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 LB: Nuclear Reactions 1 |
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Chair: A.B. Balantekin, University of Wisconsin Room: Hilton Kohala 1 |
Saturday, October 27, 2018 9:00AM - 9:15AM |
LB.00001: Fusion cross section measurement of 16C+12C near the Coulomb barrier using MUSIC Ashley A Hood, Daniel Santiago-Gonzalez, Catherine M Deibel, Clayton Dickerson, Sergio J Almaraz-Calderon, Benjamin W Asher, Kalle Auranen, Melina L Avila, Sudarsan Balakrishnan, Jeffery C Blackmon, Erin Good, Calem R Hoffman, Cheng-lie Jiang, Benjamin P Kay, Sean A Kuvin, Alexander Laminack, Scott T Marley, Graeme Morgan, Richard Pardo, Karl Ernst Rehm, Nabin Rijal, Jasmine Sethi, Rashi Talwar, Gemma L Wilson Fusion cross-section measurements around the Coulomb barrier present key information for nuclear astrophysics processes as well as an important test for theoretical models of fusion. For example, in neutron stars, fusion reactions between neutron-rich nuclei are thought to play an important role in the heating of the star. Different theoretical cross-section calculations vary by an order of magnitude from one another and from experimental values for some systems. Previously, the total fusion cross sections of different carbon isotopes (10, 14, 15C+12C) were systematically studied using the MUlti-Sampling Ionization Chamber (MUSIC) [1]. As a natural extension to more neutron-rich systems, we measured the total fusion cross section of 16C+12C at Ecm=15-30 MeV using MUSIC at Argonne National Laboratory. Our results and future plans to probe lower center-of-mass energies and measure the 16C+13C cross section near the Coulomb barrier will be discussed.
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Saturday, October 27, 2018 9:15AM - 9:30AM |
LB.00002: Sub-barrier fusion of 11Li with 208Pb Walter D Loveland We have extended our previous measurements of the complete fu- sion and breakup fusion processes in the interaction of 11 Li with spherical 208 Pb with four new measurements at laboratory frame energies of 11 Li of 26.1 to 32.7 MeV in the sub-barrier region. (Previous measurements were for Elab = 28.6 to 39.9 MeV.) Comparison of the complete fusion cross sections with coupled channel, TDHF and other models for these collisions reveals signi- cant dierences between the measured and calculated values. The implications of this nding for the fusion/breakup of halo nuclei are discussed. |
Saturday, October 27, 2018 9:30AM - 9:45AM |
LB.00003: Quantum surface friction model for fusion reactions around the Coulomb barrier Masaaki Tokieda, Kouichi Hagino For the description of heavy-ion fusion reactions at energies above the Coulomb barrier, the classical trajectory calculation with a frictional force has been developed. The necessity of a frictional force was suggested by the experimental fact that a large amount of energy loss takes place in scattering experiments. Although the classical friction model can nicely describe above barrier fusion reactions, it cannot be applied to fusion reactions at energies below the Coulomb barrier, where fusion reactions take place only by quantum tunneling. In order to achieve a unified description of sub- and above barrier fusion reactions, we focus on a quantum friction model invented by M.D. Kostin. With that model, we carry out quantum mechanical calculation of fusion reactions with friction. For the form of a frictional force, we employ the surface friction model, which is known to be one of successful models of classical trajectory calculation. In the presentation, we shall show that fusion cross sections with the quantum friction are in between fusion cross sections without friction and that of the classical trajectory calculation, and they provide better agreement with experimental data. |
Saturday, October 27, 2018 9:45AM - 10:00AM |
