Assertion: radon's life | /r/HasProperty | the time
Facets:
Source sentences:
text: Uranium has been present since the earth was formed and its most common isotope has a very long half-life (4.5 billion years), which is the time required for one-half of uranium to break down.
text: The half-life is the time it takes for half of the atoms of a radionuclide (radioactive element) to undergo radioactive decay and change it into a different element, some of which are radioactive and some are stable.