The present paper establishes a link between pairing correlations in rotating nuclei and collective vortical modes in the intrinsic frame. We show that the latter can be embodied by a simple Chandrasekhar S-type coupling between rotational and intrinsic vortical collective modes. This results from a comparison between the solutions of microscopic calculations within the Hartree-Fock-Bogoliubov (HFB) and HF Routhian formalisms. The HF Routhian solutions are constrained to have the same Kelvin circulation expectation value as the HFB ones. It is shown in several mass regions, pairing regimes, and for various spin values that this procedure yields moments of inertia, angular velocities, and current distributions which are very similar within both formalisms. We finally present perspectives for further studies.

An effective model with constituent quarks as fundamental degrees of freedom is used to predict the relative strangeness production pattern in both high energy elementary and heavy ion collisions. The basic picture is that of the statistical hadronization model, with hadronizing color-singlet clusters assumed to be at full chemical equilibrium at constituent quark level. Thus, by assuming that at least the ratio between strange and non-strange constituent quarks survives in the final hadrons, the apparent undersaturation of strange particle phase space observed in the data can be accounted for. In this framework, the enhancement of relative strangeness production in heavy ion collisions in comparison with elementary collisions is mainly owing to the excess of initial nonstrange matter over antimatter and the so-called canonical suppression, namely, the constraint of exact color and flavor conservation over small volumes.

We present a study of the $\mathrm{NN}$ system above pion threshold fully based on a constituent quark model. The calculation is performed in the framework of the coupled-channel method. A $\pi N\Delta$ vertex has been derived from the basic $\pi \mathrm{qq}$ vertex and it is probed in the $P_{33}\pi N$ partial wave. Taking into account the fact that this is a parameter-free calculation, the phase shifts and inelasticities are reasonably well reproduced.

We study the even-even U and Pu nuclei in the framework of the $\mathrm{spdf}$ interacting boson model. Analysis of the systematics of positive and negative parity bands, together with the $E1,$ $E2,$ and $E3\mathrm{}$ transitions, suggests that the properties of low-lying states can be understood without the introduction of stable octupole deformation. Double octupole phonon characteristics are also identified in certain low-lying $0^{+}$ excited states in U and Pu.

We propose a method of spin-parity assignments in decay spectroscopy. Its feasibility was tested for the $\beta$-delayed neutron decay of spin-polarized ${}^{15}\mathrm{B}.$ The $\beta$-decay asymmetries were measured in coincidence with the delayed neutrons, and the $\mathrm{AP}$ values were evaluated for five allowed transitions leading to the excited states in ${}^{15}\mathrm{C}$ ${(E}_x=3.103,$ 4.220, 4.657, 5.866, and 6.426 MeV). The spin parities of the former three states were uniquely assigned as ${1/2}^{-},$ ${5/2}^{-},$ and ${3/2}^{-},$ respectively. These assignments are consistent with the previous assignments. Because of insufficient statistics for the 5.866-MeV state ${(1/2\mathrm{}}^{-}),$ an incorrect assignment ${(3/2\mathrm{}}^{-})$ could not be excluded within the $1\sigma$ deviation. The spin-parity of the 6.417-MeV state is suggested to be ${1/2}^{-}.$ The peak analysis with detector response in the neutron time of flight spectra enabled precise determinations of the level energies and widths. The level widths were determined for the first time. The present method is also applicable for $\beta$-delayed proton, $\alpha ,$ and $\gamma$ decays, and it can be a powerful tool for spectroscopic studies of nuclei far from the stability.

Experimental results for sub-barrier nuclear fusion reactions show cross section enhancements with respect to bare nuclei which are generally larger than those expected according to electron screening calculations. We point out that energy spread of target or projectile nuclei is a mechanism that generally provides fusion enhancement. We present a general formula for calculating the enhancement factor and provide quantitative estimate for effects due to thermal motion, vibrations inside atomic, molecular, or crystal system, and due to finite beam energy width. All these effects are marginal at the energies that are presently measurable; however, they have to be considered in future experiments at still lower energies. This study allows us to exclude several effects as a possible explanation of the observed anomalous fusion enhancements, which remain a mystery.

A recent study of nuclear level densities for $20<~A<~70$ found evidence that the level densities for nuclei off the stability line were lower than those for nearby nuclei on the stability line. This analysis has been extended to cover the mass range $20<~A<~110$ with results that support the original conclusions. As part of the study, the variations with energy and mass number of the parity ratio and spin cutoff parameter are examined.

