Science, Tech, Math › Science Beta Decay Definition Share Flipboard Email Print Paper Boat Creative / Getty Images Science Chemistry Basics Chemical Laws 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 October 13, 2019 Beta decay refers to the spontaneous radioactive decay where a beta particle is produced. There are two types of beta decay where the beta particle is either an electron or a positron. How Beta Decay Works β- decay occurs when an electron is the beta particle. An atom will β- decay when a neutron in the nucleus converts to a proton by the following reaction. Here X is the parent atom, Y is the daughter atom, Z is the atomic mass of X, and A is the atomic number of X:ZXA → ZYA+1 + e- + antineutrino β+ decay occurs when a positron is the beta particle. An atom will β+ decay when a proton in the nucleus converts into a neutron by the following reaction, where X is the parent atom, Y is the daughter atom, Z is the atomic mass of X, A is the atomic number of X:ZXA → ZYA-1 + e+ + neutrino In both cases, the atomic mass of the atom remains constant but the elements are transmuted by one atomic number. Practical Examples Cesium-137 decays to Barium-137 by β- decay.Sodium-22 decays to Neon-22 by β+ decay.