Europium-154m
Eu-154m · Europium, Z = 63, A = 154 · isomeric state m
Europium-154m (Eu-154m) carries 9.76e+17 Bq/g, or 2.64e+7 Ci/g: a gigabecquerel is 1.02 ng, no weighable quantity at all. It decays by isomeric transition with a half-life of 46.3 minutes, which leaves 4.3e-8% of today's activity after a day and 2.9e-64% after a week.
At 0.0134 mGy·m²/(GBq·h) the air kerma rate constant is 5.8× less than Cs-137 and 23× less than Co-60, placing it 63 of 96 photon emitters in this dataset. 1 GBq at 1 m reads 0.0134 mGy/h, and 1 Ci at the same distance 0.496 mGy/h.
12 lines clear the 20 keV cutoff, but 7 of them carry 90% of the dose rate. The leading one is 68.2 keV at 23.7% of the total — its emission probability is 37%, which is also the highest.
Shielding barely arises: 0.0638 mm of lead halves the air kerma rate and 0.316 mm takes it to a tenth, thicknesses a source capsule is likely to exceed on its own. Steel does the halving in 0.442 mm. At 1 GBq and a metre it is already under 20 µSv/h with nothing in the way. The tenth-value layer runs 5.0 times the half-value layer, not the 3.32 a single energy would give.
Half-life, specific activity and dose rate
| Half-life | 46.3 minutes (2778 s) |
| Decay mode | isomeric transition |
| Specific activity | 9.76e+17 Bq/g (2.64e+7 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.0134 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.0134 mGy/h |
| Dose rate, 1 Ci at 1 m | 0.496 mGy/h |
| Kerma-weighted mean photon energy | 58.94 keV |
12 lines above the cutoff, and what each contributes
1 further line below the 20 keV cutoff, the highest at 6.60 keV and 29.4% emission probability in all, is excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 68.17 | 37 | 23.66 |
| 100.88 | 26.64 | 21.42 |
| 35.80 | 12.58 | 14.39 |
| 41.54 | 14.58718 | 12.99 |
| 31.78 | 5.55 | 7.89 |
| 40.90 | 8.08421 | 7.35 |
| 47.65 | 5.7812 | 4.31 |
| 47.15 | 4.59555 | 3.48 |
| 28.78 | 1.073 | 1.85 |
| 27.51 | 0.888 | 1.68 |
| 48.25 | 1.18565 | 0.87 |
| 32.61 | 0.0814 | 0.11 |
0.0638 mm of lead halves this spectrum
Solved numerically across all 12 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 0.0638 | 0.316 | 4.96 |
| tungsten | 0.0497 | 0.245 | 4.92 |
| iron | 0.442 | 3.47 | 7.86 |
| copper | 0.294 | 2.42 | 8.23 |
| concrete | 8.06 | 34.7 | 4.30 |
| water | 29.2 | 102 | 3.51 |
| aluminum | 6.35 | 29.0 | 4.56 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over the first hours
Ten half-lives is 7.72 hours, so the activity moves measurably while a count is running: every figure has to carry the time it was referred to. The mean life 1/λ is 1.11 hours.
| 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 | 2.56 hours |
| Time to fall to 1 % | 5.13 hours |
| Time to fall to 0.1 % | 7.69 hours |
Limits of these dose rates
- 0.0134 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 0.0638 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 1 line under 20 keV, carrying 29.4% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Eu-154m
Other Europium nuclides: Eu-152, Eu-152m1, Eu-152m2, Eu-154
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.