A recent paper [M. Rashdan, Phys. Rev. C 63, 044303 (2001)] introduced the parametrization NL-RA1 of the relativistic mean-field model together with a parametrization of the constant gap pairing model. Some conclusions of the paper may be doubtful as the pairing model is unrealistic, and the known ground-state deformation of particular nuclei is neglected.

A high precision measurement of the transverse spin-dependent asymmetry $A_{T^{\prime }}$ in ${}^3\mathrm{He}\to \left(\overrightarrow{e}{,e}^{\prime }\right)$ quasielastic scattering was performed in Hall A at Jefferson Lab at values of the squared four-momentum transfer, $Q^2,$ between 0.1 and 0.6 $(\mathrm{G}\mathrm{e}\mathrm{V}/{c)}^2.$ $A_{T^{\prime }}$ is sensitive to the neutron magnetic form factor, $G_M^n.$ Values of $G_M^n$ at $Q^2=0.1\mathrm{}$ and $0.2(\mathrm{G}\mathrm{e}\mathrm{V}/{c)}^2,$ extracted using Faddeev calculations, were reported previously. Here, we report the extraction of $G_M^n$ for the remaining $Q^2$ values in the range from 0.3 to $0.6(\mathrm{G}\mathrm{e}\mathrm{V}/{c)}^2$ using a plane-wave impulse approximation calculation. The results are in good agreement with recent precision data from experiments using a deuterium target.

A quasispin tensor decomposition of the two-nucleon interaction determines the most general seniority-conserving rotationally invariant two-body interaction in a j shell. Such interactions define solvable and partially solvable shell model Hamiltonians for which the unitary symplectic algebra $\mathrm{USp}\mathrm{}(2j+1)\mathrm{}$ provides a complete set of quantum numbers for a subset of states. The matrix elements of seniority-conserving interactions are deduced from the matrix elements of $\mathrm{USp}\mathrm{}(2j+1)\mathrm{}$ operators. A new and powerful numerical technique is presented for computing irreps of the $\mathrm{USp}\mathrm{}(2j+1)\mathrm{}$ algebra. Applications are reported for the low-energy spectra of $N=50\mathrm{}$ and $N=126\mathrm{}$ isotones. The effects of including seniority nonconserving interactions are investigated.

The contributions of quasiparticle correlations and of continuum coupling upon the superfluid properties of neutron-rich Ni isotopes are studied within the modified BCS (MBCS) approximation at finite temperature. The effect of quasiparticle correlations is included using a secondary Bogoliubov-type canonical transformation explicitly involving the quasiparticle occupation numbers at temperature T. The effect of continuum coupling is taken into account via the finite widths of the resonant states. It is shown that the combined effect of thermal quasiparticle correlations and of continuum coupling washes out the sharp superfluid-normal phase transition given by the standard finite-temperature BCS calculations. Within the proposed resonant-continuum MBCS approximation the fluctuations of particle number also become more suppressed especially at high temperature for nuclei closer to the drip line. Finally, it is found within the same approximation that the two-neutron separation energy for ${}^{84}\mathrm{Ni}$ drops to zero at $T\simeq 0.8\mathrm{MeV}.$

The half-life of ${}^{176}\mathrm{Lu}$ has been measured using a $\gamma -\gamma$ coincidence technique and was found to be $T_{1/2}=(4.08\mathrm{}\pm 0.03)\times {10}^{10}$ years. The method employed eliminates most of the uncertainties associated with detector efficiencies, solid angle coverage, internal conversion, self-absorption, angular correlations, and true coincidence summing.

In this paper we consider dissipative hydrodynamic equations for systems with continuous broken symmetries. We first present the case of superfluidity, in which the symmetry U(1) is broken and then generalize to the chiral symmetry $\mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_L\times \mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_R.$ The corresponding new transport coefficients are introduced.

We present the first comprehensive measurement of leading Λ’s and ${\Delta }^{++}$’s in $p+\mathrm{Pb}$ collisions at $19\mathrm{GeV}/c$ using the E941/E864 spectrometer at the AGS. In comparison with the measurement of leading protons and neutrons using the same spectrometer, it is found that the cross section for baryon flavor change is large and strongly depends on rapidity, which is very different from the expectation of simple diquark-quark fragmentation of the incident proton. A suppression of leading Λ production in the forward rapidity region compared with nonstrange leading baryons is also observed. The relative probability of the projectile proton fragmentation into a ${\Delta }^{++}$ versus into a neutron is found to be about 35% in the region of $2.7<~y<~\mathrm{3.1.}$ We will discuss the impact of these results on the dynamics of baryon fragmentation and baryon number transport in nuclear collisions.

