Abstract :
Investigations of the structure of atoms have shown that each atom possesses at its center a small, dense, positively charged core, or nucleus. Outside the nucleus the atom consists only of a small swarm of electrons, which are negatively charged and whose number is just sufficient to provide enough negative charge in the atom to balance the positive charge on the nucleus, so that the complete atom is electrically neutral. It is possible to modify the structure of atomic nuclei and thus to produce new atoms having unusual properties. In many cases these artificial atoms are radioactive and can be usefully applied in engineering, physics, chemistry, geology, and medicine.
