Radiative strength functions (RSFs) for the ${}^{56,57}\mathrm{F}\mathrm{e}$ nuclei below the separation energy are obtained from the ${}^{57}\mathrm{F}\mathrm{e}({}^3\mathrm{H}\mathrm{e},\alpha \gamma ){}^{56}\mathrm{F}\mathrm{e}$ and ${}^{57}\mathrm{F}\mathrm{e}({}^3\mathrm{H}\mathrm{e},{}^3\mathrm{H}\mathrm{e}^{\prime }\gamma ){}^{57}\mathrm{F}\mathrm{e}$ reactions, respectively. An enhancement of more than a factor of 10 over common theoretical models of the soft ($E_{\gamma }\lesssim 2\mathrm{M}\mathrm{e}\mathrm{V}$) RSF for transitions in the quasicontinuum (several MeV above the yrast line) is observed. Two-step cascade intensities with soft primary transitions from the ${}^{56}\mathrm{F}\mathrm{e}(n,2\gamma ){}^{57}\mathrm{F}\mathrm{e}$ reaction confirm the enhancement.

We have performed precision laser spectroscopy on individual ${}^6\mathrm{H}\mathrm{e}$ ($t_{1/2}=0.8\mathrm{s}$) atoms confined and cooled in a magneto-optical trap, and measured the isotope shift between ${}^6\mathrm{H}\mathrm{e}$ and ${}^4\mathrm{H}\mathrm{e}$ to be $43194.772\pm 0.056\mathrm{M}\mathrm{H}\mathrm{z}$ for the $2^3{S}_1-3^3{P}_2$ transition. Based on this measurement and atomic theory, the nuclear charge radius of ${}^6\mathrm{H}\mathrm{e}$ is determined for the first time in a method independent of nuclear models to be $2.054\pm 0.014\mathrm{f}\mathrm{m}$. The result is compared with the values predicted by a number of nuclear structure calculations and tests their ability to characterize this loosely bound halo nucleus.

We formulate the quark meson coupling model as a many-body effective Hamiltonian. This leads naturally to the appearance of many-body forces. We investigate the zero range limit of the model and compare its Hartree-Fock Hamiltonian to that corresponding to the Skyrme effective force. By fixing the three parameters of the model to reproduce the binding and symmetry energy of nuclear matter, we find that it allows a very satisfactory interpretation of the Skyrme force.

We use a single $j$-shell model with random two-body interactions to derive closed expressions for the distribution of and the correlations between spectral widths of different spins. This task is facilitated by introducing two-body operators whose squared spectral widths sum up to the squared spectral width of the random Hamiltonian. The spin-0 width is characterized by a relatively large average value and small fluctuations, while the width of maximum spin has the largest average and the largest fluctuations. The approximate proportionality between widths and spectral radii explains the preponderance of spin-0 ground states.

New, high-precision measurements of the ${}^3\mathrm{H}\mathrm{e}(e,e^{\prime }p)$ reaction using the A1 Collaboration spectrometers at the Mainz microtron MAMI are presented. These were performed in antiparallel kinematics at energy transfers below the quasielastic peak, and at a central momentum transfer of 685 MeV/c. Cross sections and distorted momentum distributions were extracted and compared to theoretical predictions and existing data. The longitudinal and transverse behavior of the cross section was also studied. Sizable differences in the cross-section behavior from theoretical predictions based on the plane wave impulse approximation were observed in both the two- and three-body breakup channels. Full Faddeev-type calculations account for some of the observed excess cross-section, but significant differences remain.

Breakup densities of hot ${}^{197}\mathrm{A}\mathrm{u}$-like residues have been deduced from the systematic trends of Coulomb parameters required to fit intermediate-mass-fragment kinetic-energy spectra. The results indicate emission from nuclei near normal nuclear density below an excitation energy $E^{*}/A\lesssim 2\mathrm{M}\mathrm{e}\mathrm{V}$, followed by a gradual decrease to a near-constant value of $\rho /{\rho }_0\sim 0.3$ for $E^{*}/A\gtrsim 5\mathrm{M}\mathrm{e}\mathrm{V}$. Temperatures derived from these data with a density-dependent Fermi-gas model yield a nuclear caloric curve that is generally consistent with those derived from isotope ratios.

