Uranium-233
U-233 · Uranium, Z = 92, A = 233
Uranium-233 (U-233) is slow enough to be handled as a material rather than as a trace: 3.57e+8 Bq/g, or 0.00964 Ci/g, puts a gigabecquerel at 2.80 g. Decay is by alpha decay, half-life 1.5919 × 10⁵ years, and shedding even one per cent of the activity takes 2,308 years.
Alpha emission is led by 4.824 MeV at 84.3%, one of 10 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 99.98% of today's activity and ten thousand years leaves 95.74%, with ten half-lives at 1.59 million years and a mean life of 229,658 years per atom.
Half-life 1.5919 × 10⁵ years, 3.57e+8 Bq/g, and no line recorded
| Half-life | 1.5919 × 10⁵ years (5.024e+12 s) |
| Decay mode | alpha decay |
| Specific activity | 3.57e+8 Bq/g (0.00964 Ci/g) |
10 alpha lines, strongest 4.824 MeV
10 recorded lines from 4.507 to 4.824 MeV, the strongest 4.824 MeV at 84.3% of 99.70% total alpha emission.
| Energy (MeV) | Emission probability (%) |
|---|---|
| 4.8242 | 84.3 |
| 4.7835 | 13.2 |
| 4.7290 | 1.61 |
| 4.7960 | 0.28 |
| 4.7540 | 0.163 |
| 4.7010 | 0.06 |
| 4.6640 | 0.042 |
| 4.5130 | 0.018 |
| 4.7580 | 0.016 |
| 4.5070 | 0.012 |
Activity over geological time
Ten half-lives is 1.59 million years. On any timescale a facility can be planned over the activity is constant — 99.98% is left after forty years — and the mean life 1/λ is 229,658 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 | 528,806 years |
| Time to fall to 1 % | 1.06 million years |
| Time to fall to 0.1 % | 1.59 million years |
Limits — intake, not external dose
- Alpha reaches nothing through skin — U-233 is an intake problem, not an external one.
- What every sheet leaves out, internal dose included.
Decay and mass calculators for U-233
Other Uranium nuclides: U-232, U-234, U-235, U-236, U-238, U-238m
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.