The halo neutron breakup cross section for ${}^{11}\mathrm{Be}$ on Si has been obtained in a wide energy range by applying an integral method and separately determining the contributions of stripping and dissociation mechanisms. A new breakup mechanism, for which the core energy is strongly dumped, has also been observed. Parallel momentum distributions of ${}^{10}\mathrm{Be}$ resulting from breakup have been deduced for both stripping and dissociation and angular and energy distributions of the neutrons coincident with different reaction products have been measured. Charge changing cross sections for ${}^{10,11}\mathrm{Be}\mathrm{}$ complemented the measurements. An extended Glauber model has been elaborated in order to provide a unitary interpretation for all the data. It takes into account both the specific structure of ${}^{11}\mathrm{Be}$ and the reaction mechanism, practically without free parameters. The effects of reaction mechanisms on the widths of observed momentum distributions are particularly important.

The energy-sharing distribution at a coplanar symmetric quasifree angle pair has been measured for the ${}^{12}\mathrm{C}(\alpha ,2\mathrm{}\alpha {)}^8\mathrm{Be}(\mathrm{g}.\mathrm{s}.\mathrm{})$ reaction at an incident energy of 200 MeV. The measured knockout cross sections are compared with distorted wave impulse approximation calculations. Extracted spectroscopic factors are found to be in reasonable agreement with a theoretical prediction and results from $(p,p\alpha )$ studies. The present results indicate a transition in the dynamics of this reaction in the incident energy region 140–200 MeV.

Angular distributions of the elastic scattering of the ${}^{6,7}\mathrm{Li}$ on ${}^{138}\mathrm{Ba}$ were measured, in the energy range $21<~E_{\mathrm{lab}}<~32$ MeV. The analysis of the data was performed via the optical model, using the Woods-Saxon potential, in order to find the energy dependence of the real and imaginary parts of the nuclear potential. The existence of a threshold anomaly for the ${}^7\mathrm{Li}$ scattering and its absence for the ${}^6\mathrm{Li}$ one was observed. It is interpreted that the breakup of ${}^6\mathrm{Li}$, with dissociation energy smaller that its first excited state, is responsible for the vanishing of the threshold anomaly.

The International Germanium Experiment (IGEX) has six HPGe detectors, isotopically enriched to 86% in ${}^{76}\mathrm{Ge},$ containing approximately 90 active moles of ${}^{76}\mathrm{Ge}.$ Three detectors of 2 kg each operate in the Canfranc Underground Laboratory (Spain) with pulse-shape analysis electronics. One detector (∼0.7 kg active volume) has been operating in the Baksan Low-Background Laboratory for several years, and two additional similar detectors will operate in Baksan. A maximum likelihood analysis of 74.84 active mole years of data yields a lower bound $T_{1/2}^{0\nu }>~0.8\times {10}^{25}\mathrm{yr}$ (90% C.L.), corresponding to $〈m_{\nu }〉<(0.5\mathrm{}–1.5)\mathrm{eV},$ depending on the theoretical nuclear matrix elements used to extract the neutrino mass parameter.

A stochastic approach based on two-dimensional Langevin equations was applied to study the main features of fission fragment mass distributions of excited fissioning systems. The forms and the variances of fission fragment mass distributions in the fissility parameter range $20<\mathrm{}{Z}^2/A<\mathrm{}40\mathrm{}$ have been calculated. The calculated fission fragment mass distributions and their variances on the whole are consistent with experimental data. The calculations were carried out within two liquid drop models (LDM’s): the LDM with the sharp surface of the nucleus and the LDM with the finite range of nuclear interaction.

The weak production of $\Lambda$’s in nucleon-nucleon scattering is studied in a meson-exchange framework. The weak transition operator for the $N\overrightarrow{N}N\Lambda$ reaction is identical to a previously developed weak strangeness-changing transition potential $\Lambda \overrightarrow{N}\mathrm{NN}$ that describes the nonmesonic decay of hypernuclei. The initial $\mathrm{NN}$ and final $\mathrm{YN}$ state interaction has been included by using realistic baryon-baryon forces that describe the available elastic scattering data. The total and differential cross sections as well as the parity-violating asymmetry are studied for the reaction $p\overrightarrow{n}p\Lambda .$ These observables are found to be sensitive to the opening of the $\Sigma$ production channel, the choice of the strong interaction potential, and the structure of the weak transition potential.

