“In some safety-critical scenarios, such as concerning the integrity of reactor containments, and metal vaults and bulkheads in maritime structures, it can be important to minimise the number of penetrations made through such metal structures for communications cabling. The use of neutrons for information transmission through such structures could negate the need for such penetrations and is perhaps also relevant to scenarios where limited transmissions are desirable in difficult circumstances, such as for emergency rescue operations.”

I don't buy it. Clearly one has to run power to this transmission device. Once you've drilled a single hole for this all it takes is one tiny wire to vastly exceed the data capacity of this system. You could probably even send data at far higher bitrate over the existing power cable itself.

Why is that obvious? Couldn't they use an RTG to power the device without the need for a wire?

Though... it does seem like a piezoelectric transducer, or even a relay, could transmit an audio signal through a solid metal bulkhead much more efficiently.

Submarines often track each other via noise. I don't think you want to make noises loud enough to be heard through a solid metal bulkhead on a regular basis, since the same will likely be true outside the submarine. Those bulkheads are also structural components, I believe, so the metal is quite thick, and the sound would likely echo through the submarine and drive the sailors mad.

You don't need to penetrate the wall if you have power sources on both sides of the wall.

Use a magnet instead then. Flip it over with the pneumatic arm.

There can be many innovative use cases in industry or military applications where wires cannot penetrate the surface of an object and other signals are too weak to penetrate the object to transmit data about something mission critical.

This warrants future investigation at the very least, however impractical it may be. Quantum computers may also benefit from this technology, etc.

It would be interesting to see what places some other alternative like sound, light, laser, VLF, etc, aren't viable options.

Just because it doesn’t have any immediate applications right now doesn’t mean it won’t in the future.

You’re basically right.

Miners trapped in a cave not penetrated by E&M waves?

Wont work.

Signal from inside a reactor?

No. No logic can modulate the signal in said reactor that isn't destroyed by the radiation.

If you have a pneumatic arm to modulate this thing, use it to flip a magnet. That’ll better penetrate any shield than neutrons.

Why wouldn't it work for the miners or the reactor?

Neutrons pass through rock quite well.

Reactors are basically just giant neutron transmitters, by modulating reactor output you also modulate their neutron output.

Flipping a magnet definitely won't penetrate a shield better than neutrons, in fact because of Gauss' law it probably won't penetrate at all.

Rock’s absorption of neutrons doesn’t matter. Neutron thermalize. Since rock has mostly low atomic weight isotopes, it thermalizes them very well [1]. Once they are thermal they scatter easily.

Gauss’ law is for the electric field. The magnetic field is very difficult to block and we have incredibly sensitive magnetometers (probably ones that can detect magnetic anomalies of a submarine from space)

In fact, thats pretty much how deep submarine communication works very low frequency fields. Thats why I proposed a magnet: a basically static field that cant be blocked.

Is my proposal practical? Well, typically not. But if the alternative is neutron communication, I dont see why not.

[1] to a first approx think of thermalizing as momentum exchange upon collision. If you’re similar in mass to the colliding mass you’ll exchange more momentum. Assuming rock is mostly silicon, w/ a mass 28 times larger than a neutron. And there’s at least a km of rock above miners.

[2] throttle a reactor to modulate neutron? Oh boy!

EDIT: actually the crust is mostly oxygen, atomic mass 16. That only strengthens my argument.

Nothing's going through a kilometer of rock, but if you have a few meters of blocked tunnel, neutrons will go through that just fine. If you actually had a kilometer of rock between the miners and help, the miners are dead.

https://en.wikipedia.org/wiki/Gauss%27s_law_for_magnetism

Flipping a dipole is literally just radio.

How do you think nuclear reactors are controlled? Nuclear reactors can vary their power output at a rate of tens or even hundreds of MW/minute. While it takes special designs to throttle at high enough speeds for load following, to send a signal you only need to change the power output enough to be detectable by a neutron detector, which need only be slightly greater than the variation due to random noise.

The first trans-atlantic telegraph message took 16 hours to send.

Probably military applications too if it evades conventional detection.

Space?

I believe the theoretical throughput of a modulated neutrons is very very high - substantially higher than the electromagnetic waves we send today.

Given that, perhaps the people of 1000 years from now will be using them to do data transfer because electromagnetic waves are far too primitive and low bandwidth.

On the basis of what physics?