Cerium-141
Ce-141 · Cerium, Z = 58, A = 141
At 1.05e+15 Bq/g — 2.85e+4 Ci/g — a gigabecquerel of Ce-141 amounts to 948 ng, which is why activity rather than mass is how anyone states the quantity. Cerium-141 decays by beta-minus decay with a half-life of 32.504 days, falling to 52.74% of today's activity in a month and 0.04% in a year.
At 0.0109 mGy·m²/(GBq·h) the air kerma rate constant is 7.1× less than Cs-137 and 28× less than Co-60, placing it 68 of 96 photon emitters in this dataset. 1 GBq at 1 m reads 0.0109 mGy/h, and 1 Ci at the same distance 0.403 mGy/h.
6 lines clear the 20 keV cutoff, but 3 of them carry 90% of the dose rate. The leading one is 145.4 keV at 73.5% of the total — its emission probability is 48.3%, which is also the highest.
Shielding barely arises: 0.165 mm of lead halves the air kerma rate and 0.808 mm takes it to a tenth, thicknesses a source capsule is likely to exceed on its own. Steel does the halving in 2.38 mm. At 1 GBq and a metre it is already under 20 µSv/h with nothing in the way. The tenth-value layer runs 4.9 times the half-value layer, not the 3.32 a single energy would give.
Half-life, specific activity and dose rate
| Half-life | 32.504 days (2.808e+6 s) |
| Decay mode | beta-minus decay |
| Specific activity | 1.05e+15 Bq/g (2.85e+4 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.0109 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.0109 mGy/h |
| Dose rate, 1 Ci at 1 m | 0.403 mGy/h |
| Kerma-weighted mean photon energy | 116.8 keV |
145 keV leads, and 3 lines make 90%
1 further line below the 20 keV cutoff, the highest at 5.64 keV and 2.46% emission probability in all, is excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 145.44 | 48.3 | 73.51 |
| 36.03 | 8.76197 | 12.21 |
| 35.55 | 4.79805 | 6.85 |
| 41.27 | 3.34797 | 3.70 |
| 40.86 | 2.66558 | 2.99 |
| 41.77 | 0.68239 | 0.74 |
0.165 mm of lead halves this spectrum
Solved numerically across all 6 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 0.165 | 0.808 | 4.88 |
| tungsten | 0.125 | 0.604 | 4.84 |
| iron | 2.38 | 12.3 | 5.17 |
| copper | 1.84 | 9.50 | 5.18 |
| concrete | 14.0 | 59.6 | 4.26 |
| water | 38.0 | 135 | 3.55 |
| aluminum | 11.9 | 52.8 | 4.44 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over months and years
Ten half-lives is 325 days — a storage problem rather than a disposal one, with 0.04% of today's activity still there after a year. The mean life 1/λ is 46.9 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 | 108 days |
| Time to fall to 1 % | 216 days |
| Time to fall to 0.1 % | 324 days |
Limits of these dose rates
- 0.0109 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 0.165 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 1 line under 20 keV, carrying 2.46% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Ce-141
Other Cerium nuclides: Ce-139, Ce-139m, Ce-144
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.