Decay Constant
The probability per unit time that a given nucleus will decay.
Formula / equation
λ = 0.693 / t½
Unit
s⁻¹
In depth
The decay constant is characteristic of each nuclide and completely independent of temperature, pressure and chemical state, which is what makes radioactive clocks so reliable. A large value means rapid decay and a correspondingly short half-life.
Examples in the real world
Carbon-14 has λ = 1.21 × 10⁻⁴ per year, matching its 5730-year half-life.