Bulletin of the American Physical Society
2008 APS April Meeting and HEDP/HEDLA Meeting
Volume 53, Number 5
Friday–Tuesday, April 11–15, 2008; St. Louis, Missouri
Session W3: Recent Developments in the Structure of Exotic Nuclei |
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Sponsoring Units: DNP Chair: Robert Janssens, Argonne National Laboratory Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), St. Louis E |
Tuesday, April 15, 2008 10:45AM - 11:21AM |
W3.00001: Measurements of magnetic moments of excited states in nuclei far from from stability. Invited Speaker: Magnetic moments of nuclear states provide information on their microscopic structure as a function of energy, spin and temperature and reveal subtle interplay between single particle and collective nuclear excitations. Advances in technology have made it possible to measure magnetic moments of states with lifetimes ranging from hours to tens of femtoseconds. In addition, the current availability of radioactive beams and the future promise of intense beams of nuclei very far from stability have opened new regions of the nuclear chart to the investigations of the nucleon-nucleon interactions in exotic nuclei. The main element of these experiments is provided by the hyperfine interaction between fast moving spin-aligned nuclei and polarized electrons in ferromagnetic materials. The new techniques that have been been recently developed for application in radioactive environments will be discussed. The results of experiments carried out, at low and intermediate energies, on radioactive beams of 132Te, 76Kr and {38,40}S, produced at ISOL or fragmentation facilities, will be presented and the future prospects of the field will be outlined. This work was supported in part by the US National Science Foundation. [Preview Abstract] |
Tuesday, April 15, 2008 11:21AM - 11:57AM |
W3.00002: Neutron-Proton Coupling and the Lifetime of the First Excited State in $^{16}$C Invited Speaker: Nuclei near the valley of $\beta $-stability have strongly correlated proton and neutron spatial distributions. This need not be the case for nuclei with a large excess of one nucleon type and the search for new phenomena and structure effects due to the ``decoupling'' of neutrons and protons is of great interest in nuclear structure physics. Cited examples of decoupled behavior include neutron-halo nuclei with measurably different proton and neutron radial distributions, and low-energy dipole modes such as ``pygmy'' resonances where, simplistically, a core of equal numbers of protons and neutrons oscillates against the excess neutron ``skin'''. Recently, another example was suggested to occur in $^{16}$C where the measurement of an anomalously quenched B(E2;2$^{+}\to ^{ }$0$^{+})$ value of 0.63 e$^{2}$fm$^{4 }$ combined with a large nuclear deformation led to the suggestion that the $^{16}$C valence neutrons were decoupled from its near-spherical proton core (N.Imai et al., PRL 92 (2004) 062501; Z.Elekes et al., PLB 586 (2004) 34; H.J.Ong et al., PRC 73 (2006) 024610). In this talk I will discuss a new lifetime measurement for the first-excited 2$^{+}$ state in $^{16}$C carried out at the LBNL 88-Inch Cyclotron using the Recoil Distance Method and $^{9}$Be($^{9}$Be,2p) fusion-evaporation reaction. The mean lifetime was found to be 11.7(20) ps corresponding to a B(E2) of 4.15(73) e$^{2}$fm$^{4}$, consistent with other even-even closed shell nuclei and neighboring systematics. Our result does not support the interpretation of decoupled protons and neutrons in $^{16}$C. The revised value provides an important benchmark for theory. Time permitting I will present results on the neutron-rich nucleus $^{30}$Ne produced in a 2p knockout reaction performed at the NSCL using the S800 spectrometer and SeGA gamma-ray detector. The measured (quenched) 2p knockout cross-section, when compared to theory, suggests a significant difference in the neutron intruder content between $^{32}$Mg and $^{30}$Ne, contrary to current shell models. [Preview Abstract] |
Tuesday, April 15, 2008 11:57AM - 12:33PM |
W3.00003: Measurement of two-halo neutron transfer p($^{11}$Li,$^{9}$Li)t reaction at 3\textit{A} MeV Invited Speaker: The p($^{11}$Li,$^{9}$Li)t reaction has been studied for an incident $^{11}$Li energy of $\sim $3*A MeV delivered from the new ISAC-2 facility at TRIUMF. The experiment was undertaken using MAYA, an active target detector. Angular distibutions for the centre of mass system have been determined for scattering angles from 20 to 160 degrees, and for transtions to the $^{9}$Li(3/2$^{-})$ ground state and the first excited state $^{9}$Li(1/2$^{-}$:2.69 MeV). Coupled channel calculations using different model $^{11}$Li wave functions, indicates that functions that take account of the strong correlations between the outer neutrons are the most sucessful in reproducing the observed differential cross sections. [Preview Abstract] |
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