
Caesium (55Cs) has 41 known isotopes, ranging in mass number from 112 to 152. Only one isotope, 133Cs, is stable. The longest-lived radioisotopes are 135Cs with a half-life of 1.33 million years, 137
Cs
with a half-life of 30.1671 years and 134Cs with a half-life of 2.0652 years. All other isotopes have half-lives less than 2 weeks, most under an hour.
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Standard atomic weight Ar°(Cs) | ||||||||||||||||||||||||||||||||||||||
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Beginning in 1945 with the commencement of nuclear testing, caesium radioisotopes were released into the atmosphere where caesium is absorbed readily into solution and is returned to the surface of the Earth as a component of radioactive fallout. Once caesium enters the ground water, it is deposited on soil surfaces and removed from the landscape primarily by particle transport. As a result, the input function of these isotopes can be estimated as a function of time.
List of isotopes
Nuclide | Z | N | Isotopic mass (Da) | Half-life | Decay mode | Daughter isotope | Spin and parity | Isotopic abundance | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Excitation energy | |||||||||||||||||||
112Cs | 55 | 57 | 111.95017(12)# | 490(30) μs | p (>99.74%) | 111Xe | 1+# | ||||||||||||
α (<0.26%) | 108I | ||||||||||||||||||
113Cs | 55 | 58 | 112.9444285(92) | 16.94(9) μs | p | 112Xe | (3/2+) | ||||||||||||
114Cs | 55 | 59 | 113.941292(91) | 570(20) ms | β+ (91.1%) | 114Xe | (1+) | ||||||||||||
β+, p (8.7%) | 113I | ||||||||||||||||||
β+, α (0.19%) | 110Te | ||||||||||||||||||
α (0.018%) | 110I | ||||||||||||||||||
115Cs | 55 | 60 | 114.93591(11)# | 1.4(8) s | β+ (99.93%) | 115Xe | 9/2+# | ||||||||||||
β+, p (0.07%) | 114I | ||||||||||||||||||
116Cs | 55 | 61 | 115.93340(11)# | 700(40) ms | β+ (99.67%) | 116Xe | (1+) | ||||||||||||
β+, p (0.28%) | 115I | ||||||||||||||||||
β+, α (0.049%) | 112Te | ||||||||||||||||||
116mCs | 100(60)# keV | 3.85(13) s | β+ (99.56%) | 116Xe | (7+) | ||||||||||||||
β+, p (0.44%) | 115I | ||||||||||||||||||
β+, α (0.0034%) | 112Te | ||||||||||||||||||
117Cs | 55 | 62 | 116.928617(67) | 8.4(6) s | β+ | 117Xe | 9/2+# | ||||||||||||
117mCs | 150(80)# keV | 6.5(4) s | β+ | 117Xe | 3/2+# | ||||||||||||||
118Cs | 55 | 63 | 117.926560(14) | 14(2) s | β+ (99.98%) | 118Xe | 2(−) | ||||||||||||
β+, p (0.021%) | 117I | ||||||||||||||||||
β+, α (0.0012%) | 114Te | ||||||||||||||||||
118m1Cs | X keV | 17(3) s | β+ (99.98%) | 118Xe | (7−) | ||||||||||||||
β+, p (0.021%) | 117I | ||||||||||||||||||
β+, α (0.0012%) | 114Te | ||||||||||||||||||
118m2Cs | Y keV | (6+) | |||||||||||||||||
118m3Cs | 65.9 keV | IT | 118Cs | (3−) | |||||||||||||||
118m4Cs | 125.9+X keV | 550(60) ns | IT | 118m1Cs | (7+) | ||||||||||||||
118m5Cs | 195.2+X keV | <500 ns | IT | 118m4Cs | (8+) | ||||||||||||||
119Cs | 55 | 64 | 118.9223 77(15) | 43.0(2) s | β+ | 119Xe | 9/2+ | ||||||||||||
β+, α (<2×10−6%) | 115Te | ||||||||||||||||||
119mCs | 50(30)# keV | 30.4(1) s | β+ | 119Xe | 3/2+ | ||||||||||||||
120Cs | 55 | 65 | 119.920677(11) | 60.4(6) s | β+ | 120Xe | 2+ | ||||||||||||
β+, α (<2×10−5%) | 116Te | ||||||||||||||||||
β+, p (<7×10−6%) | 119I | ||||||||||||||||||
120mCs | 100(60)# keV | 57(6) s | β+ | 120Xe | (7−) | ||||||||||||||
β+, α (<2×10−5%) | 116Te | ||||||||||||||||||
β+, p (<7×10−6%) | 119I | ||||||||||||||||||
121Cs | 55 | 66 | 120.917227(15) | 155(4) s | β+ | 121Xe | 3/2+ | ||||||||||||
