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 FD: Mini-Symposium: Rare Isotope Science IV |
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Chair: Paul Mantica, Michigan State University Room: Jewett Ballroom G-H |
Saturday, October 25, 2008 8:30AM - 8:42AM |
FD.00001: First identification of the $\pi $g$_{9/2}$ band in the neutron-rich $^{71,73,75}$Ga isotopes produced in deep-inelastic reactions I. Stefanescu, N. Hoteling, W.B. Walters, M.P. Carpenter, R.V.F. Janssens, T. Lauritsen, D. Seweryniak, S. Zhu, R. Broda, B. Fornal, W. Krolas, T. Pawlat Deep-inelastic reactions proved to be a very powerful technique for the study of high-spin states in the neutron-rich nuclei around $^{68}$Ni. This kind of reactions produced significant broadening of the experimental knowledge in the neutron-rich Fe, Ni, Cu and Zn isotopes. Such information, consisting of a number of isomeric states and rotational-like structures is extremely important for the understanding of the effects of the N=40 subshell closure on the collective properties in this mass-region. In the present paper we report the first identification of the bottom part of the g9/2 proton band in the neutron-rich $^{71,73,75}$Ga produced in deep-inelastic reactions at Argonne National Laboratory. The bands exhibit a rotation aligned-like character suggesting moderate prolate deformation for these nuclei. A surprisingly constant level spacing with increasing the neutron number is observed experimentally, contrary to the expectation that the addition of a pair of g9/2 neutrons induces an increase in collectivity. [Preview Abstract] |
Saturday, October 25, 2008 8:42AM - 8:54AM |
FD.00002: New Band Structures in Neutron-Rich $^{108}$Mo, and $^{108,110,112}$Ru J.H. Hamilton, Y.X. Luo, A.V. Ramayya, C. Goodin, K. Li, J.K. Hwang, S. Liu, S.J. Zhu, H.-B. Ding, X.L. Che, J.O. Rasmussen, I.Y. Lee, D. Almehed, S. Frauendorf, V. Dimitrov, J.Y. Zhang, N.J. Stone, G.M. Ter-Akopian, A.V. Daniel, M.A. Stoyer, R. Donangelo, J.D. Cole New insights into the structures of $^{108}$Mo, and $^{108,110,112}$Ru are identified in the spontaneous fission of $^{252}$Cf. The 5.7 x 10$^{11}$ triples and higher fold prompt gamma coincidences opened up the possibility to see new weakly populated band structures in these nuclei. Two phonon $\gamma $-bands that decay only to the one phonon $\gamma $-band were discovered in $^{108}$Mo and $^{110,112}$Ru. We discovered in $^{108}$Mo$^{ }$and$^{ 108,110,112}$Ru $\Delta $I=1, doublet bands. Our theoretical calculations indicate $^{108}$Ru is $\gamma $-soft and $^{110,112}$Ru are more rigid triaxial nuclei. The non-yrast band in $^{108}$Ru shows an energy level staggering not seen in its yrast partner band nor in $^{110,112}$Ru. This staggering is proposed to be related to its $\gamma $-soft shape perturbing its chiral structure. The doublet bands in $^{108}$Mo$^{ }$and $^{110,112}$Ru will be shown to have all the properties expected for chiral vibrational bands. Tilted axis cranking calculations for $^{110,112}$Ru stronly support the chiral vibrational interpretation of these bands but do not support their being accidentally degenerate energy doublets built on different configurations. [Preview Abstract] |
Saturday, October 25, 2008 8:54AM - 9:06AM |
FD.00003: Measurement of (d,p) reactions near the doubly-magic $^{132}$Sn Steven Pain \noindent Measurements of (d,p) reactions on n-rich fission fragments yield important information on nuclear structure away from stability, and are of astrophysical interest due to the proximity to suggested r-process paths. The energies, spins 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 development of re-accelerated fission fragment beams at the HRIBF at ORNL has, for the first time, made possible the measurement of (d,p) reactions at the Coulomb barrier on nuclei around the doubly-magic $^{132}$Sn nucleus. The $^{130}$Sn(d,p)$^{131}$Sn, $^{132}$Sn(d,p)$^{133}$Sn and $^ {134}$Te(d,p)$^{135}$Te reactions have been measured at the HRIBF at around 4.5 MeV/A utilizing deuterated plastic targets. 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 the Silicon Detector Array (SIDAR). Details of the experiments and the data analysis, including excitation energies and angular distributions for the states populated, will be presented. *This work is supported in part by the U.S. Department of Energy and the National Science Foundation. [Preview Abstract] |
