Excited states in ${}^{38}\mathrm{Ar}$ have been investigated by means of the heavy-ion fusion-evaporation reaction ${}^{28}\mathrm{Si}{+}^{16}\mathrm{O}.$ The level scheme reveals a subtle interplay between spherical, deformed, and superdeformed shapes. Large-scale shell-model calculations in the $\mathrm{sd}-\mathrm{fp}$ space are invoked to study the microscopic aspects of deformation and shape changes.

The dissociation reaction ${}^6\mathrm{He}\to \alpha +2n$ was studied with ${}^6\mathrm{He}$ projectiles at 23.9 MeV/nucleon in targets of C, Al, Cu, Sn, Pb, and U. Relative to Al, the $2n$ removal cross section ${\sigma }_{-2n}$ with each of the other targets was determined. With U, the Coulomb part accounts for 2/3 of ${\sigma }_{-2n}.$ The widths of the $\alpha$ particle and neutron parallel momentum distributions increase with target Z. For the $\alpha$ particle, ${}^6\mathrm{He}$ dissociation on C gave width $\sigma =40.2\mathrm{}\pm 2.3\hspace{0.5em}\mathrm{MeV}/c,$ corresponding to an rms radius of the halo neutrons of (2.95±0.17) fm, which is (0.35±0.17) fm larger than the rms radius of all four neutrons. The relation between the widths of the $\alpha$ particle and neutron distributions indicates only a small correlation between the two neutrons. This conclusion is supported by the distribution function for the angle between the two neutrons, which was obtained in kinematically complete measurements. The latter measurements with the U target also yielded an $E1\mathrm{}$ strength function, and it agreed with one determined in an experiment at ten times our beam energy.

Scaling properties of fragment size distributions are studied in a microcanonical multifragmentation model. A new method based on the global quality of the scaling function is presented. Scaling is not washed out by the long range Coulomb interaction or by secondary decays for a wide range of source masses, densities, and deposited energies. However, the influence of these factors on the precise value of the critical exponents as well as the finite size corrections to scaling are shown to be important and to affect the possible experimental determination of a specific universality class.

Superfluid states of symmetric nuclear matter with finite total momentum of Cooper pairs [nuclear Larkin-Ovchinnikov-Fulde-Ferrel (LOFF) phase] are studied with the use of Fermi–liquid theory in the model with Skyrme effective forces. It is considered the case of four-fold splitting of the excitation spectrum due to finite superfluid momentum and coupling of $T=0\mathrm{}$ and $T=1\mathrm{}$ pairing channels. It has been shown that at zero temperature the energy gap in triplet-singlet (TS) pairing channel (in spin and isospin spaces) for the ${\mathrm{SkM}}^{*}$ force demonstrates double-valued behavior as a function of superfluid momentum. As a consequence, the phase transition at the critical superfluid momentum from the LOFF phase to the normal state will be of a first order. Behavior of the energy gap as a function of density for TS pairing channel under increase of superfluid momentum changes from one-valued to universal two-valued. It is shown that two-gap solutions, describing superposition of states with singlet-triplet (ST) and TS pairing of nucleons appear as a result of branching from one-gap ST solution. Comparison of the free energies shows that the state with TS pairing of nucleons is thermodynamically most preferable.

Precise measurements of deuteron vector and tensor analyzing powers $A_y^d,$ $A_{\mathrm{xx}},$ $A_{\mathrm{yy}},$ and $A_{\mathrm{xz}}$ in $d-p$ elastic scattering were performed via ${}^1\mathrm{H}(\overrightarrow{d},d)p$ and ${}^1\mathrm{H}(\overrightarrow{d},p)d$ reactions at three incoming deuteron energies of $E_d^{\mathrm{lab}}=140,$ 200, and $270\hspace{0.5em}\mathrm{MeV}.$ A wide range of center-of-mass angles from $\approx 10°$ to $180°$ was covered. The cross section was measured at 140 and 270 MeV at the same angles. These high precision data were compared with theoretical predictions based on exact solutions of three-nucleon Faddeev equations and modern nucleon-nucleon potentials combined with three-nucleon forces. Three-body interactions representing a wide range of present day models have been used: the Tucson-Melbourne $2\pi$-exchange model, a modification thereof closer to chiral symmetry, the Urbana IX model, and a phenomenological spin-orbit ansatz. Large three-nucleon force effects are predicted, especially at the two higher energies. However, only some of them, predominantly $d\sigma /d\Omega$ and $A_y^d,$ are supported by the present data. For tensor analyzing powers the predicted effects are in drastic conflict to the data, indicating defects of the present day three-nucleon force models.