121mCs | 68.5(3) keV | 122(3) s | β+ (83%) | 121Xe | 9/2+ | ||||||||||||||
IT (17%) | 121Cs | ||||||||||||||||||
122Cs | 55 | 67 | 121.916108(36) | 21.18(19) s | β+ | 122Xe | 1+ | ||||||||||||
β+, α (<2×10−7%) | 118Te | ||||||||||||||||||
122m1Cs | 45.87(12) keV | >1 μs | IT | 122Cs | 3+ | ||||||||||||||
122m2Cs | 140(30) keV | 3.70(11) min | β+ | 122Xe | 8− | ||||||||||||||
122m3Cs | 127.07(16) keV | 360(20) ms | IT | 122Cs | 5− | ||||||||||||||
123Cs | 55 | 68 | 122.912996(13) | 5.88(3) min | β+ | 123Xe | 1/2+ | ||||||||||||
123m1Cs | 156.27(5) keV | 1.64(12) s | IT | 123Cs | 11/2− | ||||||||||||||
123m2Cs | 252(6) keV | 114(5) ns | IT | 123Cs | (9/2+) | ||||||||||||||
124Cs | 55 | 69 | 123.9122474(98) | 30.9(4) s | β+ | 124Xe | 1+ | ||||||||||||
124mCs | 462.63(14) keV | 6.41(7) s | IT (99.89%) | 124Cs | (7)+ | ||||||||||||||
β+ (0.11%) | 124Xe | ||||||||||||||||||
125Cs | 55 | 70 | 124.9097260(83) | 44.35(29) min | β+ | 125Xe | 1/2+ | ||||||||||||
125mCs | 266.1(11) keV | 900(30) ms | IT | 125Cs | (11/2−) | ||||||||||||||
126Cs | 55 | 71 | 125.909446(11) | 1.64(2) min | β+ | 126Xe | 1+ | ||||||||||||
126m1Cs | 273.0(7) keV | ~1 μs | IT | 126Cs | (4−) | ||||||||||||||
126m2Cs | 596.1(11) keV | 171(14) μs | IT | 126Cs | 8−# | ||||||||||||||
127Cs | 55 | 72 | 126.9074175(60) | 6.25(10) h | β+ | 127Xe | 1/2+ | ||||||||||||
127mCs | 452.23(21) keV | 55(3) μs | IT | 127Cs | (11/2)− | ||||||||||||||
128Cs | 55 | 73 | 127.9077485(57) | 3.640(14) min | β+ | 128Xe | 1+ | ||||||||||||
129Cs | 55 | 74 | 128.9060659(49) | 32.06(6) h | β+ | 129Xe | 1/2+ | ||||||||||||
129mCs | 575.40(14) keV | 718(21) ns | IT | 127Cs | (11/2−) | ||||||||||||||
130Cs | 55 | 75 | 129.9067093(90) | 29.21(4) min | β+ (98.4%) | 130Xe | 1+ | ||||||||||||
β− (1.6%) | 130Ba | ||||||||||||||||||
130mCs | 163.25(11) keV | 3.46(6) min | IT (99.84%) | 130Cs | 5− | ||||||||||||||
β+ (0.16%) | 130Xe | ||||||||||||||||||
131Cs | 55 | 76 | 130.90546846(19) | 9.689(16) d | EC | 131Xe | 5/2+ | ||||||||||||
132Cs | 55 | 77 | 131.9064378(11) | 6.480(6) d | β+ (98.13%) | 132Xe | 2+ | ||||||||||||
β− (1.87%) | 132Ba | ||||||||||||||||||
133Cs | 55 | 78 | 132.905451958(8) | Stable | 7/2+ | 1.0000 | |||||||||||||
134Cs | 55 | 79 | 133.906718501(17) | 2.0650(4) y | β− | 134Ba | 4+ | ||||||||||||
EC (3.0×10−4%) | 134Xe | ||||||||||||||||||
134mCs | 138.7441(26) keV | 2.912(2) h | IT | 134Cs | 8− | ||||||||||||||
135Cs | 55 | 80 | 134.90597691(39) | 1.33(19)×106 y | β− | 135Ba | 7/2+ | ||||||||||||
135mCs | 1632.9(15) keV | 53(2) min | IT | 135Cs | 19/2− | ||||||||||||||
136Cs | 55 | 81 | 135.9073114(20) | 13.01(5) d | β− | 136Ba | 5+ | ||||||||||||
136mCs | 517.9(1) keV | 17.5(2) s | β−? | 136Ba | 8− | ||||||||||||||
IT? | 136Cs | ||||||||||||||||||
137Cs | 55 | 82 | 136.90708930(32) | 30.04(4) y | β− (94.70%) | 137mBa | 7/2+ | ||||||||||||
β− (5.30%) | 137Ba | ||||||||||||||||||
138Cs | 55 | 83 | 137.9110171(98) | 33.5(2) min | β− | 138Ba | 3− | ||||||||||||
138mCs | 79.9(3) keV | 2.91(10) min | IT (81%) | 138Cs | 6− | ||||||||||||||
β− (19%) | 138Ba | ||||||||||||||||||
139Cs | 55 | 84 | 138.9133638(34) | 9.27(5) min | β− | 139Ba | 7/2+ | ||||||||||||
140Cs | 55 | 85 | 139.9172837(88) | 63.7(3) s | β− | 140Ba | 1− | ||||||||||||
140mCs | 13.931(21) keV | 471(51) ns | IT | 140Cs | (2)− | ||||||||||||||
141Cs | 55 | 86 | 140.9200453(99) | 24.84(16) s | β− (99.97%) | 141Ba | 7/2+ | ||||||||||||
β−, n (0.0342%) | 140Ba | ||||||||||||||||||
142Cs | 55 | 87 | 141.9242995(76) | 1.687(10) s | β− (99.91%) | 142Ba | 0− | ||||||||||||
