Low-lying intruder $T=0\mathrm{}$ states in ${}^8\mathrm{Be}$ have been posited and challenged. To address this issue, we performed ab initio shell model calculations in model spaces consisting of up to $10ħ\Omega$ excitations above the unperturbed ground state with the basis state dimensions reaching $1.87\times {10}^8.$ To gain predictive power we derive and use effective interactions from realistic nucleon-nucleon $\mathrm{}\left(\mathrm{NN}\right)\mathrm{}$ potentials in a way that guarantees convergence to the exact solution with increasing model space. Our $0ħ\Omega$ dominated states show good stability when the model space size increases. At the same time, we observe a rapid drop in excitation energy of the $2ħ\Omega$ dominated $T=0\mathrm{}$ states. In the $10ħ\Omega$ space the intruder $0^{+}0$ state falls below 18 MeV of excitation and, also, below the lowest $0^{+}1$ state. Our extrapolations suggest that this state may stabilize around 12 MeV. We hypothesize that these states might be the broad resonance intruder states needed in R-matrix analysis of $\alpha -\alpha$ elastic scattering. In addition, we present our predictions for the $A=8\mathrm{}$ binding energies with the CD-Bonn $\mathrm{NN}$ potential.

Theoretical aspects of the two-proton radioactivity and three-body decays are studied for nuclear systems, where three-body channel is the only (or dominating) decay channel. We briefly review the current experimental and theoretical status of the problem. We discuss the applicability of the widely used qualitative models (e.g., diproton model, direct decay to continuum) for estimates of the two-proton radioactivity. A three-body model is developed, which is free of most uncertainties typical for these estimates. It employs various forms of approximate boundary conditions for the three-body Coulomb problem and demonstrates high stability for widths and spatial distributions.

Various versions of the Hellmann-Feynman theorem that were studied in a previous paper are applied to the actual computation of certain contributions to the expectation value of the kinetic and potential energies of nuclear matter. The numerical importance of the contributions which violate the Bethe-Brandow-Petscheck theorem in some versions is examined. We also provide a discussion of the so-called conserving approximation which directly derives the expectation value of the kinetic energy from that of the potential energy.

We search for deformed neutron-rich nuclei in which peaks with a considerable amount of the Gamow-Teller (GT) strength (say, the order of $B_{\mathrm{GT}}=1\mathrm{}$ in units of $g_A^2/4\mathrm{}\pi )$ may be present in the excitation energy below a few MeV. The study is based on the Skyrme-type Hartree-Fock calculation plus Tamm-Dancoff approximation or random phase approximation. In addition to known deformed rare-earth nuclei lying at the edge of the β stability line, we suggest deformed nuclei with $Z\approx 40–46$ and $N\approx 62–70,$ which may have an appreciable amount of GT strength at very low energy.

We investigate the achievable degree of agreement between spectroscopic predictions of the geometric collective model (GCM) and the interacting boson model-1 (IBM-1). First, the GCM potential-energy surfaces are made locally equivalent with the IBM-1 semiclassical potentials close to the minimum. The GCM kinetic term is then optimized to reproduce some of the IBM-1 energy ratios. Differences between the spectra, as predicted by the two models, are discussed for the transitional region from the prolate axially symmetric rotor to the spherical vibrator.

Analysis of ${}^{252}\mathrm{Cf}$ recent spontaneous-fission $\gamma$ data from Gammasphere has enabled the discovery of transitions in ${}^{139}\mathrm{Ba}$ in coincidence with those of its Molybdenum fission partner. A new level scheme going up to $\approx 5\hspace{0.5em}\mathrm{Mev}$ includes 11 new transitions and 10 new levels. We make analogies with the 83-neutron isotone ${}^{135}\mathrm{Te}$ and discuss possible configurations in the spherical single-particle shell model. We suggest a band as a possible magnetic rotation band of the type treated by tilted-axis cranking theory.

