Resonances above the t+t threshold in ${}^6\mathrm{He}$ have been studied via the ${}^6\mathrm{Li}$${(}^7\mathrm{Li},$ ${}^7\mathrm{Be}$ $t)$${}^3\mathrm{H}$ reaction at $0°$ taken with a ${}^7\mathrm{Li}$ beam of 65 MeV/nucleon. By observing the binary triton decay, a new prominent resonance is found at $E_x=18.0\mathrm{}\pm 0.5\mathrm{MeV}$ with a width of $7.7\pm 1.0\mathrm{MeV}.$ The branching ratio for the binary triton decay from this resonance is deduced to be $90\pm 10\%,$ suggesting that the resonance at 18 MeV has a di-triton molecular structure.

We present a method that accurately approximates the shell-model ground state by products of suitable states. The optimal factors are determined by a variational principle and result from the solution of rather low-dimensional eigenvalue problems. The power of this method is demonstrated by computations of ground states and low-lying excitations in $\mathrm{sd}$-shell and $\mathrm{pf}$-shell nuclei.

Exclusive measurements of the $p\overrightarrow{p}\mathrm{pp}{\pi }^{+}{\pi }^{-}$ reaction have been carried out at $T_p=775\mathrm{}\mathrm{MeV}$ at CELSIUS using the PROMICE/WASA setup. Together with data obtained at lower energy, they point to a dominance of the Roper excitation in this process. From the observed interference of its decay routes $N^{*}\to N\sigma$ and $N^{*}\to \Delta \overrightarrow{\pi }N\sigma ,$ their energy-dependent relative branching ratio is determined.

Lifetimes of the first $4^{+}$ and $6^{+}$ states in ${}^{104}\mathrm{Mo}$ and ${}^{106}\mathrm{Mo}$ have been measured using the recoil distance method following spontaneous fission of ${}^{252}\mathrm{Cf}.$ The experiment was performed at the 88-inch cyclotron of the Lawrence Berkeley National Laboratory employing the Gammasphere array and the New Yale Plunger Device. Reduced transition probabilities in the ground state band of ${}^{104}\mathrm{Mo}$ are compared with predictions of the critical point symmetry X(5) for phase transitional nuclei between rotational and vibrational shape. While known level energies of ${}^{104}\mathrm{Mo}$ are in good agreement with the X(5) predictions, the analysis of the measured $B\left(E2\mathrm{}\right)\mathrm{}$ values favors a rotor interpretation.

We formulate the nuclear collective tunneling transition from one Hartree state to another, consistently with the Hartree states. A Hamiltonian effective for the collective tunneling as well as for Hartree states is obtained with the parameters determined by the Hartree calculations. A real-time description for the tunneling is proposed. It is shown that a nuclear system governed by the Hamiltonian symmetric between two Hartree states collectively tunnels back and forth between the two states owing to the residual interaction, so that the system makes harmonic tunneling oscillations. While a crowd of quantum fluctuations coherently shifts back and forth in phase with the tunneling oscillations of the center of mass of two wave packets, the symmetric nuclear system retains the energy for the harmonic tunneling oscillations. The collective tunneling transitions are analyzed in an adiabatic approximation.

A microscopic analysis of the $\alpha$ decay from odd mass axially deformed nuclei is performed to predict the anisotropies for ${}^{241-243}\mathrm{Am},$ ${}^{253-255}\mathrm{Es},$ and ${}^{255-257}\mathrm{Fm}$ isotopes. Realistic mean field plus pairing residual interaction has been used, together with a single particle basis consisting of two different harmonic oscillator representations. A spherical $\alpha$ formation amplitude has been used, so that the predicted anisotropy has to be ascribed, within the presented model, only to the deformed barrier penetration. Any disagreement between the present, properly filtered, theoretical predictions and future experimental data will provide evidence of relevant nuclear structure details not accounted for by the $L=0\mathrm{}$ part of the formation amplitude.

We calculate open charm and charmonium production in Au+Au reactions at $\sqrt{s}=200\mathrm{}\mathrm{GeV}$ within the hadron-string dynamics transport approach, employing open charm cross sections from $\mathrm{pN}$ and $\pi N$ reactions that are fitted to results from PYTHIA and scaled in magnitude to the available experimental data. Charmonium dissociation with nucleons and formed mesons to open charm $(D+\overline{D}$ pairs) is included dynamically. The “comover” dissociation cross sections are described by a simple phase-space model including a single free parameter, i.e., an interaction strength $M_0^2$ that is fitted to the $J/\Psi$ suppression data for Pb+Pb collisions at Super Proton Synchrotron (SPS) energies. As a novel feature we implement the backward channels for charmonium reproduction by $D\overline{D}$ channels employing detailed balance. From our dynamical calculations we find that the charmonium re-creation is comparable to the dissociation by “comoving” mesons. This leads to the final result that the total $J/\Psi$ suppression at $\sqrt{s}=200\mathrm{}\mathrm{GeV}$ as a function of centrality is slightly less than the suppression seen at SPS energies by the NA50 Collaboration, where the “comover” dissociation is substantial and the backward channels play no role. Furthermore, even in the case that all directly produced $J/\Psi$ mesons dissociate immediately (or are not formed as a mesonic state), a sizable amount of charmonia is found asymptotically due to the $D+\overline{D}\to J/\Psi$ + meson channels in central collisions of Au+Au at $\sqrt{s}=200\mathrm{}\mathrm{GeV},$ which, however, is lower than the $J/\Psi$ yield expected from binary scaling of $\mathrm{pp}$ collisions.

