In the framework of the triaxial rotor model of Davydov and Filippov, deformation parameters $\beta$ and $\gamma$ are extracted from both level energies and $E2\mathrm{}$ transition rates in even-even Hf-Hg nuclei. Three results emerge: the two sets of $\beta$ and $\gamma$ values—energy-based and transition-rate-based—are in good agreement, with only a few exceptions, thus giving confidence in the extracted values; both $\beta$ and $\gamma$ follow smooth trajectories against $N_p{N}_n;$ and the $\beta$ and $\gamma$ values themselves are correlated, pointing to the possibility of a simpler description of structural evolution.

A truncation scheme of interaction boson model 2 with an F-spin value equal to ${\mathit{F}}_{\max }$ and ${\mathit{F}}_{\max }$-1 is suggested. Wave functions with definite F-spin values are constructed. The boson coefficients of fractional parentage with F spin are calculated by a group theoretical method. The model is applied to calculate the energy levels, B(E2) values, and B(M1) values of the Sm isotopes. It was found that the energy levels including the lowest $1^{+}$ states can be reproduced quite well. The B(E2) and B(M1) values can be produced reasonably well.

Using the nuclear proximity approach and the two center nuclear shape parametrization, the interaction potential between two deformed and pole-to-pole oriented nuclei forming a necked configuration in the overlap region is calculated and its role is studied for the cluster decay half-lives. The barrier is found to move to a larger relative separation, with its proximity minimum lying in the neighborhood of the Q value of decay and its height and width reduced considerably. For cluster decay calculations in the preformed cluster model of Malik and Gupta, due to deformations and orientations of nuclei, the (empirical) preformation factor is found to get reduced considerably and agrees nicely with other model calculations known to be successful for their predictions of cluster decay half-lives. Comparison with the earlier case of nuclei treated as spheres suggests that the effects of both deformations and neck formation get compensated by choosing the position of cluster preformation and the inner classical turning point for penetrability calculations at the touching configuration of spherical nuclei.

Observations of heavy remnants emitted at forward angles with high velocities and high associated particle multiplicities have been used to select central collisions of $35A$ MeV ${}^{63}$Cu with ${}^{197}$Au. The data indicate that these remnants, both fission fragments and evaporation residuelike products, result from the deexcitation of nuclei with $A\sim 225$–240 having excitation energies of $\sim$ 800–1300 MeV. Similar particle multiplicities are observed for both evaporative and fission decay channels. Modeling the results with hybrid codes which treat entrance channel dynamics followed by sequential statistical decay requires the inclusion of some delay in the fission channel to produce heavy remnants with mass $A>~130$, but the trend of the predicted velocities of these heavy remnants is different from that of the experiments. Calculations with a dynamic model based on the molecular dynamics approach have also been performed and lead to similar results. He and Li isotope yield ratios and the apparent temperatures derived from those ratios are similar to those previously reported for excited nuclei in this mass region. Temperatures derived from other yield ratios are also similar once a self-consistent treatment, taking into account population and decay of known excited states, is applied. The derived temperatures show little variation with excitation energy, suggesting that a limiting temperature may be reached at relatively low excitation energy, although the interpretation of this result and the determination of the actual initial value of this temperature is model dependent. Comments on the application of the double isotope yield ratio technique to extraction of the nuclear caloric curve are made.

We discuss semi-inclusive $\mathrm{eA}\to e^{\prime }\mathrm{hX}$ processes in which the hadron $h$ is emitted backward in the rest frame of the target nucleus. The purpose of our analysis is the comparison of two approaches based on different descriptions of nuclear structure at short interparticle distance. The first one uses nucleonic degrees of freedom and a nuclear spectral function obtained from a microscopic many-body calculation, whereas in the second one the relativistic invariant phase-space volume available to a quark in a nucleus is computed, taking into account nucleon-nucleon correlations. The calculated proton and $\pi$-meson spectra are compared to the data taken at SLAC using 14.5 GeV $e^{+}$ and $e^{-}$ scattering off CO.

We estimate the contribution of inelastic nucleon excitations to the ${(e,e}^{\prime })$ inclusive cross section in the CEBAF kinematic range. Calculations are based upon parameterizations of the nucleon structure functions measured at SLAC. Nuclear binding effects are included in a vector-scalar field theory, and are assumed to have a minimal effect on the nucleon excitation spectrum. We find that for $q\lesssim 1$ GeV the elastic and inelastic nucleon contributions to the nuclear response functions are comparable, and can be separated, but with roughly a factor of 2 uncertainty in the latter from the extrapolation from data. In contrast, for $q\gtrsim 2$ GeV this uncertainty is greatly reduced but the elastic nucleon contribution is heavily dominated by the inelastic nucleon background.