Saturday, October 25, 2008 9:06AM - 9:18AM |
FD.00004: The $^{132}$Sn + $^{96}$Zr reaction: a study of fusion enhancement/hindrance Walter Loveland, A.M. Vinodkumar, James Neeway, Peter Sprunger, Landon Prisbrey, Donald Peterson, J.F. Liang, Dan Shapira, C.J. Gross, R.L. Varner, J.J. Kolata, A. Roberts, A.L. Caraley Capture-fission cross sections were measured for the collision of the massive nucleus $^{132}$Sn with $^{96}$Zr at center of mass energies ranging from 192.8 to 249.6 MeV in an attempt to study fusion enhancement and hindrance in this reaction involving very neutron-rich nuclei. Coincident fission fragments were detected using silicon detectors. Using angle and energy conditions, deep inelastic scattering events were separated from fission events. Coupled channels calculations can describe the data if the surface diffuseness parameter, \textbf{\textit{a}}, is allowed to be 1.10 fm, instead of the customary 0.6 fm. The measured capture-fission cross sections agree moderately well with model calculations using the dinuclear system (DNS) model. If we use this model to predict fusion barrier heights for these reactions, we find the predicted fusion hindrance, as represented by the extra push energy, is greater for the more neutron-rich system, lessening the advantage of the lower interaction barriers with neutron rich projectiles. [Preview Abstract] |
Saturday, October 25, 2008 9:18AM - 9:30AM |
FD.00005: Production of neutron-rich isotopes in reactions at beam energies well above the Coulomb Barrier Shaofei Zhu, R.V.F. Janssens, M.P. Carpenter, C.J. Chiara, E. Jackson, B.A. Kay, F.G. Kondev, T. Lauritsen, E.A. McCutchan, D. Seweryniak, N. Hoteling, I. Stefanescu, B. Fornal An experiment with a 48Ca beam at an energy of 320 MeV ($\sim$100\% above the Coulomb barrier) has been carried out in inverse kinematics on a 0.5 mg/cm$^2$ 26Mg target at Gammasphere. This experiment is a first attempt to extend the reach of complex reactions in producing neutron-rich nuclei beyond the technique of using deep inelastic reactions on a thick target at 25\% above the Coulomb barrier. The main purpose of the experiment was to explore the isotopic production of neutron-rich nuclei above doubly-magic 48Ca nucleus, as well as in the region around the target. The systematics of isotopic yields at these energies can be anticipated from Q-value arguments in the form proposed in Ref. [1]. The reaction yields will be presented. The quality of the gamma spectra from this measurement with a thin target was assessed with known isotopes. [1] A.Y. Abul-Magd et al., Phys. Lett. B 39, 166(1973). [Preview Abstract] |
Saturday, October 25, 2008 9:30AM - 9:42AM |
FD.00006: Neutron-Rich Isotopes from 208Pb at 86 MeV/u O.B. Tarasov, M. Portillo, A.M. Amthor, T. Baumann, D. Bazin, C. Folden, T. Ginter, M. Hausmann, D.J. Morrissey, J. Pereira, B.M. Sherrill, M. Thoennessen, C. Nociforo An experiment to measure production yields from a beam of $^{208}$Pb (86~MeV/u) on Be and Ni-targets has recently been performed. The A1900 fragment-separator~[1] was used to analyze products from projectile fragmentation and abrasion-fission~[2]. Isotopic identification of nuclides having $A\sim $200 has been achieved, demonstrating that adequate $A,Z,Q$ resolution at this energy region is possible when using silicon detectors. The verification