Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session CA: New Results for Exotic Nuclei in sd-pfg |
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Sponsoring Units: DNP JPS Chair: Michael Thoennessen, National Superconducting Cyclotron Laboratory at Michigan State University Room: Ritz-Carlton Hotel Salon 4 |
Tuesday, September 20, 2005 2:00PM - 2:45PM |
CA.00001: Exploring the shell structure in very neutron rich $pfg$-shell nuclei through the $\gamma$-ray spectroscopy technique Invited Speaker: Rearrangement of the shell structure is one of the prominent features of neutron rich nuclei clarified in the light mass region, such as disappearance of magicity at $N$=8 and 20, or appearance of a new magic number of $N$=16. A similar phenomenon is anticipated in the heavier mass $pfg$-shell region. For example, a new magic number of $N$=34 is predicted in the neutron rich region [1], while a new region of large deformation is suggested around neutron rich chromium isotopes with $N\sim$40 [2]. The behavior of the magicity at $Z$=28 and $N$=50 in the nuclei around the doubly magic nucleus $^{78}$Ni is of extreme importance from the point of view of both nuclear structure and nuclear astrophysics, but is far from clear yet. Aiming to investigate these intriguing subjects, experimental and theoretical effort has been made by several groups in the past few years, and some clues begin to be obtained. In the present paper, recent results on the structure study of neutron rich $pfg$-shell nuclei will be presented with the emphasis on the experiments using gamma-ray spectroscopy technique. The perspective on the experiments to be performed in the upcoming next generation RI beam facilities will also be discussed. \\ Reference: \\ 1. M. Honma et al., Phys. Rev. C65, 061301(R)(2002). \\ 2. O. Sorlin et al., Eur. Phys. J. A 16, 55-61 (2003). [Preview Abstract] |
Tuesday, September 20, 2005 2:45PM - 3:30PM |
CA.00002: Exotic neutron-rich $sd$-$pf$ nuclei and nuclear force Invited Speaker: Recent results of large-scale shell-model calculations will be overviewed for exotic neutron-rich nuclei in the $sd$-$pf$ region. One of the most exciting findings is the change of shell structures in extreme conditions. For instance, the $N$=20 gap may be quite small in some of exotic Ne-Na-Mg isotopes leading to (near-)degeneracy of positive and negative parity states, and new magic numbers such as $N$=32, 34 may emerge in neutron rich Ca-Ti. Theoretical descriptions of these nuclei will be presented in close connection to particular properties of Nucleon-Nucleon interaction. [Preview Abstract] |
Tuesday, September 20, 2005 3:30PM - 4:15PM |
CA.00003: Wavefunction-spectroscopy with rare-isotope beams Invited Speaker: The nuclear shell model pictures deeply-bound states as fully occupied by nucleons. At and above the Fermi sea, configuration mixing leads to occupancies that gradually decrease to zero. Correlation effects (short-range, soft-core, long-range, and coupling to vibrational excitations) are beyond the effective interactions employed in shell model and mean-field approaches. The picture given above is modified depending on the strength of the correlations. In stable nuclei a reduction of $R_s =0.6-0.7$ with respect to the shell model has been established from $(e,e'p)$ data. The question on the universality of this reduction beyond the valley of $\beta$-stability arises. At rare-isotope accelerators, very deeply and weakly bound exotic nuclei become accessible. One experimental approach to assess the occupation number of single-particle orbits in exotic nuclei are one-nucleon removal reactions at intermediate beam energies. The measured spectroscopic factor $C^2S$ relates to the occupation number of the orbit involved. Our recent work has demonstrated that the spectroscopic factors deduced from knockout reactions are in agreement with the electron-scattering results. Experiments close to stability and far out towards the drip lines have been performed at the Coupled Cyclotron Facility of the National Superconducting Cyclotron Laboratory at Michigan State University. Results covering a wide range of nucleon separation energies across the nuclear chart will be presented and compared. [Preview Abstract] |
Tuesday, September 20, 2005 4:15PM - 5:00PM |
CA.00004: Structure of the exotic neutron-rich nuclei 42Si, 52Ti, and 54Ti Invited Speaker: The modification of magic numbers and the shell structure of very neutron-rich systems is one of the most intriguing subjects to be studied with present and future exotic beam facilities. In a number of recent experiments, the modification of shell structure for both the neutron and proton-systems was studied for the very neutron-abundant nuclides $^{52,54}$Ti and $^{42}$Si; The excited level structure of $^{52,54}$Ti show evidence for a sub-shell closure at N=32 [1], while a recent measurement of Coulomb excitation of the 2$^+_1$ in $^{56}$Ti [2] shows that the sub-shell closure at N=34 is weaker than expected. In order to investigate the character of $^{42}$Si, we performed an experiment using a $^{44}$S beam, generated in fragmentation of 140 MeV/u $^{48}$Ca at the Coupled-Cyclotron Facility at the NSCL. This beam was delivered to the target position of the S800 spectrograph, where secondary reactions occurred. The one-proton and two-proton knockout reaction products, $^{43}$P and $^{42}$Si, were identified using the S800 spectrograph and coincident $\gamma$ rays were detected with the segmented Germanium array, SeGA, surrounding the S800 target position. We measured one-proton knockout populating the ground and first excited state of $^{43}$P. The direct reaction character of one-proton [3] knockout and two-proton knockout [4] allows to compare the observed cross-section to calculations using the eikonal-approach. We find large cross sections for the single-proton knockout, corresponding to single-particle spectroscopic factors for the $^{43}$P = $^{42}$Si + p system. Simultaneously, the measured two-proton knockout cross section corresponds to a Z=14 closed shell $^{42}$Si. Both of these aspects support the magic character of $^{42}$Si. [1] R.V.F. Janssens {\em et al.} Phys. Lett. B 546 (2002) [2] D.C. Dinca {\em et al.} Phys. Rev. C{\bf 71}, 041302R (2005) [3] Hansen, P.G. \& Tostevin, J.A., Direct Reactions with Exotic Nuclei. Annu. Rev. Nucl. Part. Sci. 53, 219-261 (2003). [4] D. Bazin {\em et al.} Phys.~Rev.~Lett. {\bf 91} 012501 (2003) [Preview Abstract] |
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