Caesium: isotope data

Naturally occurring isotopes

This table shows information about naturally occuring isotopes, their atomic masses, their natural abundances, their nuclear spins, and their magnetic moments. Further data for radioisotopes (radioactive isotopes) of caesium are listed (including any which occur naturally) below.
Isotope Mass / Da Natural abundance (atom %) Nuclear spin (I) Magnetic moment (μ/μN)
133Cs 132.905429 (7) 100 7/2 2.582024

In the above, the most intense ion is set to 100% since this corresponds best to the output from a mass spectrometer. This is not to be confused with the relative percentage isotope abundances which totals 100% for all the naturally occurring isotopes.

Radiosotope data

Further data for naturally occuring isotopes of caesium are listed above. This table gives information about some radiosotopes of caesium, their masses, their half-lives, their modes of decay, their nuclear spins, and their nuclear magnetic moments.
Isotope Mass / Da Half-life Mode of decay Nuclear spin Nuclear magnetic moment
129Cs 128.90606 1.336 d EC to 129Xe 1/2 1.49
130Cs 129.90671 29.21 m EC to 130Xe; β- to 130Ba 1 1.46
131Cs 130.90546 9.69 d EC to 131Xe 5/2 3.54
132Cs 131.906430 6.48 d EC to 132Xe; β- to 132Ba 2 2.22
134Cs 133.906714 2.065 y EC to 134Xe; β- to 134Ba 4 2.994
135Cs 134.905972 2.3 x 106 y β- to 135Ba 7/2 2.732
136Cs 135.907307 13.16 d β- to 136Ba 5 3.71
137Cs 136.907085 30.2 y β- to 137Ba 7/2 2.84

Sheffield ChemPuter isotope pattern calculator

You can use WebElements to calculate an isotope pattern for an arbitrary chemical formula:

Edit this formula :

Note the following when entering your formula:

  • Correctly nested brackets [{()}] are OK
  • 'Pseudoelements' such as Me, Ph, Cp, and many others are OK
  • Compound names and element names such as 'water' or 'manganese' are not OK
  • Experiment with your formula to see what is possible


  1. Naturally occurring isotope abundances: Commission on Atomic Weights and Isotopic Abundances report for the International Union of Pure and Applied Chemistry in Isotopic Compositions of the Elements 1989, Pure and Applied Chemistry, 1998, 70, 217. [Copyright 1998 IUPAC]
  2. For further information about radioisotopes see Jonghwa Chang's (Korea Atomic Energy Research Institute) Table of the Nuclides
  3. Masses, nuclear spins, and magnetic moments: I. Mills, T. Cvitas, K. Homann, N. Kallay, and K. Kuchitsu in Quantities, Units and Symbols in Physical Chemistry, Blackwell Scientific Publications, Oxford, UK, 1988. [Copyright 1988 IUPAC]

NMR Properties of caesium

Common reference compound: CsNO3/D2O.

Table of NMR-active nucleus propeties of caesium
  Isotope 1 Isotope 2 Isotope 3
Isotope 133Cs
Natural abundance /% 100
Spin (I) 7/2
Frequency relative to 1H = 100 (MHz) 13.116207
Receptivity, DP, relative to 1H = 1.00 0.0484
Receptivity, DC, relative to 13C = 1.00 276
Magnetogyric ratio, γ (107 rad T‑1 s-1) 3.5332539
Magnetic moment, μ (μN) 2.9277407
Nuclear quadrupole moment, Q/millibarn -3.43(10) and 302(21) [Mössbauer state]
Line width factor, 1056 l (m4) 0.0000019


  1. R.K. Harris in Encyclopedia of Nuclear Magnetic Resonance, D.M. Granty and R.K. Harris, (eds.), vol. 5, John Wiley & Sons, Chichester, UK, 1996. I am grateful to Professor Robin Harris (University of Durham, UK) who provided much of the NMR data, which are copyright 1996 IUPAC, adapted from his contribution contained within this reference.
  2. J. Mason in Multinuclear NMR, Plenum Press, New York, USA, 1987. Where given, data for certain radioactive nuclei are from this reference.
  3. P. Pyykkö, Mol. Phys., 2008, 106, 1965-1974.
  4. P. Pyykkö, Mol. Phys., 2001, 99, 1617-1629.
  5. P. Pyykkö, Z. Naturforsch., 1992, 47a, 189. I am grateful to Professor Pekka Pyykkö (University of Helsinki, Finland) who provided the nuclear quadrupole moment data in this and the following two references.
  6. D.R. Lide, (ed.), CRC Handbook of Chemistry and Physics 1999-2000 : A Ready-Reference Book of Chemical and Physical Data (CRC Handbook of Chemistry and Physics, CRC Press, Boca Raton, Florida, USA, 79th edition, 1998.
  7. P. Pyykkö, personal communication, 1998, 204, 2008, 2010.

WebElements chemistry shop

You can buy periodic table posters, mugs, T-shirts, periodic table fridge magnets, games, molecular models, and more at the WebElements periodic table shop