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 KF: Nuclear Density and Excitations |
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Sponsoring Units: DNP JPS Chair: Susumu Shimoura Room: Ritz-Carlton Hotel Plantation 3 |
Thursday, September 22, 2005 2:00PM - 2:15PM |
KF.00001: Neutron density distributions in $^{40,42,44,48}$Ca observed via polarized proton elastic scattering at 300MeV Juzo Zenihiro, Harutaka Sakaguchi, Tetsuya Murakami, Yuusuke Yasuda, Satoru Terashima, Yohei Nakatsugawa, Toshimi Suda, Hiroyuki Takeda, Tetsuya Ohnishi, Masaru Yosoi, Masatoshi Itoh, Makoto Uchida, Hidetomo Yoshida Systematic behaviors of neutron densities in $^{40,42,44,48}{\rm Ca}$ have been deduced via proton elastic scattering at $E_p=300{\rm MeV}$. For the deduction we used RIA with medium modified {\it NN} interaction and realistic point proton density distributions unfolded from charge distributions. In this work we have taken into account the effect of intrinsic charge distribution inside neutron as well as that of proton, which makes the proton distributions more gradual and the RMS radius larger than the case only proton charge assumed. We have observed that the isotope shift of neutron density distributions due to the occupation of the 1$f_{7/2}$ neutron orbit is seen around 3 fm and $^{48}$Ca has a large neutron skin of $\sim 0.2$ fm compared with the other three Ca isotopes. [Preview Abstract] |
Thursday, September 22, 2005 2:15PM - 2:30PM |
KF.00002: Systematic change of neutron density distribution in tin isotopes deduced from proton elastic scattering at 295 MeV Satoru Terashima, Harutaka Sakaguchi, Yusuke Yasuda, Hiroyuki Takeda, Masaru Yosoi, Takatsugu Ishikawa, Masatoshi Itoh, Takahiro Kawabata, Makoto Uchida, Tesuo Noro, Hidetomo Yoshida, Takashi Ishida, Shun Asaji, Takahisa Yonemura Cross sections and analyzing powers of proton elastic scattering off $^{116,118,120,122,124}$Sn at 295 MeV have been measured up to about 3.5 fm$^{-1}$ in momentum transfer to deduce a systematic change of neutron density distribution. We have used effective interaction to explain proton elastic scattering off N=Z nuclei whose density distribution are well known. For the analysis, we have used the relativistic impulse approximation with relativistic Love-Franey interaction which was tuned by using medium effect. Then, we have applied the elastic proton scattering to deduce the neutron density distribution of tin isotopes. The result of our analysis shows a clear systematic behavior which shows a gradual filling in the 3s$_{1/2}$ neutron single particle orbit. [Preview Abstract] |
Thursday, September 22, 2005 2:30PM - 2:45PM |
KF.00003: Nuclear Structure Physics at HI$\vec{\gamma}$S: Parity Assignments to Levels in $^{138}$Ba A. Tonchev, W. Tornow, C. Angell, M. Boswell, H. Karwowski, J. Kelley, J. Li, S. Mikhailov, Y. Wu, N. Tsoneva Nuclear resonance fluorescence measurements have been performed on the $^{138}$Ba nucleus using polarized $\gamma$-ray beams at the High-Intensity $\gamma$ Source (HI$\vec{\gamma}$S). Taking advantage of the monoenergetic and pulsed HI$\vec{\gamma}$S beams, negative parity assignment were made to seven J=$1$ states in the energy region of 1 MeV below the neutron separation threshold. These low-lying dipole excitations have been related to the so-called pygmy dipole resonance. Further analysis will determine the branching ratio of these E1 dipole states and their partial cross sections. In addition to the decays to the ground states, we have observed for the first time strong gamma transitions from the first three $2^{+}$ states in $^{138}$Ba to the ground state. [Preview Abstract] |
Thursday, September 22, 2005 2:45PM - 3:00PM |
