The binding energies of even-even and odd-odd $N=Z$ nuclei are compared. After correcting for the symmetry energy we find that the lowest $T=1\mathrm{}$ state in odd-odd $N=Z$ nuclei is as bound as the ground state in the neighboring even-even nucleus, thus providing evidence for isovector $\mathrm{np}$ pairing. However, $T=0\mathrm{}$ states in odd-odd $N=Z$ nuclei are several MeV less bound than the even-even ground states. We associate this difference with the $T=1\mathrm{}$ pair gap and conclude from the analysis of binding energy differences and blocking arguments that there is no evidence for an isoscalar (deuteronlike) pair condensate in $N=Z$ nuclei.

A three-dimensional reduction of the two-particle Bethe-Salpeter equation is proposed. The proposed reduction is in the framework of light-front dynamics. It yields auxiliary quantities for the transition matrix and the bound state. The arising effective interaction can be perturbatively expanded according to the number of particles exchanged at a given light-front time. An example suggests that the convergence of the expansion is rapid. This result is particular for light-front dynamics. The covariant results of the Bethe-Salpeter equation can be recovered from the corresponding auxiliary three-dimensional ones. The technical procedure is developed for a two-boson case; the idea for an extension to fermions is given. The technical procedure appears quite practicable, possibly allowing one to go beyond the ladder approximation for the solution of the Bethe-Salpeter equation. The relation between the three-dimensional light-front reduction of the field-theoretic Bethe-Salpeter equation and a corresponding quantum-mechanical description is discussed.

The reaction $p\overrightarrow{d}\mathrm{pX}$ at 305 MeV is studied with the aim of searching for supernarrow dibaryons, the decay of which into two nucleons is forbidden by the Pauli exclusion principle. The experiment was carried out at the Moscow Meson Factory using the spectrometer TAMS, which detected the proton spectator and another charged particle (either p or $d)$ from the decay of X. Narrow peaks in missing mass spectra have been observed at 1905 and 1924 MeV. Comparison of the obtained data with theoretical predictions leads to the conclusion that the peak found at 1905 MeV most likely corresponds to a supernarrow dibaryon with isotopic spin equal to 1. The possible origin of the peak at 1924 MeV is also discussed.

We used the generalized Skyrme potential to study the equation of state of polarized nuclear matter in the frame of the Thomas-Fermi model. The critical temperature of the liquid-gas phase transition is found to be $T_c=16.2\mathrm{}\mathrm{MeV}.$ This critical temperature was found to decease with the asymmetry, spin, and spin-isospin excess parameters. The isothermal compressibility of polarized nuclear matter was also studied. The volume compressibility $K_v$ was found to decrease with temperature. The symmetry compressibility $K_x,$ the spin symmetry compressibility $K_y,$ and the spin-isospin symmetry compressibility $K_z$ were found to have a little increasing behavior with temperature.

We have made a new evaluation of the $\Lambda$ decay width in nuclear matter within the propagator method. Through the local density approximation it is possible to obtain results in finite nuclei. We have also studied the dependence of the widths on the $\mathrm{NN}$ and $\Lambda N$ strong short-range correlations. Using reasonable values for the parameters that control these correlations, as well as realistic nuclear densities and $\Lambda$ wave functions, we show that it is possible to reproduce the experimental decay rates in a wide range of mass numbers (from medium to heavy hypernuclei); however, the question related to the ${\Gamma }_n/{\Gamma }_p$ ratio remains open.

