This list of nuclides shows the >900 observed nuclides that either are stable or, if radioactive, have half-lives longer than one hour. At least 3,000 nuclides have been experimentally characterized. A selection of those with decay half-lives less than 60 minutes are shown.
Contents
A nuclide is defined conventionally as an experimentally examined bound collection of one or more protons and zero or more neutrons, that either is stable or has an observed decay mode.
Introduction
254 nuclides are considered stable. Many of these in theory could decay through spontaneous fission, alpha decay, double beta decay, etc. with a very long half-life, but no radioactive decay has yet been observed. Thus the number of stable nuclides is subject to change if some of these 254 are determined to be very long-lived radioactive nuclides in the future. If a decay has been predicted theoretically but never observed experimentally, it is given in parentheses. In theory, spontaneous fission is possible for all elements with atomic numbers >40, but has not been observed for most elements up to lead (82). The list lists nuclides unstable only to this fission mechanism, before nuclides theoretically unstable to additional mechanisms. Those that have been checked for radioactivity are indicated with "> number" and show the lower limit for the half-life based on experimental observation. Such nuclides are considered to be "stable" until a decay has been observed in some fashion. For example, tellurium-123 was reported to be radioactive, but the same experimental group later retracted this report, and it presently remains observationally stable.
The next group is the primordial radioactive nuclides. These have been measured to be radioactive, or decay products have been identified (Te-130, Ba-130). There are (currently) 32 of these, of which 28 have half-lives considerably longer than the age of the universe (13.8 billion years). With most of these 28, decay is difficult to observe and for most purposes they can be regarded as effectively stable. Bismuth-209 is notable as the only natural occurring isotope of an element long considered stable. A further 4 nuclides, thorium-232, uranium-238, potassium-40 and uranium-235 have half lives between 14 billion and 700 million years, which means they have experienced measurable decay since the formation of the solar system about 4.6 billion years ago, but still exist on earth in significant quantities. They are the primary source of radiogenic heat and radioactive decay products. Together, there are a total of 286 primordial nuclides.
The list then covers the ~700 radionuclides with half-lives longer than 1 hour, split into two tables, half lives greater than one day and less than one day. There are also more than 3000 radionuclides with half lives less than an hour, listed are those that exist naturally in decay chains
Over 60 nuclides that have half-lives too short to be primordial can be detected in nature as a result of later production by natural processes, mostly in trace amounts. These include ~44 radionuclides occurring in the decay chains of primordial uranium and thorium (radiogenic nuclides), such as Radon-222. Others are the products of interactions with energetic cosmic-rays (e.g. cosmic ray spallation) (cosmogenic nuclides) such as carbon-14. This gives a total of about 350 naturally occurring nuclides. Other nuclides may be occasionally produced naturally but are difficult to detect by rare cosmogenic interactions or as a result of other natural nuclear reactions (nucleogenic nuclides).
Further shorter lived nuclides have been detected in the spectra of stars (technetium, promethium, californium). The remaining nuclides are known solely from artificial nuclear transmutation. Some, such as caesium-137, are found in the environment but as a result of contamination from man-made nuclear fission product releases (nuclear weapons, nuclear reactors, and other processes). Other are produced artificially for industrial or medical purposes.
Summary table for numbers of each class of nuclides
This is a summary table of decay class for the ~986 nuclides with half-lives longer than one hour, given in this list of nuclides. Numbers may change slightly in the future, as nuclides radioactive only in theory are observed to be radioactive, half-life measurements improve, or new isotopes are discovered.
List legend
All the radionuclides, starting with the longest-lived primordial radionuclides, are sorted by decreasing half-life, but the tables are sortable by other criteria.
A running positive integer for reference. Especially for nuclides with short half-lives, this number, i.e. position in this table, might be changed in the future.
Nuclide identifiers are given by their atomic mass number A and the symbol for the corresponding chemical element (corresponding to the unique proton number). In the cases that this is not the ground state, this is indicated by a m for metastable appended to the mass number. Sorting here sorts by mass number.
The number of protons and number of neutrons is provided.
The column labeled "energy" denotes the energy equivalent of the difference between the mass per nucleon of this nuclide and the mass of a neutron (so all nuclides get a positive value) in MeV, formally: mn − mnuclide / A. Thus the mass of the nuclide (in Daltons) is A (mn − E / k} where E is the energy, mn is 1.008664915 Da and k = 931.4941 the conversion factor between MeV and Daltons.
The main column shows times in seconds (31,556,926 seconds = 1 year), a second column showing half life in more usual units (year,days) is also provided. Entries starting with a ">" indicates that no decay has ever been observed, with null experiments establishing lower limits for the half-life. Such elements are considered stable unless a decay can be observed (establishing an actual estimate for the half-life). Note half lives may be imprecise estimates and can be subject to significant revision.
Decay modes in parentheses are still not observed through experiment but are, by their energy, predicted to occur. Numbers in brackets indicate probability of that decay mode occurring in %, tr indicate <0.1%. Spontaneous fission is not shown as a theoretical decay mode for stable nuclides where other modes are possible.
Multiple values for (maximal) decay energy are mapped to decay modes in their order. The decay energy listed is for the specific nuclide only, not for the whole decay chain. It includes the energy lost to neutrinos.
CG: Cosmogenic nuclide;
DP: Naturally occurring decay product (of Thorium-232, Uranium-238 and Uranium 235;
FP: Fission product of Uranium-235 / Plutonium-239 (only those with a half life over one day are shown);
IM: Industry or medically used radionuclide.