Abstract
Experimentation on beta spectroscopy introduces the student into the field of radioactive decay, the Fermi theory, special relativity and the weak interaction. With the help of a simple surface barrier detector-spectrometer, the continuous spectra of some beta-ray emitters have to be measured and interpreted. Here we show how students react to an unexplained difference between measurement and theory, which leads them to speculate in the end about each possible aspect that may account for it.