Bulletin of the American Physical Society
2007 Annual Meeting of the Division of Nuclear Physics
Volume 52, Number 10
Wednesday–Saturday, October 10–13, 2007; Newport News, Virginia
Session CE: Heavy Ions and Rare Isotope Beams |
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Chair: Sherry Yennello, Texas A&M University Room: Newport News Marriott at City Center Grand Salon V |
Friday, October 12, 2007 9:00AM - 9:12AM |
CE.00001: Improved Mass Measurements of Nuclei Around N = Z = 34 and The First High Precision Mass Measurement of $^{70m}$Br J. Savory, C. Bachelet, M. Block, G. Bollen, M. Facina, C.M. Folden III, G. Guenaut, E. Kwan, A.A. Kwiatkowski, D.J. Morrissey, G.K. Pang, A. Prinke, R. Ringle, H. Schatz, S. Schwarz, P. Schury, C.S. Sumithrarachchi Mass measurements of N = Z nuclei are important for the study of symmetries in nuclear structure, modeling of element synthesis in the rp-process and fundamental interactions tests. Heavy N = Z are located close to or even beyond the proton drip line. The Low Energy Beam and Ion Trap (LEBIT) facility succeeded in making the first high precision mass measurement of $^{70m}$Br, an N = Z proton drip line nuclei. In addition to $^{70m}$Br, the masses of $^{71}$Br, $^{70}$Se and $^{68}$Se were measured by Penning trap mass spectrometry of thermalized rare isotopes produced by fast-beam fragmentation. The results indicate that $^{68}$Se poses a greater waiting point in the rp-process, than previously thought. [Preview Abstract] |
Friday, October 12, 2007 9:12AM - 9:24AM |
CE.00002: Identifying spins and configurations of states in $^{13}$B A.H. Wuosmaa, J.C. Lighthall, S.T. Marley, J.P. Schiffer, C.L. Jiang, H.Y. Lee, M. Notani, R.C. Pardo, K.E. Rehm, I. Tanihata, X.D. Tang, N. Patel The $^{12}$B($d,p)^{13}$B reaction has been studied for the first time, in an effort to narrow down the spin and parity assignments of the excited states states in this nucleus. The particular aim of the measurement is to establish the odd-parity states arising from s$_{1/2}$ and d$_{5/2}$ neutrons coupled to the p$_{3/2}$ proton in this nucleus. A $^{12}$B beam produced at the ATLAS In-Flight facility, with an energy of 7 MeV/u and intensity of approximately 3$\times 10^5$ particles per second, bombarded a (CD$_2$)$_n$ target with an areal density of 100$\mu$g/cm$^2$. Protons were detected at backward laboratory angles in coincidence with $^{12,13}$B recoils identified at forward angles in an array of silicon $\Delta$E-E telescopes. Data analysis is in progress and the current status of the results will be reported. Work supported by the U. S. Department of Energy, Office of Nuclear Physics, under contract numbers DE-FG02-04ER41320 (WMU) and DE-AC02-06CH11357 (ANL). [Preview Abstract] |
Friday, October 12, 2007 9:24AM - 9:36AM |
CE.00003: First Discovery of an Isomeric State with a Penning Trap Mass Spectrometer A.A. Kwiatkowski, M. Block, C. Bachelet, G. Bollen, M. Facina, C.M. Folden III, C. Guenaut, D.J. Morrissey, G.K. Pang, A. Prinke, R. Ringle, J. Savory, P. Schury, S. Schwarz An isomeric state of $^{65}$Fe has been discovered at the Low Energy Beam and Ion Trap facility (LEBIT) at the NSCL. From its measured mass difference with the ground state, the new isomer is determined to have an excitation energy of 402(5) keV. Following the systematics of spin and energy levels of lighter isotopes, tentative spin assignments were made for the ground state and the observed isomer. In addition to $^{65}$Fe, high-precision mass measurements were made of $^{63,64}$Fe and $^{64-66}$Co using the Penning trap mass spectrometer. The mass uncertainties of all isotopes have been reduced by a factor of 10-100 compared to previous experiments. Moreover, our measurement of $^{64}$Co differs from the accepted value by about five standard deviations. One motivation for mass measurements in this region is the observed N=40 sub-shell closure. [Preview Abstract] |
Friday, October 12, 2007 9:36AM - 9:48AM |
