Question: are all isotopes of carbon radioactive?
Answer: Isotopes of Carbon Both 12C and 13C are called stable isotopes since they do not decay into other forms or elements over time. The rare carbon-14 (14C) isotope contains eight neutrons in its nucleus. Unlike 12C and 13C, this isotope is unstable, or radioactive. ... Only one out of every trillion carbon atoms is 14C.