The Gammasphere is a 12-ton gamma-ray microscope used to study the complex structure and behavior of nuclei. The nuclei studied with Gammasphere have been created in a heavy-ion induced fusion reaction where an accelerated projectile nucleus collides and fuses with a target nucleus to form a highly excited compound nucleus. These highly excited nuclei release their energy by emitting gamma rays; a form of extremely high-energy light. By measuring the energy of these emitted gamma rays with Gammasphere, researchers can gain insight into how the structure of nuclei change as both a function of proton and neutron number. Over a year ago, this $20 million national traveling physics instrument was moved from the 88-inch Cyclotron facility at Lawrence Berkeley National Laboratory to the ATLAS heavy-ion accelerator at Argonne National Laboratory to switch from a concentration of studying nuclei at "high spin" to studying the structure of exotic "nuclei far from stability."

Most of the experiments conducted using Gammasphere at Argonne have reached unique levels of sensitivity. In many instances, this has been made possible by coupling Gammasphere to the Fragment Mass Analyzer (FMA), a high resolution mass spectrometer that measures the mass of the residential nuclei produced in a heavy-ion reaction. By using Gammasphere and the FMA in tandem, structural and reaction-mechanism measurements have been made on No-254 (Z=102), the heaviest element ever studied by "in-beam" gamma-ray spectroscopy. In addition, information on the structure of nuclei lying at the limits of stability have been obtained. For example, by measuring excited states in proton emitter Ho-141 with Gammasphere, it has been independantly confirmed that this nucleus is deformed when the proton is emitted. In the same experiment, gamma-ray spectroscopy measurements were made on an isomer produced with a cross section of which is the lowest ever reported for this field of research.

Many more experiments are planned with the ATLAS accelerator at Argonne before the Gammasphere returns to Berkeley in March 2000. This research is supported by SC's Office of High Energy and Nuclear Physics.

Contact: Mike Carpenter, Argonne National Laboratory, (630) 252-5365, [email protected]

Related Information:
"The Gammasphere Detector: Probing Nuclei at the Limits of Stability," https://www.phy.anl.gov/dnp/current/gamma/[email protected]
"Gammasphere Leads Explorers Along Rim of the Valley of Nuclear Stability," Logos, Vol. 16, No. 2, Winter 1998 — Online at http://www.anl.gov/OPA/logos16-2/gammasphere1.htm