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 EC: Mini-symposium on Structure Changes of Asymmetric Nuclear Systems II |
Hide Abstracts |
Sponsoring Units: DNP JPS Chair: Michio Honma, University of Aizu Room: Ritz-Carlton Hotel Salon 2 |
Wednesday, September 21, 2005 9:00AM - 9:30AM |
EC.00001: Regularities in Nuclear Spectra and Simple Signatures Invited Speaker: Nuclei are complex quantum many-body systems, composed of two kinds of interacting fermions. Yet they display astonishing simplicities and regularities. Key challenges of nuclear physics are to identify such regularities, to use them as phenomenological signatures of structure and to understand their microscopic origins. This talk will focus on the first two of these challenges. The first involves the development of dynamical and structural symmetries and the discovery of approximate manifestations of them in real nuclei. These simple paradigms often lead to new signatures of structure. A number of examples of regularities in nuclear properties and their applications to nuclei far from stability will be discussed. These include empirical extractions of valence proton-neutron interactions, and their relation to shell structure; new signatures for phase transitional behavior in the equilibrium structure; evidence for ordered and chaotic behavior in nuclei, with a very simple signature for ordered spectra; and the evolution of collectivity in particle-particle compared to particle-hole regions. Work supported by the US DOE under Grant No. DE-FG02-91ER-40609. [Preview Abstract] |
Wednesday, September 21, 2005 9:30AM - 9:45AM |
EC.00002: Collective states in silicon and sulfur isotopes from N=20 to 28 C.M. Campbell, D. Bazin, M.D. Bowen, B.A. Brown, J.M. Dinca, D.-C. Dinca, A. Gade, T. Glasmacher, W.F. Mueller, H. Olliver, K. Starosta, J.R. Terry, N. Aoi, T. Motobayashi, H. Sakurai, S. Takeuchi, K. Yoneda, S. Kanno, H. Suzuki, S.P. Weppner The evolution of low-lying collective states in neutron-rich silicon and sulfur isotopes has been studied by inelastic proton scattering in inverse kinematics at the Coupled Cyclotron Facility of the NSCL. Gamma-ray detection was used to select inelastic events exciting specific bound states. New gamma-ray transitions were observed and placed into level schemes. Angle-integrated excitation cross-sections to the first 2+ state in each even-even silicon and sulfur isotope were used to determine quadrupole deformation parameters. The evolution of collectivity was examined by looking at trends of deformation parameters and level energies as functions of neutron number. Results will be compared with shell model predictions. This work was supported by NSF grants PHY-0110253, PHY-9875122, PHY-0244453, INT-0089581 and by the Japan Society for the Promotion of Science. [Preview Abstract] |
Wednesday, September 21, 2005 9:45AM - 10:00AM |
EC.00003: Mirror symmetry of Gamow-Teller transitions by the comparison of $^{37}$Cl($^3$He,$t$)$^{37}$Ar and $^{37}$Ca(${\beta}_+$)$^{37}$K Y. Shimbara, B.A. Brown, Y. Fujita, T. Adachi, M. Yoshifuku, G.P.A. Berg, H. Fujimura, H. Fujita, K. Fujita, K. Hatanaka, K. Kawase, Y. Kitamura, N. Nakanishi, N. Sakamoto, Y. Sakemi, Y. Shimizu, Y. Tameshige, M. Yosoi, K. Hara, K.Y. Hara, J. Kamiya, K. Katori, T. Kawabata, M. Uchida, T. Wakasa Under the assumption of isospin symmetry, the distributions of Gamow-Teller (GT) transition strengths $B$(GT) are identical between $^{37}$Cl $\rightarrow$ $^{37}$Ar and $^{37}$Ca $\rightarrow$ $^{37}$K transitions. The differences between the empirical $B$(GT) distributions from $^{37}$Cl($p,n$)$^{37}$Al and $^{37}$Ca $\beta$-decay caused a great deal of controversy. One of problems in the $(p,n)$ experiments was the rather poor resolution. In order to study the individual transitions for $^{37}$Cl $\rightarrow$ $^{37}$Ar, we performed a high-resolution, 30~keV (FWHM), $^{37}$Cl($^3$He,$t$)$^{37}$Ar experiment at 140~MeV/u $^3$He beam. The $B$(GT) distribution was extracted from the differential cross sections and compared with the $^{37}$Ca $\beta$-decay data. Overall, they had similar distributions. However, the fine structures were not necessary consistent. [Preview Abstract] |
