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Actinium (89Ac) has no stable isotopes and no characteristic terrestrial isotopic composition, thus a standard atomic weight cannot be given. There are 34 known isotopes, from 203Ac to 236Ac, and 7 isomers. Three isotopes are found in nature, 225Ac, 227Ac and 228Ac, as intermediate decay products of, respectively, 237Np, 235U, and 232Th. 228Ac and 225Ac are extremely rare, so almost all natural actinium is 227Ac.
The most stable isotopes are 227Ac with a half-life of 21.772 years, 225Ac with a half-life of 10.0 days, and 226Ac with a half-life of 29.37 hours. All other isotopes have half-lives under 10 hours, and most under a minute. The shortest-lived known isotope is 217Ac with a half-life of 69 ns.
Purified 227Ac comes into equilibrium with its decay products (227Th and 223Fr) after 185 days. [2]
Nuclide [n 1] | Historic name | Z | N | Isotopic mass (Da) [n 2] [n 3] | Half-life | Decay mode [n 4] | Daughter isotope [n 5] | Spin and parity [n 6] [n 7] | Isotopic abundance | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Excitation energy [n 7] | |||||||||||||||||||
203Ac [3] | 89 | 114 | 56+269 −26 μs | α | 199Fr | (1/2+) | |||||||||||||
204Ac [4] | 89 | 115 | 7.4+2.2 −1.4 ms | α | 200Fr | ||||||||||||||
205Ac [5] | 89 | 116 | 7.7+2.7 −1.6 ms [4] | α | 201Fr | 9/2−? | |||||||||||||
206Ac | 89 | 117 | 206.01450(8) | 25(7) ms | α | 202Fr | (3+) | ||||||||||||
206m1Ac | 80(50) keV | 15(6) ms | α | 202Fr | |||||||||||||||
206m2Ac | 290(110)# keV | 41(16) ms | α | 202mFr | (10−) | ||||||||||||||
207Ac | 89 | 118 | 207.01195(6) | 31(8) ms [27(+11−6) ms] | α | 203Fr | 9/2−# | ||||||||||||
208Ac | 89 | 119 | 208.01155(6) | 97(16) ms [95(+24−16) ms] | α (99%) | 204Fr | (3+) | ||||||||||||
β+ (1%) | 208Ra | ||||||||||||||||||
208mAc | 506(26) keV | 28(7) ms [25(+9−5) ms] | α (89%) | 204Fr | (10−) | ||||||||||||||
IT (10%) | 208Ac | ||||||||||||||||||
β+ (1%) | 208Ra | ||||||||||||||||||
209Ac | 89 | 120 | 209.00949(5) | 92(11) ms | α (99%) | 205Fr | (9/2−) | ||||||||||||
β+ (1%) | 209Ra | ||||||||||||||||||
210Ac | 89 | 121 | 210.00944(6) | 350(40) ms | α (96%) | 206Fr | 7+# | ||||||||||||
β+ (4%) | 210Ra | ||||||||||||||||||
211Ac | 89 | 122 | 211.00773(8) | 213(25) ms | α (99.8%) | 207Fr | 9/2−# | ||||||||||||
β+ (.2%) | 211Ra | ||||||||||||||||||
212Ac | 89 | 123 | 212.00781(7) | 920(50) ms | α (97%) | 208Fr | 6+# | ||||||||||||
β+ (3%) | 212Ra | ||||||||||||||||||
213Ac | 89 | 124 | 213.00661(6) | 731(17) ms | α | 209Fr | (9/2−)# | ||||||||||||
β+ (rare) | 213Ra | ||||||||||||||||||
214Ac | 89 | 125 | 214.006902(24) | 8.2(2) s | α (89%) | 210Fr | (5+)# | ||||||||||||
β+ (11%) | 214Ra | ||||||||||||||||||
215Ac | 89 | 126 | 215.006454(23) | 0.17(1) s | α (99.91%) | 211Fr | 9/2− | ||||||||||||
β+ (.09%) | 215Ra | ||||||||||||||||||
216Ac | 89 | 127 | 216.008720(29) | 0.440(16) ms | α | 212Fr | (1−) | ||||||||||||
β+ (7×10−5%) | 216Ra | ||||||||||||||||||
216mAc | 44(7) keV | 443(7) μs | α | 212Fr | (9−) | ||||||||||||||
217Ac | 89 | 128 | 217.009347(14) | 69(4) ns | α | 213Fr | 9/2− | ||||||||||||
β+ (6.9×10−9%) | 217Ra | ||||||||||||||||||
217mAc | 2012(20) keV | 740(40) ns | (29/2)+ | ||||||||||||||||
218Ac | 89 | 129 | 218.01164(5) | 1.08(9) μs | α | 214Fr | (1−)# | ||||||||||||
218mAc | 584(50)# keV | 103(11) ns | (11+) | ||||||||||||||||
