Assertion: actinium's isotope | /r/HasProperty | known with mass numbers
Facets:
value: from 203
type: OTHER
Source sentences:
text: More than 20 isotopes are known, with mass numbers from 203 to 229, but they are all highly unstable; the most long-lived isotope is the β-emitting 223 Fr(T ½ = 21.8 min), which occurs in nature.