Although quantitative measurements in radioactivity teaching and research are only believed to be possible with high technology, early work in this area was fully accomplished with very simple apparatus such as zinc sulphide screens and electroscopes. This article presents an experimental practice using the electroscope, which is a very simple apparatus that has been widely used for educational purposes, although generally for qualitative work. The main objective is to show the possibility of measuring radioactivity not only in qualitative demonstrations, but also in quantitative experimental practices. The experimental set-up is a low-cost ion chamber connected to an electroscope in a configuration that is very similar to that used by Marie and Pierre Currie, Rutherford, Geiger, Pacini, Hess and other great researchers from the time of the big discoveries in nuclear and high-energy particle physics. An electroscope leaf is filmed and projected, permitting the collection of quantitative data for the measurement of the 220Rn half-life, collected from the emanation of the lantern mantles. The article presents the experimental procedures and the expected results, indicating that the experiment may provide support for nuclear physics classes. These practices could spread widely to either university or school didactic laboratories, and the apparatus has the potential to allow the development of new teaching activity for nuclear physics.