Assertion: neptunium's isotope | /r/HasProperty | synthetic
Facets:
value: entirely
type: DEGREE
Source sentences:
text: Neptunium does not occur in nature, so all isotopes are synthetic.
text: As little as 20–30 g (one ounce) exists at any given time throughout the Earth's crust; the other isotopes (except for francium-221) are entirely synthetic.