The Dilepton Spectrometer collaboration has reported a bump in the $e^{+}$$e^{\mathrm{-}}$ mass distribution at around 2$m_{\pi }$ in 4.9 GeV proton-Be collisions. Previous calculations have shown that this bump does not have its origin in nucleon-nucleon bremsstrahlung nor in the Dalitz decay of the Δ resonance. In this paper we estimate the contribution from two-pion annihilation based on relativistic kinetic theory, on the experimentally measured cross sections for the production of up to five pions, and on a phase space generator for the pion momentum distributions. The calculation fails to reproduce the data.. The origin of the bump remains unexplained.

A recent claim of significant correlations between the fragment mass and excitation energy at a fixed total kinetic energy loss in a damped reaction is reexamined. It is shown that correlations of similar character and strength to those reported, result from incorrect assumptions made in the original analysis of kinematical coincidence data from the ${}_{}{}^{165}{}_{}{}^{}\mathrm{Fe}$ reaction at 504 MeV. Based on Monte Carlo simulations of the experiment, it is concluded, that within the uncertainties resulting from the experimental method, the data from the above reaction are consistent with a damped reaction mechanism, in which, for a fixed kinetic energy loss, the fragment excitation energy is uncorrelated with its mass.

We calculate the cross section for polarized-proton-nucleus non-spin-flip (↑↑) and spin-flip (↓↑) inelastic scattering where the polarization is perpendicular to the scattering plane. This cross section is compared with that of unpolarized-electron-nucleus scattering. We note that, in the plane-wave impulse approximation, the non-spin-flip squared form factor is essentially the same, apart from a factor of $q^2$, as one obtained in unpolarized-electron-nucleus scattering in which only the spin terms are kept and the convection terms dropped. But the spin-flip squared form factor is different.

The αα bidimensional spectra for the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$${(}^3$He, αp${)}^4$He reaction at 11, 13, and 14 MeV incident energy have been measured. The ${}_{}{}^5{}_{}{}^{}\mathrm{Li}$ state at $E_x$=(17.9±0.4) MeV has been observed and its width has been determined as (3.5±0.8) MeV. The excitation energy is in line with the shell-model calculations while the Γ value is the first quantitative estimate of the width of the above state.

The (p,pα) cluster-knockout reaction on ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ has been investigated experimentally at a bombarding energy of 200 MeV. Coincident data were obtained at five quasifree angle pairs for proton angles ranging from 40° to 80°. The data were analyzed in terms of the distorted-wave impulse approximation. The calculated energy-sharing distributions reproduce the data reasonably well, indicating that the quasifree-knockout mechanism dominates the reaction. The factorization approximation employed in the calculation is found to be valid. The absolute spectroscopic factors derived from the data are in excellent agreement with lower-energy results, and compare well with shell-model predictions.

Time delay and resonant phenomena are examined in the context of a model three-body problem. The time-delay formalism is reviewed and summarized, as it applies to a three-body system. Calculations are carried out for a three-body model containing elastic, inelastic, and rearrangement channels. The two-body interactions in the model permit two-body resonances to be embedded in the three-body structure. Eigenvalues of the time-delay matrix are shown to provide a clear, unambiguous signature of resonant behavior in the multichannel system. A resonance always shows up as a positive peak in one eigenvalue of the time-delay matrix. This result is contrasted with the more usual means of identifying resonant behavior by studying the phases of the S-matrix elements, or the eigenphases of the S matrix.

We derive a separable representation of the two-body T matrix, which is exact half on shell at all energies even when truncated to one single term. Moreover, the truncated expansion satisfies the full off-shell unitarity relation. The approach does not have recourse to some complete set of functions but rather uses properties of the Lippmann-Schwinger equation itself to arrive at the expansion. It is based on the W-matrix representation of the two-body T matrix introduced by Bartnik, Haberzettl, and Sandhas. That representation provides a splitting of the T matrix in one single separable term which contains all bound-state poles and scattering cuts and in a nonsingular, real remainder which vanishes half on shell. The method presented here yields a separable expansion of this remainder in which all its properties are preserved in each order. Increasing the order of the expansion, the amount of additional numerical work is constant at each stage. The method is ap- plicable to any kind of short-range potential, local, nonlocal, or energy dependent. Numerical tests using the semirealistic Malfliet-Tjon III potential demonstrate the smooth and rapid convergence of the expansion.

