Yttrium-88
Y-88 · Yttrium, Z = 39, A = 88
At 5.15e+14 Bq/g — 1.39e+4 Ci/g — a gigabecquerel of Y-88 amounts to 1.94 µg, which is why activity rather than mass is how anyone states the quantity. Yttrium-88 decays by electron capture with beta-plus with a half-life of 106.626 days, falling to 82.28% of today's activity in a month and 9.31% in a year.
Among the strong external emitters here: Γ of 0.313 mGy·m²/(GBq·h) ranks 3 of 96, 4.1× Cs-137 and 1.0× Co-60. 1 GBq at 1 m reads 0.313 mGy/h, and 1 Ci at the same distance 11.6 mGy/h — a metre-scale hazard at gigabecquerel activities, and 64.0 MBq is already 20 µSv/h at that distance.
7 lines clear the 20 keV cutoff, but 2 of them carry 90% of the dose rate. The leading one is 1836.1 keV at 64.3% of the total — its emission probability is 99.24%, which is also the highest.
This is a shield that has to be designed: 10.6 mm of lead for a factor of two and 37.0 mm for a factor of ten, or 17.5 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 44.7 mm of lead.
Half-life, specific activity and dose rate
| Half-life | 106.626 days (9.212e+6 s) |
| Decay mode | electron capture with beta-plus |
| Specific activity | 5.15e+14 Bq/g (1.39e+4 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.313 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.313 mGy/h |
| Dose rate, 1 Ci at 1 m | 11.6 mGy/h |
| Kerma-weighted mean photon energy | 1512 keV |
1836 keV leads, and 2 lines make 90%
6 further lines below the 20 keV cutoff, the highest at 16.09 keV and 72.8% emission probability in all, are excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 1836.06 | 99.24 | 64.27 |
| 898.04 | 93.68256 | 34.99 |
| 2734.00 | 0.71453 | 0.61 |
| 511.00 | 0.42 | 0.09 |
| 850.60 | 0.0655 | 0.02 |
| 1382.20 | 0.02084 | 0.01 |
| 3219.70 | 0.00705 | 0.01 |
10.6 mm of lead halves this spectrum
Solved numerically across all 7 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 10.6 | 37.0 | 3.48 |
| tungsten | 6.61 | 22.8 | 3.46 |
| iron | 17.5 | 59.4 | 3.40 |
| copper | 15.6 | 52.9 | 3.40 |
| concrete | 55.5 | 189 | 3.40 |
| water | 118 | 400 | 3.41 |
| aluminum | 50.0 | 170 | 3.40 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over months and years
Ten half-lives is 2.92 years — a storage problem rather than a disposal one, with 9.31% of today's activity still there after a year. The mean life 1/λ is 154 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 | 354 days |
| Time to fall to 1 % | 1.94 years |
| Time to fall to 0.1 % | 2.91 years |
Limits of these dose rates
- 0.313 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 10.6 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 6 lines under 20 keV, carrying 72.8% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Y-88
Other Yttrium nuclides: Y-88m1, Y-88m2, Y-90, Y-90m, Y-91
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.