We perform a distorted-wave impulse approximation calculation of inelastic scattering of deuterons by nuclei using effective interactions in the framework of the sudden approximation at $E_d=400\mathrm{}$ MeV. Cross sections and spin observables are expressed in terms of amplitudes for the corresponding nucleon-nucleus scattering. The calculation is examined for the excitation of ${}^{12}\mathrm{C}$ to the $2^{+}$ (2.44 MeV), $3^{-}$ (9.64 MeV), and $1^{+}$ (12.71 MeV) states and is found to give a reasonable description for most of the observables. Some discrepancies are found for the transition leading to the $1^{+}$ state, suggesting the limitation of the applicability of the effective interaction. Contributions of the deuteron D state are studied. Relations between the deuteron-nucleus and proton-nucleus scattering observables are found and are studied against existing data.

The event-to-event fluctuations of hadron multiplicities are studied for a quark system undergoing second-order phase transition to hadrons. Emphasis is placed on the search for an observable signature that is realistic for heavy-ion collisions. It is suggested that in the two-dimensional $y-\phi$ space the produced particles selected in a very narrow $p_T$ window may exhibit clustering patterns even when integrated over the entire emission time. Using the Ising model to simulate the critical phenomenon and taking into account a $p_T$ distribution that depends on the emission time, we study in the framework of the void analysis proposed earlier and find scaling behavior. The scaling exponents turn out to be larger than the ones found before for pure configurations without mixing. The result is insensitive to the precise scheme in which we simulate the time evolution of the quark system. Thus it should reveal whether or not the dense matter created in heavy-ion collisions is a quark-gluon plasma before hadronization.

In a previous work [S.J.Q. Robinson and Larry Zamick, Phys. Rev. C 63, 064416 (2001)] we studied the effects of setting all two body $T=0\mathrm{}$ matrix elements to zero in shell model calculations for ${}^{43}\mathrm{Ti}$ ${(}^{43}\mathrm{Sc})$ and ${}^{44}\mathrm{Ti}.$ The results for ${}^{44}\mathrm{Ti}$ were surprisingly good despite the severity of this approximation. In single-j shell calculations ${(f}_{7/2}^n)$ degeneracies arose between the $T=\frac{1}{2}$ $I=(\frac{1}{2}{)}_1^{-}$ and $(\frac{13}{2}{)}_1^{-}$ states in ${}^{43}\mathrm{Sc}$ as well as the $T=\frac{1}{2}$ $I=(\frac{13}{2}{)}_2^{-},$ $(\frac{17}{2}{)}_1^{-},$ and $(\frac{19}{2}{)}_1^{-}$ in ${}^{43}\mathrm{Sc}.$ For ${}^{44}\mathrm{Ti}$ the $T=0\mathrm{}$ states $3_2^{+},$ $7_2^{+},$ $9_1^{+},$ and ${10}_1^{+}$ are degenerate as are the ${10}_2^{+}$ and ${12}_1^{+}$ states. The degeneracies can be explained by certain $6j$ symbols and $9j$ symbols either vanishing or being equal as indeed they are. Previously we used Regge symmetries of $6j$ symbols to explain the vanishing $6j$ and $9j$ symbols. In this work a simpler, more physical method is used. This is Talmi’s method of calculating coefficients of fractional parentage (cfp) for identical particles to states which are forbidden by the Pauli principle. This is done for both the one particle cfp to handle $6j$ symbols and the two particle cfp for the $9j$ symbols. From this we learn that the common thread for the angular momenta I for which the above degeneracies occur is that these angular momenta cannot exist in the calcium isotopes in the $f_{7/2}$ shell. There are no $T=\frac{3}{2}$ $f_{7/2}^3$ states with angular momenta $\frac{1}{2},$ $\frac{13}{2},$ $\frac{17}{2},$ and $\frac{19}{2}.$ In the same vein there are no $T=2\mathrm{}{f}_{7/2}^4$ states with angular momenta 3, 7, 9, 10, or 12. For these angular momenta, all the states can be classified by the dual quantum numbers ${(J}_{\pi }{,J}_{\nu }).\mathrm{}$

Within an isospin-dependent transport model for nuclear reactions involving neutron-rich nuclei, we study the first-order direct transverse flow of protons and their second-order differential elliptic flow as a function of transverse momentum. It is found that the differential elliptic flow of midrapidity protons, especially at high transverse momenta, is much more sensitive to the isospin dependence of the nuclear equation of state than the direct flow. Origins of these different sensitivities and their implications to the experimental determination of the isospin dependence of the nuclear equation of state by using neutron-rich heavy-ion collisions at intermediate energies are discussed.

