The pion rescattering operator for pion production, derived recently in time-ordered perturbation theory, is compared with the one following from the simple S-matrix construction. We show that this construction is equivalent to the on-shell approximation introduced in previous articles. For a realistic NN interaction, the S-matrix approach, and its simplified fixed threshold-kinematics version, work well near threshold.

The low-lying isovector dipole strengths in the neutron-rich nuclei ${}^{26}\mathrm{Ne}$ and ${}^{28}\mathrm{Ne}$ are investigated in the quasiparticle relativistic random phase approximation. Nuclear ground-state properties are calculated in an extended relativistic mean field theory plus Bardeen-Cooper-Schrieffer (BCS) method where the contribution of the resonant continuum to pairing correlations is properly treated. Numerical calculations are tested in the case of isovector dipole and isoscalar quadrupole modes in the neutron-rich nucleus ${}^{22}\mathrm{O}$. It is found that in the present calculation, low-lying isovector dipole strengths at $E_x<10\mathrm{MeV}$ in nuclei ${}^{26}\mathrm{Ne}$ and ${}^{26}\mathrm{Ne}$ exhaust about 4.9% and 5.8% of the Thomas-Reiche-Kuhn dipole sum rule, respectively. The centroid energy of the low-lying dipole excitation is located at 8.3 MeV in ${}^{26}\mathrm{Ne}$ and 7.9 MeV in ${}^{28}\mathrm{Ne}$.

We present transverse momentum and rapidity spectra of charged pions in central $\mathrm{Ru}+\mathrm{Ru}$ collisions at $400A$ and $1528A\mathrm{MeV}$. The data exhibit enhanced production at low transverse momenta compared to expectations from a thermal model that includes the decay of $\Delta (1232)$ resonances and thermal pions. Modifications of the $\Delta$ spectral function and the Coulomb interaction are necessary to describe the detailed shape of the transverse momentum spectra. Within the framework of the thermal model, the freeze-out radii of pions are similar at both beam energies. The isospin quantum molecular dynamics model reproduces the shapes of the transverse momentum and rapidity spectra of pions, but the predicted absolute yields are larger than in the measurements, especially at lower beam energy.

Electric charge correlations were studied for p+p, C+C, Si+Si, and centrality selected Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=17.2$ GeV with the NA49 large acceptance detector at the CERN SPS. In particular, long-range pseudorapidity correlations of oppositely charged particles were measured using the balance function method. The width of the balance function decreases with increasing system size and centrality of the reactions. This decrease could be related to an increasing delay of hadronization in central Pb+Pb collisions.

We consider bremsstrahlung energy loss for hard partons traversing a quark-gluon plasma (QCP). Accounting correctly for the probabilistic nature of the energy loss, and making a leading-order-accurate treatment of bremsstrahlung, we find that the suppression of the spectrum is nearly flat, with the most suppression at energies $E~30T$ (where T is the QGP temperature), without the need for initial state effects such as shadowing and the Cronin effect. This flat pattern should also be observed at the LHC (Large Hadron Collider) out to an energy of $~30\mathrm{GeV}$.

A systematic and comprehensive study of the decay half-lives of nuclei appearing in the observed α-decay chains of superheavy elements $(Z=108-118)$ is presented. The calculation proceeds in three steps. First, the relativistic mean-field equations are solved in the axially symmetric deformed oscillator basis to obtain ground-state properties such as binding energies, radii, deformations, and densities. The results are in good agreement with the available experimental systematics, as expected. Next, the calculated densities are used in the double-folding prescription to determine the interaction potentials for the α-daughter systems. Finally, these potentials, along with calculated and experimental Q values, are used in the WKB approximation to estimate the decay half-lives. The calculated half-lives, which sensitively depend on Q values, qualitatively reproduce the experiment.

The dependence of effective pair gap on weakly bound neutron orbits is studied in deformed nuclei in comparison with that in spherical nuclei, solving the Hartree-Fock-Bogoliubov equation in a simplified model in coordinate space with the correct asymptotic boundary conditions. In spherical nuclei the effective pair gap of $s_{1/2}$ neutrons decreases to zero in the limit that the corresponding Hartree-Fock one-particle energy approaches zero. In the same limit, the effective pair gap of ${\Omega }^{\pi }=1/2^{+}$ neutrons in deformed nuclei becomes very small when the wave functions of ${\Omega }^{\pi }=1/2^{+}$ orbits contain an appreciable amount of $s_{1/2}$ components, even if a considerable amount of larger-$\ell$ components remains in the wave functions. Then, the one-particle excitation spectra of deformed even-even neutron-drip-line nuclei, in which an ${\Omega }^{\pi }=1/2^{+}$ level is weakly bound, can start at much lower energy than twice the average pair gap in the presence of many-body pair correlation.

