I. How does fusion work? Why does it require much higher temperatures and pressures than fission?
II. How does fission produce energy if it requires energy to break bonds? Why is a neutron required?
III. Why are only light/heavy elements used? What does this have to do with their binding energies?
Ryan
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I. Fusion is only possible when the atoms in question are fully ionized, that is they are completely separated from their electrons. This is only possible when they exist in the forth state of matter, plasma. Which is only possible at very high temperature levels. The very high pressure is what causes the atoms to smash into each other. Atoms are very tiny, if their wasn't a high density, caused by high pressure then the atoms would be buzzing around all day and never run into each other.
II. Fission is possible when an unstable heavy element is hit with an extra neutron. Think of a piece of wood being the element and a metal spike in the wood being its instability. The hammer is the extra neutron. It smacks into the "metal spike" and causes the atom to break apart. Yes you are putting energy into it but the energy you get out of it more than makes up for the amount you put in.
Neutrons are used because they are neutral. You can use a proton, but protons are positively charged and would therefore be repelled by the other protons in the atom. So in order to get the proton to hit the atom it would require a lot more energy. So why are neutrons used? Because it's easier.
III. The most stable element, that is the protons/neutrons are compacted just right in the best order, is iron. In the element world, everybody wants to be Iron. Iron is the "cool" element. Light elements or more susceptible for fusion because it's easier. In Hydrogen you only have to worry about fusing one proton to another proton. As the element size increases you need more and more temperature and pressure to be able to make it possible. Once you hit iron that's the stopping point. It's possible to fuse elements that are heavier but after iron the amount of energy expelled is no longer larger than the amount of energy input, therefore the reaction stops. Heavier elements are used for fission because the bonds between the protons and neutrons get weaker as you add more. Think of it like this. You are holding onto a rope and somebody starts pulling on it. You are expending 100% of your energy on that "bond". Then you get another rope that somebody starts pulling on. Now your bond strengths are at 50% each. Then you grow two more arms,each with a rope that somebody pulls on. Now each one is at 25%. As the number protons/neutrons increases the strength of their bonds gets less and less, making them a lot easier to break apart.
popovoleg70
Cold fussion going on 60 celcium about getting energy from fission. The slowly one required.