Excitation functions of the reaction $(\alpha ,n),$ $(\alpha ,2n),$ $(\alpha ,3n),$ and $(\alpha ,\alpha n)$ for ${}^{93}\mathrm{Nb}$ were measured up to 37 MeV using the stacked foil activation technique and high-purity Ge γ-ray spectroscopy method. The measured experimental values were compared with the geometry-dependent hybrid model in which the emission of particles prior to the equilibrium decay is taken into account whenever the interaction of projectile with the target nucleus is considered. It was found that the compound nucleus decay mechanism alone is unable to explain the experimental trend of our data. The isomeric cross-section ratios $({\sigma }_m/{\sigma }_g)$ for the $(\alpha ,2n)$ reaction were also calculated as a function of α-particle energy. A definite trend was observed in the variation of the ratio with α-particle energy.

This paper introduces recursive relations allowing the calculation of the number of partitions with constraints on the minimum and/or on the maximum fragment size.

We present an exact method for the calculation of fragment size correlations in a discrete finite system in which correlations explicitly due to the finite extent of the system are suppressed. To this end, we introduce the combinatorial model, which describes the fragmentation of a finite system as a sequence of independent random emissions of fragments. The sequence is accepted when the sum of the sizes is equal to the total size. The parameters of the model, which may be used to calculate all partition probabilities, are the intrinsic probabilities associated with the fragment sizes. Any fragment size correlation function can be built by calculating the ratio between the partition probabilities in the data sample (resulting from an experiment or from a Monte Carlo simulation) and the “independent emission” model partition probabilities. This technique is applied to charge correlations introduced by Moretto and collaborators. It is shown that the percolation and the nuclear statistical multifragmention model are almost independent emission models, whereas the nuclear spinodal decomposition model shows strong correlations corresponding to the breakup of the hot dilute nucleus into nearly equal size fragments.

We evaluate the strangeness production from equilibrating and transversely expanding quark-gluon plasma which may be created in the wake of relativistic heavy-ion collisions. We consider boost-invariant longitudinal and cylindrically symmetric transverse expansion of a gluon-dominated partonic plasma, which is in local thermal equilibrium. Initial conditions obtained from the self-screened parton cascade model are used. We empirically find that the final extent of the partonic equilibration rises almost linearly with the square of the initial energy density. This along with the corresponding variation with the number of participants may help us distinguish between various models of parton production.

The strong longitudinal expansion of the reaction zone formed in relativistic heavy-ion collisions is found to significantly reduce the spatially averaged pion phase-space density, compared to naive estimates based on thermal distributions. This has important implications for data interpretation and leads to larger values for the extracted pion chemical potential at kinetic freeze-out.

Angular distributions of $\sigma \left(\theta \right),$ $A_y,$ ${\mathrm{iT}}_{11},$ $T_{20},$ $T_{21},$ and $T_{22}$ have been measured for $d-p$ scattering at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=667\mathrm{}\mathrm{keV}.$ This set of high-precision data is compared to variational calculations with the nucleon-nucleon potential alone and also to calculations including a three-nucleon $\mathrm{}\left(3N\right)\mathrm{}$ potential. Agreement with cross section and tensor analyzing power data is excellent when a $3N$ potential is used. However, a comparison between the vector analyzing powers reveals differences of approximately 40% in the maxima of the angular distributions which is larger than reported at higher energies for both $p-d$ and $n-d$ scattering. The inclusion of phenomenological spin-orbit forces in a $3N$ potential improves the comparison with vector analyzing powers substantially. Single-energy phase-shift analyses were performed on this data set and a similar data set at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=431.3\mathrm{}\mathrm{keV}.$ The role of the different phase-shift parameters in fitting these data is discussed.

A study of the effects of short-range correlations over the ${(e,e}^{\prime }p)$ reaction for low missing energy in closed-shell nuclei is presented. We use correlated quasihole overlap functions extracted from the asymptotic behavior of the one-body density matrix, containing central correlations of Jastrow type, up to first order in a cluster expansion, and computed in the very high asymptotic region, up to 100 fm. The method to extract the overlap functions is checked in a simple shell model, where the exact results are known. We find that the single-particle wave functions of the valence shells are shifted to the right due to the short-range repulsion by the nuclear core. The corresponding spectroscopic factors are reduced by only a few percent with respect to the shell model. However, the ${(e,e}^{\prime }p)$ response functions and cross sections are enhanced in the region of the maximum of the missing momentum distribution due to short-range correlations.

