how does nuclear fission and fusion take place?

Question

how does nuclear fission and fusion take place?
i know this much.
fission: an atom is seperated resulting in the release of tremendous amount of energy
fusion: two or more atoms fuse together to release tremendous amount of energy
(extra question: in the sun, nuclear fusion is taking place, right? because hydrogen atoms are fusing together to make helium. then, that would also mean it would be like there's atomic bombs exploding there-right?)
i want to know what you have to do to seperate an atom, and fuse an atom.

Answer 1

in fusion two charged nuclei come together, since they are charged they need sufficient energy to overcome the repulsion - an actviation energy.



When they get close enough the strong nuclear force takes over and the nuclei fuse. The new nucleus will be either more massive or less massive than the sum of the nuclei that formed it. If it's less massive energy is released (sun) if it's more massive the kinetic energy of the nuclei is converted to mass, this occurs in supernova explosions and is the reason that elements above Fe exist.



In fission a nucleus splits and if the if the sum of the fragments is less massive than original nucleus, energy is released.



In general a fusion reaction that forms a nucleus below Fe (mass # = about 60) releases energy and atoms above Fe release energy when thy fission, otherwise the reaction requires energy and kinetic energy is converted to mass.



you'll notice that a deuterium nucleus (H-2) contains 1 proton and 1 neutron, yet it weighs less than the sum of the masses of the seperate neutron and proton. The missing mass was converted to energy in the reaction that formed it.



In the sun the activiation energy for fusion is provided by gravity and other nuclear reactions. In an H-bomb it is provided by a fission explosion.



In a typical H-bomb, plutonium fissions and this releases neutrons which fission lithium atoms into tritium (H-3), the tritium then fuses with deuterium (H-2) forming helium and releasing more neutrons which then get absorbed by U-238, the resulting U-239 is unstable so it fissions as well creating even more energy. H-bombs are fission-fusion-fission devices.



In a nuclear reactor (or A-bomb) neutrons are absorbed by nuclei such as U-235. Neutrons are not repelled by the nucleus like charged nuclei, so repulsion is not an issue. When it absorbs the neutron, the resulting U-236 is unstable and fissions releasing energy and more neutrons which can be absorbed.

Answer 2

Well that depends. Fission and fusion are two different processes. Fission, or splitting an atom, is the only form of nuclear power we can currently harness in mass quantities. Fusion, or the joining of two atoms to form a new one, requires temperatures like that of the sun to work, which means it would be using up more energy than it produces. Fusion isn't used for mass energy production, and won't be until researches are successful at "cold" fusion.

Answer 3

Yes, the thermonuclear fusion in the sun is similar to what happens in an H-bomb.



Fission is pretty easy. You just have to get a big enough concentration of certain isotopes together. Every so often, one splits spontaneously and releases neutrons that trigger more and more and more of its neighbors to fission. Such a chain reaction has happened in nature before, and it has happened accidentally in labs. Fusion is harder because you have to get the hydrogen atoms really close, which takes a lot of energy, so you have to get them really, really hot.