  We have re-purposed portable plastic scintillator muon detectors, designed by
the CosmicWatch project, for the measurement of electrons emitted by the decay
of radioactive sources. For the latter purpose we have first calibrated the
detectors using the local atmospheric muon flux, performing angular
distribution and attenuation measurements. In addition, we have simulated the
detector using Geant4 in a detailed fashion for a cross-check and better
understanding of the device. Then, we have developed a method to evaluate the
activity of $\beta$-sources and to discriminate different $\beta$-sources by
looking into their respective voltage spectrum output.
