Europium-154
Eu-154 · Europium, Z = 63, A = 154
Europium-154 decays by beta-minus decay, half-life 8.601 years. Specific activity is 9.99e+12 Bq/g (270 Ci/g), so a gigabecquerel comes to 100 µg — weighable, but on an analytical balance. Over a year the activity falls to 92.26%, and over forty years to 3.98%.
1 GBq at 1 m reads 0.158 mGy/h, and 1 Ci at the same distance 5.85 mGy/h, from an air kerma rate constant of 0.158 mGy·m²/(GBq·h) — 2.1× Cs-137 and 1.9× less than Co-60, and 11 of 96 among the photon emitters carried here.
59 lines clear the 20 keV cutoff, but 10 of them carry 90% of the dose rate. The leading one is 1274.4 keV at 34.2% of the total — its emission probability is 34.8%, which is also the highest.
This is a shield that has to be designed: 7.52 mm of lead for a factor of two and 28.3 mm for a factor of ten, or 13.4 mm of steel to halve it, at which point the mass of the shield is part of the problem. Reaching 20 µSv/h from 1 GBq at a metre takes 25.2 mm of lead.
Half-life, specific activity and dose rate
| Half-life | 8.601 years (2.714e+8 s) |
| Decay mode | beta-minus decay |
| Specific activity | 9.99e+12 Bq/g (270 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.158 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.158 mGy/h |
| Dose rate, 1 Ci at 1 m | 5.85 mGy/h |
| Kerma-weighted mean photon energy | 977.9 keV |
59 lines above the cutoff, and what each contributes
1 further line below the 20 keV cutoff, the highest at 6.86 keV and 7.11% emission probability in all, is excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 1274.43 | 34.8 | 34.16 |
| 1004.76 | 18.01 | 14.64 |
| 723.30 | 20.06 | 12.24 |
| 873.18 | 12.08 | 8.71 |
| 996.29 | 10.48 | 8.46 |
| 123.07 | 40.4 | 3.48 |
| 756.80 | 4.52 | 2.88 |
| 591.75 | 4.95 | 2.51 |
| 1596.48 | 1.797 | 2.08 |
| 247.93 | 6.89 | 1.38 |
| 692.42 | 1.777 | 1.04 |
| 43.00 | 13.16667 | 0.95 |
| 1246.12 | 0.856 | 0.83 |
| 1494.05 | 0.698 | 0.77 |
Showing the 14 largest contributors of 59 lines above the cutoff; the remainder together carry 5.86% of the dose rate.
7.52 mm of lead halves this spectrum
Solved numerically across all 59 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 7.52 | 28.3 | 3.76 |
| tungsten | 4.77 | 17.8 | 3.73 |
| iron | 13.4 | 48.1 | 3.57 |
| copper | 12.0 | 42.9 | 3.59 |
| concrete | 43.4 | 152 | 3.51 |
| water | 92.5 | 322 | 3.48 |
| aluminum | 39.0 | 137 | 3.51 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over decades and centuries
Ten half-lives is 86.0 years, which puts decay storage out of reach: 3.98% survives forty years. The mean life 1/λ, the quantity that enters an integrated dose, is 12.4 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 | 28.6 years |
| Time to fall to 1 % | 57.1 years |
| Time to fall to 0.1 % | 85.7 years |
Limits of these dose rates
- 0.158 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 7.52 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 1 line under 20 keV, carrying 7.11% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Eu-154
Other Europium nuclides: Eu-152, Eu-152m1, Eu-152m2, Eu-154m
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.