Time-correlated, particle-tagged $\gamma$ spectroscopy of the stable nucleus ${}^{179}\mathrm{Hf}$ was undertaken with incomplete fusion reactions initiated by beams of ${}^9\mathrm{Be}$ and ${}^7\mathrm{Li}$ incident on targets of ${}^{176}\mathrm{Yb}.$ Intrinsic and rotational states above the three-quasiparticle $K^{\pi }{=25/2\mathrm{}}^{-},\hspace{0.5em}{T}_{1/2}=25\mathrm{}\hspace{0.5em}\mathrm{day}$ isomer, ${}^{179}\mathrm{Hf}{}^{m2\mathrm{}},$ are reported. The rotational band based on ${}^{179}\mathrm{Hf}{}^{m2\mathrm{}}$ has $g_K-g_R$ values that are consistent with the previously suggested $\nu {9/2}^{+}\otimes {\pi }^2\left[{7/2}^{+}{,9/2\mathrm{}}^{-}\right]$ configuration assignment. A value of $g_R=0.34\mathrm{}\left(5\right)\mathrm{}$ was derived for the collective g factor of ${}^{179}\mathrm{Hf}{}^{m2\mathrm{}},$ which is considerably higher than that found for the ${9/2}^{+}$ ground state. The difference is consistent with a reduction of the proton pairing strength due to blocking in the $K^{\pi }{=25/2\mathrm{}}^{-}\nu \otimes {\pi }^2$ configuration. A number of ${\nu }^3{\pi }^2$ five-quasiparticle configurations were identified, the highest of which is an yrast $K^{\pi }{=43/2\mathrm{}}^{+},\hspace{0.5em}{T}_{1/2}=15\mathrm{}\left(5\right)\mathrm{}\hspace{0.5em}\mu \mathrm{s}$ isomer. It decays to an yrast $K^{\pi }{=39/2\mathrm{}}^{-}$ state, which in turn decays to a rotational band based on a $K^{\pi }{=33/2\mathrm{}}^{-}$ state. The $K^{\pi }{=33/2\mathrm{}}^{-}$ state decays to the rotational band associated with ${}^{179}\mathrm{Hf}{}^{m2\mathrm{}}.$ Semiempirical calculations reproduce the excitation energies of the three- and five-quasiparticle states above ${}^{179}\mathrm{Hf}{}^{m2\mathrm{}}$ to within $\sim 200\hspace{0.5em}\mathrm{keV}.$ The calculations predict that the lowest seven-quasiparticle state will arise from a ${\nu }^5{\pi }^2$ configuration with $K^{\pi }{=47/2\mathrm{}}^{-},$ which is just beyond the maximum spin accessible with the reactions employed here.

Recent discoveries of ${}^{10}\mathrm{Be}$ and ${}^{12}\mathrm{C}$ accompanied cold fission in the spontaneous fission of ${}^{252}\mathrm{Cf}$ lead to the surprising result that long living trinuclear molecules may exists. For the description of the dynamics and decay of such molecules, we used a coplanar three body cluster model (two deformed fragments and an α particle) with a three body potential computed by a double folding potential generated by M3Y effective interaction. A repulsive compression term was included. The computed α ternary cold fission yields are in agreement with the experiment. The energy and angular distributions of the three clusters at infinity and the half-lives are strongly dependent of the initial positions of the α particle relative to the two fragments and of mass asymmetry of the fragments. The evaluated lifetimes of such trinuclear molecules are quite large, of the order of one second.

The inclusive light fragment $(Z<~7)$ yield data in Au+Au reactions, measured by the EOS Collaboration at the LBNL Bevalac, are presented as a function of multiplicity. Moving from central to peripheral collisions the measured charge distributions develop progressively according to a power law which can be fitted, within errors, by a single $\tau$ exponent independently of the bombarding energy except for the data at $250A\hspace{0.5em}\mathrm{MeV}.\mathrm{}$ In addition, the location of the maximum in the individual yields of different charged fragments, for a given beam energy, shifts towards lower multiplicity as the fragment charge increases from $Z=3\mathrm{}$ to $Z=7.\mathrm{}$ This trend is common to all six measured beam energies. Moments of charge distribution are also reported. The universal features observed in the present Au + Au data are consistent with previous experimental findings in the Au + C multifragmentation reaction at $1A\hspace{0.5em}\mathrm{GeV}.$

We discuss a dynamical mechanism of pion production from disoriented chiral condensates. It leads to an explosive production of pions via the parametric resonance mechanism, which is similar to the reheating mechanism in inflationary cosmology. Classically it is related with the instability in the solutions of the Mathieu equation and we explore the quantum aspects of the mechanism. We show that nonlinearities and back reactions can be ignorable for a sufficiently long time under the small amplitude approximations of background σ oscillations, which may be appropriate for the late stage of a nonequilibrium phase transition. It allows us to obtain an explicit quantum state of the produced pions and σ, the squeezed state of BCS type. Single particle distributions and two pion correlation functions are computed within these approximations. The results obtained illuminate the characteristic features of multipion states produced through the parametric amplification mechanism. In particular, two pion correlations of various charge combinations contain back-to-back correlations which cannot be masked by the identical particle interference effect. We suggest that the parametric resonance mechanism might be a cause of the long lasting amplification of low-momentum modes in linear sigma model simulations.

