The structure of the particle-hole nucleus ${}^{132}\mathrm{Sb}$ provides a direct source of information on the effective neutron-proton interaction in the ${}^{132}\mathrm{Sn}$ region. We have performed a shell-model calculation for this nucleus using a realistic effective interaction derived from the Bonn A nucleon-nucleon potential. The results are in very good agreement with the experimental data evidencing the reliability of our effective interaction matrix elements both with isospin $T=1\mathrm{}$ and $T=0.\mathrm{}$

We summarize the recent accumulation of data on electromagnetic transitions between states belonging to the lowest positive and negative parity bands of nuclei in the actinide region, and show that, in the case of $E2\mathrm{}$ and $E3\mathrm{}$ transitions, the simple patterns exhibited by these data are well reproduced by a binary cluster model.

Fast neutron-induced depopulation of the ${}^{180}{\mathrm{Ta}}^m\hspace{0.5em}(I,\hspace{0.5em}{K}^{\pi }{=9,9\mathrm{}}^{-})$ isomer to the $1^{+}$ ground state was detected by activation techniques. Natural Ta foils together with a ${}^{232}\mathrm{Th}$ monitoring target were activated using the neutron flux produced from a 7.3 MeV electron beam by a special choice of converters and shields. The $K_{\alpha 2}$ x-ray line (54.6 keV) of Hf was successfully observed in the $\gamma$-ray spectrum from activated Ta and attributed to the decay of ${}^{180}{\mathrm{Ta}}^g{(T}_{1/2}=8.15\mathrm{}\hspace{0.5em}\mathrm{h}).$ The yields of three reactions ${}^{232}\mathrm{Th}\mathrm{}(n,f),{\hspace{0.5em}}^{181}\mathrm{Ta}(n,\gamma {)}^{182}\mathrm{T}\mathrm{a},$ and ${}^{180}{\mathrm{Ta}}^m{(n,n}^{\prime }{)}^{180}{\mathrm{Ta}}^g,$ were measured in the same conditions and compared. Finally, the mean probability for ${}^{180}{\mathrm{Ta}}^m$ depopulation after MeV neutron scattering was deduced to approach about 0.4. This establishes almost complete K mixing above the neutron binding energy.

Cross-section measurements of the ${}^9\mathrm{Be}{,}^{12}\mathrm{C}(\alpha ,2\mathrm{}\alpha )$ reaction at 580 MeV bombarding energy are presented. The data are compared with distorted-wave impulse approximation calculations. The agreement between theory and experiment suggests a dominance of the quasifree knockout mechanism. The extracted $\alpha$-particle spectroscopic factors are in reasonable agreement with theory and proton-induced knockout reactions, unlike measurements for the $(\alpha ,2\mathrm{}\alpha )$ reaction at energies $<~140$ MeV, but still show significant angular dependence.

Fissioning nuclei produce with increasing excitation varying yields of fragments. For compound nuclei ranging from ${}^{232}\mathrm{Th}$ to ${}^{242}\mathrm{Pu}$ endowed with excitation energies typically between 0 and 10 MeV, we analyze these variations in terms of a fission-channel model. Most of the variations can be attributed to changing channel probabilities. We present a systematics of channel probabilities with respect to compound nuclei and their excitation energies, and we relate the systematics to potential energy which the nuclei experience when they float to scission. The trend, which is most difficult to explain, is a shift in the energy sensitivity of the standard channels, as one compares light with heavy compound nuclei. According to their behavior, we divide nuclei into standard I increasers and decreasers and attribute the difference to the standard secondary barriers. As a basic concept, bifurcation ratios are introduced, and a novel expression for transmission coefficients is proposed.

Proton-induced fission at 190 MeV of ${}^{\mathrm{nat}}\mathrm{W},$ ${}^{197}\mathrm{Au},$ ${}^{\mathrm{nat}}\mathrm{Pb},$ ${}^{208}\mathrm{Pb},$ and ${}^{232}\mathrm{Th}$ is studied by means of an innovative method based on activation analysis. The fission-product mass distribution is reconstructed from the fission-product yields, which are obtained from off-line observed $\gamma$-ray spectra. For ${}^{\mathrm{nat}}\mathrm{W}{,}^{197}\mathrm{Au}{,}^{208}\mathrm{Pb},$ and ${}^{\mathrm{nat}}\mathrm{Pb}$ the fission process results in a symmetric mass distribution. In the case of ${}^{232}\mathrm{Th}$ the mass yield curve is decomposed into a mixed symmetric-asymmetric contribution originating from fissioning nuclides in the neighborhood of the target mass and a purely symmetric contribution from very neutron-deficient nuclides. The fission cross sections are extracted by integrating over the reconstructed mass distribution. The width of the mass distribution is determined as a function of target mass. The results for the fission cross sections are compared with other experimental data as well as with theoretical model calculations using the LAHET and the ALICE-91 codes.