219Ac | 89 | 130 | 219.01242(5) | 11.8(15) μs | α | 215Fr | 9/2− | ||||||||||||
β+ (10−6%) | 219Ra | ||||||||||||||||||
220Ac | 89 | 131 | 220.014763(16) | 26.36(19) ms | α | 216Fr | (3−) | ||||||||||||
β+ (5×10−4%) | 220Ra | ||||||||||||||||||
221Ac | 89 | 132 | 221.01559(5) | 52(2) ms | α | 217Fr | 9/2−# | ||||||||||||
222Ac | 89 | 133 | 222.017844(6) | 5.0(5) s | α (99%) | 218Fr | 1− | ||||||||||||
β+ (1%) | 222Ra | ||||||||||||||||||
222mAc | 200(150)# keV | 1.05(7) min | α (88.6%) | 218Fr | high | ||||||||||||||
IT (10%) | 222Ac | ||||||||||||||||||
β+ (1.4%) | 222Ra | ||||||||||||||||||
223Ac | 89 | 134 | 223.019137(8) | 2.10(5) min | α (99%) | 219Fr | (5/2−) | ||||||||||||
EC (1%) | 223Ra | ||||||||||||||||||
CD (3.2×10−9%) | 209Bi 14C | ||||||||||||||||||
224Ac | 89 | 135 | 224.021723(4) | 2.78(17) h | β+ (90.9%) | 224Ra | 0− | ||||||||||||
α (9.1%) | 220Fr | ||||||||||||||||||
β− (1.6%) | 224Th | ||||||||||||||||||
225Ac [n 8] | 89 | 136 | 225.023230(5) | 10.0(1) d | α | 221Fr | (3/2−) | Trace [n 9] | |||||||||||
CD (6×10−10%) | 211Bi 14C | ||||||||||||||||||
226Ac | 89 | 137 | 226.026098(4) | 29.37(12) h | β− (83%) | 226Th | (1)(−#) | ||||||||||||
EC (17%) | 226Ra | ||||||||||||||||||
α (.006%) | 222Fr | ||||||||||||||||||
227Ac | Actinium [n 10] | 89 | 138 | 227.0277521(26) | 21.772(3) y | β− (98.62%) | 227Th | 3/2− | Trace [n 11] | ||||||||||
α (1.38%) | 223Fr | ||||||||||||||||||
228Ac | Mesothorium 2 | 89 | 139 | 228.0310211(27) | 6.13(2) h | β− | 228Th | 3+ | Trace [n 12] | ||||||||||
229Ac | 89 | 140 | 229.03302(4) | 62.7(5) min | β− | 229Th | (3/2+) | ||||||||||||
230Ac | 89 | 141 | 230.03629(32) | 122(3) s | β− | 230Th | (1+) | ||||||||||||
231Ac | 89 | 142 | 231.03856(11) | 7.5(1) min | β− | 231Th | (1/2+) | ||||||||||||
232Ac | 89 | 143 | 232.04203(11) | 119(5) s | β− | 232Th | (1+) | ||||||||||||
233Ac | 89 | 144 | 233.04455(32)# | 145(10) s | β− | 233Th | (1/2+) | ||||||||||||
234Ac | 89 | 145 | 234.04842(43)# | 44(7) s | β− | 234Th | |||||||||||||
235Ac | 89 | 146 | 235.05123(38)# | 60(4) s | β− | 235Th | 1/2+# | ||||||||||||
236Ac [6] | 89 | 147 | 236.05530(54)# | 72+345 −33 s | β− | 236Th | |||||||||||||
This table header & footer: |
CD: | Cluster decay |
EC: | Electron capture |
IT: | Isomeric transition |
Actinides [7] by decay chain | Half-life range (a) | Fission products of 235U by yield [8] | ||||||
---|---|---|---|---|---|---|---|---|
4n | 4n + 1 | 4n + 2 | 4n + 3 | 4.5–7% | 0.04–1.25% | <0.001% | ||
228 Ra№ | 4–6 a | 155 Euþ | ||||||
244 Cmƒ | 241 Puƒ | 250 Cf | 227 Ac№ | 10–29 a | 90 Sr | 85 Kr | 113m Cdþ | |
232 Uƒ | 238 Puƒ | 243 Cmƒ | 29–97 a | 137 Cs | 151 Smþ | 121m Sn | ||
248 Bk [9] | 249 Cfƒ | 242m Amƒ | 141–351 a | No fission products have a half-life | ||||
241 Amƒ | 251 Cfƒ [10] | 430–900 a | ||||||
226 Ra№ | 247 Bk | 1.3–1.6 ka | ||||||
240 Pu | 229 Th | 246 Cmƒ | 243 Amƒ | 4.7–7.4 ka | ||||
245 Cmƒ | 250 Cm | 8.3–8.5 ka | ||||||
239 Puƒ | 24.1 ka | |||||||
230 Th№ | 231 Pa№ | 32–76 ka | ||||||
236 Npƒ | 233 Uƒ | 234 U№ | 150–250 ka | 99 Tc₡ | 126 Sn | |||
248 Cm | 242 Pu | 327–375 ka | 79 Se₡ | |||||
1.53 Ma | 93 Zr | |||||||
237 Npƒ | 2.1–6.5 Ma | 135 Cs₡ | 107 Pd | |||||
236 U | 247 Cmƒ | 15–24 Ma | 129 I₡ | |||||
244 Pu | 80 Ma | ... nor beyond 15.7 Ma [11] | ||||||
232 Th№ | 238 U№ | 235 Uƒ№ | 0.7–14.1 Ga | |||||
|
