Using a forest as a huge neutrino detector? A physicist thinks it’s possible

Neutrinos are a bit like the Force Star Wars. These ‘ghost particles’ surround us and penetrate us, but do not interact with the forces that bind the galaxy together. The reason they can pass not only through us, but around the entire planet, is because they are extremely light in mass and have no charge. This also makes them extremely difficult to observe and study. A physicist has a bold new proposal: Let’s use Earth’s forests to detect some of them.

This may seem completely bizarre, but neutrino detectors usually are. For example, superkamiokande in Japan is a large hollow structure filled with purified water. The walls of the container are covered with detectors that can record the very rare interactions between a neutrino and an atom.

The IceCube Neutrino Observatory, located in Antarctica. wants to detect similar collisions, but instead of using liquid water, it uses one cubic kilometer of ice, with the detectors placed in the ice. China plans to build the world’s largest detector directly under the sea.

All those detectors expect to see a flash of light when the neutrino collides with an atom. The tree approach is slightly different. It is based on the fact that the tau neutrino is the heavier version of these particles. When this neutrino interacts with our planet, it produces a tau particle – a heavy version of the electron. This particle decays into a rain of other charged particles and this rain emits radio waves.

Researchers interested in observing these events in the sky use radio antennas to pick up these signals. But the antennas should be placed away from cities (and other man-made interference), ideally on higher ground such as hills or slopes. Many locations with these features have trees, so building an array of antennas also requires finding a spot that is barren. In a new preprint (yet to be peer-reviewed), Steven Prohira, an assistant professor of physics and astronomy at the University of Kansas, considers whether we could just use the trees instead.

There is some evidence – first collected at the turn of the last century and subsequent studies in the mid-twentieth century – that trees make pretty good radio antennas. By wrapping a coil around a tree or nailing a wire to it and then connecting it to electronics, a forest could work as a complete whole.

Now there are a lot of challenges and uncertainties surrounding turning Earth’s forests into massive neutrino detectors. For starters, it’s not clear how well the trees do at detecting the range of radio waves produced by these events. But if they can capture the subtleties of these events, we can trace their origins.

There are also implementation complications. Tree differences can affect performance, as can seasons when leaves affect observations. It can also be complicated to power the array to get into the middle of a forest (but not with the new energy from space approach). Still, Prohira is confident that exploring this possibility is worth it, as long as it is done in a way that does not harm nature.

“Using trees as antennas for a full array has numerous benefits, including completely eliminating the need for antenna design and deployment,” he writes. “The author urges that, should this idea be tested or implemented, researchers take into account that they take the utmost care to protect and maintain the forest they are instrumenting, and not cause harm to this precious and fragile resource that shared by all creatures on earth. Such a detector must be built in harmony with and with respect for nature; otherwise this idea isn’t worth trying.”

The article is available in the preprint online repository ArXiv.

[H/T: Science News]

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