Actinide

Thorium

Z 90A 232mass 232.04

Decay curve

Thorium-232

half-life

14.05 billion years

half-lives elapsed1 half-life

0123456

left

50.0%

real time

14 billion years

123 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	14 billion years	50.0%	500
2	28.1 billion years	25.0%	250
3	42.1 billion years	12.5%	125
4	56.1 billion years	6.25%	63
5	70.2 billion years	3.13%	31
6	84.2 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