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 M14: Nuclear Structure: Medium Mass Nuclei |
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Sponsoring Units: DNP Chair: Nikolaos Fotiades, Los Alamos National Laboratory Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), St. Louis G |
Sunday, April 13, 2008 3:30PM - 3:42PM |
M14.00001: The g-factor measurement of the 4$^+_1$ state in $^{70}$Zn G. G\"{u}rdal, G. Kumbartzki, N. Benczer-Koller, B. Krieger, Y.Y. Sharon, D. M\"{u}cher, K. Speidel, R. Casperson, V. Werner, E. Williams The measurement of the g factors of excited nuclear states provide an indication of their microscopic structure since the g factors are very sensitive to the proton and neutron contributions to the wave functions. Recently, g factors of excited states in the even-even stable Zn nuclei were measured. The measured g factors of their 2$^+_1$ states were generally in good agreement with the results of shell model calculations as well as with the Z/A value, the characteristic of collective behavior. Also studied were the g factors of some 4$^+_1$ states, which are only weakly excited by Coulomb excitation. Possible contributions of $g_{9/2}$ neutrons to the wave function of the 4$^+_1$ states in the Zn isotopes would reduce the g factors of these states. To extend these systematic studies, the 4$^+_1$ state of $^{70}$Zn was populated by the Coulomb excitation, on a C target, of a beam of $^{70}$Zn in inverse kinematics, and its g-factor was studied using the Transient Field technique. The $\gamma$ ray transition energies in $^{70}$Zn have some near-degeneracies which make the extraction of the g-factor of 4$^+_1$ state difficult. Work supported by the U.S. National Science Foundation, U.S.D.O.E under grant DE-FG02-91ER-40609 and by German BMBF under grant number 06KY2051. [Preview Abstract] |
Sunday, April 13, 2008 3:42PM - 3:54PM |
M14.00002: Coulomb Excitation of n-rich nuclei along the N = 50 shell closure E. Padilla-Rodal, A. Galindo-Uribarri , J.C. Batchelder, J.R. Beene , C. Bingham , B.A. Brown , K.B. Lagergren , P.E. Mueller , D.C. Radford , D.W. Stracener , J.P. Urrego-Blanco , R.L. Varner , C.-H. Yu Recently, we have been investigating characteristics of nuclear states around the neutron-rich mass A=80 region [1]. Using the Radioactive Ion Beams (RIBs) produced at HRIBF, we have successfully measured the B(E2) values for $^{78,80,82}$Ge , using Coulomb excitation in inverse kinematics. For the germanium isotopes, these data allow a study of the systematic trend between the subshell $N$= 40 and the $N$=50 shell. Using the same technique, we have measured the B(E2) value of various nuclei along the $N$=50 shell including the radioactive nucleus $^{84}$Se. This value together with our previously measured $^{82}$Ge, and the recent result on $^{80}$Zn from ISOLDE [2] are providing basic experimental information needed for a better understanding of the neutron-rich nuclei around $A\sim $80. We report the new results and compare with shell model calculations. [1] E. Padilla-Rodal \textit{et al}., Phys. Rev. Lett. \textbf{94} (2005) 122501. [2] J. Van de Walle \textit{et al.}, Phys. Rev. Lett. \textbf{99} (2007) 142501. [Preview Abstract] |
Sunday, April 13, 2008 3:54PM - 4:06PM |
M14.00003: Reinvestigation of direct two-proton radioactivity of $^{94}$Ag$^{m }$(J$^{\pi }$= 21$^{+}$, 6.7 MeV) Joseph Cerny, D.W. Lee, K. Perajarvi, D.M. Moltz, B.R. Barquest, L.E. Grossman, W. Jeong, C.C. Jewett Both direct one-proton decay and direct two-proton decay of $^{94}$Ag$^{m}$ from this long-lived (0.4 s) isomeric state have been reported by Mukha et al. in experiments performed with the GSI on-line mass separator [1]. In the former decay, two proton groups with energies of 0.79 and 1.01 MeV were observed, each having a branching ratio of about 2{\%}; in the latter decay, coincident events with a threshold energy of 0.4 MeV and a summed decay energy of 1.9 MeV were observed in coincidence with $\gamma $-decays in the $^{92}$Rh daughter and were assigned to be coincident protons with a branching ratio of 0.5(3){\%}. We have recently utilized our helium-jet system at the Berkeley 88-inch cyclotron to repeat this experiment, again employing the $^{58}$Ni($^{40}$Ca,p3n) reaction at 192 MeV. Reaction products were transported via a capillary to a detection area and collected on a slowly rotating wheel in front of an assembly of 24 $\Delta $E$_{gas}-\Delta $E$_{gas}$ - E$_{Si}$ detector telescopes with a threshold of 0.4 MeV for identifying protons. The beta-particle background is reduced enough in several of these telescopes to clearly observe the 0.79 MeV single proton decay from $^{94}$Ag$^{m}$. Data analysis is continuing and results of the search for coincident, identified protons will be presented. [1] Mukha et al., Nature \underline {439}, 298 (2006) and references therein. [Preview Abstract] |
Sunday, April 13, 2008 4:06PM - 4:18PM |
