 He discovered a theoretical explanation of alpha decay by quantum tunneling, invented the liquid drop model and the first mathematical model of the atomic nucleus, and worked on radioactive decay, star formation, stellar nucleosynthesis and Big Bang nucleosynthesis (which he collectively called nucleocosmogenesis), and molecular genetics.In his middle and late career, Gamow directed much of his attention to teaching and wrote popular books on science, including "One Two Three... Infinity" and the "Mr Tompkins" series of books (1939–1967).Some of his books are still in print more than a half-century after their original publication.