Europium-152
Eu-152 · Europium, Z = 63, A = 152
Europium-152 decays by electron capture with beta-plus, half-life 13.517 years. Specific activity is 6.44e+12 Bq/g (174 Ci/g), so a gigabecquerel comes to 155 µg — weighable, but on an analytical balance. Over a year the activity falls to 95.00%, and over forty years to 12.86%.
1 GBq at 1 m reads 0.152 mGy/h, and 1 Ci at the same distance 5.63 mGy/h, from an air kerma rate constant of 0.152 mGy·m²/(GBq·h) — 2.0× Cs-137 and 2.0× less than Co-60, and 12 of 96 among the photon emitters carried here.
58 lines clear the 20 keV cutoff, but 15 of them carry 90% of the dose rate. The leading one is 1408.0 keV at 22.9% of the total — its emission probability is 20.87%, which is also the highest.
This is a shield that has to be designed: 6.24 mm of lead for a factor of two and 27.7 mm for a factor of ten, or 12.1 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 23.9 mm of lead. The tenth-value layer runs 4.4 times the half-value layer, not the 3.32 a single energy would give.
Half-life, specific activity and dose rate
| Half-life | 13.517 years (4.266e+8 s) |
| Decay mode | electron capture with beta-plus |
| Specific activity | 6.44e+12 Bq/g (174 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.152 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.152 mGy/h |
| Dose rate, 1 Ci at 1 m | 5.63 mGy/h |
| Kerma-weighted mean photon energy | 924.9 keV |
58 lines above the cutoff, and what each contributes
2 further lines below the 20 keV cutoff, the highest at 6.86 keV and 14.2% emission probability in all, are excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 1408.01 | 20.87 | 22.92 |
| 1112.08 | 13.67 | 12.51 |
| 964.06 | 14.51 | 11.82 |
| 1085.84 | 10.11 | 9.08 |
| 778.90 | 12.93 | 8.77 |
| 344.28 | 26.59 | 8.03 |
| 867.38 | 4.23 | 3.15 |
| 40.12 | 37.8 | 3.10 |
| 121.78 | 28.53 | 2.52 |
| 39.52 | 20.87 | 1.76 |
| 1299.14 | 1.633 | 1.69 |
| 1089.74 | 1.734 | 1.56 |
| 244.70 | 7.55 | 1.54 |
| 1212.95 | 1.415 | 1.39 |
Showing the 14 largest contributors of 58 lines above the cutoff; the remainder together carry 10.17% of the dose rate.
6.24 mm of lead halves this spectrum
Solved numerically across all 58 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 6.24 | 27.7 | 4.43 |
| tungsten | 3.99 | 17.3 | 4.34 |
| iron | 12.1 | 46.6 | 3.84 |
| copper | 10.8 | 41.6 | 3.86 |
| concrete | 39.5 | 148 | 3.75 |
| water | 85.5 | 313 | 3.66 |
| aluminum | 35.4 | 133 | 3.76 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over decades and centuries
Ten half-lives is 135 years, which puts decay storage out of reach: 12.86% survives forty years. The mean life 1/λ, the quantity that enters an integrated dose, is 19.5 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 | 44.9 years |
| Time to fall to 1 % | 89.8 years |
| Time to fall to 0.1 % | 135 years |
Limits of these dose rates
- 0.152 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 6.24 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 2 lines under 20 keV, carrying 14.2% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Eu-152
Other Europium nuclides: Eu-152m1, Eu-152m2, Eu-154, Eu-154m
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.