Cadmium-109m2
Cd-109m2 · Cadmium, Z = 48, A = 109 · isomeric state m2
Cadmium-109m2 (Cd-109m2) carries 3.62e+26 Bq/g, or 9.77e+15 Ci/g: a gigabecquerel is 2.77 ag, no weighable quantity at all. It decays by isomeric transition with a half-life of 10.6 microseconds, which leaves 0% of today's activity after a day and 0% after a week.
1 GBq at 1 m reads 0.0579 mGy/h, and 1 Ci at the same distance 2.14 mGy/h, from an air kerma rate constant of 0.0579 mGy·m²/(GBq·h) — 1.3× less than Cs-137 and 5.3× less than Co-60, and 38 of 96 among the photon emitters carried here.
7 lines clear the 20 keV cutoff, but 3 of them carry 90% of the dose rate. The leading one is 259.5 keV at 49.3% of the total — its emission probability is 85.61%, which is lower than the 93.81% of the 203.2 keV line it outranks.
A half-value layer of 0.712 mm in lead puts this in foil and thin sheet, with 5.65 mm needed if the material is steel; ten-fold attenuation comes at 2.84 mm of lead. Reaching 20 µSv/h from 1 GBq at a metre takes 1.18 mm of lead.
Half-life, specific activity and dose rate
| Half-life | 10.6 microseconds (0.00001060 s) |
| Decay mode | isomeric transition |
| Specific activity | 3.62e+26 Bq/g (9.77e+15 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.0579 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.0579 mGy/h |
| Dose rate, 1 Ci at 1 m | 2.14 mGy/h |
| Kerma-weighted mean photon energy | 212.6 keV |
260 keV leads, and 3 lines make 90%
1 further line below the 20 keV cutoff, the highest at 3.39 keV and 1.21% emission probability in all, is excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 259.50 | 85.61 | 49.28 |
| 203.20 | 93.81 | 40.49 |
| 23.17 | 7.96637 | 5.00 |
| 22.98 | 4.23572 | 2.70 |
| 26.38 | 2.62467 | 1.26 |
| 26.18 | 2.22053 | 1.08 |
| 26.64 | 0.40414 | 0.19 |
0.712 mm of lead halves this spectrum
Solved numerically across all 7 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 0.712 | 2.84 | 3.99 |
| tungsten | 0.529 | 2.10 | 3.97 |
| iron | 5.65 | 21.3 | 3.77 |
| copper | 4.73 | 17.9 | 3.78 |
| concrete | 21.0 | 79.0 | 3.76 |
| water | 46.2 | 169 | 3.66 |
| aluminum | 18.8 | 70.6 | 3.76 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over the first hours
Ten half-lives is 0.000106 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 0.0000153 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 | 0.0000352 seconds |
| Time to fall to 1 % | 0.0000704 seconds |
| Time to fall to 0.1 % | 0.000106 seconds |
Limits of these dose rates
- 0.0579 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 0.712 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 1 line under 20 keV, carrying 1.21% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Cd-109m2
Other Cadmium nuclides: Cd-109, Cd-109m1
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.