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 KJ: Nuclear Reactions: Heavy Ion Induced |
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Sponsoring Units: DNP JPS Chair: Tadashi Shimoda, Osaka University Room: Ritz-Carlton Hotel Hawaii |
Thursday, September 22, 2005 2:00PM - 2:15PM |
KJ.00001: Isovector Quadrupole Resonance observed in the $^{60}$Ni($^{13}$C,$^{13}$N)$^{60}$Co reaction at \emph{E/A} = 100 MeV Takashi Ichihara, Masayasu Ishihara, Hajime Ohnuma, Takashi Niizeki, Yoshiteru Satou, Hiroyuki Okamura, Shigeru Kubono, Masahiko Tanaka, Yoshihide Fuchi The charge-exchange reaction $^{60}$Ni($^{13}$C,$^{13}$N)$^{60}$Co at $E/A$ = 100 MeV has been studied to locate isovector ($\Delta T$ = 1) non-spin-flip ($\Delta S = 0$) giant resonances. Besides the giant dipole resonance at $E_x$ = 8.7 MeV, another resonance has been observed at $E_x$ = 20 MeV with a width of 9 MeV. DWBA analysis on the angular distribution clearly indicated the $L$ = 2 multipolarity, attributing the $E_x$ = 20 MeV state to the giant isovector quadrupole resonance. The present analysis further indicates that the observed peak exhausts approximately 50 \% strength of the isovector L=2 classical energy-weighted sum rule. The same ($^{13}$C,$^{13}$N) reactions at $E/A$ = 100 MeV for other target nuclie will be also presented and discussed. A part of this result can be found at the reference of T. Ichihara \emph{et al.}, Phys.\ Rev. Lett. {\bf 89}, 142501 (2002). [Preview Abstract] |
Thursday, September 22, 2005 2:15PM - 2:30PM |
KJ.00002: $\alpha$-stripping reactions with light exotic nuclei: $^{12}C(^7Be,^3He)^{16}O$ H. Amro, F.D. Becchetti , H. Jiang, H. Griffin, Y. Chen, J.J. Kolata, B. Skorodumov, J.D. Hinnefeld, G. Peaslee Considerable experimental and theoretical efforts have been devoted to examine the importance of $\alpha$-particle clustering in $p$-shell and $sd$-shell nuclei which is essential for the analysis of the helium- and silicon-burning processes in nuclear astrophysics. $\alpha$-stripping reactions such as $(^6Li,d)$ and $(^7Li,t)$ were used to prope the $\alpha$ structure of $^{16}$O. These studies shown that the $(^7Li,t)$ reaction is significantly more sellective than $(^6Li,d)$ reaction. New reaction, $(^7Be,^3He)$ has been studied at E($^7$Be)=34 MeV using the University of Michigan-University of Notre Dame radiactive nuclear beam facility. Angular distributions have been measured for several states in $^{16}$O. At this energy, this reaction exhibits a high selectivity for populating $\alpha$-cluster states in $^{16}$O. Furthermore, $^3$He-stripping reaction $(^7Be,\alpha)$ populating several states in $^{15}$O, never been reported befor for $(^7Li,t)$ or $(^6Li,d)$ reactions, was observed in our data. Experimental and theoretical analysis of this data will be presented. [Preview Abstract] |
Thursday, September 22, 2005 2:30PM - 2:45PM |
KJ.00003: Production of Very Neutron-rich Nuclei with Low Energy Beam Masahiro Notani, K. Bailey, J. Greene, D. Henderson, R.J. Holt, R.V.F. Janssens, C.L. Jiang, Z.-T. Lu, P. Mueller, T.P. O'Connor, R.C. Pardo, K.E. Rehm, J.P. Schiffer, X. Tang, M. Paul, G.W.F. Drake, L.-B. Wang The production cross section of very neutron-rich nuclei, $^{8} $He, has been investigated using multi-nucleon transfer reaction with a $^{9}$Be beam at 14 MeV/nucleon. The cross section data will be used to optimize the produced neutron-rich nuclei beam for the study of nuclear structure. The experiment was performed at ATLAS facility at Argonne, where the $^{9}$Be beam bombarded production targets of Be, BN, C, and U. Particle identification of reaction products was carried out by means of the magnetic split-pole-spectrograph with a focal plane detector that consists of PPAC’s and ion chambers. The momentum distribution of 8He yield was measured by varying the magnetic field. The angular distribution was measured at 0 and 5 degree. The production cross section was obtained for integration of the observed yield for each target. The production cross section of the $^{9}$Be ($^{9}$Be, $^{8} $He) X reaction is smaller than that of the $^{238}$U ($^{9}$Be, $^{8}$He) X by one order of magnitude. In the present talk, we will report details of the experiment and discuss the production mechanism of neutron-rich nuclei with low energy beams. [Preview Abstract] |
Thursday, September 22, 2005 2:45PM - 3:00PM |
