Neutrino: and the Future of Energy

The idea that matter is made up of small building blocks is very old. Ancient Greek thinkers like Leucippus suggested such a theory and even coined the term "atom" as the name of the tiny unit. By the 1800s, modern scientists expanded on this idea and began to unlock the secrets of the atom. They discovered that atoms were made up of smaller "subatomic" particles like electrons.

Yet, these early physicists did not realize that even smaller particles existed until radioactivity was discovered near the beginning of the 20th century. Ernest Rutherford, an early British researcher in radioactive elements, discovered that electrons were emitted when a radioactive substance decays. Further study revealed that there was an unexplained loss of energy during this decay process. The law of the conservation of energy tipped off scientists that there must be a mysterious particle which contained the missing energy.

Physicist Wolfgang Pauli theorized that an unidentified sub atomic particle is emitted along with an electron during the decay process, and called it a "neutron." In 1931, Italian physicist Enrico Fermi renamed the particle "neutrino" to distinguish it from the just discovered larger neutral particle, the neutron.

It would take scientists another 25 years to verify the existence of neutrinos. In 1956, Los Alamos scientists Clyde Cown, Frederick Reines, and three other researchers detected neutrinos in a laboratory experiment that used large tanks of water located near a nuclear reactor. The physicists were able to detect neutrinos emitted from the reactor by recording their interactions with protons in the water. This was the confirmation of Pauli's theory and proof that neutrinos did exist. The team of scientists eventually won the 1995 Nobel Prize for their discovery.

However, the potential of the tiny particle was unknown at first, since researchers believed neutrinos lack any mass. Without mass, there would be little practical benefit to be harnessed from the sub-atomic particle. It would take another generation of research before the value of neutrinos would be seen.

Researchers have found that neutrinos possess some valuable properties. First, the tiny particles have mass. This fact eluded scientists for many decades. "Scientists have assumed for decades that, because they interact so little with matter, neutrinos must lack any measurable mass," writes Jennifer Chu of the Massachusetts Institute of Technology.

This belief changed when scientists discovered that neutrinos oscillate. Two physicists, working independently of each other, discovered that neutrinos can change between three different "flavors." This is called "oscillation." Takaaki Kajita and Arthur B. McDonald shared the 2015 Nobel Prize in Physics for their simultaneous discovery of this feature. For oscillation to occur, a neutrino must possess mass. The mass is minute and still not precisely measured, but its existence settled a question that had been open for decades.

That mass is not a fuel. Energy deposited in a material does not come from converting a neutrino's rest mass by way of E=mc²; it comes from the momentum and energy transferred in individual interaction events. Work on neutrinovoltaic concepts therefore follows a different chain: which excitation channels deposit energy in a material, how that material couples to them, how the resulting charge carriers are separated, and what output can actually be measured at the terminals.

Another defining property of the neutrino is how weakly it interacts. It carries no electric charge and is subject only to the weak nuclear force and to gravity, so the probability that any single neutrino interacts while crossing a given piece of matter is extremely small — but it is not zero. Most pass through the Earth without leaving a trace; a measurable few do not. Coherent elastic neutrino-nucleus scattering, first observed in 2017, is one of the channels that make these interactions accessible in the laboratory.

Because the flux is continuous and reaches every point on the planet, it does not depend on daylight, weather or location. That is what makes it interesting for energy research — independently of how efficiently it can be used.

With a better understanding of the neutrino, several lines of applied research have opened up. One concerns the inner depths of the Earth. This is due to the tiny particles' reactions when passing through materials. A neutrino spins as it travels, and this movement is influenced by the material through which it passes. Scientists believe they could develop neutrino scanners which could "see" into the Earth's core and identify specific minerals or oil deposits.

Another concerns communication. Electromagnetic radiation has been the traditional medium for transmitting communication, but it has its limitations. For example, seawater interferes with efficient communication with submerged nuclear submarines. Yet, neutrinos easily pass through seawater, which would make them an ideal carrier of communication. While physicists have long theorized that neutrino-based communication was possible, it was not proven possible until a 2012 experiment at Fermilab in Batavia, Illinois. Researchers there used the lab's neutrino beam projector to transmit the word "neutrino" 1 km.