In a series of recent publications, a new approach to the nonrelativistic reduction of the electromagnetic current operator in calculations of electronuclear reactions has been introduced, which can be applied to any target nucleus. In the work by Jeschonnek and Donnelly [Phys. Rev. C 57, 2438 (1998)], the conjecture that at energies of a few GeV, the bulk of the relativistic effects comes from the current and not from the nuclear dynamics was made, based on the large relativistic effects in the transverse-longitudinal response. Here, we explicitly compare a manifestly covariant calculation performed with the Gross equation, with a calculation that uses a nonrelativistic wave function and the current operator discussed by Jeschonnek and Donnelly. We find very good agreement up to missing momenta of 400 MeV/c, thus confirming the previous conjecture. We discuss slight deviations in cross sections for higher missing momenta and their possible origin, namely P-wave contributions and off-shell effects.

The $\pi$-nucleus optical potential is extended to open shell nuclei by employing the generalized seniority model and partial Pauli blocking. The calculated optical potentials are fit to $\pi$-nucleus elastic scattering data on ${}^{90}\mathrm{Zr}$ and ${}^{208}\mathrm{Pb}$ at resonance as well as low energies. The ranges of the $\pi N$ interaction are determined by a best fit to experimental data. The angular distribution at 48 MeV pion lab energy and energy dependence of the double charge exchange cross section on Te isotopes are calculated. The existing experimental data are reproduced by using the ranges in the vicinity of the averaged ranges of ${}^{90}\mathrm{Zr}$ and ${}^{208}\mathrm{Pb}$ determined in fitting elastic-scattering data.

The effect of the continuous emission hypothesis on the two-pion Bose-Einstein correlation function is discussed and compared with the corresponding results based on the usual freeze-out. Sizable differences in the correlation function appear in these different descriptions of the decoupling process. This means that, when extracting properties of the hot matter formed in high-energy heavy-ion collisions from the data, completely different conclusions may be reached according to the description of the particle emission process adopted.

Using a hadron-string cascade model, JPCIAE, we study the effect of the orientation of deformed nucleus on $J/\psi$ suppression in the central collision of uranium bombarding with uranium at $200A$ $\mathrm{GeV}/c.\mathrm{}$ We find that the $J/\psi$ survival probability is much smaller if the major axes of both deformed nuclei are along the beam direction than if they are perpendicular to the beam direction.

We discuss the theoretical and experimental situations for charge symmetry violation (CSV) effects in the elastic scattering of ${\pi }^{+}$ and ${\pi }^{-}$ on deuterium (D) and ${}^3\mathrm{He}{/}^3\mathrm{H}.$ Accurate comparison of data for both types of targets provides evidence for the presence of CSV effects. While there are indications of a CSV effect in deuterium, it is much more pronounced in the case of ${}^3\mathrm{He}{/}^3\mathrm{H}.$ We provide a description of the CSV effect on the deuteron in terms of single- and double-scattering amplitudes. The $\Delta$-mass splitting is taken into account. Theoretical predictions are compared with existing experimental data for $\pi -d$ scattering; a future article will speak to the $\pi$-three nucleon case.

We propose a method that allows for the efficient solution of the three-body Faddeev equations in the presence of infinitely rising confinement interactions. Such a method is useful in calculations of nonrelativistic and especially semirelativistic constituent quark models. The convergence of the partial wave series is accelerated and possible spurious contributions in the Faddeev components are avoided. We demonstrate how the method works with the example of the Goldstone-boson-exchange chiral quark model for baryons.

Experimental data for $M1\mathrm{}$ matrix elements in the $T=1/2\mathrm{}$ mirror nuclei ${}^{27}\mathrm{Al}$ and ${}^{27}\mathrm{Si}$ are used to determine the isoscalar and isovector $M1\mathrm{}$ components. The obtained isovector $M1\mathrm{}$ matrix elements are compared to the Gamow-Teller matrix elements deduced from $\beta$ decay and the ${}^{27}\mathrm{Al}{(}^3\mathrm{He}{,t)}^{27}\mathrm{Si}$ charge exchange reaction to determine the contributions of the isovector spin and orbital components. The exchange current effects are taken into account. The results are compared with shell model calculations.

Excited states in ${}^{139}\mathrm{Te}$ were observed for the first time, using EUROGAM2 multidetector array to measure prompt-$\gamma$ radiation following the spontaneous fission of ${}^{248}\mathrm{Cm}.$ The systematic behavior of excitation energies in the $N=87\mathrm{}$ isotones and the multipolarity measurements suggest spin ${7/2}^{-}$ for the ground state and ${9/2}^{-}$ for the 271.0 keV level in ${}^{139}\mathrm{Te}.$ The 271.0 keV level most likely corresponds to the $\nu h_{9/2}$ single-particle excitation. A shape transition from spherical to prolate Te isotopes is observed at the neutron number $N=87,$ in accord with the Hartree-Fock plus BCS, PES calculations. Predictions for excitations in the ${}^{137}\mathrm{Sn}$ nucleus are made based on the extended systematics obtained for the $N=87\mathrm{}$ isotones.

