Where does all that energy come from

Nuclear fission reactions release a lot of energy. Where does the energy come from Well, if you make very accurate measurements of the masses of all the atoms and subatomic particles you start with and all the atoms and subatomic pcirticles you end up with, you find that some mass is missing. Matter disappectfs during the nuclear reaction. This loss of matter is called the mass defect. The missing matter is converted into energy. 

You can actually calculate the amount of energy produced during a nuclear reaction with a fairly simple equation developed by Einstein E = mc. In this equation, E is the amount 

A chain reaction depends on the release of more neutrons than are used during the nuclear reaction. If you were to write the equation for the nucleeir fission of U-238, the more abundant isotope of uranium, you d use one neutron and get only one back out. So you can t have a chain reaction with U-238. But isotopes that produce an excess of neutrons in their fission support a chain reaction. This type of isotope is said to be fissionable, and only two main fissionable isotopes cire used during nuclear reactions U-235 and plutonium-239 (Pu-239). 

Critical mass is the minimum eimount of fissionable matter you need to support a self-sustaining chain reaction. That cimount is related to those neutrons. If the sample is small, then the neutrons are likely to shoot out of the sample before hitting a U-235 nucleus. If they don t hit a U-235 nucleus, no extra electrons and no energy are released. The reaction just fizzles. Anjdhing less than the critical mass is called subcritical. 

Soon after researchers discovered the fission process, they discovered another process, Ccdled fusion. Fusion is essentially the opposite of fission. In fission, a heavy nucleus is split into smaller nuclei. With fusion, lighter nuclei are fused into a heavier nucleus. 

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