A microscopic Green’s function doorway formalism is used to study Coulomb sum rule saturation in inclusive quasielastic electron scattering as a function of momentum transfer. Form factor, kinematical restriction, and final-state interaction effects on the approach to saturation are examined in detail, as are the roles of nonhermiticity, energy dependence, and the analytic behavior of the final-state interactions. The implications of relativistic kinematics and dynamics for the approach to saturation at not-too-high values of the momentum transfer are assessed. Because the pair production of relativistic treatments destroys the asymptotic nature of the nonrelativistic Coulomb sum rule, the degree to which a regime of validity can be expected for this sum rule, and its location, is considered. The breakdown of the sum rule as the momentum transfer increases is also examined. Similar theoretical studies of an analogous nonrelativistic transverse sum in its saturation region are developed as well. Theoretical predictions are compared with the experimental data for ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ both directly and using a variety of theoretical prescriptions and limits. Neutron knockout contributions and associated uncertainties due to ambiguity in the free neutron form factors are examined.

Using monochromatic photons from (n,γ) and (p,γ) capture reactions, the elastic scattering of photons was studied in the mass range A=181–238 and energy range E=8–18 MeV. It is shown that the A dependence of the enhancement of E1 strength located in the giant-dipole resonance as revealed by part of the photoneutron cross sections is confirmed by our photon-scattering data. The possibility is discussed that the concentration of E1 strength in the giant dipole resonance may be larger for closed-shell nuclei as compared to open-shell nuclei.

Anomalies in low-energy positron scattering from thorium are searched for. The incident positrons were emitted from a ${}_{}{}^{68}{}_{}{}^{}\mathrm{Ga}$ source with an end-point energy of 1.90 MeV. Coincidences between electrons and positrons in the energy range 245–445 keV were registered in a double beta spectrometer. The electron and positron energy spectra are best described in terms of Bhabha scattering with a small additional structure at an energy of about 320 keV for both the electrons and the positrons. The significance of this peak is estimated to be three standard deviations. The spectrometer was also used in a study of scattering of electrons emitted in the decay of ${}_{}{}^{90}{}_{}{}^{}\mathrm{Y}$, with an end-point energy of 2.28 MeV. The electron-electron coincidence spectrum in the energy range 245–445 keV is well described as resulting from Möller scattering alone.

We implement a simple approach to the inclusive cross section for single nucleon removal by relativistic nucleons and nuclei. We first develop the projectile and target dependence of the mean number, N(b), of nucleon-nucleon collisions as a function of impact parameter in the peripheral region. Using the Glauber approximation, we obtain a simple parametrization for a critical impact parameter $b_c$ such that the reaction cross sections for both N-B and A-B collisions are well represented by π$b_c^2$. Further study of the b dependence of N(b) around b=$b_c$ allows us to develop a parametrization of single nucleon abrasion cross sections. Next, we employ the Weizsacker-Williams approximation with $b_c$ as the cutoff impact parameter to calculate the Coulomb contribution to the single nucleon removal process. The results are compared with recent data which suggest that the Weizsacker-Williams approximation is inadequate for heavy projectiles. Using our estimates for the nuclear contribution, we find that the data yields good agreement with the Weizsacker-Williams results for virtually all projectile-target combinations. We therefore conclude that the measured deviations from the Weizsacker-Williams results do not represent new physics, but rather reflect uncertainties in the estimation of the nuclear contribution to the single nucleon removal process. As an elementary example of the possible new physics that may be observed in this process, we calculate the contributions from a coherent nuclear process and the possible interference effects. For heavy projectiles, we find that the interference effects are comparable to the present experimental uncertainties.

Energy spectra and angular distributions have been measured for high-energy gamma rays ($E_{\gamma }$>40 MeV) from the heavy-ion reaction ${}_{}{}^{136}{}_{}{}^{}$Xe+Sn at bombarding energies of E/A=89 and 124 MeV. Gamma rays are observed with energies up to 160 MeV, and the energy spectra are roughly exponential above 40 MeV. The angular distributions of the gamma rays are forward peaked in the laboratory frame and are consistent with emission from a source moving with a velocity equal to the nucleon-nucleon center-of-mass velocity. The angular distributions show no significant anisotropy in the nucleon-nucleon frame. The production cross sections agree with systematics observed for lighter systems.

A time-dependent entrance channel formalism, which treats the relative motion of the heavy ions classically, and the internal excitations quantum mechanically, is used to study prompt nucleon emission from deep-inelastic collisions of the ${}_{}{}^{58}{}_{}{}^{}$Ni${+}^{165}$Ho system at $E_{\mathrm{lab}=930\mathrm{}}$ MeV. The calculations employ an external, time-dependent, one-body potential. We investigate the correlation between the most probable velocity of the heavy ions when the nucleons are emitted and the exit channel total kinetic energy of the system, and compare with experimental data. We found that the model predicts a source velocity for the ions which is 10% below the measured projectilelike fragment velocity, and 34% above the measured velocity for the prompt emission source.

