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 Beryllium Isotopes Lithium Isotopes - Radioactive Decay and Half-Life Why Does Radioactive Decay Occur? Isotope Definition and Examples in Chemistry Definition of Radioactivity 10 Helium Facts Island of Stability - Discovering New Superheavy Elements Atomic Number 2 on the Periodic Table 10 Interesting Facts About Radioactive Tritium Helium Facts (Atomic Number 2 or He) Americium Facts: Element 95 or Am Rate of Radioactive Decay Worked Example Problem What Is Half-Life? Spontaneous Fission Definition Daughter Isotope Definition - Chemistry Glossary How Are New Elements Discovered?