Bulletin of the American Physical Society
2005 APS April Meeting
Saturday–Tuesday, April 16–19, 2005; Tampa, FL
Session K13: Nuclear Structure |
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Sponsoring Units: DNP Chair: T. L. Khoo, Argonne National Laboratory Room: Marriott Tampa Waterside Room 12 |
Sunday, April 17, 2005 1:15PM - 1:27PM |
K13.00001: Characterization of levels in $^{17}$O from the reaction $^{12}$C($^{7}$Li,d)$^{17}$O at 34 MeV A.M. Crisp, W.D. Weintraub, B.T. Roeder, K.W. Kemper, O. Momotyuk, M. Wiedeking, N. Keeley, F. Mar\'{e}chal, K. Rusek Angular distributions and analyzing power data have been taken for the reaction $^{12}$C($^{7}$Li,d)$^{17}$O at 34 MeV using the FSU Tandem/LINAC accelerator. Selective population of $^{17}$O levels at 6.86, 7.58, 8.47, 11.82, 12.00, 12.22, and 12.42 MeV were observed. Possible spin values have been determined for the states listed above 11 MeV by comparisons to angular distributions and analyzing powers of other $^{17}$O levels with known spin, and by DWBA calculations. The spin values of the states and suggestions for their structure will be presented. [Preview Abstract] |
Sunday, April 17, 2005 1:27PM - 1:39PM |
K13.00002: Probing $sd-pf$ cross-shell interactions via terminating configurations in $N \sim Z$ scandium isotopes C.J. Chiara, M. Devlin, E. Ideguchi, F. Lerma, W. Reviol, S.K. Ryu, D.G. Sarantites, J.N. Wilson, C. Baktash, A. Galindo-Uribarri, D. Rudolph, D.R. LaFosse, M.P. Carpenter, R.V.F. Janssens, T. Lauritsen, C.J. Lister, P. Reiter, D. Seweryniak, P. Fallon, A. G\"orgen, A.O. Macchiavelli Comparisons of terminating states based on $f_{7/2}^{n}$ and $d_{3/2}^{-1}f_{7/2}^{n+1}$ configurations in $N \approx Z$, $A \approx 40$ nuclei can provide information about two-body matrix elements that are not well-defined in current realistic forces. Specifically, effective interactions can be studied by examining these $\pi d_{3/2}^{-1}f_{7/2}$ particle-hole excitations through states that have simple structural purity. The {\it sd-pf} nuclides $^{42}_{21}$Sc$^{}_{21}$ and $^{43}_{21}$Sc$^{}_{22}$ were produced via the $\alpha pn$ and $\alpha p$ channels, respectively, in two reactions: 84-MeV $^{20}$Ne + $^{28}$Si and 94-MeV $^{24}$Mg + $^{24}$Mg. Both experiments were performed using the Gammasphere spectrometer in conjunction with the Microball charged-particle detector array. States have been observed to excitation energies of 15 MeV and higher in both nuclei, and include candidates for the terminating states of interest. Shell-model and mean-field approaches are being applied to these results. [Preview Abstract] |
Sunday, April 17, 2005 1:39PM - 1:51PM |
K13.00003: Level density from evaporation spectra for proton rich nuclei Alexander Voinov, Steven Grimes, Carl R. Brune, Saleh Al-Quraishi, Michael Hornish, Thomas Massey, John O'Donnell, Americo Salas The level density is an important characteristic of atomic nuclei. It tells us about the nuclear structure and is needed to calculate reaction rates. The experimental information about the level density and corresponding model parameter systematics are available for the nuclei close to the stability line but little is known for the nuclei beyond the stability line. It follows from theoretical consideration that several physical effects might give the of Fermi-gas parameter `a' dependence on N and/or Z rather than on simply on A [1]. To study this and other features, the level density from neutron evaporation spectra has been measured for proton-rich nuclei $^{60}$Zn and $^{56}$Ni as well as for corresponding stable nuclei $^{60}$Ni and$^{ 56}$Fe of the same A. Targets of $^{58}$Ni, $^{54}$Fe,$^{ 58}$Fe, and $^{55}$Mn were bombarded with beams of 3He and deuterium at Ohio University's Edwards Accelerator Laboratory. Neutron energies were determined by the time-of-flight method. The different level density models have been tested in the excitation energy interval up to 8-10 MeV and the best parameters have been found. The results are compared to available systematics as well as to calculations performed on the basis of microscopic model recommended in RIPL data base. [1] S.I. Al-Quraishi, S.M.Grimes, T.N. Massey and D.A.Resler, Phys.Rev. C63, 065803 (2001). [Preview Abstract] |
Sunday, April 17, 2005 1:51PM - 2:03PM |
