List of elements by stability of isotopes

Of the first 82 chemical elements in the periodic table, 80 have isotopes considered to be stable.^[1] Overall, there are 251 known stable isotopes in total.

Isotope half-lives. The darker more stable isotope region departs from the line of protons (Z) = neutrons (N), as the element number Z becomes larger.

Background

Atomic nuclei consist of protons and neutrons, which attract each other through the nuclear force, while protons repel each other via the electric force due to their positive charge. These two forces compete, leading to some combinations of neutrons and protons being more stable than others. Neutrons stabilize the nucleus, because they attract protons, which helps offset the electrical repulsion between protons. As a result, as the number of protons increases, an increasing ratio of neutrons to protons is needed to form a stable nucleus; if too many or too few neutrons are present with regard to the optimum ratio, the nucleus becomes unstable and subject to certain types of nuclear decay. Unstable isotopes decay through various radioactive decay pathways, most commonly alpha decay or beta decay, but rarer types of decay including spontaneous fission and cluster decay are known; more detail can be found at radioactive decay.

Of the first 82 elements in the periodic table, 80 have isotopes considered to be stable.^[1] The 83rd element, bismuth, was traditionally regarded as having the heaviest stable isotope, bismuth-209, but in 2003 researchers in Orsay, France, measured the half-life of ²⁰⁹
Bi to be 1.9×10¹⁹ years.^[2][3] Technetium and promethium (atomic numbers 43 and 61, respectively^[a]) and all the elements with an atomic number over 82 only have isotopes that are known to undergo radioactive decay. No undiscovered elements are expected to be stable; therefore, lead is considered the heaviest stable element. However, it is possible that some isotopes that are now considered stable will be revealed to decay with extremely long half-lives (as happened with ²⁰⁹
Bi).

For each of the 80 stable elements, the number of stable isotopes is given. Only 90 isotopes are stable against any possible decay, and an additional 161 are energetically unstable (see List of nuclides) but have never been observed to decay. Thus, 251 isotopes (nuclides) are stable by definition (including an excited state, tantalum-180m, for which no decay has yet been observed).

In April 2019 it was announced that the half-life of xenon-124 had been measured to 1.8 × 10²² years.^[4] This is the longest half-life directly measured for any unstable isotope; only the (indirectly measured) half-life of tellurium-128 is longer.

Of the chemical elements, only 1 element (tin) has 10 such stable isotopes, 5 have 7 stable isotopes, 7 have 6 stable isotopes, 11 have 5 stable isotopes, 9 have 4 stable isotopes, 5 have 3 stable isotopes, 16 have 2 stable isotopes, and 26 have 1 stable isotope.^[1]

Additionally, 31 nuclides of the naturally occurring elements have unstable isotopes with a half-life long enough to have survived for the age of the Solar System (10⁸ years or more), and an additional four such nuclides represent three elements (bismuth, thorium, uranium) having no stable isotope. These 35 radioactive naturally occurring nuclides comprise the radioactive primordial nuclides. The total number of primordial nuclides is then 251 (the stable nuclides) plus the 35 radioactive primordial nuclides, for a total of 286.

The longest known half-life of 2.2 × 10²⁴ years of tellurium-128 was measured by the method of detecting its radiogenic daughter xenon-128; this has been used for other isotopes with noble-gas daughters and barium-130 has also been measured no other way.^[5] Another notable example is the only naturally occurring isotope of bismuth, bismuth-209, which has been predicted to be unstable with a very long half-life, but has been observed to decay. Because of their long half-lives, such isotopes are still found on Earth in various quantities, and together with the stable isotopes they are called primordial isotopes. All the primordial isotopes of each element are given in order of their decreasing abundance on Earth.^[b] For a list of primordial nuclides in order of half-life, see List of nuclides.

118 chemical elements are known to exist. The first 94 are found in nature, and the remainder of the discovered elements are artificially produced, with isotopes all known to be radioactive with relatively short half-lives (see below). The elements in this list are ordered according to the lifetime of their most stable isotope.^[1] Of these, three elements (bismuth, thorium, and uranium) are primordial because they have half-lives long enough to still be found on the Earth,^[c] while all the others are produced either by radioactive decay or are synthesized in laboratories and nuclear reactors. Only 13 of the 38 unstable elements have a known isotope with a half-life of at least 100 years. Every known isotope of the remaining 25 elements is highly radioactive; these are used in academic research and sometimes in industry and medicine.^[d] Some of the heavier elements in the periodic table may be revealed to have yet-undiscovered isotopes with longer lifetimes than those listed here.^[e]

About 338 nuclides are found naturally on Earth. These comprise not only the 286 primordials, but also include about 52 shorter-lived isotopes that either are daughters of primordial isotopes (such as radium from uranium) or are made by energetic natural processes, such as carbon-14 made from atmospheric nitrogen by bombardment from cosmic rays.