CE.00004: Observation of new neutron-rich Mg, Al, and Si isotopes T. Baumann, A.M. Amthor, D. Bazin, C.M. Folden III, A. Gade, T.N. Ginter, M. Hausmann, M. Matos, D.J. Morrissey, A. Nettleton, M. Portillo, A. Schiller, B.M. Sherrill, A. Stolz, O.B. Tarasov, M. Thoennessen We report on the first observation of the neutron-rich isotopes $^{40}$Mg, $^{42,43}$Al, and $^{44}$Si. The rare isotopes were produced by fragmentation of $^{48}${Ca} at 142~MeV/u at NSCL using tungsten targets, and subsequently separated in the A1900 fragment separator. For the discovery of $^{40}${Mg} and $^{42,43}$Al, the A1900 was used in combination with the S800 analysis beam line, resulting in an exceptional selectivity. The comparison of the observed isotopes---especially the odd-odd $^{42}$Al---to established theoretical model calculations suggests that the drip line lies further out to heavier isotopes, at least for aluminum and silicon. [Preview Abstract] |
Friday, October 12, 2007 9:48AM - 10:00AM |
CE.00005: Constraining the density dependence of the symmetry energy and the nuclear equation of state: A dynamical and statistical model approach D.V. Shetty, S.J. Yennello, G.A. Souliotis The density dependence of the symmetry energy is important for studying the equation of state of systems as diverse as the atomic nuclei and neutron stars. Our current understanding of this very important quantity remains largely unconstrained due to a lack of understanding of the basic nucleon-nucleon interaction for matter that is highly asymmetric and at non-normal nuclear density. Theoretical studies based on microscopic ``ab-initio'' calculations predict variety of different form of the density dependence of the symmetry energy. Recent studies carried out at Texas A{\&}M University to investigate the the equation of state of isospin asymmetric nuclear matter using the statistical and the dynamical model approaches of multifragmentation reaction will be presented. These studies along with several other independent studies rule out an extremely ``stiff'' and ``soft'' form of the density dependence of the symmetry energy and have important implications for astrophysical and nuclear physics studies. The importance of further constraints for studying the symmetry energy of finite nuclei will also be emphasized. [Preview Abstract] |
Friday, October 12, 2007 10:00AM - 10:12AM |
CE.00006: The single-particle states in $^{133}$Sn studied through the $^{132}$Sn (d,p) reaction Kate Jones, Jolie Cizewski It is important, both to nuclear structure physics and to understanding the synthesis of heavy elements in the cosmos, to understand how single-particle states change as we move away from the valley of stability, especially around shell closures. A beam of $^{132}$Sn, produced at ORNL's Holifield Radioactive Ion Beam Facility, was used in a transfer reaction experiment to study single-particle states beyond the double-shell closure. The beam impinged on a target of CD$_{2}$ with effective thickness of 160g/cm$^{2}$. Charged ejectiles were detected in an array of position sensitive silicon detectors, mostly of the new ORRUBA type, with SIDAR detectors at very backward angles. At forward laboratory angles, telescopes of detectors were used to discriminate protons from heavier, elastically scattered particles. From the angles and energies of the protons, the energies of the states populated in $^{133}$Sn were measured. The extraction of angular distributions for individual states is in progress. The most recent results from this measurement will be presented. [Preview Abstract] |
Friday, October 12, 2007 10:12AM - 10:24AM |
CE.00007: Fusion of $^{134}$Sn, $^{134}$Sb and $^{134}$Te with $^{64}$Ni at near and subbarrier energies Dan Shapira, J.F. Liang, C.J. Gross, R.L. Varner, J.R. Beene, P.E. Mueller, D.W. Stracener, W. Loveland, J.J. Kolata, H. Amro, A. Roberts, K. Grzywacz-Jones, S. Padgett, A.L. Caraley Evaporation Residues (ER) from collisions of $^{134}$Sn, $^{134}$Sb and $^{134}$Te ions with a $^{64}$Ni target were measured at three beam energies (530, 500 and 480 MeV). The purpose of the experiment is to find out to what degree fusion near and below the Coulomb barrier is enhanced (or supressed) due to the presence of loosely bound valence neutrons in the collisions induced by the Sn and Sb isobars. The technique used to obtain cross sections for all three isobars and a comparison of ER yields in the three systems will be presented. [Preview Abstract] |
