321–330 of 375 posts
> could be ready for use in a decade. That's the standard issue joke. "Nuclear fusion has been just ten years away for the last fifty years" It is so common as a joke I'm surprised the article didn't mention it.
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>How much dangerous are the neutrons from such device? Similar to radiation, worst? Neutrons are radiation. Also It's the worst kind of radiation because unlike X-rays or Gamma, neutrons make other things radioactive.
> "neutrons make other things radioactive." Source for this claim: http://en.wikipedia.org/wiki/Neutron_activation Neutrons are radiation, but not electromagnetic radiation. I'm guessing that nitpicking this is why you were downvoted? Dunno.
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It's always a safe bet that the top Hacker News comment will always be "won't work, it's too hard." It's like sitting around for a year trying to sell a project at my current employer, with everybody and their lead telling you "that'll never work," then you implement in a weekend and those same people start nitpicking what you've come up with. (What happened to it'll never work? "Well, your CSS isn't great.") Honestl…
That's hardly ever true. In my experience, Hacker News is full of people from the software field; folks whose professions are often unconstrained by physics,[1] and who have a generally optimistic "this can happen" mentality. That's why everyone here believes we'll have fully self-driving cars in 5-6 years. In the rest of the engineering world, the answer to any question is: it'll be harder than you think it'll be (p…
Among people who have a common mindset, yes. But in general people don't like to take risks or expend insane efforts to make something happen. When they see others doing it, they like to stop them. Generally its because they don't want the regret 'They tried and got it, If I had ...' Or they are plainly jealous and can't stand some one else do progress.
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How much dangerous are the neutrons from such device? Similar to radiation, worst? Time sell any oil company stocks, mutual fund holding?
>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 m…
I'm not seeing any top physicists working in this program (McGuire is not one). I would be willing to bet 1000 EUR that their math and modeling does not add up, or they have skipped some details. Problem with fusion research like this is that the closer you get self sustainment or energy generation, the harder it gets and problems pile up. This project looks like many other similar projects that have gone bust. They…
How much dangerous are the neutrons from such device? Similar to radiation, worst? Time sell any oil company stocks, mutual fund holding?
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.
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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.
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.
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Physicists recognize the constraints on development imposed by the laws of physics. Software professionals recognize the constraints on development imposed by entropy, information theory, and other esoteric branches of mathematics. Rather than scoff at this article because Lockheed is making extraordinary claims without the backing of extraordinary evidence, I prefer to scoff because nuclear physics modeling and simu…
Simulations are way easier to write than almost anything else (I'm a nuclear physicist who did this professionally for many years.) The reason why: physics. Or more specifically: conservation laws. Conservation laws are the book-keeping of physics, and they act as global checks on correctness. If your code conserves energy, mass, particle number, charge, momentum, etc it is probably correct in the ways that matter, b…
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>Compare this with ITER, where they still don't know what material some fairly critical components can even be theoretically made of. It's just night and day. the Skunk Works and EMC2 haven't even reached the stage where they would face the same issue of material - all of them would ultimately have to contain the same type of fast neutrons and there is no good known material to do it.
What part of the reactor degrades so quickly? Can't it be replaced continuously? Why isn't the shielding done with some non-degradable matter, like water or some oil?
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> coal plants, which still make up the majority of U.S. energy production This is no longer the case. http://en.wikipedia.org/wiki/Coal_power_in_the_United_States
electricity generation is only a small part of energy consumption.
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That's hardly ever true. In my experience, Hacker News is full of people from the software field; folks whose professions are often unconstrained by physics,[1] and who have a generally optimistic "this can happen" mentality. That's why everyone here believes we'll have fully self-driving cars in 5-6 years. In the rest of the engineering world, the answer to any question is: it'll be harder than you think it'll be (p…
"Hacker News is full of people from the software field; folks whose professions are often unconstrained by physics" Lockheed Skunk Works, on the other hand, is not. They've been pushing the frontiers of engineering in areas that are very much constrained by physics since 1943, and succeeding. Many times.