Scandium-46m
Sc-46m · Scandium, Z = 21, A = 46 · isomeric state m
Scandium-46m (Sc-46m) carries 4.84e+20 Bq/g, or 1.31e+10 Ci/g: a gigabecquerel is 2.06 pg, no weighable quantity at all. It decays by isomeric transition with a half-life of 18.75 seconds, which leaves 0% of today's activity after a day and 0% after a week.
At 0.0100 mGy·m²/(GBq·h) the air kerma rate constant is 7.7× less than Cs-137 and 30× less than Co-60, placing it 70 of 96 photon emitters in this dataset. 1 GBq at 1 m reads 0.0100 mGy/h, and 1 Ci at the same distance 0.371 mGy/h.
One line at 142.5 keV carries all of that.
A half-value layer of 0.267 mm in lead puts this in foil and thin sheet, with 4.14 mm needed if the material is steel; ten-fold attenuation comes at 0.887 mm of lead. 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 | 18.75 seconds (18.75 s) |
| Decay mode | isomeric transition |
| Specific activity | 4.84e+20 Bq/g (1.31e+10 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.0100 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.0100 mGy/h |
| Dose rate, 1 Ci at 1 m | 0.371 mGy/h |
| Kerma-weighted mean photon energy | 142.5 keV |
A single photon line at 143 keV
3 further lines below the 20 keV cutoff, the highest at 4.47 keV and 6.55% emission probability in all, are excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 142.53 | 62 | 100.00 |
0.267 mm of lead halves this spectrum
Solved numerically across all 1 line, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 0.267 | 0.887 | 3.32 |
| tungsten | 0.199 | 0.663 | 3.32 |
| iron | 4.14 | 13.7 | 3.32 |
| copper | 3.18 | 10.6 | 3.32 |
| concrete | 20.5 | 68.1 | 3.32 |
| water | 45.3 | 151 | 3.32 |
| aluminum | 18.1 | 60.3 | 3.32 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over the first hours
Ten half-lives is 3.13 minutes, 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 27.1 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 | 1.04 minutes |
| Time to fall to 1 % | 2.08 minutes |
| Time to fall to 0.1 % | 3.11 minutes |
Limits of these dose rates
- 0.0100 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 0.267 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 3 lines under 20 keV, carrying 6.55% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Sc-46m
Other Scandium nuclides: Sc-46
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.