A clustering model which allows the recognition of mass fragments from dynamical simulations has been developed. Studying the evolution of a microscopic computation based on the nuclear Boltzman equation, a suitable time is chosen to define bound clusters. At this stopping time the cluster cores for each member of the distribution are defined as a function of the overall density. Then an iterative routine is applied to estimate the coalescence of the surrounding nucleons. Once the fragment formation has been established, a statistical decay code is used to generate the final fragment distributions. Applications are shown to the reactions ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$ + ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Cu}$ at 50 MeV/nucleon and ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ on ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ and ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Cu}$ at 45 MeV/nucleon. A general improvement in cluster identification is found over approaches where a standard cluster separation algorithm has been used. © 1996 The American Physical Society.

The production cross sections of various fragments from proton-induced reactions on ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ have been analyzed by the quantum molecular dynamics (QMD) plus statistical decay model (SDM). It was found that the mass and charge distributions calculated with and without the statistical decay have very different shapes. These results also depend strongly on the impact parameter, showing an importance of the dynamical treatment as realized by the QMD approach. The calculated results were compared with experimental data in the energy region from 50 MeV to 5 GeV. The QMD+SDM calculation could reproduce the production cross sections of the light clusters and intermediate-mass to heavy fragments in a good accuracy. The production cross section of ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ was, however, underpredicted by approximately 2 orders of magnitude, showing the necessity of another reaction mechanism not taken into account in the present model. © 1996 The American Physical Society.

A single particle basis consisting of two different harmonic oscillator representations is introduced with the aim of studying microscopically α- and cluster-decay processes. A correct description of the wave functions at large distances is obtained within a minimal single particle basis. Experimental data corresponding to a large number of α decay transitions from even-even nuclei are well reproduced. © 1996 The American Physical Society.

The single particle levels for the heavy-ion emission process are computed. This decay mode is treated like a superasymmetric fission process. The nuclear shape parametrization is characterized by three degrees of freedom. The difficulties encountered in the microscopic determination of the energy scheme at these very large mass asymmetries are presented. Thereby, a new version of the two-center model, especially designed for very large mass asymmetries, is described. The ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ heavy-ion spontaneous emission from the parent nucleus ${}_{}{}^{223}{}_{}{}^{}\mathrm{Ra}$ is treated in the frame of this model. The principal trends of the variations obtained for the energetic levels during this superasymmetric nuclear decay are discussed. Mainly, for this kind of decay mode, the levels with lower values of the angular momentum projection Ω show more pronounced variations than those with higher Ω. Also, a qualitative explanation for the favoring of the first excited states in the fine structure in this radioactive process is given. © 1996 The American Physical Society.

The elastic scattering of the halo nucleus ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ is investigated within the relativistic mean field theory. The interaction potentials of the systems ${}_{}{}^{11}{}_{}{}^{}\mathrm{-}_{}^{12}{}_{}{}^{}$C and ${}_{}{}^{11}{}_{}{}^{}\mathrm{-}_{}^{28}{}_{}{}^{}$Si are calculated using both the nonlinear NLC and NL-SH and the linear LFS forces. It is found that the nonlinear NLC and NL-SH forces present more attractive potentials in the surface and tail regions than the linear LFS force. The potentials calculated by considering the halo structure of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ are deeper than those calculated by neglecting this halo. Furthermore, it is pointed out that the potentials of the nonlinear NLC and NL-SH forces (calculated with the halo structure of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$) better describe the unusual constancy behavior of the cross section which was found experimentally for halo nuclei. © 1996 The American Physical Society.

We have shown that the large enhancement of sub-barrier fusion cross sections for heavy-ion collision processes can be partially accounted for by using the variation of the effective mass due to nonlocal effects in WKB theory. Although reasonable agreement of our predicted results for the fusion cross sections and average angular momenta with the observed experimental data for several systems have been observed, it is evident that the nonlocal effects alone cannot explain the entire enhancement as claimed by Galetti et al. [Phys. Rev. C 50, 2136 (1994)]. It is then suggested that nonlocality needs to be supplemented by nuclear deformation and other degrees of freedom. © 1996 The American Physical Society.

The ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(e,${\mathit{e}}^{\prime }$${\mathrm{\pi }}^{+}$${)}^3$H reaction is the simplest of the coherent charged pion electroproduction reactions in nuclear physics. It is sensitive to the structure of the trinucleons, and can be studied with the high duty factor electron accelerators now available. It may also provide some insight for understanding the basic p(e,${\mathit{e}}^{\prime }$${\mathrm{\pi }}^{+}$)n reaction if the latter can be described within the constituent quark models of nucleons. In this work, we calculate the ratio of p(e,${\mathit{e}}^{\prime }$${\mathrm{\pi }}^{+}$)n and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(e,${\mathit{e}}^{\prime }$${\mathrm{\pi }}^{+}$${)}^3$H cross sections for two kinematical conditions with invariant photon-nucleon mass W=1160 and 1230 MeV, respectively. The four important contributions to this ratio are identified as (i) the finite size (i.e., the form factor) of the trinucleons, (ii) the spin-isospin correlations in the trinucleons, (iii) the finite range of the propagation of the struck proton, and (iv) the possible pion-nucleon final state interactions. Together they reduce the ratio of the cross section to ∼0.4 in this kinematic range. © 1996 The American Physical Society.

Nonfusion, fissionlike reactions in collisions of four heavy systems (well below the fusion extra-push energy threshold), for which Hinde and co-workers had measured the prescission neutron multiplicities, have been analyzed in terms of the deterministic dynamic model of Feldmeier coupled to a time-dependent statistical cascade calculation. In order to reproduce the measured prescission multiplicities and the observed (nearly symmetric) mass divisions, the energy dissipation must be dramatically changed with regard to the standard one-body dissipation: In the entrance channel, in the process of forming a composite system, the energy dissipation has to be reduced to at least half of the one-body dissipation strength (${\mathit{k}}_{\mathit{s}}^{\mathrm{in}}$≤0.5), and in the exit channel (from a mononucleus shape to scission) it must be increased by a factor ranging for the studied reactions from ${\mathit{k}}_{\mathit{s}}^{\mathrm{out}}$=4 to ${\mathit{k}}_{\mathit{s}}^{\mathrm{out}}$=12. These results are compared with the temperature dependence of the friction coefficient, recently deduced by Hofman, Back, and Paul from data on the prescission giant dipole resonance emission in fusion-fission reactions. The combined picture of the temperature dependence of the friction coefficient, for both fusion-fission and nonfusion reactions, may indicate the onset of strong two-body dissipation already at a nuclear temperature of about 2 MeV. © 1996 The American Physical Society.

Using the experimental p¯N amplitude and multiple scattering theory, we obtained the antiproton optical potential at incident energies from 180 to 1800 MeV with the impulse approximation. It is found that the imaginary parts of the optical potential strengths are nearly constant between 130 and 140 MeV. The elastic data of the 180 MeV antiproton on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ and the inelastic data of the 180 MeV antiproton on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ are analyzed within the framework of the eikonal approximation. The collective excitations to one-phonon levels are treated using the antiproton optical potential with the adiabatic approximation. The differential cross section of elastic scattering of 180 to 1833 MeV antiproton on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, on ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ and the inelastic scattering of 180 to 1833 MeV antiproton ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ are predicted. © 1996 The American Physical Society.

Deuteron coalescence, during a relativistic nucleus-nucleus collision, is carried out in a model incorporating a minimal quantal treatment of the formation of the cluster from its individual nucleons by evaluating the overlap of initial cascading nucleon wave packets with the final deuteron wave function. The nucleon wave packet sizes are estimated dynamically using the coalescing pair’s past light-cone history. A parameter free determination of the absolute deuteron yields results, and a globally consistent picture of the Si+Au measurements is achieved. In light of the deuteron’s evident fragility, information obtained from this analysis may be useful in establishing freeze-out volumes and help in heralding the presence of high-density phenomena in a baryon-rich environment. © 1996 The American Physical Society.