Friday, October 12, 2007 10:24AM - 10:36AM |
CE.00008: Sub-barrier Fusion of radioactive $^{132}$Sn and $^{64}$Ni J.F. Liang, D. Shapira, C.J. Gross, R.L. Varner, J.R. Beene, P.E. Mueller, D.W. Stracener Fusion induced by neutron-rich radioactive ion beams has received substantial interest experimentally and theoretically in recent years. The fusion excitation function of radioactive $^{132}$Sn on $^{64}$Ni has been measured. The cross section for the lowest energy data point had a large uncertainty and was anomalously large. With an improved apparatus, an experiment was carried out to investigate the fusion of $^{132}$Sn and $^{64}$Ni at sub-barrier energies. The technique and results of the new measurement will be presented. [Preview Abstract] |
Friday, October 12, 2007 10:36AM - 10:48AM |
CE.00009: Measurement of the $^{134}$Te(d,p)$^{135}$Te Reaction in Inverse Kinematics Steven Pain \noindent The development of high quality radioactive beams, such as those at the HRIBF at ORNL, has made possible the performance of transfer reactions on unstable nuclei. Measurements of (d,p) reactions on n-rich fission fragments yield data on nuclear structure away from stability, and are of astrophysical interest due to the proximity to suggested r- process paths. The energies and spectroscopic information of single-particle states near to shell closures are of particular importance, since they provide both an important constraint on nuclear structure models and are directly relevant to direct neutron-capture cross sections. The single-neutron states in $^ {135}$Te, one neutron beyond the N=82 shell closure, are of particular interest, both for r-process nucleosynthesis and its relevance to an isotopic anomaly of Xe found in pre-solar meteoritic grains. The $^{134}$Te(d,p)$^{135}$Te reaction has been measured in inverse kinematics at the HRIBF utilizing a beam of $^{134}$Te at 643 MeV and a deuterated plastic target. Proton ejectiles were detected forward and backwards of $\theta_{lab}$ = $90^{\circ}$ using an early implementation of the Oak Ridge Rutgers University Barrel Array (ORRUBA) in conjunction with SIDAR. Details of the experiment and the current stage of the data analysis will be presented. [Preview Abstract] |
Friday, October 12, 2007 10:48AM - 11:00AM |
CE.00010: Nucleon Transfer Calculations Using the HIPSE Model Z. Kohley, D. Lacroix, G.A. Souliotis, A.L. Keksis, B. Stein, D.V. Shetty, S. Soisson, S.J. Yennello The HIPSE (Heavy-Ion Phase-Space Exploration) model has been used to examine nucleon transfer during the interaction of the projectile and target. The results of the HIPSE model were compared to experimental data obtained on the FAUST array for $^{20}$F + $^{108}$Ag, $^{20}$F + $^{197}$Au, $^{20}$Na + $^{197}$Au, and $^{20}$Ne + $^{197}$Au at 32 MeV/u. The apparent mass change of the projectile was calculated for fully reconstructed events, in which the total detected charge was equal to the charge of the beam. The experimental results had shown that both the mean values and the distribution widths of the mass transfer plots varied with the N/Z of the compound system. The HIPSE results were in good agreement with the experimental data for the more neutron-rich systems. For the less neutron-rich systems, the HIPSE model overestimated the loss of neutrons from the projectile. The difference between the theoretical and experimental data may be due to the fact that the HIPSE model does not treat the transfer of neutrons and protons differently. The HIPSE code was modified to allow for the percent transfer of neutrons and protons to be controlled separately. Comparisons of HIPSE coupled with the SMM, SIMON and Gemini de-excitation codes will be presented. [Preview Abstract] |
Friday, October 12, 2007 11:00AM - 11:12AM |