M14.00004: Spectroscopy of exotic 123,125Ag produced in fragmentation reactions I. Stefanescu, W.B. Walters, N. Hoteling, B. Tomlin, P.F. Mantica, J. Pereira, A. Becerril, T. Fleckenstein, A.A. Hecht, G. Lorusso, M. Quinn, J.S. Pinter, J.B. Stoker We extended the experimental knowledge in the mass-region around 132Sn by identifying the decay of high-spin isomers in the exotic odd-mass 123,125Ag. The two isotopes were produced at the NSCL laboratory by projectile fragmentation of a 136Xe beam at 120MeV/u directed onto a thick Be target. The NSCL Beta Counting System, was used identify secondary beam fragments. Prompt and delayed gamma-rays following the deexcitation of the fragments were detected with the SEGA array. Partial level schemes for 123,125Ag are proposed for the first time. The observed states show single-particle characteristics, indicating strong Z=50 and N=82 shell gaps and also support the proposed weakened nucleon-nucleon interaction in this mass-region. [Preview Abstract] |
Sunday, April 13, 2008 4:18PM - 4:30PM |
M14.00005: Nuclear Dipole Response of Bound States in N=82 Nuclei Below Particle Threshold A. Tonchev, A. Hutcheson, E. Kwan, G. Rusev, W. Tornow, C. Angell, S. Hammond, H. Karwowski, J. Kelley Nuclear resonance fluorescence measurements have been performed on N=82 nuclei using 100\% linearly polarized $\gamma$-ray beams at the High-Intensity $\gamma$-ray Source (HI$\vec{\gamma}$S) at energies below the particle emission threshold. The low-lying dipole excitations have been related to the so-called ``pygmy'' dipole resonance. The electric dipole character of this low-energy mode of excitation was experimentally verified from E$_{\gamma}$=4.5-8.5 MeV. Missing dipole strength is revealed in inelastic scattering measurements using the monoenergetic HI$\vec{\gamma}$S beams. The dipole-strength distribution will be compared with microscopic calculations within the framework of the quasiparticle-phonon model. [Preview Abstract] |
Sunday, April 13, 2008 4:30PM - 4:42PM |
M14.00006: Single-particle states outside the N=82 core Benjamin Kay, John Schiffer, Sean Freeman, Jason Clark, Catherine Deibel, Andreas Heinz, Anuj Parikh, Chris Wrede A systematic study of the high-$j$ single-neutron states outside the $N$=82 isotones was carried out with the ($\alpha$,$^{3}$He) reaction on $^{138}$Ba, $^{140}$Ce, $^{142}$Nd and $^{144}$Sm at a beam energy of 51~MeV. The separation between the i$_{13/2}$ and h$_{9/2}$ single-neutron states, was measured. Spectroscopic factors for the states populated in the high-$\ell$ transfers indicate significant fragmentation for the $\ell$=5 and $\ell$=6 strength, but the summed strengths on these targets are constant. The centroids of the single-particle strength display a change in the relative energies of these two nodeless single-particle orbits, similar to the trend observed in the Sb isotopes$^{1}$. The centroid shifts with neutron number are in agreement with those expected from the monopole term in the tensor component of the residual interaction between nucleons of Otsuka et al.$^{2}$. This research was supported by the DOE Office of Nuclear Physics under Contract Nos. DE-FG02-91ER-40609 and DE-AC02-06CH11357. $^{1}$J.P. Schiffer et al. Phys. Rev. Lett. {\bf 92}, 162501 (2004). $^{2}$T. Otsuka et al. Phys. Rev. Lett. {\bf 95}, 232502 (2005). [Preview Abstract] |
Sunday, April 13, 2008 4:42PM - 4:54PM |
M14.00007: CENS: A computational environment for nuclear structure Morten Hjorth-Jensen, Gustav R. Jansen We present a recently developed software written in Python which merges several Fortran95 and C++ codes for doing `ab initio' nuclear structure calculations. Combined with a pedagogical graphical user interface, the software allows the user to perform nuclear structure calculations starting from the free nucleon-nucleon interaction, and via various renormalization techniques one obtains an effective interaction for shell-model calculations. The included shell-model code allow the user to compute spectra and transition probabilities for practically all mass areas. Several methods for renormalizing a nucleon-nucleon interaction and taylor it to specific model spaces are available, ranging from no-core shell-model interaction to interactions derived from many-body perturbation theory. [Preview Abstract] |
Sunday, April 13, 2008 4:54PM - 5:06PM |
M14.00008: Trends in Thermostatic Properties of Excited Finite Nuclei Michael Quinlan, Yun-Tse Tsai, Iwona Pawelczak, Jan T\~oke, Udo Schr\"oder To help understand the phenomenon of statistical nuclear multifragmentation, evolution of nuclear matter distribution with increasing excitation energy was studied within the framework of nuclear thermodynamics. A schematic Fermi-gas model combined with Thomas-Fermi approximation was used to model nuclear matter characterized by a realistic equation of state (EOS). Trends in bulk matter density, surface diffuseness, surface energy, surface level density parameter, and effective surface tension are discussed. The study demonstrates the role of the diffuse surface domain in stabilizing the excited nuclei against particle evaporation while facilitating Coulomb fragmentation at elevated excitation energies. [Preview Abstract] |
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