K13.00004: High-spin states in the N=50 nucleus $^{85}$Br N. Fotiades, J.A. Cizewski, R. Kr\"{u}cken, R.M. Clark, P. Fallon, I.Y. Lee, A.O. Macchiavelli, J.A. Becker, L.A. Bernstein, D.P. McNabb, W. Younes High-spin states in $^{85}$Br have been studied following the fission of the $^{226}$Th compound nucleus formed in a fusion-evaporation reaction. The Gammasphere array was used to detect $\gamma$-ray coincidences. The level scheme has been extended up to $\sim$5~MeV excitation energy. Two states at $\sim$2~MeV excitation energy are candidates for the 9/2$^{+}$ state originating from the odd proton occupying the $g_{9/2}$ orbital. The experimental results are compared with predictions of shell model calculations. The results are compared with concurrent studies of $^{85}$Br as a product of deep-inelastic processes in heavy-ion multi-nucleon tranfer reactions published in Ref.~[1]. This work has been supported in part by the U.S. Department of Energy under Contracts No. W-7405-ENG-36 (LANL), W-7405-ENG-48 (LLNL) and AC03-76SF00098 (LBNL) and by the National Science Foundation (Rutgers). [1] Y. H. Zhang {\it et al.}, Phys. Rev. C {\bf 70} 024301 (2004). [Preview Abstract] |
Sunday, April 17, 2005 2:03PM - 2:15PM |
K13.00005: Evolution of deformation accross the main shell N=82-126 M.-A. Deleplanque, S.Y. Chu, S. Frauendorf, V. Pashkevich, A. Unzhakova We show that the deviations of the experimental moments of inertia from the rigid-body values at high spins, as well as deviations of the binding energies from the liquid-drop values, are due to shell effects. They are called ``shell moments of inertia'' and ``shell energies.'' The semiclassical Periodic Orbit Theory (POT) calculates these shell effects in terms of contributions from a few classical periodic orbits in the nuclear potential. The comparison of shell energies obtained in quantal calculations and in POT provides a new perspective on the occurrence of spherical magic numbers and of deformation in nuclei. In particular the evolution of the nuclear deformation with neutron number in the main shell N = 82-126 will be discussed. [Preview Abstract] |
Sunday, April 17, 2005 2:15PM - 2:27PM |
K13.00006: Chaotic Behavior in Ytterbium Nuclei F.S. Stephens, M.A. Deleplanque, I.Y. Lee, A.O. Macchiavelli, D. Ward, P. Fallon, M. Cromaz, R.M. Clark, M. Descovich, R.M. Diamond, E. Rodriguez-Vieitez We describe a new method to study the order-to-chaos transition in rotational Yb nuclei. Correlations between successive (unresolved) gamma rays are used to determine the average complexity of the intermediate levels and thereby the average ratio, v/d, of the interaction potential between levels to the level spacing. The measured ratios, 0.15 to 1.5, span the range from nearly fully ordered to nearly fully chaotic [1]. We will also describe a new project to measure the spreading width, the energy region over which a given level is mixed. Together with v/d (which measures the amplitude remaining in the initial state), this would allow us to determine v and d separately. [1] F.S. Stephens et al., Phys. Rev. Lett., in press. [Preview Abstract] |
Sunday, April 17, 2005 2:27PM - 2:39PM |
K13.00007: Proton - Neutron Interactions and The New Atomic Masses R.B. Cakirli, R.F. Casten, D.S. Brenner, E.A. Millman Proton - neutron interactions determine structural evolution with N and Z including the onset of collectivity, deformation, and phase transitions. We have extracted the interaction of the last proton and the last neutron, called $\delta$V$_{pn}$, from a specific double difference of binding energies using the new mass tabulation [1]. Striking variations are seen near closed shells. In the Pb region, these are interpreted using overlaps of shell model orbits, which are large when both protons and neutrons are in similar orbits, and small when they are not. Further, we used the idea that shell filling follows a typical systematic pattern to look at the correlation of $\delta$V$_{pn}$ values to the fractions of the proton and neutron shells that are filled. These results provide useful signatures of structure in exotic nuclei.\\ This work was supported by US DOE Grant Nos. DE-FG02-91ER40609 and DE-FG02-88ER-40417. \\ \mathbb{[1]} G. Audi, A.H. Wapstra and C. Thibault, Nucl. Phys.A729, 337 (2003). [Preview Abstract] |
Sunday, April 17, 2005 2:39PM - 2:51PM |
K13.00008: IBM-2 calculation with configuration mixing for Ge isotopes Elizabeth Padilla-Rodal, Octavio H. Casta\~{n}os, Roelof Bijker, Alfredo Galindo-Uribarri Recent results on Coulomb excitation experiments of radioactive neutron-rich Ge isotopes at the Holifield Radioactive Ion Beam Facility allow the study of the systematic trend of $B(E2; 0^+ \rightarrow 2^+)$ between the sub-shell closures at $N=40$ and the $N=50$ [1]. The new information on the $E2$ transition strengths constitutes a stringent test for the nuclear models and has motivated us to revisit the use of Interacting Boson Model in this region. We show that the IBM-2 with configuration mixing is a successful model to describe the shape transition phenomena that take place around $N=40$ in stable germanium isotopes, as well as the predictions given by this model about the evolution of the structure for the radioactive $^{78, 80, 82}$Ge nuclei. \newline \newline [1] E. Padilla-Rodal Ph.D. Thesis UNAM; submitted for publication. [Preview Abstract] |
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