CE.00011: Microscopic calculations of heavy-residue formation in quasielastic and deep-inelastic collisions below the Fermi energy. G.A. Souliotis, D.V. Shetty, S. Galanopoulos, S.J. Yennello During the last several years we have undertaken a systematic study of heavy residues formed in quasi-elastic and deep- inelastic collisions near and below the Fermi energy [1,2]. Presently, we are exploring the possibility of extracting information on the dynamics by comparing our heavy residue data to calculations using microscopic models based on the quantum molecular dynamics approach (QMD). We have performed detailed calculations of QMD type using the recent version of the constrained molecular dynamics code CoMD of M. Papa [3]. CoMD is especially designed for reactions near the Fermi energy. It implements an effective interaction with a nuclear-matter compressibility of K=200 (soft EOS) with several forms of the density dependence of the nucleon-nucleon symmetry potential. CoMD imposes a constraint in the phase space occupation for each nucleon, thus restoring the Pauli principle at each time step of the collision. Results of the calculations and comparisons with our residue data will be presented and discussed in detail. [1] G.A. Souliotis et al., Phys. Rev. Lett. 91, 022701 (2003); Nucl. Instrum. Methods B 204 166 (2003). [2] G.A. Souliotis et al., Phys. Lett. B 588, 35 (2004). [3] M. Papa et al., Phys. Rev. C 64, 024612 (2001). [Preview Abstract] |
Friday, October 12, 2007 11:12AM - 11:24AM |
CE.00012: Observation of isomer production in abrasion fission of $^{238}$U on a $^{9}$Be Target A.S. Nettleton, A.M. Amthor, C.M. Folden III, T.N. Ginter, M. Hausmann, D.J. Morrissey, M. Portillo, B.M. Sherrill, O.B. Tarasov, T. Kubo, T. Nakao, H. Takeda, W.D. Loveland, S.L. Manikonda, G.A. Souliotis This talk will present the observation of gamma decay from isomeric states produced in abrasion fission of $^{238}$U on a $^{9}$Be target at 80 MeV/nucleon. This experiment was performed at the National Superconducting Cyclotron Laboratory at Michigan State University. The fission products were identified by A, Z and Q, with the gamma decay observed within a 20 microsecond window following implantation in a silicon telescope. This technique, for identification of breakup products is known as isomer tagging,. Isomer tagging has become an important tool for in-flight fragment identification of fission and fragmentation products. Unfortunately an extensive database of isomers is unavailable for much of the neutron rich region populated by fission. Because of this, one of the goals of fission studies at the NSCL has been to measure the population of isomeric states. These results along with the possible identification of previously unknown isomeric states will be presented. [Preview Abstract] |
Friday, October 12, 2007 11:24AM - 11:36AM |
CE.00013: Development of an Advanced Fission - Fusion - Evaporation Residue Detection System A.L. Caraley, D. Shapira, J.F. Liang, C.J. Gross, R.L. Varner, J.R. Beene, E. Chavez A detector system, to measure fission fragments and evaporation residues resulting from collisions induced by rare neutron-rich nuclei, is being designed. The detector system is intended for use with radioactive ion beams and with low intensity stable beams ($\leq$ 5$\times$10$^{4}$ particles per second) and will require high efficiency. The primary detector will consist of an ionization chamber lined with double-sided silicon-strip detectors and will provide for tracking and particle identification capabilities over a wide angular range. Design and simulation of the detector system, using {\sc GEANT4}, is ongoing. Complete tracking and response simulations for fragments and residues will be performed by incorporating statistical-model-code events ({\it e.g.} from {\sc GEMINI} or {\sc PACE2}) into the calculations. Details of the detector design and simulations and results of fission fragment and evaporation residue efficiency calculations will be presented. The impact of the expected performance on planned radioactive beam experiments, including attempts to synthesize heavy elements, will be discussed as well. [Preview Abstract] |
