Barium-133m
Ba-133m · Barium, Z = 56, A = 133 · isomeric state m
Barium-133m (Ba-133m) carries 2.24e+16 Bq/g, or 6.06e+5 Ci/g: a gigabecquerel is 44.6 ng, no weighable quantity at all. It decays by isomeric transition with a half-life of 38.93 hours, which leaves 5.02% of today's activity after a week and 1.3e-15% after three months.
At 0.0178 mGy·m²/(GBq·h) the air kerma rate constant is 4.3× less than Cs-137 and 17× less than Co-60, placing it 58 of 96 photon emitters in this dataset. 1 GBq at 1 m reads 0.0178 mGy/h, and 1 Ci at the same distance 0.658 mGy/h.
11 lines clear the 20 keV cutoff, but 4 of them carry 90% of the dose rate. The leading one is 275.9 keV at 35.7% of the total — its emission probability is 17.7%, which is lower than the 28.8% of the 32.2 keV line it outranks.
Shielding barely arises: 0.0547 mm of lead halves the air kerma rate and 2.31 mm takes it to a tenth, thicknesses a source capsule is likely to exceed on its own. Steel does the halving in 0.301 mm. At 1 GBq and a metre it is already under 20 µSv/h with nothing in the way. The tenth-value layer runs 42.3 times the half-value layer, not the 3.32 a single energy would give.
Half-life, specific activity and dose rate
| Half-life | 38.93 hours (1.401e+5 s) |
| Decay mode | isomeric transition |
| Specific activity | 2.24e+16 Bq/g (6.06e+5 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.0178 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.0178 mGy/h |
| Dose rate, 1 Ci at 1 m | 0.658 mGy/h |
| Kerma-weighted mean photon energy | 120.1 keV |
11 lines above the cutoff, and what each contributes
2 further lines below the 20 keV cutoff, the highest at 12.33 keV and 18.0% emission probability in all, are excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 275.93 | 17.7 | 35.65 |
| 32.19 | 28.8 | 30.13 |
| 31.82 | 15.6 | 16.68 |
| 36.83 | 10.6 | 8.69 |
| 36.48 | 8.5 | 7.09 |
| 37.26 | 2.13 | 1.71 |
| 632.59 | 0.0103 | 0.05 |
| 30.97 | 0.00388 | 0.00 |
| 30.63 | 0.0021 | 0.00 |
| 35.41 | 0.00141 | 0.00 |
| 35.09 | 0.00113 | 0.00 |
0.0547 mm of lead halves this spectrum
Solved numerically across all 11 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 0.0547 | 2.31 | 42.27 |
| tungsten | 0.0429 | 1.70 | 39.62 |
| iron | 0.301 | 13.9 | 46.17 |
| copper | 0.200 | 11.9 | 59.44 |
| concrete | 6.67 | 48.9 | 7.34 |
| water | 28.6 | 116 | 4.07 |
| aluminum | 5.09 | 43.8 | 8.62 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over days and weeks
Ten half-lives is 16.2 days — a storage problem rather than a disposal one, with 1.6e-66% of today's activity still there after a year. The mean life 1/λ is 2.34 days.
| 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 | 5.39 days |
| Time to fall to 1 % | 10.8 days |
| Time to fall to 0.1 % | 16.2 days |
Limits of these dose rates
- 0.0178 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 0.0547 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 2 lines under 20 keV, carrying 18.0% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Ba-133m
Other Barium nuclides: Ba-133, Ba-137m
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.