Bulletin of the American Physical Society
2016 Fall Meeting of the APS Division of Nuclear Physics
Volume 61, Number 13
Thursday–Sunday, October 13–16, 2016; Vancouver, BC, Canada
Session HF: Nuclear Reactions: Heavy-Ions/Rare isotope Beams |
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Chair: Jutta Escher, Lawrence Livermore National Laboratory Room: Pavilion Ballroom A |
Saturday, October 15, 2016 8:30AM - 8:42AM |
HF.00001: A New Look at 29Al and 27Mg from the 18O $+$ 14C Reaction Samuel Tabor, Rutger Dungan, Alexander Volya, Vandana Tripathi, Brittany Abromeit, David Caussyn, Konstantinos Kravvaris, Rebeka Lubna, Pei-Luan Tai It was possible to compare moderately high-spin states in a nearby pair of odd proton and odd neutron s-d shell nuclei by observing proton-gamma-gamma or alpha-gamma-gamma coincidences, respectively, following the fusion of long-lived radioactive 14C with neutron-rich 18O at a beam energy of 40 MeV using the FSU gamma detector array with digital data acquisition. Eight new states were seen in 29Al, all of which decay directly or indirectly to the 9/2$+$ level, the highest previously known spin in 29Al. Some of the new states form a very likely yrast M1 decay sequence from (15/2$+)$ down to the 5/2$+$ ground state. The new states are relatively well described by pure s-d shell model calculations using the USDA interaction. By contrast the 4 new states found in 27Mg are divided between positive and negative parities reaching up to (13/2$+)$ and (11/2-). Radiative decays of neutron unbound states in 27Mg will be discussed. [Preview Abstract] |
Saturday, October 15, 2016 8:42AM - 8:54AM |
HF.00002: Validating (d,p$\gamma )$ as (n,$\gamma )$ surrogate in normal kinematics J.A. Cizewski, A. Ratkiewicz, J.T. Burke, R.J. Casperson, J.E. Escher, G. Potel, M. McCleskey Neutron capture through the s and r processes is responsible for almost all of the synthesis of the heavy elements. However, it is very difficult to measure (n,$\gamma )$ reactions on unstable nuclei especially when t$_{\mathrm{1/2}}$\textless 100 days. Given the importance of (n,$\gamma )$ reactions for understanding nucleosynthesis and applications in nuclear energy and national security, it is critical that a valid surrogate for (n,$\gamma )$ be developed. The 95Mo(d,p$\gamma )$ reaction was measured in normal kinematics at TAMU with the STARLiTER system [1] of segmented annular silicon strip detectors and clover HPGe detectors. Preliminary calculations of the formation of the compound nucleus and Hauser-Feshbach decay reproduce the measured 95Mo(n,$\gamma )$ cross sections[2]. By incorporating a calculation [3] of the transferred angular momentum in the (d,p) reaction as a function of excitation energy, preliminary analysis reproduces the observed (d,p) gamma-ray transition probabilities as a function of excitation energy. This preliminary analysis and those from using the observed gamma-ray transition probabilities to predict (n,$\gamma )$ cross sections will be presented. [1] R.J. Casperson et al., Phys. Rev. C 90, 034601 (2014) [2] A.R. De L. Musgrove et al., Nucl. Phys. A 270, 108 (1976) [3] G. Potel, F.M. Nunes, and I.J. Thompson, Phys. Rev C 92, 034611 (2015). [Preview Abstract] |
Saturday, October 15, 2016 8:54AM - 9:06AM |
HF.00003: Developing the (d,p$\gamma$) reaction as a surrogate for (n,$\gamma$) in inverse kinematics Alexandre Lepailleur, Travis Baugher, Jolie Cizewski, Andrew Ratkiewicz, David Walter, Steven Pain, Karl Smith, Heather Garland The r-process that proceeds via (n,$\gamma$) reactions on neutron-rich nuclei is responsible for the synthesis of about half of the elements heavier than iron. Because (n,$\gamma$) measurements on short-lived isotopes are not possible, the (d,p$\gamma$) reaction is being investigated as a surrogate for (n,$\gamma$). Of particular importance is validating a surrogate in inverse kinematics. Therefore, the $^{95}$Mo(d,p$\gamma$) reaction was measured in inverse kinematics with stable beams from ATLAS and CD$_{2}$ targets. Reaction protons were measured in coincidence with gamma rays with GODDESS $-$ Gammasphere ORRUBA: Dual Detectors for Experimental Structure Studies. The Oak Ridge Rutgers University Barrel Array (ORRUBA) of position-sensitive silicon strip detectors was augmented with annular arrays of segmented strip detectors at backward and forward angles, resulting in a high-angular coverage for light ejectiles. Preliminary results from the $^{95}$Mo(d,p$\gamma$) study will be presented. [Preview Abstract] |
Saturday, October 15, 2016 9:06AM - 9:18AM |
HF.00004: ABSTRACT WITHDRAWN |
Saturday, October 15, 2016 9:18AM - 9:30AM |
HF.00005: Tests of Multi-Nucleon Transfer Models Using Gamma-Ray Spectroscopy Kyle McCaleb, Ricardo Yanez, Walter Loveland It has been suggested that multi-nucleon transfer (MNT) reactions can be effective tools in synthesizing N=126 and n-rich heavy nuclei. We are engaged in a program to measure the yields of projectile-like fragments (PLFs) and target-like fragments (TLFs) in the interaction of 450 MeV $^{136}$Xe with $^{208}$Pb, 860 MeV $^{136}$Xe with $^{198}$Pt, and 1360 and 1700 MeV $^{204}$Hg with $^{208}$Pb. The use of in-beam, out of beam and post irradiation $\gamma$-ray spectroscopy using Gammasphere and single Ge detectors. We compare our results to the predictions of Zagrebaev and Greiner and semi-classical models such as GRAZING-F. We find the predictions of the GRAZING-F model represent, at best, the yields of the $\Delta$Z=$\pm$ 0,1,2 products while the Z-G predictions do a much better job of representing the yields of the large transfers. [Preview Abstract] |
