Density fluctuations of expanding nuclear matter are studied within a mean-field model in which fluctuations are generated by an external stochastic field. The time evolution of the system is studied in a kinetic-theory approach. In this model, fluctuations develop about a mean one-body phase-space density corresponding to a hydrodynamic motion that describes a slow expansion of the system. A fluctuation-dissipation relation suitable for a uniformly expanding medium is obtained and used to constrain the strength of the stochastic field. The coupling between the kinetics of fluctuations and the hydrodynamic expansion is analyzed, and the distribution of the liquid domains in the spinodal decomposition of this expanding nuclear matter is derived. It is found that the formation of the domains can be envisaged as a stationary process. Comparison of the related distribution of the fragment size with experimental data on the nuclear multifragmentation is quite satisfactory.

Statistical fragment emission from excited nuclear systems is studied within the framework of a schematic Fermi-gas model combined with Weisskopf’s detailed balance approach. The model considers thermal expansion of finite nuclear systems and pays special attention to the role of the diffuse surface region in the decay of hot equilibrated systems. It is found that with increasing excitation energy, effects of surface entropy lead to a systematic and significant reduction of effective emission barriers for fragments and, eventually, to the vanishing of these barriers. The model predicts a maximum (effective) nuclear temperature and the occurrence of negative nuclear heat capacities, effects that have been reported in the literature. It also accounts for the observed linearity of pseudo-Arrhenius plots of the logarithm of the fragment emission probability versus the inverse square root of the excitation energy, but does not predict true Arrhenius behavior of these emission probabilities.

An experiment measuring ternary particle yields in ${}^{249}\mathrm{Cf}{(n}_{\mathrm{th}},f)$ was carried out at the high flux reactor of the Institut Laue-Langevin using the Lohengrin recoil mass separator. Parameters of energy distributions were determined for 27 ternary particles up to ${}^{30}\mathrm{Mg}$ and their yields were calculated. The yields of 17 further ternary particles were estimated on the basis of the systematics developed. The heaviest particles observed in the experiment are ${}^{37}\mathrm{Si}$ and ${}^{37}\mathrm{S};$ their possible origin is discussed.

Single-particle spectra and two-particle Bose-Einstein correlation functions are determined analytically utilizing a self-similar solution of nonrelativistic hydrodynamics for ellipsoidally symmetric, expanding fireballs, by assuming that the symmetry axes of the ellipsoids are tilted in the frame of the observation. The directed, elliptic, and third flows are calculated analytically. The mass dependences of the slope parameters in the principal directions of the expansion, together with the mass and angular dependences of the HBT radius parameters, reflect directly the ellipsoidal properties of the flow.

The fast simultaneous hadronization and chemical freeze-out of supercooled quark-gluon plasma, created in relativistic heavy ion collisions, can lead to the reheating of the expanding matter and to the change in a collective flow profile. We use the assumption of statistical nature of the hadronization process, and study quantitatively the freeze-out in the framework of hydrodynamical Bjorken model with different simple quark-gluon plasma equations of state.

We explore the impact of a resolution-dependent constituent quark mass, as recently applied to diffractive meson production, in QCD correlation functions of several spin-0 and spin-1 meson channels. We compare the resulting correlators with experimental and lattice data, analyze the virtues and limitations of the approach, and discuss the channel dependence of the obtained effective quark masses.

We show that the radiative corrections to charged current (CC) nuclear reactions with an electron (positron) in the final state are described by a universal function. The consistency of our treatment of the radiative corrections with the procedure used to extract the value of the axial coupling constant $g_A$ is discussed. To illustrate we apply our results to (anti) neutrino deuterium disintegration and to $\mathrm{pp}$ fusion in the sun. The limit of vanishing electron mass is considered, and a simple formula sufficiently accurate for $E_{\mathrm{obs}}\gtrsim 1\mathrm{MeV}$ is obtained. The size of the nuclear structure-dependent effects is also discussed. Finally, we consider CC transitions with an electron (positron) in the initial state and discuss some applications to electron capture reactions.

The threshold energy of the ${}^{14}\mathrm{N}{\mathrm{}(p,n)\mathrm{}}^{14}\mathrm{O}$ reaction has been measured to be 6354.35(18) keV relative to a 1-V standard, and an earlier value has been withdrawn. This leads to a $Q_{\mathrm{ec}}$ value for the superallowed positron decay of ${}^{14}\mathrm{O}$ of 2831.53(17) keV and a recommended mean value of $Q_{\mathrm{ec}}=2831.47\mathrm{}\left(14\right)\mathrm{}\mathrm{keV}.$

Effective field theory requires all observables to be independent of the representation used for the quantum field operators. It means that off-shell properties of the interactions should not lead to any observable effects. We analyze this issue in the context of many-body approaches to nuclear matter, where it should be possible to shift the contributions of lowest order in purely off-shell two-body interactions into three-body forces. We show that none of the commonly used truncations of the two-body scattering amplitude such as the ladder, Brueckner-Hartree-Fock, or parquet approximations respect this requirement.