Using the charge exchange facility and second arm spectrometer at TRIUMF, we have measured the ${}^{31}\mathrm{P}\mathrm{}(n,p)\mathrm{}$ double differential cross section for 198 MeV incident neutrons, at scattering angles of $0–30°,$ and excitation energies up to 30 MeV. Via a multipole decomposition analysis we have extracted both the Gamow-Teller strength distribution and the GT transition probabilities to low-lying ${}^{31}\mathrm{Si}$ bound states. Comparison to a shell model calculation, using the full $1s-0d$ space and universal SD interaction, shows reasonable agreement in the strength distribution, but reduced summed strength in the experiment $(\sum B_{\mathrm{GT}}=2.32\mathrm{}\pm 0.20$ for $E_x<~10\hspace{0.5em}\mathrm{MeV})$ relative to the theory $(\sum B_{\mathrm{GT}}=3.33\mathrm{}$ for $E_x<~10\hspace{0.5em}\mathrm{MeV}).\mathrm{}$ We discuss the role of configuration mixing and Pauli blocking on the ${}^{31}{P}^{31}\mathrm{Si}$ GT strength distribution.

Fusion-fission dynamics in superheavy elements is investigated by an approximate fluctuation-dissipation model, i.e., a diffusion model in the deformation space, assuming that the kinetic energy of the incident ion dissipates immediately after the contact. The probability accumulated inside the fission barrier is calculated by the one-dimensional Smoluchowski equation taking account of the temperature dependence of the shell correction energy. A new mechanism for an optimum condition is found as a compromise of two conflicting requirements: higher incident energy for larger fusion probability and lower excitation energy of compound nuclei for larger survival probability. Enhancements of the residue cross sections at the optimum condition are obtained for the cases in which the cooling is quick to restore the shell correction energy, combined with slow fissioning motion due to the strong friction. With symmetric combinations of incident ions, the (HI, $3-4n)$ channels show the enhancement.

We suggest several ways to study the dynamical effects of the momentum dependence of the nuclear mean field in medium energy heavy ion collisions, from incomplete fusion to multifragmentation events. We present dynamical simulations based on a new transport code with a quite general form of mean field nonlocality and we compare with local effective forces giving the same equilibrium properties. We clearly see sizable effects on the onset of instabilities, on rates and angular distributions of preequilibrium particle emission, and on rapidity distributions of vaporization events for central collisions.

The $\alpha {+}^6\mathrm{He}$ elastic scattering is investigated within a microscopic multicluster model, involving a realistic description of the ${}^6\mathrm{He}$ halo nucleus. Phase shifts and elastic-scattering cross sections are calculated up to $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=15\mathrm{}\hspace{0.5em}\mathrm{MeV}$ with two variants of the resonating-group method. The model gives rise to $1^{-}$ and $3^{-}$ molecular states near $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=0.5\mathrm{}\hspace{0.5em}\mathrm{MeV}$ and $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=3.7\mathrm{}\hspace{0.5em}\mathrm{MeV},$ respectively. We suggest that the broad $3^{-}$ resonance should be observable by comparing elastic cross sections at different energies. We also evaluate the order of magnitude of the ${}^6\mathrm{He}$ breakup cross section.

The inverse-scattering theory at a fixed energy for the scattering of a particle by a potential in the Schrödinger equation formulated by Alam and Malik, which is based on the earlier work of Hooshyar and Razavy, is extended, in this paper, to the scattering of spinless particles at relativistic energies governed by the Klein-Gordon equation. The differential equation is replaced by a set of difference equations. This reduces the inverse-scattering problem to solving a continued fraction equation. The solution provides the values of the potential at a number of points which are equal to (one plus the number of partial waves). The theory is tested for three widely different complex potentials, one of which is relevant to pion-nucleus scattering. The points of the potentials determined from the inverse-scattering formalism are in accord with the actual ones in all three cases. Since the Klein-Gordon equation is effectively a Schrödinger equation with an energy-dependent potential, the method may, in the appropriate cases, be suitable for the latter case.

A systematic study of the effect of fragment-fragment interaction, quantum statistics, $\gamma$-feeding, and collective flow is made in the extraction of the nuclear temperature from the double ratio of the isotopic yields in the statistical model of one-step (prompt) multifragmentation. Temperature is also extracted from the isotope yield ratios generated in the sequential binary-decay model. Comparison of the thermodynamic temperature with the extracted temperatures for different isotope ratios show some anomaly in both models which is discussed in the context of experimentally measured caloric curves.

We present a calculation of higher order effects for the impact-parameter-dependent probability for single and multiple electron-positron pairs in (peripheral) relativistic heavy ion collisions. Also total cross sections are given for SPS and RHIC energies. We make use of the expression derived recently by several groups where the summation of all higher orders can be done analytically in the high-energy limit. An astonishing result is that the cross section, that is, integrating over all impact parameters, is found to be identical to the lowest-order Born result for symmetric collisions. For the probability itself, on the other hand, we find rather large effects at small impact parameters compared to the lowest order results, which translate to large effects for the cross section for multiple pair production.

