Half-life / Decay

First-order radioactive (or any exponential) decay.

Inputs

• Half-life t½ with unit (s / min / h / d / y) or pick an isotope preset.
• Initial amount N₀ (atoms, mass, or activity).
• Time t.

Output

• Decay constant λ = ln 2 / t½ and mean lifetime τ = 1/λ.
• Fraction remaining and N(t).
• Activity A₀ and A(t) = λ N(t).
• 10-row half-life table for quick mental estimates.