3 ms·

Fusion of tritium and deuterium Input: - 1 deuterium atom: 1 proton and 1 neutron - 1 tritium atom: 1 proton and 2 neutrons Output: -

Fusion of tritium and deuterium Input: - 1 deuterium atom: 1 proton and 1 neutron - 1 tritium atom: 1 proton and 2 neutrons Output: - 1 helium atom: 2 protons and 2 neutrons Overall: 5 particles become 4, 20% become free to hit other atoms or turn into energy. Decay of uranium-235 into barium and krypton Input: - 1 atom of uranium: 235 particles Output: - 1 atom of barium: 144 particles - 1 atom of krypton: 89 particles Overall: 235 particles become 233, less than 1% become free to hit other atoms or turn into energy. Fission is much more similar to radioactive decay: big atoms turn into smaller atoms releasing a few free particles. Fusion releases basically the same amount of particles with much smaller atoms. Of course, this is an extreme simplification of the process. Energy required to start each reaction is ignored, but the idea is mostly correct, I think. EDIT: fixed tritium number of protons and neutrons and grammar.

4WIW 5y ago
Not to nitpick but: trituim is 1 proton and 2 neutrons, otherwise it would be helium
- marcodiego 5y ago
  Thanks! I'll fix it.
cecilpl2 5y ago
This is not quite right. In no cases are nucleons converted into energy. D+T fusion releases a He4 atom and a free neutron - 5 in, 5 out. U235 absorbs a neutron, then decays into Ba144, Kr89, and 3 neutrons - 236 in, 236 out. In the fission case, the neutrons escape to hit other U235 atoms, which causes the well-known chain reaction. In the fusion case, neutrons are not an input to the process. The released energy comes from the binding energy of the nuclei. The nucleons in a U-235 atom are held together weakly. My lay understanding which is probably wrong, is that the protons are trying to repel each other electromagnetically but are held together by the strong force, so splitting the atom means less strong force is "required" to hold the two new nuclei together. I don't have a solid understanding of exactly how the binding energy is lower in a He4 nuclei, and would love someone to explain!
- formerly_proven 5y ago
  There's a balance of forces which results in binding energy per nucleon depending on the number of nucleons, but overall it's something like 8 MeV per nucleon, so He-4 ends up with ~28.3 MeV of binding energy, while U-235 goes up to 1.8 GeV due to the sheer number of nucleons. Note the downwards slope of the binding energy per nucleon in the graph, this kinda indicates how stability goes down. There are however "magic numbers" and iirc there is a hypothesis that you get a sort of "island of stability" way into not-yet-existing super-heavy trans-uranic elements. https://upload.wikimedia.org/wikipedia/commons/thumb/5/53/Binding_energy_curve_-_common_isotopes.svg/1280px-Binding_energy_curve_-_common_isotopes.svg.png https://upload.wikimedia.org/wikipedia/commons/thumb/5/53/Bi... https://www.youtube.com/watch?v=SgM2wxELF4U https://www.youtube.com/watch?v=SgM2wxELF4U

4WIW 5y ago

Not to nitpick but: trituim is 1 proton and 2 neutrons, otherwise it would be helium

marcodiego 5y ago
Thanks! I'll fix it.

cecilpl2 5y ago

This is not quite right. In no cases are nucleons converted into energy. D+T fusion releases a He4 atom and a free neutron - 5 in, 5 out. U235 absorbs a neutron, then decays into Ba144, Kr89, and 3 neutrons - 236 in, 236 out. In the fission case, the neutrons escape to hit other U235 atoms, which causes the well-known chain reaction. In the fusion case, neutrons are not an input to the process. The released energy comes from the binding energy of the nuclei. The nucleons in a U-235 atom are held together weakly. My lay understanding which is probably wrong, is that the protons are trying to repel each other electromagnetically but are held together by the strong force, so splitting the atom means less strong force is "required" to hold the two new nuclei together. I don't have a solid understanding of exactly how the binding energy is lower in a He4 nuclei, and would love someone to explain!

formerly_proven 5y ago
There's a balance of forces which results in binding energy per nucleon depending on the number of nucleons, but overall it's something like 8 MeV per nucleon, so He-4 ends up with ~28.3 MeV of binding energy, while U-235 goes up to 1.8 GeV due to the sheer number of nucleons. Note the downwards slope of the binding energy per nucleon in the graph, this kinda indicates how stability goes down. There are however "magic numbers" and iirc there is a hypothesis that you get a sort of "island of stability" way into not-yet-existing super-heavy trans-uranic elements. https://upload.wikimedia.org/wikipedia/commons/thumb/5/53/Binding_energy_curve_-_common_isotopes.svg/1280px-Binding_energy_curve_-_common_isotopes.svg.png https://upload.wikimedia.org/wikipedia/commons/thumb/5/53/Bi... https://www.youtube.com/watch?v=SgM2wxELF4U https://www.youtube.com/watch?v=SgM2wxELF4U