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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.
There are 19 known radioisotopes ranging from 233Cm to 251Cm. There are also ten known nuclear isomers. The longest-lived isotope is 247Cm, with half-life 15.6 million years – orders of magnitude longer than that of any known isotope beyond curium, and long enough to study as a possible extinct radionuclide that would be produced by the r-process. [2] [3] The longest-lived isomer is 246mCm with a half-life of 1.12 seconds.
Nuclide [n 1] | Z | N | Isotopic mass (Da) [n 2] [n 3] | Half-life [n 4] | Decay mode [n 5] | Daughter isotope | Spin and parity [n 6] [n 4] | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Excitation energy [n 4] | |||||||||||||||||||
233Cm | 96 | 137 | 233.05077(8) | 23+13 −6 s | β+ (80%) | 233Am | 3/2+# | ||||||||||||
α (20%) | 229Pu | ||||||||||||||||||
234Cm | 96 | 138 | 234.05016(2) | 52(9) s | β+ (71%) | 234Am | 0+ | ||||||||||||
α (27%) | 230Pu | ||||||||||||||||||
SF (2%) | (various) | ||||||||||||||||||
235Cm [4] | 96 | 139 | 235.05143(22)# | 300+250 −100 s | β+ (99.0%) | 235Am | (5/2+) | ||||||||||||
α (1.0%) | 231Pu | ||||||||||||||||||
236Cm | 96 | 140 | 236.05141(22)# | 6.8(8) min | β+ (82%) | 236Am | 0+ | ||||||||||||
α (18%) | 232Pu | ||||||||||||||||||
SF (<0.1%) [5] | (various) | ||||||||||||||||||
237Cm [6] [4] | 96 | 141 | 237.05290(22)# | >660 s | β+ | 237Am | (5/2+) | ||||||||||||
α (<1%) | 233Pu | ||||||||||||||||||
238Cm [6] | 96 | 142 | 238.05303(4) | 2.2(4) h | EC (~94%) | 238Am | 0+ | ||||||||||||
α (~6%) | 234Pu | ||||||||||||||||||
239Cm [1] | 96 | 143 | 239.05496(11)# | 2.5(4) h | β+ | 239Am | (7/2−) | ||||||||||||
α (6.2x10−3%) | 235Pu | ||||||||||||||||||
240Cm | 96 | 144 | 240.0555295(25) | 27(1) d | α (99.5%) | 236Pu | 0+ | ||||||||||||
EC (.5%) | 240Am | ||||||||||||||||||
SF (3.9×10−6%) | (various) | ||||||||||||||||||
241Cm | 96 | 145 | 241.0576530(23) | 32.8(2) d | EC (99%) | 241Am | 1/2+ | ||||||||||||
α (1%) | 237Pu | ||||||||||||||||||
242Cm [n 7] | 96 | 146 | 242.0588358(20) | 162.8(2) d | α [n 8] | 238Pu | 0+ | ||||||||||||
SF (6.33×10−6%) | (various) | ||||||||||||||||||
CD (10−14%) [n 9] | 208Pb 34Si | ||||||||||||||||||
242mCm | 2800(100) keV | 180(70) ns | |||||||||||||||||
243Cm | 96 | 147 | 243.0613891(22) | 29.1(1) y | α (99.71%) | 239Pu | 5/2+ | ||||||||||||
EC (.29%) | 243Am | ||||||||||||||||||
SF (5.3×10−9%) | (various) | ||||||||||||||||||
243mCm | 87.4(1) keV | 1.08(3) μs | IT | 243Cm | 1/2+ | ||||||||||||||
244Cm [n 7] | 96 | 148 | 244.0627526(20) | 18.10(2) y | α | 240Pu | 0+ | ||||||||||||
SF (1.34×10−4%) | (various) | ||||||||||||||||||
244m1Cm | 1040.188(12) keV | 34(2) ms | IT | 244Cm | 6+ | ||||||||||||||
244m2Cm | 1100(900)# keV | >500 ns | SF | (various) | |||||||||||||||
245Cm | 96 | 149 | 245.0654912(22) | 8.5(1)×103 y | α | 241Pu | 7/2+ | ||||||||||||
SF (6.1×10−7%) | (various) | ||||||||||||||||||
245mCm | 355.92(10) keV | 290(20) ns | IT | 245Cm | 1/2+ | ||||||||||||||
246Cm | 96 | 150 | 246.0672237(22) | 4.76(4)×103 y | α (99.97%) | 242Pu | 0+ | ||||||||||||
SF (.0261%) | (various) | ||||||||||||||||||
246mCm | 1179.66(13) keV | 1.12(0.24) s | IT | 246Cm | 8− | ||||||||||||||
247Cm | 96 | 151 | 247.070354(5) | 1.56(5)×107 y | α | 243Pu | 9/2− | ||||||||||||
247m1Cm | 227.38(19) keV | 26.3(0.3) μs | IT | 247Cm | 5/2+ | ||||||||||||||
247m2Cm | 404.90(3) keV | 100.6(0.6) ns | IT | 247Cm | 1/2+ | ||||||||||||||
248Cm | 96 | 152 | 248.072349(5) | 3.48(6)×105 y | α (91.74%) | 244Pu | 0+ | ||||||||||||
SF (8.26%) | (various) | ||||||||||||||||||
248mCm | 1458.1(1) keV | 146(18) μs | IT | 248Cm | (8−) | ||||||||||||||
249Cm | 96 | 153 | 249.075953(5) | 64.15(3) min | β− | 249Bk | 1/2(+) | ||||||||||||
