List of nuclides

There are presently 251 known 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 this has not yet been observed. Thus, the number of stable nuclides is subject to change if some of these 251 have radioactive decay observed 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) except to spontaneous fission, which is not considered plausible in this mass range; one for nuclides that can theoretically undergo forms of decay other than spontaneous fission but have no published lower bound on lifetime from experimental evaluations; and one for nuclides that can theoretically decay and have been examined without detecting any decay, allowing a lower bound to be published. In this last table, where a decay has been predicted theoretically but never observed experimentally (either directly or by finding an excess of the daughter), the theoretical decay mode is given in parentheses, and "> (lifetime in years)" is shown in the half-life column to show this lower limit in scientific notation. Such nuclides are considered to be "stable", also called "observationally stable" indicating the tentative nature of the conclusion, until some decay has been observed. For example, tellurium-123 was reported to be radioactive, but the same experimental group later retracted this report, and it is again listed as stable.

The next group is the primordial radioactive nuclides. These have been measured to be radioactive, or decay products have been identified in natural samples (tellurium-128, barium-130). There are 35 of these (see these nuclides), of which 25 have half-lives longer than 10¹³ years. For 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 long considered stable. The other 10, 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 7×10⁸ and 5×10¹¹ years, which means they have undergone 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.^[a]

The list then covers the other radionuclides with half-lives longer than 1 hour, split into several tables in order of successively shorter lifetimes.

Some 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 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 (the cosmogenic nuclides), such as carbon-14. This gives a total of about 350 naturally occurring nuclides, some of which are difficult to detect. Other nuclides may be occasionally produced naturally by rare cosmogenic interactions or as a result of other natural nuclear reactions (nucleogenic nuclides), and these are generally even less detectable.

Non-primordial nuclides may also be detected in the spectra of stars; technetium is well established,^[2] and others have been claimed. The remaining nuclides are known solely from artificial nuclear transmutations. Some, such as caesium-137 and krypton-85, are detected in the environment, but only (or practically only) from deliberate or accidental release of artificial production, as fission products (from nuclear weapons or nuclear reactors), for industrial or medical uses, or otherwise.

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. All columns sort by usual lexicographical order; in the case of the nuclide column this gives order on the mass number A.

No. (number) column

A running positive integer for reference, equal to the position in the tables. This number may change in the future, especially for nuclides with short lives, as better half-life estimates become available.

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; the conventional numbers are further appended to distinguish multiple metastable states but '1' is omitted if the others are much less stable.

A, Z, N columns

The total number of protons and neutrons together (A) and the separate numbers of protons (Z) and of neutrons (N).

Energy column

The column labeled "energy" denotes the energy equivalent of (the mass of a neutron minus the mass per nucleon), that is of the mass defect with respect to the neutron, in MeV. Use of the neutron as reference guarantees all nuclides will have a positive value. Mathematically: m_n − m_nuclide / A. Note that this means that a higher "energy" value actually means that the nuclide has a lower energy. Inversely the mass is A (m_n − E / k) where E is the energy, m_n is 1.0086649159 and k = 931.4941037 MeV (energy equivalent of the dalton). Omitted if there is no experimental mass determination within 0.0001.

Half-life column

The first column shows times in seconds; the second column in the more usual units (years, days, hours). As the first column is converted from the second, it is given enough digits to ensure consistent sorting.

Entries starting with a ">" indicates that no decay has ever been observed, with experiments having established lower limits on the half-life. Such elements are considered stable unless decay is observed (establishing an actual estimate for the half-life). Half-lives are imprecise estimates and may be subject to significant revision. When shown to a smaller than usual number of significant figures, it is not known accurately enough to justify more.

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 given for observationally stable nuclides (these and these); they are then those allowed to occur by energy (in the next column), but spontaneous fission (and cluster decay, which is never shown in the tables) are neglected as they should never be observed for these nuclides. Those with multiple significant decay modes have the probability of each decay mode in percent given, in small figures, in parentheses; those less than 0.05% are rounded to zero and omitted, and 100 (>99.5% of observed decays) is not used but replaced by bold unless the only other decays are SF or double beta, assumed to be minority decays if not listed first. If more than one of α, β⁻, β⁺/ε, IT is given without numbers or bold, one can assume no experimental data is available. Note that, by widely used convention, β⁺ (technically positron emission) includes ε, and conversely, if positron emission is energetically possible; the two are never separated on this page.

Decay energy column

Multiple values for decay energy for each given decay mode (skipping SF), in respective order. Decay energies are the whole energy difference to the ground state of the product, and so include energy lost to neutrinos. Further decays in a decay chain are not included.

Notes column

CG

Cosmogenic nuclide.

DP

Naturally occurring decay product (of thorium-232, uranium-238, or uranium-235), including products of neutron reactions other than fission.

ESS

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

FP

Nuclear fission product ,^[b] may occur naturally from spontaneous fission.

IM

Industry or medically used radionuclide.^[3]

Of the 701 non-primordial nuclides in the tables below, 101 have the label FP (99 true fission products), 65 IM, 32 DP, 24 CG, 13 ESS, and 7 both CG and ESS.

The tables are based now on the standard reference NUBASE2020^[4] and its companion, based on the same data, AME2020.^[5] All observational data not otherwise cited should be found in those sources, or calculated from them, and only observed data, not theoretical extrapolations, should be present in these tables.