Nuclear binding energy and the mass defect

Nuclear binding energy and the mass defect - Einstein's...

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Nuclear binding energy and the mass defect A neutron has a slightly larger mass than the proton. These are often given in terms of an atomic mass unit, where one atomic mass unit (u) is defined as 1/12th of the mass of a carbon-12 atom. Something should probably strike you as being a bit odd here. The carbon-12 atom has a mass of 12.000 u, and yet it contains 12 objects (6 protons and 6 neutrons) that each have a mass greater than 1.000 u. The fact is that these six protons and six neutrons have a larger mass when they're separated than when they're bound together into a carbon-12 nucleus. This is true for all nuclei, that the mass of the nucleus is a little less than the mass of the individual neutrons and protons. This missing mass is known as the mass defect, and is essentially the equivalent mass of the binding energy.
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Unformatted text preview: Einstein's famous equation relates energy and mass: If you convert some mass to energy, Einstein's equation tells you how much energy you get. In any nucleus there is some binding energy, the energy you would need to put in to split the nucleus into individual protons and neutrons. To find the binding energy, then, all you need to do is to add up the mass of the individual protons and neutrons and subtract the mass of the nucleus: The binding energy is then: In a typical nucleus the binding energy is measured in MeV, considerably larger than the few eV associated with the binding energy of electrons in the atom. Nuclear reactions involve changes in the nuclear binding energy, which is why nuclear reactions give you much more energy than chemical reactions; those involve changes in electron binding energies....
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