Californium-249
Cf-249 · Californium, Z = 98, A = 249
A gigabecquerel of Cf-249 is 6.61 mg of material, which follows from a specific activity of 1.51e+11 Bq/g (4.09 Ci/g). Californium-249 decays by alpha decay with a half-life of 351 years; forty years leaves 92.40% of today's activity and ten thousand years leaves 2.7e-7%.
Alpha emission is led by 5.811 MeV at 82.4%, one of 12 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 92.40% of today's activity and ten thousand years leaves 2.7e-7%, with ten half-lives at 3,510 years and a mean life of 506 years per atom.
Half-life 351 years, 1.51e+11 Bq/g, and no line recorded
| Half-life | 351 years (1.108e+10 s) |
| Decay mode | alpha decay |
| Specific activity | 1.51e+11 Bq/g (4.09 Ci/g) |
12 alpha lines, strongest 5.811 MeV
12 recorded lines from 5.559 to 6.192 MeV, the strongest 5.811 MeV at 82.4% of 99.88% total alpha emission.
| Energy (MeV) | Emission probability (%) |
|---|---|
| 5.8105 | 82.4 |
| 5.7569 | 4.68 |
| 5.9438 | 3.29 |
| 5.9015 | 3.17 |
| 6.1924 | 2.44 |
| 5.8475 | 1.44 |
| 6.1385 | 1.32 |
| 5.7824 | 0.35 |
| 6.0728 | 0.34 |
| 5.6923 | 0.29 |
Activity over millennia
Ten half-lives is 3,510 years, which puts decay storage out of reach: 92.40% survives forty years. The mean life 1/λ, the quantity that enters an integrated dose, is 506 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 | 1,166 years |
| Time to fall to 1 % | 2,332 years |
| Time to fall to 0.1 % | 3,498 years |
Limits — intake, not external dose
- Alpha reaches nothing through skin — Cf-249 is an intake problem, not an external one.
- What every sheet leaves out, internal dose included.
Decay and mass calculators for Cf-249
Other Californium nuclides: Cf-252
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.