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Comment by java-man | Hacker News Reader

During the Cold War, I've heard rumors of one directional communication system with submarines using neutrinos.

I don't know what the utility of the system described in the article though - neutrons will be absorbed pretty quickly, so the communication must have a very short range.

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How could a nuclear-powered submarine possibly host a neutrino detector? You're sitting meters away from one of the brightest neutrino sources on the planet!

please see my comment below in this thread.

“… using neutrinos”

“… neutrons will be absorbed…”

I made the same confusion for a second. Neutrons are easily absorbed. Neutrinos (little neutrons) are almost impossible to interact with (and therefore absorb)

It takes something like 18 light years of lead to attenuate a neutrino beam by half, so they’d need a pretty big receiver :)

It's possible to detect neutrinos with a scintillation chamber, but in general only a tiny fraction of neutrinos passing through would be observed. They really don't interact with regular matter much.

However, it's the transmitter that would be nearly impossible, because blocking neutrinos or affecting them in such a way as to modulate the beam would be extremely difficult.

I think we can probably rule out neutrino based communications during the cold war, especially since VLF did the job just fine.

The "rumor" referred to an array of scintillators dragged behid the submarine, with the ocean water as a detecting medium. In theory, with clear enough water and large enough detector volume, that idea might work. I vaguely recall data rate of less than one bit per second.

That sounds a lot like the ELF radio system they used, which basically was used to order submarines to surface (or near enough) to receive new orders as the bandwidth was <1 baud.

https://en.m.wikipedia.org/wiki/Extremely_low_frequency

The data-rate would be far below 1 bps. The event-rate in SuperK [1] from the Sun was ~0.1/day/kiloton of water.

Signalling to submarines would require a Fermilab or T2K-caliber accelerator with an ability to direct a beam, with a properly-oriented pion-decay hall, generally in the known direction of the submarine and highly-synchronized clocks (or a clever time-structure strategy) to allow coincidence-detection for background-suppression.

For scale, the MINOS detector [2] detected a couple thousand events with a couple of years of beam-time.

[1] https://en.wikipedia.org/wiki/Super-Kamiokande#/media/File:N...

[2] https://arxiv.org/pdf/1103.0340.pdf

Sure you can detect neutrinos that way, especially at higher energies. But you're going to be swamped by natural neutrinos (e.g. atmospherics), unless you have quite the beam. And how do you know where to point the beam?

Modulating neutrinos is easy. You just control the production rate. For example ramping a fission reactor up and down will create pulses of neutrinos (though it's not terribly efficient). For practical neutrino communications, you'd want to use a muon beam to generate your neutrinos. The neutrinos are emitted roughly in the same direction the muons were moving when they decay, so you can make a directional beam, and by controlling the number of muons decaying at any given point in time, either by directly controlling the number of muons or how much time dilation they experience in the beam, you can ramp up and down neutrino production.

For that modulation to be reflected in the detection array, the beam would have to be accurately targeted on the submarine?

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