Right after the Big Bang, giant showers of neutrinos were spewed across the universe. These subatomic particles, produced by the decay of radioactive elements, are the focus of intense research by scientists in laboratories around the world. They are hoping these phantoms of physics could unlock mysteries about dark matter and about how the universe was formed.
Some neutrinos — geoneutrinos — come from natural uranium and thorium decay in the Earth’s crust and mantle. Other neutrinos are emitted by nuclear reactors. Every second there are 10 to 45 geoneutrinos shooting out from inside the Earth. And now scientists have composed a global map of these neutrinos that shows some surprising hotspots.
“This is the real golden fleece of geology because it points to how much power the Earth is generating inside, keeping itself warm and governing the cooling rate of the planet,” says Stephen Dye, a professor of physics at Hawaii Pacific University and an author of a paper on concentrated streams of neutrinos that was recently published in the Journal of Scientific Reports.
Some of the hot spots that show up on the new neutrino map are close to nuclear reactors.
“Think about a light bulb,” Dye says, “If you're close to the light bulb, the light bulb appears quite bright to you. As you get farther and farther away from the light bulb, of course it gets dimmer and dimmer. The same effect applies here with the nuclear reactors. So if you're close to those, you will see — if you could see the neutrinos — a very bright spot.”
In addition to nuclear hot spots, there are also bright areas near Tibet. This, Dye explains, is because, in Tibet, “the India plate is colliding with the Asian plate. And we have double the layer of continental crust there, and so that appears to be a bright blob, shall we say, on the surface of the Earth.”
Dye hopes his work with neutrinos will have an impact on politics and global security. If scientists are able to map neutrinos, he hopes they might be able to recognize a previously unknown nuclear reactor.
“We're very excited about that possibility,” Dye says, “Knowing where all the reactors are that are registered with the IAEA and what their power cycles are and so forth is incredibly valuable information for uncovering the potential clandestine reactor.”
Even more than monitoring possible nuclear treaty violations, Dye says scientists are excited about the answers their research on neutrinos can give them to Earth’s origins.
“It provides us a window inside the Earth, which we can't access that information by other means directly. And one of the main questions in geology is how much energy is being produced inside the Earth. This tells us things like when did the inner core form and what's its rate of formation?” Dye says. “This tells us stuff about how the planet formed, what materials it formed from, and how it got to its present state from its initial state.”
Dye and his colleagues hope to take their research even further.
“Our dream is to build an observatory that could go down into the deep ocean and measure the geo neutrinos coming most directly out of the mantle,” he says. “That will give us the best direct measurement of the heat being generated inside the planet and unlock some of the answers to these questions we raised earlier.”