Double-$\gamma$ vibrations in deformed nuclei are studied in the context of the interacting boson model with special reference to their anharmonic character. It is shown that large anharmonicities can be obtained with interactions that are (at least) of three-body nature between the bosons. As an example the $\gamma$ vibrations of the nucleus ${}_{\hspace{0.5em}68}^{166}{\mathrm{Er}}_{98}$ are studied in detail.

We present a translationally invariant formulation of the no-core shell model approach for few-nucleon systems. We discuss a general method of antisymmetrization of the harmonic-oscillator (HO) basis depending on Jacobi coordinates. The use of a translationally invariant basis allows us to employ larger model spaces than in traditional shell-model calculations. Moreover, in addition to two-body effective interactions, three- or higher-body effective interactions as well as real three-body interactions can be utilized. In the present study we apply the formalism to solve three and four nucleon systems interacting by the CD-Bonn nucleon-nucleon (NN) potential in model spaces that include up to $34ħ\Omega$ and $16ħ\Omega$ HO excitations, respectively. Results of ground-state as well as excited-state energies, rms radii, and magnetic moments are discussed. In addition, we compare charge form factor results obtained using the CD-Bonn and Argonne ${\mathrm{V}8\mathrm{}}^{\prime }$ NN potentials.

Dimensional regularization is applied to the Lippmann-Schwinger equation for a separable potential which gives rise to logarithmic singularities in the Born series. For this potential a subtraction at a fixed energy can be used to renormalize the amplitude and produce a finite solution to the integral equation for all energies. This can be done either algebraically or numerically. In the latter case dimensional regularization can be implemented by solving the integral equation in a lower number of dimensions, fixing the potential strength, and computing the phase shifts, while taking the limit as the number of dimensions approaches three. We demonstrate that these steps can be carried out in a numerically stable way, and show that the results thereby obtained agree with those found when the renormalization is performed algebraically to four significant figures.

Low spin states in the odd-odd nucleus ${}^{54}\mathrm{Co}$ were investigated with the ${}^{54}\mathrm{Fe}(p,n\gamma {)}^{54}\mathrm{Co}$ fusion evaporation reaction at the FN-TANDEM accelerator in Cologne. $\gamma \gamma$-coincidences, $\gamma \gamma$-angular correlations, and Compton asymmetries were measured. 28 low spin states were observed. 19 for the first time, eight new spin assignments and six new parity assignments were made, and seven $\gamma$-branching ratios were measured for the first time. $M1\mathrm{}$ and $E2\mathrm{}$ transition strengths between low-lying states in ${}^{54}\mathrm{Co}$ were calculated in the shell-model framework. The experimental branching ratios and multipole mixing ratios indicate the existence of very strong isovector $M1\mathrm{}$ transitions.

The emission of the ${}^{34}\mathrm{Si}$ cluster, with respect to the $\alpha$ particle, in the spontanous decay of the ${}^{242}\mathrm{Cm}$ nucleus is studied within a preformed cluster model developed by one of us (R.K.G.) and collaborators. The preformation factors are predicted to be very small, $\sim {10}^{-9}$ and $\sim {10}^{-24},$ respectively, for the $\alpha$ particle and ${}^{34}\mathrm{Si}$ cluster. With no parameter of the model fitted to experimental data, the half-life times for both the $\alpha$ particle and ${}^{34}\mathrm{Si}$ decays of ${}^{242}\mathrm{Cm}$ are predicted within only one to two orders of magnitude of the experimental values.

A comparison of the nuclear matter equations of state based on Skyrme, Myers-Swiatecki, and Tondeur interactions is given. It is shown that the difference among these equations of state is not significant in most of the relative neutron excess range which is of interest for both heavy ion collisions and supernova explosion calculations. However, if the equation is fitted to the same standard state, the equation based on the Tondeur interaction is softer than others provided the relative neutron excess is not close to 0.

