Hi! This is my first post here. I am a digital artist who develops interactive learning for science and engineering subjects, hence my ID. Today, I built a simple 'cloud chamber' to detect atomic particle tracks--a photo is below. The particle source I used is a small button of Am-241. Most of the tracks I observed seem to be either straight (alpha?) or curved (beta particles?). The one exception is the bulls-eye pictured below, with two lobes (arrows)--two particles of opposite charge? I have never seen such a track in a cloud chamber in all I have seen--do you have any idea what it is?
The picture below is a composite of several shots taken of the trails.
Someone in another forum suggested the Am-241 button moved, leaving that mark. However, this is the first thing I checked. Below shows a sequence of shots at approx. 1 second intervals, with the "bull's-eye" visible in the middle frame, and the button has not moved.