I have a query assigned with the formation of elements in particle accelerators. We know that two hydrogen atoms for example fuse under extreme conditions to give a helium atom to release a lot of energy. But then, why is it that fusion of much heavier elements in a particle accelerator occurs under a relatively achievable condition and that too without it being as much exothermic as the former??

Please forgive my lack of knowledge but I'd appreciate it if someone could clarify this for me.

  • $\begingroup$ What do you mean by heavier elements? Do you mean hitting uranium with neutron to form another isotope? Heavier elements are known for fission rather than fusion. Even if more heavier nuclei is formed, they are incredibly unstable hardly lasting a second. $\endgroup$ Jan 11 at 5:30
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    $\begingroup$ It requires 4 hydrogen atoms to make a helium atom. See en.wikipedia.org/wiki/Proton%E2%80%93proton_chain $\endgroup$
    – PM 2Ring
    Jan 11 at 10:00
  • $\begingroup$ We can still obtain elements like plutonium by irradiation of uranium with neutrons, though the conditions available for this reaction is hardly as extreme as it needs to be for a fusion process. Why is that possible?? $\endgroup$ Jan 11 at 10:01
  • $\begingroup$ PM 2Ring, Thank you for letting me know. $\endgroup$ Jan 11 at 10:02

1 Answer 1


To address the question in the title:

The fusion process in a star stops at iron, because a star is a fusion reactor that requires exothermic reactions to keep it alive- and fusion beyond iron does not release energy, it consumes it. In an accelerator we can furnish as much energy as is needed to fuse elements beyond iron by slamming heavy ions together (and then turn around and crack them apart to determine their binding energies) because the fusion reaction is not what's powering the accelerator.

  • $\begingroup$ Would just smashing two atoms into each other result in a fusion of their nuclei for a short period? Also won't it still require a huge amount of energy just to achieve it? I mean, we can't still achieve the fusion of hydrogen atoms in lab conditions. So how do you even momentarily fuse a much heavier atom?? $\endgroup$ Jan 11 at 9:56
  • $\begingroup$ @SiddharthNair Of course we can do hydrogen fusion in the lab. Even amateurs can do it in their basement. See fusor.net The tricky part is to do it efficiently, so that you get back more energy than you consume. $\endgroup$
    – PM 2Ring
    Jan 11 at 10:04
  • $\begingroup$ @PM 2Ring Thank you for providing that link l. It was very informative $\endgroup$ Jan 11 at 10:22

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