Bulletin of the American Physical Society
2005 APS April Meeting
Saturday–Tuesday, April 16–19, 2005; Tampa, FL
Session R12: Nuclear Reactions |
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Sponsoring Units: DNP Chair: M. B. Tsang, Michigan State University Room: Marriott Tampa Waterside Room 11 |
Monday, April 18, 2005 10:45AM - 10:57AM |
R12.00001: Measurement of Spin-Correlation Coefficients for p-$^{3}$He Elastic Scattering T.V. Daniels, T. Katabuchi, T.B. Clegg, H.J. Karwowski As part of an investigation of the A=4 system, we measured the spin-correlation coefficients A$_{yo}$, A$_{oy}$, A$_{yy}$, and A$_{xx}$ for p-$^{3}$He elastic scattering at E$_{lab}$ of 2.3, 2.7, 4.0, and 5.5 MeV and $\Theta _{lab}$ between 30$^{o}$ and 150$^{o}$. The data were taken using TUNL's atomic beam polarized ion source and a new spin-exchange optical pumping polarized $^{3}$He target\footnote{ T. Katabuchi \textit{et al.,} to be published in Rev. Sci. Instrum.}. We aim to resolve ambiguities in the phase shifts of George and Knutson\footnote{ E.A. George and L.D. Knutson, Phys Rev C 67, 027001 (2003)}, which seem most sensitive to A$_{xx }$and A$_{yy}$ at the lowest of these energies. Our 5.5 MeV data compare well with earlier data\footnote{ B.M. Fisher \textit{et al.}, in: Proceedings of FB17, eds. W. Glockle and W. Tornow, Elsevier 2004}$^{,}$\footnote{ M.T. Alley and L.D. Knutson, Phys Rev C 48, 1901 (1993)}. Our new measurements will be shown with phase-shift-analysis solutions. [Preview Abstract] |
Monday, April 18, 2005 10:57AM - 11:09AM |
R12.00002: Coupled reaction channels analysis of $^{7}$Li + $^{6}$Li interactions O.A. Momotyuk, K.W. Kemper, B.T. Roeder, W. Cluff, N. Keeley, B.G. Schmidt, M. Wiedeking, F. Mar$\'{e}$chal, S. Mezhevych, J. Liendo Cross sections and the analyzing powers $^{T}$T$_{10}$, $^{T}$T$_{20}$, and $^{T}$T$_{30}$ were measured for the reactions $^{6}$Li($^{7}$Li,$^{7}$Li)$^{6}$Li, $^{6}$Li($^{7}$Li,$^{7}$Li$^{*}$$_{0.48}$)$^{6}$Li, $^{6}$Li($^{7}$Li,$^{7}$Li)$^{6}$Li$^{*}$$_{2.186}$ MeV and the one-nucleon transfer reactions $^{6}$Li($^{7}$Li,$^{6}$He)$^{7}$Be and $^{6}$Li($^{7}$Li,$^{6}$He)$^{7}$Be$^{*}$$_{0.43}$ MeV at 42 MeV using the FSU Polarized Li-ion source and the FSU Tandem/LINAC Accelerator. These reactions were analyzed using Coupled Reaction Channels Calculations that employed optical potentials of Woods-Saxon type, double-folded and cluster-folded potentials in order to understand the origin of the observed analyzing powers. The results of these calculations and their interpretation in terms of virtual and real couplings as well as spin-orbit and tensor forces will be presented. [Preview Abstract] |
Monday, April 18, 2005 11:09AM - 11:21AM |
R12.00003: Can the CDCC calculation be improved? George Rawitscher, Israel Koltracht The Continuum Discretized Coupled Channels method of including breakup effects in the calculation of nuclear reactions, when applied to unstable nuclei, requires the inclusion of a large number of coupled channels, and the numerical computational effort increases correspondingly. The computing time with traditional finite difference techniques [1] scales with the cube of the number of channels $N$. The scaling with a new spectral integral method ($SIEM$) [2] of solving coupled equations is likewise $N^{3}$. However, the structure of the matrices that occur in the numerical algorithm of the $SIEM$ is different from that of the finite difference methods, and lends itself well to iterative solutions, reducing the numerical complexity to $N^ {2}$ times the number of required iterations. Various iterative schemes will be considered, and their convergence properties will be examined. \bigskip\newline[1] \ I. J. Thompson, code FRESCO, Comp. Phys. Rep. \textbf{7}, 167 (1988);\newline[2] \ R. A. Gonzales, S. -Y. Kang, I. Koltracht and G. Rawitscher, J. of Comput. Phys. \textbf{153}, 160 (1999). [Preview Abstract] |
Monday, April 18, 2005 11:21AM - 11:33AM |
R12.00004: Survival of Very Neutron Rich Fragments in Multifragmentation G.A. Souliotis, D.V. Shetty, M. Veselsky, A. Botvina, E. Bell, A. Keksis, M. Jandel, S.J. Yennello The yield distributions of isotopically resolved projectile residues from semi-peripheral collisions of 86Kr (25 MeV/nucleon), 64Ni (25 MeV/nucleon) and 136Xe (20 MeV/nucleon) beams on a variety of targets are studied in this work. The reactions of 86Kr with 64,58Ni, 124,112Sn and 208Pb were studied with the MARS recoil separator of the Cyclotron Institute of Texas A&M [1]. The reactions of 64Ni and 136Xe with 64,58Ni and 124,112Sn, as well as 208PB, 232Th were studied with the Superconducting Solenoid (BigSol) Line. Special attention is given to projectile residues, escpecially the most neutron rich ones, produced at excitation energies near the multifragmentation threshold(2-3MeV/nucleon). Both the N/Z and the kinematical properties of the observed fragments are well described by a hybrid calculation involving a deep inelastic transfer model for the dynamical stage of the collision and the statistical multifragmentation model (SMM) [2] for the de- excitation stage. Apart from a nuclear reaction standpoint, the observed survival of very neutron-rich fragments also addresses the practical issue of the production of neutron-rich rare isotopes in multifragmentation. [1] G.A. Souliotis et al., Phys. Rev. Lett. 91 (2003) 022701; Nucl. Instrum. Methods B 204 (2003) 166, [2] A.S. Botvina et al. Phys. Rev. C 65 044610 (2002) and references therein. [Preview Abstract] |
