Bulletin of the American Physical Society
2008 Annual Meeting of the Division of Nuclear Physics
Volume 53, Number 12
Thursday–Sunday, October 23–26, 2008; Oakland, California
Session ME: Nuclear Structure: Medium Mass A=50-100 |
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Chair: Volker Werner, Yale University Room: Simmons Ballroom 1 |
Sunday, October 26, 2008 10:30AM - 10:42AM |
ME.00001: Neutron Transfer Dynamics and Doorway to Fusion in TDHF Theory Sait Umar, Volker Oberacker Within the time-dependent Hartree-Fock (TDHF) theory, we analyze in detail the mass exchange in the vicinity of the Coulomb barrier for heavy-ion collisions involving neutron-rich nuclei. Two examples are considered: 16O + 24O and 40Ca + 96Zr. Specifically, we study the neutron densities of the neutron-rich nucleus as a function of time, and we examine the neutron single-particle probabilities long after the recoil. In the 16O + 24O reaction, most of the mass transfer originates from the 2s1/2 neutron state of 24O. In the 40Ca + 96Zr reaction, the 2d5/2 state in 96Zr dominates the mass transfer, in particular the magnetic substates with the most positive quadrupole moments. We find that the potential barriers seen by individual single-particle states can be considerably different than the effective barrier of the ion-ion potential. Hence, we observe a substantial transfer probability even at energies below the effective fusion barrier. Ref. 1: A.S. Umar, V.E. Oberacker, and J.A. Maruhn, Eur. Phys. J A (2008), in print [Preview Abstract] |
Sunday, October 26, 2008 10:42AM - 10:54AM |
ME.00002: Systematics of Hot Giant Dipole Resonance Parameters Andreas Schiller, Michael Thoennessen, Katherine McAlpine The dependence of the Giant Dipole Resonance (GDR) width on spin and temperature is a much debated subject in the literature. A universal scaling law has been proposed by Kusnezov \it et al.\ \rm [D. Kusnezov \it et al.\ \rm Phys.\ Rev.\ Lett.\ \bf 81\rm, 542 (1998)]\@. Recently, we completed a literature survey of GDR parameters which provided us with a data set about five times as big as the one which was used by Kusnezov {\it et al.} [A. Schiller and M. Thoennessen, At.\ Data Nucl.\ Data Tables \bf 93\rm, 549 (2007)]\@. The Kusnezov scaling law is tested over this larger data set. The data is also broken down into subsets of data with common characteristics such as deformation. We will discuss the limits of applicability of the Kusnezov scaling law. [Preview Abstract] |
Sunday, October 26, 2008 10:54AM - 11:06AM |
ME.00003: On Isoscalar magnetic moments of excited states Yitzhak Sharon, Larry Zamick, Sean Yeager We first review the isoscalar magnetic moments of odd A mirror pairs of closed major shells plus or minus one nucleon. We note systematic deviations in experiment-Schmidt. For j=l+1/2 the deviation is positive (stretch) but for j=l-1/2 it is negative (jackknife). But the main emphasis is on 2+ states of even-even N=Z nuclei which have isospin T=0 and hence isoscalar moments. This work is stimulated by recent measurements by Speidel's and Koller's group on 2+ states 32S,36Ar and 44Ti and on 4+ in 20Ne. The measured values of g factors for all these nuclei are very close to 0.5, which is also the rotational value for a K=0 band. But we also note that we get close to 0.5 in the single j shell model for intermediate and heavy nuclei. In single j the expression for j=l+1/2 is g=0.5+0.38/(2l+1) while for j=l-1/2 it is 0.5-0.38/(2l+1). Hence from a measured value close to 0.5 one cannot conclude that the rotational model or the single j shell model are approximately correct, or whether one needs or does not need intruder state admixtures. Odd-odd nuclei are also considered where the story is similar. For closed major shell plus or minus one nucleon there are no first order corrections and the second order ones are due to the tensor force. [Preview Abstract] |
Sunday, October 26, 2008 11:06AM - 11:18AM |
ME.00004: High-lying, non-yrast shell structure in 52Ti Shaofei Zhu, R.V.F. Janssens, M.P. Carpenter, B.P. Kay, F.G. Kondev, T. Lauritsen, C.J. Lister, A. Robinson, D. Seweryniak, X. Wang, B. Fornal, R. Broda, W. Krolas, T. Pawlat, J. Wrzesinski, S.J. Freeman, A. Deacon, J.F. Smith, D. Steppenbeck, M. Honma, P.F. Mantica, S.N. Liddick, B.E. Tomlin, T. Otsuka, A. Larabee The level structure of 52Ti was studied following fusion-evaporation and incomplete-fusion reactions. As a result, an extensive level scheme is now available for high-lying, non-yrast states in this nucleus. The newly-established level sequence provides further tests of full pf-shell calculations with the GXPF1A interaction. With only 2 protons and 2 neutrons outside the double-magic nucleus 48Ca, 52Ti can be described very well by the shell-model calculations without the need for a larger model space. In addition, the observed high-energy gamma transitions at high spin are attribued to the N=32 shell gap in neutron-rich Ti isotopes, which reflects the large energy separation between the neutron p3/2 and p1/2 orbitals due to the weakening of the attractive monopole interaction beween the proton f7/2 and the neutron f5/2 orbitals. [Preview Abstract] |
Sunday, October 26, 2008 11:18AM - 11:30AM |