The caloric curve for mononuclear configurations is studied with a schematic model. We investigate the dependence of the entropy on the density and effective-mass profiles. In finite nuclei, a plateau in the caloric curve is a consequence of decreasing density and the destruction of correlations rather than an indication of phase coexistence. The mononuclear regime is metastable with respect to binary fission at low excitation energy and with respect to multifragmentation at high excitation. The statistical framework presented here is suitable to treat scenarios where experimental conditions are set to favor a population of highly excited mononuclei.

Evidence is presented to show that a group of nuclei, spanning a range of structures, corresponds to a previously proposed isolated region of regular behavior between vibrational and rotational structures that was never before observed empirically. Nuclei predicted to show such regular spectra correspond to Hamiltonian parameters that lie amidst those giving more chaotic spectra. We identify a key observable that has a one-to-one correspondence to this arc of regularity and which therefore provides both an empirical signature for it and a clue to its underlying nature.

Differential cross sections for elastic scattering of 21.5 MeV positive and negative pions by Si, Ca, Ni, and Zr have been measured as part of a study of the pion-nucleus potential across the threshold. The “anomalous” repulsion in the $s$-wave term was observed, as is the case with pionic atoms. The extra repulsion can be accounted for by a chiral-motivated model where the pion decay constant is modified in the medium. Unlike in pionic atoms, the anomaly cannot be removed by merely introducing an empirical on-shell energy dependence.

The apparent persistence of symmetry in the face of strong symmetry-breaking interactions is examined in a many-boson model. The model exhibits a transition between two phases associated with U(5) and O(6) symmetries, respectively, as the value of a control parameter progresses from 0 to 1. The remarkable fact is that, in spite of strong mixing of the symmetries for intermediate values of the control parameter, the model continues to exhibit the characteristics of its closest symmetry limit for all but a relatively narrow transition region that becomes progressively narrower as the boson number increases. This phenomenon is explained in terms of quasidynamical symmetry.

Fine structure in the energy region of the isoscalar giant quadrupole resonance in nuclei is observed in high-resolution proton scattering experiments at iThemba LABS over a wide mass range. A novel method based on wavelet transforms is introduced for the extraction of scales characterizing the fine structure. A comparison with microscopic model calculations including two-particle two-hole ($2\mathrm{p}2\mathrm{h}$) degrees of freedom identifies the coupling to surface vibrations as the main source of the observed scales. A generic pattern is also found for the stochastic coupling to the background of the more complex states.

We estimate the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer through the scattering off a parton in the proton. We relate the two-photon exchange amplitude to the generalized parton distributions which appear in hard exclusive processes. We find that when taking the polarization transfer determinations of the form factors as input, adding in the 2-photon correction does reproduce the Rosenbluth cross sections.

We have measured three axial polarization observables in $\overrightarrow{d}\overrightarrow{p}$ breakup with a polarized 270 MeV deuteron beam on a polarized proton target. Axial observables are zero by parity conservation in elastic scattering but can be easily observed in the breakup channel at the present energy. Based on a symmetry argument, the sensitivity of these observables to the three-nucleon force might be enhanced. Calculations without three-nucleon force are in fair agreement with our measurement, indicating that the expected sensitivity of axial observables to the three-nucleon force is not confirmed. Including a three-nucleon force in the calculation does not improve the agreement with the data.

