Monday, 10 March 2014

Did a 13-year-old really perform nuclear fusion at school?

Another high school fusor in operation (not Jamie's)
There was a big kerfuffle in the UK media last week when a 13-year-old schoolboy apparently made a nuclear fusion reactor at school. Jamie Edwards built the device at the Penwortham Priory Academy in Preston.

I got several emails baffled by the TV news coverage, which was skimpy on details. So here's the home-brew fusion Q&A.

  • Could a schoolboy really build a nuclear fusion reactor? Yes, he could. We have to be a little careful about what we mean by a reactor. We're not talking a miniature power station, we're talking a device in which a very small amount of fusion takes place. Bear in mind that all you need to create a nuclear fission reactor in the same sense is a cardboard box with a lump of uranium in it. Fission will take place in the box. It's no use, but it will happen. It's the same here (though harder to make). This type of reactor dates back to the 1960s, devised by the magnificently named Philo T. Farnsworth, the hugely under-appreciated inventor who also came up with the electronic TV system (as opposed to Logie Baird's impractical electro-mechanical system).
  • Should a schoolboy be doing this? Isn't it dangerous? Someone on the news mentioned blowing up the school! Yes, he should be doing it. First, it's absolutely brilliant a 13-year-old should have the initiative to do this, and second it wouldn't blow up the school. There's a lot of confusion over, erm, fusion. It is the reaction behind the hydrogen bomb - but it only works like that with a conventional atomic bomb to trigger it. As a stand-alone reaction it is actually very difficult to keep going. It can't go critical or explode. It does produce neutrons, which are ionising radiation, so needs to be properly shielded, and involves high voltages, which need to be treated with care, but with those provisos, it is very safe.
  • How does it work? Fusion is the power source of the sun. When two small atomic nuclei are forced together very hard, they will fuse to form a new atom. They have to be very close to do this, as the strong nuclear force that holds the nucleus together only kicks in at very short distances - and that means overcoming a whole lot of repulsive force. If you do manage it, the new atom has less total internal energy than the original ones and the excess is released in the kinetic energy of the resultant particles. This is where the energy for the sun or a fusion power station comes from. In a magnetic confinement fusor (which is what Jamie's is), deuterium gas (hydrogen with an added neutron in the nucleus) is zapped with an electric charge, which strips off its electron, and accelerates it to a high speed. Some of those nuclei will collide, and some collisions have enough oomph to enable the charged nuclei to fuse.
  • If a schoolboy can do it, how come it has taken us decades and we still don't have a fusion power station? There are two important things to bear in mind. One is that a fusor like this needs a lot more energy in than is produced by the fusion reaction, so it's not a candidate for power generation. The other is that to take fusion up to the sort of scale required to produce around 1 gigawatt of power (a mid-sized power station) is nightmarishly complex. Fusion reactions are very difficult to get going and keep running on this scale, especially as the charged collection of nuclei (a plasma) writhes and wriggles like a living thing, and if it touches the walls of the vessel, the fusion stops. Current best estimate for the first working fusion power station is 2050 - but if we achieve it, this a brilliant source of energy - it's green, and uses readily available fuel. And it doesn't produce radioactive waste, except for the metal in the device which will gain a low level of radioactivity, but nothing like the problems of fission waste.
  • So was it news at all? Yes, I think it was. A good few people have made fusors, but Jamie was the youngest, and it's good to have interesting and inspiring science stuff in the news. if it encourages more teenagers to take an interest in science it's worth all the publicity. It's just a shame that the media reports were generally not very good at explaining just what was happening.

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