ME.00005: First detailed structure information on the r-process path nucleus $^{63}$Fe A. Baluyut, H. Mach, E. Ruchowska, U. Koester, L.M. Fraile, H. Bradley, R. Boutami, N. Braun, Ch. Fransen, E.M. Reillo, V. Ugryumov The nucleus $^{63}$Fe is located exactly at the point of transition between lighter Fe isotopes which show spherical structures and heavier Fe, where a sudden increase in quadrupole collectivity is manifested from lowering of the first excited 2$^{+}$ states in the even Fe nuclei. Very little is actually known on the exotic neutron-rich nuclei in this region. A substantial modification of the information on the nuclear structure of $^{63}$Fe and nuclei in its vicinity was obtained from a fast timing study conducted at the ISOLDE facility at CERN where levels in $^{63}$Fe were populated from the beta-decay of $^{63}$Mn. The new level scheme of $^{63}$Fe includes 21 gamma-transitions and 10 excited states. Although $^{63}$Fe seems to be understood in a shell model picture, a clear departure from spherical sequence is observed. From the measured log\textit{ft} values, gamma-ray branching ratios, and level half-lives in the ps range, we deduce spins and parities of 1/2$^{-}$, 3/2$^{-}$ and 5/2$^{-}$ for the lowest states in $^{63}$Fe which represent an inverted sequence in comparison to the heavier (and spherical) $N=37$ isotones, namely $^{65}$Ni and $^{67}$Zn. [Preview Abstract] |
Sunday, October 26, 2008 11:30AM - 11:42AM |
ME.00006: Measurements of the g-factors of the $4^+$ states in $^{72,76}$Ge isotopes G. G\"urdal, G. Kumbartzki, N. Benczer-Koller, Y.Y. Sharon, Z. Berant, R. Casperson, A. Heinz, G. Henning, J. Qian, A. Schmidt, J.R. Terry, W. Werner, E. Williams, R. Winkler In this work, the g factors of the excited $4^+_1$ states of $^{72,76}$Ge were measured, using the Transient Field (TF) technique, and the results will be presented. The $4^+_1$ states of $^{72,76}$Ge were populated by using projectile excitation. The $^{72,76}$Ge beams were accelerated to 200 MeV at the Yale Tandem accelerator and were Coulomb excited as they interacted with a Mg target. The systematic studies of the g factors of $2^+_1$ and $4^+_1$ nuclear states provide an understanding of the microscopic structure of the wave functions of these low-lying excited states, since the g factors are very sensitive to the proton and neutron configurations in the wave functions. The measured g factor results can be compared to the predictions of either large-scale shell model calculations or of collective models. The measured g factors of the $2^+_1$ states in the Ge isotopes show reasonable agreement with the $Z/A$ values that are characteristic of collective behavior. The lack of data for the g factors of the corresponding $4^+_1$ states motivated the present investigations. Work supported by the U.S. National Science Foundation and U.S.D.O.E under grant DE-FG02-91ER-40609. [Preview Abstract] |
Sunday, October 26, 2008 11:42AM - 11:54AM |
ME.00007: Investigating nuclear structure relevant to neutrinoless double $\beta $ decay: $^{76}$Ge and $^{76}$Se B.P. Kay, J.P. Schiffer, K.E. Rehm, S.J. Freeman, J.A. Clark, C.M. Deibel, C. Wrede, A.C.C. Villari, P. Grabmayr, T. Adachi, H. Fujita, Y. Fujita, K. Hatanaka, D. Ishikawa, Y. Meada, H. Matsubara, H. Okamura, Y. Sakemi, Y. Shimizu, H. Shimoda, K. Suda, Y. Tameshige, A. Tamii Disagreements between theoretical predictions of matrix elements relevant to neutrinoless double beta decay motivated measurements of valence occupations in the ground states of $^{76}$Ge and $^{76}$Se. Results from neutron transfer reactions indicate that the Fermi surface is much more diffuse than theoretical calculations suggest$^{a}$. Recently, similar measurements have been carried out to determine the difference in proton occupations of these nuclei. This program of work is complemented by results probing pair correlations in these nuclei, obtained using the (p,t) reaction$^{b}$. $^{a}$J.P. Schiffer \textit{et al. }Phys. Rev. Lett. \textbf{100}, 112501 (2008) $^{b}$S.J. Freeman \textit{et al.} Phys. Rev. C \textbf{75}, 051301(R) (2007) [Preview Abstract] |
Sunday, October 26, 2008 11:54AM - 12:06PM |
ME.00008: Photon Scattering from the Stable Even-Mass Mo Isotopes Below the Neutron-Separation Energy G. Rusev, A. Hutcheson, E. Kwan, A.P. Tonchev, W. Tornow, C. Angell, S. Hammond, H.J. Karwowski, J.H. Kelley, R. Schwengner, F. D\"onau, A. Wagner We present results from photon-scattering experiments on the stable even-mass molybdenum isotopes below the neutron-separation energy carried out with bremsstrahlung at the superconducting electron accelerator ELBE at the Research Center Dresden-Rossendorf in Germany, and with monoenergetic photon beams at the HI$\gamma$S facility at TUNL. We applied statistical methods in order to correct for the branching and cascade transitions and to determine the photoabsorption cross section. The obtained results allowed us to extend the tail of the Giant Dipole Resonance below the $(\gamma,n)$ threshold down to 4 MeV. The photoabsorption cross sections deduced from the present experiments show that the dipole strength increases with the neutron number of the Mo isotopes. The experimental results are discussed in the frame of Quasiparticle-Random-Phase-Approximation in a deformed basis which describe the increasing strength as a result of the deformation. [Preview Abstract] |
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