Calcium-41
Ca-41 · Calcium, Z = 20, A = 41
A gigabecquerel of Ca-41 is 308 mg of material, which follows from a specific activity of 3.25e+9 Bq/g (0.0878 Ci/g). Calcium-41 decays by electron capture with a half-life of 9.94 × 10⁴ years; forty years leaves 99.97% of today's activity and ten thousand years leaves 93.26%.
At 3.25e+9 Bq per gram, a 1 kBq aliquot of Ca-41 is 308 ng — the quantity that has to be recovered, dissolved and counted, because this dataset carries no photon, beta or alpha line for it above the reporting thresholds.
Decay is the only handle: forty years leaves 99.97% of today's activity and ten thousand years leaves 93.26%, with ten half-lives at 993,979 years and a mean life of 143,401 years per atom.
Half-life 9.94 × 10⁴ years, 3.25e+9 Bq/g, and no line recorded
| Half-life | 9.94 × 10⁴ years (3.137e+12 s) |
| Decay mode | electron capture |
| Specific activity | 3.25e+9 Bq/g (0.0878 Ci/g) |
Activity over millennia
Ten half-lives is 993,979 years. On any timescale a facility can be planned over the activity is constant — 99.97% is left after forty years — and the mean life 1/λ is 143,401 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 | 330,193 years |
| Time to fall to 1 % | 660,385 years |
| Time to fall to 0.1 % | 990,578 years |
Limits of these figures
- What every sheet leaves out, internal dose included.
Decay and mass calculators for Ca-41
Other Calcium nuclides: Ca-45
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.