Indium-111m
In-111m · Indium, Z = 49, A = 111 · isomeric state m
Indium-111m (In-111m) carries 8.15e+18 Bq/g, or 2.20e+8 Ci/g: a gigabecquerel is 123 pg, no weighable quantity at all. It decays by isomeric transition with a half-life of 7.7 minutes, which leaves 5.1e-55% of today's activity after a day and 0% after a week.
1 GBq at 1 m reads 0.0668 mGy/h, and 1 Ci at the same distance 2.47 mGy/h, from an air kerma rate constant of 0.0668 mGy·m²/(GBq·h) — 1.2× less than Cs-137 and 4.6× less than Co-60, and 34 of 96 among the photon emitters carried here.
6 lines clear the 20 keV cutoff, but one of them carries 90% of the dose rate. The leading one is 537.0 keV at 95.1% of the total — its emission probability is 87%, which is also the highest.
Halving the air kerma rate calls for 3.88 mm of lead, or 10.0 mm of steel where lead is unwelcome, and a factor of ten calls for 13.6 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 6.97 mm of lead.
Half-life, specific activity and dose rate
| Half-life | 7.7 minutes (462.0 s) |
| Decay mode | isomeric transition |
| Specific activity | 8.15e+18 Bq/g (2.20e+8 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.0668 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.0668 mGy/h |
| Dose rate, 1 Ci at 1 m | 2.47 mGy/h |
| Kerma-weighted mean photon energy | 511.7 keV |
537 keV carries 95% of the dose rate
1 further line below the 20 keV cutoff, the highest at 3.57 keV and 0.811% emission probability in all, is excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 537.00 | 87 | 95.05 |
| 24.21 | 4.85414 | 2.41 |
| 24.00 | 2.58726 | 1.31 |
| 27.58 | 1.62074 | 0.61 |
| 27.37 | 1.36196 | 0.52 |
| 27.86 | 0.25877 | 0.10 |
3.88 mm of lead halves this spectrum
Solved numerically across all 6 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 3.88 | 13.6 | 3.51 |
| tungsten | 2.64 | 9.27 | 3.51 |
| iron | 10.0 | 35.2 | 3.51 |
| copper | 8.89 | 31.2 | 3.51 |
| concrete | 32.3 | 113 | 3.51 |
| water | 68.7 | 240 | 3.49 |
| aluminum | 29.1 | 102 | 3.51 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over the first hours
Ten half-lives is 1.28 hours, so the activity moves measurably while a count is running: every figure has to carry the time it was referred to. The mean life 1/λ is 11.1 minutes.
| 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 | 25.6 minutes |
| Time to fall to 1 % | 51.2 minutes |
| Time to fall to 0.1 % | 1.28 hours |
Limits of these dose rates
- 0.0668 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 3.88 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 1 line under 20 keV, carrying 0.811% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for In-111m
Other Indium nuclides: In-111
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.