Scandium-46
Sc-46 · Scandium, Z = 21, A = 46
At 1.25e+15 Bq/g — 3.39e+4 Ci/g — a gigabecquerel of Sc-46 amounts to 797 ng, which is why activity rather than mass is how anyone states the quantity. Scandium-46 decays by beta-minus decay with a half-life of 83.79 days, falling to 78.02% of today's activity in a month and 4.87% in a year.
Among the strong external emitters here: Γ of 0.256 mGy·m²/(GBq·h) ranks 6 of 96, 3.3× Cs-137 and 1.2× less than Co-60. 1 GBq at 1 m reads 0.256 mGy/h, and 1 Ci at the same distance 9.47 mGy/h — a metre-scale hazard at gigabecquerel activities, and 78.1 MBq is already 20 µSv/h at that distance.
2 lines clear the 20 keV cutoff, but 2 of them carry 90% of the dose rate. The leading one is 1120.5 keV at 54.8% of the total — its emission probability is 99.987%, which is also the highest.
This is a shield that has to be designed: 8.58 mm of lead for a factor of two and 28.8 mm for a factor of ten, or 14.8 mm of steel to halve it, at which point the mass of the shield is part of the problem. Reaching 20 µSv/h from 1 GBq at a metre takes 31.9 mm of lead.
Half-life, specific activity and dose rate
| Half-life | 83.79 days (7.239e+6 s) |
| Decay mode | beta-minus decay |
| Specific activity | 1.25e+15 Bq/g (3.39e+4 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.256 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.256 mGy/h |
| Dose rate, 1 Ci at 1 m | 9.47 mGy/h |
| Kerma-weighted mean photon energy | 1016 keV |
1121 keV leads, and 2 lines make 90%
2 further lines below the 20 keV cutoff, the highest at 4.51 keV and 0.00461% emission probability in all, are excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 1120.55 | 99.987 | 54.76 |
| 889.28 | 99.984 | 45.24 |
8.58 mm of lead halves this spectrum
Solved numerically across all 2 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 8.58 | 28.8 | 3.35 |
| tungsten | 5.42 | 18.1 | 3.35 |
| iron | 14.8 | 49.1 | 3.33 |
| copper | 13.2 | 43.9 | 3.33 |
| concrete | 46.7 | 155 | 3.33 |
| water | 98.6 | 328 | 3.33 |
| aluminum | 42.0 | 140 | 3.33 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over months and years
Ten half-lives is 2.29 years — a storage problem rather than a disposal one, with 4.87% of today's activity still there after a year. The mean life 1/λ is 121 days.
| 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 | 278 days |
| Time to fall to 1 % | 1.52 years |
| Time to fall to 0.1 % | 2.29 years |
Limits of these dose rates
- 0.256 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 8.58 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 2 lines under 20 keV, carrying 0.00461% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Sc-46
Other Scandium nuclides: Sc-46m
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.