of PID is done via detection of multiple charge state distributions of the primary beam, as well as $\gamma $-decay of known isomers with half-lives in the microsecond range. The results demonstrate that experiments with heavy nuclei are possible at the NSCL using beams of A$>$200. Production cross-sections have been extracted from the data that can help improve the accuracy of production models such as Abrasion-Ablation and Abrasion-Fission used in the LISE++ code [3]. The data reveal the existence of previously unreported isomeric transitions and further analysis is ongoing that may also lead to the observation of new isotopes. References: [1] D.J.Morrissey et al., Nucl. Instrum. Meth. B204 (2003) 90--96. [2] O.B. Tarasov, Tech. Rep. MSUCL1300, NSCL, Michigan St.Univ., 2005. [3] O.B. Tarasov, D. Bazin, Nucl. Phys. A 746 (2004) 411; www.nscl.msu.edu/lise . [Preview Abstract] |
Saturday, October 25, 2008 9:42AM - 9:54AM |
FD.00007: Time-of-Flight Mass Measurements of Neutron Rich Nuclides A. Estrade, M. Matos, A.M. Amthor, A. Becerril, T. Elliot, G. Lorusso, A. Rogers, H. Schatz, D. Bazin, A. Gade, M. Portillo, A. Stolz, D. Galaviz, J. Pereira, D. Shapira, E. Smith, M. Wallace Nuclear masses of neutron rich isotopes in the region of Z $\sim$ 20-30 have been measured using the time-of-flight technique at the National Superconducting Cyclotron Laboratory (NSCL). The masses of 5 isotopes have been measured for the first time, and the precision of several other masses has been improved. The time-of-flight technique has shown the potential to access nuclear masses very far from stability when applied at radioactive beam facilities like the NSCL. Such measurements are important for understanding nuclear structure far from the valley of $\beta$-stability, and provide valuable information for astrophysical model calculations of processes involving very unstable nuclides. [Preview Abstract] |
Saturday, October 25, 2008 9:54AM - 10:06AM |
FD.00008: Development of a Versatile Array of Neutron Detectors at Low Energy Catalin Matei, D.W. Bardayan, J.C. Blackmon, J.A. Cizewski, W.A. Peters, R.K. Grzywacz, S.N. Liddick, S.W. Padgett, S.D. Pain, F. Sarazin The development of radioactive ion beams at the Holifield Radioactive Ion Beam Facility at ORNL allows the study of many neutron- and proton-rich nuclei. Proton transfer with (d,n) reactions is an excellent tool for measuring single-proton strength in neutron-rich nuclei near the Z=28 and 50 shell closures. On the proton-rich side (d,n) reactions on $^{56}$Ni and $^{25}$Al are relevant for nuclear astrophysics. We also propose measurements of beta decay properties in nuclei near $^{78}$Ni and $^{132}$Sn to determine beta decay lifetimes and branching ratios. The Versatile Array of Neutron Detectors at Low Energy (VANDLE) is a new array of plastic scintillator bars under development at ORNL. The array is highly modular allowing the configuration of the individual elements to be optimized for particular experimental requirements. We propose one configuration optimized for beta-delayed neutron emission studies and one optimized for (d,n) reactions. The scientific motivation and details of the testing and design of the array will be presented. [Preview Abstract] |
Saturday, October 25, 2008 10:06AM - 10:18AM |
FD.00009: Blurred femtoscopy in two-proton decay Carlos Bertulani The effects of final state interactions in two-proton emission by nuclei is discussed. The study is based on the solution the time-dependent Schroedinger equation. The relative energy between the protons is substantially influenced by the final state interactions. Alternative correlation functions can be constructed showing large sensitivity to the spin of the diproton system. The prospects of using di-proton emission as an EPR experiment is explored. [Preview Abstract] |
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