Barium-133
Ba-133 · Barium, Z = 56, A = 133
Barium-133 decays by electron capture, half-life 10.551 years. Specific activity is 9.43e+12 Bq/g (255 Ci/g), so a gigabecquerel comes to 106 µg — weighable, but on an analytical balance. Over a year the activity falls to 93.64%, and over forty years to 7.22%.
1 GBq at 1 m reads 0.0733 mGy/h, and 1 Ci at the same distance 2.71 mGy/h, from an air kerma rate constant of 0.0733 mGy·m²/(GBq·h) — 1.1× less than Cs-137 and 4.2× less than Co-60, and 29 of 96 among the photon emitters carried here.
14 lines clear the 20 keV cutoff, but 7 of them carry 90% of the dose rate. The leading one is 356.0 keV at 40.4% of the total — its emission probability is 62.05%, which is also the highest.
A half-value layer of 0.582 mm in lead puts this in foil and thin sheet, with 2.69 mm needed if the material is steel; ten-fold attenuation comes at 5.16 mm of lead. Reaching 20 µSv/h from 1 GBq at a metre takes 2.25 mm of lead. The tenth-value layer runs 8.9 times the half-value layer, not the 3.32 a single energy would give.
Half-life, specific activity and dose rate
| Half-life | 10.551 years (3.330e+8 s) |
| Decay mode | electron capture |
| Specific activity | 9.43e+12 Bq/g (255 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.0733 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.0733 mGy/h |
| Dose rate, 1 Ci at 1 m | 2.71 mGy/h |
| Kerma-weighted mean photon energy | 223.4 keV |
14 lines above the cutoff, and what each contributes
1 further line below the 20 keV cutoff, the highest at 4.75 keV and 15.3% emission probability in all, is excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 356.01 | 62.05 | 40.37 |
| 30.97 | 60.2 | 16.41 |
| 302.85 | 18.33578 | 10.00 |
| 30.63 | 32.6 | 9.07 |
| 383.85 | 8.9414 | 6.32 |
| 35.41 | 21.9 | 4.68 |
| 81.00 | 32.94855 | 4.02 |
| 35.09 | 17.6 | 3.82 |
| 276.40 | 7.16057 | 3.51 |
| 35.82 | 4.29 | 0.90 |
| 79.61 | 2.64954 | 0.32 |
| 53.16 | 2.14073 | 0.26 |
| 223.24 | 0.45297 | 0.17 |
| 160.61 | 0.63787 | 0.16 |
0.582 mm of lead halves this spectrum
Solved numerically across all 14 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 0.582 | 5.16 | 8.88 |
| tungsten | 0.384 | 3.72 | 9.70 |
| iron | 2.69 | 22.4 | 8.33 |
| copper | 2.27 | 19.5 | 8.59 |
| concrete | 12.9 | 75.9 | 5.88 |
| water | 39.3 | 163 | 4.16 |
| aluminum | 10.8 | 68.1 | 6.27 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over decades and centuries
Ten half-lives is 106 years, which puts decay storage out of reach: 7.22% survives forty years. The mean life 1/λ, the quantity that enters an integrated dose, is 15.2 years.
| Elapsed | Fraction remaining |
|---|---|
| 1 half-life | 50.0 % |
| 2 half-lives | 25.0 % |
| 5 half-lives | 3.13 % |
| 10 half-lives | 0.0977 % |
| Time to fall to 10 % of today's activity | 35.0 years |
| Time to fall to 1 % | 70.1 years |
| Time to fall to 0.1 % | 105 years |
Limits of these dose rates
- 0.0733 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 0.582 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 1 line under 20 keV, carrying 15.3% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Ba-133
Other Barium nuclides: Ba-133m, Ba-137m
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.