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The elements in nature consist of molecules formed from atoms. The atoms
are characterised by a positively charged nucleus and by peripheral negative
electrons, which determine their species.
The nucleus in turn is formed of
neutrons and protons – collectively known as nucleons – held together by
extremely intense forces within a short range of action. The mass of the
nucleus is less than the sum of the masses of the nucleons (protons and neutrons)
that form it. The mass difference (Δm), which
is related to the binding energy according to the mass-energy equivalence
principle ΔE=Δmc2 , is called
the mass defect.
What about nuclear fuels? The nuclei that have the lowest binding energy per nucleon provide nuclear energy by fusion if they have low atomic mass and by fission if their atomic mass is high.
For the same amount of reactants, the energy released during a nuclear reaction is millions of times the energy released during chemical reactions (combustion).
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