Carbon and nitrogen are not typically considered radioactive elements. They have atomic numbers 6 and 7, respectively, and are stable in their most common isotopic forms. Radioactive elements generally have atomic numbers higher than 82, as they tend to have larger atomic nuclei that are prone to instability.
However, it is possible for carbon and nitrogen isotopes to be radioactive when they have additional neutrons in their nuclei. Isotopes are variants of an element with different numbers of neutrons but the same number of protons. By changing the number of neutrons, isotopes can have different stability properties.
For example, carbon-14 (14C) is a radioactive isotope of carbon. It has 6 protons and 8 neutrons, which makes it unstable. Carbon-14 is produced naturally in the Earth's atmosphere by cosmic rays and is used in radiocarbon dating to determine the age of organic materials.
Similarly, nitrogen-13 (13N) is a radioactive isotope of nitrogen. It has 7 protons and 6 neutrons, making it unstable. Nitrogen-13 is commonly used in positron emission tomography (PET) scans to visualize and diagnose certain medical conditions.
These radioactive isotopes of carbon and nitrogen are relatively short-lived, meaning they decay into more stable forms relatively quickly. Their radioactivity arises from the imbalance between the number of protons and neutrons in their nuclei, which leads to their eventual decay and the emission of radiation.