Introduction to GAMMASPHERE

GAMMASPHERE is a spectrometer of unparalleled detection sensitivity to nuclear electromagnetic radiation due to its high resolution, granularity and efficiency. This powerful combination of features makes it the ideal device for studying rare and exotic nuclear processes. GAMMASPHERE is a National Facility funded by the Department of Energy and constructed at the Lawrence Berkeley National Laboratory with the participation of other US national laboratories and universities.

GAMMASPHERE consists of a spherical shell of 110 large volume, high-purity germanium detectors, each enclosed in a bismuth-germanate Compton-suppression shield. This new gamma-ray spectrometer is about 100 times more powerful than its predecessors and was commissioned in December 1995, although experiments using parts of the system, the so-called Early Implementation phase, began in mid 1993. A suite of powerful auxiliary detectors has been specially developed to enhance the resolving abilities of GAMMASPHERE even further.

From 1993 to 1997, GAMMASPHERE was constructed and sited at the 88-Inch Cyclotron of the Lawrence Berkeley National Laboratory's Nuclear Science Division. The cyclotron is a low-energy accelerator providing beams for diverse programs in nuclear physics, biology and technology. In a year, through August of 1997, it provided over 6000 hours of beam on target with approximately 60% being used by GAMMASPHERE. The smooth operation of the cyclotron epitomizes the dedication of the crew and staff. The GAMMASPHERE community owes a huge thanks to them.

During GAMMASPHERE's stay at Berkeley over 130 experiments (excluding the 50 or so experiments of the "early implementation" phase) were performed. Over 200 outside users from nearly 50 institutions worldwide came to perform their forefront experiments. A large body of work (papers, theses, etc.) has already been published and, of course, the analysis of many experiments is still ongoing.

The physics addressed using GAMMASPHERE has ranged over many issues in nuclear structure and from nuclear astrophysics to tests of the Standard Model. A major focus has been to investigate the behavior and response of nuclear systems when they are excited to extremely high angular momenta. Many entirely unexpected discoveries have been made reminding us that the unique quantal system of the atomic nucleus holds many secrets! This booklet contains a selection of key scientific results obtained so far using GAMMASPHERE and attempts to convey the excitement felt by the worldwide community of scientists who are charting new realms of discovery with this revolutionary device.

On September 14, 1997 the period of GAMMASPHERE at Lawrence Berkeley National Laboratory came to a close. The array was shipped to the Argonne National Laboratory to begin a new phase of running, where investigating the structure of nuclei far from the line of stability is a central theme. Everyone looks forward to many more years of exciting results and world leading science from GAMMASPHERE.

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GAMMASPHERE's resolving power, ie. its ability to observe weak gamma-ray signals, improved over time as detectors were delivered and installed in the array.

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GAMMASPHERE closed and ready for beam!