Billion volt atomic particles in Brookhaven National Laboratory's Cosmotron particle accelerator. This is one of the first cloud chamber images obtained with the Cosmotron. It shows high energy particles resulting form a single pulse of 1.2 billion electron volt protons striking a 1/8" brass target inside the Cosmotron. The chamber was located 195 feet from the target. Particles reaching the chamber from the accelerator traversed an inch of stainless steel in the outside wall of the vacuum chamber of the Cosmotron, two heavy doors, and the 1/4" stainless steel wall of the cloud chamber. On May 20, 1957, the giant atomic accelerator produced protons with an energy of 1.2 billion volts, the first time humans have produced energies above the billion mark. A month later, the level went above two billion volts. When protons with billion volt energies collide with nuclei of atoms, the resultant fragments provide clues in studies of the structure and properties of nuclei.