Niobium-95m
Nb-95m · Niobium, Z = 41, A = 95 · isomeric state m
Niobium-95m (Nb-95m) carries 1.41e+16 Bq/g, or 3.81e+5 Ci/g: a gigabecquerel is 70.9 ng, no weighable quantity at all. It decays by beta-minus decay with a half-life of 3.61 days, which leaves 26.08% of today's activity after a week and 2.6e-6% after three months.
At 0.00764 mGy·m²/(GBq·h) the air kerma rate constant is 10× less than Cs-137 and 40× less than Co-60, placing it 74 of 96 photon emitters in this dataset. 1 GBq at 1 m reads 0.00764 mGy/h, and 1 Ci at the same distance 0.283 mGy/h.
4 lines clear the 20 keV cutoff, but one of them carries 90% of the dose rate. The leading one is 235.7 keV at 96.6% of the total — its emission probability is 24.8%, which is also the highest.
A half-value layer of 0.877 mm in lead puts this in foil and thin sheet, with 6.75 mm needed if the material is steel; ten-fold attenuation comes at 2.93 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 | 3.61 days (3.119e+5 s) |
| Decay mode | beta-minus decay |
| Specific activity | 1.41e+16 Bq/g (3.81e+5 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.00764 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.00764 mGy/h |
| Dose rate, 1 Ci at 1 m | 0.283 mGy/h |
| Kerma-weighted mean photon energy | 235.8 keV |
236 keV carries 97% of the dose rate
11 further lines below the 20 keV cutoff, the highest at 19.79 keV and 53.7% emission probability in all, are excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 235.69 | 24.8 | 96.58 |
| 204.12 | 0.9553 | 3.14 |
| 582.08 | 0.0198 | 0.20 |
| 786.19 | 0.00559 | 0.08 |
0.877 mm of lead halves this spectrum
Solved numerically across all 4 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 0.877 | 2.93 | 3.34 |
| tungsten | 0.650 | 2.17 | 3.34 |
| iron | 6.75 | 22.4 | 3.32 |
| copper | 5.66 | 18.8 | 3.33 |
| concrete | 25.0 | 83.2 | 3.32 |
| water | 53.6 | 178 | 3.32 |
| aluminum | 22.4 | 74.4 | 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 36.1 days — a storage problem rather than a disposal one, with 3.5e-29% of today's activity still there after a year. The mean life 1/λ is 5.21 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 | 12.0 days |
| Time to fall to 1 % | 24.0 days |
| Time to fall to 0.1 % | 36.0 days |
Limits of these dose rates
- 0.00764 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 0.877 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 11 lines under 20 keV, carrying 53.7% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Nb-95m
Other Niobium nuclides: Nb-95
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.