Radionuclide

The degree of harm will depend on the nature and extent of the radiation produced, the amount and nature of exposure (close contact, inhalation or ingestion), and the biochemical properties of the element; with increased risk of cancer the most usual consequence.

For example, polonium can be found in uranium ores at about 0.1 mg per metric ton (1 part in 1010).

[7][8] Further radionuclides may occur in nature in virtually undetectable amounts as a result of rare events such as spontaneous fission or uncommon cosmic ray interactions.

Key: Z = atomic number; N = neutron number; DM = decay mode; DE = decay energy; EC = electron capture Radionuclides are present in many homes as they are used inside the most common household smoke detectors.

In the presence of smoke, some of the ions are neutralized, thereby decreasing the current, which activates the detector's alarm.

[14][15] Radionuclides that find their way into the environment may cause harmful effects as radioactive contamination.

They can also cause damage if they are excessively used during treatment or in other ways exposed to living beings, by radiation poisoning.

They include 30 nuclides with measured half-lives longer than the estimated age of the universe (13.8 billion years[17]), and another four nuclides with half-lives long enough (> 100 million years) that they are radioactive primordial nuclides, and may be detected on Earth, having survived from their presence in interstellar dust since before the formation of the Solar System, about 4.6 billion years ago.

Numbers are not exact, and may change slightly in the future, as "stable nuclides" are observed to be radioactive with very long half-lives.

This list covers common isotopes, most of which are available in very small quantities to the general public in most countries.

Others that are not publicly accessible are traded commercially in industrial, medical, and scientific fields and are subject to government regulation.