The long standing problem of proton-neutron pairing and, in particular, the limitations imposed on the solutions by the available symmetries, is revisited. We look for solutions with nonvanishing expectation values of the proton ${\Delta }_p,$ the neutron ${\Delta }_n,$ and the isoscalar ${\Delta }_0$ gaps. For an equal number of protons and neutrons we find two solutions with ${\Delta }_p=\pm {\Delta }_n,$ respectively. The behavior and structure of these solutions differ for spin saturated (single l shell) and spin unsaturared systems (single j shell). In the former case the BCS results are checked against an exact calculation.

The parameters of form factors representing single particle central, spin-orbit, and Coulomb potentials as well as the effective nucleon mass are extracted from the relativistic mean field model of nuclei. The central and the spin-orbit nuclear potentials are proportional to the sum and the difference of the relativistic scalar- and vector-meson potentials, respectively. The latter enter the Dirac equation of the nucleon. The form factors representing the potentials are parametrized in terms of Woods-Saxon functions. They reproduce nearly exactly the single particle spectra of the self-consistent relativistic mean field theory. The effective mass is parametrized in the similar fashion. The Coulomb single particle potential parameters for protons are given as well. Calculations are based on the 116 spherically symmetric even-even nuclei from light $\mathrm{}(A=16\mathrm{})\mathrm{}$ to heavy $\mathrm{}(A=220\mathrm{})\mathrm{}$ ones, with known mass.

We present the results of a search for optical model potentials for use in the description of elastic scattering and transfer reactions involving stable and radioactive p-shell nuclei. This was done in connection with our program to use transfer reactions to obtain data for nuclear astrophysics, in particular for the determination of the astrophysical $S_{17}$ factor for ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ using two ${(}^7\mathrm{Be}{,}^8\mathrm{B})$ proton transfer reactions. Elastic scattering was measured using ${}^7\mathrm{Li},$ ${}^{10}\mathrm{B},$ ${}^{13}\mathrm{C},$ and ${}^{14}\mathrm{N}$ projectiles on ${}^9\mathrm{Be}$ and ${}^{13}\mathrm{C}$ targets at or about $E/A=10\mathrm{}\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{n}\mathrm{u}\mathrm{c}\mathrm{l}\mathrm{e}\mathrm{o}\mathrm{n}.$ Woods-Saxon type optical model potentials were extracted and are compared with potentials obtained from a microscopic double folding model. Several nucleon-nucleon effective interactions were used: M3Y with zero range and finite range exchange term, two density dependent versions of M3Y and the effective interaction of Jeukenne, Lejeune, and Mahaux. We find that the latter one, which has an independent imaginary part, gives the best description. Furthermore, we find the renormalization constant for the real part of the folding potential to be nearly independent of the projectile-target combination at this energy and that no renormalization is needed for the imaginary part. From this analysis, we are able to eliminate an ambiguity in optical model parameters and thus better determine the asymptotic normalization coefficient for ${}^{10}{\overrightarrow{\mathrm{B}}}^9\mathrm{B}+p.\mathrm{}$ Finally we use these results to find optical model potentials for unstable nuclei with emphasis on the reliability of the description they provide for peripheral proton transfer reactions. We discuss the uncertainty introduced by the procedure in the prediction of the distorted wave Born approximation cross sections for the ${(}^7\mathrm{Be}{,}^8\mathrm{B})$ reactions used in extracting the astrophysical factor $S_{17}\mathrm{}\left(0\right).$

We investigate flow in semiperipheral nuclear collisions at Alternating Gradient Synchrotron and Super Proton Synchrotron energies within macroscopic as well as microscopic transport models. The hot and dense zone assumes the shape of an ellipsoid which is tilted by an angle $\Theta$ with respect to the beam axis. If matter is close to the softest point of the equation of state, this ellipsoid expands predominantly orthogonal to the direction given by $\Theta .$ This antiflow component is responsible for the previously predicted reduction of the directed transverse momentum around the softest point of the equation of state.

We have studied the interactions of gold nuclei ${}_{79}^{197}\mathrm{Au}$ at eight different energies between 0.9 and $4.0A\mathrm{GeV},$ in targets ranging in mass from hydrogen to lead. This paper combines the results of these studies with earlier measurements at higher and lower energies. We discuss the production of fragments with charges Z between 81 and 50. The systematic trends found have allowed us to improve previously developed empirical relations which predict the cross sections in any target or energy for the production of fragments with $77<~Z<~67.$ Fragments with single and double charge pickup are observed in all targets at all energies. Fragments which have lost a single charge represent a special case, due presumably to the effects of electromagnetic dissociation. The energy variations of the total cross sections and the approach with increasing energy to limiting fragmentation are studied.

