Assertion: radon's isotope | /r/HasProperty | short-lived
Facets:
Source sentences:
text: Radon is rare in nature because its isotopes are all short-lived and because its source, radium, is a scarce element.
text: Radon is rare in nature because its isotopes are so short-lived and because its main source radium is also quite rare, according to Encyclopaedia Britannica.