Thorium-230
Th-230 · Thorium, Z = 90, A = 230
Thorium-230 (Th-230) is slow enough to be handled as a material rather than as a trace: 7.61e+8 Bq/g, or 0.0206 Ci/g, puts a gigabecquerel at 1.31 g. Decay is by alpha decay, half-life 75584 years, and shedding even one per cent of the activity takes 1,096 years.
Alpha emission is led by 4.687 MeV at 76.3%, one of 4 recorded lines. None of it reaches through skin, so the limit here is intake, not external dose.
Decay is the only handle: forty years leaves 99.96% of today's activity and ten thousand years leaves 91.24%, with ten half-lives at 755,824 years and a mean life of 109,042 years per atom.
Half-life 75584 years, 7.61e+8 Bq/g, and no line recorded
| Half-life | 75584 years (2.385e+12 s) |
| Decay mode | alpha decay |
| Specific activity | 7.61e+8 Bq/g (0.0206 Ci/g) |
4 alpha lines, strongest 4.687 MeV
4 recorded lines from 4.438 to 4.687 MeV, the strongest 4.687 MeV at 76.3% of 99.85% total alpha emission.
| Energy (MeV) | Emission probability (%) |
|---|---|
| 4.6870 | 76.3 |
| 4.6205 | 23.4 |
| 4.4798 | 0.12 |
| 4.4384 | 0.03 |
Activity over millennia
Ten half-lives is 755,824 years. On any timescale a facility can be planned over the activity is constant — 99.96% is left after forty years — and the mean life 1/λ is 109,042 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 | 251,079 years |
| Time to fall to 1 % | 502,159 years |
| Time to fall to 0.1 % | 753,238 years |
Limits — intake, not external dose
- Alpha reaches nothing through skin — Th-230 is an intake problem, not an external one.
- What every sheet leaves out, internal dose included.
Decay and mass calculators for Th-230
Other Thorium nuclides: Th-228, Th-229, Th-232
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.