Saturday, October 15, 2016 9:30AM - 9:42AM |
HF.00006: A Model for the Coalescence of Abraded Nucleons in Heavy Charged Particle Collisions Wouter de Wet, Lawrence Townsend, Charles Werneth, William Ford Accurate nuclear reaction models are required by the radiation transport codes used to predict the radiation field behind shielding in the space radiation environment. The resulting particle spectra and their corresponding biological response functions are used to estimate radiation risk to astronauts. Radiation transport codes use nuclear fragmentation models to describe the breakup of heavy charged particles in collisions with constituent nuclei of spacecraft and astronauts. The Relativistic Abrasion-Ablation and De-Excitation Fragmentation code, or RAADFRG, uses an abrasion-ablation reaction mechanism to calculate total and isotopic production cross sections of fragment species from a projectile nucleus. In this reaction mechanism, a fraction of nucleons, which sheared from the projectile nucleus during the abrasion step, coalesce to form various light ions. As with its predecessors, the Nuclear Fragmentation (NUCFRG) series, RAADFRG is being developed for implementation in NASA's deterministic High Charge (Z) and Energy radiation TRaNsport code, HZETRN. In this work, we derive the formalism used in RAADFRG to handle this process. Also, characterization of the model and its sensitivity to the coalescence radius parameterization are investigated. [Preview Abstract] |
Saturday, October 15, 2016 9:42AM - 9:54AM |
HF.00007: Constraining the Symmetry Energy Using Radioactive Ion Beams Krystin Stiefel, Zachary Kohley, Dave Morrissey, Michael Thoennessen Calculations from the constrained molecular dynamics (CoMD) model have shown that the N/Z ratio of the residue fragments and neutron emissions from projectile fragmentation reactions is sensitive to the form of the symmetry energy, a term in the nuclear equation of state. In order to constrain the symmetry energy using the N/Z ratio observable, an experiment was performed using the MoNA-LISA and Sweeper magnet arrangement at the NSCL. Beams of $^{\mathrm{30}}$S and $^{\mathrm{40}}$S impinged on $^{\mathrm{9}}$Be targets and the heavy residue fragments were measured in coincidence with fast neutrons. Comparison of the new experimental data with theoretical models should provide a constraint on the form of the symmetry energy. Some of the data from this experiment will be presented and discussed. [Preview Abstract] |
Saturday, October 15, 2016 9:54AM - 10:06AM |
HF.00008: Characterizing N-Z equilibration in nuclear reaction with sub-zeptosecond resolution Andrea Jedele, Alan McIntosh, Alis Manso Rodriguez, Lauren Heilborn, Larry May, Michael Youngs, Andrew Zarrella, Sherry Yennello The process of neutron-proton (N-Z) equilibration is governed by the symmetry energy component of the nuclear equation of state. The extent of equilibration is governed by the contact time and the gradient of the potential driving the equilibration. We have examined correlations between the largest two fragments of the PLF* (both isotopically identified) produced in collisions of 70Zn$+$70Zn, 64Zn$+$64Zn and 64Ni$+$64Ni at 35A MeV. Using the rotation angle between the fragments as a clock, we observe the N-Z composition of the fragments evolve from initially dissimilar to converging exponentially, consistent with first-order kinetics. The rate constant is 3 zs-1, corresponding to a mean equilibration time of 0.3 zs. This technique enables new insight into the nuclear equation of state. [Preview Abstract] |
Saturday, October 15, 2016 10:06AM - 10:18AM |
HF.00009: LCP correlations with improved resolution Lauren Heilborn, Alan McIntosh, Andrea Jedele, Mike Youngs, Andrew Zarrella, Sherry Yennello Nuclear Equation of State (EoS) is important to a fundamental understanding of nuclear matter. The density dependence of the asymmetry energy, the least constrained term in the EoS, is critical to describing exotic systems such as neutron-rich heavy-ion collisions and neutron stars. Correlation functions of particles emitted in heavy ion reactions (such a p-p correlations) have been predicted to be sensitive to the asymmetry energy. In order to measure correlation functions with high resolution, the Forward Array Using Silicon Technology (FAUST) at the Cyclotron Institute at Texas A{\&}M University has been recently re-commissioned with position-sensitive silicons as the delta-E detectors. A new method of position calibration for FAUST has been developed to take advantage of the 200um position resolution within each detector. Data has been collected from reactions of 40Ar$+$70Zn, 40Ar$+$58Fe and 40Ca$+$58Ni at 40 MeV/nucleon. The three systems allow correlation functions to be compared for systems with varying (N-Z)/A while holding constant either the total charge or the total mass. Light charged particles have been measured, and preliminary investigation of correlations from this campaign will be shown. Transport simulations will also be compared and presented. [Preview Abstract] |
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