Assertion: berkelium's number | /r/HasProperty | atoms of the same element
Facets:
Source sentences:
text: Number of isotopes (atoms of the same element with a different number of neutrons): 12, including one stable isotope.
text: Number of natural isotopes (atoms of the same element with a different number of neutrons): 0.
text: Number of isotopes (atoms of the same element with a different number of neutrons): 20 isotopes whose half-lives are known with mass numbers 237 to 256.