A relativistic Lagrangian for the nuclear matter consisting of nucleons and pions with a pseudoscalar interaction term is considered. It is shown that a nonrelativistic reduction of the problem automatically introduces a Lorentz scalar, isoscalar coupling of nucleons with two correlated pions. The corresponding Hamiltonian is used to study the properties of infinite nuclear matter nonperturbatively, treating both the nucleons and pions as quantized fields. The model is shown to reproduce the characteristic nuclear matter properties very nicely without the necessity of σ and ω fields, as is usually done in the mean field Walecka model. The corresponding equation of state for zero temperature nuclear matter is calculated and is shown to be consistent with the known phenomenological equations of state. The binding energy of nuclear matter is calculated to be 15.3 MeV at a saturation density of 0.153 ${\mathrm{fm}}^{\mathrm{-}3}$. The model reproduces a softer nuclear matter with the incompressibility of 134 MeV. © 1996 The American Physical Society.

A quark-meson coupling (QMC) model is extended to finite nuclei in the relativistic mean-field or Hartree approximation. The ultrarelativistic quarks are assumed to be bound in nonoverlapping nucleon bags, and the interaction between nucleons arises from a coupling of vector and scalar meson fields to the quarks. We develop a perturbative scheme for treating the spatial nonuniformity of the meson fields over the volume of the nucleon as well as the nucleus. Results of calculations for spherical nuclei are given, based on a fit to the equilibrium properties of nuclear matter. Several possible extensions of the model are also considered. © 1996 The American Physical Society.

Parity nonconservation (PNC) measurements utilizing charged-particle resonance reactions are proposed. PNC observables have been calculated for over 300 resonance pairs (with the same angular momentum and opposite parity) in five s-d shell nuclei. Detailed numerical results are presented for the longitudinal analyzing powers in the ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$(p→,${\mathrm{\alpha }}_0$) reaction. There is strong dependence on energy, angle, and resonance parameters. A figure of merit that includes both the relative enhancement of the parity violation and the cross section is used to identify the most promising resonances for study. A proposed detector design and experimental procedure are described. These measurements should provide information on the weak spreading width (the effective nucleon-nucleus weak interaction) in light nuclei. © 1996 The American Physical Society.

The ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(n,γ${)}^8$Li cross section is important in inhomogeneous big bang models, and as a constraint on model parameters used to determine the solar ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$(p,γ${)}^8$B reaction rate. Values of the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(n,${\gamma }_0$${)}^8$Li reaction cross section were measured for neutron energies between 1.5 and 1340 eV at the Oak Ridge Electron Linear Accelerator. The normalization of the cross section was determined by measuring the gamma-ray yield from the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(n,${\gamma }_0$${)}^8$Li reaction relative to that from the ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$(n,αγ${)}^7$Li reaction. The cross section was found to have the inverse neutron-velocity relationship (1/v) indicative of s-wave capture. These results help resolve ambiguities in previous measurements. © 1996 The American Physical Society.

The cross sections of the ${}_{}{}^{36}{}_{}{}^{}\mathrm{Cl}$(${\mathit{n}}_{\mathrm{th}}$,p)${\mathrm{}}^{36}$S and the ${}_{}{}^{36}{}_{}{}^{}\mathrm{Cl}$(${\mathit{n}}_{\mathrm{th}}$,α${)}^{33}$P reactions were measured with thermal neutrons at the high flux reactor of the ILL in Grenoble. For the ${}_{}{}^{36}{}_{}{}^{}\mathrm{Cl}$(${\mathit{n}}_{\mathrm{th}}$,p${)}^{36}$S reaction cross section a precise value of (47±2) mb was obtained and for the ${}_{}{}^{36}{}_{}{}^{}\mathrm{Cl}$(${\mathit{n}}_{\mathrm{th}}$,α${)}^{33}$P reaction a cross section value of (0.59±0.07) mb was determined. © 1996 The American Physical Society.