LB.00004: Fusion Dynamics for Hot Fusion Reactions revealed in Quasielastic Fusion Barrier Distributions Taiki Tanaka, Kosuke Morita, Kouji Morimoto, Daiya Kaji, Hiromitsu Haba, Rose Ann Boll, Nathan T. Brewer, Shelley Van Cleve, David Jarvis Dean, Satoshi Ishizawa, Yuta Ito, Yukiko Komori, Katsuhisa Nishio, Toshitaka Niwase, B. C. Rasco, James B. Roberto, Krzysztof P. Rykaczewski, Hideyuki Sakai, Daniel W. Stracener, Kouichi Hagino In order to clarify the fusion dynamics for hot fusion reactions, we measured the excitation functions on quasielastic (QE) scattering cross sections σQE for 22Ne+248Cm, 26Mg+248Cm, and 48Ca+238U systems. In contrast to previous QE fusion barrier distribution studies which measured the recoiled projectile nuclei at backward angles (θlab ∼ 170◦), this work obtained successfully the σQE for l = 0 by measuring the target nuclei recoiling into forward angle employing the gas-filled-type recoil ion separator GARIS. The QE fusion barrier distribution DQE were successfully extracted, and compared with coupled-channels calculations. The calculation results clearly shows that the DQE values are strongly affected by the deformation of the target nucleus and influenced by vibrational and rotational excitations of the colliding nuclei. Comparing the peak of the evaporation residue cross sections σER with the experimental average Coulomb barrier height B0, we found that the peaks appear well above the B0 in the barrier distributions. This indicates that the σER values are enhanced at the energy which corresponds to a compact collision geometry with the projectile impacting the side of the deformed target nucleus. |
Saturday, October 27, 2018 10:00AM - 10:15AM |
LB.00005: One-Body Fluctuation Mechanism in Deep-Inelastic Reactions Kazuyuki Sekizawa Time-dependent Hartree-Fock (TDHF) theory (or TDEDF, TDDFT) has shown remarkable successes in describing complex nuclear dynamics microscopically from nucleonic degrees of freedom. However, the well-known drawback is that the width of fragment mass distribution in deep-inelastic reactions is severely underestimated within the TDHF approach. Here we show, that the description can be dramatically improved by including one-body fluctuation, based on a prescription of Balian and Vénéroni, which may be comparable to TDRPA. In this contribution, the case of deep-inelastic 58,60Ni+60Ni reactions will be presented, in the light of detailed experimental/theoretical analyses. |
Saturday, October 27, 2018 10:15AM - 10:30AM |
LB.00006: Benchmarking the Active Catcher Array for Detecting Heavy Elements Produced in Multi-Nucleon Transfer Reactions Aditya Wakhle, Alan B McIntosh, Kris Hagel, Marina Barbui, Jerome Gauthier, Bryan Matthew Harvey, Lauren Heilborn, Ian Jeanis, Andrea Jedele, Joseph B Natowitz, Alis Rodriguez Manso, Elysia Salas, Roy Wada, Andrew Zarella, Sherry J Yennello All known elements from Fm to Og have been synthesized by heavy-ion fusion reactions, and are neutron-deficient relative to beta-stability. Multi-Nucleon Transfer (MNT) reactions have been suggested as an alternate pathway to synthesize new neutron-rich heavy nuclei and to approach the N=184 shell. The limited success of making heavy nuclides in radiochemical studies in the 70’s and 90’s led to skepticism over the veracity of these predictions. A reexamination of older data, and new predictions from microscopic and macroscopic models have reinvigorated efforts directed at making neutron-rich isotopes of Z=104-108 with these reactions. The Active Catcher Array (AC) is a device at Texas A&M University built to study heavy residues produced in MNT reactions. It consists of 40 YAP scintillators coupled to PMTs at forward angles, and 8 IC-Si detectors at backward angles. A measurement of the 238U + 232Th reaction showed promising signatures of residues with Z up to 116 being produced in this reaction. A new campaign of experiments aims to benchmark the AC, develop an algorithm for identifying alpha chains, and make the case for a much improved active catcher array with higher granularity, better energy resolution and linear energy response using single crystal diamond detectors.
