The Holifield Radioactive Ion Beam facility at Oak Ridge National Laboratory where UNIRIB researchers study the fundamental structure of nuclei. Photo courtesy of Oak Ridge National Laboratory.
The UNIRIB (University Radioactive Ion Beam) consortium and its predecessor UNISOR (University Isotope Separator – Oak Ridge) have operated, since 1971, a facility and carried out basic nuclear physics research, within the ORNL HRIBF facility and its predecessors. Following the closure of HRIBF in April, 2012, the UNIRIB university researchers and staff continued to analyze data, publish papers and bring to closure the development of two experimental systems that were underway. Under development were a He-jet ion source and a time-of-flight mass analysis system, ORISS, (Oak Ridge Isomer Spectrometer and Separator). UNIRIB researchers demonstrated full offline operation and obtained initial performance figures for both. Both systems were delivered to the NSCL (National Superconducting Cyclotron Laboratory) at Michigan State University. UNIRIB ceased operation June 29, 2015.
It was in 1970 that eleven universities formed the UNISOR consortium and jointly developed the first isotope separator on-line to a heavy-ion cyclotron (ORIC), dedicated to nuclear structure studies. This development precipitated the study of far-from-stability proton-rich nuclei in the U.S. UNISOR was a bold and innovative move for the period since it represented a new direction in which nuclear scientists would move their research from their campuses to a national laboratory. The founding universities, Emory, Furman, Georgia Tech, Louisiana State University, University of Tennessee, Tennessee Tech, Alabama (Birmingham), Kentucky, Massachusetts, South Carolina, Vanderbilt, and Virginia Tech formed UNISOR under the administrative umbrella of ORAU. A report describing the initial operation of UNISOR was published in 1974 [Science 185:819-24]. During the ensuing years, Mississippi College, Mississippi State, Maryland, Michigan State, Oregon State, Oxford University (England), Notre Dame, Rutgers, and Texas A&M, joined the consortium.
Over the years the UNISOR/UNIRIB staff and researchers maintained cutting edge research capabilities by continually developing new experimental devices and techniques. Among these: on line ion sources to extend the range of isotopes studied; numerous experimental techniques utilizing online isotope separators; a tuneable dye laser system for measuring atomic hyperfine structure; a low temperature nuclear orientation facility; ion sources for the first accelerated radioactive ion beam facility (HRIBF); and the use of the UNISOR isotope separator as the HRIBF radioactive ion beam test facility. While focusing in the area of online isotope separators the group led the development of a new generation state-of-the-art recoil mass separator for HRIBF, developed many different gamma-ray and electron detector systems and was among the first in the implementation of digital electronics. In every case, these new facilities and/or instruments greatly enlarged the research possibilities at HRIBF. In the final two years, the He Jet ion source and the time-of-flight mass system ORISS (Oak Ridge Isomer Spectrometer and Separator) were brought to closure and moved to the NSCL at Michigan State University.
The scientific legacy that UNIRIB/UNISOR leaves behind includes more than 400 refereed scientific publications, more than 40 Ph.D. students, and two instrument systems, now at NSCL, that will be incorporated into the NSCL and FRIB when it becomes operational. A paper describing the work of the consortium over the past 44 years is being prepared.