Information on gross $\beta$-decay properties of neutron-rich noble gas isotopes ${}^{49,50}\mathrm{Ar}$ was obtained at the PSB-ISOLDE facility at CERN using isobaric selectivity achieved by the combination of a plasma ion source with a cooled transfer line and subsequent mass separation. A doubly charged beam was used in the case of ${}^{49}\mathrm{Ar}$ to suppress the corresponding multicharged background from heavier noble gas fission products. The comparison of the obtained data with results of quasiparticle random-phase approximation calculations indicates that the $N=28\mathrm{}$ shell is not disturbed significantly for neutron-rich Ar nuclei. The obtained results are useful for better understanding of the origin of the ${}^{48}\mathrm{Ca}{/}^{46}\mathrm{Ca}$ isotopic anomaly discovered in inclusions from the Allende meteorite.

A perturbative approach for the description of elastic and inelastic nucleon-deuteron scattering is developed. Its validity is discussed. The aim of the perturbative approach is the isolation of details of different reaction mechanisms. The dynamics is based on a two-baryon potential allowing for the excitation of a nucleon to a $\Delta$ isobar. The coupled-channel potential yields an effective three-nucleon force in three-nucleon scattering. The purely nucleonic reference potential is the charge-dependent CD-Bonn potential.

We reexamine the Glauber model and calculate the total reaction cross section as a function of energy in the low and intermediate energy range, where many of the corrections in the model are effective. The most significant effect in this energy range is by the modification of the trajectory due to the Coulomb field. The modification in the trajectory due to nuclear field is also taken into account in a self-consistent way. The energy ranges in which particular corrections are effective are quantified, and it is found that when the center of mass energy of the system becomes 30 times the Coulomb barrier, none of the trajectory modification to the Glauber model is really required. The reaction cross sections for light and heavy systems, from the Coulomb barrier to intermediate energies, have been calculated. The exact nuclear densities and free nucleon-nucleon (NN) cross sections have been used in the calculations. The center of mass correction, which is important for light systems, has also been taken into account. There is an excellent agreement between the calculations with the modified Glauber model and the experimental data. This suggests that the heavy ion reactions in this energy range can be explained by the Glauber model in terms of free NN cross sections without incorporating any medium modification.

Low-spin states built on the $\pi h_{11/2}\nu h_{11/2}$ configuration in ${}^{134}\mathrm{Pr}$ have been studied using a ${}^{119}\mathrm{Sn}{(}^{19}\mathrm{F},4n)$ fusion-evaporation reaction. A planar low-energy photon spectrometer along with a low-$Z$ target chamber was utilized in an array of five high-purity Ge detectors for the purpose of measuring low-energy $\gamma$ rays. A 39.3-keV $\gamma$ ray was discovered as a new transition at the bottom of the band. The transition was found to have an $M1\mathrm{}$ multipolarity, determined from the internal conversion coefficients evaluated from the missing transition intensity. The new bandhead was assigned and was identified as an isomeric state with a mean lifetime of $\tau =4.6\mathrm{}\left(1\right)\mathrm{}\mathrm{ns}.$ This bandhead decays by a 306-keV $\gamma$-ray transition that was found to have an $E1\mathrm{}$ multipolarity through the analysis of the angular distribution asymmetry.

Structures above the two-particle isomeric states in ${}^{188}\mathrm{Pb}$ have been identified. Their properties imply the presence of three minima in the nuclear potential well, associated with spherical, oblate, and prolate deformations. The fragmented decay of the $K^{\pi }{=8\mathrm{}}^{-},$ $1\mu \mathrm{s}$ prolate isomer leads to the identification of the yrare collective band presumably based on the excited $0^{+}$ state. Analysis of the excitation energies, branching ratios, and $E2\mathrm{}$ and $E0\mathrm{}$ decay widths through a three-band-mixing model provides evidence for shape differences and the hybridization of the wave functions at low spin.