The g factors of the short-lived $2_1^{+},4_1^{+}$, and $3_1^{-}$ states in ${}^{64}\mathrm{Zn}$ and the $2_1^{+},4_1^{+},2_2^{+}$, and $3_1^{-}$ states in ${}^{68}\mathrm{Zn}$ have been measured using the combined technique of projectile Coulomb excitation in inverse kinematics and transient magnetic fields. In addition, $B(E2)$'s have been deduced from remeasured lifetimes of several excited states employing the Doppler-shift-attenuation method. Whereas the present data for the $2_1^{+}$ states agree very well with our previous results, the g factors of the other states have been determined for the first time. All experimental data were compared with results from large-scale shell model calculations based on proton and neutron configurations in the $\mathrm{fp}$ and $\mathrm{fpg}$ model spaces with ${}^{40}\mathrm{Ca}$ and ${}^{56}\mathrm{Ni}$ as inert cores, respectively.

The 100% polarized photon beam at the high intensity $\gamma$ ray source $(\text{HI}\gamma \text{S})$ at Duke University has been used to determine the parity of six dipole excitations between 2.9 and 3.6 MeV in the deformed nuclei ${}^{172,174}\mathrm{Yb}$ in photon scattering $(\overrightarrow{\gamma },{\gamma }^{\text{'}})$ experiments. The measured parities are compared with previous assignments based on the K quantum number that had been assigned in nuclear resonance fluorescence (NRF) experiments by using the Alaga rules. A systematic survey of the relation between $\gamma$-decay branching ratios and parity quantum numbers is given for the rare earth nuclei.

The degree to which the $(p,\gamma )$ and $(p,\alpha )$ reactions destroy ${}^{18}\mathrm{F}$ at temperatures $(1-4)\times {10}^8\mathrm{K}$ is important for understanding the synthesis of nuclei in nova explosions and for using the long-lived radionuclide ${}^{18}\mathrm{F}$, a target of γ-ray astronomy, as a diagnostic of nova mechanisms. The reactions are dominated by low-lying proton resonances near the ${}^{18}\mathrm{F}+p$ threshold $(E_x=6.411\mathrm{MeV}$ in ${}^{19}\mathrm{Ne})$. To gain further information about these resonances, we used a radioactive ${}^{18}\mathrm{F}$ beam from the Holifield Radioactive Ion Beam Facility to selectively populate corresponding mirror states in ${}^{19}\mathrm{F}$ via the inverse ${}^2\mathrm{H}({}^{18}\mathrm{F},p){}^{19}\mathrm{F}$ neutron transfer reaction. Neutron spectroscopic factors were measured for states in ${}^{19}\mathrm{F}$ in the excitation energy range $0–9\mathrm{MeV}$. Widths for corresponding proton resonances in ${}^{19}\mathrm{Ne}$ were calculated using a Woods-Saxon potential. The results imply significantly lower ${}^{18}\mathrm{F}$$(p,\gamma )$${}^{19}\mathrm{Ne}$ and ${}^{18}\mathrm{F}$$(p,\alpha )$${}^{15}\mathrm{O}$ reaction rates than reported previously, thereby increasing the prospect of observing the $511\mathrm{keV}$ annihilation radiation associated with the decay of ${}^{18}\mathrm{F}$ in the ashes ejected from novae.

We employed the Skyrme-Hartree-Fock model to investigate the density distributions and their dependence on nuclear shapes and isospins in the superheavy mass region. Different Skyrme forces were used for the calculations with a special comparison to the experimental data in ${}^{208}\mathrm{Pb}$. The ground-state deformations, nuclear radii, neutron-skin thicknesses and α-decay energies were also calculated. Density distributions were discussed with the calculations of single-particle wave functions and shell fillings. Calculations show that deformations have considerable effects on the density distributions, with a detailed discussion on the ${}^{292}120$ nucleus. Earlier predictions of remarkably low central density are not supported when deformation is allowed for.

