Gold-198
Au-198 · Gold, Z = 79, A = 198
At 9.06e+15 Bq/g — 2.45e+5 Ci/g — a gigabecquerel of Au-198 amounts to 110 ng, which is why activity rather than mass is how anyone states the quantity. Gold-198 decays by beta-minus decay with a half-life of 2.6941 days, falling to 16.51% of today's activity in a week and 6.8e-9% in three months.
1 GBq at 1 m reads 0.0546 mGy/h, and 1 Ci at the same distance 2.02 mGy/h, from an air kerma rate constant of 0.0546 mGy·m²/(GBq·h) — 1.4× less than Cs-137 and 5.6× less than Co-60, and 39 of 96 among the photon emitters carried here.
8 lines clear the 20 keV cutoff, but one of them carries 90% of the dose rate. The leading one is 411.8 keV at 97.7% of the total — its emission probability is 95.62%, which is also the highest.
Halving the air kerma rate calls for 2.77 mm of lead, or 9.47 mm of steel where lead is unwelcome, and a factor of ten calls for 9.32 mm of lead — sheet thicknesses that a glovebox or a transport container can carry. Reaching 20 µSv/h from 1 GBq at a metre takes 4.02 mm of lead.
Half-life, specific activity and dose rate
| Half-life | 2.6941 days (2.328e+5 s) |
| Decay mode | beta-minus decay |
| Specific activity | 9.06e+15 Bq/g (2.45e+5 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.0546 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.0546 mGy/h |
| Dose rate, 1 Ci at 1 m | 2.02 mGy/h |
| Kerma-weighted mean photon energy | 416.2 keV |
412 keV carries 98% of the dose rate
1 further line below the 20 keV cutoff, the highest at 11.78 keV and 1.19% emission probability in all, is excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 411.80 | 95.62 | 97.72 |
| 675.88 | 0.80512 | 1.34 |
| 1087.68 | 0.15892 | 0.40 |
| 70.82 | 1.36883 | 0.22 |
| 68.89 | 0.80747 | 0.13 |
| 81.28 | 0.60066 | 0.10 |
| 80.32 | 0.46455 | 0.08 |
| 82.48 | 0.13611 | 0.02 |
2.77 mm of lead halves this spectrum
Solved numerically across all 8 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 2.77 | 9.32 | 3.37 |
| tungsten | 1.95 | 6.58 | 3.36 |
| iron | 9.47 | 31.7 | 3.34 |
| copper | 8.32 | 27.8 | 3.34 |
| concrete | 31.2 | 104 | 3.33 |
| water | 66.2 | 220 | 3.33 |
| aluminum | 28.0 | 93.4 | 3.33 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over days and weeks
Ten half-lives is 26.9 days — a storage problem rather than a disposal one, with 1.5e-39% of today's activity still there after a year. The mean life 1/λ is 3.89 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 | 8.95 days |
| Time to fall to 1 % | 17.9 days |
| Time to fall to 0.1 % | 26.8 days |
Limits of these dose rates
- 0.0546 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 2.77 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 1 line under 20 keV, carrying 1.19% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Au-198
Other Gold nuclides: Au-198m
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.