KJ.00004: Scaling of projectile residue yields from peripheral heavy-ion collisions below the Fermi energy G.A. Souliotis, D.V. Shetty, A. Keksis, M. Jandel, M. Veselsky, S.J. Yennello The scaling properties of the yields of isotopically resolved projectile residues from very peripheral collisions of $^{86} $Kr(25MeV/nucleon) and $^{64}$Ni(25MeV/nucleon) on $^{64,58}$Ni and $^{124,112}$Sn target pairs are invesrigated. The reactions of $^{86}$Kr were studied with the MARS recoil separator. Their yields and isoscaling properties have already been discussed [1,2]. The reactions of $^{64}$Ni were studied with the Superconducting Solenoid (BigSol) Line. In the present study, special attention is given to neutron-rich projectile fragments produced in peripheral collisions. For these fragments, isoscaling in the usual sense is not observed: e.g. the yield ratios of the isotopes of a given element do not follow an exponential dependennce on neutron number. Comparison of the measured yield ratios with model calculations using either a deep-inelastic transfer code (DIT) [3] code or a BNV transport code [4] followed by a deexcitation code seem to reproduce the observed hehavior of the measured yield ratios. These comparisons may offer the possibility to extract information on the nuclear symmetry energy (and its density dependence) from the process of peripheral nucleon exchange. [1] G.A. Souliotis et al., Phys. Rev. C 68, 024605 (2003). [2] G.A. Souliotis et al., Phys. Rev. Lett. 91, 022701 (2003). [3] L. Tassan-Got et al., Nucl. Phys. A524, 121 (1991). [4] V. Baran et al., Nucl. Phys. A 730, 329 (2004). [Preview Abstract] |
Thursday, September 22, 2005 3:00PM - 3:15PM |
KJ.00005: Target effect of fragmentation reactions at intermediate energy Sadao Momota, Yoichi Nojiri, Mitsutaka Kanazawa, Atsushi Kitagawa, Mitsuru Suda, Makoto Sasaki, Shinji Sato To investigate the production mechanism of projectile-like fragments (PLF's) at intermediate energies, the momentum distributions of PLF's produced from Ar beam at intermediate energy were measured. The production cross sections were derived by integrating observed momentum distributions. The present results are useful to design experiments, which will be done at new RIB facilities. The measurements were performed by using HIMAC facility at NIRS. The longitudinal and transverse momentum distributions of PLF's produced in the reactions with ZP = 18 and ZT = 6 $\sim $ 79 at E/A = 290 MeV were measured. In the reaction with heavier targets, the transverse momentum distribution was broader than that measured with lighter targets. This broadening effect is remarkable for heavier PLF's (AF $>$ 20) and negligible for lighter ones. This result implies that the effect of the Coulomb force shrinks caused by the nuclear force in the case of lighter PLF's. The target effect was found in the production cross sections of PLF's derived from observed momentum distributions as well. The production mechanism of PLF's will be discussed based on the present results by comparing with the theoretical results. [Preview Abstract] |
Thursday, September 22, 2005 3:15PM - 3:30PM |
KJ.00006: Study of Fusion enhancement/hindrance with $^{132}$Sn A.M. Vinodkumar, W. Loveland, D. Peterson, P. Sprunger, J.F. Liang, D. Shapira, R.L. Varner, C.J. Gross, J.J. Kolata, L. Westerberg One of the interesting aspects of the study of nuclear reactions induced by radioactive ion beams is the possibility of using neutron rich projectiles to synthesize new, neutron rich heavy nuclei. Also, large fusion cross section enhancement has been predicted for fusion reactions with massive neutron rich radioactive nuclei by different authors. This is due to the lowering of the fusion barrier, excitation of the soft dipole modes and lowering of reaction Q values. However, previous experimental data with stable beams indicates fusion hindrance in the case of massive neutron rich nuclei. We have measured the fusion excitation function of $^{96}$Zr with neutron-rich short-lived $^{132}$Sn and stable $^{124}$Sn projectiles near the Coulomb barrier. The measurement was carried out at ORNL. The coincident fission fragments were detected using 4 Si strip detectors. The time of flight of the beam as well as the fragments were measured using 2 upstream timing MCP's and timing signal from strip detectors. Using different energy,time and position conditions, the fusion-fission events were separated from other reaction processes. The experimental results will be presented along with theoretical model predictions. [Preview Abstract] |
Thursday, September 22, 2005 3:30PM - 3:45PM |
