Americium 241
From ScienceZero
Americium 241 emits alpha and gamma radiation. Most of the radiation does not travel very far from the sample but at close range it is intense enought to affect electronic devices. Even small samples ionize the air around it, this effect is used in some smoke detectors. The radiation caused a 74HCT14 Schmitt trigger to oscillate at a couple of cm distance. Most likely this was because the air becoming ionized by the radiation and conducting a weak current from an output pin to an input pin.
This video shows how the radiation affects a CCD imaging chip covered with a glass plate. Hot pixels show up at random moments. This would be suitable for generating true random numbers.
