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Author Topic: How does fusion work?  (Read 1944 times)

nicholas french

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How does fusion work?
« on: 10/06/2009 10:30:02 »
nicholas french asked the Naked Scientists:
   
What is it, and how close are we to achieving harnessing it? I heard a single atom would yield the same amount of energy as the Sun has in its entire life... how could be harness that safely?

What do you think?


 

Offline chris

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How does fusion work?
« Reply #1 on: 11/06/2009 11:31:48 »
Put simply, fusion means joining smaller things together to make larger things. In so doing (in the context of nuclear fusion) strong interactions occur which make the resulting bodies stable (for variable lengths of time) and some of the mass from the two starting bodies is converted into energy (according to E=mc^2).

The Sun produces energy by fusing hydrogen atoms (1H) to make helium (2He), an atom twice as large. But rather than 2 hydrogens linking to form 1 helium in fact 4 hydrogens fuse to make each helium. Where does the mass from the other 3 go? Some of it turns into neutrinos and gamma rays - i.e. matter has been converted into energy, which is what makes the sun shine. The prediction is that the Sun loses about 4 million tonnes of mass every second - impressive even by Fern Britton's standards...

Here is a link to the basis of nuclear fusion as occurs in stars: http://www.astrophysicsspectator.com/topics/stars/FusionHydrogen.html

We've also talked about fusion as a power source on the Naked Scientists on a number of occasions:

http://www.thenakedscientists.com/HTML/podcasts/show/2008.10.19/

http://www.thenakedscientists.com/HTML/content/news/news/1151/

Chris
« Last Edit: 12/06/2009 18:07:14 by chris »
 

lyner

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How does fusion work?
« Reply #2 on: 12/06/2009 09:38:45 »
Chris
There seems to be some confusion with, perhaps, the notation?
A Helium nucleus has a mass of four Hydrogen atoms. There are two protons (to make it, chemically, Helium) and two neutrons, which need to be there to bind it together.
The total mass is a tiny bit less which accounts for the energy produced. The process in stars takes several steps, involving the production of Deuterium and Tritium (Hydrogen nuclei with one or two added neutrons). In a fusion machine, it is these two isotopes which are used because the probability of H+H giving Deuterium is very low. The D and T are extracted from vast quantities of ordinary water, in which they exist in trace quantities. A bit of a cheat, really - but it gets results.
 

Offline chris

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How does fusion work?
« Reply #3 on: 12/06/2009 18:06:29 »
Thanks SC - the actual pathway is in the link I provided. I simplified it for the sake of keeping it brief, but maybe too much so. (I've added "some" to clarify the explanation).

chris
 

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How does fusion work?
« Reply #3 on: 12/06/2009 18:06:29 »

 

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