Collaborative Research: Nuclear Reaction and Structure Studies with Radioactive and Stable Beams

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

The research funded by this award is designed to promote a better understanding of atomic nuclei, the basic building blocks of all normal matter in the Universe. How did they form following the Big Bang, and how do they now interact to change their basic elemental nature? Are there new forms of matter made up from very exotic types of atomic nuclei and how might we make and study these? To this end the group will develop special new techniques in nuclear science, as well as train future scientists that can help answer some of these questions. One important training component will be a continuation of the well-established and highly successful outreach to faculty and students at New Buffalo High School in Michigan that has introduced these students to interesting, important, and exciting careers in the sciences. The technology developed and used in this research will have applications in other important areas, such as homeland security (nuclear terrorism), the safe storage and monitoring of nuclear wastes, and applications in nuclear medicine, including radiation therapy. The latter includes a new modality directly related to this research: the production and imaging of ion beams to treat particular forms of cancer tumors. Nearly 50% of graduate students and other personnel trained in the group's past research projects are currently pursuing careers in nuclear security or nuclear medicine, and it is anticipated that this will continue as a result of the present grant. The proposed project will involve the study of nuclear reactions utilizing stable as well as short-lived radioactive nuclear beams, together with the development of instrumentation, techniques, and apparatus to facilitate such studies. This includes use of the TwinSol low-energy radioactive ion-beam facility in operation at the University of Notre Dame (ND), developed jointly by the University of Michigan (UM) and ND. Specific experiments will emphasize the investigation of the structure and reaction mechanisms of neutron- and proton-rich nuclei near the limits of nuclear stability to elucidate the effect that the exotic "nuclear halo" structure, which appears for weakly-bound systems at the limits of stability, has on fusion, transfer, inelastic excitation, and breakup probabilities near the Coulomb barrier. Of particular interest here is the influence that higher-order couplings to and within the continuum have on the various reaction mechanisms, since proximity to the continuum is the characteristic defining feature of weakly-bound systems. These studies will be carried out at TwinSol in collaboration with a group from the National Superconducting Cyclotron Laboratory (NSCL), utilizing a prototype active-target time-projection chamber (AT-TPC). A related program will use the full AT-TPC recently commissioned at the reaccelerated beam facility (ReA3) at NSCL. In addition, the UM-UND collaboration, under the primary direction of the UM research group and their colleagues, will continue advanced development and application of deuterated scintillators for nuclear measurements involving neutrons. This will include selected measurements of (d,n) and (3He,n) reactions involving both stable and unstable beams, and in particular 7Be(d,n) which is of interest in astrophysics. Since these detectors permit neutron spectroscopy and cross section measurements without neutron time-of-flight, they have a particular advantage when used with the high-intensity, low-energy, non-pulsed accelerators suitable for nuclear astrophysics measurements. The latter includes the new 5 MV accelerator recently installed at ND and we will pursue such experiments, and in particular several key (A,n) measurements, together with the nuclear astrophysics group at ND. The unique neutron detector array the group has recently developed has potential for wide-spread applications both in nuclear science as well as in homeland-security and nuclear non-proliferation. As in the past, the proposed work will involve graduate and undergraduate students from ND and UM, together with faculty members and students from several primarily undergraduate schools located in close proximity to these universities. The highly-technical nature of the proposed research will thus contribute significantly to the training of a technically-literate work force.