strong efforts by groups interested in hosting RIA have developed facility plans and the required technology for a U.S. FRIB. These groups had developed impressive technical plans with significant similarities, each incorporated a 400 MeV/A superconducting radio-frequency linear accelerator driver and capabilities to produce rare isotopes by in-flight fragmentation, the traditional Isotope Separator On-Line (ISOL) technique, and gas stopping and reacceleration. The expected cost of either facility was about $1.1 billion.

After RISAC began its work, the DOE announced that it intended to pursue a FRIB at about half the cost, with funds for project-engineering definition not to begin until 2011. In response to these new guidelines for a U.S. FRIB, both groups pursuing a FRIB presented the committee with new plans for a smaller facility based on a 200 MeV/A linear accelerator (linac) and somewhat reduced experimental capabilities. Although the committee could not review these preliminary design concepts in detail, it is important to note that both plans significantly scaled back the multiuser capabilities of the facility in order retain as much of the intensity and diversity of rare isotopes as possible. Thus, the suggested designs for a FRIB would have much reduced access compared with that of the earlier RIA proposals. However, this revised approach could engender a useful series of upgrades. While arguments can be mustered about the dire consequences of delay, experience shows that it is not always a bad choice, especially when accounting for the uncertainties in any predictions about the future of science. For these reasons and because it lay outside the charge, the committee chose not to specifically evaluate the consequences of the proposed change in schedule. Healthy stewardship of the U.S. nuclear science community and continued exploitation of the key scientific opportunities will be matters that NSAC will need to consider carefully in its next long-range plan.

In response to these events and the charge, the committee proceeded to assess the science that could be accomplished with a reduced-scope FRIB as described by the proponents, taking account of the time frame consistent with a 2011 start for engineering definition. The committee was not charged to recommend a specific facility or to make recommendations about the utility of a FRIB in comparison with other possible initiatives for U.S. nuclear science. Indeed, a new long-range planning process for nuclear science will begin in 2007, and the community will have the opportunity to assert its priorities.

SCIENTIFIC CONTEXT

Nuclear structure physics as pursued at a FRIB aims to describe nuclei as a collection of neutrons and protons. Current theoretical approaches are much more powerful than the pioneering models developed in the 1940s and 1950s. The



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