Wednesday, September 21, 2005 10:00AM - 10:15AM |
EC.00004: Study of High-Spin States in neutron-rich Ti Isotopes M. Niikura, E. Ideguchi, H. Iwasaki, S. Shimoura, M. Tamaki, T. Fukuchi, H. Baba, T. Kubo, M. Kurokawa, S. Michimasa, K. Morimoto, T. Ohnishi, T. Suda, K. Yoshida, S. Ota, N. Hokoiwa, Y. Wakabayashi, C. Ishida, T. Koike, T. Komatsubara, K. Miyakawa, A. Ozawa, I. Tanihata We have studied high-spin states of neutron-rich Ti isotopes $^{49-52}$Ti by using a fusion reaction of a secondary beam. The experiment was performed at RIPS facility in RIKEN. The secondary $^{46}$Ar beam was produced by a projectile fragmentation reaction of a $^{48}$Ca primary beam with 63 MeV/nucleon. By using aluminium degraders placed at the first and second focal planes, an energy of the secondary beam was reduced to 4.0$\pm$0.9 MeV/nucleon. The $^{46}$Ar beam was transported to the final focal plane and bombarded to a $^{9}$Be target in order to induce the secondary fusion reaction, $^{9}$Be($^{46}$Ar, $xn$)$^{55-x}$Ti. Gamma rays from the high-spin states of the reaction products $^{49-51}$Ti were detected by the GRAPE (Gamma-Ray detector Array with Position and Energy sensitivity) system. Based on excitation functions and $\gamma \gamma $-coincidence measurements, we have identified new high-spin states in $^{49}$Ti and $^{51}$Ti. In the present talk, we will report on the experimental results and discuss the newly observed high-spin states. [Preview Abstract] |
Wednesday, September 21, 2005 10:15AM - 10:30AM |
EC.00005: Intermediate-energy Coulomb excitation of $^{46}$V, $^{50}$Mn, and $^{54}$Co L.A. Riley, M.J. Bojazi, J.W. Kremenak, D.C. McGlinchey, D. Bazin, A.D. Becerril, J.M. Cook, A. Gade, T. Glasmacher, W.F. Mueller, C. Vaman, P.D. Cottle, K.W. Kemper, R.R. Reynolds, B.T. Roeder The reduced transition strengths $B(E2;0^+_{\mathrm{g.s.} \rightarrow 2^+_1)$ for the $N=Z$ nuclei $^{46}$V, $^{50}$Mn, and $^{54}$Co have been measured via intermediate-energy Coulomb excitation at 60 MeV/nucleon. The $0^+_\mathrm{g.s.}$ and $2^+_1$ states of these $T_z = 0$ nuclei are the $T=1$ analog states of the ground states and $2^+_1$ states of the corresponding $T_z = \pm 1$ nuclei. The present result for $^{54}$Co is combined with the existing $B(E2\uparrow)$ results [1,2] for the corresponding $T = 1$ states in $^{54}$Fe and $^{54}$Ni to test isospin purity in the mass 54 $T=1$ multiplet. [1] S. Raman et al., Atomic Data Nucl. Data Tables \textbf{78}, 1 (2001). [2] K. L. Yurkewicz et al., Phys. Rev. \textbf{C70}, 054319 (2004). [Preview Abstract] |
Wednesday, September 21, 2005 10:30AM - 10:45AM |
EC.00006: Inelastic proton scattering on the neutron rich Cr isotopes Eri Takeshita Inelastic proton scattering on the neutron rich Cr isotopes at around $N=40$ has been investigated. Spectroscopy of these nuclei is of great importance because of the strong deformation suggested by the low excitation energies of the first 2$^{+}$ states in $^{60,62}$Cr [1]. In the present work, the structures of the neutron rich Cr isotopes were studied by measuring the excitation energies and the (p,p$'$) cross sections to these states. The experiment was performed at RIPS in RIKEN. The Cr isotopes were produced by the fragmentation of 63MeV/nucleon $^{70}$Zn and were excited by bombarding a liquid hydrogen target. De-excitation $\gamma$ rays were detected by the NaI(Tl) array DALI2 in coincidence with the scattered particles. A time of flight spectrometer is newly developed to greatly improve the particle identification resolution %and acceptance for the scattered particles. With the cross sections to the first excited states derived from the $\gamma$-ray spectra, the structure of the neutron rich Cr isotopes will be discussed. \\ {\bf Reference:} 1. O. Sorlin et al., Eur. Phys. J. A {\bf 16}, 55-61 (2003). [Preview Abstract] |
Wednesday, September 21, 2005 10:45AM - 11:00AM |
