>How much dangerous are the neutrons from such device?
Fusion neutron (14 MeV) from fusion reactor is exactly as energetic as fusion neutron emitted by a neutron bomb and causes equal damage (just distributed over longer time). They have 10x as much energy as fission neutrons and travel at speed of 52,000 km/s (17.3% of the speed of light). Neutron capture before they hit and damage magnets, electronics or wear out materials is important part of the fusion reactor design.
This is a DD machine. Neutron energies from the primary reaction are comparable to fission neutrons, 2.4 MeV. There will be some from secondary DT reactions, which are 14 MeV, but the bulk of the neutron production will be at the lower energy.
> How much dangerous are the neutrons from such device? Similar to radiation, worst?
Neutrons are interesting in that they dump all their energy into a very small region. Instead of losing energy continually and gradually, they travel a ways and then dump all their energy into one spot. This makes them potentially very useful for things like cancer treatment (you can select neutrons to ensure they deliver most of their energy into the cancer, rather than evenly along their travel path). I suspect this effect means that, for reactors, the wear and tear is more localized, but of a larger amplitude.
> I suspect this effect means that, for reactors, the wear and tear is more localized, but of a larger amplitude.
Not exactly. The initial collisions do indeed cause localised damage cascades, but the overall effect of a large neutron flux is embrittlement of the material. This is a problem already in fission reactor vessels, but the neutron fluxes are a whole order of magnitude larger in fusion reactors, and it's a very difficult problem to solve. To my knowledge, current materials can only just about deal with with the neutron fluxes in standard fission reactors, with no current materials being capable of withstanding neutron fluxes in a fusion reactor over any long (i.e. commercial) timescale at present. It would be a big achievement and a big jump in materials science to discover such a material, completely separate of any fusion project.
(Disclaimer: this is not remotely my field, but I have looked at some of this stuff in the past, and been to talks about ITER.)
It's a simple geometric analysis: neutrons can't be deflected, so whatever concentration of reacting mass you have emits neutrons isotropically. So to my knowledge no (you can only radiate more in one direction if the reaction is more extended in the perpendicular direction).
The majority of those suppliers provide boron-impregnated plastic, which is fine for e.g. shielding spallation neutrons from a medical linac head. Reactor shielding is orders of magnitude higher, so material damage is a real concern. Not to say that people can't or don't use that material, but it is not the most cost effective stuff.
Frankly, the best neutron shielding in the world, on a per-cost basis, is water with borax. I don't know why people don't use this more. We used to use stacked bags of borax as neutron shielding when I built a fusion reactor (non-self sustaining, of course), and we had more than enough shielding to handle 2.45 MeV neutrons for under $1000.
So in this reactor design, the neutron shield would be quite thin, if that drawing is to scale I'd say like 30-50cm? in that case water in borax wouldn't be dense enough right?
A cool thing about the shield being liquid is that you could theoretically replace it while it's running. It could make the neuron shield double as the heat transfer medium too.
Of course I'm a total layman so this is just highlevel blabbering.
Are you sure you're not mixing up neutrons and protons? Here are some typical depth dose curves from google images(http://www.nap.edu/books/11976/xhtml/images/p20014b2bg205001...). Neutrons, being neutral particles, don't exhibit the Bragg Peak (large increase in energy deposition at the end of the particle's track) that you get for heavy charged particles.
I was pretty sure neutrons beahved that way (recalling from a course I took in grad school), but it has been a few years, and I do not have references handy. I am not entirely sure what the y-axes are, on the plot you linked, so I am not sure how it correponds to what I was saying.
The do not. Protons have a quite definite range, and can be controlled in the way you suggest. This is because they lose energy primarily by scattering (much lighter) electrons out of their path. This means protons have relatively straight paths and the dynamics of the electromagnetic interaction gives an energy deposition curve that is sharply peaked at the end.
Neutrons slow down via interaction with nuclei (all of which except hydrogen are heavier) so they lose energy slowly and scatter all over the place. They have no definite range (search for "fermi age theory" to get a rough idea of the distribution) and can't be meaningfully beamed (unless they are ultra-cold, which is not relevant to fusion power.)
I've made a longer comment above that goes into neutron physics in a little more detail.
There are a variety of more-or-less sort-of correct answers below, but I'll throw in my two cents regardless. I am a nuclear physicist who spent a lot of time worrying about neutrons, which are a major source of backgrounds in neutrino detectors.
Two points made reply to you are correct: neutrons are radiation, but not electromagnetic radiation; and neutrons can make other things radioactive.
Some thing other people are saying are less correct: any individual neutron will deposit most of its energy in one place, but averaging over many neutrons their energy deposition will be spread out. Furthermore, neutrons will come out in all directions. The problem of neutron damage is not small, but no one seriously believes it's a show-stopper.
