Bulletin of the American Physical Society
75th Annual Meeting of the Southeastern Section of APS
Volume 53, Number 13
Thursday–Saturday, October 30–November 1 2008; Raleigh, North Carolina
Session JA: Nuclear Exotic Beams |
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Chair: David Ernst, Vanderbilt University Room: Holiday Inn Brownstone Washington |
Friday, October 31, 2008 1:30PM - 2:00PM |
JA.00001: Spectroscopy of light exotic nuclei in resonance reactions Invited Speaker: Light exotic nuclei is an important arena where predictions of modern ab initio theories can be tested. Unfortunately, experimental information on the structure of many light exotic isotopes is very incomplete due to experimental difficulties. With Radioactive Nuclear Beams, however, one can use simple resonance reactions to probe the structure 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. Recent experimental advances in the spectroscopy of light exotic nuclei using resonance reactions will be discussed. More specifically the following nuclei will be considered: $^{8}$B was studied in an elastic and inelastic scattering of protons on $^{7}$Be, T=3/2 isobaric chain of A=9 nuclei was studied using the $^{1}$H($^{8}$B,p) and $^{1}$H($^{8}$Li,p) reactions, populating resonances in $^{9}$C and T=3/2 states in $^{9}$Be respectively. Similar studies were performed for T=3/2, A=13 isobaric chain, where states in $^{13}$O and T=3/2 resonances in $^{13}$C were populated using $^{1}$H($^{12}$N,p) and $^{1}$H($^{12}$B,p) reactions. Level structure of these exotic nuclear systems will be discussed and compared to theoretical predictions. Experimental difficulties and possible ways to resolve them will be considered. [Preview Abstract] |
Friday, October 31, 2008 2:00PM - 2:30PM |
JA.00002: $^{78}$Ni, Nuclear Structure and LeRIBSS: New results from the HRIBF Invited Speaker: The nuclide $^{78}$Ni is the most neutron-rich doubly magic nuclide ($N/Z\!\approx\!1.79$) which can be reached using the available experimental techniques for the foreseeable future. Or at least we have long considered this nuclide to be doubly magic. Recent theoretical studies have shown the importance of the tensor component of the neutron-proton interaction [1] and coupling to continuum states [3] in causing a shift in the single particle energies for this neutron-rich region. The net effect is that we may no longer live in a happy little world of robust shell closures at $Z\!=\!28$ and $N\!=\!50$ once we move away from stability. Hence, we have a region of great interest for experimental studies. At the Holifield Radioactive Ion Beam Facility (HRIBF) of ORNL, the UNIRIB Consortium has begun a systematic study of nuclei in the $^{78}$Ni region. This began two years ago with a successful campaign using re-accelerated radioactive beams of $^{76-79}$Cu and $^{83-85}$Ga. This year, we made our first measurements using the Low-energy Radioactive Ion Beam Spectroscopy Station (LeRIBSS). I will give an overview of the results of the earlier experiment, present some preliminary results from the LeRIBSS runs, and discuss our future plans. Funded by DOE grant DE-FG02-96ER41006.\\ \noindent [1] T. Otsuka \textit{et al.}, Phys. Rev. Lett. \textbf {97}, 162501 (2006)\\ \noindent [2] J. Dobaczewski \textit{et al.}, Prog. Part. Nucl. Phys. \textbf{59}, 432 (2007) [Preview Abstract] |
Friday, October 31, 2008 2:30PM - 3:00PM |
JA.00003: Direct measurements with low-energy, rare isotope beams for nuclear astrophysics Invited Speaker: Measurements with beams of rare isotopes are now providing data that is helping to improve our understanding of stellar explosions. Beams of exotic proton-rich nuclei at low energies ($E_{cm} < 2$~ MeV/u) are of special interest since they allow cross sections for reactions that are important in novae and X-ray bursts to be directly measured over the energy range relevant in the stellar environment. These are challenging measurements due to small cross sections, but sensitive new techniques are allowing measurements even with weak radioactive ion beams. Measurements with 17F and 18F beams at the Holifield Radioactive Ion Beam Facility will be reviewed, focusing on a recent measurement of the $^{17}$F($p,\gamma$)$^{18}$Ne cross section using the Daresbury Recoil Separator. The exciting future prospects for measurements will also be discussed, including a program with reaccelerated fragmentation beams at the National Superconducting Cyclotron Laboratory and the possibilities with a next-generation Facility for Rare Isotopes Beams now under development by the U.S. Department of Energy. [Preview Abstract] |
Friday, October 31, 2008 3:00PM - 3:30PM |
JA.00004: Alpha decay studies near $^{100}$Sn Invited Speaker: Nuclei around the exotic doubly-magic $^{100}$Sn can provide key information to, and serve as rigorous tests of, the nuclear shell model. In particular, the energy splitting between neutron single-particle orbits in this region, the $\nu d_{5/2}$ - $\nu g_{7/2}$, can be extracted from the low-energy excited states in the odd-N Sn isotopes, ideally from $^{101}$Sn. Identification and examination of these nuclei is aided by the presence of an island of alpha and proton radioactivity for nuclei with Z $>$ 50 near $^{100}$Sn. The isotopes $^{109}$Xe and $^{105}$Te were identified at the Holifield Radioactive Ion Beam Facility using the Recoil Mass Spectrometer through the observation of the characteristic alpha decay chain $^{109}$Xe $\rightarrow$ $^{105}$Te $\rightarrow$ $^{101}$Sn. The efficient identification of the fast $^{105}$Te alpha decay was enabled through the use of digital signal processing using advanced pulse shape analysis alogrithms. The unique double alpha decay pulse provided an ideal tag to observe gamma-ray emission from the excited states of both $^{105}$Te and $^{101}$Sn at approximately 150 and 172 keV, respectively. Both excited states in $^{105}$Te and $^{101}$Sn were populated through alpha decay. The observation of the first excited state in $^{101}$Sn provides the $\nu d_{5/2}$ - $\nu g_{7/2}$ energy splitting. Using the experimental value in shell model calculations suggests an ordering of single particle states in $^{101}$Sn that contradicts previous expectations. The possibility of reaching the $^{108}$Xe $\rightarrow$ $^{104}$Te $\rightarrow$ $^{100}$Sn alpha decay chain will also be discussed. [Preview Abstract] |
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