Germanium-68
Ge-68 · Germanium, Z = 32, A = 68
At 2.63e+14 Bq/g — 7.10e+3 Ci/g — a gigabecquerel of Ge-68 amounts to 3.81 µg, which is why activity rather than mass is how anyone states the quantity. Germanium-68 decays by electron capture with a half-life of 270.93 days, falling to 92.61% of today's activity in a month and 39.28% in a year.
All 6 recorded photon lines sit below the 20 keV cutoff, so Γ is zero by convention and no external dose rate is quoted. The strongest line is 10.37 keV. A monitor calibrated on Cs-137 under-responds at these energies, so a reading taken without an energy correction understates Ge-68 rather than missing it outright. The recorded spectrum runs 1.13 to 10.4 keV and carries 51.9% emission probability in all, which sets what a thin-window or proportional detector has to see.
The photon field around Ge-68 is Ga-68's. Ga-68 (67.71 minutes) follows close enough to be present in any aged source, and its air kerma rate constant is 0.129 mGy·m²/(GBq·h), where no photon line is recorded for Ge-68. Shield for Ga-68.
Decay is the only handle: a month leaves 92.61% of today's activity and a year leaves 39.28%, with ten half-lives at 7.42 years and a mean life of 1.07 years per atom.
Half-life 270.93 days, 2.63e+14 Bq/g, and no line recorded
| Half-life | 270.93 days (2.341e+7 s) |
| Decay mode | electron capture |
| Specific activity | 2.63e+14 Bq/g (7.10e+3 Ci/g) |
Activity over months and years
Ten half-lives is 7.42 years — a storage problem rather than a disposal one, with 39.28% of today's activity still there after a year. The mean life 1/λ is 1.07 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 | 2.46 years |
| Time to fall to 1 % | 4.93 years |
| Time to fall to 0.1 % | 7.39 years |
Limits of these figures
- Γ excludes 6 lines under 20 keV, carrying 51.9% of all emissions.
- What every sheet leaves out, internal dose included.
Decay and mass calculators for Ge-68
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.