Tin-113m
Sn-113m · Tin, Z = 50, A = 113 · isomeric state m
Tin-113m (Sn-113m) carries 2.88e+18 Bq/g, or 7.78e+7 Ci/g: a gigabecquerel is 347 pg, no weighable quantity at all. It decays by isomeric transition with a half-life of 21.4 minutes, which leaves 5.5e-19% of today's activity after a day and 1.6e-140% after a week.
At 0.0173 mGy·m²/(GBq·h) the air kerma rate constant is 4.5× less than Cs-137 and 18× less than Co-60, placing it 59 of 96 photon emitters in this dataset. 1 GBq at 1 m reads 0.0173 mGy/h, and 1 Ci at the same distance 0.639 mGy/h.
11 lines clear the 20 keV cutoff, but 5 of them carry 90% of the dose rate. The leading one is 25.3 keV at 41.6% of the total — its emission probability is 23.74282%, which is also the highest.
Shielding barely arises: 0.0137 mm of lead halves the air kerma rate and 0.0468 mm takes it to a tenth, thicknesses a source capsule is likely to exceed on its own. Steel does the halving in 0.0709 mm. At 1 GBq and a metre it is already under 20 µSv/h with nothing in the way.
Half-life, specific activity and dose rate
| Half-life | 21.4 minutes (1284 s) |
| Decay mode | isomeric transition |
| Specific activity | 2.88e+18 Bq/g (7.78e+7 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.0173 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.0173 mGy/h |
| Dose rate, 1 Ci at 1 m | 0.639 mGy/h |
| Kerma-weighted mean photon energy | 26.06 keV |
11 lines above the cutoff, and what each contributes
2 further lines below the 20 keV cutoff, the highest at 3.75 keV and 6.40% emission probability in all, are excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 25.27 | 23.74282 | 41.65 |
| 25.04 | 12.68579 | 22.68 |
| 28.81 | 8.03615 | 10.71 |
| 28.58 | 6.71358 | 9.10 |
| 24.21 | 3.52081 | 6.76 |
| 24.00 | 1.87659 | 3.67 |
| 29.11 | 1.32257 | 1.73 |
| 27.58 | 1.17555 | 1.72 |
| 27.37 | 0.98786 | 1.47 |
| 27.86 | 0.18769 | 0.27 |
| 77.00 | 0.501 | 0.25 |
0.0137 mm of lead halves this spectrum
Solved numerically across all 11 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 0.0137 | 0.0468 | 3.40 |
| tungsten | 0.0107 | 0.0364 | 3.40 |
| iron | 0.0709 | 0.242 | 3.42 |
| copper | 0.0469 | 0.160 | 3.41 |
| concrete | 2.12 | 7.22 | 3.40 |
| water | 13.9 | 46.9 | 3.36 |
| aluminum | 1.51 | 5.16 | 3.41 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over the first hours
Ten half-lives is 3.57 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 30.9 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 | 1.18 hours |
| Time to fall to 1 % | 2.37 hours |
| Time to fall to 0.1 % | 3.55 hours |
Limits of these dose rates
- 0.0173 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 0.0137 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 2 lines under 20 keV, carrying 6.40% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Sn-113m
Other Tin nuclides: Sn-113
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.