The relativistic mean field models with the different parameter sets are extended to investigate the properties of $\Delta$-excited nuclear matter. The calculated results show that the critical densities for the $\Delta$-excited nuclear matter predicted in a chiral hadronic model are larger than those obtained in the nonlinear Walecka model with the parameter sets Tm1 and NL1. The inclusion of the $\Delta$ leads to the decrease in the maximum mass of neutron stars in a chiral hadronic model, while the opposite behavior is shown in the nonlinear Walecka model.

We study the local dynamic polarization potential (DPP) component of the ${}^6\mathrm{He}+p$ interaction, determining that part which is due to breakup processes. Results are presented for c.m. energies of 21.57 and 35.06 MeV. The DPP is found by subjecting the elastic scattering S matrix from continuum-discretized coupled-channels calculations to S matri$\overrightarrow{\mathrm{x}}$potential inversion. The iterative-perturbative inversion method is employed, and the method is shown to give reliable potentials down to projectile-target separation close to zero, a necessary requirement for this case. The contributions of different continuum states are compared, and the way they interact to give the overall DPP is studied. The DPP is found to be very different from that determined using the weighted trivially equivalent approximate method.

We calculate the emission of large mass dileptons originating from the annihilation of quark jets passing through quark gluon plasma. Considering central collisions of heavy nuclei at SPS, RHIC, and LHC energies, we find that the yield due to the jet-plasma interaction gets progressively larger as the collision energy increases. We find it to be negligible at SPS energies, of the order of the Drell-Yan contribution and much larger than the normal thermal yield at RHIC energies and up to a factor of 10 larger than the Drell-Yan contribution at LHC energies. An observation of this new dilepton source would confirm the occurrence of jet-plasma interactions and of conditions suitable for jet quenching to take place.

The mass shift of charmonium states in nuclear matter is studied in the perturbative QCD approach. The leading-order effect due to the change of gluon condensate in nuclear matter is evaluated using the leading-order QCD formula, while the higher-twist effect due to the partial restoration of chiral symmetry is estimated using a hadronic model. We find that while the mass of $J/\psi$ in nuclear matter decreases only slightly, those of $\psi \mathrm{}\left(3686\right)\mathrm{}$ and $\psi \mathrm{}\left(3770\right)\mathrm{}$ states are reduced appreciably. Experimental study of the mass shift of charmonium states in nuclear matter can thus provide valuable information on the changes of the QCD vacuum in nuclear medium.

We investigate parity-violating asymmetries in $\overrightarrow{n}p$ radiative capture at thermal neutron energies and in deuteron electrodisintegration in quasielastic kinematics, using the Desplanques, Donoghue, and Holstein model for the parity-violating nucleon-nucleon interaction. We find dramatic cancellations between the asymmetries induced by the parity-violating interaction and those arising from the associated parity-violating pion-exchange currents. In the $\overrightarrow{n}p$ capture, the model dependence of the result is nevertheless quite small, because of constraints arising through the Siegert evaluation of the relevant $E_1$ matrix elements. In quasielastic electron scattering, these processes are found to be insignificant compared to the asymmetry produced by $\gamma -Z$ interference on individual nucleons. These two experiments, then, provide clean probes of different aspects of weak-interaction physics associated with parity violation in the $\mathrm{np}$ system.

High-spin states in ${}^{46}\mathrm{Ti}$ have been investigated with the reaction ${}^{28}\mathrm{Si}{(}^{24}\mathrm{Mg},\alpha 2p)$ at 100 MeV, using the GASP γ-ray array and the charged-particle detector ISIS. The positive parity yrast sequence has been observed up to the ${14}^{+}$ terminating state and several high-energy transitions have been established above the termination state. Both the signatures of a negative parity band have been observed up to the ${16}^{-}$ and ${17}^{-}$ terminating states, plus one more transition from an ${18}^{-}$ state at 19.086 MeV excitation. The observed states are interpreted within the frame of large scale shell model calculations in the full $\mathrm{pf}$ space (positive parity) and as particle-hole excitations from the $d_{3/2}$ shell (negative parity).

