Gallium-67
Ga-67 · Gallium, Z = 31, A = 67
Gallium-67 (Ga-67) carries 2.21e+16 Bq/g, or 5.98e+5 Ci/g: a gigabecquerel is 45.2 ng, no weighable quantity at all. It decays by electron capture with a half-life of 3.2617 days, which leaves 22.59% of today's activity after a week and 4.0e-7% after three months.
At 0.0189 mGy·m²/(GBq·h) the air kerma rate constant is 4.1× less than Cs-137 and 16× less than Co-60, placing it 55 of 96 photon emitters in this dataset. 1 GBq at 1 m reads 0.0189 mGy/h, and 1 Ci at the same distance 0.699 mGy/h.
10 lines clear the 20 keV cutoff, but 4 of them carry 90% of the dose rate. The leading one is 300.2 keV at 34.8% of the total — its emission probability is 16.64%, which is lower than the 21.41% of the 184.6 keV line it outranks.
A half-value layer of 0.656 mm in lead puts this in foil and thin sheet, with 5.36 mm needed if the material is steel; ten-fold attenuation comes at 4.28 mm of lead. At 1 GBq and a metre it is already under 20 µSv/h with nothing in the way. The tenth-value layer runs 6.5 times the half-value layer, not the 3.32 a single energy would give.
Half-life, specific activity and dose rate
| Half-life | 3.2617 days (2.818e+5 s) |
| Decay mode | electron capture |
| Specific activity | 2.21e+16 Bq/g (5.98e+5 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.0189 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.0189 mGy/h |
| Dose rate, 1 Ci at 1 m | 0.699 mGy/h |
| Kerma-weighted mean photon energy | 241.4 keV |
10 lines above the cutoff, and what each contributes
4 further lines below the 20 keV cutoff, the highest at 9.61 keV and 59.6% emission probability in all, are excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 300.22 | 16.64 | 34.85 |
| 184.58 | 21.41 | 25.16 |
| 93.31 | 38.81 | 20.67 |
| 393.53 | 4.56 | 12.83 |
| 208.95 | 2.46 | 3.36 |
| 91.27 | 3.11 | 1.63 |
| 887.69 | 0.148 | 0.91 |
| 794.38 | 0.054 | 0.30 |
| 494.17 | 0.0684 | 0.24 |
| 703.11 | 0.0105 | 0.05 |
0.656 mm of lead halves this spectrum
Solved numerically across all 10 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 0.656 | 4.28 | 6.52 |
| tungsten | 0.484 | 3.10 | 6.39 |
| iron | 5.36 | 22.1 | 4.12 |
| copper | 4.35 | 18.8 | 4.33 |
| concrete | 23.6 | 81.6 | 3.46 |
| water | 51.9 | 177 | 3.41 |
| aluminum | 20.9 | 72.8 | 3.48 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over months and years
Ten half-lives is 32.6 days — a storage problem rather than a disposal one, with 2.0e-32% of today's activity still there after a year. The mean life 1/λ is 4.71 days.
| 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 | 10.8 days |
| Time to fall to 1 % | 21.7 days |
| Time to fall to 0.1 % | 32.5 days |
Limits of these dose rates
- 0.0189 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 0.656 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 4 lines under 20 keV, carrying 59.6% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Ga-67
Other Gallium nuclides: Ga-68
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.