In many statistical models of nuclear fragmentation it is assumed that the disassembly takes place in a volume larger than the normal nuclear volume. Nucleons and composites appear in this volume according to laws of equilibrium statistical mechanics. The different particles are not supposed to overlap with each other, hence the available volume within which the particles can move freely is reduced. For typical nuclear cases we calculate this reduction.

Antisymmetrized molecular dynamics (AMD) with quantum branching processes is reformulated so that it can be applicable to the collisions of heavy nuclei such as ${}^{197}\mathrm{Au}{+}^{197}\mathrm{Au}$ multifragmentation reactions. The quantum branching process due to the wave packet diffusion effect is treated as a random term in a Langevin-type equation of motion, whose numerical treatment is much easier than the method of the previous papers. Furthermore, a new approximation formula, called the triple-loop approximation, is introduced in order to evaluate the Hamiltonian in the equation of motion with much less computation time than the exact calculation. A calculation is performed for the ${}^{197}\mathrm{Au}{+}^{197}\mathrm{Au}$ central collisions at 150 MeV/nucleon. The result shows that AMD almost reproduces the copious fragment formation in this reaction.

The Feshbach, Kerman, and Koonin [Ann. Phys. (N.Y.) 125, 429 (1980)] model of the statistical multistep compound (MSC) process is calculated microscopically, and comparisons of the microscopically calculated MSC process with a phenomenological phase-space model are made. The microscopic model gives a small particle emission probability in comparison with the constant wave function approximation, and a simple way to reconcile the difference is proposed. A $2p-1h$ doorway state formation cross section is calculated with the spherical Nilsson model, and a strength of the residual interaction $V_0$ is estimated from the doorway state formation cross section. The obtained $V_0$ is of the same magnitude as those derived in the previous multistep direct analyses. Comparisons of the microscopic MSC calculations with the experimental data show that the calculated particle emission spectra reproduce the measurements at backward angles.

The NA50 experiment at the CERN SPS has been equipped with a Cerenkov quartz detector to measure the charge of projectilelike fragments emitted in interactions of the lead beam of $158A\hspace{0.5em}\mathrm{GeV}$ with a 12 mm thick lead target. A clear fission peak has been observed in the light output distribution of the fragment detector and the measured number of fission events per incident Pb ion is $(1.26\mathrm{}\pm 0.16)\times {10}^{-2}.$ The information provided by the NA50 zero-degree calorimeter has allowed us to check that fission occurs in extremely peripheral collisions. To provide the first information about the fission mechanism, the expected yield of electromagnetic fission events in our experimental conditions has been computed: it turns out to be about $40\%$ smaller than the observed one. The approximations necessarily made in our calculation as well as the contribution due to fission induced by nuclear interaction could account for such a difference.

Directed flow of deuterons, tritons, ${}^3\mathrm{He},$ and ${}^4\mathrm{He}$ is studied in Au+Au collisions at a beam momentum of $10.8A\mathrm{GeV}/c.\mathrm{}$ Flow of all particles is analyzed as a function of transverse momentum for different centralities of the collision. The directed flow signal, $v_1{(p}_t),$ is found to increase with particle mass. This mass dependence is strongest in the projectile rapidity region.

We describe a class of pionic breather solutions (PBS) which appear in the chiral Lagrangian description of low-energy QCD. These configurations are long lived, with lifetimes greater than ${10}^3\hspace{0.5em}\mathrm{fm}/c,$ and could arise as remnants of disoriented chiral condensate (DCC) formation at RHIC. We show that the chiral Lagrangian equations of motion for a uniformly isospin-polarized domain reduce to those of the sine-Gordon model. Consequently, our solutions are directly related to the breather solutions of sine-Gordon theory in 3+1 dimensions. We investigate the possibility of PBS formation from multiple domains of DCC, and show that the probability of formation is non-negligible.

The general formalism of homogeneous nucleation theory is applied to study the hadronization pattern of the ultrarelativistic quark-gluon plasma (QGP) undergoing a first order phase transition. A coalescence model is proposed to describe the evolution dynamics of hadronic clusters produced in the nucleation process. The size distribution of the nucleated clusters is important for the description of the plasma conversion. The model is most sensitive to the initial conditions of the QGP thermalization, time evolution of the energy density, and the interfacial energy of the plasma-hadronic matter interface. The rapidly expanding QGP is first supercooled by about $\Delta T=T-T_c=4\mathrm{}–6\%.\mathrm{}$ Then it reheats again up to the critical temperature $T_c.$ Finally it breaks up into hadronic clusters and small droplets of plasma. This fast dynamics occurs within the first 5–10 fm/c. The finite size effects and fluctuations near the critical temperature are studied. It is shown that a drop of longitudinally expanding QGP of the transverse radius below 4.5 fm can display a long-lived metastability. However, both in the rapid and in the delayed hadronization scenarios, the bulk pion yield is emitted by sources as large as 3–4.5 fm. This may be detected experimentally both by a Hanbury–Brown-Twiss interferometry signal and by the analysis of the rapidity distributions of particles in narrow $p_T$ intervals at small $|p_T|$ on an event-by-event basis.