Legend. Isotope shown as superscripted mass left of symbol (e.g., ¹³⁷Cs). Columns give Z, A, Stability, Half‑life, Decay modes (main branches), Daughter(s), Emissions (α/β/γ), Origin (Nat.=natural; FP=fission product; Synth.=laboratory), and Uses (R=research, I=industrial, M=medical). Data (half‑lives/branches/daughters) are from the evaluated “Isotopes of caesium” table; CIAAW gives natural isotopic composition; specific use‑cases are cited inline in notes below. (Wikipedia, ciaaw.org)
Notes up front (for context & quality):
• Natural composition: Caesium is mononuclidic: only ¹³³Cs occurs in nature (100%). (ciaaw.org)
• Time standard: The SI second is defined using the hyperfine transition of ¹³³Cs. (Wikipedia)
• Key application isotopes: ¹³¹Cs (brachytherapy, t½ 9.69 d); ¹³⁴Cs (environmental tracer, t½ 2.065 y); ¹³⁵Cs (LLFP, t½ ≈1.33 Myr); ¹³⁷Cs (γ via ¹³⁷ᵐBa at 662 keV, industry & environmental tracer, t½ ≈30.04 y). (gtmedtech.com, PMC, Wikipedia)
Ground‑state isotopes
| Isotope | Z | A | Stable? | Half‑life | Decay mode(s) (main %) | Daughter(s) | Emissions | Origin | Typical uses |
|---|---|---|---|---|---|---|---|---|---|
| ¹¹²Cs | 55 | 112 | Unstable | 490 µs | p (>99.74%), minor α | ¹¹¹Xe, ¹⁰⁸I | p, α | Synth. | R |
| ¹¹³Cs | 55 | 113 | Unstable | 16.94 µs | p | ¹¹²Xe | p | Synth. | R |
| ¹¹⁴Cs | 55 | 114 | Unstable | 570 ms | β⁺ (91.1%), β⁺p (8.7%), tiny α branches | ¹¹⁴Xe, ¹¹³I, ¹¹⁰Te/¹¹⁰I | β⁺, p, α | Synth. | R |
| ¹¹⁵Cs | 55 | 115 | Unstable | 1.4 s | β⁺ (99.93%), β⁺p (0.07%) | ¹¹⁵Xe, ¹¹⁴I | β⁺, p | Synth. | R |
| ¹¹⁶Cs | 55 | 116 | Unstable | 700 ms | β⁺ (99.67%), β⁺p (0.28%), tiny α | ¹¹⁶Xe, ¹¹⁵I, ¹¹²Te | β⁺, p, α | Synth. | R |
| ¹¹⁷Cs | 55 | 117 | Unstable | 8.4 s | β⁺ | ¹¹⁷Xe | β⁺ | Synth. | R |
| ¹¹⁸Cs | 55 | 118 | Unstable | 14 s | β⁺ (≈99.98%), β⁺p (~0.021%), tiny α | ¹¹⁸Xe, ¹¹⁷I, ¹¹⁴Te | β⁺, p, α | Synth. | R |
| ¹¹⁹Cs | 55 | 119 | Unstable | 43.0 s | β⁺ | ¹¹⁹Xe | β⁺ | Synth. | R |
| ¹²⁰Cs | 55 | 120 | Unstable | 60.4 s | β⁺ (dominant), traces p/α | ¹²⁰Xe, ¹¹⁹I | β⁺ (+tiny p/α) | Synth. | R |
| ¹²¹Cs | 55 | 121 | Unstable | 155 s | β⁺ | ¹²¹Xe | β⁺ | Synth. | R |
| ¹²²Cs | 55 | 122 | Unstable | 21.18 s | β⁺ | ¹²²Xe | β⁺ | Synth. | R |
| ¹²³Cs | 55 | 123 | Unstable | 5.88 min | β⁺ | ¹²³Xe | β⁺ | Synth. | R |
| ¹²⁴Cs | 55 | 124 | Unstable | 30.9 s | β⁺ | ¹²⁴Xe | β⁺ | Synth. | R |
| ¹²⁵Cs | 55 | 125 | Unstable | 44.35 min | β⁺ | ¹²⁵Xe | β⁺ | Synth. | R |
| ¹²⁶Cs | 55 | 126 | Unstable | 1.64 min | β⁺ | ¹²⁶Xe | β⁺ | Synth. | R |
| ¹²⁷Cs | 55 | 127 | Unstable | 6.25 h | β⁺ | ¹²⁷Xe | β⁺ | Synth. | R |