Elements by number of primordial isotopes

An even number of protons or neutrons is more stable (higher binding energy) because of pairing effects, so even–even nuclides are much more stable than odd–odd. One effect is that there are few stable odd–odd nuclides: in fact only five are stable, with another four having half-lives longer than a billion years.

Another effect is to prevent beta decay of many even–even nuclides into another even–even nuclide of the same mass number but lower energy, because decay proceeding one step at a time would have to pass through an odd–odd nuclide of higher energy. (Double beta decay directly from even–even to even–even, skipping over an odd-odd nuclide, is only occasionally possible, and is a process so strongly hindered that it has a half-life greater than a billion times the age of the universe.) This makes for a larger number of stable even–even nuclides, up to three for some mass numbers, and up to seven for some atomic (proton) numbers and at least four for all stable even-Z elements beyond argon.

Since nuclei with odd numbers of protons is relatively less stable, odd-numbered elements tend to have fewer stable isotopes. Of the 26 ]monoisotopic elements (those with exactly one stable isotope), all but one have an odd atomic number—the single exception being beryllium. In addition, no odd-numbered element has more than two stable isotopes, while every even-numbered element heavier than carbon with stable isotopes has at least three. Only a single odd-numbered element, potassium, has three primordial isotopes and none more than that.

Tables

The following tables give the elements with primordial nuclides (half-life of most stable isotope > 10⁸ years). A list of nuclides sorted by half-life is found instead at List of nuclides.

The tables of elements are sorted by decreasing number of nuclides per element. Stable and unstable nuclides are given, with symbols for the unstable ones in italics. By convention, nuclides are counted as "stable" if they have never been observed to decay by experiment or from observation of decay products (so that nuclides unstable in theory, such as tantalum-180m, are counted as stable).

The first table is for even-atomic numbered elements, which tend to have far more primordial nuclides, due to the stability conferred by proton pairing. A second separate table is given for odd-atomic numbered elements, which tend to have far fewer stable and long-lived nuclides.

Primordial isotopes (in order of decreasing abundance on Earth^[b]) of even-Z elements

