Bulletin of the American Physical Society
5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 63, Number 12
Tuesday–Saturday, October 23–27, 2018; Waikoloa, Hawaii
Session 1WBA: Physics and Chemistry of the Heaviest Elements and Nuclei I |
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Chair: Krzysztof Rykaczewski, Oak Ridge National Laboratory Room: Hilton Kohala 1 |
Tuesday, October 23, 2018 9:00AM - 9:30AM |
1WBA.00001: Actinide materials for the synthesis of heaviest nuclei Invited Speaker: James Roberto The use of heavy actinides as targets in “hot fusion” reactions with intense 48Ca ion beams has enabled a significant expansion of the nuclear chart, adding five new elements and more than 50 new heaviest isotopes since 2000, and providing evidence for the existence of the predicted “island of stability” for super-heavy nuclei. These discoveries, made using the Dubna Gas-Filled Recoil Separator at the Joint Institute for Nuclear Research (JINR) in Russia [1], have utilized actinide targets from specialized facilities at Oak Ridge National Laboratory (ORNL) and the Research Institute of Advanced Reactors at Dmitrovgrad. These facilities, including the High Flux Isotope Reactor and Radiochemical Engineering Development Center at ORNL [2], provide unique capabilities to produce, separate, and purify rare actinide materials, and fabricate actinide targets. New, more powerful accelerator facilities have been developed at JINR and at RIKEN in Japan to expand research on super-heavy nuclei, including the search for new elements 119 and 120. These facilities will require increased quantities of actinide target materials, including 248Cm, 249Bk, and mixed Cf. This paper will review the role of actinide materials in advancing super-heavy element research, as well as opportunities to enhance the production of actinide target materials for the synthesis of super-heavy nuclei. [1] Yu. Ts. Oganessian and V. K. Utyonkov, Nucl. Phys. A 944, 62 (2015). [2] J. B. Roberto, et al., Nucl. Phys. A 944, 99 (2015).
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Tuesday, October 23, 2018 9:30AM - 10:00AM |
1WBA.00002: Mechanism of fusion reactions for superheavy elements Invited Speaker: Kouichi Hagino In heavy-ion fusion reactions at energies around the Coulomb barrier, excitations of low-lying collective motions play an important role. In order to take into account those excitations during fusion reactions, the coupled-channels approach has been a standard tool. The channel coupling effect leads to a distribution of fusion barriers, which has a responsibility to enhance capture cross sections below the Coulomb barrier as compared to a prediction of a simple potential model. The fusion barrier distribution can be actually extracted from measured fusion cross sections, taking the second energy derivative of the product of the incident energy and fusion cross sections, which has been performed experimentally for many systems. The extracted fusion barrier distributions have revealed that the barrier distribution is sensitive to the channel couplings, thus providing a finger print of the underlying dynamics of fusion reactions. Recently, this technique has been applied to a hot fusion system relevant to superheavy nuclei, that is, the 48Ca+248Cm system. The coupled-channels analysis for the measured barrier distribution, which takes into account the deformation of the target nucleus 248Cm, has clearly shown that the maximum of the evaporation residue cross sections for this system appears at an energy slightly above the barrier height for the side collision, in good agreement with the notion of compactness. In this contribution, we will present the analysis of barrier distribution for the 48Ca+248Cm system using the coupled-channels approach. We will also discuss the reaction dynamics of fusion reactions of a deformed nucleus in general, in particular, the role of deformation of the target nucleus in the synthesis of superheavy elements, by using the extended version of fusion-by-diffusion model. |
Tuesday, October 23, 2018 10:00AM - 10:30AM |
1WBA.00003: Reaction studies for the synthesis of heavy nuclei Invited Speaker: Katsuhisa Nishio Heavy-ion reaction studies at the JAEA tandem accelerator facility will be discussed. In order to predict cross sections to produce super-heavy nuclei in fusion-evaporation reactions, it is essential to determine fusion probability, i.e. the probability to produce compound nucleus after a system overcome and/or penetrate the Coulomb barrier. Our attempt to determine fusion probability from the measurement of fission fragments mass distributions and evaporation residue cross sections will be presented, particularly placing emphasis on the effects of static deformation of the target nucleus 238U on fusion, using various projectile nuclei 16O - 48Ca [1-4]. Recently, we are promoting a program of reaction studies in multi-nucleon transfer (MNT) reactions using various actinide target nuclei [5,6]. The MNT reaction allows us to produce neutron-rich nuclei, which cannot be populated by particle capture/fusion reactions. The MNT reactions are also used to measure fission properties and fission barrier heights for various nuclei. From the data, competition between neutron-emission and fission is discussed [7]. Reference [1] K. Nishio et al., Phys. Rev. Lett. 93, 162701 (2004). [2] K. Nishio et al., Phys. Rev. C 77, 064607 (2008). [3] K. Nishio et al., Phys. Rev. C 82, 024611 (2010), Phys. Rev. C 82, 044604 (2010). [4] K. Nishio et al., Phys. Rev. C 86, 034608 (2012). [5] R. Léguillon et al., Phys. Lett. B 761, 125 (2016). [6] A.N. Andreyev, K. Nishio, K.-H. Schmidt, Rep. Prog. Phys. 81, 016301 (2018). [7] K. Hirose et al., Phys. Rev. Lett. 119, 222501 (2017). |
Tuesday, October 23, 2018 10:30AM - 11:00AM |
1WBA.00004: COFFEE BREAK
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