We study the possibility of producing a new kind of nuclear system that in addition to ordinary nucleons contains a few antibaryons $(\stackrel{-}{B}=\stackrel{-}{p},\stackrel{-}{\Lambda }$, etc.). The properties of such systems are described within the relativistic mean-field model by employing G-parity transformed interactions for antibaryons. Calculations are first done for infinite systems and then for finite nuclei from ${}^4\mathrm{He}$ to ${}^{208}\mathrm{Pb}$. It is demonstrated that the presence of a real antibaryon leads to a strong rearrangement of a target nucleus, resulting in a significant increase of its binding energy and local compression. Noticeable effects remain even after the antibaryon coupling constants are reduced by a factor of 3–4 compared to G-parity motivated values. We have performed detailed calculations of the antibaryon annihilation rates in the nuclear environment by applying a kinetic approach. It is shown that owing to significant reduction of the reaction Q values, the in-medium annihilation rates should be strongly suppressed, leading to relatively long-lived antibaryon-nucleus systems. Multinucleon annihilation channels are analyzed too. We have also estimated formation probabilities of bound $\stackrel{-}{B}+A$ systems in $\stackrel{-}{p}A$ reactions and have found that their observation will be feasible at the future GSI antiproton facility. Several observable signatures are proposed. The possibility of producing cold multi-quark-antiquark clusters is discussed.

Schiff moments were calculated for a set of nuclei with full account of core polarization effects. A finite range P- and T-violating weak nucleon-nucleon interaction has been used in the calculations. Although in the absence of core polarization the Schiff moment depends on one combination of the weak interaction constants, in the presence of core polarization the Schiff moment depends on all three constants separately. The dominant contribution comes from isovector, $\Delta T=1$, part of the weak interaction. The effects of core polarization were found to have in general a large effect on the Schiff moments.

We propose a scheme for extracting an effective three-body interaction originating from a two-nucleon interaction. This is based on the $\stackrel{\wedge }{Q}$-box method of Kuo and collaborators, where folded diagrams are obtained by differentiating a sum of nonfolded diagrams with respect to the starting energy. To gain insight we have studied several examples using the Lipkin model where the perturbative approach can be compared with exact results. Numerically the three-body interactions can be significant and in a matrix example good accuracy was not obtained simultaneously for both eigenvalues with two-body interactions alone.

Applying thermofield dynamics, we reformulate the exact quantum number projection in the finite-temperature Hartree-Fock-Bogoliubov theory. Explicit formulas are derived for the simultaneous projection of particle number and angular momentum, in parallel to the zero-temperature case. We also propose a practical method for the variation-after-projection calculation, by approximating entropy consistently with the Peierls inequality. Using quantum number projection in finite-temperature mean-field theory will be useful for studying the effects of quantum fluctuations associated with the conservation laws on thermal properties of nuclei.

Within the constrained Hartree-Fock (CHF) theory, an analytic condition is derived to estimate whether a concept of the self-consistent mean field is realized in the level repulsive region. The derived condition states that an iterative calculation of the CHF equation does not converge when the quantum fluctuations coming from two-body residual interaction and quadrupole deformation become larger than a single-particle energy difference between two avoided crossing orbits. By means of numerical calculation, it is shown that the analytic condition works well for a realistic case.

The collective dynamics of low-energy fission in ${}^{238}\mathrm{U}$ is described within a time-dependent formalism based on the Gaussian overlap approximation of the time-dependent generator coordinate method. The intrinsic deformed configurations of the nucleus are determined from the self-consistent Hartree-Fock-Bogoliubov procedure employing the effective force D1S with constraints on the quadrupole and octupole moments. Fragment kinetic energy and mass distributions are calculated and compared with experimental evaluations. The effect of the collective dynamics along the fission paths and the influence of initial conditions on these distributions are analyzed and discussed.

Superdeformed excitations in ${}^{198}\mathrm{Po}$ were studied using the ${}^{174}\mathrm{Yb}({}^{29}\mathrm{Si},5\mathrm{n})$ reaction and γ-ray spectroscopy with Gammasphere. Energy-spin entry distributions for populating normal (ND) and superdeformed (SD) excitations were extracted by gating on discrete ND and SD transitions, respectively. Information on the SD excitation energy, SD well depth, and fission barrier in ${}^{198}\mathrm{Po}$ was deduced.

Quantum mechanics super symmetry (SuSy) provides a general framework for studies using phenomenological potentials for nucleons (or clusters) interacting with a core. The SuSy potentials result from the transformation of the mean-field potential to account for the Pauli blocking of the core orbitals. In this article, we discuss how other potentials (such as external probes or residual interactions between the valence nucleons) are affected by the SuSy transformation. We illustrate how the SuSy transformations induce off-diagonal terms in coordinate space that play an essential role on the induced transition probabilities for two examples: electric operators and Gaussian external fields. We show that excitation operators, doorway states, strength, and sum rules are all modified.