Bulletin of the American Physical Society
2008 Annual Meeting of the Division of Nuclear Physics
Volume 53, Number 12
Thursday–Sunday, October 23–26, 2008; Oakland, California
Session ED: Mini-Symposium: Rare Isotope Science III |
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Chair: Roby Austin, St. Mary's University Room: Jewett Ballroom G-H |
Friday, October 24, 2008 4:00PM - 4:36PM |
ED.00001: Challenges and new opportunities in the study of neutron-rich isotopes Invited Speaker: Neutron-rich isotopes are the new frontier for RIB studies. The large neutron excess and reduced importance of the Coulomb barrier allow for exotic phenomena such as halos and skins and an expected modification of the effective interaction and shell- structure far from stability. Important features of these isotopes that can now be studied with existing RIB facilities will be presented. Remaining challenges will be highlighted and future prospects introduced, with a special emphasis on the CARIBU upgrade that will soon make available neutron-rich isotopes from 252Cf fission reaccelerated at energies above the Coulomb barrier. [Preview Abstract] |
Friday, October 24, 2008 4:36PM - 4:48PM |
ED.00002: $\beta$ decay of $^{51,52}$Ar P.F. Mantica, H.L. Crawford, J. Pereira, J.S. Pinter, J.B. Stoker, R. Broda, B. Fornal, R.V.F. Janssens, X. Wang, S. Zhu, N. Hoteling, W.B. Walters, C.R. Hoffman, S.L. Tabor The neutron-rich $^{51,52}$Ar isotopes were produced by fragmentation of a $^{76}$Ge primary beam of energy 130 MeV/A at NSCL. The A1900 fragment separator, with a wedge degraded and plastic scintillator placed at its intermediate image, was used to select the Ar isotopes of interest from other reaction products. The full 5\% momentum acceptance of the A1900 was used, and other neutron-rich isotopes of K, Ca, Sc, and Ti were available for study as well. Seven implantations unambiguously identified as $^{52}$Ar based on energy loss, total energy, time-of-flight, and magnetic rigidity provided first evidence for the existence of this nuclide. We will report the $\beta$-decay half-lives of $^{51,52}$Ar deduced from event-by-event time correlations between implantations and subsequent $\beta$ decays measured with the NSCL Beta Counting System. [Preview Abstract] |
Friday, October 24, 2008 4:48PM - 5:00PM |
ED.00003: Beta Decay Studies of Neutron-Rich Nuclei near $^{52}$Ca H.L. Crawford, P.F. Mantica, G.F. Grinyer, K. Minamisono, J.S. Pinter, J.B. Stoker, R.V.F. Janssens, M. Carpenter, B. Kay, T. Lauritsen, S. Zhu, R. Broda, B. Fornal, N. Hoteling, I. Stefanescu, W.B. Walters The $\beta$ decay and isomeric properties of neutron-rich nuclei near semi-magic $^{52}$Ca were studied at NSCL. The presence of a significant energy gap, separating the neutron \textit{f}$_{5/2}$ and \textit{p}$_{1/2}$ single-particle states from the \textit{p}$_{3/2}$ level at \textit{N}=32, has a stabilizing effect on the low-energy structure of nuclides in this region. We report the results for the low-energy structure of $^{50}$K, which has one proton hole and one neutron hole outside $^{52}$Ca, determined from isomeric decay. We also discuss new levels in $^{53}$Sc, one proton outside $^{52}$Ca, populated following the $\beta$ decay of $^{53}$Ca. Both findings reinforce previous evidence for the doubly-magic character of the $^{52}$Ca core. [Preview Abstract] |
Friday, October 24, 2008 5:00PM - 5:12PM |
ED.00004: Study of the $\beta$-decay of $^{11}$Li at ISAC/TRIUMF Fred Sarazin, C.M. Mattoon, C. Andreoiu, A. Andreyev, R.A.E. Austin, G.C. Ball, R.S. Chakrawarthy, D. Cross, E.S. Cunningham, J. Daoud, P.E. Garrett, G.F. Grinyer, G. Hackman, D. Melconian, C. Morton, C. Pearson, J. Ressler, J. Schwartzenberg, M.B. Smith, C.E. Svensson The $\beta$-decay of $^{11}$Li was investigated using the 8$\pi$ $\beta$-decay spectrometer, an array of 20 Compton-suppressed HPGe detectors and 20 plastic scintillators for $\beta$-particle detection. Doppler-broadened line shapes resulting from the decay of excited states of $^{10}$Be populated by $\beta$-delayed neutron emission are analyzed using Monte Carlo simulations. New $\beta$-delayed neutron decay branches are shown to contribute to the complex decay of $^{11}$Li. Results, comparison with previous works, as well as implications for the beta-decay of the $^{11}$Li halo neutrons will be discussed. This work is partially supported by the US Department of Energy through Grant / Contract No. DE-FG03-93ER40789. [Preview Abstract] |
