How can both nuclear fission and nuclear fusion release energy?
Coming from a chemistry point of view, we are familiar with the concept that making bonds requires energy, and breaking bonds releases energy. So, it follows that fusion should require energy, and fission release energy. However, from a nuclear point of view we know that they both release energy.
Anyone care to explain this to me? I have an exam tomorrow!!!!!
The answer has to incorporate:
-Binding energy per nucleon
-Iron being the most stable element because of its binding energy per nucleon
-driving force of nuclear reactors.
July 20th, 2010 at 3:43 am
Look up “National Ignition Facility” it may have some answers for you. It’s breaking bonds to release energy
July 20th, 2010 at 4:24 am
In fusion, the total binding energy for the lighter nuclei is greater than the binding energy for the resulting heavier nucleus, so the excess energy is released during the fusion reaction. An example is the fusion of four hydrogen nuclei into one helium nucleus in our Sun.
In nuclear fission, the total atomic mass of the decay products is less than the total mass of the fuel, so the excess mass is converted into energy.
Fusion can’t produce any elements with atomic numbers higher than iron because of the reason you mentioned – iron has the highest binding energy per nucleon. You can’t make iron out of lighter elements, because the total binding energy of the lighter elements would be lower than the binding energy of iron, so you would actually have to *add* energy to the reaction to make iron out of lighter elements.
July 20th, 2010 at 4:32 am
The process of fusion you already understand that as bonds are formed when two protons and two neutrons fuse together to form helium nucleus. But these bonds are very strong and release binding energy of around 8 MeV per nucleon (proton or electron). In chemical bonds electrons with light mass interact. In nuclear case quarks do te same.
In case of fusion the heavier nucleus like Uranium has more number of protons which are at the periphery much away to be influenced by attractive nuclear force but repel each other effectively. When such a nucleus breaks into two smaller nuclei the protons at te periphery in both fragments are at lesser distance so the disruptive coulomb force is less effective. So binding energy per nucleon in lighter fragments of a heavy nucleus is much larger than the binding energy per nucleon of a heavy nucleus like uranium and beyond. You ca look into any book of nuclear physics which gives the graph of nuclear binding energy per nucleon for all nuclei starting from He to uranium and beyond. There are peaks around helium oxygen ad so on and s on and a broad peak around Fe
July 20th, 2010 at 4:34 am
matter is destroyed in a fusion and a fission process.
in fission a neutron is destroyed normally, and this is converted into energy, but in fusion the helium atom that is formed is smaller than the sum of it’s parts (sometimes up to 4 hydrogen atoms, but even 2 are very slightly heavier than helium) and as such, the excess matter is again turned into energy.
the matter converted into energy can be worked out using the sum E=MC2
in my physics a-level we had to work out the amount of matter destroyed at hiroshima, and it was 7 grammes (approx) and that amount of matter gave rise to the massive explosion that occured
July 20th, 2010 at 5:17 am
Actually, this is not exactly that fusion and fission release energy. It is the fusion of *light* nucleus and fission of *heavy* nucleus release energy.
If you try to fuse uranium, of fission helium, you will have to provide energy.
The point is that the static nuclear energy is at lowest for a specific nickel isotope, but for all practical purpose, this is about the same as for the most common iron isotope, so this is usually what is being quoted as the most stable nucleon. Everything lighter would release energy when fusing, everything heavier would release energy when fissioned.
Of course, there is a problem with fission, as breaking a nucleus in 2 means having two pieces that are about 1/2 the mass of the original. And each piece cannot be lighter than iron, or else the fission would absorb a bit of energy instead of liberating energy.
This has interesting implication. Any element heavier than iron that exists around us thus required energy to be provided, hence could only be made in a process where lots of energy forces light elements to fuse despite them absorbign energy while doing so. This occurs naturally only in supernova.
That is where gold, lead, uranium, etc. originates from.
November 14th, 2010 at 2:06 am
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November 14th, 2010 at 2:10 am
i think the nuclear fission and fusion, is both release enrgy. but im not sure
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