It is studied to what extent the characteristics of multi-IMF (intermediate-mass fragments) events can be derived from the properties of the observed single-IMF transverse-energy spectra. It is found that the spectra of total transverse IMF energy ${(E}_t)$ in multi-IMF events are well represented by “synthetic” spectra obtained by a multiple folding of the single-IMF transverse energy spectrum. Further, it is shown that, using the experimental IMF multiplicity distribution in the folding procedure, it is possible to reproduce the observed trends in the IMF multiplicity distributions for fixed values of the total transverse energy $E_t.$ Accordingly, the “synthetic” multiplicity distributions show a binomial reducibility and an Arrhenius-like scaling similar to that reported in the recent literature. Consistent with the concept of a statistical independence of multiple IMF production, similar results are obtained when the above folding-type synthesis is replaced with one based on mixing of events with different IMF multiplicities. For statistically independent IMF emission, the observed binomial reducibility and Arrhenius-like scaling are shown to be merely reflections of the shape of the single-IMF transverse-energy spectrum. Hence, a valid interpretation of these IMF distributions in terms of a particular production scenario has to explain independently the observed shape of the single-IMF $E_t$ spectrum.

The semiclassical distorted wave (SCDW) model is extended to include three-step process in multistep direct (MSD) processes in nucleon-induced preequilibrium nucleon-emission reactions. The extended SCDW model is applied to analyses of MSD processes in ${}^{58}\mathrm{Ni}{(p,p}^{\prime }{x),}^{90}\mathrm{Zr}{(p,p}^{\prime }{x),}^{90}\mathrm{Zr}\mathrm{}(p,nx),$ and ${}^{209}\mathrm{Bi}{(p,p}^{\prime }x)$ in the incident energy range of 62–160 MeV. SCDW calculations with no adjustable parameter give overall good agreement with experimental double differential cross sections, except at very small and large angles. The nonlocality of distorting potentials is taken into account in terms of the Perey factor, and is found to be essential for reproducing the absolute magnitude of the cross sections. Effects of the density and momentum distributions of target nucleons and the use of in-medium $N-N$ cross sections on the SCDW calculation are discussed. Comparison with other models is made, in particular regarding the contributions of individual multistep processes to the calculated cross sections. Validity of the local semiclassical approximation to distorted waves, which is essential to SCDW is discussed on the basis of a numerical test.

The use of Watson’s theorem in the analysis of $p-d$ radiative capture measurements at low energies is discussed. The principle of Watson’s theorem is outlined, and a detailed description of how the theorem can be used in a matrix element analysis of radiative capture data is presented. It is shown that with Watson’s theorem it is possible to reduce the number of unknown parameters in a matrix element analysis by essentially a factor of 2. This is done by employing a representation in which the capture matrix elements are all real. The phase information needed to construct the reaction amplitudes is then obtained from a separate phase shift analysis of elastic scattering data. Details concerning the extension of Watson’s theorem to situations in which there is mixing between angular momentum states are given. The paper presents a consistent formulation which facilitates the simultaneous analysis of the elastic scattering and radiative capture channels.

We have studied the pion single-charge-exchange reaction on ${}^7\mathrm{Li}$ leading to isobaric analog state under distorted-wave impulse approximation. A cluster-model wave function is used to describe the ground state of ${}^7\mathrm{Li}$ and ${}^7\mathrm{Be},$ and the results are compared with those of the shell-model calculation. The forward cross section above 50 MeV is well explained but the theoretical value is larger than the experimental cross section about a factor 2–2.5 at lower energies. The shell-model and the cluster-model wave functions predict quite different second rank tensor polarization.

We propose a practical numerical method for treating the Coulomb interaction in momentum space. The Coulomb potential is regularized by expanding its inner part $r<~R$ as the superposition of the Gaussian functions. This smooth-cutoff Coulomb potential decreases rapidly in momentum space without oscillation. In addition, the partial-wave decomposition can be done analytically without numerical integration. First, the phase shifts are calculated with the regularized Coulomb plus short-range strong potentials. Then, the correct phase shifts or the wave functions can be reconstructed with the aid of coordinate-space calculation from the asymptotic region inward to R. Another possibility is to calculate the logarithmic derivative at R directly by the Fourier transform, which is matched to the point-Coulomb wave functions $F_L$ and $G_L.$ This method is examined for calculating the phase shifts of proton-nucleus elastic scattering and found to be accurate over wide energy regions.

