I have added an updated Mathematica file here named as “DecayModelling.nb” that has more details on how to drive the model from a set of differential equations and initial conditions. Additionally, it has all the analytical solution at the end with thoughtfully organized modules. The modules can be mixed and matched to build several models.

At the end of the page there is an embbeded mathematica notebook. Unfortunately I couldn’t resolve the issue that stops the generation of the plot. The temporary solutions are, downloading the Mathematica Notebook file and open it in wolfram player or Mathematica. Additionally, you can make a copy of this code in your own wolfram cloud account to see the plot and play with the sliders.