Tantalum-182
Ta-182 · Tantalum, Z = 73, A = 182
At 2.31e+14 Bq/g — 6.25e+3 Ci/g — a gigabecquerel of Ta-182 amounts to 4.32 µg, which is why activity rather than mass is how anyone states the quantity. Tantalum-182 decays by beta-minus decay with a half-life of 114.74 days, falling to 83.42% of today's activity in a month and 11.01% in a year.
1 GBq at 1 m reads 0.162 mGy/h, and 1 Ci at the same distance 6.01 mGy/h, from an air kerma rate constant of 0.162 mGy·m²/(GBq·h) — 2.1× Cs-137 and 1.9× less than Co-60, and 10 of 96 among the photon emitters carried here.
48 lines clear the 20 keV cutoff, but 10 of them carry 90% of the dose rate. The leading one is 1121.3 keV at 30.4% of the total — its emission probability is 35.24%, which is also the highest.
This is a shield that has to be designed: 8.30 mm of lead for a factor of two and 31.3 mm for a factor of ten, or 13.8 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 28.3 mm of lead.
Half-life, specific activity and dose rate
| Half-life | 114.74 days (9.914e+6 s) |
| Decay mode | beta-minus decay |
| Specific activity | 2.31e+14 Bq/g (6.25e+3 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.162 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.162 mGy/h |
| Dose rate, 1 Ci at 1 m | 6.01 mGy/h |
| Kerma-weighted mean photon energy | 1069 keV |
48 lines above the cutoff, and what each contributes
1 further line below the 20 keV cutoff, the highest at 9.74 keV and 23.6% emission probability in all, is excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 1121.29 | 35.24 | 30.44 |
| 1221.39 | 27.22995 | 25.19 |
| 1189.04 | 16.48527 | 14.92 |
| 1231.00 | 11.6151 | 10.81 |
| 67.75 | 42.92232 | 2.27 |
| 1001.70 | 2.08621 | 1.65 |
| 1257.41 | 1.50933 | 1.43 |
| 1289.14 | 1.37189 | 1.32 |
| 222.11 | 7.56603 | 1.29 |
| 100.11 | 14.20172 | 0.93 |
| 59.32 | 17.46147 | 0.91 |
| 152.43 | 7.01628 | 0.76 |
| 264.07 | 3.6121 | 0.76 |
| 1157.30 | 0.73299 | 0.65 |
Showing the 14 largest contributors of 48 lines above the cutoff; the remainder together carry 6.67% of the dose rate.
8.30 mm of lead halves this spectrum
Solved numerically across all 48 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 8.30 | 31.3 | 3.77 |
| tungsten | 5.17 | 19.5 | 3.76 |
| iron | 13.8 | 50.5 | 3.65 |
| copper | 12.3 | 45.1 | 3.66 |
| concrete | 44.9 | 160 | 3.55 |
| water | 96.1 | 337 | 3.51 |
| aluminum | 40.3 | 144 | 3.56 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over months and years
Ten half-lives is 3.14 years — a storage problem rather than a disposal one, with 11.01% of today's activity still there after a year. The mean life 1/λ is 166 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 | 1.04 years |
| Time to fall to 1 % | 2.09 years |
| Time to fall to 0.1 % | 3.13 years |
Limits of these dose rates
- 0.162 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 8.30 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 1 line under 20 keV, carrying 23.6% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Ta-182
Other Tantalum nuclides: Ta-182m1, Ta-182m2
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.