The interacting gluon model developed to describe the inelasticity distribution in hadron-nucleon collisions has been generalized and applied to hadron-nucleus and nucleus-nucleus interactions. Leading particle spectra and energy distributions in hadron-nucleus and nucleus-nucleus collisions are calculated.

The ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$${(}^{18}$O,3n${)}^{223}$Th reaction at 83 MeV bombarding energy was used to populate the alpha-radioactive nucleus ${}_{}{}^{223}{}_{}{}^{}\mathrm{Th}$. Out-of-beam alpha-gamma coincidences were recorded at correlation angles of 90° and 180°. The $a_2$ angular correlation coefficient was extracted for an alpha-gamma cascade to the ${}_{}{}^{215}{}_{}{}^{}\mathrm{Rn}$ ground state via the 0.316 MeV excited state. This limited the assignment of the ground-state spin of ${}_{}{}^{219}{}_{}{}^{}\mathrm{Ra}$ to ((7/2, 11) / 2 ${)}^{+}$. .AE

Measurements of the inelastic scattering of 210 MeV ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ ions from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, and ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ have been made. Differential cross sections leading to the first excited ($2^{+}$) states of the target nuclei were obtained. The angular distributions for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ (6.8°–60.6°), ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ (4.9°–45.9°), and ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ (7.2°–48.3°) are similar in shape to those for elastic scattering, with diffractive oscillations at forward angles followed by smooth exponential falloff, characteristic of refractive nuclear scattering, at the larger angles. Distorted-wave Born approximation calculations provide good fits to the data when unique ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ optical-model potentials, derived from elastic scattering data, are used. Calculations with discrete ambiguous potentials deviate from the data at large angles. Coupled-channels calculations reproduce both the elastic and inelastic scattering data without significant changes in the unique potentials. The deformation lengths, ${\beta }_2$R, derived from the analyses are compared with results of previous measurements. The deduced quadrupole moments, $q_{20}$, are in excellent agreement with those obtained from electromagnetic measurements.

The target fragment production cross sections, angular distributions, and range distributions have been measured for the interaction of 12–16 MeV/nucleon ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ with ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$. The fragment isobaric yield distribution and the fragment moving frame angular distributions have been deduced from the data. Symmetry properties of the moving frame angular distributions have been used to establish a relative time scale for the reaction mechanism(s). No fission fragment moving frame angular distribution is symmetric about 90°, suggesting that these products are produced, in part, by a fast, non- equilibrium process. The range distributions are used to deduce energy spectra, which suggest that the heavy residues are the result of complete or incomplete fusion and also of an inelastic process such as deep inelastic scattering.

Rotational states have been populated in γ-soft ${}_{}{}^{132}{}_{}{}^{}\mathrm{Ba}$ following the ${}_{}{}^{122}{}_{}{}^{}\mathrm{Sn}$${(}^{13}$C,3nγ) reaction. The ground state of this nucleus is predicted to possess maximal triaxiality γ∼-30°. Two ΔI=2 bands were established, based on quasineutron configurations with large negative γ deformations close to the collective oblate shape γ=-60°. The bandhead of one of these bands, associated with a [ν$h_{11/2}$${]}^2$ configuration, was found to be isomeric with a mean lifetime τ=12.5±0.3 ns. A third ΔI=2 band was observed, built on a two-quasiproton configuration with a near-prolate shape (γ∼0°). In addition, two ΔI=1 bands, built on mixed proton-neutron four-quasiparticle configurations with oblate shapes (γ∼-60°), were established.

Measurements of projectile-like-fragment–target-like-fragment coincidences in the reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Al}$ are simulated using a Monte Carlo version of the random walk model. The predictions of the model are compared with recent measurements. The good agreement between predictions and data obtained here and elsewhere indicates that the underlying physical picture constitutes a viable model of the reaction mechanism.

The possibilities of nuclear molecular configurations in symmetric and asymmetric heavy ion collisions are investigated by choosing a proper parametrization for the molecule-like compound state. We treat the nucleus as a rotating liquid drop in terms of the elliptic lemniscatoid parametrization suggested by Royer and Remaud which describes all deformed shapes that occur during the process of fusion of two nuclei, starting from two touching spheres to a single one with the intermediate formation of a deep neck. Only one parameter (s for the symmetric and $s_1$ for the conditional asymmetric case) is needed to define all the shapes encountered in the process. The shape has a neck as long as s or $s_1$ is less than 1/ √2 . In this parametrization, analytical expressions can be obtained for volume, surface, and moment of inertia while the Coulomb energy has to be evaluated numerically. The total energy of the system is calculated as a function of the parameter s or $s_1$, for various spins and if the stable shape corresponding to minimum energy is one with a neck, then it is concluded that the molecular configuration is possible. Our model yields results which are in good agreement with the experimental findings.