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Saturday, October 27, 2018 10:30AM - 10:45AM |
LB.00007: Effects of Multichance Fission on Fission Fragment Mass Distributions at High Energies Shoya Tanaka, Kentaro Hirose, Katsuhisa Nishio, Yoshihiro Aritomo Nuclear fission is an extremely complex reaction, and still not understood completely. Especially, the behavior at high excitation energy has not been explained because of the lack of experimental data. Recently, fission-fragment mass distributions (FFMDs) were measured for 237–240U, 239–242Np, and 241–244Pu populated in the excitation-energy range from 10 to 60 MeV by multinucleon transfer channels in the reaction 18O + 238U at the Japan Atomic Energy Agency tandem facility. A persistence of predominantly asymmetric FFMDs was observed up to the highest measured excitation energy for all the studied nuclides. To understand this behavior, we use the fluctuation-dissipation model and employ Langevin equations to obtain FFMDs and clarify multichance fission (MCF) effects. The MCF concept is well-known from studies of several fission observables, however FFMDs are almost not investigated. FFMDs are calculated for twenty-nine compound nuclides 231-234Th, 233-236Pa, 234-240U, 236-242Np and 238-244Pu with the excitation energy range from 15 to 55 MeV. The calculation results show generally good agreement with experimental data. It was shown that a reliable understanding of the observed FFMDs can be obtained only by invoking MCF. |
Saturday, October 27, 2018 10:45AM - 11:00AM |
LB.00008: Identification of Fission and Fragmentation Products from 238U at the NSCL Elaine Kwan, Oleg B. Tarasov, Alan M. Amthor, Thomas Baumann, Daniel Bazin, Peter C Bender, Michael D Bowry, Alexandra Gade, Thomas N. Ginter, Marc Hausmann, David J. Morrissey, Mauricio Portillo, Jorge Pereira, Andrew M Rogers, Jenna K. Smith, Chandana Sumithrarachchi, Andreas Stolz, Michael R Thoennessen, Antonio C.C. Villari The ability to resolve and identify particles up to atomic number Z~92 is an important goal for the Facility for Rare Isotope Beams. It is anticipated that a large fraction of experiments will use 238U to produce radioactive ion beams (RIB) at a similar energies relative to that currently employed at the National Superconducting Cyclotron Laboratory (NSCL). Projectile fragmentation serves as a powerful experimental tool to access exotic radioactive nuclei approaching the proton/neutron driplines and is the primary RIB production method at the NSCL. The A1900 fragment separator is the main apparatus used to select and purify radioactive beams. The ability to separate, resolve and identify fragments becomes more challenging with increasing Z. At intermediate energies, projectile-like fragments produced from 238U are the most challenging in part due to the many charge states that an isotope populates. To address this challenge, an experiment was conducted at the NSCL to identify nuclei produced from the fragmentation/fission of an E/A= 80 MeV/u 238U beam. The experimental technique and results from the first successful identification of fragments up to Z~93 will be presented.
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Saturday, October 27, 2018 11:00AM - 11:15AM |
LB.00009: Energy Dependence of Fission Product Yields from 235U, 238U and 239Pu with Monoenergetic Neutrons between thermal and 14 MeV Matthew Gooden, Anton P Tonchev, Jack A. Silano, Werner Tornow, Sean Finch, Todd Allen Bredeweg, Jerry Barnard Wilhelmy, Calvin R Howell, FNU Krishichayan Under a collaboration between TUNL-LANL-LLNL, a set of absolute fission product yield measurements has been performed. The energy dependence of a number of cumulative fission product yields (FPY) have been measured using quasi-monoenergetic neutron beams for three actinide targets, 235U, 238U and 239Pu, between thermal and 14.8 MeV. The FPYs were measured by a combination of fission counting using specially designed dual-fission chambers and γ-ray counting. γ-ray counting of the activation target was performed on well-shielded HPGe detectors over a period of two months post irradiation to properly identify fission products. Reported are absolute cumulative fission product yields for incident neutron energies of 0.5, 1.37, 2.4, 3.6, 4.6, 5.5, 7.5, 9 and 14.8 MeV. Preliminary results from thermal irradiations at the MIT research reactor will also be presented. |
Saturday, October 27, 2018 11:15AM - 11:30AM |
LB.00010: Acceleration induced neutron emission in heavy nuclei Nicolae Carjan The quantum version of the "water-tank problem" is applied to the independent-particle nuclear shell-model . The question to answer is: to what extend the acceleration of a nucleus influences its single particle states? From the classical analogue, one expects the nucleus to loose its less bound nucleons if the acceleration is high enough. Most probable this could happen to neutrons since, contrary to protons, they are not protected by a Coulomb barrier. |
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