249mCm | 48.758(17) keV | 23 μs | α | 245Pu | (7/2+) | ||||||||||||||
250Cm | 96 | 154 | 250.078357(12) | 8300# y | SF (74%) [n 10] | (various) | 0+ | ||||||||||||
α (18%) | 246Pu | ||||||||||||||||||
β− (8%) | 250Bk | ||||||||||||||||||
251Cm | 96 | 155 | 251.082285(24) | 16.8(2) min | β− | 251Bk | (1/2+) | ||||||||||||
This table header & footer: |
CD: | Cluster decay |
EC: | Electron capture |
SF: | Spontaneous fission |
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 | |||||
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Protactinium (91Pa) has no stable isotopes. The four naturally occurring isotopes allow a standard atomic weight to be given.
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.
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.
There are 39 known isotopes of radon (86Rn), from 193Rn to 231Rn; all are radioactive. The most stable isotope is 222Rn with a half-life of 3.823 days, which decays into 218
Po
. Six isotopes of radon, 217, 218, 219, 220, 221, 222Rn, occur in trace quantities in nature as decay products of, respectively, 217At, 218At, 223Ra, 224Ra, 225Ra, and 226Ra. 217Rn and 221Rn are produced in rare branches in the decay chain of trace quantities of 237Np; 222Rn is an intermediate step in the decay chain of 238U; 219Rn is an intermediate step in the decay chain of 235U; and 220Rn occurs in the decay chain of 232Th.
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.
Natural holmium (67Ho) contains one observationally stable isotope, 165Ho. The below table lists 36 isotopes spanning 140Ho through 175Ho as well as 33 nuclear isomers. Among the known synthetic radioactive isotopes; the most stable one is 163Ho, with a half-life of 4,570 years. All other radioisotopes have half-lives not greater than 1.117 days in their ground states, and most have half-lives under 3 hours.
Naturally occurring dysprosium (66Dy) is composed of 7 stable isotopes, 156Dy, 158Dy, 160Dy, 161Dy, 162Dy, 163Dy and 164Dy, with 164Dy being the most abundant. Twenty-nine radioisotopes have been characterized, with the most stable being 154Dy with a half-life of 1.4 million years, 159Dy with a half-life of 144.4 days, and 166Dy with a half-life of 81.6 hours. All of the remaining radioactive isotopes have half-lives that are less than 10 hours, and the majority of these have half-lives that are less than 30 seconds. This element also has 12 meta states, with the most stable being 165mDy, 147mDy and 145mDy.
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.
Naturally occurring praseodymium (59Pr) is composed of one stable isotope, 141Pr. Thirty-eight radioisotopes have been characterized with the most stable being 143Pr, with a half-life of 13.57 days and 142Pr, with a half-life of 19.12 hours. All of the remaining radioactive isotopes have half-lives that are less than 5.985 hours and the majority of these have half-lives that are less than 33 seconds. This element also has 15 meta states with the most stable being 138mPr, 142mPr and 134mPr.
Naturally occurring lanthanum (57La) is composed of one stable (139La) and one radioactive (138La) isotope, with the stable isotope, 139La, being the most abundant (99.91% natural abundance). There are 39 radioisotopes that have been characterized, with the most stable being 138La, with a half-life of 1.02×1011 years; 137La, with a half-life of 60,000 years and 140La, with a half-life of 1.6781 days. The remaining radioactive isotopes have half-lives that are less than a day and the majority of these have half-lives that are less than 1 minute. This element also has 12 nuclear isomers, the longest-lived of which is 132mLa, with a half-life of 24.3 minutes. Lighter isotopes mostly decay to isotopes of barium and heavy ones mostly decay to isotopes of cerium. 138La can decay to both.
