Lanthanide or lanthanoid chemical elements are the 15 metallic chemical elements with atomic numbers 57-71, ranging from lanthanum to lutetium. These elements, together with the chemically related scandium and yttrium, are commonly referred to as rare-earth elements or rare-earth metals.
Alpha decay usually occurs in heavy nuclei such as uranium or plutonium, and therefore is a major part of the radioactive fallout from a nuclear explosion.
Alpha decay occurs most often in massive nuclei that have too large a proton to neutron ratio. An alpha particle, with its two protons and two neutrons, is a very stable configuration of particles.
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