Science, Tech, Math › Science What Is the Most Radioactive Element? Is It Naturally-Occurring or Man-Made? Share Flipboard Email Print A thin film of polonium over a stainless-steel disk, used as an alpha-particle source. Lapp, Ralph E. LIFE. ed. MATTER. LIFE Science Library 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 May 08, 2019 Radioactivity is a measure of the rate an atomic nucleus decomposes into pieces that are more stable. It's somewhat complicated, trying to determine relative radioactivity because there can be many unstable steps in the decay process before an element finally breaks into stable pieces. All of the elements from element 84 on up are extremely radioactive. These elements have no stable isotopes. Polonium Because it is a naturally-occurring element that releases a huge amount of energy, many sources cite polonium as the most radioactive element. Polonium is so radioactive it glows blue, which is caused by excitation of the gas particles by radiation. A single milligram of polonium emits as many alpha particles as 5 grams of radium. It decays to release energy at the rate of 140W/g. The decay rate is too high that it can raise the temperature of a half gram sample of polonium to over 500°C and subject you to a contact gamma-ray dose rate of 0.012 Gy/h, which is more than enough radiation to kill you. Nobelium and Lawrencium Other elements besides polonium actually emit more particles, such as nobelium and lawrencium. The half-life for these elements is measured in mere minutes! Contrast this with the half-life of polonium, which is 138.39 days. Element Number 118 According to the Periodic Table of Radioactivity, at this time the most radioactive element known to man is element number 118, Oganesson. The decay rates for the latest man-made elements are so fast that it's hard to quantify how quickly they break apart, but element 118 has the heaviest known nucleus to date. These elements break apart essentially the instant they are created. It is reasonable to expect the title of "most radioactive" will be taken over by some new, as-yet-undiscovered element. Perhaps element 120, which scientists are working to produce, will be the new most radioactive element.