Science, Tech, Math › Science Helium Isotopes, Radioactive Decay and Half-Life Share Flipboard Email Print This is a periodic table tile for the element helium. Todd Helmenstine Science Chemistry Periodic Table Basics Chemical Laws Molecules 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 February 28, 2020 It takes two protons to make a helium atom. The difference between isotopes is the number of neutrons. Helium has seven known isotopes, ranging from He-3 to He-9. Most of these isotopes have multiple decay schemes where the decay type depends on the overall energy of the nucleus and its total angular momentum quantum number. This table lists helium isotopes, half-life, and type of decay: Isotope Half-Life Decay He-3 Stable N/A He-4 Stable≈ 0.5 x 10-21 sec - 1 x 10-21 sec N/Ap or n He-5 1 x 10-21 sec n He-6 0.8 sec5 x 10-23 sec - 5 x 10-21 sec β-n He-7 3 x 10-22 sec - 4 x 10-21 sec n He-8 0.1 sec0.5 x 10-21 sec - 1 x 10-21 sec β-n/α He-9 unknown unknown p proton emissionn neutron emissionα alpha decayβ- beta- decay Radioactive Decay and Half-Life Beryllium Isotopes What Are the Radioactive Decay and Half-Life of Lithium Isotopes? What You Need To Know About Why Radioactive Decay Occurs Know What Isotopes Are in Chemistry 10 Quick Facts About Helium How the Island of Stability May Help Us Discover New Elements 10 Interesting Facts About Radioactive Tritium What Element Is Atomic Number 2? Interesting Americium Element Facts What Is Radioactivity? What Is Spontaneous Fission? What Is a Daughter Isotope? How Are New Elements Discovered? Get Facts About the Element Indium Get Facts About the Element Helium What Is the Azimuthal Quantum Number?