Development of an application simulating radioactive sources This paper presents an application simulating radioactive gamma sources developed in the ``Ecole des Mines'' of Douai (France). It generates raw counting data as an XML file which can then be statistically exploited to illustrate the various concepts of radioactivity (exponential decay law, isotropy of the radiation, attenuation of radiation in matter). The application, with a spreadsheet for data analysis and lab procedures, has been released under free license.