In this paper Au+Au collisions at $11.6A$ $\mathrm{GeV}/c$ are characterized by two global observables: the energy measured near zero degrees ${(E}_{\mathrm{ZCAL}})$ and the total event multiplicity. Particle spectra are measured for different event classes that are defined in a two-dimensional grid of both global observables. For moderately central events $(\sigma /{\sigma }_{\mathrm{int}}<12\%)$ the proton $dN/dy$ distributions do not depend on $E_{\mathrm{ZCAL}}$ but only on the event multiplicity. In contrast the shape of the proton transverse spectra shows little dependence on the event multiplicity. The change in the proton $dN/dy$ distributions suggests that different conditions are formed in the collision for different event classes. These event classes are studied for signals of new physics by measuring pion and kaon spectra and yields. In the event classes doubly selected on $E_{\mathrm{ZCAL}}$ and multiplicity there is no indication of any unusual pion or kaon yields, spectra, or $K/\pi$ ratio even in the events with extreme multiplicity.

We develop a formalism describing Coulomb excitation in relativistic heavy-ion collisions as a general coupled-channel problem. The Schrödinger equation for the target nucleus is expressed as a set of coupled integral equations for a $T\left(\omega \right)$ matrix, whose on-shell matrix elements give the excitation amplitudes. The method of Kowalsky and Noyes is used to regularize the kernels of these integral equations, making the equations amenable to numerical solution. An application of the method is made to the study of the population of a model state representing an ${L=2\mathrm{}}^{+}$ giant resonance in ${}^{40}\mathrm{Ca}$ at an excitation energy of 20 MeV, due to the electromagnetic field of a ${}^{208}\mathrm{Pb}$ projectile with kinetic energy per nucleon up to 100 GeV. The results of the numerical solution of the regularized coupled integral equations are compared to results obtained from the Born series, and from the long-wavelength approximation. These approximations are found to be adequate up to bombarding energies per nucleon of 3 GeV. We investigate the reasons for failure of these approximations at higher bombarding energy. Due to the finite travel time of the electromagnetic pulse across the target nucleus, the sudden approximation is found to be inapplicable to the excitation of the giant resonance. Thus the method of numerical solution of the regularized coupled integral equations seems to be the most suitable approach to the study of very high-energy Coulomb excitation of giant resonances.

We propose a new method for the Coulomb wave function correction which includes the momentum resolution for charged hadron pairs and apply it to the precise data on ${\pi }^{+}{\pi }^{-}$ correlations obtained in the $p+\mathrm{Ta}$ reaction at 70 $\mathrm{GeV}/c$. We find that interaction regions of this reaction (assuming Gaussian source function) are $9.8\pm 5.8$ and $7.7\pm 4.8$ fm for the thicknesses of the target 8 and $1.4\hspace{0.5em}\mu \mathrm{m}$, respectively. We also analyze the data by the formula including strong interaction effect. The physical picture of the source size obtained in this way is discussed.

Correlations of two like charged pions emitted from a hot and charged spherically expanding nuclear system are investigated. The motion of the pions is described quantum mechanically using the Klein-Gordon equation which includes Coulomb field and pion absorption. Flow modifies the radial distribution of the source function and rescales the pion wave functions. The radii extracted from the correlation functions are calculated in sideward and outward direction as a function of the pair momentum. Comparison with recent measurements at bombarding energies of 1 GeV and 11 GeV per nucleon is made.