EC.00007: Proton Inelastic Scattering on $^{74}$Ni S. Kanno, N. Aoi, H. Sakurai, T. Motobayashi, T. Kubo, S. Takeuchi, K. Yoneda, H. Iwasaki, H. Suzuki, T. Nakamura, D. Bazin, M.D. Bowen, C.M. Campbell, J.M. Cook, D.-C. Dinca, A. Gade, T. Glasmacher, W.F. Mueller, H. Olliver, J.R. Terry The proton inelastic scattering on the neutron-rich nucleus $^{74}$Ni has been investigated aiming at exploring the evolution of the magicity at $Z$=28 in a very neutron-rich region. In the Ni isotopes lighter than $^{72}$Ni, the first 2$^{+}$ states are located higher than those of the neighboring isotones, reflecting the magicity at $Z$=28. In the present experiment, the excitation energy of the first 2$^{+}$ state ($E_{x}(2^{+}) $) and the deformation parameter of a more neutron-rich Ni isotope $^{74}$Ni were measured by proton inelastic scattering. $^{74}$Ni was produced at NSCL by the projectile fragmentation of a 140 MeV/nucleon $^{86}$Kr beam on a $^{9}$Be target. The $^{74}$Ni beam impinged on a liquid hydrogen (LH$_{2}$) target and the NaI(Tl) scintillator array (APEX) placed around the LH$_{2}$ target detected the de-excitation $\gamma$ rays. $E_{x}(2^{+})$ was determined from the $\gamma$-ray spectrum measured in coincidence with the scattered $^{74}$Ni ions. The deformation parameter was extracted from the angle-integrated cross section. [Preview Abstract] |
Wednesday, September 21, 2005 11:00AM - 11:15AM |
EC.00008: Quadrupole deformation of the self-conjugate nucleus $^{72}$Kr A. Gade, D. Bazin, A. Becerril, C.M. Campbell, J.M. Cook, D.-C. Dinca, T. Glasmacher, G.W. Hitt, W.F. Mueller, H. Olliver, J.R. Terry, K. Yoneda, D.J. Dean, M.E. Howard We report on the first determination of the absolute $B(E2; 0^+_1 \rightarrow 2^+_1)$ excitation strength in the $N=Z$ nucleus $^{72}$Kr via intermediate-energy Coulomb excitation performed at the National Superconducting Cyclotron Laboratory at Michigan State University. $^{72}$Kr is the heaviest self-conjugate system for which this quantity has been measured. The deduced quadrupole deformation strength is compared to predictions of a variety of self-consistent models predicting shape coexistence. Large-scale shell-model Monte Carlo calculations reproduce the experimental $B(E2)$ value and link the result to the gap between the $fp$ and $gds$ major shells and the occupation of the deformation-driving $g_{9/2}$ orbit. [Preview Abstract] |
Wednesday, September 21, 2005 11:15AM - 11:30AM |
EC.00009: Microscopic description of single-particle levels with modern NN interactions Shinichiro Fujii, Ryoji Okamoto, Kenji Suzuki Recently, {\it ab initio} nuclear structure calculations starting with realistic NN interactions have been possible beyond few-nucleon systems. The coupled-cluster method (CCM) will be one of the promising ones for this kind of study, and actually the application of the CCM to nuclear structure calculations has been increasing. We have developed a many-body theory, the unitary-model-operator approach (UMOA), to perform {\it ab initio} structure calculations for a wide range of the mass numbers of nuclei. The UMOA can be regarded as one of the CCM, and leads to an energy independent and Hermitian effective interaction through a unitary transformation of the original Hamiltonian. The unitary transformation employed in the UMOA has also been used to derive the effective interaction in the {\it ab initio} no-core shell model (NCSM). In the UMOA, the energies of ground states and single-particle (- hole) levels can be calculated taking into account a sufficiently large model space. I will show some recent results for nuclei around $^{14}$C, $^ {16}$O, $^{24}$O, and $^{40}$Ca using modern NN interactions. [Preview Abstract] |
Wednesday, September 21, 2005 11:30AM - 11:45AM |
EC.00010: Hartree-Fock-Bogoliubov calculations with Gaussian expansion method Hitoshi Nakada An algorithm of the Hartree-Fock-Bogoliubov (HFB) calculations using the Gaussian expansion method is newly developed. By this method we can handle various effective interactions on the same footing, and the wave-function asymptotics, either exponential or oscillatory ones, are efficiently handled even for finite-range interactions. In the previous study we have shown by the spherical Hartree-Fock calculations that the shell structure around N=16 and 32 depends on the effective interactions (e.g. the Skyrme, the Gogny interaction and M3Y-type interactions) and their parameters, to an appreciable extent. Applying the HFB calculations, influence of the pair correlations on the magicity of N=16 and 32 will be discussed. [Preview Abstract] |
