Cadmium-109m1
Cd-109m1 · Cadmium, Z = 48, A = 109 · isomeric state m1
Cadmium-109m1 (Cd-109m1) carries 3.25e+26 Bq/g, or 8.78e+15 Ci/g: a gigabecquerel is 3.08 ag, no weighable quantity at all. It decays by isomeric transition with a half-life of 11.8 microseconds, which leaves 0% of today's activity after a day and 0% after a week.
At 0.0192 mGy·m²/(GBq·h) the air kerma rate constant is 4.0× less than Cs-137 and 16× less than Co-60, placing it 54 of 96 photon emitters in this dataset. 1 GBq at 1 m reads 0.0192 mGy/h, and 1 Ci at the same distance 0.712 mGy/h.
6 lines clear the 20 keV cutoff, but 4 of them carry 90% of the dose rate. The leading one is 23.2 keV at 46.8% of the total — its emission probability is 24.79173%, which is also the highest.
Shielding barely arises: 0.0117 mm of lead halves the air kerma rate and 0.0435 mm takes it to a tenth, thicknesses a source capsule is likely to exceed on its own. Steel does the halving in 0.0594 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 | 11.8 microseconds (0.00001180 s) |
| Decay mode | isomeric transition |
| Specific activity | 3.25e+26 Bq/g (8.78e+15 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.0192 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.0192 mGy/h |
| Dose rate, 1 Ci at 1 m | 0.712 mGy/h |
| Kerma-weighted mean photon energy | 25.42 keV |
6 lines above the cutoff, and what each contributes
1 further line below the 20 keV cutoff, the highest at 3.39 keV and 5.11% emission probability in all, is excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 23.17 | 24.79173 | 46.82 |
| 22.98 | 13.18177 | 25.32 |
| 26.38 | 8.1681 | 11.76 |
| 26.18 | 6.91041 | 10.10 |
| 59.90 | 9.7 | 4.23 |
| 26.64 | 1.25769 | 1.77 |
0.0117 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 | 0.0117 | 0.0435 | 3.71 |
| tungsten | 0.00914 | 0.0339 | 3.71 |
| iron | 0.0594 | 0.223 | 3.74 |
| copper | 0.0394 | 0.148 | 3.74 |
| concrete | 1.79 | 6.52 | 3.63 |
| water | 12.4 | 42.7 | 3.45 |
| aluminum | 1.27 | 4.66 | 3.66 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over the first hours
Ten half-lives is 0.000118 seconds, 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 0.0000170 seconds.
| 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 | 0.0000392 seconds |
| Time to fall to 1 % | 0.0000784 seconds |
| Time to fall to 0.1 % | 0.000118 seconds |
Limits of these dose rates
- 0.0192 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 0.0117 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 1 line under 20 keV, carrying 5.11% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Cd-109m1
Other Cadmium nuclides: Cd-109, Cd-109m2
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.