Plastic Deformation in Laser-Induced Shock Compression of Monocrystalline Copper

Copper monocrystals were subjected to shock compression at pressures of 10–60 GPa by a short (3 ns initial) duration laser pulse. Transmission electron microscopy revealed features consistent with previous observations of shock-compressed copper, albeit at pulse durations in the µs regime. The results suggest that the defect structure is generated at the shock front. A mechanism for dislocation generation is presented, providing a realistic prediction of dislocation density as a function of pressure. The threshold stress for deformation twinning in shock compression is calculated from the constitutive equations for slip, twinning, and the Swegle-Grady relationship

Nuclear forces from chiral EFT: The unfinished business

In spite of the great progress we have seen in recent years in the derivation of nuclear forces from chiral effective field theory (EFT), some important issues are still unresolved. In this contribution, we discuss the open problems which have particular relevance for microscopic nuclear structure, namely, the proper renormalization of chiral nuclear potentials and sub-leading many-body forces.Comment: 16 pages, 3 figures; contribution to J. Phys. G, Special Issue, Focus Section: Open Problems in Nuclear Structur

Direct Observation of Martensitic Phase-Transformation Dynamics in Iron by 4D Single-Pulse Electron Microscopy

The in situ martensitic phase transformation of iron, a complex solid-state transition involving collective atomic displacement and interface movement, is studied in real time by means of four-dimensional (4D) electron microscopy. The iron nanofilm specimen is heated at a maximum rate of ∼10^(11) K/s by a single heating pulse, and the evolution of the phase transformation from body-centered cubic to face-centered cubic crystal structure is followed by means of single-pulse, selected-area diffraction and real-space imaging. Two distinct components are revealed in the evolution of the crystal structure. The first, on the nanosecond time scale, is a direct martensitic transformation, which proceeds in regions heated into the temperature range of stability of the fcc phase, 1185−1667 K. The second, on the microsecond time scale, represents an indirect process for the hottest central zone of laser heating, where the temperature is initially above 1667 K and cooling is the rate-determining step. The mechanism of the direct transformation involves two steps, that of (barrier-crossing) nucleation on the reported nanosecond time scale, followed by a rapid grain growth typically in ∼100 ps for 10 nm crystallites

Coulomb breakup of neutron-rich 29,30^{29,30}Na isotopes near the island of inversion

First results are reported on the ground state configurations of the neutron-rich $^{29,30}$Na isotopes, obtained via Coulomb dissociation (CD) measurements as a method of the direct probe. The invariant mass spectra of those nuclei have been obtained through measurement of the four-momentum of all decay products after Coulomb excitation on a $^{208}Pb$ target at energies of 400-430 MeV/nucleon using FRS-ALADIN-LAND setup at GSI, Darmstadt. Integrated Coulomb-dissociation cross-sections (CD) of 89 $(7)$ mb and 167 $(13)$ mb up to excitation energy of 10 MeV for one neutron removal from $^{29}$Na and $^{30}$Na respectively, have been extracted. The major part of one neutron removal, CD cross-sections of those nuclei populate core, in its' ground state. A comparison with the direct breakup model, suggests the predominant occupation of the valence neutron in the ground state of $^{29}$Na${(3/2^+)}$ and $^{30}$Na${(2^+)}$ is the $d$ orbital with small contribution in the $s$-orbital which are coupled with ground state of the core. The ground state configurations of these nuclei are as $^{28}$Na_{gs (1^+)\otimes\nu_{s,d} and $^{29}$Na$_{gs}(3/2^+)\otimes\nu_{ s,d}$, respectively. The ground state spin and parity of these nuclei, obtained from this experiment are in agreement with earlier reported values. The spectroscopic factors for the valence neutron occupying the $s$ and $d$ orbitals for these nuclei in the ground state have been extracted and reported for the first time. A comparison of the experimental findings with the shell model calculation using MCSM suggests a lower limit of around 4.3 MeV of the sd-pf shell gap in $^{30}$Na.Comment: Modified version of the manuscript is accepted for publication in Journal of Physics G, Jan., 201

Suppression of soft nuclear bremsstrahlung in proton-nucleus collisions

Photon energy spectra up to the kinematic limit have been measured in 190 MeV proton reactions with light and heavy nuclei to investigate the influence of the multiple-scattering process on the photon production. Relative to the predictions of models based on a quasi-free production mechanism a strong suppression of bremsstrahlung is observed in the low-energy region of the photon spectrum. We attribute this effect to the interference of photon amplitudes due to multiple scattering of nucleons in the nuclear medium.Comment: 12 pages, 3 figures, submitted to Phys. Rev. Let

Spectroscopy of η′\eta'-nucleus bound states at GSI and FAIR --- very preliminary results and future prospects ---

The possible existence of \eta'-nucleus bound states has been put forward through theoretical and experimental studies. It is strongly related to the \eta' mass at finite density, which is expected to be reduced because of the interplay between the $U_A(1)$ anomaly and partial restoration of chiral symmetry. The investigation of the C(p,d) reaction at GSI and FAIR, as well as an overview of the experimental program at GSI and future plans at FAIR are discussed.Comment: 7 pages, 3 figures; talk at the International Conference on Exotic Atoms and Related Topics (EXA2014), Vienna, Austria, 15-19 September 2014. in Hyperfine Interactions (2015

Living on the edge of stability, the limits of the nuclear landscape

A first-principles description of nuclear systems along the drip lines presents a substantial theoretical and computational challenge. In this paper, we discuss the nuclear theory roadmap, some of the key theoretical approaches, and present selected results with a focus on long isotopic chains. An important conclusion, which consistently emerges from these theoretical analyses, is that three-nucleon forces are crucial for both global nuclear properties and detailed nuclear structure, and that many-body correlations due to the coupling to the particle continuum are essential as one approaches particle drip lines. In the quest for a comprehensive nuclear theory, high performance computing plays a key role.Comment: Contribution to proceedings of Nobel Symposium 152: Physics with radioactive beams, June 2012, Gothenburg, Swede

Proton-deuteron radiative capture cross sections at intermediate energies

Differential cross sections of the reaction $p(d,^3{\rm He})\gamma$ have been measured at deuteron laboratory energies of 110, 133 and 180 MeV. The data were obtained with a coincidence setup measuring both the outgoing $^3$He and the photon. The data are compared with modern calculations including all possible meson-exchange currents and two- and three- nucleon forces in the potential. The data clearly show a preference for one of the models, although the shape of the angular distribution cannot be reproduced by any of the presented models.Comment: 6 pages, 6 figures, accepted for publication in EPJ

Nuclear Physics Experiments with Ion Storage Rings

In the last two decades a number of nuclear structure and astrophysics experiments were performed at heavy-ion storage rings employing unique experimental conditions offered by such machines. Furthermore, building on the experience gained at the two facilities presently in operation, several new storage ring projects were launched worldwide. This contribution is intended to provide a brief review of the fast growing field of nuclear structure and astrophysics research at storage rings.Comment: XVIth International Conference on Electro-Magnetic Isotope Separators and Techniques Related to their Applications, December 2--7, 2012 at Matsue, Japa

Search for the Lepton Flavor Violation Process J/ψ→eμJ/\psi \to e\mu at BESIII

We search for the lepton-flavor-violating decay of the $J/\psi$ into an electron and a muon using $(225.3\pm2.8)\times 10^{6}$ $J/\psi$ events collected with the BESIII detector at the BEPCII collider. Four candidate events are found in the signal region, consistent with background expectations. An upper limit on the branching fraction of $\mathcal{B}(J/\psi \to e\mu)< 1.5 \times 10^{-7}$ (90% C.L.) is obtained