Friday, October 12, 2007 11:36AM - 11:48AM |
CE.00014: Fission of $^{238}$U at 80 MeV/u and Search for New Neutron-Rich Isotopes C.M. Folden III, A.M. Amthor, T.N. Ginter, M. Hausmann, D.J. Morrissey, A.S. Nettleton, M. Portillo, B.M. Sherrill, O.B. Tarasov, T. Kubo, T. Nakao, H. Takeda, W.D. Loveland, S.L. Manikonda, G.A. Souliotis Calculations for existing and future radioactive beam facilities indicate that fission of $^{238}$U may provide the highest intensities for many secondary beams, although only limited data exist for uranium energies in the range 50-500 MeV/u. An experiment to measure the cross sections and momentum distributions of fragments produced via fission following abrasion of an 80-MeV/u $^{238}$U beam with Be targets has been conducted at the National Superconducting Cyclotron Laboratory at Michigan State University. Recoiling fragments were spatially separated from the primary beam and identified using the A1900 fragment separator with magnetic rigidity varied in steps from 2.5 to 3.9 T m. Standard particle identification techniques were augmented through the observation of gamma decays originating from known microsecond isomers. Additionally, a search for new neutron-rich isotopes was conducted and preliminary analysis has shown the production of many events along the limit of presently known isotopes. The latest results on these experiments and comparisons with theoretical models will be presented. [Preview Abstract] |
Friday, October 12, 2007 11:48AM - 12:00PM |
CE.00015: N/Z Equilibration in Deep Inelastic Collisions and the Fragmentation of the Resulting Quasiprojectiles August Keksis, Martin Veselsky, George Souliotis, Dinesh Shetty, Marian Jandel, Elizabeth Bell, Ananya Ruangma, Eileen Winchester, Josh Garey, Sara Parketon, Cass Richers, Sherry Yennello When target and projectile nuclei have different N/Z, the quasiprojectiles formed in deep inelastic collisions should have a mean N/Z between that of the N/Z of the target and the N/Z of the projectile. This depends on the amount of N/Z equilibration that occurred. Six reaction systems with different N/Z between target and projectile were studied at Texas A{\&}M University Cyclotron Institute. The fragments were measured with FAUST, the Forward Array Using Silicon Technology. Two techniques were used to determine the quasiprojectile N/Z, which were then compared to a fully N/Z equilibrated system to study the amount of N/Z equilibration. The fragmentation of the quasiprojectiles was studied using isobaric, isotopic, fractional and mean N/Z yield comparisons between systems. The results show that the neutron richness of the system affects the fragment yields, with the neutron-rich nuclides populated preferentially by the neutron-rich systems. The N/Z distribution of the fragment yields was also studied and an inhomogeneous N/Z distribution between the LCPs (Z$<$3) and IMF's (Z$>$2) was observed. This research was funded in part by the Department of Energy through grant DE-FG03-93ER40773 and the Robert A. Welch Foundation through grant A-1266. [Preview Abstract] |
Friday, October 12, 2007 12:00PM - 12:12PM |
CE.00016: Determining the Density Dependence of the Nuclear Symmetry Energy and Its Impacts in Astrophysics with Heavy-Ion Reactions Lie-Wen Chen, Wei-Zhou Jiang, Plamen Krastev, Andrew Steiner, Aaron Worley, Jun Xu, Gao-Chan Yong The density dependence of the nuclear symmetry energy is important for both nuclear physics and astrophysics. Recent data on isospin transport in heavy-ion reactions have allowed us to constrain significantly the symmetry energy at sub-saturation densities. In this talk we discuss promising probes of the symmetry energy at supra-normal densities using heavy-ion reactions induced by high energy radioactive beams. Astrophysical impacts of the constrained symmetry energy on cooling mechanisms and mass-radius correlations of neutron stars as well as the changing rate of the gravitational ``constant G'' will also be discussed. [Preview Abstract] |
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