In this paper we compare a model that contains the mechanisms of $\Delta$ excitation in the projectile and Roper excitation in the target with experimental data from two ${(d,d}^{\prime })$ experiments on a proton target. The agreement of the theory with the experiment is fair for the data taken at $T_d=2.3\mathrm{}$ GeV. The $\Delta$ excitation in the projectile is predicted close to the observed energy with the correct width. The theory, however, underpredicts by about 40% the cross sections measured at $T_d\hspace{1em}=\hspace{1em}1.6$ GeV at angles where the cross section has fallen by about two orders of magnitude. The analysis done here allows us to extract an approximate strength for the excitation of the Roper $\left[N^{*}\mathrm{}\right(1440\left)\mathrm{}\right]$ excitation and a qualitative agreement with the theoretical predictions is also found.

The gamma decay of excited states in the nucleus ${}^{100}\mathrm{Cd},$ which is two proton holes and two neutrons away from doubly magic $\mathrm{}(N=Z=50\mathrm{})\mathrm{}$ ${}^{100}\mathrm{Sn},$ has been studied with the Gammasphere array following the ${}^{46}\mathrm{Ti}{(}^{58}\mathrm{Ni},2p2n)$ reaction at 215 MeV. Residues were identified by detection of evaporated charged particles in the Microball CsI array, by neutron detection in a set of liquid scintillator detectors, and by a tag on the delayed gamma-ray decay of the known $8^{+}$ isomeric state. The level scheme has been extended up to $20ħ$ in angular momentum and to nearly 10 MeV in excitation energy. The results are compared with shell-model calculations.

Parity nonconservation (PNC) was studied in p-wave resonances in indium by measuring the helicity dependence of the neutron total cross section in the neutron energy range 6.0–316 eV with the time-of-flight method at LANSCE. A total of 36 p-wave neutron resonances were studied in ${}^{115}\mathrm{In},$ and statistically significant asymmetries were observed for nine cases. An analysis treating the PNC matrix elements as random variables yields a weak matrix element of ${M=(0.67\mathrm{}}_{-0.12}^{+0.16\mathrm{}})\hspace{0.5em}\mathrm{meV}$ and a weak spreading width of ${\Gamma }_w{=(1.30\mathrm{}}_{-0.43}^{+0.76\mathrm{}})\times {10}^{-7}\hspace{0.5em}\mathrm{eV}.$

The structure of ${}^{10}\mathrm{Be}$ is investigated using a microscopic $\alpha +\alpha +n+n$ model based on the molecular orbit (MO) model. The low-lying states are characterized by several configurations of valence neutrons, which are constructed as combinations of three basic orbits. The model space employed is extended from the traditional MO models, and the orbits are expressed as linear combinations of local Gaussians. Their positions are determined variationally. Using this model, we reanalyze the structure of ${}^9\mathrm{Be}$ and show that this extension enables us to use the original two-body spin-orbit interaction determined from a scattering phase-shift analysis of $\alpha -n.\mathrm{}$ In ${}^{10}\mathrm{Be},$ all of the observed positive-parity bands and the negative-parity bands are described within the model. The $0^{+}$ ground state of ${}^{10}\mathrm{Be}$ is described by a dominant ${(3/2\mathrm{}}^{-}{)}^2$ configuration. The state has a rather large binding energy (8.38 MeV from the $\alpha +\alpha +n+n$ threshold experimentally), and the mechanism leading to binding, such as a pairing effect and reduction of the kinetic energy between two clusters, is discussed in detail. In spite of this large binding, the $\alpha -\alpha$ clustering in the ground state persists due to a coupling effect between the ${}^6\mathrm{He}+\alpha$ configuration and the ${}^5\mathrm{He}{+}^5\mathrm{He}$ configuration, which provides a smooth potential for the valence neutrons. The second $0^{+}$ state of ${}^{10}\mathrm{Be}$ has a large $\alpha -\alpha$ structure with a ${(1/2\mathrm{}}^{+}{)}^2$ configuration. An enlargement of the $\alpha -\alpha$ distance due to two-valence neutrons along the $\alpha -\alpha$ axis makes their wave function smooth and reduces the kinetic energy drastically. Furthermore, the contribution of the spin-orbit interaction due to coupling between the $S_z=0\mathrm{}$ and the $S_z=1\mathrm{}$ configurations is important. We also show the mediation effect of two valence neutrons between two $\alpha$ clusters.