Uranium-236

U-236 · Uranium, Z = 92, A = 236

Uranium-236 (U-236) is slow enough to be handled as a material rather than as a trace: 2.39e+6 Bq/g, or 0.0000647 Ci/g, puts a gigabecquerel at 418 g. Decay is by alpha decay, half-life 2.342 × 10⁷ years, and shedding even one per cent of the activity takes 339,573 years.

Alpha emission is led by 4.494 MeV at 73.8%, one of 3 recorded lines. None of it reaches through skin, so the limit here is intake, not external dose.

Decay is the only handle: forty years leaves 100.00% of today's activity and ten thousand years leaves 99.97%, with ten half-lives at 234 million years and a mean life of 33.8 million years per atom.

Half-life 2.342 × 10⁷ years, 2.39e+6 Bq/g, and no line recorded

Half-life	2.342 × 10⁷ years (7.391e+14 s)
Decay mode	alpha decay
Specific activity	2.39e+6 Bq/g (0.0000647 Ci/g)

3 alpha lines, strongest 4.494 MeV

3 recorded lines from 4.332 to 4.494 MeV, the strongest 4.494 MeV at 73.8% of 99.85% total alpha emission.

Energy (MeV)	Emission probability (%)
4.4940	73.8
4.4450	25.9
4.3320	0.15

Activity over geological time

Ten half-lives is 234 million years. On any timescale a facility can be planned over the activity is constant — 100.00% is left after forty years — and the mean life 1/λ is 33.8 million years.

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	77.8 million years
Time to fall to 1 %	156 million years
Time to fall to 0.1 %	233 million years

Limits — intake, not external dose

Alpha reaches nothing through skin — U-236 is an intake problem, not an external one.
What every sheet leaves out, internal dose included.

Decay and mass calculators for U-236

Other Uranium nuclides: U-232, U-233, U-234, U-235, U-238, U-238m

Computed from the IAEA Nuclear Data Section — Livechart API (ENSDF) and the NIST X-Ray Mass Attenuation Coefficients. Derivations and citations.