The first three terms of a Taylor expansion of the astrophysical S factor are determined in the potential model of radiative-capture reactions. As input, the radial Schrödinger equation and its inhomogeneous energy derivatives are solved at zero energy. The radial wave function and its energy derivatives are obtained by matching the solutions of these equations with the corresponding exact asymptotic forms. Explicit expressions are derived for the S factor and for its first and second derivatives at zero energy. The same algorithm allows one to accurately determine the first terms of the effective-range expansion. In particular, the effective-range formula converges much faster than the Schwinger-Bethe formula. The method is illustrated with potential-model descriptions of the ${}^3\mathrm{He}(\alpha ,\gamma {)}^7\mathrm{Be},$ ${}^6\mathrm{Li}(p,\gamma {)}^7\mathrm{Be},$ ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B},$ and ${}^{16}\mathrm{O}(p,\gamma {)}^{17}\mathrm{F}$ reactions.

We have developed a formalism for microscopic Brueckner-type calculations of dense nuclear matter that includes all types of baryon-baryon interactions and allows us to treat any asymmetry in the fractions of the different species (n, p, $\Lambda ,$ ${\Sigma }^{-},$ ${\Sigma }^0,$ ${\Sigma }^{+},$ ${\Xi }^{-},$ and ${\Xi }^0).\mathrm{}$ We present results for the different single-particle potentials, focusing on situations that can be relevant in future microscopic studies of beta-stable neutron star matter with strangeness. We find that both the hyperon-nucleon and hyperon-hyperon interactions play a non-negligible role in determining the chemical potentials of the different species.

High spin states in ${}^{127}\mathrm{La}$ have been studied using the ${}^{32}\mathrm{S}{(}^{100}\mathrm{Mo},p4n)$ reaction at a beam energy of 155 MeV. Gamma rays were detected using the EUROBALL III spectrometer. One of the side bands in ${}^{127}\mathrm{La}$ is observed to be populated to a spin of ${\frac{83}{2}}^{+}.$ These data are compared with cranked Nilsson-Strutinski calculations which suggest that the structure is a smoothly terminating band, in valence space, based upon a $\pi \left[{(g}_{7/2}{d}_{5/2}{)}^5{(h}_{11/2}{)}^2\right]\otimes \nu \left[{(g}_{7/2}{d}_{5/2}{)}^{12}{(h}_{11/2}{)}^6{(d}_{3/2}{s}_{1/2}{)}^2\right]$ configuration, which can carry a maximum spin of $47.5ħ.$ This is the first identification of such a structure in this mass region.

The $\eta -d$ scattering length $A_{\eta d}$ has been calculated using as input a variety of possible $\eta -N$ scattering length values that have been presented in the literature. The calculated $A_{\eta d}$ are in perfect agreement with the values obtained previously by summation of multiple-scattering series but we disagree with another Faddeev-type calculation. We show that the present $\eta -N$ data rule out the possibility of a quasibound $\eta -d$ state. The imaginary part of the $K^{-}-d$ scattering length calculated by using a single-channel absorptive $K^{-}$-nucleon interaction is found to be in good agreement with the value obtained from the full multichannel approach but the mismatch in the corresponding real parts is about 40%.

The reaction ${}^{58}\mathrm{Ni}{(}^{28}\mathrm{Si},\alpha n\gamma )$ at 90 MeV of projectile energy has been used to populate the $T_z=\frac{1}{2}$ nucleus ${}^{81}\mathrm{Zr}.$ $\gamma$ rays have been detected with the GASP array, and charged particles with the ISIS Silicon ball. The charged particle information allowed unambiguous assignment of $\gamma$ rays to ${}^{81}\mathrm{Zr}.$ Two rotational band structures with both signatures have been observed. They are discussed by comparison with similar bands in the $N=41\mathrm{}$ isotones and in $T_z=\frac{1}{2}$ nuclei from the $A\approx 80$ region, and on the basis of the cranked shell model and interacting boson-fermion model calculations.

We search for low-lying resonances in the ${}^8\mathrm{B}$ and ${}^8\mathrm{Li}$ nuclei using a microscopic cluster model and a variational scattering method, which is analytically continued to complex energies. After fine-tuning the nucleon-nucleon interaction to get the known $1^{+}$ state of ${}^8\mathrm{B}$ at the right energy, we reproduce the known spectra of the studied nuclei. In addition, our model predicts a $1^{+}$ state at 1.3 MeV in ${}^8\mathrm{B},$ relative to the ${}^7\mathrm{Be}+p$ threshold, whose corresponding pair is situated right at the ${}^7\mathrm{Li}+n$ threshold in ${}^8\mathrm{Li}.$ Lacking any experimental evidence for the existence of such states, it is presently uncertain whether these structures really exist or whether they are spurious resonances in our model. We demonstrate that the predicted state in ${}^8\mathrm{B},$ if it exists, would have important consequences for the understanding of the astrophysically important ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ reaction.

