Actinide

Uranium

Z 92A 238mass 238.03

Decay curve

Uranium-238

half-life

4.47 billion years

half-lives elapsed1 half-life

0123456

left

50.0%

real time

4.47 billion years

115 left

Each dot is one nucleus. Decay is random for each one — but the pattern that emerges is the exponential curve on the left.

Half-lives	Time elapsed	Remaining	Of 1000
0	—	100.0%	1000
1	4.47 billion years	50.0%	500
2	8.94 billion years	25.0%	250
3	13.4 billion years	12.5%	125
4	17.9 billion years	6.25%	63
5	22.3 billion years	3.13%	31
6	26.8 billion years	1.56%	16

N = N₀ × (½)ⁿ — never exactly zero

Thorium-23214.05 billion years

Uranium-2384.47 billion years

Potassium-401.25 billion years

Neptunium-2372.14 million years

Plutonium-23924,110 years

Carbon-145,730 years