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Neutrinos could encode messages to submarines
19:17 05 October 2009 by MacGregor Campbell
Earth-penetrating neutrinos might one day be used to send messages to lurking submarines. The scheme could provide one-way communication with subs without requiring them to surface.
Neutrinos are particles that interact so weakly with matter that they can pass through the planet like light through glass. In 1977, physicists proposed that they might be used to send messages around, or through, the globe. But because neutrinos interact so rarely, the conclusion was that it would be almost impossible to detect a signal.
Now advances in emitters and detectors make a neutrino com-link feasible in the near future, says physicist Patrick Huber of Virginia Tech in Blacksburg, Virginia.
"This whole thing started as a lunch discussion," says Huber. "You say, yeah people have been talking about that, but it's basically impossible. Then you sit down, do a little calculation, and you find that actually the numbers are not that crazy."
The technique might be best suited to communication with nuclear submarines, which currently use extremely-low-frequency and very-low-frequency radio waves.
ELF can reach a sub travelling at its operating depth but has a very low data rate, about 1 bit per minute. VLF can send messages at around 50 bits per second, but cannot penetrate sea water and so requires the sub to deploy a floating antenna, which limits its manoeuvrability. Huber has calculated that neutrinos could at the very least rival ELF and VLF.
The biggest technical advance is in producing neutrinos. Proposed devices called muon storage rings should be able to generate an intense beam carrying around 1014 neutrinos per second, says Huber.
Most of them would pass straight through the planet, but a few would collide with the nuclei of atoms along the way, and just a very few of these collisions – about 2 per second – would happen near the submarine.
Each collision produces a high-energy muon, and a sub could detect the faint glow given off as the muon travels through seawater. High-energy-neutrino detectors such as IceCube at the South Pole work by picking up this light, known as Cerenkov radiation.
Huber calculates that neutrinos could transmit data at around 10 bits per second. That is less than VLF but can be done while the sub is operating at normal speed and depth. One disadvantage is that subs would have to go to a prearranged area to receive the signal