For billions of years, unstable suns have been erupting in vast explosions that race across dust-churned reaches of interstellar space. These supernovae bursts produce a menagerie of unstable, evanescent atomic nuclei that even today remain unknown to contemporary science.

To identify and examine exotic nuclear "isotopes," researchers from distinguished American universities, Dept. Of Energy national laboratories, and research institutes in the United States and abroad are calling for the creation of an advanced ISOL (Isotope Separation On-Line) facility. The DOE's long-range nuclear physics plan identifies such a facility as the highest construction priority for the Department.

In October 1998, at the request of DOE and the National Science Foundation, the Nuclear Science Advisory Committee (NSAC) commissioned an ISOL Task Force to review the research community's readiness to develop, plan and design an advanced ISOL facility. Two members of Jefferson Lab are at the forefront of the group: Lab director Hermann Grunder serves as the ISOL Task Force chair and JLab Accelerator Division scientist Charlie Reece provides critical assistance to Grunder in his role as chair.

The planning group is composed of a dozen members, including ISOL experts from CERN, Geneva, Switzerland; and TRIUMF, Canada's national lab in Vancouver, BC. Additional consultants from France, Great Britain, Japan, Finland, and DOE laboratories are also involved. This past January, ISOL members and consultants met at JLab to address the complexity of typical ISOL target designs. This coming October the Task Force is expected to provide its final report to NSAC.

"If a next-generation ISOL can be built at reasonable cost, it would make an astounding difference in a number of fields, from nuclear physics to astrophysics," says Jefferson Lab director Hermann Grunder. "It should substantially deepen our understanding of elements and their formation. It will change our textbooks."

An ISOL center would explore what some have called the "chemistry" of nuclear physics. The facility would provide to researchers high-intensity, high-resolution accelerated beams of rare radioactive ions, many of which are thought to normally exist only briefly as a byproduct of stellar explosions. An ISOL facility would use an accelerated drive beam comprised of either protons or stable heavy ions to strike a thick target, producing the desired exotic nuclei. The targets are designed to quickly release these ions so they may be separated, fed through a post-accelerator and delivered to experiments before the ions have had time to decay.

An advanced ISOL laboratory should significantly deepen understanding of the nucleus as a "many-body" system built of protons and neutrons and governed almost exclusively by one of the four known forces, the strong nuclear force. Such a laboratory would also test the limits of what is known as the Standard Model: that theory that represents present understanding of the basic laws that govern the way elementary particles interact.

Key Applications

Hermann Grunder ISOL Task Force Chair

Using the ISOL beam, researchers would be able to focus on the unusual properties of loosely bound quantum systems, especially those with unique geometries. Some nuclei, for instance, are characterized by particle halos or by "skins" of neutron matter. Others interact not just within the nucleus, but outside it as well. ISOL investigations could also examine novel states involving superfluidity and new forms of atomic shell structure.

In particular, ISOL studies should be of benefit to the field of nuclear astrophysics. Processes central to the synthesis of the elements in stars and to the detonation of supernovae are thought to be crucial to life, climate and geology. A star's nuclear reactions involve proton and neutron capture which, in turn, are dependent on the formation and action of unstable nuclei. Study of those nuclei should deepen understanding of the synthesis of elements within stars and the ways in which stars develop and mature.

In the short term, the ion beams produced by a major ISOL facility could have a wide variety of applications to medicine and to industry. In the case of medical treatment, for instance, estimates are that one out of three hospitalized patients in the United States undergoes diagnostic procedures involving nuclear medicine. In the case of diagnostic implants that require a specific radioactive source, an ISOL facility ion beam would offer a range of energies, half-lives and decay types, which can be used to control the depth, intensity and location of implantation. These same characteristics could also be used as diagnostics to boost the efficiency of microchip manufacture and to improve the properties of metals and other materials.

Thus far, Oak Ridge and Argonne national laboratories, with assistance from existing, albeit modest ISOL facilities in Europe and Canada, have actively pursued ISOL feasibility studies, supporting their research with in-house discretionary funds. DOE, however, is planning to direct $10 million to ISOL-related research and development in fiscal year 2001.

If policymakers opt to continue with the project, construction could begin as early as 2002. For the full facility presently envisioned, total costs should run in the neighborhood of $400 million, with facility staffing levels projected to be roughly half those of Jefferson Laboratory's complement of 600.

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