A study of the decay of hot and heavy composite nuclei produced in the violent collisions between ${}^{63}$Cu and ${}^{232}$Th at 35$A$ MeV is presented. The measurement of fission fragment correlations indicates that $\sim$ 70$\%$ of the projectile linear momentum can be transferred to the fissioning system. Heavy reaction products were observed at a laboratory angle of $\theta$=6$°$ in coincidence with neutrons, light charged particles, and intermediate mass fragments. The dynamical aspects of the collisions between the projectile and target nuclei were investigated using the computer code CHIMERA which is based upon the molecular dynamics concept. Asymptotic characteristics of the reaction products were confronted with results of calculations of the tandem CHIMERA plus GEMINI codes. The data and model comparisons show that a composite system of mass as high as 275 amu and with an excitation energy $\sim$ 1 GeV is formed in the most violent collisions. Some of the heavy reaction remnants are located on the fragment mass versus velocity plane inside the area where the evaporation residues resulting from the decay of the hot composite system are expected. A high neutron multiplicity associated with these events indicates their origin in the most dissipative events. However, a low cross section for the production of these remnants and the close similarity of their characteristics to the fission fragments do not allow more conclusive statements.

The role of higher order coupling of surface vibrations to the relative motion in heavy-ion fusion reactions at near-barrier energies is investigated. The coupled channels equations are solved to all orders and also in the linear and the quadratic coupling approximations. Taking ${}^{64}$Ni + ${}^{92,96}$Zr reactions as examples, it is shown that all order couplings lead to considerably improved agreement with the experimentally measured fusion cross sections and average angular momenta of the compound nucleus for such heavy, nearly symmetric systems. The importance of higher order coupling is also examined for asymmetric systems like ${}^{16}$O + ${}^{112}$Cd, ${}^{144}$Sm, for which previous calculations of the fusion cross section seemed to indicate that the linear coupling approximation was adequate. It is shown that the shape of the barrier distributions and the energy dependence of the average angular momentum can change significantly when the higher order couplings are included, even for systems where measured fusion cross sections may seem to be well reproduced by the linear coupling approximation.

Analyses of recent measurements of the scattering of alpha particles by ${}^{58}$Ni at energies of 129 and 240 MeV have indicated that only about a third of the sum rule limit for isoscalar monopole transitions was found in the giant resonance region of excitation energies ${(E}_x$ from 10 to 30 MeV). Here we examine the theoretical aspects of these analyses of inelastic scattering, both in the optical potentials obtained from elastic data and in the models used to represent the inelastic transitions. In particular we introduce the folding model and compare the use of folded optical and transition potentials with those obtained by deforming phenomenological optical potentials. We also study the effects of dynamic corrections on the folding interaction when this is density dependent. Both aspects are shown to have significant effects. We use more extensive elastic data at 139 and 340 MeV to illustrate the need for a density dependence in the folding interaction, as well as a need for different shapes for the real and imaginary parts of the potentials. Although these various features are shown to have non-neglible effects on the theoretical cross sections for the excitations at small angles, none of them is sufficient to account for all the apparently missing strength. We estimate, based upon the most realistic folding models, that about 50% of the sum rule limit for monopole excitation was observed within the two components of the spectra centered at 17.42 and 20.76 MeV. The sharing between these two components depends upon the assumptions made about the distribution of the giant dipole strength which also results in angular distributions that peak at 0$°$. Thus about one-half of the sum rule limit appears to have been observed, rather than the one-third originally inferred from these data using the deformed potential model. These conclusions are based, on the one hand, upon the spectral decomposition proposed for the results of the 240 MeV experiment and, on the other hand, upon assuming that the simple breathing mode form is adequate for the monopole transition densities. The results may be sensitive to deviations from either assumption. In a similar way we also infer that at least 55%, and perhaps as much as 70%, of the isoscalar quadrupole sum rule limit may be present in this giant resonance range of excitation energies in ${}^{58}$Ni.

Simple theoretical estimates of the cross sections for $2n$ removal from ${}^6\mathrm{He}$ and for combined $2n$ and $4n$ removal from ${}^8\mathrm{He}$ are compared with new measurements on Si targets at 0–55 MeV/nucleon. Nuclear effects, described by a microscopic theory of Esbensen and Bertsch, account for nearly all of the observed cross sections. The electric dipole response function for ${}^6\mathrm{He}$ obtained by Danilin et al., whose calculations include valence $n-n$ correlations, is used to predict a Coulomb dissociation cross section about 10% as large as that for nuclear dissociation. A smaller upper limit for ${}^8\mathrm{He}$ Coulomb dissociation is found by applying the non-energy-weighted sum rule. Equally good fits to the 800-MeV/nucleon ${}^{6,8}\mathrm{H}\mathrm{e}+\mathrm{C}$ fragmentation data are obtained.

