Session J3: Nuclear Physics II

Clustering in Alpha Conjugate Nuclei Reactions

Reaction products from alpha conjugate nuclei systems of 35 MeV/u $^{40}$Ca $+ ^{40}$Ca, $^{40}$Ca $+$ $^{12}$C, $^{40}$Ca $ + ^{181}$Ta, $^{28}$Si $+ ^{28}$Si, $^{28}$Si $+$ $^{12}$C and $^{28}$Si $ + ^{181}$Ta are presented. Alpha particles and alpha conjugate fragments emitted in these reactions are observed with large probabilities. Alpha particles appear to be emitted from a neck like source. Reactions are compared to model calculations and interesting similarities and differences are discussed.   

Equilibration between projectile and target in heavy-ion nuclear collisions

Understanding equilibration in heavy-ion collisions is of significant importance to nuclear physics. Since nuclei are composed of neutrons and protons, the difference in the number of neutrons and protons, or asymmetry, can be used to study equilibration processes in the nucleus. We can study the equilibration occurring between two nuclei with differing asymmetry compositions in Fermi energy heavy-ion collisions by using the ratios of the yields of fragments, as well as the reconstructed asymmetry of quasi-projectiles. Studying the asymmetry difference of fragments produced in reactions of Zn and Ni at 35MeV/nucleon will allow us to examine the equilibration that occurs in these systems.   

Nucleation and cluster formation in low-density nucleonic matter: A mechanism for ternary fission

Ternary fission yields from the reaction of 241Pu(nth,f) are studied in the context of nucleation moderated equilibrium. The temperature, density, proton fraction and fission time required to fit the experimental data will be discussed. This model provides natural explanations of some known problematic features of ternary fragment yield distributions. In addition, the systematic behavior of this model across several fissioning nuclei will be presented.   

Measurement of the plasma astrophysical S factor for the $^{3}$He(d,~p)$^{4}$He reaction in exploding molecular clusters

The plasma astrophysical S factor for the $^{3}$He(d,~p)$^{4}$He fusion reaction was measured for the first time at temperatures of few keV, using the interaction of intense ultrafast laser pulses with molecular deuterium clusters mixed with $^{3}$He atoms. Different proportions of D$_{2}$ and $^{3}$He or CD$_{4}$ and $^{3}$He were mixed in the gas jet target in order to allow the measurement of the cross-section for the $^{3}$He(d,~p)$^{4}$He reaction. The yield of 14.7 MeV protons from the $^{3}$He(d,~p)$^{4}$He reaction was measured in order to extract the astrophysical $S$ factor at low energies. Results of the experiment performed at the Center for High Energy Density Science at The University of Texas at Austin will be presented [PRL, 111, 082502].   

A Static Potential from $Q\bar{Q}$ Free Energy Lattice QCD Data

A long-standing problem in the physics of the QGP is the definition of the in-medium potential between two heavy quarks $Q\bar{Q}$. We develop a formalism that enable us to obtain a potential from $Q\bar{Q}$ free energy lattice QCD data. The resulting potential lies significantly above the $Q\bar{Q}$ free energy and more closely resembling the internal energy. This potential is characterized by a significant long-distance contribution from the remains of the confining force. This long range potential provides more binding than free energy and generates a larger transport coefficient. The set-up in this paper gives insights into the long-standing problem of finding the QCD force in medium.   

Hot Nuclear Correction to J/psi suppression in dAu collision at 200GeV

The production of J/$\psi$ mesons in high-energy collisions of heavy nuclei is believed to be a sensitive probe of the possible formation of a new state of matter in these collisions, the quark-gluon plasma (QGP). The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Lab affords us with a lot of experimental information on J/$\psi$ production in different collision systems. The dAu collisions usually provide us information on so-called cold nuclear matter effects. However, recently it has been conjectured that also in these small systems a hot thermal medium could form. In the present work we theoretically investigate whether such a hypothesis can be consistent with J/$\psi$ and $\psi'$ suppression data. To do so, we adapt our charmonium transport approach, developed for AuAu collisions, to the smaller dAu system. In this way we extend our cold matter theoretical result to include hot medium corrections, and compare the results to J/$\psi$ and $\psi$' data from the PHENIX collaboration. We find indications that the data are better described when including hot nuclear matter effects. This has the potential to better quantify the relevant mechanisms in heavy systems, and thus provide deeper insights into the physics of the quark-gluon plasma.   

