Science, Tech, Math › Science Spontaneous Fission Definition What Is Spontaneous Fission? Share Flipboard Email Print Spontaneous fission is the splitting of an atomic nucleus from natural radioactive decay. Ian Cuming / Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated January 15, 2020 Spontaneous fission (SF) is a form of radioactive decay where an atom's nucleus splits into two smaller nuclei and generally one or more neutrons.Spontaneous fission generally occurs in atoms with atomic numbers above 90.Spontaneous fission is a relatively slow process except for the heaviest isotopes. For example, uranium-238 decays by alpha decay with a half-life on the order of 109 years, but also decays by spontaneous fission on the order of 1016 years. Examples Cf-252 undergoes spontaneous fission to produce Xe-140, Ru-108 and 4 neutrons. Sources Krane, Kenneth S. (1988). Introductory Nuclear Physics. John Wiley & Sons. ISBN 978-0-471-80553-3.Scharff-Goldhaber, G.; Klaiber, G. S. (1946). "Spontaneous Emission of Neutrons from Uranium." Phys. Rev. 70 (3–4): 229. doi:10.1103/PhysRev.70.229.2Shultis, J. Kenneth; Faw, Richard E. (2008). Fundamentals of Nuclear Science and Engineering. CRC Press. ISBN 978-1-4200-5135-3.