Rhenium-188
Re-188 · Rhenium, Z = 75, A = 188
Rhenium-188 (Re-188) carries 3.63e+16 Bq/g, or 9.80e+5 Ci/g: a gigabecquerel is 27.6 ng, no weighable quantity at all. It decays by beta-minus decay with a half-life of 17.005 hours, which leaves 37.60% of today's activity after a day and 0.11% after a week.
At 0.00762 mGy·m²/(GBq·h) the air kerma rate constant is 10× less than Cs-137 and 40× less than Co-60, placing it 75 of 96 photon emitters in this dataset. 1 GBq at 1 m reads 0.00762 mGy/h, and 1 Ci at the same distance 0.282 mGy/h.
51 lines clear the 20 keV cutoff, but 13 of them carry 90% of the dose rate. The leading one is 155.0 keV at 36.4% of the total — its emission probability is 15.49%, which is also the highest.
Halving the air kerma rate calls for 1.43 mm of lead, or 7.48 mm of steel where lead is unwelcome, and a factor of ten calls for 16.7 mm of lead — sheet thicknesses that a glovebox or a transport container can carry. At 1 GBq and a metre it is already under 20 µSv/h with nothing in the way. The tenth-value layer runs 11.7 times the half-value layer, not the 3.32 a single energy would give.
Half-life, specific activity and dose rate
| Half-life | 17.005 hours (6.122e+4 s) |
| Decay mode | beta-minus decay |
| Specific activity | 3.63e+16 Bq/g (9.80e+5 Ci/g) |
| Air kerma rate constant Γ (δ = 20 keV) | 0.00762 mGy·m²/(GBq·h) |
| Dose rate, 1 GBq at 1 m | 0.00762 mGy/h |
| Dose rate, 1 Ci at 1 m | 0.282 mGy/h |
| Kerma-weighted mean photon energy | 539.7 keV |
51 lines above the cutoff, and what each contributes
1 further line below the 20 keV cutoff, the highest at 10.39 keV and 3.04% emission probability in all, is excluded here and from Γ. Why the two columns rank differently.
| Energy (keV) | Emission probability (%) | Share of dose rate (%) |
|---|---|---|
| 155.04 | 15.49 | 36.41 |
| 633.03 | 1.37 | 15.36 |
| 931.34 | 0.595 | 9.41 |
| 478.00 | 1.076 | 9.18 |
| 829.47 | 0.444 | 6.36 |
| 63.00 | 2.41348 | 2.68 |
| 1610.40 | 0.1037 | 2.51 |
| 634.97 | 0.1604 | 1.80 |
| 1132.31 | 0.0908 | 1.69 |
| 61.49 | 1.40054 | 1.55 |
| 1308.03 | 0.0705 | 1.46 |
| 672.54 | 0.1198 | 1.42 |
| 72.34 | 1.0336 | 1.18 |
| 1802.05 | 0.0392 | 1.03 |
Showing the 14 largest contributors of 51 lines above the cutoff; the remainder together carry 7.95% of the dose rate.
1.43 mm of lead halves this spectrum
Solved numerically across all 51 lines, narrow beam. Why not one representative energy.
| Material | HVL (mm) | TVL (mm) | TVL / HVL |
|---|---|---|---|
| lead | 1.43 | 16.7 | 11.73 |
| tungsten | 0.993 | 10.8 | 10.88 |
| iron | 7.48 | 33.5 | 4.48 |
| copper | 6.26 | 29.6 | 4.72 |
| concrete | 29.4 | 112 | 3.80 |
| water | 64.2 | 238 | 3.71 |
| aluminum | 26.1 | 100 | 3.83 |
A single energy would give 3.32. What a spread of energies does instead.
Activity over days and weeks
Ten half-lives is 7.09 days, so the activity moves measurably while a count is running: every figure has to carry the time it was referred to. The mean life 1/λ is 1.02 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 | 2.35 days |
| Time to fall to 1 % | 4.71 days |
| Time to fall to 0.1 % | 7.06 days |
Limits of these dose rates
- 0.00762 mGy/h at a metre — bare point source, no capsule, no self-absorption.
- 1.43 mm of lead halves this spectrum, narrow beam, scatter not added back.
- Γ excludes 1 line under 20 keV, carrying 3.04% of all emissions.
- What every sheet leaves out, internal dose included.
Gamma and decay calculators for Re-188
Other Rhenium nuclides: Re-188m
Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.