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Can someone explain why this is considered fusion? The reaction involves shooting a proton (hydrogen) at a boron nuclei and outputting 3 alpha particles. That s

Can someone explain why this is considered fusion? The reaction involves shooting a proton (hydrogen) at a boron nuclei and outputting 3 alpha particles. That seems more like the nuclei being split apart than fused together.

DennisP 7y ago
The explanation I've heard from a fusion scientist is that as far as they're concerned, if you're initiating the reaction by colliding nuclei, it's fusion, and if you're initiating it by hitting a large nucleus with a neutron, it's fission.
- wefarrell 7y ago
  Makes sense, thanks!
cstross 7y ago
Start here: https://en.wikipedia.org/wiki/Aneutronic_fusion https://en.wikipedia.org/wiki/Aneutronic_fusion (TLDR version: proton-boron fusion is a less energetically efficient alternative to 3He fusion, but with the howlingly significant advantage that boron -- the fuel -- is lying around in heaps and drifts on Earth, rather than being so exotic a substance that annual global production is measured in single-digit kilograms and a significant energy economy would require mining it from the Lunar regolith. It's not as well-known as 3He fusion, though, because the space cadets don't see the point -- there are no Moon colonies required. Advantages of 3He or B + p fusion over D-T fusion: it doesn't produce a surplus of neutrons, so there's less radioactive waste created as a by-product of the process.)
- baq 7y ago
  space cadets would love to have that kind of a reactor on a deep solar system exploration mission, especially if you could make it into a rocket engine by spitting the resulting super high energy helium out of the business end without negative side effects.
acidburnNSA 7y ago
I has to do with something called the Binding Energy Per Nucleon. If you march up the curve from small numbers to get energy you are fusion. If you march down the curve from high numbers, you are fission. If you march up the curve from small numbers and go all the way to large numbers even though that's endothermic, you are a supernova. https://en.wikipedia.org/wiki/Nuclear_binding_energy#Nuclear_binding_energy_curve https://en.wikipedia.org/wiki/Nuclear_binding_energy#Nuclear...
ars 7y ago
Because you are fusing a proton to a boron. After that there is radioactive decay (the splitting). To be fission you have to actually [actively] break the atom apart, which isn't happening here.

DennisP 7y ago

The explanation I've heard from a fusion scientist is that as far as they're concerned, if you're initiating the reaction by colliding nuclei, it's fusion, and if you're initiating it by hitting a large nucleus with a neutron, it's fission.

wefarrell 7y ago
Makes sense, thanks!

cstross 7y ago

Start here: https://en.wikipedia.org/wiki/Aneutronic_fusion https://en.wikipedia.org/wiki/Aneutronic_fusion (TLDR version: proton-boron fusion is a less energetically efficient alternative to 3He fusion, but with the howlingly significant advantage that boron -- the fuel -- is lying around in heaps and drifts on Earth, rather than being so exotic a substance that annual global production is measured in single-digit kilograms and a significant energy economy would require mining it from the Lunar regolith. It's not as well-known as 3He fusion, though, because the space cadets don't see the point -- there are no Moon colonies required. Advantages of 3He or B + p fusion over D-T fusion: it doesn't produce a surplus of neutrons, so there's less radioactive waste created as a by-product of the process.)

baq 7y ago
space cadets would love to have that kind of a reactor on a deep solar system exploration mission, especially if you could make it into a rocket engine by spitting the resulting super high energy helium out of the business end without negative side effects.

acidburnNSA 7y ago

I has to do with something called the Binding Energy Per Nucleon. If you march up the curve from small numbers to get energy you are fusion. If you march down the curve from high numbers, you are fission. If you march up the curve from small numbers and go all the way to large numbers even though that's endothermic, you are a supernova. https://en.wikipedia.org/wiki/Nuclear_binding_energy#Nuclear_binding_energy_curve https://en.wikipedia.org/wiki/Nuclear_binding_energy#Nuclear...

ars 7y ago

Because you are fusing a proton to a boron. After that there is radioactive decay (the splitting). To be fission you have to actually [actively] break the atom apart, which isn't happening here.