Z	Element	Stable [1]	Decays [1]	unstable in bold odd neutron number in pink
50	tin	10	—	120 Sn	118 Sn	116 Sn	119 Sn	117 Sn	124 Sn	122 Sn	112 Sn	114 Sn	115 Sn
54	xenon	7	2	132 Xe	129 Xe	131 Xe	134 Xe	136 Xe	130 Xe	128 Xe	124 Xe	126 Xe
48	cadmium	6	2	114 Cd	112 Cd	111 Cd	110 Cd	113 Cd	116 Cd	106 Cd	108 Cd
52	tellurium	6	2	130 Te	128 Te	126 Te	125 Te	124 Te	122 Te	123 Te	120 Te
44	ruthenium	7	—	102 Ru	104 Ru	101 Ru	99 Ru	100 Ru	96 Ru	98 Ru
66	dysprosium	7	—	164 Dy	162 Dy	163 Dy	161 Dy	160 Dy	158 Dy	156 Dy
70	ytterbium	7	—	174 Yb	172 Yb	173 Yb	171 Yb	176 Yb	170 Yb	168 Yb
80	mercury	7	—	202 Hg	200 Hg	199 Hg	201 Hg	198 Hg	204 Hg	196 Hg
42	molybdenum	6	1	98 Mo	96 Mo	95 Mo	92 Mo	100 Mo	97 Mo	94 Mo
56	barium	6	1	138 Ba	137 Ba	136 Ba	135 Ba	134 Ba	132 Ba	130 Ba
64	gadolinium	6	1	158 Gd	160 Gd	156 Gd	157 Gd	155 Gd	154 Gd	152 Gd
60	neodymium	5	2	142 Nd	144 Nd	146 Nd	143 Nd	145 Nd	148 Nd	150 Nd
62	samarium	5	2	152 Sm	154 Sm	147 Sm	149 Sm	148 Sm	150 Sm	144 Sm
76	osmium	5	2	192 Os	190 Os	189 Os	188 Os	187 Os	186 Os	184 Os
46	palladium	6	—	106 Pd	108 Pd	105 Pd	110 Pd	104 Pd	102 Pd
68	erbium	6	—	166 Er	168 Er	167 Er	170 Er	164 Er	162 Er
20	calcium	5	1	40 Ca	44 Ca	42 Ca	48 Ca	43 Ca	46 Ca
34	selenium	5	1	80 Se	78 Se	76 Se	82 Se	77 Se	74 Se
36	krypton	5	1	84 Kr	86 Kr	82 Kr	83 Kr	80 Kr	78 Kr
72	hafnium	5	1	180 Hf	178 Hf	177 Hf	179 Hf	176 Hf	174 Hf
78	platinum	5	1	195 Pt	194 Pt	196 Pt	198 Pt	192 Pt	190 Pt
22	titanium	5	—	48 Ti	46 Ti	47 Ti	49 Ti	50 Ti
28	nickel	5	—	58 Ni	60 Ni	62 Ni	61 Ni	64 Ni
30	zinc	5	—	64 Zn	66 Zn	68 Zn	67 Zn	70 Zn
32	germanium	4	1	74 Ge	72 Ge	70 Ge	73 Ge	76 Ge
40	zirconium	4	1	90 Zr	94 Zr	92 Zr	91 Zr	96 Zr
74	tungsten	4	1	184 W	186 W	182 W	183 W	180 W
16	sulfur	4	—	32 S	34 S	33 S	36 S
24	chromium	4	—	52 Cr	53 Cr	50 Cr	54 Cr
26	iron	4	—	56 Fe	54 Fe	57 Fe	58 Fe
38	strontium	4	—	88 Sr	86 Sr	87 Sr	84 Sr
58	cerium	4	—	140 Ce	142 Ce	138 Ce	136 Ce
82	lead	4	—	208 Pb	206 Pb	207 Pb	204 Pb
8	oxygen	3	—	16 O	18 O	17 O
10	neon	3	—	20 Ne	22 Ne	21 Ne
12	magnesium	3	—	24 Mg	26 Mg	25 Mg
14	silicon	3	—	28 Si	29 Si	30 Si
18	argon	3	—	40 Ar	36 Ar	38 Ar
2	helium	2	—	4 He	3 He
6	carbon	2	—	12 C	13 C
92	uranium	0	2	238 U[c]	235 U
4	beryllium	1	—	9 Be
90	thorium	0	1	232 Th[c]

Primordial isotopes of odd-Z elements

Z	Element	Stab	Dec	unstable: bold odd N in pink
19	potassium	2	1	39 K	41 K	40 K
1	hydrogen	2	—	1 H	2 H
3	lithium	2	—	7 Li	6 Li
5	boron	2	—	11 B	10 B
7	nitrogen	2	—	14 N	15 N
17	chlorine	2	—	35 Cl	37 Cl
29	copper	2	—	63 Cu	65 Cu
31	gallium	2	—	69 Ga	71 Ga
35	bromine	2	—	79 Br	81 Br
47	silver	2	—	107 Ag	109 Ag
51	antimony	2	—	121 Sb	123 Sb
73	tantalum	2	—	181 Ta	180m Ta
77	iridium	2	—	193 Ir	191 Ir
81	thallium	2	—	205 Tl	203 Tl
23	vanadium	1	1	51 V	50 V
37	rubidium	1	1	85 Rb	87 Rb
49	indium	1	1	115 In	113 In
57	lanthanum	1	1	139 La	138 La
63	europium	1	1	153 Eu	151 Eu
71	lutetium	1	1	175 Lu	176 Lu
75	rhenium	1	1	187 Re	185 Re
9	fluorine	1	—	19 F
11	sodium	1	—	23 Na
13	aluminium	1	—	27 Al
15	phosphorus	1	—	31 P
21	scandium	1	—	45 Sc
25	manganese	1	—	55 Mn
27	cobalt	1	—	59 Co
33	arsenic	1	—	75 As
39	yttrium	1	—	89 Y
41	niobium	1	—	93 Nb
45	rhodium	1	—	103 Rh
53	iodine	1	—	127 I
55	caesium	1	—	133 Cs
59	praseodymium	1	—	141 Pr
65	terbium	1	—	159 Tb
67	holmium	1	—	165 Ho
69	thulium	1	—	169 Tm
79	gold	1	—	197 Au
83	bismuth	0	1	209 Bi

