The dirty little secret of fusion is that it is dependent on nuclear fission. The fusion reaction is D + T --> He-4 + n. But tritium is not found in nature; it is manufactured by Li-6 + n --> He-4 + T. You could use the neutron produced in the fusion to make the tritium, but free neutrons tend to get lost, and need to be replenished. The neutrons are supplied by nuclear fission in a reactor, which is where tritium is made. So when somebody says fusion will obsolesce nuclear reactors, you know they are lying. Well, there is a loophole. The D + D --> He-4 reaction requires no neutrons, but does require higher operating temperature and pressure. There are also more exotic reactions like Li-7 + p --> 2 He-4 and B-11 + p --> 3 He-4, but these have a higher Coulomb barrier, so require yet higher temperature. One might imagine using D+T fusion as a stepping stone on the way to D+D fusion. Edward Teller has suggested hybrid fission-fusion. Operate fusion, accepting an energy loss, and use the 14 MeV neutrons to fission uranium (and other actinides). Even U-238 is easily fissioned at this energy. Then the fission neutrons are used to make tritium, as well as breeding fission fuel. This is far more likely to succeed than a pure fusion reactor. In addition to tritium, another gift to science from the hydrogen bomb arsenal is helium-3 (the decay product of tritium), much beloved as an exotic fermionic superfluid at millikelvin temperatures. There is also a potential medical application, MRI imaging of air-space in lungs. There are only two gases safe to inhale that have nuclear spin 1/2; they are helium-3 and xenon-129. -- Gene
________________________________ From: Whitfield Diffie <whitfield.diffie@gmail.com> To: math-fun <math-fun@mailman.xmission.com> Sent: Saturday, October 18, 2014 4:52 PM Subject: Re: [math-fun] Lockheed Martin Claims Fusion Breakthrough That Could Change World Forever
I don't know how judge Lockheed-Martin's prospects but this doesn't seem much like cold fusion. It isn't cold and they seem to be claiming an improvement on magnetic-confinement approach. That seems like the way technology moves.
Of the little said, one or two things puzzle me. One of the articles says deuterium and tritium are cheap and tritium certainly isn't. Chase's talk talks about using lithium, which is what is done in weapons, and mentions producing tritium from the lithium but it doesn't say how. In bombs that depends on having a lot of neutrons available and I don't see where they would come from in this setup.
Whit