β−, n (0.089%) | 141Ba | ||||||||||||||||||
143Cs | 55 | 88 | 142.9273473(81) | 1.802(8) s | β− (98.38%) | 143Ba | 3/2+ | ||||||||||||
β−, n (1.62%) | 142Ba | ||||||||||||||||||
144Cs | 55 | 89 | 143.932075(22) | 994(6) ms | β− (97.02%) | 144Ba | 1− | ||||||||||||
β−, n (2.98%) | 143Ba | ||||||||||||||||||
144mCs | 92.2(5) keV | 1.1(1) μs | IT | 144Cs | (4−) | ||||||||||||||
145Cs | 55 | 90 | 144.9355289(97) | 582(4) ms | β− (87.2%) | 145Ba | 3/2+ | ||||||||||||
β−, n (12.8%) | 144Ba | ||||||||||||||||||
145mCs | 762.9(4) keV | 0.5(1) μs | IT | 145Cs | 13/2# | ||||||||||||||
146Cs | 55 | 91 | 145.9406219(31) | 321.6(9) ms | β− (85.8%) | 146Ba | 1− | ||||||||||||
β−, n (14.2%) | 145Ba | ||||||||||||||||||
146mCs | 46.7(1) keV | 1.25(5) μs | IT | 146Cs | 4−# | ||||||||||||||
147Cs | 55 | 92 | 146.9442615(90) | 230.5(9) ms | β− (71.5%) | 147Ba | (3/2+) | ||||||||||||
β−, n (28.5%) | 146Ba | ||||||||||||||||||
147mCs | 701.4(4) keV | 190(20) ns | IT | 147Cs | 13/2# | ||||||||||||||
148Cs | 55 | 93 | 147.949639(14) | 151.8(10) ms | β− (71.3%) | 148Ba | (2−) | ||||||||||||
β−, n (28.7%) | 147Ba | ||||||||||||||||||
148mCs | 45.2(1) keV | 4.8(2) μs | IT | 148Cs | 4−# | ||||||||||||||
149Cs | 55 | 94 | 148.95352(43)# | 112.3(25) ms | β− (75%) | 149Ba | 3/2+# | ||||||||||||
β−, n (25%) | 148Ba | ||||||||||||||||||
150Cs | 55 | 95 | 149.95902(43)# | 81.0(26) ms | β− (~56%) | 150Ba | (2−) | ||||||||||||
β−, n (~44%) | 149Ba | ||||||||||||||||||
151Cs | 55 | 96 | 150.96320(54)# | 59(19) ms | β− | 151Ba | 3/2+# | ||||||||||||
This table header & footer: |
- mCs – Excited nuclear isomer.
- ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
- # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
- Modes of decay:
EC: Electron capture IT: Isomeric transition n: Neutron emission p: Proton emission - Bold italics symbol as daughter – Daughter product is nearly stable.
- Bold symbol as daughter – Daughter product is stable.
- ( ) spin value – Indicates spin with weak assignment arguments.
- # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
- Order of ground state and isomer is uncertain.
- Used to define the second
- Fission product
Caesium-131
Caesium-131, introduced in 2004 for brachytherapy by Isoray, has a half-life of 9.7 days and 30.4 keV energy.
Caesium-133
Caesium-133 is the only stable isotope of caesium. The SI base unit of time, the second, is defined by a specific caesium-133 transition. Since 1967, the official definition of a second is:
The second, symbol s, is defined by taking the fixed numerical value of the caesium frequency, ΔνCs, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be 9192631770 Hz, which is equal to s−1.
Caesium-134
Caesium-134 has a half-life of 2.0652 years. It is produced both directly (at a very small yield because 134Xe is stable) as a fission product and via neutron capture from nonradioactive 133Cs (neutron capture cross section 29 barns), which is a common fission product. Caesium-134 is not produced via beta decay of other fission product nuclides of mass 134 since beta decay stops at stable 134Xe. It is also not produced by nuclear weapons because 133Cs is created by beta decay of original fission products only long after the nuclear explosion is over.
The combined yield of 133Cs and 134Cs is given as 6.7896%. The proportion between the two will change with continued neutron irradiation. 134Cs also captures neutrons with a cross section of 140 barns, becoming long-lived radioactive 135Cs.
