The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope. A number of artificial radioactive isotopes of cesium are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation.Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.esium is a member of the alkali family, which consists of elements in Group 1 (IA) of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. The alkalis include lithium, sodium, potassium, rubidium, and francium. Cesium is considered the most active metal.