We present a simple quantum mechanical model exploiting the optical potential approach for the description of collision damping in the reaction ${\pi }^3\mathrm{He}\to d^{\prime }N$ near the threshold, which recently has been measured at TRIUMF. The influence of the open $d^{\prime }\overrightarrow{N}\mathrm{NNN}$ channel is taken into account. It leads to a suppression factor of about 10 in the $d^{\prime }$ survival probability. Applications of the method to other reactions are outlined.

Using the quark mass density- and temperature-dependent model, we have studied the thermodynamical properties and the stability of strangelets at finite temperature. The temperature, charge, and strangeness dependences on the stability of strangelets are investigated. We find that the stable strangelets only occur in the high strangeness and high negative charge region.

We discuss a fully relativistic Landau Fermi liquid theory based on the quantum hadrodynamics effective field picture of nuclear matter. From the linearized kinetic equations we get the dispersion relations of the propagating collective modes. We focus our attention on the dynamical effects of the interplay between scalar and vector channel contributions. An interesting “mirror” structure in the form of the dynamical response in the isoscalar-isovector degree of freedom is revealed, with a complete parallelism in the role respectively played by the compressibility and the symmetry energy. All that seems to support the introduction of an explicit coupling to the scalar-isovector channel of the nucleon-nucleon interaction. In particular we study the influence of this coupling (to a $\delta$-meson-like effective field) on the collective response of asymmetric nuclear matter (ANM). Interesting contributions are found on the propagation of isovectorlike modes at normal density and on an expected smooth transition to isoscalarlike oscillations at high baryon density. Important “chemical” effects on the neutron-proton structure of the mode are shown. For dilute ANM we have the isospin distillation mechanism of the unstable isoscalarlike oscillations, while at high baryon density we predict an almost pure neutron wave structure of the propagating sounds.

For excited nucleon states $N^{*}$ of arbitrary spin coupling to nucleon (N) and meson $\mathrm{}\left(M\right),$ we propose a Lorentz covariant orbital-spin $\mathrm{}(L-S)\mathrm{}$ scheme for the effective $N^{*}\mathrm{NM}$ couplings. To be used for the partial wave analysis of various $N^{*}$ production and decay processes, it combines merits of two conventional schemes, i.e., covariant effective Lagrangian approach and multipole analysis with amplitudes expanded according to angular momentum L. As examples, explicit formulas are given for $N^{*}\to N\pi ,$ $N^{*}\to N\omega ,$ and $\overrightarrow{\psi }{N}^{*}\overline{N}$ processes which are under current experimental studies.

Isoscalar Cooper pairing in isospin asymmetric nuclear matter occurs between states populating two distinct Fermi surfaces, each for neutrons and protons. The transition from a BCS-like to the normal (unpaired) state, as the isospin asymmetry is increased, is intervened by superconducting phases which spontaneously break translational and rotational symmetries. One possibility is the formation of a condensate with a periodic crystallinelike structure where Cooper pairs carry net momentum (the nuclear Larkin-Ovchinnikov-Fulde-Ferrell phase). Alternatively, perturbations of the Fermi surfaces away from spherical symmetry allow for minima in the condensate free energy which correspond to states with quadrupole deformations of Fermi surfaces and zero momentum of the Cooper pairs. In a combined treatment of these phases we show that, although the Cooper pairing with finite momentum might arise as a local minimum, the lowest energy state features are deformed Fermi surfaces and Cooper pairs with vanishing total momentum.

Three exactly solvable Hamiltonians of complex structure are studied in the framework of a semiclassical approach. The quantized trajectories for intrinsic coordinates correspond to energies which may be classified in collective bands. For two of the chosen Hamiltonians the symmetry SU(2)⊗SU(2) is the appropriate one to classify the eigenstates in the laboratory frame. Connections of the results presented here with those obtained by various microscopic formalisms are pointed out. The present approach suggests that the intrinsic states, which in standard formalism are heading rotational bands, are forming themselves “rotational” bands, the rotations being performed in a fictitious boson space.