Actinium is a chemical element; it has symbol Ac and atomic number 89. It was first isolated by Friedrich Oskar Giesel in 1902, who gave it the name emanium; the element got its name by being wrongly identified with a substance André-Louis Debierne found in 1899 and called actinium. Actinium gave the name to the actinide series, a set of 15 elements between actinium and lawrencium in the periodic table. Together with polonium, radium, and radon, actinium was one of the first non-primordial radioactive elements to be isolated.
In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". The typical radioisotope does not decay directly to a stable state, but rather it decays to another radioisotope. Thus there is usually a series of decays until the atom has become a stable isotope, meaning that the nucleus of the atom has reached a stable state.
Protactinium (91Pa) has no stable isotopes. The four naturally occurring isotopes allow a standard atomic weight to be given.
Radium (88Ra) has no stable or nearly stable isotopes, and thus a standard atomic weight cannot be given. The longest lived, and most common, isotope of radium is 226Ra with a half-life of 1600 years. 226Ra occurs in the decay chain of 238U. Radium has 34 known isotopes from 201Ra to 234Ra.
Astatine (85At) has 41 known isotopes, all of which are radioactive; their mass numbers range from 188 to 229. There are also 24 known metastable excited states. The longest-lived isotope is 210At, which has a half-life of 8.1 hours; the longest-lived isotope existing in naturally occurring decay chains is 219At with a half-life of 56 seconds.
Lead (82Pb) has four observationally stable isotopes: 204Pb, 206Pb, 207Pb, 208Pb. Lead-204 is entirely a primordial nuclide and is not a radiogenic nuclide. The three isotopes lead-206, lead-207, and lead-208 represent the ends of three decay chains: the uranium series, the actinium series, and the thorium series, respectively; a fourth decay chain, the neptunium series, terminates with the thallium isotope 205Tl. The three series terminating in lead represent the decay chain products of long-lived primordial 238U, 235U, and 232Th. Each isotope also occurs, to some extent, as primordial isotopes that were made in supernovae, rather than radiogenically as daughter products. The fixed ratio of lead-204 to the primordial amounts of the other lead isotopes may be used as the baseline to estimate the extra amounts of radiogenic lead present in rocks as a result of decay from uranium and thorium.
Bismuth (83Bi) has 41 known isotopes, ranging from 184Bi to 224Bi. Bismuth has no stable isotopes, but does have one very long-lived isotope; thus, the standard atomic weight can be given as 208.98040(1). Although bismuth-209 is now known to be radioactive, it has classically been considered to be a stable isotope because it has a half-life of approximately 2.01×1019 years, which is more than a billion times the age of the universe. Besides 209Bi, the most stable bismuth radioisotopes are 210mBi with a half-life of 3.04 million years, 208Bi with a half-life of 368,000 years and 207Bi, with a half-life of 32.9 years, none of which occurs in nature. All other isotopes have half-lives under 1 year, most under a day. Of naturally occurring radioisotopes, the most stable is radiogenic 210Bi with a half-life of 5.012 days. 210mBi is unusual for being a nuclear isomer with a half-life multiple orders of magnitude longer than that of the ground state.
