Noun
English Wikipedia has an article on:Isotopes of calciumWikipedia
calcium-45 (uncountable)
(physics) A radioactive isotope of calcium, 20Ca, having twenty protons and twenty-five neutrons, and a half-life of 162.6 days; it is used as a tracer in studying calcium metabolism. As it decays it undergoes transformation (nuclear transmutation) via electron emission, also called negative beta decay (β−-decay), into scandium.