The long-standing problem of experimental signatures for clustering effects in light nuclei is discussed for the conditions corresponding to a recent experiment. The specific reaction ${}^{12}\mathrm{C}{(p,p}^{\prime }\alpha {)}^8\mathrm{Be}$ at incident proton energy 300 MeV and fixed proton and alpha-particle angles near the quasielastic peak is discussed. The Glauber approximation with a simple parametrization of the elementary nucleon-nucleon amplitude is used for calculating the cross section. The main emphasis is on the existence of virtually excited cluster configurations and their manifestation in experimental observables. The shell model wave function of the ${}^{12}\mathrm{C}$ ground state is used to extract the weights of excited cluster components and to calculate their contributions to the cross section. The presence of several excited components and their complicated interference influence the shape and the height of the quasielastic peak; the change can reach an order of magnitude. It is shown that the cross section for cluster emission with the excitation of ${}^8\mathrm{Be}$ into the first excited $2^{+}$ state is small as compared to the process leaving ${}^8\mathrm{Be}$ in its ground state.

We present calculations of the reaction ${A(e,e}^{\prime }\pi N)B$ in the distorted (and plane) wave impulse approximation. The reaction allows for the study of the production process in the nuclear medium without being obscured by the details of nuclear transition densities. First, a pion electroproduction operator suitable for nuclear calculations is obtained by extending the Blomqvist-Laget photoproduction operator to the virtual photon case, which describes the existing data reasonably well. It is applied in nuclei to predict nuclear cross sections under a variety of kinematic arrangements. Issues such as the effects of the interference of the $\Delta$ resonance with the background, sensitivities to the quadrupole component of the $\Delta$ excitation and to the electromagnetic form factors, and the role of final-state interactions are studied in detail. It is found that the longitudinal and the LT interference structure functions in ${(e,e}^{\prime }{\pi }^{0}N)$ are sufficiently sensitive to extract medium modifications of the $\Delta$ quadrupole component. Methods on how to experimentally separate the various pieces in the coincidence cross section are suggested. Finally, the model is compared to a recent SLAC experiment.

The electromagnetic inclusive transverse response of nuclear matter at saturation density is studied within the correlated basis function perturbation theory for momentum transfers $q$ from $300$ to 550 MeV/$c$. The correlation operator includes a Jastrow component, accounting for the short range repulsion, as well as longer range spin, tensor, and isospin ones. Up to correlated one-particle–one-hole intermediate states are considered. The spreading due to the decay of particle (hole) states into two-particle–one-hole (two-hole–one-particle) states is considered via a realistic optical potential model. The Schiavilla-Pandharipande-Riska model for the two-body electromagnetic currents, constructed so as to satisfy the continuity equation with realistic $v_{14}$ potentials, is adopted. Currents due to intermediate $\Delta$-isobar excitations are also included. The global contribution of the two-body currents turns out to be positive and provides an enhancement of the one-body transverse response ranging from $\sim 20\%$ for the lower momenta to $\sim 10\%$ for the higher ones. This finding is in agreement with the Green’s function Monte Carlo studies of the transverse Euclidean response in $A=3,4\mathrm{}$ nuclei and contradicts previous results obtained within the Fermi gas and shell models. The tensor-isospin component of the correlation is found to be the leading factor responsible for such a behavior. The nuclear matter response is compared to recent experimental data on ${}^{40}$Ca and ${}^{56}$Fe.

It is known from measurements of the spin-transfer coefficients, $D_{\mathrm{xx}}$ and $D_{\mathrm{zz}},$ that the spin-transverse part of the cross section is enhanced with respect to the nuclear mean field theory in the $\mathrm{}(p,n)\mathrm{}$ reaction on various targets, such as ${}^2$H and ${}^{12}$C. To account for the enhancement, the effect of the two-body current due to spin-transverse component is studied together with the impulse approximations. In particular, we calculate the inclusive cross section of the $d(p,n)\mathrm{}$ reaction and show that most of the excessive strength in the spin-transverse channel can be explained by the inclusion of the two-body current effect.

Dispersion theory of proton Compton scattering is extended to energies up to ∼1 GeV where excitations of higher resonances and nonresonance double-pion photoproduction become important photoabsorption mechanisms. To saturate s-channel dispersion relations, the VPI partial-wave analysis of single-pion photoproduction and resonance photocouplings is used. Models for double-pion photoproduction and dispersion asymptotic contributions are constructed. The latter are mainly given by ${\mathrm{\pi }}^0$ and σ(600) exchanges. Being used in dispersion calculations, they result in a reasonable agreement with all available data on both differential cross sections and polarization observables in Compton scattering. Some unsolved problems are outlined.

