When the photons collide with the layers of metal, they break into negatively and positively charged particles that show up in the scintillating fibers. Each layer of fibers runs at a 90 degree angle to the next layer - like the X and Y axes on a grid. The scientists know where any two fibers cross, pinpointing the spot of collision like pencil marks on a piece of graph paper. This small shower of particles then hits the next sheet of metal and diffuses further. The particles are tracked as they cascade deeper through layers of metal sheets and grid-like scintillating fibers.
Heavy metal is used to increase the chances of intercepting gamma rays.
Then, like forensic detectives determining the trajectory of a bullet by looking at the trail of destruction it left behind, scientists use algorithms to reconstruct the direction and energy of the gamma ray at the moment of impact. In addition to providing improved gamma-ray tracking, Pendleton's system is capable of measuring gamma rays of higher energy levels than current instruments, like the ones aboard the Compton Gamma Ray Observatory. That means the photons it sees are 300 billion times as energetic as visible light. The lower section of the system is a calorimeter made up of 35 planes of metal and fiber designed to measure extremely high-energy gamma rays. The data acquisition system includes photomultiplier tubes to detect the flashes and computers to translate the flashes into understandable images.