A new global map of antineutrino activity emerging from the Earth’s mantle reveals which areas are the richest sources of these mysterious antimatter particles.
We usually look for scary contaminants in the soil before building a house, but maybe we should check for antimatter, too. Researchers from the US National Geospatial-Intelligence Agency have published a global map of all the antineutrinos hiding beneath Earth’s surface, so you won’t even have to hire a specialist.
Antineutrinos are the antimatter versions of neutrinos, a type of subatomic particle with no electric charge and such little mass that they barely interact with matter — so you don’t really have to worry about living on top of a particularly rich antineutrino deposit. Both antineutrinos and neutrinos are both generated from radioactive decay, but antineutrinos have the opposite spin from their neutrino siblings. Many of these ghostly particles reach Earth from great galactic distances, but the antineutrinos mapped in this new study come from a source much closer to home — nuclear fission reactions happening both on and within Earth.
Like their neutrino siblings, antineutrinos have very light masses and can flit through most substances without being detected. So how did the researchers track down these elusive particles?
It turns out antineutrinos do occasionally interact with matter, but only very weakly. Every once in a while, an antineutrino smacks into a proton, which causes it to split into a positron (a positively charged electron) and a neutron. That neutron then combines with a hydrogen atom to form deuterium, a heavier version of hydrogen. Each time deuterium forms, it releases a double flash of light.
But only about 1 in 100 billion antineutrinos collides with a proton, so catching the resulting flashes of light requires detectors that provide tons of target protons. The Kamioka Liquid Scintillator Antineutrino Detector in Japan, one of the detectors used in the study, has 1,000 tons of liquid containing materials for the antineutrinos to interact with. The Borexino detector in Italy contains 300 tons of liquid, and also uses 2,200 sensors to detect the light flashes. Both detectors provided data that helped the researchers form their maps.
These antineutrino maps will help researchers quantify how much radioactive decay is occurring in Earth’s mantle. The map includes antineutrinos coming from nuclear fission reactions occurring in both man-made power plants, as well as natural uranium and thorium deposits. While we can already estimate how much uranium and thorium exist in the crust through mining, digging deeper to access ores buried in the mantle is more difficult. By tracing these elements via the antineutrinos produced by their radioactive decay, scientists can gauge their natural abundance.
The radioactive decay of uranium and thorium combines with residual heat from our planet’s formation to power the movement of tectonic plates. Locating antineutrinos and their radioactive sources could help determine how quickly Earth is cooling off, and may also give insight into our planet’s formation and ever-changing structure.
Another good reason to monitor antineutrinos is because hidden deposits of uranium and thorium can turn into natural nuclear reactors. While you probably don’t have to worry about your house succumbing to a nuclear meltdown, it still might be interesting to consult the map and see how many antineutrinos have been passing through your body all this time.