Neutrons are the exploding billiard-balls of nuclear physics. Fusion produces "fast" neutrons, with moderate energies. This is a deuterium-deuterium device, so most of the neutrons will come out with 2.4 MeV, which happens to be the same as fission neutrons. The DD reaction produces tritium as a byproduct about half the time, though, and DT fusion will lead to 14 MeV neutrons. There will be fewer of these in most designs, and some designs incorporate ideas to get rid of the tritium quickly to suppress these higher energy neutrons.
At high energies neutrons don't tend to interact very much with light nuclei, and for a variety of reasons fusion reactor design is dominated by light nuclei. What they do do is bounce off, which is where the billiard-ball analogy comes in. Each time a neutron bounces off another nucleus it loses energy (because the nucleus it bounces off of recoils, carrying some energy with it.) This is just pure Newtonian mechanics.
Neutrons typically travel a few metres in the process of slowing down, depending on the material. Light materials slow them down faster: a light ball bouncing off a heavy ball doesn't loss much energy, but bouncing off another light ball it does (hydrogen is the best material for slowing neutrons down because of this, and hydrogen-rich materials like water are good too.)
The neutron never completely stops because the nuclei it is bouncing off of are in thermal motion. At room temperature a neutron in thermal equilibrium moves at about 2200 m/s. But not for very long, because this is where the exploding comes in.
You can think of it in these terms: once thermalized, a neutron is passing by other nuclei rather slowly (2200 m/s is slow when you're a neutron). This gives it lots of time to react with nuclei, rather than just bouncing off, and eventually it does. When a nucleus absorbs a neutron it becomes a different isotope of the same element, and in many cases adding a neutron to a stable isotope makes it radioactive. Carbon-12 is a stable isotope that, with the addition of a neutron becomes carbon-13, and if it happens to get another neutron added later on, radioactive carbon-14.
Neutrons are a pain, even to fission engineers, and fission depends absolutely on them to happen. They get everywhere, are hard to shield, make stuff radioactive and damage materials. But we know pretty much how to deal with them, and it's unlikely they will make the difference between working and not working in a device like this.
The neutrons from these reactor makes surrounding matters radioactive? Doesn't sound too good. The fission reactor is not really as clean as it sound at first?
Putting a mice next to this system can make it a "carbon-14" mice? Can it glow in the dark? :-)
Time to buy airline stocks. If you can put a miniature fusion power plant on an 747 equivalent, airline profit margins will skyrocket.
Actually even if you believed there's a chance this Lockheed concept can work, the time to buy airline stocks would be on the back end of this dead bull market that's about to fall off a cliff. And then there's the 20 year wait before it's finally deployed to a commercial airplane.
A fusion powered 747 might be the result, but
maybe not! Instead, let's see: With the CFR,
we've got dirt cheap electric power. Okay,
then we can also use that power to make dirt cheap,
very clean water. Then, yup, we can take that water,
more of that power, and coal and make jet fuel.
And maybe that is what the 747s would continue to
use! Maybe!
If we get a working CFR as described, I'd be shocked if the cost of coal extraction and usage remained low enough for this to be a sound idea. In the face of extremely cheap, clean power, I'd sincerely hope that the government would incentivize its use. Coal and oil lobbies might be able to fight this to some extent, but once a safe and economically viable alternative is present, the days of fossil fuel reliance are numbered. This can't happen soon enough.
From what I've read at just the level of
Wikipedia, I'd guess yes. But nuclear
physics just is not my field.
I wanted my Ph.D. in mathematical physics,
but all the physics courses I could find
did the math in very sloppy ways, and my
hope for any research progress in physics
wanted to do the math with full care. I
did get much of that math, but by then
I was occupied with my money making work
and didn't get back to physics. I'd like
to, maybe, someday! Then maybe I'll be
able to give you a solid answer.
For now, some of the discussions claim that
a lot of neutrons will make a metal brittle
but don't go the next step and explain just
why. Before I'd say anything about what
neutrons do, if only as a check on the level
of understanding, I'd want to know why.
Whatever production process partially relies on arranging the crystal structure of the metal to arrive at desirable properties, the neutrons disrupt it.
Okay, I'll accept that: What used to be
the usual isotopes of iron, carbon, aluminum,
etc. with some extra neutrons, after
whatever gamma rays, alpha particles, etc.
boil off, becomes some other isotope or
element that doesn't fit in the crystal
and, thus, makes the crystal brittle.
It can happen without neutron absorption, the neutrons simply knock the atoms out of alignment, and they bounce around a bit (so each neutron can cause more than 1 defect).
(if it doesn't follow why that would matter, look into the heat treatment of steel)
Time sell any oil company stocks, mutual fund holding?