Wednesday, September 21, 2005 11:45AM - 12:00PM |
EC.00011: Ground and single-particle properties in Gogny+Tensor mean-field calculations Daisuke Abe, Takaharu Otsuka In the study of the nuclear structure with the mean-field method, the D1S interaction as the standard Gogny-type effective interaction has been used. The results obtained from D1S are generally in good agreement with the experimental data. But some behaviors of D1S results are not so close to experiments. We have therefore proposed a new Gogny-type interaction `GT2'. GT2 is similar to D1S in many respects, but the tensor term is introduced and the parameters are modified to remedy certain shortcomings. The tensor force plays an important role in the structure of nuclei. So it is essential for us to take into account the tensor force. We showed the data calculated with D1S and GT2. The difference between proton and neutron single-particle energies h$_{11/2}$ and g$_{7/2}$ of Sb isotope was investigated. We found the tensor force and the effect of neutron skin resulted in the interesting interplay. In this study, we shall present some results calculated from GT2. The isotope shifts of Ca and Pb will be included. The isotope shift means the changes of the nuclear charge radii with increasing neutron number. In the case of Ca and Pb, the experimental data show unusual behaviors. We study such isotope shifts by using GT2. We further discuss some properties of exotic nuclei, focusing on the competition between tensor-force effect and neutron-skin effect. [Preview Abstract] |
Wednesday, September 21, 2005 12:00PM - 12:15PM |
EC.00012: Looking at nuclei in the black sphere picture Akihisa Kohama, Kei Iida, Kazuhiro Oyamatsu We review our method for systematically analyzing proton elastic scattering data for stable nuclei, by assuming that the target nucleus is a ``black'' sphere. This method gives a length scale, $a$, the values of which are determined so as to reproduce the angle of the first diffraction maximum in the scattering data. We find that the absorption cross section, $\pi a^2$, agrees with the empirical total reaction cross section for C, Sn, and Pb to within error bars for proton incident energies, $T_p$, higher than $\sim800$ MeV. Our preliminary results suggest that this agreement is retained for $T_p$ down to a few hundreds MeV. For $T_p>\sim800$ MeV, we also find that $\sqrt{3/5}a$ almost completely agrees with the empirically deduced values of the r.m.s. matter radius for nuclei having mass larger than about 50, while it systematically deviates from the deduced values for $A<\sim50$. This tendency suggests a significant change of the nuclear matter distribution from a rectangular one for $A<\sim50$. Possible application of our method to neutron-rich unstable nuclei is finally discussed. [Preview Abstract] |
Wednesday, September 21, 2005 12:15PM - 12:30PM |
EC.00013: Equation of state of nuclear matter and nuclei in laboratories and neutron-star crusts Kazuhiro Oyamatsu, Kei Iida We systematically examine how sensitive macroscopic properties of nuclei in laboratories and neutron-star crusts are to the density dependence of the symmetry energy. Using macroscopic nuclear models constructed in such a way that they reproduce empirical data for masses and radii of stable nuclei equally well, while depending on the still uncertain parameters such as the symmetry energy density derivative coefficient $L$ and the nuclear matter incompressibility $K_0$, we calculate radii and masses of heavy unstable nuclei, the charge number of nuclei in neutron star crusts, and the deepest end of the crust at which nuclei melt into uniform matter. We find that the results for all these quantities show almost no $K_0$ dependence but appreciable $L$ dependence. Future possible determination of $L$ from radioactive ion beam experiments and its significance for the presence of ``pasta'' nuclei in neutron star crusts are finally discussed. [Preview Abstract] |
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