Historic hydrogen bubble chamber photograph from the Lawrence Berkeley National Laboratory. It shows a sequence of two catalyzed nuclear reactions - two links in a chain-like reaction. At the top left center of the photo, a muon generated by the Bevatron comes in at a slight angle from left to right. At the first bend in the track, a mesic atom has been formed, a deuteron and proton have been fused into helium, and the muon has been ejected on a track that zigs downward and sharply to the right. At the next sharp angle in the track, another catalyzed reaction has taken place, and the muon is ejected horizontally to left across the picture. At the final angle, the muon has come to rest, and decayed into an electron, which makes a sweeping curve to the right and upward.