Caesium-134 undergoes beta decay (β−), producing 134Ba directly and emitting on average 2.23 gamma ray photons (mean energy 0.698 MeV).
Caesium-135
Nuclide | t1⁄2 | Yield | Q | βγ |
---|---|---|---|---|
(Ma) | (%) | (keV) | ||
99Tc | 0.211 | 6.1385 | 294 | β |
126Sn | 0.230 | 0.1084 | 4050 | βγ |
79Se | 0.327 | 0.0447 | 151 | β |
135Cs | 1.33 | 6.9110 | 269 | β |
93Zr | 1.53 | 5.4575 | 91 | βγ |
107Pd | 6.5 | 1.2499 | 33 | β |
129I | 16.14 | 0.8410 | 194 | βγ |
Caesium-135 is a mildly radioactive isotope of caesium with a half-life of 1.33 million years. It decays via emission of a low-energy beta particle into the stable isotope barium-135. Caesium-135 is one of the seven long-lived fission products and the only alkaline one. In most types of nuclear reprocessing, it stays with the medium-lived fission products (including 137
Cs which can only be separated from 135
Cs via isotope separation) rather than with other long-lived fission products. Except in the Molten salt reactor, where 135
Cs is created as a completely separate stream outside the fuel (after the decay of bubble-separated 135
Cs). The low decay energy, lack of gamma radiation, and long half-life of 135Cs make this isotope much less hazardous than 137Cs or 134Cs.
Its precursor 135Xe has a high fission product yield (e.g., 6.3333% for 235U and thermal neutrons) but also has the highest known thermal neutron capture cross section of any nuclide. Because of this, much of the 135Xe produced in current thermal reactors (as much as >90% at steady-state full power) will be converted to extremely long-lived (half-life on the order of 1021 years) 136
Xe before it can decay to 135
Cs despite the relatively short half life of 135
Xe. Little or no 135
Xe will be destroyed by neutron capture after a reactor shutdown, or in a molten salt reactor that continuously removes xenon from its fuel, a fast neutron reactor, or a nuclear weapon. The xenon pit is a phenomenon of excess neutron absorption through 135
Xe buildup in the reactor after a reduction in power or a shutdown and is often managed by letting the 135
Xe decay away to a level at which neutron flux can be safely controlled via control rods again.
A nuclear reactor will also produce much smaller amounts of 135Cs from the nonradioactive fission product 133Cs by successive neutron capture to 134Cs and then 135Cs.
The thermal neutron capture cross section and resonance integral of 135Cs are 8.3 ± 0.3 and 38.1 ± 2.6 barns respectively. Disposal of 135Cs by nuclear transmutation is difficult, because of the low cross section as well as because neutron irradiation of mixed-isotope fission caesium produces more 135Cs from stable 133Cs. In addition, the intense medium-term radioactivity of 137Cs makes handling of nuclear waste difficult.
- ANL factsheet
Caesium-136
Caesium-136 has a half-life of 13.01 days. It is produced both directly (at a very small yield because 136Xe is beta-stable) as a fission product and via neutron capture from long-lived 135Cs, which is a common fission product. It is also not produced by nuclear weapons because 135Cs is created by beta decay of original fission products only long after the nuclear explosion is over. Caesium-136 undergoes beta decay (β−), producing 136Ba directly.
Caesium-137
Caesium-137, with a half-life of 30.17 years, is one of the two principal medium-lived fission products, along with 90Sr, which are responsible for most of the radioactivity of spent nuclear fuel after several years of cooling, up to several hundred years after use. It constitutes most of the radioactivity still left from the Chernobyl accident and is a major health concern for decontaminating land near the Fukushima nuclear power plant.137Cs beta decays to barium-137m (a short-lived nuclear isomer) then to nonradioactive barium-137. Caesium-137 does not emit gamma radiation directly, all observed radiation is due to the daughter isotope barium-137m.
137Cs has a very low rate of neutron capture and cannot yet be feasibly disposed of in this way unless advances in neutron beam collimation (not otherwise achievable by magnetic fields), uniquely available only from within muon catalyzed fusion experiments (not in the other forms of Accelerator Transmutation of Nuclear Waste) enables production of neutrons at high enough intensity to offset and overcome these low capture rates; until then, therefore, 137Cs must simply be allowed to decay.
137Cs has been used as a tracer in hydrologic studies, analogous to the use of 3H.
Other isotopes of caesium
The other isotopes have half-lives from a few days to fractions of a second. Almost all caesium produced from nuclear fission comes from beta decay of originally more neutron-rich fission products, passing through isotopes of iodine then isotopes of xenon. Because these elements are volatile and can diffuse through nuclear fuel or air, caesium is often created far from the original site of fission.
References
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- Isoray. "Why Cesium-131". Archived from the original on 2019-06-30. Retrieved 2017-12-05.
