Uranium has a half-life of 4.4 billion years, so a 4.4-billion-year-old rock has only half of the uranium with which it started. How fast an element decays is measured in terms of the element "half-life", or the amount of time for one half of a given amount of the element to decay. The decay of each radioactive element occurs at a very specific rate. The four isotopes that follow radon in the decay chains all have relatively short half-lives and are collectively known as radon daughters.
#Air doc radon series
Uranium and thorium are the parent elements in a long series of radioactive decays (see Uranium and Thorium Decay Chains in our Water Science Basics section) that produces intermediate radium and radon daughter isotopes on the way to a stable isotope of lead.
Radon isotopes are also radioactive because they also decay, emitting another alpha particle and forming an unstable isotope of the element polonium, the first of four short-lived (radioactive) radon daughters, some of which emit yet more alpha radiation and some emitting beta and gamma radiation.Įlements that have important naturally-radioactive isotopes include uranium, thorium, and potassium, as well as radon and radium potassium is the only element in this list that has stable, nonradioactive isotopes.
When solid radium decays to form radon gas, it emits a bundle of two protons and two neutrons, an alpha particle, with great velocity (kinetic energy). Radioactive decay is a natural, spontaneous process in which an atom of an unstable or radioactive isotope decays or breaks down to form another isotope by losing atomic particles (protons, neutrons, or electrons). Radon is a gas produced by the radioactive decay of the element radium whose remote parent is either uranium or thorium.