The ${}^{18}\mathrm{F}(p,\alpha {)}^{15}\mathrm{O}$ reaction is recognized to be one of the most important reactions for nova $\gamma$-ray astronomy, as it governs the early $E<~511\mathrm{keV}$ $\gamma$ emission. However, in the nova temperature regime, its rate remains largely uncertain due to unknown low-energy resonance strengths. We report here the measurement of the ${}^2\mathrm{H}{(}^{18}\mathrm{F}{,p)}^{19}\mathrm{F}(\alpha {)}^{15}\mathrm{N}$ one-nucleon transfer reaction, induced by a 14-MeV ${}^{18}\mathrm{F}$ radioactive beam impinging on a ${\mathrm{CD}}_2$ target; outgoing protons and ${}^{15}\mathrm{N}$ (or $\alpha$ particles) were detected in coincidence in two silicon strip detectors. A distorted-wave Born approximation analysis of the data resulted in new limits to the contribution of low-energy resonances to the rate of the ${}^{18}\mathrm{F}(p,\alpha {)}^{15}\mathrm{O}$ reaction.

An improvement of the recently developed effective interaction method for the hyperspherical formalism is presented. The method is extended to include contributions of three-body effective forces and of the nonadiabatic kinetic energy term. The role of these two additional contributions is tested on the binding energy of ${}^4\mathrm{He}$ and ${}^6\mathrm{Li}$ using semirealistic and more realistic NN potential models. The rate of convergence is improved considerably, opening up the possibility to use the method with realistic two- and three-body potentials for the $\alpha$-particle and for few-body nuclei with more than four nucleons.

We present a study of weakly bound, neutron-rich nuclei using the nuclear shell model employing the complex Berggren ensemble representing bound single-particle states, unbound Gamow states, and the nonresonant continuum. In the proposed Gamow shell model, the Hamiltonian consists of a one-body finite depth (Woods-Saxon) potential and a residual two-body interaction. We discuss the basic ingredients of the Gamow shell model. The formalism is illustrated by calculations involving several valence neutrons outside the double-magic core: ${}^{6–10}\mathrm{He}$ and ${}^{18–22}\mathrm{O}.$

In this work the microsecond isomers in ${}^{129}\mathrm{In}$ and ${}^{129}\mathrm{Sb}$ were investigated. These nuclei were produced by the thermal-neutron-induced fission of ${}^{241}\mathrm{Pu}.$ The detection is based on a time correlation between the fission fragments selected by the LOHENGRIN spectrometer at the ILL (Grenoble) and the $\gamma$ rays or conversion electrons from the isomers. The decay schemes of the new ${17/2}^{-}$ isomer in ${}^{129}\mathrm{In}$ and ${23/2}^{+}$ isomer in ${}^{129}\mathrm{Sb}$ are reported. A shell-model study of these two nuclei was performed using a realistic effective interaction derived from the CD–Bonn nucleon-nucleon potential. Comparison shows that the calculated energy levels and electromagnetic transition rates are in very good agreement with the experimental data.

We analyze the one-dimensional anharmonic oscillator using effective operator methods in both the strong and weak coupling limits. We show that in the case of a one-dimensional model space, the similarity transformation needed to define the effective Hamiltonian is related to the coefficients in the expansion of the wave function in the unperturbed harmonic oscillator basis. We obtain an infinite system of equations which is equivalent to those obtained from the Hill determinant solution of the anharmonic oscillator. The analytic properties of the resulting equations reveal the nonperturbative features of the underlying problem. Thus, we demonstrate the utility of the effective operator method for solving a nonanalytic strong coupling problem.

The parameters obtained from the theoretical analysis of the single-photon spectra observed by the WA98 Collaboration at Super Proton Synchrotron (SPS) energies have been used to evaluate the two-photon correlation functions. The single-photon spectra and the two-photon correlations at relativistic heavy ion collider (RHIC) energies have also been evaluated, taking into account the effects of the possible spectral change of hadrons in a thermal bath. We find that the ratio $R_{\mathrm{side}}{/R}_{\mathrm{out}}\sim 1$ for SPS and $R_{\mathrm{side}}{/R}_{\mathrm{out}}<1\mathrm{}$ for RHIC energy.

The initial stages of relativistic heavy ion collisions are studied numerically in the framework of a $\mathrm{}(2+1)\mathrm{}$-dimensional classical Yang-Mills theory. We calculate the energy and number densities and momentum spectra of the produced gluons. The model is also applied to noncentral collisions. The numerical results are discussed in the light of RHIC measurements of energy and multiplicity and other theoretical calculations. Some problems of the present approach are pointed out.

We study the $A+\overrightarrow{B}{\mathcal{l}}^{+}{\mathcal{l}}^{-}+\mathrm{jet}+X$ process in nucleus-nucleus collisions at relativistic energies. The dilepton as well as the jet will pass through the matter produced in such collisions. The recoiling dilepton will carry information about the kinematical features of the jet, and will thus prove to be a very effective tool in isolating in-medium effects such as energy-loss and fragmentation function modifications. We estimate the contributions due to correlated charm and bottom decay, and identify a window where they are small as compared to pairs from the NLO Drell-Yan process.