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The availability of radioactive ion beams represents a major advance in the capbaility to attack important problems of basic and applied nuclear physics. For the first time we are able to study nuclear reactions on nuclides outside the valley of stability. These nuclides represent about 80% of particle-stable isotopes. Questions of nuclear reaction mechanisms, nuclear properties of bound and continuum states, and basic symmetries for these unstable nuclides can therefore be answered by direct mesurement rather than by speculation. The applications of radioactive ion beams are widespread and extensive. In astrophysical studies, nuclear reactions of radioactive ion beams are essential to understanding a wide range of problems in energy generation, nucleosynthesis, neutrino effects, and the implications of gamma-ray astrophysical measurements. In material studies, the implantation of radioactive ions has already seen important use. Well defined beams of these ions will greatly increase the specifity and sensititivity of this technology. Radioactive ion beams may also have significant applications in medical diagnostics and therapy. Finally, standard sources of beta and gamma radiation can be prepared with much greater precision than formerly available.
In this paper we discuss efforts underway at LLNL to develop the technology for the measurement of proton and alpha-particle reactions with unstable nuclei which are necessary for understanding the nucleosynthesis and energy generation in hot hydrogen-burning environments. 16 refs., 5 figs.
Several modifications and additions have been made to improve the radioactive beam facility at Livermore with the main aim of measuring the cross section for 7Be(p, .gamma.)8B (which is important in determining the solar neutrino flux) and other reactions of astrophysical interest. The quadrupole sextuplet spectrometer has been upgraded by inserting an electrostatic deflection element near the midpoint and by installing a movable beam stop near the 7Be production target. These changes have allowed an improvement in the purity, and a large increase in the intensity, of the 7Be beam. Six large NaI(Tl) detectors and the gas cell from the OSU system along with its active and passive shielding have been incorporated into the Lawrence Livermore facility. True events are to be identified by a multiple coincidence. The first requirement is the detection of a .gamma.-ray from the proton capture 7Be(p, .gamma.)8B. After the candidate capture gamma is observed the 8B decay signature is required. This signature is a positron (from 8B .-->. 8Be* + e + .nu.) along with the two .cap alpha.'s from 8Be .-->. .cap alpha. + .cap alpha. observed in a CaF2 detector into which the 8B have implanted. Also a detector telescope inside the gas cell monitors the incoming 7Be beam. The current status of the 7Be(p, .gamma.)8B measurement is discussed.
Early in 1995, the ORNL Holifield Facility is scheduled to return to operation as a dedicated radioactive ion beam (RIB) facility. This enhanced capability will open up new possibilities for research on the structure of and phenomena occurring in proton-rich nuclei. Among the opportunities will be the creation of heavier N(approximately)Z nuclei, approaching 1°°Sn, and the study of exotic nuclear shapes, extensions of studies of the p-n interaction and super-allowed beta decay, and examination of nuclear structure near the proton drip line. In addition to new nuclear and atomic physics research opportunities, the beams from the Holifield RIB facility are expected to provide new capabilities for measurements important to nuclear astrophysics. To carry out this experimental program, various upgrades are planned to the existing experimental apparatus, and a new, third-generation, recoil-mass separator is being constructed.
This report contains the proceedings of a 2-1/2 day workshop on the Science of Intense Radioactive Ion Beams which was held at the Los Alamos National Laboratory on April 10--12, 1990. The workshop was attended by 105 people, representing 30 institutions from 10 countries. The thrust of the workshop was to develop the scientific opportunities which become possible with a new generation intense Radioactive Ion Beam (RIB) facility, currently being discussed within North America. The workshop was organized around five primary topics: (1) reaction physics; (2) nuclei far from stability/nuclear structure; (3) nuclear astrophysics; (4) atomic physics, material science, and applied research; and (5) facilities. Overview talks were presented on each of these topics, followed by 1-1/2 days of intense parallel working group sessions. The final half day of the workshop was devoted to the presentation and discussion of the working group summary reports, closing remarks and a discussion of future plans for this effort.
Beams of radioactive ions can be produced as secondary beams following the interaction of conventional accelerator beams with suitable targets. For example we have used beams of 7Li and 12C from an EN Tandem Van de Graaff accelerator to produce beams of 7Be and 13N via the (p, n) and (d, n) reactions respectively. These beams are focused by a system of magnetic quadrupole lenses to a secondary target. Reactions of such nuclides, especially proton capture and (p, .cap alpha.) reactions, are of interest in solar physics and in the CNO multi-cycle in massive stars. Progress toward the measurement of these reactions is discussed.