KJ.00007: Decrease of Coulomb Barrier Height due to Charge Polarization for Cold Fusion Reactions Akira Iwamoto, Takatoshi Ichikawa We estimate the decrease of Coulomb-barrier height between colliding partners due to static charge polarization in the entrance channel of cold-fusion reactions [1]. Charge displacement between protons and neutrons is modeled as the sum of two components, one is surface-type and the other is volume-type. The strength of both types of polarization is determined by the energy-balance between the decrease of mutual Coulomb energy and the increase of self-energies for both target and projectile. It is shown that the surface-type-dominant polarization for light nuclei changes gradually toward comparable surface-and-volume polarization for heavy nuclei, which feature is similar to what was obtained in the study of giant dipole resonance [2]. Although the strength of the induced polarization is not large, the decrease of the Coulomb barrier height amounts to 1 to 2 MeV for typical cold-fusion reactions, which is not negligible in fine tuning of the most-favorable incident energies to synthesize super-heavy elements. [1] Takatoshi Ichikawa and Akira Iwamoto, Phy. Rev. C, in press. [2] W.D. Myers, W.J. Swiatecki, T. Kodama, E.J. El-Jaick and E.R. Hilf., Phys. Rev. C {\textbf 15}, 2032 (1977). [Preview Abstract] |
Thursday, September 22, 2005 3:45PM - 4:00PM |
KJ.00008: Probing fusion barrier distributions with large-angle quasielastic scattering of $^{48}$Ti, $^{56}$Fe and $^{64}$Ni on $^{208}$Pb Shinichi Mitsuoka, Hiroshi Ikezoe, Katsuhisa Nishio, Kaoru Tsuruta, Sun-Chan Jeong, Yutaka Watanabe As a new procedure to extract representations of fusion barrier distributions, it has been proposed to take the first derivative of the ratio of the quasielastic cross section to the Rutherford cross section with respect to the center-of-mass energy. We measured the excitation functions of quasielastic scattering at large-backward angles of 162$^{\circ}$, 168$^{\circ}$ and 172$^ {\circ}$ from $^{208}$Pb target bombarded with heavy-ion beams of $^{48}$Ti, $^{56}$Fe and $^{64}$Ni from the JAERI Tandem- booster accelerator at energies near the Coulomb barrier. The result for quasielastic barrier distributions will be discussed by comparing with couple-channel calculations and data of fusion barrier distribution in the $^{208}$Pb based cold fusion reactions for superheavy element synthesis. [Preview Abstract] |
Thursday, September 22, 2005 4:00PM - 4:15PM |
KJ.00009: Attempt to confirm superheavy element production in the \textbf{$^{48}$Ca + $^{238}$ }U reaction W. Loveland, K.E. Gregorich, D. Peterson, P.M. Zielinski, S.L. Nelson, Ch. E. Duellmann, C.M. Folden III, D.C. Hoffman, G.K. Pang, R. Sudowe, R.E. Wilson, H. Nitsche, Y.H. Chung, K. Aleklett, R. Eichler, S. Soverna, J.P. Omtvedt, P. Sprunger, J.M. Schwantes An attempt to confirm production of superheavy elements in the reaction of $^{48}$Ca beams with actinide targets has been performed using the $^{238}$U($^{48}$Ca,3n)$^{283}$112 reaction. Two $^{48}$Ca projectile energies were used, that spanned the energy range where the largest cross sections have been reported for this reaction. No spontaneous fission events were observed. No alpha decay chains consistent with either reported or theoretically predicted element 112 decay properties were observed. The cross section limits reached are significantly smaller than the recently reported cross sections [Preview Abstract] |
Thursday, September 22, 2005 4:15PM - 4:30PM |
KJ.00010: Entrance Channel in Heavy-ion Reactions for Superheavy Element Production Takatoshi Ichikawa, Akira Iwamoto, Peter M\"oller, Arnold J. Sierk We discuss both cold fusion reactions of the type that lead to the formation of elements with proton number Z from 107 to 113 and hot fusion, that is reactions with deformed actinide targets [1]. In cold fusion with Pb-like targets we show that for reactions eading to the heavier evaporation residues deformation and shell effects lead to a fusion barrier that is more than 10 MeV lower that what is obtained in a standard spherical macroscopic liquid-drop model. Inside touching we calculate the macroscopic-microscopic potential energies of the composite system in a five-dimensional deformation space consisting of about 4 million nuclear shapes. We find that the composite system exhibits a well-established fusion channel in which the initial composite shape closely matches the shape-polarized shapes just outside touching. In hot-fusion reactions that target is deformed and experimental and theoretical considerations indicate that ``equatorial'' collision are the most likely to lead to evaporation residue formation. Also in this case we show that shape polarizations lead to a significant decrease of the equatorial fusion barrier. [1] T. Ichikawa, A. Iwamoto, P.M\"oller, A. J. Sierk, Phys. Rev. C {\bf 71}, 044608 (2005). [Preview Abstract] |
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