Monday, April 18, 2005 11:33AM - 11:45AM |
R12.00005: Evolution of isoscaling Jorge Lopez, C.O. Corso, C. Escudero The evolution of isoscaling is studied using classical molecular dynamics simulations of several reactions at various energies. Isoscaling at different stages of the reaction was calculated and the validity of the isoscaling power law was estimated. [Preview Abstract] |
Monday, April 18, 2005 11:45AM - 11:57AM |
R12.00006: Critical analysis of data from peripheral Si+Sn reaction at 50 MeV/nucleon - probing N/Z degree of freedom M. Jandel, S. Wuenschel, S.J. Yennello, G.A. Souliotis, D.V. Shetty, E. Bell, A. Keksis, J. Iglio, B. Stein, S. Soisson Evidence of nuclear liquid-gas phase transition in small mass systems A$\sim $36 has been reported previously [1], where the minimum of the critical topological exponent $\tau $ as a function of temperature of the multifragmenting source has been checked by two theoretical models which include liquid-gas phase transition, with good agreement. We will present an analysis of the fragmentation of quasiprojectiles obtained in the reactions $^{28}$Si+$^{124,112}$Sn at 30 and 50 MeV/nucleon [2]. We will show that apparent critical behavior is present also in smaller systems where the charge of the reconstructed quasiprojectiles is Z=12-15. We extracted the critical exponent $\tau $ as well as the second moment of charge distribution S$_{2}$. The minimum of $\tau $ and maximum of S$_{2}$ lie in the vicinity of excitation energy of qusiprojectiles E$^{\ast }\sim $5 MeV/nucleon. The dependence of $\tau $ and S$_{2}$ on N/Z degree of freedom of quasiprojectile will be discussed. [1] Y. G. Ma et al., Phys. Rev. \textbf{C69}, 031604(R) (2004) [2] R. Laforest et al., Phys. Rev. \textbf{C59}, 2567 (1999) [Preview Abstract] |
Monday, April 18, 2005 11:57AM - 12:09PM |
R12.00007: Using Light Cluster Production to Explore the Density Dependence of the Nuclear Symmetry Energy Sarah Soisson, L.W. Chen, E. Bell, S.J. Yennello The production of deuteron, triton, and $^{3}$He in heavy-ion collisions induced by a neutron-rich nuclei has been studied using a coalescence model for treating cluster production from an isospin-dependent Boltzmann-Uehling-Uhlenbeck(iBUU) transport model. Using this approach, it has been shown that the both the multiplicities and energy spectra of light clusters are sensitive to the density dependence of the nuclear symmetry energy but not to the isospin-independent part of the EOS or the in-medium nucleon-nucleon cross sections. Isotopically identified light charged particles have been measured with the NIMROD detector for reactions of $^{58}$Fe and $^{58}$Ni at 45 MeV/A. The energy spectra and multiplicities of these fragments will be compared with predictions from the iBUU and Antisymmetrized Molecular Dynamics (AMD) theoretical codes. [Preview Abstract] |
Monday, April 18, 2005 12:09PM - 12:21PM |
R12.00008: The amalgamation stage of fusion reactions Genevieve Mouze, Christian Ythier There is no need of a repulsive potential in the amalgamation stage for explaining the small fusion cross sections. The repulsive potential proposed by A. Adamian et al.(1) can advantageously be replaced by the affinity of the reaction of re-dissociation of the compound nucleus into its entrance-channel configuration. This reaction, which occurs after the penetration of the Coulomb barrier, is an equilibrium between dual and compact form of the compound nucleus, and the energy Q released in the dissociation is equal to the energy required for amalgamating. The total energy of the confined system being equal to the height B of the Coulomb barrier, the intrinsic excitation energy of the compact nucleus is equal to (B - Q). In the reaction 82Se+ 138Ba (2), the dissociation of 220Th releases 180.524 MeV, and B= 196.08 MeV. With an intrinsic excitation energy of 15.56 MeV, the confined compact 220Th has enough energy for emitting two neutrons ( S(2n) = 13.85 MeV). Thus the favored xn channel of fusion reactions can be precisely predicted. This new, mass-data-based model of fusion is completely parameter-free. 1 G.G. Adamian et al., PRC 69 (2004) 044601. 2 K. Satou et al. PRC C 65(2002) 054602. [Preview Abstract] |
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