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Scientific Opportunities with a Rare-Isotope Facility in the United States
There are two major U.S. facilities running dedicated user programs primarily in exotic beams:
The National Superconducting Cyclotron Laboratory (NSCL) located at Michigan State University (MSU), and
The Holifield Radioactive Ion Beam Facility (HRIBF) located at the Oak Ridge National Laboratory (ORNL), Tennessee.
Other laboratories have capabilities to provide exotic beams: the Argonne Tandem Linear Accelerator System (ATLAS) at the Argonne National Laboratory (ANL), the Cyclotron Institute at Texas A&M University, the 88-inch Cyclotron at the Lawrence Berkeley National Laboratory (LBNL), and the TwinSol facility at the University of Notre Dame. The ATLAS facility and the Texas A&M laboratory are planning major upgrades of their exotic-beam capabilities, as described below. The current U.S. program is world leading, with the highest-intensity fast exotic beams available at the NSCL and a unique set of beams from actinide targets at HRIBF. The approximate size of the U.S. rare-isotope science community is 600 researchers and 150 graduate students. In addition, about 100 users from the international community come to the United States each year to conduct experiments at these facilities.
The NSCL at MSU provides approximately 4,000 hours of exotic fast-beam experiments per year. The facility is currently able to produce the most-intense fast beams of exotic isotopes worldwide through the use of two coupled superconducting cyclotrons and the A1900 fragment separator. Beams of between 20 and 200 MeV/A are available for experiments. During the laboratory’s first few years of operation, more than 100 different secondary beams have been used for experiments. Key experimental equipment includes the superconducting high-resolving power, large solid angle S800 magnetic spectrograph. This device is used in approximately 60 percent of all experiments. Other equipment includes the highly segmented germanium array (SeGA), a sweeper magnet plus neutron wall system for measuring neutron unbound states, a high-resolution array (HiRA) made of silicon, and a gas-stopping and Penning trap system for precision measurements of short-lived nuclei. Near-term upgrades include the addition of a radio-frequency (RF) separator for the purification of proton-rich nuclei, gamma-ray tracking using the SeGA array, and an improved gas-stopping system based on a cyclical system. In the medium term, plans are being developed to add postacceleration and to develop a modest program of reaccelerated beams. Ion beam intensities of up to 108 particles per second will be possible for many species.
HRIBF at ORNL employs the Isotope Separator On-Line (ISOL) method to produce radioactive ion beams using the Oak Ridge Isochronous Cyclotron