Assessment Committee (RISAC). The committee was charged by the Department of Energy and the National Science Foundation to define the science agenda for a next-generation U.S. Facility for Rare-Isotope Beams (U.S. FRIB). RISAC members included several experts in rare-isotope science, but the committee consisted largely of scientists from outside the rare-isotope science community; it also included members from Canada, Europe, and Asia. Soon after RISAC was formed, the DOE announced that the budget of what was then understood as RIA would be reduced by about half. In response to this announcement and the charge, the committee focused on articulating the science that could be accomplished at a rare-isotope facility of reduced scope, referred to as a FRIB or a U.S. FRIB in this report. The charge also directed the committee to evaluate the scientific impact of a FRIB in the overall context of the national and international nuclear physics programs.

The committee heard presentations about applications of a FRIB for nuclear physics studies and also about applications in areas of medical research and stockpile stewardship. RISAC was not asked to give advice on whether a facility should be constructed or to compare the relative merits of various possibilities. For its analysis, the committee interpreted “U.S. FRIB” as a general-purpose rare-isotope production facility with a cost about half that of the earlier RIA concept. To gain a better understanding of the potential impact on the scientific agenda of such a cost reduction, the committee heard views from some of the proponents of a U.S. FRIB in a public meeting; these individuals gave the committee their views on production techniques and beam intensities that they judged to be technically feasible. As indicated in these presentations, the primary trade-off expected from such a decrease in cost would be a modest reduction in the quantity and diversity of possible isotopes and a significant reduction in the multiuser aspects of the facility.

In developing its conclusions regarding a FRIB, the committee took into account the worldwide portfolio of related experiments and the likely time frame in which the facility might begin operations (2016, according to current DOE plans). Despite the uncertainty inherent in predicting what will be the important scientific questions in the far future, a powerful new rare-isotope facility could resolve scientific issues of clear importance. Arguments from the groups that have conducted the research and development for a FRIB convinced the committee that most of the major technical issues have been addressed. The committee concluded that the case for a next-generation, radioactive-beam facility of the type embodied in the U.S. FRIB concept represents a unique opportunity to explore the nature of nuclei under conditions that only exist otherwise in supernovae and to challenge current understanding of nuclear structure through the exploration of new forms of nuclear matter and the development of a more robust quantitative description.

A rare-isotope facility produces beams of unstable atomic nuclei for direct



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