Using an eikonal formulation a phenomenological representation is constructed which simulates multiparticle production processes initiated by hadron-hadron collisions from threshold to 250 GeV/$c$ laboratory momentum. Essential features examined include the multiplicity distribution, rapidity distribution, and transverse momentum distribution with a bias in rapidity. A specific technique is developed to ensure that conservation of energy momentum and conservation of charge is maintained for individual events. This event generator can be used directly as part of a kernel of a more complicated event generator describing heavy-ion collisions based on geometrically orientated hadronic cascading processes.

Transverse energy dependence ${\mathrm{dE}}_T/d\eta$ of O+Ag, S+Ag, and S+W collisions at 200 GeV/$c$ are analyzed in a parameter-free phenomenological model of cascade and clustering based on $p$+$p$ and $p$+Ag collisions. The model uses an event generator which explicitly displays the impact parameter dependence of the colliding hadrons and incorporates basic features of multiparticle production in $p$+$p$ collisions. $p$+Ag data at 200 GeV/$c$ are first analyzed with special attention to the time ordering of the cascading many-body processes using the space-time geometry and the impact parameter dependence of the colliding hadrons. We introduce a relaxation time parameter $\tau ,$ the size of a time interval of the overlapping regions of space-time in the center-of-momentum frame of the colliding hadrons. Within a $\tau$ interval of relaxation, impacts of all collisions are accumulative. Only after this time has passed are pions allowed to be emitted from excited nuclear matter according to a set of rules for cascade. A value of $\tau \sim 0.1$ fm/$c$ used for $p$+Ag data leads to a description of the gross features of the transverse energy dependence ${\mathrm{dE}}_T/d\eta$ of O+Ag and S+Ag data of WA80 and S+W data in the forward region of HELIOS.

We study relativistic S+Au collisions at $200A$ GeV/$c$ using a hydrodynamical approach. We test various equations of state (EOS’s), which are used to describe the strongly interacting matter at densities attainable in the CERN-SPS heavy ion experiments. For each EOS, suitable initial conditions can be determined to reproduce the experimental hadron spectra; this emphasizes the ambiguity between the initial conditions and the EOS in such an approach. Simultaneously, we calculate the resulting thermal photon and dielectron spectra, and compare with experiments. If one allows the excitation of resonance states with increasing temperature, the electromagnetic signals from scenarios with and without phase transition are very similar and are not resolvable within the current experimental resolution. Only EOS’s with a few degrees of freedom up to very high temperatures can be ruled out presently. We deduce an upper bound of about 250 MeV for the initial temperature from the single photon spectra of WA80. With regard to the CERES dilepton data, none of the EOS’s considered, in conjunction with the standard leading order dilepton rates, succeed in reproducing the observed excess of dileptons below the $\rho$ peak. Our work, however, suggests that an improved measurement of the photon and dilepton spectra has the potential to strongly constrain the EOS.

We investigate the influence of medium corrections to the pion dispersion relation on the pion dynamics in intermediate energy heavy ion collisions. To do so a pion potential is extracted from the in-medium dispersion relation and used in QMD calculations and thus we take care of both, real and imaginary part of the pion optical potential. The potentials are determined from different sources, i.e., from the $\Delta$-hole model and from phenomenological approaches. Depending on the strength of the potential, a reduction of the anticorrelation of pion and nucleon flow in noncentral collisions is observed as well as an enhancement of the high-energetic yield in transverse pion spectra. A comparison to experiments, in particular to $p_t$ spectra for the reaction Ca+Ca at 1 GeV/nucleon and the pion in-plane flow in Ne+Pb collisions at 800 MeV/nucleon, generally favors a weak potential.

We reconsider the Dirac-Foldy contribution ${\mu }^2/m$ to the neutron electric polarizability. Using a Dirac equation approach to neutron-nucleus scattering, we review the definitions of Compton continuum $\left(\overline{\alpha }\right)$, classical static $\left({\alpha }_E^n\right)$, and Schrödinger $\left({\alpha }_{\mathrm{Sch}}\right)$ polarizabilities and discuss in some detail their relationship. The latter ${\alpha }_{\mathrm{Sch}}$ is the value of the neutron electric polarizability as obtained from an analysis using the Schrödinger equation. We find in particular ${\alpha }_{\mathrm{Sch}}=\overline{\alpha }-{\mu }^2/m$, where $\mu$ is the magnitude of the magnetic moment of a neutron of mass $m$. However, we argue that the static polarizability ${\alpha }_E^n$ is correctly defined in the rest frame of the particle, leading to the conclusion that twice the Dirac-Foldy contribution should be added to ${\alpha }_{\mathrm{Sch}}$ to obtain the static polarizability ${\alpha }_E^n.$