Samarium-147
Sm-147 · Samarium, Z = 62, A = 147
Samarium-147 (Sm-147) is slow enough to be handled as a material rather than as a trace: 839 Bq/g, or 2.27e-8 Ci/g, puts a gigabecquerel at 1.19 t. Decay is by alpha decay, half-life 1.073 × 10¹¹ years, and shedding even one per cent of the activity takes 1.56 billion years.
Alpha emission is led by 2.248 MeV at 100%. None of it reaches through skin, so the limit here is intake, not external dose.
Decay is the only handle: forty years leaves 100.00% of today's activity and ten thousand years leaves 100.00%, with ten half-lives at 1.07 trillion years and a mean life of 155 billion years per atom.
Half-life 1.073 × 10¹¹ years, 839 Bq/g, and no line recorded
| Half-life | 1.073 × 10¹¹ years (3.386e+18 s) |
| Decay mode | alpha decay |
| Specific activity | 839 Bq/g (2.27e-8 Ci/g) |
One alpha line at 2.248 MeV
One recorded line, 2.248 MeV at 100% — monoenergetic as far as this dataset goes.
| Energy (MeV) | Emission probability (%) |
|---|---|
| 2.2480 | 100 |
Activity over geological time
Ten half-lives is 1.07 trillion years. On any timescale a facility can be planned over the activity is constant — 100.00% is left after forty years — and the mean life 1/λ is 155 billion 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 | 356 billion years |
| Time to fall to 1 % | 713 billion years |
| Time to fall to 0.1 % | 1.07 trillion years |
Limits — intake, not external dose
- Alpha reaches nothing through skin — Sm-147 is an intake problem, not an external one.
- What every sheet leaves out, internal dose included.
Decay and mass calculators for Sm-147
Other Samarium nuclides: Sm-151, Sm-153, Sm-153m
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.