Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session B2: Light Exotic Nuclei |
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Sponsoring Units: DNP Chair: Michael Thoenessen, Michigan State University Room: Hyatt Regency Dallas Landmark B |
Saturday, April 22, 2006 10:45AM - 11:21AM |
B2.00001: Studies of Neutron-Rich Nuclei with the MoNA/Sweeper System at the NSCL Invited Speaker: Binding energies and excitation spectra of nuclei are important benchmarks for nuclear structure calculations. In the case of very neutron-rich or neutron-unbound nuclei, changes of the shell structure and the effects from the continuum have to be taken into account in theoretical calculations. The Modular Neutron Array (MoNA) was completed in late 2003 and was commissioned in 2004 along with the 4 T sweeper magnet. The measurements done with the system have focused on the structure of very neutron-rich p-shell nuclei near where the magic N = 8 or N = 20 numbers may disappear. To date, measurements of $^{25}$O (ground state energy), $^{24}$O* (neutron-unbound excited state), $^{13}$Li (two-neutron decay), and $^{12}$Be (spectroscopic factor) have been completed. A summary of the state of theses experiments will be given. The results of a more global study of nuclei at the neutron dripline using fragmentation will also be shown. In addition to a discussion of the physics being studied, the current role of undergraduate students in experiments and analysis will be discussed. An update on how the widely-separated members of the collaboration interact in between experiments will be presented. [Preview Abstract] |
Saturday, April 22, 2006 11:21AM - 11:57AM |
B2.00002: Nucleon transfer reactions with exotic light nuclei Invited Speaker: There has been considerable renewed interest in the structure of light nuclei, especially away from stability, in recent years. Modern theoretical techniques for calculating nuclear structure, often referred to as ``{\em ab-initio}'' methods, have been extremely successful in predicting a variety of properties for systems with 10 or fewer nucleons. These include excitation energies, transition matrix elements and charge radii. The possibility to use simple direct transfer reactions such as {\em (d,p)} to study the properties of exotic light nuclei extends our ability to test these models at the extremes of neutron number where data were not previously available. Of particular interest are very loosely or even unbound systems where questions may remain about the applicability of these theoretical approaches. I will discuss some of the opportunities and challenges presented in this new domain, and present two recent examples of neutron transfer measurements to study the nuclei $^9 $Li and $^7$He. This work supported by the U. S. Department of Energy, Office of Nuclear Physics under contract DE-FG02-04R41320. [Preview Abstract] |
Saturday, April 22, 2006 11:57AM - 12:33PM |
B2.00003: The Structure of $^9$C and $^7$He. Invited Speaker: Light exotic nuclei provide important insights into the understanding of nuclear forces at large neutron to proton ratios, unreachable for heavier nuclei. The progress in development of modern theoretical approaches such as quantum Monte-Carlo calculations (QMC) and no-core shell model (NCSM) allows for predictions of properties of light nuclei (A<12) from the basic principles, starting from bare nucleon-nucleon interaction. Unfortunately, experimental information on the structure of many light exotic isotopes is very incomplete making it difficult to judge the accuracy of the $\textit{ab initio}$ models in case of large excess of neutrons or protons. Scarcity of spectroscopic information for many exotic isotopes is mostly related to the experimental difficulties one has to overcome to populate these isotopes and extract useful information. Development of Radioactive Nuclear Beams allowed application of simple resonance reactions, such as elastic scattering or resonance charge exchange reaction for spectroscopy studies of exotic nuclei. The advantage of this approach is mainly related to the fact that resonance reactions have high cross section and provide direct way to extract spectroscopic information. Application of resonance reactions for spectroscopy of exotic nuclei will be considered in two examples: $^{9}$C and $^{7}$He. The proton rich nucleus $^{9}$C was studied via resonance elastic scattering of protons on $^{8}$B. Only one excited state was known in $^{9}$C before this study. Method of inverse geometry and very thick target was used to obtain the excitation function of p +$^{8}$B elastic scattering up to the excitation energy of 4.5 MeV. The neutron rich nucleus $^{7}$He was studied through the T=3/2 Isobaric Analog States in $^{7}$Li. These states were populated in resonance charge exchange reaction $^{6}$He(p,n)$^{6}$Li$^{*}$(0$^{+}$). Two complimentary experimental techniques were developed to measure the excitation function of this process. In one, neutrons are measured in coincidence with $\gamma$ rays from the decay of 0$^{+}$ excited state of $^{6}$Li [1] and in the other Doppler shift of these $\gamma$ rays is used to extract information on the total cross section and angular distribution of $^{6}$He(p,n)$^{6}$Li(0$^{+}$) process [2]. [1] G.V. Rogachev, et al., Phys. Rev. Lett. 92, 232502 (2004). [2] P. Boutachkov, et al., Phys. Rev. Lett. 95, 132502 (2005). [Preview Abstract] |
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