The effects of collective expansion on light-fragment emission from central heavy-ion collisions are studied by carrying out calculations in a transport model with dynamic production of A≤3 fragments. Beam energies of few hundred MeV/nucleon are considered. In the simulations the formation of a region of dense excited nuclear matter is observed, which expands in transverse directions. The expansion is reflected in the angular distributions and in the mean transverse energies of emitted fragments. At the late stage of expansion the characteristic features of local thermodynamic equilibrium are identified. Different particles share nearly the same collective energy per nucleon, and nearly the same thermal energy. The calculated mean transverse energies of the fragments reflect the collective energy whose magnitude varies with impact parameter. However, the fragment energies only partially agree with available data. The calculated spectra exhibit different slopes at angles around c.m. 90° in central reactions.

Experimental fusion excitation functions have been fitted for several systems using an energy-dependent barrier-penetration model as suggested in our earlier work where the barrier height is written as a function of the radial kinetic energy ɛ at the interaction barrier. This form of the energy dependence of the fusion barrier leads also to an implied l dependence of the barrier. It is shown that the enhancement of 〈l〉 over 〈l${\mathrm{〉}}_{\mathit{o}\mathit{d}}$ predicted by a simple energy-independent barrier-penetration model is maximum around the Coulomb barrier. A correlation has also been oberved between this maximum enhancement factor and the product of the charges of the colliding nuclei.

A method is given for calculating the heavy ion subbarrier fusion cross section for nuclei which are described by the interacting boson model. Explicit formulas are given for the case when the target is rotational, including both quadrupole and hexadecapole couplings. Calculations of the fusion cross section, average angular momentum, and distribution of barriers for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{154}$Sm are compared with experimental results and with predictions of the geometrical model.

We present two methods for the calculation of state densities with linear momentum. The first is exact, convoluting single-particle and hole densities in momentum space, and can be used for nuclear excitations with small numbers of particles and holes. The second, based on statistical arguments, is applicable for excitations of many particles and holes and leads to state densities with a Gaussian linear-momentum dependence. Together, these two techniques allow state densities with linear momentum to be determined for any particle-hole excitation. The relationship between linear- and angular-momentum state densities is discussed, and we show how the familiar Gaussian angular-momentum distribution of states can be obtained from state densities with linear momentum. We argue that these state densities provide the most elegant and straightforward means for obtaining angular distributions in semiclassical preequilibrium theories, avoiding inconsistencies inherent in the commonly adopted procedure of using a nucleon-nucleon scattering kernel. In our approach the angular distribution of preequilibrium particles emitted from a two-particle–one-hole state is identical to that found by Kikuchi and Kawai. Angular distributions from more complex particle-hole states do, however, differ from a convolution of Kikuchi-Kawai scattering kernels, since we do not make a leading-particle approximation. As an illustrative example to the use of the Gaussian form of state densities with linear momentum, we calculate the angular distributions of emitted particles in the preequilibrium reaction ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$(α,p), ${\mathit{E}}_{\mathrm{\alpha }}$=109 MeV. Our calculations account for the experimental angular distributions well, even at large backward angles where many semiclassical approaches fail.

Mean ranges and forward-to-backward ratios have been determined by the thick-target, thick-catcher technique for fragments from the interaction of 13.6-GeV/nucleon ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ with copper. Experimental data are analyzed in terms of a two-step model and results are discussed in the context of limiting fragmentation and factorization and the predictions of a simple model for momentum transfer. Momenta imparted in the initial interactions of 13.6-GeV/nucleon ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ were inferred to be ∼12% lower than those for fragmentation of Cu by high-energy protons.

Relativistic hydrodynamics including final-state interactions is used for a detailed description of the experimental data on particle spectra of sulphur-sulphur collisions at 200A GeV from the NA35 Collaboration. Under the assumption of thermalization of the entire detected baryonic matter it is found that a consistent reproduction of both pion and proton spectra requires strong stopping as an initial condition for the expanding fireball. The results from these calculations are then used to extract a transverse radius which includes also contributions from the decay of unstable particle resonances. Its value is found to be rapidity dependent within the range of 3–4 fm, which agrees with experimental results from Bose-Einstein correlations. In addition, the analysis of the strange particle distribution indicates chemical equilibrium for ${\mathit{K}}^0$ and Λ particles.

A nonlocal Nambu–Jona-Lasinio model is used to calculate strong interaction contributions to the ω-ρ mass splitting. We analyze the contributions of the ρ→ππ, ω→ρπ, and ω→πππ self-energy diagrams and fully account for their momentum dependence. We determine that, of these, the ρ→ππ term dominates to the point where the other terms may be neglected. The meson loop expansion in this model is therefore seen to be rapidly convergent. The results of our calculation suggest some qualitative constraints on the confining part of the q-q¯ interaction in models of this type.

