Manganese-54
Mn-54 · Manganese, Z = 25, A = 54
At 2.87e+14 Bq/g — 7.75e+3 Ci/g — a gigabecquerel of Mn-54 amounts to 3.49 µg, which is why activity rather than mass is how anyone states the quantity. Manganese-54 decays by electron capture with beta-plus with a half-life of 312.20 days, falling to 93.56% of today's activity in a month and 44.44% in a year.
1 GBq at 1 m reads 0.110 mGy/h, and 1 Ci at the same distance 4.06 mGy/h, from an air kerma rate constant of 0.110 mGy·m²/(GBq·h) — 1.4× Cs-137 and 2.8× less than Co-60, and 18 of 96 among the photon emitters carried here.
One line at 834.8 keV carries all of that.
This is a shield that has to be designed: 7.18 mm of lead for a factor of two and 23.9 mm for a factor of ten, or 13.4 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 17.6 mm of lead.
Half-life, specific activity and dose rate
| Half-life | 312.20 days (2.697e+7 s) |
| Decay mode | electron capture with beta-plus |
| Specific activity | 2.87e+14 Bq/g (7.75e+3 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.110 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.110 mGy/h |
| Dose rate, 1 Ci at 1 m | 4.06 mGy/h |
| Kerma-weighted mean photon energy | 834.8 keV |
A single photon line at 835 keV
3 further lines below the 20 keV cutoff, the highest at 5.97 keV and 25.7% emission probability in all, are excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 834.85 | 99.976 | 100.00 |
7.18 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 | 7.18 | 23.9 | 3.32 |
| tungsten | 4.62 | 15.4 | 3.32 |
| iron | 13.4 | 44.6 | 3.32 |
| copper | 12.0 | 39.8 | 3.32 |
| concrete | 42.6 | 141 | 3.32 |
| water | 89.9 | 299 | 3.32 |
| aluminum | 38.3 | 127 | 3.32 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over months and years
Ten half-lives is 8.55 years — a storage problem rather than a disposal one, with 44.44% of today's activity still there after a year. The mean life 1/λ is 1.23 years.
| 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 | 2.84 years |
| Time to fall to 1 % | 5.68 years |
| Time to fall to 0.1 % | 8.52 years |
Limits of these dose rates
- 0.110 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 7.18 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 3 lines under 20 keV, carrying 25.7% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Mn-54
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.