Friday, October 24, 2008 5:12PM - 5:24PM |
ED.00005: Fusion of $^{9}$Li with $^{208}$Pb A.M. Vinodkumar, W. Loveland, P. Sprunger, J. Neeway, L. Prisbrey, M. Trinczek, M. Dombsky, P. Machule, D. Ottewell, J.J. Kolata, A. Roberts, T. Spencer The fusion of weakly bound nuclei is one of the active areas of research with radioactive beams. The main issue is whether the fusion cross section will be enhanced due to large nuclear size of the halo nuclei or breakup of the weakly bound valence nucleons will lead to decreased fusion cross section. In the case of $^{11}$Li with $^{208}$Pb, differences between theoretical predictions are very large. We observed large sub barrier fusion enhancement in the case of $^{9}$Li with $^{70}$Zn. As an extension to this study, measurements were carried out at TRIUMF using $^{9}$Li beams in the energy range 25-45 MeV on $^{208}$Pb. The alpha decay of the evaporation residues were detected using 16 silicon detectors placed close to the target. The study of $^{9}$Li with $^{208}$Li will be very important to understand the halo effect on fusion of $^{11}$Li with $^{208}$Pb. The experimental results will be presented along with theoretical model predictions. [Preview Abstract] |
Friday, October 24, 2008 5:24PM - 5:36PM |
ED.00006: Studying the structure of the neutron-unbound $^{12}$Li A. Spyrou, M. Thoennessen, P.A. DeYoung, C.C. Hall The decay-energy spectrum of $^{12}$Li was measured in a neutron-fragment coincidence experiment at the National Superconducting Cyclotron Laboratory at MSU. $^{12}$Li was produced in the two-proton knockout reaction from a $^{14}$B secondary beam at 54 MeV/u. $^{12}$Li is neutron unbound and decays into $^{11}$Li and a neutron. The $^{11}$Li fragments were detected with position sensitive detectors behind the sweeper magnet, while the Modular Neutron Array (MoNA) was used to detect the emitted neutrons. The decay energy of $^{12}$Li was reconstructed event-by-event from the four-momentum vectors of the two products. Two resonances were observed in the invariant-mass spectrum at $\sim$200 keV and $\sim$500 keV. The measurement of the structure of $^{12}$Li is an essential first step for the understanding of the two-neutron decay mode of $^{13}$Li. The latter was also measured during the experiment in the one-proton knockout reaction from $^{14}$Be and the analysis is in progress. [Preview Abstract] |
Friday, October 24, 2008 5:36PM - 5:48PM |
ED.00007: N minus Z dependence of intruder states near the island of inversion Samuel Tabor, Trisha Hinners, Vandana Tripathi, Alexander Volya Almost 3 decades after the discovery of deformed, intruder-dominated ground states in nuclei with Z $\sim$ 10 and N $\sim$ 20, many questions remain about the behavior of the N = 20 shell gap and how correlation effects can bridge the gap in this region of nuclei, later dubbed the ``Island of Inversion,'' because intruder states expected to lie at higher energies actually fall below the ``normal'' s-d states. Recent work has illustrated how some intruder dominated states fall systematically with increasing N and decreasing Z until reaching inversion. These N and Z dependences have been treated quite differently in the most successful calculations. The fall with increasing N is generally attributed to the rising Fermi level for neutrons, while the fall with decreasing Z seems to require a reduction in the N = 20 shell gap with lowering Z, perhaps due to the tensor interaction. The recent assignment of a negative-parity intruder band in $^{30}$Al at reduced energy and a subsequent survey of similar 4$^-$ bandheads in neighboring odd-odd nuclei has led to an intriguing discovery: the excitation energy of these lowest intruder states depends only on N minus Z to an accuracy of 10 to 20 keV. [Preview Abstract] |
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