List of nuclides

There are 251 known so-called stable nuclides. 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 251 are determined to be very long-lived radioactive nuclides in the future. In this article, the "stable" nuclides are divided into three tables, one for nuclides that are theoretically stable (meaning no decay mode is possible) and nuclides that can theoretically undergo spontaneous fission but have not been evaluated to check for evidence of this happening, one for nuclides that can theoretically undergo forms of decay other than spontaneous fission but have not been evaluated, and finally a table of nuclides that can theoretically decay and have been evaluated but without detecting any decay. In this latter table, where a decay has been predicted theoretically but never observed experimentally (either directly or through finding an excess of the daughter), the theoretical decay mode is given in parentheses and have "> number" in the half-life column to 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 (tellurium-128, barium-130). There are (currently) 35 of these (see these nuclides), of which 25 have half-lives longer than 10¹³ years. With most of these 25, decay is difficult to observe and for most purposes they can be regarded as effectively stable. Bismuth-209 is notable as it is the only naturally occurring isotope of an element which was long considered stable. A further 10 nuclides, platinum-190, samarium-147, lanthanum-138, rubidium-87, rhenium-187, lutetium-176, thorium-232, uranium-238, potassium-40, and uranium-235 have half-lives between 7.0×10⁸ and 4.83×10¹¹ years, which means they have experienced at least 0.5% depletion since the formation of the Solar System about 4.6×10⁹ years ago, but still exist on Earth in significant quantities. They are the primary source of radiogenic heating and radioactive decay products. Together, there are a total of 286 primordial nuclides.[lower-alpha 1]

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.

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 by rare cosmogenic interactions or as a result of other natural nuclear reactions (nucleogenic nuclides), but are difficult to detect.

Further shorter-lived nuclides have been detected in the spectra of stars, such as isotopes of technetium, promethium, and some actinides. 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 releases of man-made nuclear fission product (from nuclear weapons, nuclear reactors, and other processes). Other are produced artificially for industrial or medical purposes.

Each group of radionuclides, starting with the longest-lived primordial radionuclides, is sorted by decreasing half-life, but the tables are sortable by other columns.

no (number) column

A running positive integer for reference. This number, i.e. position in this table, might be changed in the future, especially for nuclides with short half-lives.

nuclide column

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.

Z, N column

The number of protons (Z column) and number of neutrons (N column).

energy column

The column labeled "energy" denotes the energy equivalent of the mass of a neutron minus the mass per nucleon of this nuclide (so all nuclides get a positive value) in MeV, formally: m_n − m_nuclide / A, where A = Z + N is the mass number. Note that this means that a higher "energy" value actually means that the nuclide has a lower energy. The mass of the nuclide (in daltons) is A (m_n − E / k) where E is the energy, m_n is 1.008664916 Da and k = 931.49410242 the conversion factor between MeV and daltons.

half-life column

The main column shows times in seconds (31,556,926 seconds = 1 tropical year); a second column showing half-life in more usual units (year, day) 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 mode column

α	α decay
β−	β− decay
β−β−	double β− decay
ε	electron capture
β+	β+ decay
β+β+	double β+ decay
SF	spontaneous fission
IT	isomeric transition

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 (see these nuclides).

decay energy column

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.

notes column

CG

Cosmogenic nuclide;

DP

Naturally occurring decay product (of thorium-232, uranium-238, and uranium-235);

ESS

Present in the early Solar System (first few million years), but extinct now as a primordial nuclide.

FP

Nuclear fission product (only those from uranium-235 or plutonium-239) (only those with a half-life over one day are shown);

IM

Industry or medically used radionuclide.[2]