Indium-111
In-111 · Indium, Z = 49, A = 111
Indium-111 (In-111) carries 1.55e+16 Bq/g, or 4.20e+5 Ci/g: a gigabecquerel is 64.4 ng, no weighable quantity at all. It decays by electron capture with a half-life of 2.8047 days, which leaves 17.73% of today's activity after a week and 1.7e-8% after three months.
1 GBq at 1 m reads 0.0807 mGy/h, and 1 Ci at the same distance 2.98 mGy/h, from an air kerma rate constant of 0.0807 mGy·m²/(GBq·h) — 1.0× Cs-137 and 3.8× less than Co-60, and 27 of 96 among the photon emitters carried here.
8 lines clear the 20 keV cutoff, but 5 of them carry 90% of the dose rate. The leading one is 245.3 keV at 36.4% of the total — its emission probability is 94.09%, which is also the highest.
Shielding barely arises: 0.158 mm of lead halves the air kerma rate and 1.94 mm takes it to a tenth, thicknesses a source capsule is likely to exceed on its own. Steel does the halving in 1.49 mm. Reaching 20 µSv/h from 1 GBq at a metre takes 0.874 mm of lead. The tenth-value layer runs 12.2 times the half-value layer, not the 3.32 a single energy would give.
Half-life, specific activity and dose rate
| Half-life | 2.8047 days (2.423e+5 s) |
| Decay mode | electron capture |
| Specific activity | 1.55e+16 Bq/g (4.20e+5 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.0807 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.0807 mGy/h |
| Dose rate, 1 Ci at 1 m | 2.98 mGy/h |
| Kerma-weighted mean photon energy | 138.0 keV |
8 lines above the cutoff, and what each contributes
1 further line below the 20 keV cutoff, the highest at 3.39 keV and 6.76% emission probability in all, is excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 245.35 | 94.09 | 36.40 |
| 171.28 | 90.65 | 22.75 |
| 23.17 | 44.32507 | 19.97 |
| 22.98 | 23.56764 | 10.80 |
| 26.38 | 14.60372 | 5.01 |
| 26.18 | 12.35509 | 4.31 |
| 26.64 | 2.24863 | 0.76 |
| 150.81 | 0.003 | 0.00 |
0.158 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 | 0.158 | 1.94 | 12.22 |
| tungsten | 0.118 | 1.44 | 12.17 |
| iron | 1.49 | 16.0 | 10.77 |
| copper | 1.22 | 13.3 | 10.85 |
| concrete | 7.39 | 61.9 | 8.38 |
| water | 26.8 | 133 | 4.98 |
| aluminum | 6.09 | 55.3 | 9.09 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over days and weeks
Ten half-lives is 28.0 days — a storage problem rather than a disposal one, with 6.3e-38% of today's activity still there after a year. The mean life 1/λ is 4.05 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 | 9.32 days |
| Time to fall to 1 % | 18.6 days |
| Time to fall to 0.1 % | 28.0 days |
Limits of these dose rates
- 0.0807 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 0.158 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 1 line under 20 keV, carrying 6.76% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for In-111
Other Indium nuclides: In-111m
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.