| ¹²⁸Cs | 55 | 128 | Unstable | 3.640 min | β⁺ | ¹²⁸Xe | β⁺ | Synth. | R |
| ¹²⁹Cs | 55 | 129 | Unstable | 32.06 h | β⁺ | ¹²⁹Xe | β⁺ | Synth. | R |
| ¹³⁰Cs | 55 | 130 | Unstable | 29.21 min | β⁺ (98.4%), β⁻ (1.6%) | ¹³⁰Xe, ¹³⁰Ba | β⁺/β⁻ | Synth. | R |
| ¹³¹Cs | 55 | 131 | Unstable | 9.689 d | EC | ¹³¹Xe | X‑rays (≈30 keV), Auger | Synth. | M (low‑energy brachytherapy seeds/tiles) |
| ¹³²Cs | 55 | 132 | Unstable | 6.480 d | β⁺ (98.13%), β⁻ (1.87%) | ¹³²Xe, ¹³²Ba | β⁺/β⁻ | Synth./FP | R |
| ¹³³Cs | 55 | 133 | Stable | — | — | — | — | Nat. (100%) | Time standard (atomic clocks) |
| ¹³⁴Cs | 55 | 134 | Unstable | 2.0650 y | β⁻ (dominant), tiny EC | ¹³⁴Ba, ¹³⁴Xe (trace) | β⁻ + γ cascade | FP (activation of ¹³³Cs) | R (ocean/fallout tracer) |
| ¹³⁵Cs | 55 | 135 | Unstable | 1.33×10⁶ y | β⁻ | ¹³⁵Ba | β⁻ (low‑E) | FP (LLFP) | R (waste, transmutation studies) |
| ¹³⁶Cs | 55 | 136 | Unstable | 13.01 d | β⁻ | ¹³⁶Ba | β⁻ + γ | FP | R |
| ¹³⁷Cs | 55 | 137 | Unstable | 30.04 y | β⁻→¹³⁷ᵐBa (94.7%), β⁻→¹³⁷Ba (5.3%) | ¹³⁷ᵐBa/¹³⁷Ba | β⁻; γ 661.7 keV (from ¹³⁷ᵐBa) | FP | I (gauging, radiography, calibration), R (tracer) |
| ¹³⁸Cs | 55 | 138 | Unstable | 33.5 min | β⁻ | ¹³⁸Ba | β⁻ + γ | FP | R |
| ¹³⁹Cs | 55 | 139 | Unstable | 9.27 min | β⁻ | ¹³⁹Ba | β⁻ | FP | R |
| ¹⁴⁰Cs | 55 | 140 | Unstable | 63.7 s | β⁻ | ¹⁴⁰Ba | β⁻ | FP | R |
| ¹⁴¹Cs | 55 | 141 | Unstable | 24.84 s | β⁻ (99.97%), β⁻,n (0.034%) | ¹⁴¹Ba, ¹⁴⁰Ba | β⁻; β‑delayed n | FP | R |
| ¹⁴²Cs | 55 | 142 | Unstable | 1.687 s | β⁻ (99.91%), β⁻,n (0.089%) | ¹⁴²Ba, ¹⁴¹Ba | β⁻; β‑delayed n | FP | R |
| ¹⁴³Cs | 55 | 143 | Unstable | 1.802 s | β⁻ (98.38%), β⁻,n (1.62%) | ¹⁴³Ba, ¹⁴²Ba | β⁻; β‑delayed n | FP | R |
| ¹⁴⁴Cs | 55 | 144 | Unstable | 994 ms | β⁻ (97.02%), β⁻,n (2.98%) | ¹⁴⁴Ba, ¹⁴³Ba | β⁻; β‑delayed n | FP | R |
| ¹⁴⁵Cs | 55 | 145 | Unstable | 582 ms | β⁻ (87.2%), β⁻,n (12.8%) | ¹⁴⁵Ba, ¹⁴⁴Ba | β⁻; β‑delayed n | FP | R |
| ¹⁴⁶Cs | 55 | 146 | Unstable | 321.6 ms | β⁻ (85.8%), β⁻,n (14.2%) | ¹⁴⁶Ba, ¹⁴⁵Ba | β⁻; β‑delayed n | FP | R |
| ¹⁴⁷Cs | 55 | 147 | Unstable | 230.5 ms | β⁻ (71.5%), β⁻,n (28.5%) | ¹⁴⁷Ba, ¹⁴⁶Ba | β⁻; β‑delayed n | FP | R |
| ¹⁴⁸Cs | 55 | 148 | Unstable | 151.8 ms | β⁻ (71.3%), β⁻,n (28.7%) | ¹⁴⁸Ba, ¹⁴⁷Ba | β⁻; β‑delayed n | FP | R |
| ¹⁴⁹Cs | 55 | 149 | Unstable | 112.3 ms | β⁻ (75%), β⁻,n (25%) | ¹⁴⁹Ba, ¹⁴⁸Ba | β⁻; β‑delayed n | FP | R |
| ¹⁵⁰Cs | 55 | 150 | Unstable | 81.0 ms | β⁻ (~56%), β⁻,n (~44%) | ¹⁵⁰Ba, ¹⁴⁹Ba | β⁻; β‑delayed n | FP | R |
| ¹⁵¹Cs | 55 | 151 | Unstable | 59 ms | β⁻ | ¹⁵¹Ba | β⁻ | FP | R |
Source for all half‑lives/decay branches/daughters above: “Isotopes of caesium” (evaluated table). (Wikipedia)
