Nuclear Energy and Nuclear Disasters. A proton is a subatomic particle found in the nucleus of every atom. The particle has a positive electrical charge, equal and opposite to that of the electron. If isolated, a single proton would have a mass of only 1.673 ? 10^-27 kilogram, just slightly less than the mass of a neutron. The number of protons in an element's nucleus is called the atomic number. This number gives each element its unique identity. In the atoms of any particular element, the number of protons in the nuclei is always the same. An atom of simple hydrogen has a nucleus consisting of a single proton all by itself. The nuclei of all other elements nearly always contain neutrons in addition to protons. Protons need not be confined to the nuclei of atoms. When protons are found outside atomic nuclei, they acquire fascinating, bizarre, and potentially dangerous properties, similar to those of neutrons in similar circumstances. But protons have an additional property. Because they carry an electric charge, they can be accelerated by electric and/or magnetic fields. High-speed protons, and atomic nuclei containing them, are emitted in large numbers during solar flares. The particles are accelerated by the earth's magnetic field, causing ionospheric disturbances known as geomagnetic storms