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Gammasphere is one of the world’s most powerful spectrometers for nuclear structure research and is especially suited to collecting gamma-ray data following the fusion of heavy ions.

Gammasphere was completed in 1995 by a consortium of scientists from national laboratories and many universities. The project was coordinated by scientists at Lawrence Berkeley National Laboratory, where the device was first assembled. It consists of 110 high-purity germanium detectors, each about the size of a coffee cup, in a spherical arrangement. Each germanium detector is surrounded by a BGO shield which allows for the suppression of background resulting from gamma-rays whose energies are not completely absorbed by the germanium detector.

Beams of ions from ATLAS are directed at a target (usually a thin metal film). Nuclei from the beam fuse with those in the target, producing highly excited, much heavier nuclei. Gammasphere detects gamma rays — high-energy light particles — emitted from the excited nuclei as they spin and cool. Gammasphere first moved from Lawrence Berkeley National Laboratory to Argonne in the fall of 1997 and returned to Argonne again in 2003. At Argonne, Gammasphere research has centered on studying nuclei far from stability.