curve.fit

Double Exponential

The sum of two exponential decays on a constant background. Use it when a decay has a fast and a slow component, such as a mixture of two radioactive isotopes or a two-stage relaxation.

Start with your own data

Parameters

Amplitude of the first component at x = 0.
Time constant of the first component: it falls by a factor of e over τ₁.
Amplitude of the second component at x = 0.
Time constant of the second component.
Constant background.

Tips

  • The two components are interchangeable: swapping (A₁, τ₁) with (A₂, τ₂) gives the same curve, so which one is labeled first is arbitrary.
  • The components can be separated only when their time constants differ clearly and the data cover both time scales.
  • Each component’s half-life is its time constant times ln 2.

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