Nuclear resonance fluorescence experiments were performed on the rare-earth nuclei ${}^{151,153}\mathrm{Eu},$ and with considerably increased sensitivity on ${}^{163}\mathrm{Dy}$ and ${}^{165}\mathrm{Ho}$ to study the fragmentation of the $M1\mathrm{}$ scissors mode in odd-mass nuclei, and to clarify the puzzle of the missing total $M1\mathrm{}$ strength observed for odd-mass nuclei so far. Using the bremsstrahlung photon beam of the Stuttgart Dynamitron (end point energy 4.05 MeV) and high-resolution Ge $\gamma$-ray spectrometers, detailed information was obtained on excitation energies, decay widths, transition probabilities, and branching ratios. Whereas in ${}^{151}\mathrm{Eu}$ only 11 weak excitations were observed, 161 and 138 excitations could be detected in the heavier nuclei ${}^{163}\mathrm{Dy}$ and ${}^{165}\mathrm{Ho},$ respectively. The results are compared to those observed recently at the Stuttgart facility for the neighboring odd-mass nuclei ${}^{161}\mathrm{Dy},$ ${}^{155,157}\mathrm{Gd},$ and ${}^{159}\mathrm{Tb}.$ The measured total strengths increase with the mass number $A.\mathrm{}$ Ascribing the same portion of the dipole strength to $M1\mathrm{}$ excitations as measured in the neighboring even-even nuclei, the total $M1\mathrm{}$ strength deduced from the most sensitive experiment on ${}^{163}\mathrm{Dy}$ is comparable to those found in the neighboring even-even nuclei. The results for ${}^{163}\mathrm{Dy}$ and ${}^{165}\mathrm{Ho}$ are compared with a fluctuation analysis of the photon scattering spectra to estimate the amount of still unresolved strength eventually hidden in the background due to the extreme fragmentation of the $M1\mathrm{}$ scissors mode in odd-mass rare-earth nuclei. For ${}^{165}\mathrm{Ho},$ the total derived strength of $B\left(M1\mathrm{}\right)\mathrm{}\uparrow =2.9\mathrm{}\left(5\right)\mathrm{}{\mu }_N^2$ agrees within error bars with an earlier analysis of a different measurement of the ${}^{165}\mathrm{Ho}(\gamma ,{\gamma }^{\prime })$ reaction. In ${}^{163}\mathrm{Dy}$ the method leads to an unphysical background shape, underlining the experimental observation of a significantly reduced fragmentation pattern of the dipole modes in this nucleus, which must be traced back to structure features of the Dy isotopes.

The superdeformed bands in ${}^{58}\mathrm{Cu},$ ${}^{59}\mathrm{Cu},$ ${}^{60}\mathrm{Zn},$ and ${}^{61}\mathrm{Zn}$ are analyzed within the frameworks of the Skyrme-Hartree-Fock as well as Strutinsky-Woods-Saxon total Routhian surface methods with and without $T=1\mathrm{}$ pairing correlations between like particles. It is shown that a consistent description within these standard approaches cannot be achieved. A $T=0\mathrm{}$ neutron-proton pairing configuration mixing of signature-separated bands in ${}^{60}\mathrm{Zn}$ is suggested as a possible solution to the problem.

The nuclei ${}^{55,56}\mathrm{Cr}$ were populated to high spin following the reaction ${}^{48}\mathrm{Ca}{(}^{11}\mathrm{B}{,pxn)}^{58-x}\mathrm{Cr}$ at a beam energy of 35–40 MeV. The level scheme of ${}^{55}\mathrm{Cr}$ has been confirmed and extended to $J^{\pi }={\frac{25}{2}}^{+}.$ The level scheme of ${}^{56}\mathrm{Cr}$ has been extended to $J=13.\mathrm{}$ The spins and parity of the majority of levels have been determined unambiguously for the first time. The first firm evidence for an intruder band based on the $\nu g_{9/2}$ orbital has been observed in ${}^{55}\mathrm{Cr}.$ In ${}^{56}\mathrm{Cr},$ the position of the first $4^{+}$ state has been determined unambiguously and the presence of a subshell closure at $N=32\mathrm{}$ has been confirmed on the basis of the $E_{4_1^{+}}{/E}_{2_1^{+}}$ systematics. The properties of both nuclei are compared with total Routhian surface calculations and with previous predictions of subshell closures at $N=32\mathrm{}$ and 34. The systematics in the region are discussed in terms of the strong $\nu f_{5/2}-\pi f_{7/2}$ interaction and its effect on the underlying single-particle structure.

The imaging technique is applied to two-proton correlation functions to extract quantitative information about the space-time properties of the emitting source and about the fraction of protons which can be attributed to fast emission mechanisms. These new analysis techniques resolve important ambiguities that bedeviled prior comparisons between measured correlation functions and those calculated by transport theory. Quantitative comparisons to transport theory are presented here. The results of the present analysis differ from those reported previously for the same reaction systems. The shapes of the two-proton emitting sources are strongly sensitive to the details about the in-medium nucleon-nucleon cross sections and their density dependence.

We apply the single quark transition model to resonance transition amplitudes extracted from photo-production and electroproduction data. We use experimental data on the $S_{11}\mathrm{}\left(1535\right)\mathrm{}$ and $D_{13}\mathrm{}\left(1520\right)\mathrm{}$ nucleon resonances to extract the amplitudes for the electromagnetic transition from the nucleon ground state $[56,\hspace{0.5em}{0}^{+}]$ to the $[70,\hspace{0.5em}{1}^{-}]$ supermultiplet, and make predictions for the transition amplitudes of all other states associated with the $[70,\hspace{0.5em}{1}^{-}].$ We compare the predictions with data and find surprisingly good agreement. The comparison is hampered by the poor data quality for many of the states especially in the electroproduction sector.