The dynamic separation into phases of high and low baryon density in a heavy ion collision can enhance fluctuations of the net rapidity density of baryons compared to model expectations. We demonstrate that event-by-event proton and antiproton measurements can be used to observe this phenomenon. We then perform real-time lattice simulations to show how these fluctuations arise and how they can survive through freeze-out.

We adopt the quasiparticle-phonon nuclear model to compute the $M1\mathrm{}$ strength distribution in the energy range 4–10 MeV in the deformed ${}^{154}\mathrm{Sm}.$ We show that the coupling with two-phonon configurations enhances considerably the fragmentation of the $M1\mathrm{}$ strength with respect to the random-phase approximation but not enough to reach a complete agreement with experiments. The results obtained contribute also to shed light on the controversial properties of the $M1\mathrm{}$ spectrum in this energy range.

Non-Markovian transport equations for nuclear large amplitude motion are derived from the collisional kinetic equation. The memory effects are caused by Fermi surface distortions and depend on the relaxation time. It is shown that nuclear collective motion and nuclear fission are influenced strongly by memory effects at the relaxation time $\tau >~5\times {10}^{-23}\hspace{0.5em}\mathrm{s}.$ In particular, the descent of the nucleus from the fission barrier is accompanied by characteristic shape oscillations. The eigenfrequency and the damping of the shape oscillations depend on the contribution of the memory integral in the equations of motion. The shape oscillations disappear at the short relaxation time regime at $\overrightarrow{\mathrm{\tau }}$0, which corresponds to the usual Markovian motion in the presence of friction forces. We show that the elastic forces produced by the memory integral lead to a significant delay for the descent of the nucleus from the barrier. Numerical calculations for the nucleus ${}^{236}\mathrm{U}$ show that due to the memory effect the saddle-to-scission time grows by a factor of about 3 with respect to the corresponding saddle-to-scission time obtained in liquid drop model calculations with friction forces.

(96 MeV) ${}^{16}\mathrm{O}{+}^{58}\mathrm{Ni}$ and (133 MeV) ${}^{16}\mathrm{O}{+}^{48}\mathrm{Ti}$ reactions have been experimentally investigated by using coincident charged particle techniques. A closed-form theoretical approach, describing in a single picture the nonequilibrium component and the evaporation component of the angular correlation between particles and reaction residues emitted in a peripheral heavy-ion collision, is applied—in the hypothesis of sequential process—to the $\mathrm{C}-\alpha ,$ $\mathrm{N}-\alpha ,$ and $\mathrm{O}-\alpha$ differential multiplicities for the ${}^{16}\mathrm{O}{+}^{58}\mathrm{Ni}$ at 6 MeV/nucleon and ${}^{16}\mathrm{O}{+}^{48}\mathrm{Ti}$ at 8.3 MeV/nucleon deep inelastic collisions. From this analysis some reaction mechanism information is deduced.

Multifragmentation MF results from $1A\mathrm{GeV}$ Au on C have been compared with the Copenhagen statistical multifragmentation model (SMM). The complete charge, mass, and momentum reconstruction of the Au projectile was used to identify high momentum ejectiles leaving an excited remnant of mass A, charge Z, and excitation energy $E^{*}$ which subsequently multifragments. Measurement of the magnitude and multiplicity (energy) dependence of the initial free volume and the breakup volume determines the variable volume parametrization of SMM. Very good agreement is obtained using SMM with the standard values of the SMM parameters. A large number of observables, including the fragment charge yield distributions, fragment multiplicity distributions, caloric curve, critical exponents, and the critical scaling function are explored in this comparison. The two stage structure of SMM is used to determine the effect of cooling of the primary hot fragments. Average fragment yields with $Z>~3$ are essentially unaffected when the excitation energy is ⩽7 MeV/nucleon. SMM studies suggest that the experimental critical exponents are largely unaffected by cooling and event mixing. The nature of the phase transition in SMM is studied as a function of the remnant mass and charge using the microcanonical equation of state. For light remnants $A<~100,$ backbending is observed indicating negative specific heat, while for $A>~170$ the effective latent heat approaches zero. Thus for heavier systems this transition can be identified as a continuous thermal phase transition where a large nucleus breaks up into a number of smaller nuclei with only a minimal release of constituent nucleons. $Z<~2$ particles are primarily emitted in the initial collision and after MF in the fragment deexcitation process.