KF.00004: Candidate for the superdeformed band in $^{32}$S Masatoshi Itoh, Harutaka Sakaguchi, Satoshi Kishi In the measurement of inelastic $\alpha$ scattering for the isoscalar giant dipole resonance in $^{32}$S, we have found the candidate state of the head of the superdeformed band, which has been searched during 20 years by many researchers in the world. It is interesting because the superdeformed band of $^{32}$S is a clue to understand the relation between the superdeformed state and the molecular resonance such as $^{16}$O + $^{16}$O. The experiment was performed using 400 MeV $\alpha$ particles from the RCNP ring cyclotron. The background-free energy spectra at angles from 0$^{\circ}$ to 10$^{\circ}$ were obtained by applying the optics of the GRAND RAIDEN spectrometer. The J$^{\pi}$ values were determined by the multipole decomposition analysis. The excitation energies and moment of inertia of the observed superdeformed band were consistent with the theoretical prediction. [Preview Abstract] |
Thursday, September 22, 2005 3:00PM - 3:15PM |
KF.00005: Fully self-consistent HF-based RPA calculations for giant resonances in nuclei Shalom Shlomo The study of collective modes in nuclei provides important information on the structure and bulk properties of nuclear systems. In particular, the excitation energies of compression modes and of isovector modes in nuclei are sensitive to the values of the symmetric nuclear matter incompressibility coefficient K and the symmetry energy coefficient J, respectively. Accurate knowledge of the values of K and J is very important in the study of properties of nuclei, heavy ion collisions, neutron stars and supernova. Hartree Fock (HF)-based random phase approximation (RPA) theory is very successful in providing microscopic description of giant resonances. However, although not always stated in the literature, self-consistency is violated in actual implementation of the RPA calculations. We will present results of highly accurate calculations of the consequences of self-consistency violations (SCV) on the values of the centroid energies E of isoscalar and isovector modes and show that the effects of SCV on E are larger than the current experimental uncertainties. We also point out that the effects of SCV on the centroid energy of the isoscalar giant monopole resonance (breathing mode) may lead to a discrepancy as large as 20{\%} in the extracted value of K. [Preview Abstract] |
Thursday, September 22, 2005 3:15PM - 3:30PM |
KF.00006: Nuclear Resonances at Zero and Finite Temperatures Nguyen Dinh Dang The theoretical description of nuclear resonances at zero and finite temperatures is discussed, which includes 1 -- giant dipole resonances (GDR) in highly excited nuclei, including both low and high regions of temperature; 2 -- multiple-phonon resonances in relativistic Coulomb excitations; 3 -- pygmy dipole resonances in neutron rich nuclei within the framework of the phonon-damping model [1]. The theoretical predictions are put in direct comparison with the most recent experimental data. In particular, in (1) the role of thermal pairing in the description of the GDR width at low temperature T=1 MeV in the latest experiment using O-17 scattered inelastically on Sn-120 will be discussed in detail [2]; in (2) the emphasis will be put on the double GDR in Xe-136 and Pb-208, where a large enhancement is seen as compared to the prediction by the independent phonon picture; in (3) the effect of pairing and coupling of GDR to complicated configurations on the pygmy dipole resonances is be analyzed. \newline \newline References: \newline [1] N. Dinh Dang, and. A. Arima, Phys. Rev. Lett. 80, 4145 (1998), Nucl. Phys. A 636, 427 (1998). \newline [2] N. Dinh Dang and A. Arima, Phys. Rev. C 68 (2003) 044303. [Preview Abstract] |
Thursday, September 22, 2005 3:30PM - 3:45PM |
