nuclear fission+fusion

[person]

according to my teacher, nuclear fission creates a lot of energy, yet nuclear fusion creates more energy

and this doesnt make much sense to me considering that they seem to be the exact opposite of eachother...can anyone explain?

[rdrake]

Nuclear fission is when a neutron smashes into a large atom and breaks it apart. This requires no extermal energy as the neutron has all the energy the reaction needs. This neutron collision releases another few neutrons which repeats the process.

Nuclear fusion on the other hand is when the smaller atoms combine to produce a larger one. The atoms repel each other so they must be travelling at very high speeds in order to get close enough to combine.

Basically, nuclear fission is easier to perform and happens quicker, while nuclear fusion takes high speeds in order to happen. This is due to the positive nature of the atoms. They repel and it takes more to combine them.

[person]

i know all that, but im talking about like why do tehy both release energy when they seem to be opposite to eachother

[1of42]

Because fission is tapping into the electromagnetic force for its energy, while fusion is tapping into the strong nuclear force - both release energy, with the latter being MUCH stronger.

[Tony]

Wikipedia is great.

In short, Fission releases energy as atoms split. There's a lot of energy holding the core together, and once it is made to let go - that energy is released.

Fusion is quite different. Atoms combine to form heavier elements, and require a lot of energy to be forced to do so. The reaction may or may not release energy. Further Reading explains it better

Wikipedia wrote:

If two light nuclei come close enough to each other, they may fuse to form a single nucleus with a slightly smaller mass than the sum of their original masses. The difference in mass is released as energy according to Einstein's relationship E = mc². (If the two nuclei are too heavy, then the resulting fusion product will be heavier than the reactants, and the reaction requires the addition of energy to convert into the additional mass; in this case the reverse process of nuclear fission will release energy which can be used, for example, in nuclear reactors or bombs.)

[rdrake]

When the nucleus splits in nuclear fission, energy is released. In nuclear fusion, there is energy released because the helium nucleus has a much larger binding energy than deuterium/tritium. Energy is absorbed by nuclear fusion if the product element is further down on the periodic table than iron, so anything with an atomic number of about 55/56 (I forget) and up will produce energy.

If you have the textbook Physics 12 by McGraw-Hill Ryerson, then you can find all of this information on pages 566-568.

[Andy]

the key is to notice that not all elements are fissiable and fusable. Lead is the cut off line for fission and Iron is the cut off line for fusion, so you cant simply split an atom then fuse it back and then split it again forever, also, remember that at each step, mass is lost so they're not reverse reactions.

[Tony]

Andy wrote:

remember that at each step, mass is lost so they're not reverse reactions.

Actually if you fuse two elements heavier than Iron, mass is gained You loose energy though.

[person]

Quote:

If two light nuclei come close enough to each other, they may fuse to form a single nucleus with a slightly smaller mass

but in the chemical formulas of fusion, the mass on the left is teh same as the mass on the right

[rdrake]

person wrote:

Quote:

If two light nuclei come close enough to each other, they may fuse to form a single nucleus with a slightly smaller mass

but in the chemical formulas of fusion, the mass on the left is teh same as the mass on the right

In fusion, mass is often lost between the products and reactants. This is called the mass defect and is important. We use the formula E=mc^2 to determine the energy which is produced, based on the mass defect. This loss of mass is where the energy comes from, as the mass is converted into useful energy.

[Andy]

Tony wrote:

Andy wrote:

remember that at each step, mass is lost so they're not reverse reactions.

Actually if you fuse two elements heavier than Iron, mass is gained You loose energy though.

except tony, you cant fuse elements heavier than iron together

[Tony]

Wikipedia implies otherwise

Quote:

The fusion of two nuclei to produce a nucleus lighter than iron or nickel generally gives off energy while the fusion of nuclei heavier than them absorbs energy.

Perhaps you should edit the article

[rdrake]

Andy wrote:

except tony, you cant fuse elements heavier than iron together

You can, but then energy is absorbed, not released.

[Paul]

I dunno if this helps, but... simply put:

The sun: Fusion on a massive scale
Atomic Bombs: fission

They both produce energy. The advantage to fusion is that it doesn't produce all the waste products that fission does.

[Drakain Zeil]

bonds hold energy, breaking them requires energy, building them gives energy. end of story.