Isotope

Isotopes are different species under a particular chemical element.

All isotopes under the same element have the same number of protons but different numbers of neutrons. These isotopes occupy the same position in the periodic table of chemical elements, hence their name.

For example, hydrogen elements such as protium (hydrogen-1), deuterium (hydrogen-2), and tritium (hydrogen-3) have one proton in their nuclei, but their nuclei have zero neutrons, one neutron and two neutrons, so they are isotopes of each other.

Each element has multiple isotopes, most of which are radioactive and have a long half-life, called radioisotopes, such as tritium, carbon-14, potassium-40, cobalt-60, iodine-131. If all isotopes of an element are radioactive, it is called radioactive elements, such as uranium, radium and radon.