KF.00007: Giant resonance study by $^{6}$Li scattering X. Chen, Y.-W. Lui, H.L. Clark, Y. Tokimoto, D.H. Youngblood The compressibility of nuclear matter K$_{nm}$ can be related to the energies of the isoscalar giant monopole resonance (ISGMR). Essentially all of the precise data on the ISGMR energies have been obtained with inelastic $\alpha $ scattering. Dennert et al[1] have successfully studied the ISGMR in $^{24}$Mg with $^{6}$Li scattering, and we have chosen to study $^{6}$Li scattering as an alternate means of obtaining these energies. A $^{6}$Li target might also be viable for studying the ISGMR in unstable nuclei. A beam of 240MeV $^{6}$Li ions from the Texas A{\&}M University K500 superconducting cyclotron bombarded self-supporting target foils of $^{24}$Mg, $^{28}$Si, $^{116}$Sn in the target chamber of the multipole-dipole-multipole(MDM) spectrometer. Elastic scattering from 5$^{0}\sim $35$^{0}$ and inelastic scattering from 0$^{0}\sim $6$^{0}$ deg were measured. Both Woods-Saxon phenomenological potentials and N-N effective M3Y interaction folded potentials have been used to fit the elastic scattering data from $^{116}$Sn. $^{6}$Li inelastic scattering to low-lying states and the giant resonance region of $^{116}$Sn was analyzed by both the deformed potential model and folded potential model. [1] H. Dennert et al, Phys. Rev. C \underline {52}, 3195 (1995) [Preview Abstract] |
Thursday, September 22, 2005 3:45PM - 4:00PM |
KF.00008: Probing the Pygmy Dipole Resonance in $^{124}$Sn M. Boswell, C. Angell, H. Karwowski, J. Kelley, A. Tonchev, W. Tornow, N. Tsoneva A high-resolution nuclear fluorescence experiment of enriched $^{124}$Sn has been performed using the 100\% polarized photon beam at the High Intensity Gamma-Ray Source (HI$\gamma$S). Four HPGe detectors were used to observe 37 dipole transitions with excitation energies between 6.9 MeV and 8.4 MeV. The parity of each of the 14 previously known transitions was found to be J$^{\pi}$=1$^{-}$. The 8.269 MeV level tentatively assigned J$^{\pi}$=1$^{+}$ was also found to be a 1$^{-}$ state.\footnote{K. Govaert et. al., Phys. Rev. C 57, 2229 (1998).} In addition, 10 new levels were identified, all of which are E1 excitations with the exception of a 6.917 MeV state excited by an M1 transition. The observations will be compared with calculations using quasiparticle random-phase approximation. [Preview Abstract] |
Thursday, September 22, 2005 4:00PM - 4:15PM |
KF.00009: The energy and multiplicity correlation of resonances in $^{151,153}$Eu(n,$\gamma )$ reaction U. Agvaanluvsan, J. Becker, R. Macri, W. Parker, P. Wilk, C.Y. Wu, R. Clement, T. Bredeweg, E. Esch, J. O'Donnell, R. Reifarth, R. Rundberg, J. Schwantes, J. Wouters, J. Ullmann, D. Vieira, J. Wilhelmy, S. Sheets, D. Dashdorj, G. Mitchell, C. Folden, D. Hoffmann, H. Nitsche, A. Alpizar-Vicente, R. Hatarik Highly granulated with 160 BaF$_{2}$ crystals and a 4$\pi $ solid-angle$_{ }$ coverage, the state-of-the-art DANCE array at LANSCE offers an opportunity to study detailed statistical properties of atomic nuclei. The neutron capture for neutron energies $<$1eV up to 100 keV has been measured for $^{151,153}$Eu targets. Stable Eu isotopes on Be backings were used. In this presentation, the resonances in $^{151,153}$Eu are considered. The parameters characterizing most of the resonances were previously known. For each resonance the gamma-ray multiplicity and energy distribution are deduced. The variation from resonance to resonance is investigated. In addition, radiative cascades following the neutron capture are simulated and compared with the experimental results shedding light on the nearly unknown subject of transitions between highly excited states in the compound nucleus. [Preview Abstract] |
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