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List of isotopes

Caesium-131

Caesium-131, introduced in 2004 for brachytherapy by Isoray,³⁶ 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,³⁷ 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).³⁸

Caesium-135

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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 137Cs which can only be separated from 135Cs via isotope separation) rather than with other long-lived fission products. Except in the Molten salt reactor, where 135Cs is created as a completely separate stream outside the fuel (after the decay of bubble-separated 135Cs). 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)⁴³ will be converted to extremely long-lived (half-life on the order of 1021 years) 136Xe before it can decay to 135Cs despite the relatively short half life of 135Xe. Little or no 135Xe 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 135Xe buildup in the reactor after a reduction in power or a shutdown and is often managed by letting the 135Xe 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.⁴⁴ 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.⁴⁵

• ANL factsheet

Caesium-136

Caesium-136 has a half-life of 13.01 days.⁴⁶ 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,⁴⁷ 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.⁴⁸

Caesium-137

Main article: 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.⁴⁹ 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.

• 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.

References

1. "NNDC | National Nuclear Data Center". www.nndc.bnl.gov. Retrieved 2025-02-22. https://www.nndc.bnl.gov/ ↩

2. "Characteristics of Caesium-134 and Caesium-137". Japan Atomic Energy Agency. Archived from the original on 2016-03-04. Retrieved 2014-10-23. https://web.archive.org/web/20160304100452/http://c-navi.jaea.go.jp/en/background/remediation-following-major-radiation-accidents/characteristics-of-caesium-134-and-caesium-137.html ↩

3. mCs – Excited nuclear isomer. /wiki/Nuclear_isomer ↩

4. 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. /wiki/Doi_(identifier) ↩

5. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits. ↩

6. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS). ↩

7. Kondev, 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. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf ↩

8. Kondev, 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. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf ↩

9. Modes of decay: EC:Electron captureIT:Isomeric transitionn:Neutron emissionp:Proton emission /wiki/Electron_capture ↩

10. Bold italics symbol as daughter – Daughter product is nearly stable. ↩

11. Bold symbol as daughter – Daughter product is stable. ↩

12. Kondev, 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. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf ↩

13. ( ) spin value – Indicates spin with weak assignment arguments. ↩

14. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN). ↩

15. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN). ↩

16. Order of ground state and isomer is uncertain. ↩

17. Order of ground state and isomer is uncertain. ↩

18. 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.; Sarén, J.; Tann, H.; Uusitalo, J.; Zimba, G.; Cederwall, B.; Aktas, ö.; Ertoprak, A.; Zhang, W.; Guo, S.; Liu, M. L.; Zhou, X. H.; Kuti, I.; Nyakó, B. M.; Sohler, D.; Timár, 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. https://www.researchgate.net/publication/355502046_Rich_band_structure_and_multiple_long-lived_isomers_in_the_odd-odd_Cs_118_nucleus ↩

19. 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.; Sarén, J.; Tann, H.; Uusitalo, J.; Zimba, G.; Cederwall, B.; Aktas, ö.; Ertoprak, A.; Zhang, W.; Guo, S.; Liu, M. L.; Zhou, X. H.; Kuti, I.; Nyakó, B. M.; Sohler, D.; Timár, 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. https://www.researchgate.net/publication/355502046_Rich_band_structure_and_multiple_long-lived_isomers_in_the_odd-odd_Cs_118_nucleus ↩

20. Order of ground state and isomer is uncertain. ↩

21. 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.; Sarén, J.; Tann, H.; Uusitalo, J.; Zimba, G.; Cederwall, B.; Aktas, ö.; Ertoprak, A.; Zhang, W.; Guo, S.; Liu, M. L.; Zhou, X. H.; Kuti, I.; Nyakó, B. M.; Sohler, D.; Timár, 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. https://www.researchgate.net/publication/355502046_Rich_band_structure_and_multiple_long-lived_isomers_in_the_odd-odd_Cs_118_nucleus ↩

