Xenon-133
Xe-133 · Xenon, Z = 54, A = 133
At 6.93e+15 Bq/g — 1.87e+5 Ci/g — a gigabecquerel of Xe-133 amounts to 144 ng, which is why activity rather than mass is how anyone states the quantity. Xenon-133 decays by beta-minus decay with a half-life of 5.2475 days, falling to 39.67% of today's activity in a week and 6.0e-4% in three months.
At 0.0140 mGy·m²/(GBq·h) the air kerma rate constant is 5.5× less than Cs-137 and 22× less than Co-60, placing it 62 of 96 photon emitters in this dataset. 1 GBq at 1 m reads 0.0140 mGy/h, and 1 Ci at the same distance 0.518 mGy/h.
10 lines clear the 20 keV cutoff, but 5 of them carry 90% of the dose rate. The leading one is 31.0 keV at 35.8% of the total — its emission probability is 25.10439%, which is lower than the 36.9% of the 81.0 keV line it outranks.
Shielding barely arises: 0.0342 mm of lead halves the air kerma rate and 0.330 mm takes it to a tenth, thicknesses a source capsule is likely to exceed on its own. Steel does the halving in 0.186 mm. At 1 GBq and a metre it is already under 20 µSv/h with nothing in the way. The tenth-value layer runs 9.7 times the half-value layer, not the 3.32 a single energy would give.
Half-life, specific activity and dose rate
| Half-life | 5.2475 days (4.534e+5 s) |
| Decay mode | beta-minus decay |
| Specific activity | 6.93e+15 Bq/g (1.87e+5 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.0140 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.0140 mGy/h |
| Dose rate, 1 Ci at 1 m | 0.518 mGy/h |
| Kerma-weighted mean photon energy | 43.96 keV |
10 lines above the cutoff, and what each contributes
1 further line below the 20 keV cutoff, the highest at 4.75 keV and 5.82% emission probability in all, is excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 30.97 | 25.10439 | 35.78 |
| 81.00 | 36.9 | 23.52 |
| 30.63 | 13.589 | 19.77 |
| 35.41 | 9.1239 | 10.19 |
| 35.09 | 7.33433 | 8.33 |
| 35.82 | 1.78958 | 1.96 |
| 79.61 | 0.44 | 0.28 |
| 160.61 | 0.1066 | 0.14 |
| 302.85 | 0.0055 | 0.02 |
| 383.85 | 0.0027 | 0.01 |
0.0342 mm of lead halves this spectrum
Solved numerically across all 10 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 0.0342 | 0.330 | 9.65 |
| tungsten | 0.0227 | 0.0876 | 3.86 |
| iron | 0.186 | 1.93 | 10.36 |
| copper | 0.123 | 1.33 | 10.80 |
| concrete | 4.73 | 22.0 | 4.66 |
| water | 22.9 | 81.2 | 3.54 |
| aluminum | 3.53 | 17.9 | 5.07 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over months and years
Ten half-lives is 52.5 days — a storage problem rather than a disposal one, with 1.1e-19% of today's activity still there after a year. The mean life 1/λ is 7.57 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 | 17.4 days |
| Time to fall to 1 % | 34.9 days |
| Time to fall to 0.1 % | 52.3 days |
Limits of these dose rates
- 0.0140 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 0.0342 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 1 line under 20 keV, carrying 5.82% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Xe-133
Other Xenon nuclides: Xe-133m
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.