Nuclear attenuation of the leading (${\mathit{x}}_{\mathit{f}}$>0) hadron and the nuclear enhancement of target fragmentation (${\mathit{x}}_{\mathit{f}}$<0) hadrons in lepton-nucleus reactions are calculated via a (3+1)-dimensional string-parton model. A (1+1)-dimensional string model is used to investigate the dependence of rapidity distributions on the lepton energy loss, ν=10–100 GeV, the atomic number, A=1–200, the effective string tension, κ=0.5–2 GeV/fm, the string decay constant, ${\mathrm{\tau }}_0$=0.5–2 fm/c, and the string flip cross section, ${\mathrm{\sigma }}_{\mathit{l}\mathit{q}}$=0–30 mb. The (3+1)-dimensional string-parton model includes inelastic final state cascading of produced hadrons in the nucleus. We show how the A dependence of hadronic production in lepton-nucleus collisions, especially in the ${\mathit{x}}_{\mathit{f}}$<0 region, may be used to extract information on quark propagation and hadronization in nuclei.

Radiative and ordinary muon capture are studied in medium heavy nuclei using a relativistic mean field theory approach. A relativistic Fermi gas model is used to describe the nucleus and the local density approximation, together with realistic density distributions, are used to relate the process in infinite nuclear matter to finite nuclei. A number of density dependent effects not considered in previous nonrelativistic calculations are considered, as, for example, the variation of the effective nucleon mass and of the Fermi momentum with the nuclear density. The photon spectrum and the total experimentally accessible radiative rate (i.e., the part of the spectrum with photon momentum k≥57 MeV) are calculated for a variety of nuclei, along with the ordinary muon capture rate. The aim is to understand the sensitivities to the various components and to assess the reliability of such models for extracting the induced pseudoscalar coupling constant ${\mathit{g}}_{\mathit{P}}$ from the experimental data. We find that the rates are quite dependent on the various inputs, which suggests that it will be difficult to extract ${\mathit{g}}_{\mathit{P}}$ and casts some doubt on the validity of previous similar calculations. Some interesting qualitative features emerge from a comparison with recent data, however. The absolute rates are too high, which is consistent with other calculations. However, the model does reproduce rather well the Z dependence of both relative and absolute radiative rates without requiring any quenching of ${\mathit{g}}_{\mathit{P}}$ in heavy nuclei. Furthermore the model gives an enhancement in the spectrum near the end point as compared to the uniform density model. Such an enhancement seems to be suggested by the data.

A threshold associated with a small mixing of a heavy neutrino in beta decay cannot be interpreted as due to the production of a fictitious neutral scalar in conjunction with a light neutrino.

B(E1) values are deduced for several transitions in ${}_{}{}^{168}{}_{}{}^{}\mathrm{Er}$. The ranges of hindrance factors with respect to the single particle estimates are ${10}^3$ to ${10}^9$ for transitions of ΔK=0 to 4, respectively. These values show that E1 transitions are quite weak in the ${}_{}{}^{168}{}_{}{}^{}\mathrm{Er}$ nucleus and thereby reconfirm the recently established collective γγ character of the positive parity K=4 band with a bandhead at 2055 keV.

A 6α-chain state has recently been discovered in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ which is some 16–17 MeV above the 6α-breakup threshold and yet paradoxically only 4–5 MeV wide. This surprising discovery raises the question of the possible existence of Nα-chain states in other 4N-nuclei. The excitation energy of this 6α-chain state is very close to the value predicted by the Bloch-Brink cluster model. Therefore, to aid the experimental search for similar states in other nuclei, we present here predictions of the excitation energies of the Nα-chain state bandheads in the 4N-nuclei from ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ to ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ obtained using the Bloch-Brink cranked cluster model with the Brink-Boeker effective interaction and free variation of all parameters.

The Moszkowski model with cranking is studied at a finite temperature in the mean field approximation and in terms of a thermal boson expansion.

We derive a qualitative and quantitative connection between the quantal spectral distribution and energies and actions of classical orbits in the symmetric pairing model.

An expression, previously derived, which relates the energy-weighted sum rule for orbital magnetic dipole (M1) excitations to summed electric quadrupole (E2) strength, is further developed. It is shown that with a quadrupole-quadrupole interaction, the energy-weighted M1 strength is proportional to the difference in summed isoscalar and isovector E2 strengths.

We propose methods for the determination of the intrinsic deformation corresponding to one or a set (band) of shell-model wave functions.

It is pointed out that strong mixing between proton two-particle two-hole (2p-2h) $0^{+}$, $2^{+}$, intruder configurations, and the quadrupole phonon vibrational states modifies the original quadrupole vibrational intensity and selection rules. This approach explains the possibility for certain states to exhibit apparently both intruder and vibrational characteristics and results mainly from strong mixing of the $0^{+}$ states. We present interacting boson model calculations and compare in detail, for ${}_{}{}^{114}{}_{}{}^{}\mathrm{Cd}$, the quintuplet of levels near ${\mathit{E}}_{\mathit{x}}$≃1.2 MeV.