- Although the phase used here is more terse than in the previous definition, it still has the same meaning. This is made clear in the 9th SI Brochure, which almost immediately after the definition on p. 130 states: "The effect of this definition is that the second is equal to the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the unperturbed ground state of the 133Cs atom."
- John L. Groh (2004). "Supplement to Chapter 11 of Reactor Physics Fundamentals" (PDF). CANTEACH project. Archived from the original (PDF) on 10 June 2011. Retrieved 14 May 2011.
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- Ohki, Shigeo; Takaki, Naoyuki (2002). "Transmutation of Cesium-135 With Fast Reactors" (PDF). Proceedings of the Seventh Information Exchange Meeting on Actinide and Fission Product Partitioning & Transmutation, Cheju, Korea.
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- Isotope masses from:
- Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
- Half-life, spin, and isomer data selected from the following sources.
- Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
- National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory.
- Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.
Caesium 55Cs has 41 known isotopes ranging in mass number from 112 to 152 Only one isotope 133Cs is stable The longest lived radioisotopes are 135Cs with a half life of 1 33 million years 137 Cs with a half life of 30 1671 years and 134Cs with a half life of 2 0652 years All other isotopes have half lives less than 2 weeks most under an hour Isotopes of caesium 55Cs Main isotopes Decayabun dance half life t1 2 mode pro duct131Cs synth 9 7 d e 131Xe133Cs 100 stable134Cs synth 2 0648 y e 134Xeb 134Ba135Cs trace 1 33 106 y b 135Ba137Cs synth 30 04 y b 137BaStandard atomic weight Ar Cs 132 905451 96 0 000000 06132 91 0 01 abridged viewtalkedit Beginning in 1945 with the commencement of nuclear testing caesium radioisotopes were released into the atmosphere where caesium is absorbed readily into solution and is returned to the surface of the Earth as a component of radioactive fallout Once caesium enters the ground water it is deposited on soil surfaces and removed from the landscape primarily by particle transport As a result the input function of these isotopes can be estimated as a function of time List of isotopesNuclide Z N Isotopic mass Da Half life Decay mode Daughter isotope Spin and parity Isotopic abundanceExcitation energy112Cs 55 57 111 95017 12 490 30 ms p gt 99 74 111Xe 1 a lt 0 26 108I113Cs 55 58 112 9444285 92 16 94 9 ms p 112Xe 3 2 114Cs 55 59 113 941292 91 570 20 ms b 91 1 114Xe 1 b p 8 7 113Ib a 0 19 110Tea 0 018 110I115Cs 55 60 114 93591 11 1 4 8 s b 99 93 115Xe 9 2 b p 0 07 114I116Cs 55 61 115 93340 11 700 40 ms b 99 67 116Xe 1 b p 0 28 115Ib a 0 049 112Te116mCs 100 60 keV 3 85 13 s b 99 56 116Xe 7 b p 0 44 115Ib a 0 0034 112Te117Cs 55 62 116 928617 67 8 4 6 s b 117Xe 9 2 117mCs 150 80 keV 6 5 4 s b 117Xe 3 2 118Cs 55 63 117 926560 14 14 2 s b 99 98 118Xe 2 b p 0 021 117Ib a 0 0012 114Te118m1Cs X keV 17 3 s b 99 98 118Xe 7 b p 0 021 117Ib a 0 0012 114Te118m2Cs Y keV 6 118m3Cs 65 9 keV IT 118Cs 3 118m4Cs 125 9 X keV 550 60 ns IT 118m1Cs 7 118m5Cs 195 2 X keV lt 500 ns IT 118m4Cs 8 119Cs 55 64 118 9223 77 15 43 0 2 s b 119Xe 9 2 b a lt 2 10 6 115Te119mCs 50 30 keV 30 4 1 s b 119Xe 3 2 120Cs 55 65 119 920677 11 60 4 6 s b 120Xe 2 b a lt 2 10 5 116Teb p lt 7 10 6 119I120mCs 100 60 keV 57 6 s b 120Xe 7 b a lt 2 10 5 116Teb p lt 7 10 6 119I121Cs 55 66 120 917227 15 155 4 s b 121Xe 3 2 121mCs 68 5 3 keV 122 3 s b 83 121Xe 9 2 IT 17 121Cs122Cs 55 67 121 916108 36 21 18 19 s b 122Xe 1 b a lt 2 10 7 118Te122m1Cs 45 87 12 keV gt 1 ms IT 122Cs 3 122m2Cs 140 30 keV 3 70 11 min b 122Xe 8 122m3Cs 127 07 16 keV 360 20 ms IT 122Cs 5 123Cs 55 68 122 912996 13 5 88 3 min b 123Xe 1 2 123m1Cs 156 27 5 keV 1 64 12 s IT 123Cs 11 2 123m2Cs 252 6 keV 114 5 ns IT 123Cs 9 2 124Cs 55 69 123 9122474 98 30 9 4 s b 124Xe 1 124mCs 462 63 14 keV 6 41 7 s IT 99 89 124Cs 7 b 0 11 124Xe125Cs 55 70 124 9097260 83 44 35 29 min b 125Xe 1 2 125mCs 266 1 11 keV 900 30 ms IT 125Cs 11 2 126Cs 55 71 125 909446 11 1 64 2 min b 126Xe 1 126m1Cs 273 0 7 keV 1 ms IT 126Cs 4 126m2Cs 596 1 11 keV 171 14 ms IT 126Cs 8 127Cs 55 72 126 