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What is RIA?
Updated 9-20-05

A schematic of the RIA facility is shown in Figure 1. The key to the scientific discovery potential of the facility is its ability to provide the highest-intensity beams of stable heavy ions for the production of rare isotopes. This concept builds on developments in superconducting technology in the U.S. and Europe over the past two decades. RIA's driver accelerator will be a flexible device capable of providing beams from protons to uranium at energies of at least 400 MeV per nucleon, with beam power in excess of 100 kW. With this flexibility, the production reaction can be chosen to optimize the yield of a desired isotope. In comparison to the two main competing in-flight facilities, the Radioactive Ion Beam Factory at RIKEN and the GSI upgrade, RIA has two advantages. First, RIA's capability for post acceleration (not included in either of the other two projects) will allow a wider range of studies and will include the measurement of nuclear reactions at astrophysical energies and the search for new heavy elements with long lifetimes. Second, the acceleration scheme of RIA's primary-beam linac is planned to be 20-fold more efficient than either of the other facilities and, hence, able to deliver significantly more primary-beam power. In comparison to the main ISOL competition, ISAC at TRIUMF, RIA has higher primary-beam power and a more flexible combination of ion sources, which will provide higher intensities and a wider variety of rare isotopes.

Figure 1: RIA Concept illustration

Figure 1.
The heart of the facility is composed of a driver accelerator capable of accelerating every element of the periodic table up to at least 400 MeV/nucleon. Rare isotopes will be produced in a number of dedicated production targets. Upon extraction from the targets, these isotopes can be used at rest for experiments in Area 3, or they can be accelerated to energies below or near the Coulomb barrier and used in Areas 2 and 1, respectively. Isotopes will also be harvested for applications (Isotope recovery). Fast beams of rare isotopes can also be used directly after separation in a high-resolution fragment separator (Area 4). RIA brings together the most powerful known techniques for rare isotope production in a single facility.

The extraction of exotic nuclei at RIA will employ three methods. In the first, a thick ISOL-type target will be coupled to an ion source and a post accelerator for energies beyond the Coulomb barrier. This method will provide the most intense reaccelerated beams of those elements with chemistry favorable for rapid release. A second target area will utilize a thinner target and a recoil mass separator that can operate in two modes. In one mode, the fast mass separated exotic nuclei will be energy-degraded and then stopped in a gas catcher from which they can be rapidly extracted for reacceleration in the post accelerator. This will provide intense beams of short-lived isotopes or elements that are difficult to obtain from the standard ISOL target. In the second mode of thin-target operation, after mass separation, the ions from the target can be used directly as fast beams for experiments at high energies. In all cases, stopped nuclei can also be used for decay experiments, they can be injected into atom or ion traps, or they can be accelerated to low energies suitable for astrophysics studies.

Expected mass-separated intensities from RIA are shown in Figure 2. Many of these nuclei have never before been available as in-flight or reaccelerated beams. Generally, the intensity of rare isotopes will be more than two orders of magnitude greater than with any existing or planned facility. As shown in the figure, essentially all the nuclei that participate in the various astrophysical processes, such as the rp- and r-processes, will be available for study. The high intensities of rare isotopes will allow a full exploration of the limits of nuclear stability and will provide a wide range of isotopes for each element.

Figure 2 illustration

Figure 2:
Estimated yields for RIA in ions per second. The detailed description of how these yields were calculated can be found in C.L. Jiang et al., Nuclear Instruments and Methods in Physics Research A 492, 57 (2002).

Worldwide, the study of exotic nuclei is in rapid advance. Major projects are planned or already underway in Europe and Japan. The field is vital and intensely active. Progress can be made, at a reduced level, of course, without RIA, but RIA stands alone, 1 – 2 orders of magnitude better than any existing, or ever envisioned, facility. RIA is, simply put, second to none. With RIA, the U.S. will maintain a world leadership position in nuclear physics for decades.

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