The conditions for the restoration of chiral symmetry and the subsequent formation of the disoriented chiral condensates in ultrarelativistic nucleus-nucleus collisions are studied by using the linear $\sigma$ model. A rapid increase of temperature in the initial thermalization stage is parametrized so as to simulate the result of the parton cascade model. The subsequent decrease of temperature in the cooling stage is described in terms of the one- or three-dimensional scaling hydrodynamics. The effective potential at each temperature is calculated in the massless free particle approximation. Those ingredients are used to solve numerically the equation of motion for the chiral condensates. In general, solutions exhibit characteristic damped oscillations of which patterns are very sensitive to the maximum temperature $T_m$ and the time when the maximum temperature is attained. In particular, it is found that the maximum temperature must be much higher than the critical temperature $T_c$ in order that the chiral symmetry is restored temporarily, e.g., $T_m>~175$ MeV for $T_c\sim 123$ MeV with longitudinal expansion. Moreover, it is suggested that the disoriented chiral condensates will be formed most easily in the $-\sigma$ direction.

New scaling, z scaling, in the inclusive particle production in $\mathrm{pA}$ collisions is studied. The concept of z scaling is based on fundamental principles such as self-similarity, locality, scale relativity, and fractality reflecting the general features of particle interactions. The scaling function $H_A\mathrm{}\left(z\right)\mathrm{}$ is expressed via the invariant cross section ${\mathrm{Ed}}^3\sigma {/dq}^3$ and the average multiplicity density $dN/d\eta$ of particles produced at pseudorapidity $\eta =0\mathrm{}$ in the corresponding nucleon-nucleon interaction. The dependence of $H_A\mathrm{}\left(z\right)\mathrm{}$ on scaling variable $z$, the center-of-mass energy $\sqrt{s},$ and the atomic number A is investigated. It is shown that the available experimental data on cross sections in $\mathrm{pA}$ collisions confirm the scaling properties of the function $H_A\mathrm{}\left(z\right).$ The obtained results can be of interest for future experiments at BNL relativistic heavy-ion collider and CERN large hadron collider in searching for new physical phenomena in $pp,$ $pA,$ and $\mathrm{AA}$ collisions.

A new mechanism of ${\pi }^{+}$-meson emission from $\mathrm{the}{\hspace{0.5em}}_{\Lambda }^4\mathrm{He}$ hypernucleus is suggested. It consists of a weak $\overrightarrow{\Lambda }n+{\pi }^{+}+{\pi }^{-}$ decay followed by ${\pi }^{-}$ absorption by the hypernuclear core. The contribution of this mechanism is compared to that of the “standard” one $(\overrightarrow{\Lambda }n+{\pi }^0$ decay followed by the ${\pi }^0\to {\pi }^{+}$ charge exchange on the core). Uncertainties of the estimated effect are discussed.

The neutrino capture rate measured by the Russian-American Gallium Experiment is well below that predicted by solar models. To check the response of this experiment to low-energy neutrinos, a 517 kCi source of ${}^{51}$Cr was produced by irradiating 512.7 g of 92.4%-enriched ${}^{50}$Cr in a high-flux fast neutron reactor. This source, which mainly emits monoenergetic 747-keV neutrinos, was placed at the center of a 13.1 ton target of liquid gallium and the cross section for the production of ${}^{71}$Ge by the inverse beta decay $\mathrm{reaction}{\hspace{0.5em}}^{71}\mathrm{Ga}({\nu }_e{,e}^{-}{)}^{71}\mathrm{Ge}$ was measured to be $[5.55\pm 0.60(\mathrm{stat})\pm 0.32(\mathrm{syst}\left)\right]\times {10}^{-45}{\mathrm{cm}}^2.$ The ratio of this cross section to the theoretical cross section of Bahcall for this reaction is 0.95 ±0.12 ${\mathrm{}\left(\mathrm{expt}\right)\mathrm{}}_{-0.027}^{+0.035\mathrm{}}$ (theor) and to the cross section of Haxton is 0.87±0.11 (expt)±0.09 (theor). This good agreement between prediction and observation implies that the overall experimental efficiency is correctly determined and provides considerable evidence for the reliability of the solar neutrino measurement.

Photon scattering experiments have been performed on the nuclei ${}^{190,192}\mathrm{Os}$ in order to investigate low-lying dipole excitations in the energy range $E_{\gamma }<4\mathrm{}\hspace{0.5em}\mathrm{MeV}$ in nuclei which are transitional between well-deformed rotors and $\gamma$-soft nuclei. We determined excitation energies, spins, and absolute photon scattering cross sections. The low-lying dipole strength in these even-even nuclei is highly fragmented.