Neutron

The atom's structure has a nucleus at the center, surrounded by a cloud of electrons. Inside the nucleus are two types of particles, neutrons (electrically neutral) and protons (positively charged). Under special experimental conditions, neutrons can be released from the nucleus. They are useful for creating new radioactive materials or for producing large amounts of nuclear energy.

The atom is so small that it would take several million of them to equal the size of the period at the end of this sentence. The nucleus is much smaller still, about 1/100,000 of an atom's size. Finally, neutrons and protons appear to be made up of three even smaller components called "quarks." Evidence for quarks comes from experiments done with very high energy particle accelerators.