Because a knowledge of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${/}^{16}$O ratio is crucial to the understanding of the later evolution of massive stars, new R- and K-matrix fits have been completed using the available angular distribution data from radiative α capture and elastic α scattering on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$. Estimates of the total ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(α,γ${)}^{16}$O rate at stellar energies are reported. In contrast with previous work, the analyses generally involve R- and K-matrix fits directly to the primary data, i.e., the energy- and angle-dependent differential yields, with all relevant partial waves fitted simultaneously (referred to here as surface fits). It is shown that, while the E1 part of the reaction is well constrained by a recent experiment on the β-delayed α-particle decay of ${}_{}{}^{16}{}_{}{}^{}\mathrm{N}$, only upper limits can be placed on the E2 ground state cross section factor which we take conservatively as ${\mathit{S}}_{\mathit{E}2}$(300)<140 keV b. Simulations were then carried out to explore what kind of new data could lead to better restrictions on ${\mathit{S}}_{\mathit{E}2}$(300). We find that improved elastic scattering data may be the best short-term candidate for such restrictions while significantly improving S(300) with new radiative capture data may require a longer-term effort. Theoretical models and estimates from α-transfer reactions for the E2 part of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(α,γ${)}^{16}$O are then discussed for comparison with the R- and K-matrix fits of the present work. © 1996 The American Physical Society.

We present a systematic evaluation of the shape of the neutrino energy spectrum produced by beta decay of ${}_{}{}^8{}_{}{}^{}\mathrm{B}$. We place special emphasis on determining the range of uncertainties permitted by existing laboratory data and theoretical ingredients (such as forbidden and radiative corrections). We review and compare the available experimental data on the ${}_{}{}^8{}_{}{}^{}\mathrm{B}$(${\mathrm{\beta }}^{+}$${)}^8$Be(2α) decay chain. We analyze the theoretical and experimental uncertainties quantitatively. We give a numerical representation of the best-fit (standard-model) neutrino spectrum, as well as two extreme deviations from the standard spectrum that represent the total (experimental and theoretical) effective ±3σ deviations. Solar neutrino experiments that are currently being developed will be able to measure the shape of the ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ neutrino spectrum above about 5 MeV. An observed distortion of the ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ solar neutrino spectrum outside the range given in the present work could be considered as evidence, at an effective significance level greater than three standard deviations, for physics beyond the standard electroweak model. We use the most recent available experimental data on the Gamow-Teller strengths in the A=37 system to calculate the ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ neutrino absorption cross section on chlorine: ${\mathrm{\sigma }}_{\mathrm{Cl}}$=(1.14±0.11)×${10}^{\mathrm{-}42}$ ${\mathrm{cm}}^2$ (±3σ errors). The chlorine cross section is also given as a function of the neutrino energy. The ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ neutrino absorption cross section in gallium is ${\mathrm{\sigma }}_{\mathrm{Ga}}$=(2.${46}_{\mathrm{-}1.1}^{+2.1\mathrm{}}$)×${10}^{\mathrm{-}42}$ ${\mathrm{cm}}^2$ (±3σ errors). © 1996 The American Physical Society.

A review of kinematically incomplete n-d breakup data and their comparison to rigorous 3N calculations using realistic nucleon-nucleon interactions revealed unexplained differences of more than 25% in regions where a large number of different three-nucleon configurations contribute to the cross section. © 1996 The American Physical Society.

The half-life of ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ has been measured with high precision using a high-purity germanium detector: ${\mathit{T}}_{1/2}$=53.12±0.07 d. © 1996 The American Physical Society.

An excited superdeformed band has been observed in ${}_{}{}^{131}{}_{}{}^{}\mathrm{Ce}$ consisting of 13 γ rays and extending to spin ∼50ħ. Possible configurations are discussed in terms of particle-hole excitations in a deformed Woods-Saxon potential. © 1996 The American Physical Society.