9074175 60 6 25 10 h b 127Xe 1 2 127mCs 452 23 21 keV 55 3 ms IT 127Cs 11 2 128Cs 55 73 127 9077485 57 3 640 14 min b 128Xe 1 129Cs 55 74 128 9060659 49 32 06 6 h b 129Xe 1 2 129mCs 575 40 14 keV 718 21 ns IT 127Cs 11 2 130Cs 55 75 129 9067093 90 29 21 4 min b 98 4 130Xe 1 b 1 6 130Ba130mCs 163 25 11 keV 3 46 6 min IT 99 84 130Cs 5 b 0 16 130Xe131Cs 55 76 130 90546846 19 9 689 16 d EC 131Xe 5 2 132Cs 55 77 131 9064378 11 6 480 6 d b 98 13 132Xe 2 b 1 87 132Ba133Cs 55 78 132 905451958 8 Stable 7 2 1 0000134Cs 55 79 133 906718501 17 2 0650 4 y b 134Ba 4 EC 3 0 10 4 134Xe134mCs 138 7441 26 keV 2 912 2 h IT 134Cs 8 135Cs 55 80 134 90597691 39 1 33 19 106 y b 135Ba 7 2 135mCs 1632 9 15 keV 53 2 min IT 135Cs 19 2 136Cs 55 81 135 9073114 20 13 01 5 d b 136Ba 5 136mCs 517 9 1 keV 17 5 2 s b 136Ba 8 IT 136Cs137Cs 55 82 136 90708930 32 30 04 4 y b 94 70 137mBa 7 2 b 5 30 137Ba138Cs 55 83 137 9110171 98 33 5 2 min b 138Ba 3 138mCs 79 9 3 keV 2 91 10 min IT 81 138Cs 6 b 19 138Ba139Cs 55 84 138 9133638 34 9 27 5 min b 139Ba 7 2 140Cs 55 85 139 9172837 88 63 7 3 s b 140Ba 1 140mCs 13 931 21 keV 471 51 ns IT 140Cs 2 141Cs 55 86 140 9200453 99 24 84 16 s b 99 97 141Ba 7 2 b n 0 0342 140Ba142Cs 55 87 141 9242995 76 1 687 10 s b 99 91 142Ba 0 b n 0 089 141Ba143Cs 55 88 142 9273473 81 1 802 8 s b 98 38 143Ba 3 2 b n 1 62 142Ba144Cs 55 89 143 932075 22 994 6 ms b 97 02 144Ba 1 b n 2 98 143Ba144mCs 92 2 5 keV 1 1 1 ms IT 144Cs 4 145Cs 55 90 144 9355289 97 582 4 ms b 87 2 145Ba 3 2 b n 12 8 144Ba145mCs 762 9 4 keV 0 5 1 ms IT 145Cs 13 2 146Cs 55 91 145 9406219 31 321 6 9 ms b 85 8 146Ba 1 b n 14 2 145Ba146mCs 46 7 1 keV 1 25 5 ms IT 146Cs 4 147Cs 55 92 146 9442615 90 230 5 9 ms b 71 5 147Ba 3 2 b n 28 5 146Ba147mCs 701 4 4 keV 190 20 ns IT 147Cs 13 2 148Cs 55 93 147 949639 14 151 8 10 ms b 71 3 148Ba 2 b n 28 7 147Ba148mCs 45 2 1 keV 4 8 2 ms IT 148Cs 4 149Cs 55 94 148 95352 43 112 3 25 ms b 75 149Ba 3 2 b n 25 148Ba150Cs 55 95 149 95902 43 81 0 26 ms b 56 150Ba 2 b n 44 149Ba151Cs 55 96 150 96320 54 59 19 ms b 151Ba 3 2 This table header amp footer viewmCs Excited nuclear isomer Uncertainty 1s is given in concise form in parentheses after the corresponding last digits Atomic mass marked value and uncertainty derived not from purely experimental data but at least partly from trends from the Mass Surface TMS Modes of decay EC Electron captureIT Isomeric transitionn Neutron emissionp Proton emission Bold italics symbol as daughter Daughter product is nearly stable Bold symbol as daughter Daughter product is stable spin value Indicates spin with weak assignment arguments Values marked are not purely derived from experimental data but at least partly from trends of neighboring nuclides TNN Order of ground state and isomer is uncertain Used to define the second Fission productCaesium 131Caesium 131 introduced in 2004 for brachytherapy by Isoray has a half life of 9 7 days and 30 4 keV energy Caesium 133Caesium 133 is the only stable isotope of caesium The SI base unit of time the second is defined by a specific caesium 133 transition Since 1967 the official definition of a second is The second symbol s is defined by taking the fixed numerical value of the caesium frequency DnCs the unperturbed ground state hyperfine transition frequency of the caesium 133 atom to be 9192 631 770 Hz which is equal to s 1 Caesium 134Caesium 134 has a half life of 2 0652 years It is produced both directly at a very small yield because 134Xe is stable as a fission product and via neutron capture from nonradioactive 133Cs neutron capture cross section 29 barns which is a common fission product Caesium 134 is not produced via beta decay of other fission product nuclides of mass 134 since beta decay stops at stable 134Xe It is also not produced by nuclear weapons because 133Cs is created by beta decay of original fission products only long after the nuclear explosion is over The combined yield of 133Cs and 134Cs is given as 6 7896 The proportion between the two will change with continued neutron irradiation 134Cs also captures neutrons with a cross section of 140 barns becoming long lived radioactive 135Cs Caesium 134 undergoes beta decay b producing 134Ba directly and emitting on average 2 23 gamma ray photons mean energy 0 698 MeV Caesium 135Long lived