The decay rate of ${}^{\mathrm{7}}\mathrm{B}\mathrm{e}$ electron capture was measured in ${\mathrm{C}}_{60}$ and Be metal with a reference method. The half-life of ${}^{\mathrm{7}}\mathrm{B}\mathrm{e}$ endohedral ${\mathrm{C}}_{\mathrm{60}}$ (${}^{\mathrm{7}}\mathrm{B}\mathrm{e}\mathrm{@}{\mathrm{C}}_{\mathrm{60}}$) and ${}^{\mathrm{7}}\mathrm{B}\mathrm{e}$ in Be metal (Be metal (${}^{\mathrm{7}}\mathrm{B}\mathrm{e}$)) is found to be $52.68\pm 0.05$ and $53.12\pm 0.05$ days, respectively. This amounts to a $0.83\%$ difference in electron-capture decay half-life between ${}^{\mathrm{7}}\mathrm{B}\mathrm{e}@{\mathrm{C}}_{60}$ and Be metal (${}^{\mathrm{7}}\mathrm{B}\mathrm{e}$). Our result is a reflection of the different electron wave functions for ${}^{\mathrm{7}}\mathrm{B}\mathrm{e}@{\mathrm{C}}_{60}$ inside ${\mathrm{C}}_{\mathrm{60}}$ compared to the situation when ${}^{\mathrm{7}}\mathrm{B}\mathrm{e}$ is in a Be metal.

We study classical trajectories corresponding to $L=0$ vibrations in the geometric collective model of nuclei with stable axially symmetric quadrupole deformations. It is shown that with increasing stability against the onset of triaxiality the dynamics passes between a fully regular and semiregular limiting regime. In the transitional region, an interplay of chaotic and regular motions results in complex oscillatory dependence of the regular phase space on the Hamiltonian parameter and energy.

Classical mechanics and time dependent Hartree-Fock (TDHF) calculations of heavy ions collisions are performed to study the rotation of a deformed nucleus in the Coulomb field of its partner. This reorientation is shown to be independent of the charges and relative energy of the partners. It only depends upon the deformations and inertias. TDHF calculations predict an increase by 30% of the induced rotation due to quantum effects while the nuclear contribution seems negligible. This reorientation modifies strongly the fusion cross section around the barrier for light deformed nuclei on heavy collision partners. For such nuclei a hindrance of the sub-barrier fusion is predicted.

Transverse momentum spectra and rapidity densities, $dN/dy$, of protons, antiprotons, and net protons ($p-\overline{p}$) from central (0%–5%) $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$ were measured with the BRAHMS experiment within the rapidity range $0\le y\le 3$. The proton and antiproton $dN/dy$ decrease from midrapidity to $y=3$. The net-proton yield is roughly constant for $y<1$ at $dN/dy\sim 7$, and increases to $dN/dy\sim 12$ at $y\sim 3$. The data show that collisions at this energy exhibit a high degree of transparency and that the linear scaling of rapidity loss with rapidity observed at lower energies is broken. The energy loss per participant nucleon is estimated to be $73\pm 6\mathrm{G}\mathrm{e}\mathrm{V}$.

The beta-neutrino correlation coefficient, , in is inferred from detecting the and low-energy recoil daughter nucleus. is produced at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory and 800 000 atoms are maintained in a magneto-optical trap. From the measured time of flight of recoil ions in the presence of a drift electric field, we find . There may be a dependence on the trapped atom population. This and other systematic uncertainties are discussed.

Event-by-event fluctuations of the average transverse momentum of produced particles near midrapidity have been measured by the PHENIX Collaboration in $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$ $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$, and $p+p$ collisions at the Relativistic Heavy Ion Collider. The fluctuations are observed to be in excess of the expectation for statistically independent particle emission for all centralities. The excess fluctuations exhibit a dependence on both the centrality of the collision and on the $p_T$ range over which the average is calculated. Both the centrality and $p_T$ dependence can be well reproduced by a simulation of random particle production with the addition of contributions from hard-scattering processes.

The Cronin effect that refers to the enhancement of hadron spectra at intermediate $p_T$ with increasing $A$ in $pA$ collisions is traditionally explained in terms of the broadening of the parton transverse momentum in the initial state. We show that recent data on the nuclear modification factor at $\eta =0$ for $d+\mathrm{A}\mathrm{u}$ collisions can be understood in terms of the recombination of soft and shower partons in the final state. It is the centrality dependence of the soft parton density that leads to the Cronin effect.