Radioactive Half-Life
The time required for half the nuclei in a radioactive sample to decay.
Formula / equation
t½ = 0.693 / λ
Unit
s
In depth
Because decay is first order, the half-life is constant regardless of how much material is present or of any external condition. Half-lives span an extraordinary range, from fractions of a microsecond to billions of years, which is why different isotopes suit different dating ranges.
Examples in the real world
Uranium-238 at 4.5 billion years; carbon-14 at 5730 years; polonium-214 at 164 microseconds.