<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom, discovered in 1911 by Ernest Rutherford based on the 1909 Geiger--Marsden gold foil experiment . After the discovery of the neutron in 1932, models for a nucleus composed of protons and neutrons were quickly developed by Dmitri Ivanenko and Werner Heisenberg . An atom is composed of a positively - charged nucleus, with a cloud of negatively - charged electrons surrounding it, bound together by electrostatic force . Almost all of the mass of an atom is located in the nucleus, with a very small contribution from the electron cloud . Protons and neutrons are bound together to form a nucleus by the nuclear force . </P> <P> The diameter of the nucleus is in the range of 6985175659999999999 ♠ 1.7566 fm (6985175659999999999 ♠ 1.7566 × 10 m) for hydrogen (the diameter of a single proton) to about 6986117142000000000 ♠ 11.7142 fm for the heaviest atom uranium . These dimensions are much smaller than the diameter of the atom itself (nucleus + electron cloud), by a factor of about 26,634 (uranium atomic radius is about 6990156000000000000 ♠ 156 pm (6990156000000000000 ♠ 156 × 10 m)) to about 60,250 (hydrogen atomic radius is about 6989529200000000000 ♠ 52.92 pm). </P>

What is contained in the nucleus of an atom