On ¹⁵²Cs: The discovery literature lists Cs isotopes from A=112 up to A=152 (forty‑one known); however, current public summary tables often stop at ¹⁵¹Cs. ENSDF/NUBASE index entries confirm ¹⁵²Cs exists in the mass‑152 chain, but detailed adopted decay data are limited/unpublished in open summaries; treat ¹⁵²Cs as an extremely short‑lived, neutron‑rich β⁻ emitter with no applications. (ScienceDirect, nndc.bnl.gov)
Targeted application/usage notes (abridged, with sources)
- ¹³¹Cs (EC, 9.69 d): Low‑energy X‑ray brachytherapy (e.g., GammaTile implants for select brain tumors; seeds cleared by FDA). (gtmedtech.com, ScienceDirect)
- ¹³³Cs (stable): Defines the SI second via the 9 192 631 770 Hz hyperfine transition; cornerstone of atomic clocks. (Wikipedia)
- ¹³⁴Cs (2.065 y, β⁻ + γ): Powerful environmental tracer—the ¹³⁴Cs/¹³⁷Cs ratio fingerprints Fukushima‑derived radiocesium because ¹³⁴Cs decays away on ~2‑year timescales. (ScienceDirect, Phys.org)
- ¹³⁵Cs (1.33 Myr, β⁻): Long‑lived fission product (LLFP); central to waste management and transmutation studies. (ChemEurope, nwtrb.gov, ScienceDirect)
- ¹³⁷Cs (30.04 y, β⁻ → ¹³⁷ᵐBa, γ 661.7 keV): Ubiquitous industrial source (gauging/level/density, γ‑irradiators, calibration), and environmental tracer (fallout forensics, hydrology). (lnhb.fr, Ionactive, Nature)
Element‑level recap for Caesium (Z = 55)
- Total known Cs isotopes: 41 (mass numbers A = 112–152). Stable: 1 (¹³³Cs). Radioactive: 40. (Wikipedia)
- Naturally occurring isotope(s): ¹³³Cs only (100% abundance). (ciaaw.org)
- Primary application nuclides: ¹³¹Cs (M), ¹³⁴Cs (R), ¹³⁵Cs (R), ¹³⁷Cs (I/R). (See notes & citations above.)
Citations / primary data sources
- Evaluated half‑lives, decay modes, daughters (table): Isotopes of caesium (continuously maintained summary). (Wikipedia)
- Natural isotopic composition: CIAAW (IUPAC) standard atomic weight/isotopic abundance for Cs (mononuclidic ¹³³Cs). (ciaaw.org)
- ¹³¹Cs clinical use & half‑life: GammaTile IFU (9.69 d) and peer‑reviewed articles on Cs‑131 brachytherapy. (gtmedtech.com, PMC, ScienceDirect)
- ¹³⁷Cs decay scheme & γ line: LNHB/CEA decay tables; also encyclopedia summary. (lnhb.fr, Wikipedia)
- ¹³⁴Cs/¹³⁷Cs environmental tracing: Multiple studies (oceanography/radioecology) and explainer on the ¹³⁴Cs “tag.” (ScienceDirect, Phys.org)
- ¹³⁵Cs longevity & LLFP context; Cs capsule inventory: Review/fact sheets & LLFP analyses. (nwtrb.gov, ScienceDirect)
- ¹⁵²Cs index presence: ENSDF mass‑152 index; discovery review paper noting A = 112–152. (nndc.bnl.gov, ScienceDirect)
Next element: Barium (Ba, Z = 56).