Europium-152m2
Eu-152m2 · Europium, Z = 63, A = 152 · isomeric state m2
Europium-152m2 (Eu-152m2) carries 4.77e+17 Bq/g, or 1.29e+7 Ci/g: a gigabecquerel is 2.10 ng, no weighable quantity at all. It decays by isomeric transition with a half-life of 96 minutes, which leaves 3.1e-3% of today's activity after a day and 2.5e-30% after a week.
At 0.00996 mGy·m²/(GBq·h) the air kerma rate constant is 7.7× less than Cs-137 and 31× less than Co-60, placing it 71 of 96 photon emitters in this dataset. 1 GBq at 1 m reads 0.00996 mGy/h, and 1 Ci at the same distance 0.368 mGy/h.
8 lines clear the 20 keV cutoff, but 3 of them carry 90% of the dose rate. The leading one is 89.8 keV at 68.3% of the total — its emission probability is 69.7%, which is also the highest.
Shielding barely arises: 0.0718 mm of lead halves the air kerma rate and 0.251 mm takes it to a tenth, thicknesses a source capsule is likely to exceed on its own. Steel does the halving in 1.03 mm. At 1 GBq and a metre it is already under 20 µSv/h with nothing in the way. The tenth-value layer runs 3.5 times the half-value layer, not the 3.32 a single energy would give.
Half-life, specific activity and dose rate
| Half-life | 96 minutes (5760 s) |
| Decay mode | isomeric transition |
| Specific activity | 4.77e+17 Bq/g (1.29e+7 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.00996 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.00996 mGy/h |
| Dose rate, 1 Ci at 1 m | 0.368 mGy/h |
| Kerma-weighted mean photon energy | 75.23 keV |
89.8 keV leads, and 3 lines make 90%
3 further lines below the 20 keV cutoff, the highest at 18.21 keV and 27.3% emission probability in all, are excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 89.85 | 69.7 | 68.25 |
| 41.54 | 11.62045 | 13.95 |
| 40.90 | 6.44005 | 7.89 |
| 47.65 | 4.60543 | 4.63 |
| 47.15 | 3.66091 | 3.73 |
| 48.25 | 0.94452 | 0.93 |
| 77.23 | 0.68306 | 0.60 |
| 39.75 | 0.0134 | 0.02 |
0.0718 mm of lead halves this spectrum
Solved numerically across all 8 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 0.0718 | 0.251 | 3.50 |
| tungsten | 0.0538 | 0.185 | 3.44 |
| iron | 1.03 | 5.25 | 5.07 |
| copper | 0.711 | 3.67 | 5.16 |
| concrete | 12.1 | 45.7 | 3.78 |
| water | 34.9 | 119 | 3.40 |
| aluminum | 10.0 | 39.1 | 3.90 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over the first hours
Ten half-lives is 16.0 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 2.31 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 | 5.32 hours |
| Time to fall to 1 % | 10.6 hours |
| Time to fall to 0.1 % | 15.9 hours |
Limits of these dose rates
- 0.00996 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 0.0718 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 3 lines under 20 keV, carrying 27.3% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Eu-152m2
Other Europium nuclides: Eu-152, Eu-152m1, 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.