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.
Fit the example dataStart with your own data
Example: NIST’s MGH17 double-exponential test data, 33 points with y uncertainties, opened as a new copy you can edit.
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.
- Fit the same data with Exponential Decay (Half-life) as well. Previous ranks both fits by AIC; keep the second component only if it lowers the AIC by more than about 2.