Nuclide reference
Cs-137 — Caesium-137
The half-life of Cs-137 is 30.08 years. Main decay mode: β⁻ decay to Ba-137m (94.7%).
Identification
- Element
- Caesium (Cs)
- Atomic number Z
- 55
- Mass number A
- 137
- State
- Radioactive
Key quantities
- Half-life
- 30.08 years
- Specific activity
- 3.21e+12 Bq/g
- Gamma constant Γ (H*(10))
- 0.09221 µSv·m²/(MBq·h)
- Dose rate, 1 GBq at 1 m
- ≈ 92.2 µSv/h
- A1 / A2 for transport (SSR-6, НП-053-16)
- 2 TBq / 0.6 TBq
- D-value (НП-067-24)
- 0.1 TBq
Decay modes
- β⁻ decay → Ba-137m — 94.7 %
- β⁻ decay → Ba-137 — 5.301 %
Main gamma lines
| Energy, keV | Yield, % |
|---|---|
| 661.657 (Ba-137m) | 85.13 |
| 32.193 (Ba-137m) · X-ray line | 3.635 |
| 31.817 (Ba-137m) · X-ray line | 1.993 |
| 283.5 | 0.00058 |
Includes daughter nuclides in equilibrium: Ba-137m (yield per decay of Cs-137); the emitting nuclide is in brackets. Equilibrium is reached in about 18 min.
Alpha and beta particles
| Radiation | Energy, keV | Yield, % |
|---|---|---|
| β⁻, E max | 513.97 | 94.7 |
| 1,175.6 | 5.3 |
For β⁻ the endpoint (maximum) energy of the spectrum is given. ENDF/B-VIII.0.
Related calculators
Other isotopes of this element
Reference data vs computed valuesHalf-life, gamma lines and D-value are reference data (ENDF/B-VIII.0, НП-067-24).Gamma constant Γ is H*(10) at 1 m computed from ICRP-107 spectra (NIST µ_en/ρ, ICRP-74 Table A.21) including short-lived progeny in equilibrium (e.g. Cs-137/Ba-137m, Ra-226 series); specific activity uses molar mass M ≈ mass number A.Dose rate example: point source, no shielding or scatter, Ḣ = Γ·A/r².K-series X-ray energies are from NIST SRD 128 (Deslattes et al., 2003): in ENDF/B-VIII.0 they are given to 1 % and shifted by up to 0.7 keV for heavy elements. L-series lines and all yields are ENDF/B-VIII.0.