22. Order of ground state and isomer is uncertain. ↩

23. 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.; Sarén, J.; Tann, H.; Uusitalo, J.; Zimba, G.; Cederwall, B.; Aktas, ö.; Ertoprak, A.; Zhang, W.; Guo, S.; Liu, M. L.; Zhou, X. H.; Kuti, I.; Nyakó, B. M.; Sohler, D.; Timár, 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. https://www.researchgate.net/publication/355502046_Rich_band_structure_and_multiple_long-lived_isomers_in_the_odd-odd_Cs_118_nucleus ↩

24. Order of ground state and isomer is uncertain. ↩

25. 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.; Sarén, J.; Tann, H.; Uusitalo, J.; Zimba, G.; Cederwall, B.; Aktas, ö.; Ertoprak, A.; Zhang, W.; Guo, S.; Liu, M. L.; Zhou, X. H.; Kuti, I.; Nyakó, B. M.; Sohler, D.; Timár, 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. https://www.researchgate.net/publication/355502046_Rich_band_structure_and_multiple_long-lived_isomers_in_the_odd-odd_Cs_118_nucleus ↩

26. 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.; Sarén, J.; Tann, H.; Uusitalo, J.; Zimba, G.; Cederwall, B.; Aktas, ö.; Ertoprak, A.; Zhang, W.; Guo, S.; Liu, M. L.; Zhou, X. H.; Kuti, I.; Nyakó, B. M.; Sohler, D.; Timár, 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. https://www.researchgate.net/publication/355502046_Rich_band_structure_and_multiple_long-lived_isomers_in_the_odd-odd_Cs_118_nucleus ↩

27. Order of ground state and isomer is uncertain. ↩

28. Order of ground state and isomer is uncertain. ↩

29. Used to define the second /wiki/Second ↩

30. Fission product /wiki/Fission_product ↩

31. Fission product /wiki/Fission_product ↩

32. Fission product /wiki/Fission_product ↩

33. Fission product /wiki/Fission_product ↩

34. 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. /wiki/Doi_(identifier) ↩

35. 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. /wiki/Doi_(identifier) ↩

36. Isoray. "Why Cesium-131". Archived from the original on 2019-06-30. Retrieved 2017-12-05. https://web.archive.org/web/20190630105241/https://isoray.com/why-cesium-131/ ↩

37. 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." ↩

38. "Characteristics of Caesium-134 and Caesium-137". Japan Atomic Energy Agency. Archived from the original on 2016-03-04. Retrieved 2014-10-23. https://web.archive.org/web/20160304100452/http://c-navi.jaea.go.jp/en/background/remediation-following-major-radiation-accidents/characteristics-of-caesium-134-and-caesium-137.html ↩

39. Decay energy is split among β, neutrino, and γ if any. /wiki/Beta_particle ↩

40. Per 65 thermal neutron fissions of 235U and 35 of 239Pu. /wiki/Uranium-235 ↩

41. Has decay energy 380 keV, but its decay product 126Sb has decay energy 3.67 MeV. ↩

42. Lower in thermal reactors because 135Xe, its predecessor, readily absorbs neutrons. /wiki/Xenon-135 ↩

43. 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. https://web.archive.org/web/20110610131653/http://canteach.candu.org/library/20041204.pdf ↩

44. Hatsukawa, Y.; Shinohara, N; Hata, K.; et al. (1999). "Thermal neutron cross section and resonance integral of the reaction of135Cs(n,γ)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. /wiki/Doi_(identifier) ↩

45. 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. http://www.nea.fr/html/pt/docs/iem/jeju02/session6/SessionVI-08.pdf ↩

46. "NNDC | National Nuclear Data Center". www.nndc.bnl.gov. Retrieved 2025-02-22. https://www.nndc.bnl.gov/ ↩

47. "NGAtlas/ZV". www-nds.iaea.org. Retrieved 2025-02-22. https://www-nds.iaea.org/ngatlas2/ ↩

48. "NNDC | National Nuclear Data Center". www.nndc.bnl.gov. Retrieved 2025-02-22. https://www.nndc.bnl.gov/ ↩

49. Dennis (1 March 2013). "Cooling a Hot Zone". Science. 339 (6123): 1028–1029. doi:10.1126/science.339.6123.1028. PMID 23449572. /wiki/Doi_(identifier) ↩