Subatomic particle tracks. Photograph from the 4.6 metre (15-foot) bubble chamber at the Fermi National Accelerator Laboratory (Fermilab) near Chicago. The bubble chamber was filled with liquid hydrogen & subjected to a beam of neutrinos. The neutrinos are electrically neutral & so do not produce tracks themselves, but one of them has interacted with a proton in the bubble chamber's liquid, producing the spray of charged particle tracks that shoots up from the bottom of the picture. These particles bend & curl in the bubble chamber's powerful magnetic field. The white arc at top right is part of the bubble chamber's structure. Photograph taken in 1984.