Nucleus

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Positively charged nucleus of an atom. Its diameter amounts to some 10-13 (ten trillionths) of a cm, i.e. around 1/100,000 of the atom's diameter. It contains almost the total mass of the atom. The nucleus of an atom, apart from the nucleus of normal hydrogen, is made up of protons and neutrons. The number of protons determines the nucleus charge or atomic number Z, the number of protons plus neutrons - the nucleons - the nucleon or mass number M of the nucleus.

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