Europium-152m1
Eu-152m1 · Europium, Z = 63, A = 152 · isomeric state m1
Europium-152m1 (Eu-152m1) carries 8.20e+16 Bq/g, or 2.22e+6 Ci/g: a gigabecquerel is 12.2 ng, no weighable quantity at all. It decays by beta-minus decay with a half-life of 9.3116 hours, which leaves 16.75% of today's activity after a day and 3.7e-4% after a week.
At 0.0404 mGy·m²/(GBq·h) the air kerma rate constant is 1.9× less than Cs-137 and 7.6× less than Co-60, placing it 45 of 96 photon emitters in this dataset. 1 GBq at 1 m reads 0.0404 mGy/h, and 1 Ci at the same distance 1.49 mGy/h.
54 lines clear the 20 keV cutoff, but 7 of them carry 90% of the dose rate. The leading one is 841.6 keV at 38.9% of the total — its emission probability is 14.2%, which is also the highest.
This is a shield that has to be designed: 6.22 mm of lead for a factor of two and 24.8 mm for a factor of ten, or 11.5 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 6.32 mm of lead.
Half-life, specific activity and dose rate
| Half-life | 9.3116 hours (3.352e+4 s) |
| Decay mode | beta-minus decay |
| Specific activity | 8.20e+16 Bq/g (2.22e+6 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.0404 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.0404 mGy/h |
| Dose rate, 1 Ci at 1 m | 1.49 mGy/h |
| Kerma-weighted mean photon energy | 819.7 keV |
54 lines above the cutoff, and what each contributes
2 further lines below the 20 keV cutoff, the highest at 6.86 keV and 4.72% emission probability in all, are excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 841.63 | 14.2 | 38.87 |
| 963.38 | 11.6 | 35.63 |
| 40.12 | 13.2 | 4.09 |
| 1314.61 | 0.93 | 3.66 |
| 1389.03 | 0.82 | 3.36 |
| 344.29 | 2.4 | 2.73 |
| 121.77 | 7 | 2.33 |
| 39.52 | 7.3 | 2.32 |
| 970.33 | 0.56 | 1.73 |
| 46.00 | 5.2 | 1.35 |
| 45.52 | 4.1 | 1.08 |
| 562.98 | 0.22 | 0.42 |
| 961.14 | 0.128 | 0.39 |
| 46.58 | 1.07 | 0.27 |
Showing the 14 largest contributors of 54 lines above the cutoff; the remainder together carry 1.77% of the dose rate.
6.22 mm of lead halves this spectrum
Solved numerically across all 54 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 6.22 | 24.8 | 3.99 |
| tungsten | 3.97 | 15.8 | 3.97 |
| iron | 11.5 | 44.1 | 3.83 |
| copper | 10.3 | 39.4 | 3.84 |
| concrete | 37.3 | 140 | 3.75 |
| water | 81.5 | 296 | 3.63 |
| aluminum | 33.5 | 126 | 3.76 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over days and weeks
Ten half-lives is 3.88 days, 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 13.4 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 | 1.29 days |
| Time to fall to 1 % | 2.58 days |
| Time to fall to 0.1 % | 3.87 days |
Limits of these dose rates
- 0.0404 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 6.22 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 2 lines under 20 keV, carrying 4.72% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Eu-152m1
Other Europium nuclides: Eu-152, 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.