Microsecond yrast isomers were observed in the ${}^{125,127,129}\mathrm{Sn}$ isotopes. These nuclei are produced by thermal neutron induced fission of ${}^{233}\mathrm{U}$ and ${}^{239}\mathrm{Pu}.$ The detection is based on time correlation between fission fragments selected by the LOHENGRIN spectrometer at ILL (Grenoble) and the $\gamma$ rays or conversion electrons from isomers. In this paper, the decay schemes of the new ${19/2}^{+}$ yrast isomers in ${}^{125,127,129}\mathrm{Sn}$ are reported. The measured low-lying negative parity states are compared with the results of various calculations. This work suggests also the presence of high spin $\beta$ isomers in ${}^{127,129}\mathrm{In}.$

The astrophysically important $l=0\mathrm{}$ resonance that occurs at an excitation energy of 7.07 MeV in ${}^{19}\mathrm{Ne}$ has an appreciable fraction of the $2s\frac{1}{2}$ single-proton strength. Hence, the excitation energy in ${}^{19}\mathrm{Ne}$ should be considerably lower than for its mirror in ${}^{19}\mathrm{F},$ which we predict at $E_x=7.4\mathrm{}\pm 0.1$ MeV.

We progressively refine a previously reported method for the selection of cluster and core in a binary cluster model, and hence reinforce our conclusions concerning the occurrence of exotic clustering in actinide nuclei. The extended method also reveals a competing binary mode in these nuclei in which the cluster charge and mass are substantially larger than those corresponding to an exotic decomposition.

Multinucleon transfer reactions have been investigated in the system ${}^{40}\mathrm{Ca}{+}^{124}\mathrm{Sn}$ at $E_{\mathrm{LAB}}=170\mathrm{}$ MeV. The setup was the GASP multidetector array and two bidimensional position sensitive parallel plate detectors, from which $\gamma -\mathrm{particle}$ and $\gamma -\gamma -\mathrm{particle}$ coincidences were taken for a large variety of transfer channels. Differential and total cross sections to the lowest excited levels of the heavy and light nuclei produced in the transfer process have been measured down to the $-4p$ channel. A comparison with a first-order complex WKB Born approximation for the $+1n$ and $-1p$ transfer channels has been done, showing an overall good agreement with the data.

The cross section of deuteron-triton sub-barrier fusion is calculated using the selective resonant tunneling model with the assumption of a square-well nuclear potential. A complex potential is assumed to describe the absorption inside the nuclear well. The surprisingly good agreement between the theoretical calculation and the experimental data implies that the compound nucleus model might not be applicable to the light-nuclei sub-barrier fusion. Instead, the selective resonant tunneling model is proposed.

An elaborated investigation was done into the reaction mechanism of heavy ion collisions at intermediate energies of small nuclear systems. Experimental data measured with the Huygens detectors and isospin quantum molecular dynamics (IQMD) simulations of ${}^{24}{\mathrm{M}\mathrm{g}+}^{27}\mathrm{Al}$ at 45 and $95A\mathrm{MeV}$ were analyzed with respect to the impact-parameter selection, the in-plane flow and the IMF production at midrapidity. It was found that only the midcentral impact-parameter class could be identified effectively. The event-plane reconstruction and flow measurements were studied with IQMD and a GEANT detector simulation. This showed that the azimuthal-correlation method gives the best reconstruction. The experimentally measured in-plane flow was consistent with the balancing energy derived from literature of $114\pm 10A\mathrm{MeV}.$ The azimuthal correlations and polar-angle distributions of IMF’s emitted at midrapidity were used to distinguish between a dynamic scenario, i.e., IQMD, and a statistical scenario described by a simple decaying-source model. The IQMD simulations were in good agreement with the experimental data while a single decaying-source simulation fails to describe the data which shows that multifragmentation in these small systems is consistent with a dynamic process.

In this paper the dynamical string model is applied to the numerical simulation of the ultrarelativistic heavy-ion collision ${}^{32}\mathrm{S}(200\mathrm{}\hspace{0.5em}\mathrm{G}\mathrm{e}\mathrm{V}/\mathrm{n}\mathrm{u}\mathrm{c}\mathrm{l}\mathrm{e}\mathrm{o}\mathrm{n}{)+}^{32}\mathrm{S}.$ The results are in qualitative agreement with experimental data.

A quark model calculation of the processes $\gamma \overrightarrow{\gamma }{\pi }^{+}{\pi }^{-}$ and $\gamma \overrightarrow{\gamma }{\pi }^0{\pi }^0$ is performed. At tree level, only charged pions couple to the initial state photons and neutral pions are not expected in the final state. However, a small but significant $\gamma \overrightarrow{\gamma }{\pi }^0{\pi }^0$ cross section is observed. We demonstrate that this may be accounted for by a rotation in isospin space induced by final-state interactions. The resulting ${\pi }^{+}{\pi }^{-}$ cross section is in good agreement with experiment, while the ${\pi }^0{\pi }^0$ cross section is in qualitative agreement with the data.

A simple and elegant model, based on Reggeized t-channel exchanges, is successful in reproducing the main features of all existing data of the reactions $e\overrightarrow{p}{e}^{\prime }{K}^{+}\Lambda$ and $e\overrightarrow{p}{e}^{\prime }{K}^{+}{\Sigma }^0.$ In particular, the original way in which gauge invariance is taken into account is found to be essential to describe the ratio between the Coulomb and the transverse cross sections at large $Q^2$ that has been measured recently at the Jefferson Laboratory.