Relativistic Viscous Hydrodynamics for Nuclear Collisions and Applications to Thermalizing Color Glass

There have been early theoretical arguments that collisions of nuclei at large energies can be described by relativistic hydrodynamics. The experimental heavy ion programs at RHIC and LHC have finally provided strong evidence that quark gluon plasma in those collisions, behaves like a liquid and cools and expands hydrodynamically. In recent years precision hydrodynamic calculations have become key tools for successful calculations of hard probes, heavy quarks, electromagnetic probes etc., in heavy ion collisions. We adopted the flux based algorithm called SHASTA to solve the relativistic hydrodynamical equations. The hydrodynamical equations are precisely the energy momentum conservation $\partial_{\mu} T^{\mu\nu}=0$, continuity equations for other conserved currents, and equations for the time evolution of shear and bulk stress. To test the code we will present results for setups with analytic solutions, e.g. the Riemann shock problem and the boost-invariant Bjorken expansion. We find that our code performs well. Then we apply it to the time evolution of nuclear collisions using initial conditions from thermalizing gluon fields (color glass) recently obtained by Chen et al. We discuss implications of the initial flow fields found in that work on experimental observables.   

Analyzing Data from Beam Halo at RHIC

The QGP phase transition point is beneath 7.7 GeV. RHIC is incapable of colliding two accelerating ions at such low energy levels. Therefore fixed target collisions are studied to learn more about the QGP phase transition point. A fixed target collision means that accelerating heavy ions from the beam collide with a non-moving target, lowering the momentum exchanged and lowering the energy level of the experiment. A gold plate was installed along the beam pipe at RHIC for the purpose of studying fixed target collisions between the beam halo and the gold plate. However, all previous collisions at RHIC have been between gold ions. Therefore gold must exist within the beam halo if collisions between the beam halo and a fixed gold target along the beam pipe are to provide useful data comparable to previous experiments. The main goal of the project was to determine whether gold existed within the beam halo using Glauber Monte Carlo methods. How the Glauber Model identifies type of ions in collisions will be explained, and data taken from a Single Beam Fixed Target test run at RHIC will be examined. The conclusions reached so far indicate that heavy ions exist within the halo, and the ongoing task is to use Glauber Monte Carlo methods to determine definitively if they are gold ions.   

Accelerator Driven Systems: a human-scale solution for responsible nuclear energy

Conventional fission creates dangerous and long-lived transuranic waste that needs to be stored for millions of years. Accelerator driven systems (ADS) provide an option to instead destroy this dangerous waste and extract additional energy from these reserves, extending the non-recyclable fuel horizon by an order of magnitude. A plan for molten salt-based ADS in the US will be presented, along with design for the key components.   

Superconducting Cable-in-Conduit: New Basis for Practical Applications

A new technology for superconducting cable-in-conduit is being developed at Texas A\&M University. A single layer of round-wire superconductors is cabled onto a thin-wall metal spring tube, then sheathed in a high-strength tube. The CIC cable integrates the mechanical support, cryogenic cooling, quench protection within the cable so it can be fabricated into windings for magnets, motors, generators, and energy storage applications with far less complication than any previous conductor. Three applications will be summarized: a 4.5 T NbTi dipole for a 100 TeV hadron collider, a 3 T solenoid for superconducting magnetic energy storage, and a 3 T transport gantry for proton- and ion-beam cancer therapy.