A study conducted in 2013 showed that about 70-80% of teens and young adults in the United States own a smartphone. Furthermore the number of tablet PC users in the United States will increase up to more than 80% by 2015. As a result, these devices have increasingly become everyday tools, particularly for the younger generation. In recent years, various articles have been published about the use of smartphones and tablet PCs as experimental tools especially in the physics classroom. This is possible because today's smartphones and tablet PCs are equipped with many sensors, which can be used to perform quantitative measurements of sound, acceleration, magnetic flux density, air pressure, light intensity, humidity, angular velocity, temperature, or position on Earth (GPS). While previous articles mainly present experiments on mechanics or acoustics, in which the acceleration sensor or the microphone is used (for a synopsis of different examples, see Ref. 3; for recent papers, see Refs. 4-11 ), in this article we focus on experiments for studying radioactivity using the camera sensor.