Promethium (61Pm) is an artificial element, except in trace quantities as a product of spontaneous fission of 238U and 235U and alpha decay of 151Eu, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. It was first synthesized in 1945.
Technetium (43Tc) is one of the two elements with Z < 83 that have no stable isotopes; the other such element is promethium. It is primarily artificial, with only trace quantities existing in nature produced by spontaneous fission or neutron capture by molybdenum. The first isotopes to be synthesized were 97Tc and 99Tc in 1936, the first artificial element to be produced. The most stable radioisotopes are 97Tc, 98Tc, and 99Tc.
Naturally occurring vanadium (23V) is composed of one stable isotope 51V and one radioactive isotope 50V with a half-life of 2.71×1017 years. 24 artificial radioisotopes have been characterized (in the range of mass number between 40 and 65) with the most stable being 49V with a half-life of 330 days, and 48V with a half-life of 15.9735 days. All of the remaining radioactive isotopes have half-lives shorter than an hour, the majority of them below 10 seconds, the least stable being 42V with a half-life shorter than 55 nanoseconds, with all of the isotopes lighter than it, and none of the heavier, have unknown half-lives. In 4 isotopes, metastable excited states were found (including 2 metastable states for 60V), which adds up to 5 meta states.
Neptunium (93Np) is usually considered an artificial element, although trace quantities are found in nature, so a standard atomic weight cannot be given. Like all trace or artificial elements, it has no stable isotopes. The first isotope to be synthesized and identified was 239Np in 1940, produced by bombarding 238
U
with neutrons to produce 239
U
, which then underwent beta decay to 239
Np
.
Plutonium (94Pu) is an artificial element, except for trace quantities resulting from neutron capture by uranium, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. It was synthesized long before being found in nature, the first isotope synthesized being plutonium-238 in 1940. Twenty plutonium radioisotopes have been characterized. The most stable are plutonium-244 with a half-life of 80.8 million years; plutonium-242 with a half-life of 373,300 years; and plutonium-239 with a half-life of 24,110 years; and plutonium-240 with a half-life of 6,560 years. This element also has eight meta states; all have half-lives of less than one second.
Americium (95Am) is an artificial element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no known stable isotopes. The first isotope to be synthesized was 241Am in 1944. The artificial element decays by ejecting alpha particles. Americium has an atomic number of 95. Despite 243
Am being an order of magnitude longer lived than 241
Am, the former is harder to obtain than the latter as more of it is present in spent nuclear fuel.
Curium (96Cm) is an artificial element with an atomic number of 96. Because it is an artificial element, a standard atomic weight cannot be given, and it has no stable isotopes. The first isotope synthesized was 242Cm in 1944, which has 146 neutrons.
Berkelium (97Bk) is an artificial element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 243Bk in 1949. There are 20 known radioisotopes, from 230Bk and 233Bk to 253Bk, and 6 nuclear isomers. The longest-lived isotope is 247Bk with a half-life of 1,380 years.
Californium (98Cf) is an artificial element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 245Cf in 1950. There are 20 known radioisotopes ranging from 237Cf to 256Cf and one nuclear isomer, 249mCf. The longest-lived isotope is 251Cf with a half-life of 898 years.
Meitnerium (109Mt) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 266Mt in 1982, and this is also the only isotope directly synthesized; all other isotopes are only known as decay products of heavier elements. There are eight known isotopes, from 266Mt to 278Mt. There may also be two isomers. The longest-lived of the known isotopes is 278Mt with a half-life of 8 seconds. The unconfirmed heavier 282Mt appears to have an even longer half-life of 67 seconds.
Darmstadtium (110Ds) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 269Ds in 1994. There are 11 known radioisotopes from 267Ds to 281Ds and 2 or 3 known isomers. The longest-lived isotope is 281Ds with a half-life of 14 seconds.
Plutonium-242 is one of the isotopes of plutonium, the second longest-lived, with a half-life of 375,000 years. The half-life of 242Pu is about 15 times that of 239Pu; so it is one-fifteenth as radioactive, and not one of the larger contributors to nuclear waste radioactivity. 242Pu's gamma ray emissions are also weaker than those of the other isotopes.
Actinium-225 is an isotope of actinium. It undergoes alpha decay to francium-221 with a half-life of 10 days, and is an intermediate decay product in the neptunium series. Except for minuscule quantities arising from this decay chain in nature, 225Ac is entirely synthetic.