We have measured the resonant cross section ${\sigma }_n$ for nuclear excitation of ${}^{115}\mathrm{In}$ via the radiationless annihilation of a positron with a K-shell electron using a monoenergetic positron beam and a thin In target. We find an upper limit on the resonant cross section ${\sigma }_n<4.3\mathrm{}\times {10}^{-26}{\mathrm{cm}}^2$ at a 99% confidence level, compared to the cross section ${\sigma }_{\beta }=1.7\mathrm{}\times {10}^{-25}{\mathrm{cm}}^2$ determined by two previous measurements of nuclear excitation of ${}^{115}\mathrm{In}$ using the broad spectrum of positrons from the beta decay of ${}^{64}\mathrm{Cu}.$ Together these results imply the existence of a hitherto unidentified nonresonant channel for nuclear excitation via energetic positrons.

We have analyzed the latest NA50 data on transverse energy distributions and $J/\psi$ suppression in Pb+Pb collisions. The transverse energy distribution was analyzed in the geometric model of $\mathrm{AA}$ collisions. In the geometric model, fluctuations in the number of $\mathrm{NN}$ collisions at a fixed impact parameter are taken into account. The transverse energy dependence of $J/\psi$ suppression was obtained following the model of Blaizot et al., where charmonium suppression is assumed to be 100% effective above a threshold density. When fluctuations in the number of $\mathrm{NN}$ collisions are taken into account, the NA50 data on $J/\psi$ suppression can be well fitted with a single parameter, the threshold density.

Using the recent shell-model evaluation of stellar weak interaction rates, we have calculated the neutrino spectra arising from electron capture on $\mathrm{pf}$-shell nuclei under presupernova conditions. We present a simple parametrization of the spectra that allows for an easy implementation into collapse simulations. We discuss that the explicit consideration of thermal ensembles in the parent nucleus broadens the neutrino spectra and results in larger average neutrino energies. The capture rates and neutrino spectra can be easily modified to account for phase space blocking by neutrinos, which becomes increasingly important during the final stellar collapse.

Calculations predict a connection between the isotopic composition of particles emitted during an energetic nucleus-nucleus collision and the density dependence of the asymmetry term of the nuclear equation of state (EOS). This connection is investigated for central ${}^{112}{\mathrm{S}\mathrm{n}+}^{112}\mathrm{Sn}$ and ${}^{124}{\mathrm{S}\mathrm{n}+}^{124}\mathrm{Sn}$ collisions at $E/A=50\mathrm{}\mathrm{MeV}$ in the limit of an equilibrated freeze-out condition. Comparisons between measured isotopic yield ratios and theoretical predictions in the equilibrium limit are used to assess the sensitivity to the density dependence of the asymmetry term of the EOS. This analysis suggests preference for a stiff density dependence and indicates that such comparisons may provide an opportunity to constrain the asymmetry term of the EOS.

We have simulated the possible $\Theta$ vacua states in heavy ion collisions. In a quenchlike scenario, random phases of the chiral fields were evolved in a zero temperature potential incorporating the breaking of $U_A\mathrm{}\left(1\right)\mathrm{}$ symmetry. Initial random phases very quickly settle into oscillation around the values dictated by the potential. The simulation indicates that $\Theta$ vacua states that can be populated in heavy ion collisions are a coherent superposition of a number of modes.