So far no theoretical tool for the comprehensive description of exclusive electroproduction of vector mesons off nuclei at medium energies has been developed. We suggest a light-cone QCD formalism that is valid at any energy and incorporates formation effects (color transparency), the coherence length, and the gluon shadowing. At medium energies, color transparency (CT) and the onset of coherence length (CL) effects are not easily separated. Indeed, although nuclear transparency measured by the HERMES experiment rises with $Q^2,$ it agrees with predictions of the vector-dominance model (VDM) without any CT effects. Our new results and observations are as follows. (i) The good agreement with the VDM found earlier is accidental and related to the specific correlation between $Q^2$ and CL for HERMES kinematics; (ii) CT effects are much larger than have been estimated earlier within the two-channel approximation. They are even stronger at low energies than at high energies and can be easily identified by HERMES or at JLab; (iii) gluon shadowing, which is important at high energies, is calculated and included; (iv) our parameter-free calculations explain well available data for variation of nuclear transparency with virtuality and energy of the photon; and (v) predictions for electroproduction of ρ and $\phi$ are provided for future measurements at HERMES and JLab.

It is shown that the quark mass density-dependent model cannot be used to explain the process of the quark deconfinement phase transition because the quark confinement is permanent in this model. A quark mass density- and temperature-dependent model in which the quark confinement is not permanent has been suggested. We argue that the vacuum energy density B is a function of the temperature and satisfies ${B=B}_0\left[1-{(T/T}_c{)}^2\right],$ where $T_c$ is the critical temperature of quark deconfinement. The dynamical and thermodynamical properties of bulk strange quark matter for quark mass density- and temperature-dependent model are discussed.

Lifetimes of three excited $K^{\pi }{=0\mathrm{}}^{+}$ bands have been measured in the same deformed nucleus ${(}^{178}\mathrm{Hf}).\mathrm{}$ Evidence is presented for the first observation of two excited $K^{\pi }{=0\mathrm{}}^{+}$ bands connected via collective $E2\mathrm{}$ transitions. Five-band mixing calculations show that these collective transitions are not the result of mixing between the various bands. It is therefore suggested that the $K^{\pi }{=0\mathrm{}}_5^{+}$ band at 1772.2 keV is a collective excitation built on the single phonon $K^{\pi }{=0\mathrm{}}_2^{+}$ band at 1199.4 keV.

The three-nucleon bound state problem is studied employing a nucleon-nucleon potential obtained from a basic quark-quark interaction in a five-channel Faddeev calculation. The obtained triton binding energy is comparable to those predicted by conventional models of the $\mathrm{NN}$ force.

We present the results of an investigation of the contribution to decay of the nucleus by an unexplored mode of internal conversion in which an excited nuclear state deexcites with promotion of an electron to an intermediate filled bound state. This process, which apparently violates the Pauli exclusion principle, may make a significant contribution to the nuclear decay rate when very close matching of the atomic and nuclear transitions is achieved. For an $M1\mathrm{}$ transition, we show that Pauli-forbidden bound internal conversion (PFBIC) transition may occur by excitation of an inner electron to an initially occupied outer orbital. Numerical calculations of the PFBIC process are presented for the decay of the 77.351 keV level of ${}^{197}\mathrm{Au},$ in the neutral atom and in ions up to ${69}^{+}.$ The PFBIC process is found to have a maximum probability in ${}^{197}\mathrm{Au}$ ions with charge state of approximately ${40}^{+},$ due to close energy matching of the nuclear transition to the $1\overrightarrow{s}3s$ electronic excitation. The expected dependence of the nuclear lifetime on PFBIC is analyzed.

We discuss the possibility that narrow states observed in the ${\Delta }_{33}-\mathrm{C}$ system are due to a mechanism of coupling through the continuum when long-lived states are formed in addition to the broad “super-radiant” state. Expressions and estimates for the narrow widths are presented.

The Gerasimov-Drell-Hearn and Baldin-Lapidus sum rules are evaluated in the dressed K-matrix model for photon-induced reactions on the nucleon. For the first time the sum $\alpha +\beta$ of the electric and magnetic polarizabilities and the forward spin polarizability ${\gamma }_0$ are explicitly calculated in two alternative ways—from the sum rules and from the low-energy expansion of the real Compton scattering amplitude—within the same framework. The two methods yield compatible values for $\alpha +\beta$ but differ somewhat for ${\gamma }_0.$ Consistency between the two ways of determining the polarizabilities is a measure of the extent to which basic symmetries of the model are obeyed.

We demonstrate that, in bond percolation of a small system, two phases can be visually identified by displaying the probability distribution of the ejected mass as a function of the number of broken bonds. The phases can be separated using the ratio of the masses of the second largest and largest fragments. The nature of the transition and application to studies of nuclear multifragmentation are discussed.