Niobium-95
Nb-95 · Niobium, Z = 41, A = 95
At 1.45e+15 Bq/g — 3.93e+4 Ci/g — a gigabecquerel of Nb-95 amounts to 687 ng, which is why activity rather than mass is how anyone states the quantity. Niobium-95 decays by beta-minus decay with a half-life of 34.991 days, falling to 55.20% of today's activity in a month and 0.07% in a year.
1 GBq at 1 m reads 0.101 mGy/h, and 1 Ci at the same distance 3.76 mGy/h, from an air kerma rate constant of 0.101 mGy·m²/(GBq·h) — 1.3× Cs-137 and 3.0× less than Co-60, and 21 of 96 among the photon emitters carried here.
3 lines clear the 20 keV cutoff, but one of them carries 90% of the dose rate. The leading one is 765.8 keV at 100.0% of the total — its emission probability is 99.808%, which is also the highest.
This is a shield that has to be designed: 6.54 mm of lead for a factor of two and 21.7 mm for a factor of ten, or 12.9 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 15.3 mm of lead.
Half-life, specific activity and dose rate
| Half-life | 34.991 days (3.023e+6 s) |
| Decay mode | beta-minus decay |
| Specific activity | 1.45e+15 Bq/g (3.93e+4 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.101 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.101 mGy/h |
| Dose rate, 1 Ci at 1 m | 3.76 mGy/h |
| Kerma-weighted mean photon energy | 765.7 keV |
766 keV carries 100% of the dose rate
6 further lines below the 20 keV cutoff, the highest at 19.96 keV and 0.120% emission probability in all, are excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 765.80 | 99.808 | 99.98 |
| 561.88 | 0.015 | 0.01 |
| 204.12 | 0.028 | 0.01 |
6.54 mm of lead halves this spectrum
Solved numerically across all 3 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 6.54 | 21.7 | 3.32 |
| tungsten | 4.25 | 14.1 | 3.32 |
| iron | 12.9 | 42.7 | 3.32 |
| copper | 11.5 | 38.1 | 3.32 |
| concrete | 40.9 | 136 | 3.32 |
| water | 86.4 | 287 | 3.32 |
| aluminum | 36.8 | 122 | 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 350 days — a storage problem rather than a disposal one, with 0.07% of today's activity still there after a year. The mean life 1/λ is 50.5 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 | 116 days |
| Time to fall to 1 % | 232 days |
| Time to fall to 0.1 % | 349 days |
Limits of these dose rates
- 0.101 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 6.54 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 6 lines under 20 keV, carrying 0.120% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Nb-95
Other Niobium nuclides: Nb-95m
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.