Elements with no primordial isotopes

No primordial isotopes
Longest-lived isotope > 1 day

Z	Element	t1⁄2[f][1]	Longest- lived isotope
94	plutonium	8.08×107 yr	244 Pu
96	curium	1.56×107 yr	247 Cm
43	technetium	4.21×106 yr	97 Tc[a]
93	neptunium	2.14×106 yr	237 Np
91	protactinium	32,760 yr	231 Pa
95	americium	7,370 yr	243 Am
88	radium	1,600 yr	226 Ra
97	berkelium	1,380 yr	247 Bk
98	californium	900 yr	251 Cf
84	polonium	125 yr	209 Po
89	actinium	21.772 yr	227 Ac
61	promethium	17.7 yr	145 Pm[a]
99	einsteinium	1.293 yr	252 Es[e]
100	fermium	100.5 d	257 Fm[e]
101	mendelevium	51.3 d	258 Md[e]
86	radon	3.823 d	222 Rn

No primordial isotopes
Longest-lived isotope < 1 day

Z	Element	t1⁄2[f][1]	Longest- lived isotope
105	dubnium	16 h	268 Db[e]
103	lawrencium	11 h	266 Lr[e]
85	astatine	8.1 h	210 At
102	nobelium	58 min	259 No[e]
104	rutherfordium	48 min	267 Rf[e]
87	francium	22 min	223 Fr
106	seaborgium	14 min	269 Sg[e]
107	bohrium	2.4 min	270 Bh[e]
111	roentgenium	1.7 min	282 Rg[e]
112	copernicium	28 s	285 Cn[e]
108	hassium	16 s	269 Hs[e]
110	darmstadtium	12.7 s	281 Ds[e]
113	nihonium	9.5 s	286 Nh[e]
109	meitnerium	4.5 s	278 Mt[e]
114	flerovium	1.9 s	289 Fl[e]
115	moscovium	650 ms	290 Mc[e]
116	livermorium	57 ms	293 Lv[e]
117	tennessine	51 ms	294 Ts[e]
118	oganesson	690 μs	294 Og[e]

Periodic table with elements colored according to the half-life of their most stable isotope.

See also

• Island of stability
• Isotope § Nuclear properties and stability
• List of nuclides
• List of radioactive nuclides by half-life
• Primordial nuclide
• Stable nuclide
• Stable isotope ratio
• Table of nuclides

Footnotes

1. See Stability of technetium isotopes and Stability of promethium isotopes for a discussion as to why technetium and promethium have no stable isotopes.
2. There are unstable isotopes with extremely long half-lives that are also found on Earth, and some of them are even more abundant than all the stable isotopes of a given element (for example, beta-active ¹⁸⁷Re is twice as abundant as stable ¹⁸⁵Re). Also, a bigger natural abundance of an isotope just implies that its formation was favored by the stellar nucleosynthesis process that produced the matter now constituting the Earth (and, of course, the rest of the Solar System) (see also Formation and evolution of the Solar System). In the case of argon the cosmically rarer ⁴⁰
   Ar dominates on Earth over ³⁶
   Ar as argon is too volatile to have been retained in the early proto-atmosphere of Earth while ⁴⁰
   Ar is a decay product of long-lived and non-volatile ⁴⁰
   K. Most argon in Earth's atmosphere is a product of potassium-40 decay. Most argon in the universe is not. At the present time 0.012% (120 ppm) of potassium on Earth is ⁴⁰
   K. Taking the age of Earth and the half life of ⁴⁰
   K (~1.25 billion years), this ratio was approximately an order of magnitude higher when the planet first formed. About 10.72% of that since-decayed ⁴⁰
   K produced ⁴⁰
   Ar, the rest having decayed to ⁴⁰
   Ca.
3. Of these three primordial but unstable elements, two more non-primordial isotopes are found in nature in significant amounts: ²³⁴
   U and ²³⁰
   Th, both radiogenic as decay products of ²³⁸
   U.
4. See many different industrial and medical applications of radioactive elements in Radionuclide, Nuclear medicine, Common beta emitters, Commonly used gamma-emitting isotopes, Fluorine-18, Cobalt-60, Strontium-90, Technetium-99m, Iodine-123, Iodine-124, Promethium-147, Iridium-192, etc.
5. For elements with a higher atomic number than californium (with Z>98), there might exist undiscovered isotopes that are more stable than the known ones.
6. Legend: yr=year, d=day, h=hour, min=minute, s=second.