Naturally occurring barium (56Ba) is a mix of six stable isotopes and one very long-lived radioactive primordial isotope, barium-130, identified as being unstable by geochemical means (from analysis of the presence of its daughter xenon-130 in rocks) in 2001. This nuclide decays by double electron capture (absorbing two electrons and emitting two neutrinos), with a half-life of (0.5–2.7)×1021 years (about 1011 times the age of the universe).
Indium (49In) consists of two primordial nuclides, with the most common (~ 95.7%) nuclide (115In) being measurably though weakly radioactive. Its spin-forbidden decay has a half-life of 4.41×1014 years, much longer than the currently accepted age of the Universe.
Naturally occurring cadmium (48Cd) is composed of 8 isotopes. For two of them, natural radioactivity was observed, and three others are predicted to be radioactive but their decays have not been observed, due to extremely long half-lives. The two natural radioactive isotopes are 113Cd (beta decay, half-life is 8.04 × 1015 years) and 116Cd (two-neutrino double beta decay, half-life is 2.8 × 1019 years). The other three are 106Cd, 108Cd (double electron capture), and 114Cd (double beta decay); only lower limits on their half-life times have been set. Three isotopes—110Cd, 111Cd, and 112Cd—are theoretically stable. Among the isotopes absent in natural cadmium, the most long-lived are 109Cd with a half-life of 462.6 days, and 115Cd with a half-life of 53.46 hours. All of the remaining radioactive isotopes have half-lives that are less than 2.5 hours and the majority of these have half-lives that are less than 5 minutes. This element also has 12 known meta states, with the most stable being 113mCd (t1/2 14.1 years), 115mCd (t1/2 44.6 days) and 117mCd (t1/2 3.36 hours).
Natural palladium (46Pd) is composed of six stable isotopes, 102Pd, 104Pd, 105Pd, 106Pd, 108Pd, and 110Pd, although 102Pd and 110Pd are theoretically unstable. The most stable radioisotopes are 107Pd with a half-life of 6.5 million years, 103Pd with a half-life of 17 days, and 100Pd with a half-life of 3.63 days. Twenty-three other radioisotopes have been characterized with atomic weights ranging from 90.949 u (91Pd) to 128.96 u (129Pd). Most of these have half-lives that are less than 30 minutes except 101Pd, 109Pd, and 112Pd.
Arsenic (33As) has 32 known isotopes and at least 10 isomers. Only one of these isotopes, 75As, is stable; as such, it is considered a monoisotopic element. The longest-lived radioisotope is 73As with a half-life of 80 days.
Naturally occurring scandium (21Sc) is composed of one stable isotope, 45Sc. Twenty-five radioisotopes have been characterized, with the most stable being 46Sc with a half-life of 83.8 days, 47Sc with a half-life of 3.35 days, and 48Sc with a half-life of 43.7 hours and 44Sc with a half-life of 3.97 hours. All the remaining isotopes have half-lives that are less than four hours, and the majority of these have half-lives that are less than two minutes, the least stable being proton unbound 39Sc with a half-life shorter than 300 nanoseconds. This element also has 13 meta states with the most stable being 44m2Sc.
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.
Fermium (100Fm) is a synthetic element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be discovered was 255Fm in 1952. 250Fm was independently synthesized shortly after the discovery of 255Fm. There are 20 known radioisotopes ranging in atomic mass from 241Fm to 260Fm, and 4 nuclear isomers, 247mFm, 250mFm, 251mFm, and 253mFm. The longest-lived isotope is 257Fm with a half-life of 100.5 days, and the longest-lived isomer is 247mFm with a half-life of 5.1 seconds.
Einsteinium (99Es) 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 discovered was 253Es in 1952. There are 18 known radioisotopes from 240Es to 257Es, and 5 nuclear isomers. The longest-lived isotope is 252Es with a half-life of 471.7 days, or around 1.293 years.
Mendelevium (101Md) is a synthetic 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 256Md in 1955. There are 17 known radioisotopes, ranging in atomic mass from 244Md to 260Md, and 5 isomers. The longest-lived isotope is 258Md with a half-life of 51.3 days, and the longest-lived isomer is 258mMd with a half-life of 57 minutes.