fission productsvte Nuclide t1 2 Yield Q bg Ma keV 99Tc 0 211 6 1385 294 b126Sn 0 230 0 1084 4050 bg79Se 0 327 0 0447 151 b135Cs 1 33 6 9110 269 b93Zr 1 53 5 4575 91 bg107Pd 6 5 1 2499 33 b129I 16 14 0 8410 194 bgDecay energy is split among b neutrino and g if any Per 65 thermal neutron fissions of 235U and 35 of 239Pu Has decay energy 380 keV but its decay product 126Sb has decay energy 3 67 MeV Lower in thermal reactors because 135Xe its predecessor readily absorbs neutrons Caesium 135 is a mildly radioactive isotope of caesium with a half life of 1 33 million years It decays via emission of a low energy beta particle into the stable isotope barium 135 Caesium 135 is one of the seven long lived fission products and the only alkaline one In most types of nuclear reprocessing it stays with the medium lived fission products including 137 Cs which can only be separated from 135 Cs via isotope separation rather than with other long lived fission products Except in the Molten salt reactor where 135 Cs is created as a completely separate stream outside the fuel after the decay of bubble separated 135 Cs The low decay energy lack of gamma radiation and long half life of 135Cs make this isotope much less hazardous than 137Cs or 134Cs Its precursor 135Xe has a high fission product yield e g 6 3333 for 235U and thermal neutrons but also has the highest known thermal neutron capture cross section of any nuclide Because of this much of the 135Xe produced in current thermal reactors as much as gt 90 at steady state full power will be converted to extremely long lived half life on the order of 1021 years 136 Xe before it can decay to 135 Cs despite the relatively short half life of 135 Xe Little or no 135 Xe will be destroyed by neutron capture after a reactor shutdown or in a molten salt reactor that continuously removes xenon from its fuel a fast neutron reactor or a nuclear weapon The xenon pit is a phenomenon of excess neutron absorption through 135 Xe buildup in the reactor after a reduction in power or a shutdown and is often managed by letting the 135 Xe decay away to a level at which neutron flux can be safely controlled via control rods again A nuclear reactor will also produce much smaller amounts of 135Cs from the nonradioactive fission product 133Cs by successive neutron capture to 134Cs and then 135Cs The thermal neutron capture cross section and resonance integral of 135Cs are 8 3 0 3 and 38 1 2 6 barns respectively Disposal of 135Cs by nuclear transmutation is difficult because of the low cross section as well as because neutron irradiation of mixed isotope fission caesium produces more 135Cs from stable 133Cs In addition the intense medium term radioactivity of 137Cs makes handling of nuclear waste difficult ANL factsheetCaesium 136Caesium 136 has a half life of 13 01 days It is produced both directly at a very small yield because 136Xe is beta stable as a fission product and via neutron capture from long lived 135Cs which is a common fission product It is also not produced by nuclear weapons because 135Cs is created by beta decay of original fission products only long after the nuclear explosion is over Caesium 136 undergoes beta decay b producing 136Ba directly Caesium 137Caesium 137 with a half life of 30 17 years is one of the two principal medium lived fission products along with 90Sr which are responsible for most of the radioactivity of spent nuclear fuel after several years of cooling up to several hundred years after use It constitutes most of the radioactivity still left from the Chernobyl accident and is a major health concern for decontaminating land near the Fukushima nuclear power plant 137Cs beta decays to barium 137m a short lived nuclear isomer then to nonradioactive barium 137 Caesium 137 does not emit gamma radiation directly all observed radiation is due to the daughter isotope barium 137m 137Cs has a very low rate of neutron capture and cannot yet be feasibly disposed of in this way unless advances in neutron beam collimation not otherwise achievable by magnetic fields uniquely available only from within muon catalyzed fusion experiments not in the other forms of Accelerator Transmutation of Nuclear Waste enables production of neutrons at high enough intensity to offset and overcome