Neutron transmission is not useful in any of these scenarios. Not in a fusion reactor because a fusion reactor produces a ton of neutrons itself, many orders of

Neutron transmission is not useful in any of these scenarios. Not in a fusion reactor because a fusion reactor produces a ton of neutrons itself, many orders of magnitude higher than any transmission you'd be able to make so it'd be drowned out (most neutron generators use fusion to produce neutrons too so they're probably also at similar energies to what the reactor makes). Plus the problem with the inside of a tokamak vessel is that it's a super extreme environment and not much can survive in there and like I said in another comment you still have to power your neutron generator. Neutrons are also relatively short ranged and more-or-less isotropic in emission (not able to be focused effectively), meaning you need really high fluence (=dangerous) to transmit more than a few meters. For submarines, water actually attenuates neutrons extremely quickly making it completely useless there. And also let's not forget that neutrons activate materials and make them radioactive for long periods even after you stop with the neutrons. For totally sealed rooms there are better solutions (e.g an acoustic transducer). On top of all this, the physics of neutrons mean this will always be very low bandwidth. None of the applications mentioned in the article are remotely credible, IMO, and this is my area of expertise. Perhaps there is some application where this is the best solution. My point is that at best it's extremely niche; the article makes it out like this is revolutionary but it is definitely not nor is it even particularly interesting. This is not military research with an intended application, this is someone slowly moving a block of plastic back and forth in front of a californium source in a university lab and a press release declaring victory. The actual article published by the scientists in NIM is much more reasonable, but the one linked here is greatly playing up the utility. A fairly reasonable analogy that captures some of the downsides of using neutrons for this is that you could also transmit information by shooting at a metal plate with a pellet gun and having someone listen for the pinging sound. Sure it's possible, but the list of drawbacks is pretty long.