Thus, not to belabor the issue further but to quote from the conclusion of the NSAC subcommittee:

There have been numerous previous studies that have made a strong science case associated with the study of rare-isotopes and we reaffirm those findings. The RIA and GSI facilities are largely quite distinct in their strengths and are indeed, as the proponents claim, complementary. RIA clearly has a much larger reach as a rare-isotope facility, and hence the better facility to address the science associated with rare-isotopes. The existence of an upgraded GSI facility does not, by itself, constitute justification for de-scoping the rare-isotope capability of RIA as there is only modest overlap in their rare-isotope capabilities. However, the rare-isotope capability at the future GSI facility is only one part of a remarkably versatile and multifaceted accelerator complex. We expect the U.S. research community to have a strong interest in several of the GSI capabilities.5

The present Rare-Isotope Science Assessment Committee is in accord with the findings of this NSAC subcommittee and further notes that since FAIR will be pursuing a broad program of which rare-isotope beams are only a part, significant annual operations would make a FRIB quite competitive. That is, beam-time availability for exotic species would be a key determining factor in the success of a FRIB over FAIR.

No such complete study exists comparing the capabilities of RIA to RIKEN’s RIBF, let alone for a U.S. FRIB. However, the following observations can be made. RIKEN is currently designed as a heavy-ion-fragmentation facility. It aims for a heavy-ion driver power of somewhat less than 100 kW for a 350 MeV/A 238U beam. The suite of experimental systems planned for installation in the second phase of construction is impressive. The planned storage ring (with a mass resolution Δm/m = 10−6) will be an important capability for measurements of masses approaching the neutron drip line. The addition of a 300 MeV electron storage ring to investigate the charge distribution of radioactive ion species will be a unique capability unmatched at any other facility.

There are no plans for a light-ion ISOL capability. The goal for the RIBF primary accelerator requires a tenfold improvement in the performance of the cyclotron-ion source and proof of performance for the stripper foil technology at these intensities. With the considerable investments being made and the sharp focus on physics with rare ions, RIKEN’s RIBF will be the leading facility in the region and a major facility in the world with several unique features.

5

U.S. Department of Energy, NSAC Subcommittee on the Comparison of RIA and the GSI Project Opportunities and Capabilities, Washington, D.C., February 2004, p. 30.



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