orders of magnitude, commercial reactors are the greatest generator of neutrinos on Earth,” he added. Nuclear reactors generate huge amounts of neutrinos each second in regular operation. They occur when atoms inside the reactor split up into lighter elements, releasing part of the energy as neutrinos.

There is, however, an issue. Because neutrinos are so light and interact so seldom, scientists must often identify them by filling a massive tank with detecting fluids and then searching for the telltale signal that a passing particle has created one of a handful of known reactions in it.

A multi-ton detector, however, would not fit inside a commercial nuclear reactor. The scientists need something much, much smaller. Collar, fortunately, is a specialist in the construction of such devices; he previously led a team that created the world’s tiniest neutrino detector.

In a second stroke of luck, Illinois is one of the top nuclear energy states, with nuclear reactors generating almost half of the state’s power. Collar was given permission to test the detector at the Dresden Generating Station, one of the country’s first commercial nuclear facilities.

Collar and his colleagues had previously tested their small detectors at Oak Ridge National Laboratory in Tennessee, where they were able to precisely regulate much of the environment in order to produce a strong signal. However, in order for the detector to function in Dresden, scientists had to create a second version that was designed to cope with the significantly louder environment of a commercial reactor in operation.

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Collar said, “You’re receiving radiation, heat, vibration from the turbines, RF noise from the pumps and other machines.” “However, we were able to work past all of the obstacles that were thrown our way.”

To protect the detector from additional stray particles that may pollute the data, they constructed it with a complicated multi-layered shielding. They were eventually able to keep the detector running unattended for many months, collecting data the whole time.

The team aims to collect data from another reactor nearby, Constellation’s Braidwood Generating Station, or the Vandells nuclear station on the coast of Spain. “This technology has the potential to significantly improve our knowledge of neutrino characteristics,” Collar added. “Our data can provide a lot of theoretical information.”

Knowledge of how to operate tiny detectors in such loud conditions is in great demand as well. “There is a lot of interest in the nuclear nonproliferation community in putting detectors adjacent to reactors because they can tell you what’s going on in the core and show any deviations from the stated usage,” Collar said.

The emission of neutrinos varies depending on the kind of fuel used in the reactor and what it produces, thus detectors should be able to detect early warning indications of weapons manufacturing or if fuel is being surreptitiously moved elsewhere. However, in order to achieve this aim, such detectors must be tiny, sturdy, and simple to use; Collar said that the Dresden effort contributes vital data to the development of such detectors.

Neutrino detectors might potentially be used for a variety of different purposes. “For example, if we have sufficiently sensitive neutrino detectors, you might use them to map the interior of the Earth—and maybe even find oil or other important reserves,” Collar said. “A lot of thought has gone into this, but it is still in the future.”

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Collar was reminded while working on the design that his campus laboratory follows a line of study begun by Prof. Willard Libby in the 1950s to find how to utilize carbon-dating to determine the age of an item.

“These forefathers had to devise ways that we still use today to locate a relatively modest signal amid a huge volume of background noise,” he said. “It’s gratifying to know that our work is part of a lengthy local history.” For similar reasons, Illinois is a distinctive area for nuclear power production.”

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