these low capture rates until then therefore 137Cs must simply be allowed to decay 137Cs has been used as a tracer in hydrologic studies analogous to the use of 3H Other isotopes of caesiumThe other isotopes have half lives from a few days to fractions of a second Almost all caesium produced from nuclear fission comes from beta decay of originally more neutron rich fission products passing through isotopes of iodine then isotopes of xenon Because these elements are volatile and can diffuse through nuclear fuel or air caesium is often created far from the original site of fission ReferencesKondev F G Wang M Huang W J Naimi S Audi G 2021 The NUBASE2020 evaluation of nuclear properties PDF Chinese Physics C 45 3 030001 doi 10 1088 1674 1137 abddae NIST Radionuclide Half Life Measurements NIST Retrieved 2011 03 13 Standard Atomic Weights Caesium CIAAW 2013 Prohaska Thomas Irrgeher Johanna Benefield Jacqueline Bohlke John K Chesson Lesley A Coplen Tyler B Ding Tiping Dunn Philip J H Groning Manfred Holden Norman E Meijer Harro A J 2022 05 04 Standard atomic weights of the elements 2021 IUPAC Technical Report Pure and Applied Chemistry doi 10 1515 pac 2019 0603 ISSN 1365 3075 NNDC National Nuclear Data Center www nndc bnl gov Retrieved 2025 02 22 Characteristics of Caesium 134 and Caesium 137 Japan Atomic Energy Agency Archived from the original on 2016 03 04 Retrieved 2014 10 23 Wang Meng Huang W J Kondev F G Audi G Naimi S 2021 The AME 2020 atomic mass evaluation II Tables graphs and references Chinese Physics C 45 3 030003 doi 10 1088 1674 1137 abddaf Zheng K K Petrache C M Zhang Z H Astier A Lv B F Greenlees P T Grahn T Julin R Juutinen S Luoma M Ojala J Pakarinen J Partanen J Rahkila P Ruotsalainen P Sandzelius M Saren J Tann H Uusitalo J Zimba G Cederwall B Aktas o Ertoprak A Zhang W Guo S Liu M L Zhou X H Kuti I Nyako B M Sohler D Timar J Andreoiu C Doncel M Joss D T Page R D 21 October 2021 Rich band structure and multiple long lived isomers in the odd odd Cs 118 nucleus Physical Review C 104 4 doi 10 1103 PhysRevC 104 044325 Retrieved 29 December 2024 Browne E Tuli J K October 2007 Nuclear Data Sheets for A 137 Nuclear Data Sheets 108 10 2173 2318 doi 10 1016 j nds 2007 09 002 Isoray Why Cesium 131 Archived from the original on 2019 06 30 Retrieved 2017 12 05 Although the phase used here is more terse than in the previous definition it still has the same meaning This is made clear in the 9th SI Brochure which almost immediately after the definition on p 130 states The effect of this definition is that the second is equal to the duration of 9192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the unperturbed ground state of the 133Cs atom John L Groh 2004 Supplement to Chapter 11 of Reactor Physics Fundamentals PDF CANTEACH project Archived from the original PDF on 10 June 2011 Retrieved 14 May 2011 Hatsukawa Y Shinohara N Hata K et al 1999 Thermal neutron cross section and resonance integral of the reaction of135Cs n g 136Cs Fundamental data for the transmutation of nuclear waste Journal of Radioanalytical and Nuclear Chemistry 239 3 455 458 doi 10 1007 BF02349050 S2CID 97425651 Ohki Shigeo Takaki Naoyuki 2002 Transmutation of Cesium 135 With Fast Reactors PDF Proceedings of the Seventh Information Exchange Meeting on Actinide and Fission Product Partitioning amp Transmutation Cheju Korea NGAtlas ZV www nds iaea org Retrieved 2025 02 22 Dennis 1 March 2013 Cooling a Hot Zone Science 339 6123 1028 1029 doi 10 1126 science 339 6123 1028 PMID 23449572 Isotope masses from Audi Georges Bersillon Olivier Blachot Jean Wapstra Aaldert Hendrik 2003 The NUBASE evaluation of nuclear and decay properties Nuclear Physics A 729 3 128 Bibcode 2003NuPhA 729 3A doi 10 1016 j nuclphysa 2003 11 001 Half life spin and isomer data selected from the following sources Audi Georges Bersillon Olivier Blachot Jean Wapstra Aaldert Hendrik 2003 The NUBASE evaluation of nuclear and decay properties Nuclear Physics A 729 3 128 Bibcode 2003NuPhA 729 3A doi 10 1016 j nuclphysa 2003 11 001 National Nuclear Data Center NuDat 2 x database Brookhaven National Laboratory Holden Norman E 2004 11 Table of the Isotopes In Lide David R ed CRC Handbook of Chemistry and Physics 85th ed Boca Raton Florida CRC Press ISBN 978 0 8493 0485 9