The exotic nuclear decay of ${}^{230}\mathrm{U}$ by emission of heavy ions has been investigated by use of ${}^{230}\mathrm{Pa}$ $\stackrel{{\beta }^{-}}{\to }$ ${}^{230}\mathrm{U}$ sources and polyester track detectors. After a run of 248 d, two cases of decay via heavy ion emission, which were most probably for the neon decays of ${}^{230}\mathrm{U},$ were observed for the first time. The preliminary branching ratio for the emission of heavy ions relative to $\alpha$ particles from ${}^{230}\mathrm{U}$ comes out to be $(1.3\mathrm{}\pm 0.8)\times {10}^{-14}.$

Classical novae are potential sources of $\gamma$ rays, like the 1.275 MeV gamma emission following ${}^{22}\mathrm{Na}$ beta decay, that could be detected by appropriate instruments on board of future satellites like INTEGRAL. It has been shown that the production of ${}^{22}\mathrm{Na}$ by novae is affected by the uncertainty on the ${}^{21}\mathrm{Na}(p,\gamma {)}^{22}\mathrm{Mg}$ rate and in particular by the unknown partial widths of the $E_x=5.714,$ $J^{\pi }{=2\mathrm{}}^{+},$ ${}^{22}\mathrm{Mg}$ level. To reduce these uncertainties, we performed shell model calculations with the OXBASH code, compared the results with available spectroscopic data, and calculated the missing partial widths. Finally, we discuss the influence of these results on the ${}^{21}\mathrm{Na}(p,\gamma {)}^{22}\mathrm{Mg}$ reaction rate and ${}^{22}\mathrm{Na}$ synthesis.

The mixed symmetry states identified in a recent experiment on ${}^{94}\mathrm{Mo}$ and successfully described within the interacting boson model (IBM) are studied microscopically within the quasiparticle-phonon model (QPM). The results are in agreement with experiments and consistent with the IBM picture of these states. New branches of the scissors mode are also predicted.

The factorial moments of the pion multiplicity distributions are calculated with HIJING and UrQMD and found to be independent of the $p_T$ range included, in contrast to recent simulations with the linear $\sigma$ model which leads to large enhancements for pions with transverse kinetic energies below 200 MeV. This supports the use of the ratio of the factorial moments of low and high $p_T$ pions as a signal of “new” physics at low momentum scales, such as the formation of disoriented chiral condensates.

The nucleon-nucleon (NN) t matrix is calculated directly as function of two vector momenta for different realistic NN potentials. To facilitate this a formalism is developed for solving the two-nucleon Lippmann-Schwinger equation in momentum space without employing a partial wave decomposition. The total spin is treated in a helicity representation. Two different realistic NN interactions, one defined in momentum space and one in coordinate space, are presented in a form suited for this formulation. The angular and momentum dependence of the full amplitude is studied and displayed. A partial wave decomposition of the full amplitude it carried out to compare the presented results with the well-known phase shifts provided by those interactions.

The double-dipole mode of excitation is calculated for ${}^{16}\mathrm{O}$ and ${}^{40}\mathrm{Ca}$ in a large shell-model basis space that includes a full $2ħ\omega$ basis. The energies, distribution of strength and the spin, isospin splittings are computed. Sum rules are obtained and compared to the shell model results.

The density fluctuations of nuclear matter are studied within a mean-field model in which fluctuations are generated by an external stochastic field. The constraints imposed on the random force by the fluctuation-dissipation theorem are analyzed. It is shown that in the proximity of the borders of the spinodal region the assumption of a white-noise stochastic field can be reliably used. The domain distribution of the liquid phase in the spinodal decomposition of nuclear matter is derived. The related distribution of fragment sizes compares favorably with the experimental fragment distribution observed in heavy ion collisions.

The chiral quark model describes the strangeness components of the light quarks as fluctuations into strange mesons and quarks. The single strange pseudoscalar and vector meson loop fluctuations of the constituent u and d quarks give rise to only very small strangeness form factors for the proton. This result is in line with recent experimental results, given their wide uncertainty range.

A semiempirical shell model mass equation applicable to superheavy elements up to $Z=126\mathrm{}$ is presented and shown to have a high predictive power. The equation is applied to the recently discovered superheavy nuclei ${}^{293}118$ and ${}^{289}114$ and their decay products.

The ${}^3\mathrm{He}(\gamma ,{\pi }^{\pm }p)$ reactions were measured simultaneously over a tagged photon energy range of $800<~E_{\gamma }<~1120$ MeV, well above the $\Delta$ resonance region. An analysis was performed to kinematically isolate $\Delta$ knockout events from conventional $\Delta$ photoproduction events, and a statistically significant excess of ${\pi }^{+}p$ events was identified, consistent with ${\Delta }^{++}$ knockout. Two methods were used to estimate the $\Delta \mathrm{NN}$ probability in the ${}^3\mathrm{He}$ ground state corresponding to the observed knockout cross section. The first gave a lower probability limit of $1.5\pm 0.6\pm 0.5\%;$ the second yielded an upper limit of about $2.6\%.$

Using up-to-date values of nuclear radii and of the nuclear surface tension, the 1977 proximity treatment of nucleus-nucleus interaction is confronted with 113 measured fusion barriers. The $\approx 4\%$ overestimate of theory with respect to experiment, seen in a similiar comparison in 1981, is no longer present. The calculated proximity barriers, when applied to fusion reactions used to produce heavy elements with atomic number $Z=102\mathrm{}$–118, suggest that the unexpectedly large cross section observed in the reaction ${}^{86}\mathrm{Kr}{+}^{208}{\overrightarrow{\mathrm{Pb}}}^{293}118+1n$ may be due to the sinking of the Coulomb barrier below the level of the bombarding energy. Tests of this hypothesis are suggested. Some consequences of the appearance of such “unshielded” reactions for very heavy systems are discussed. An Appendix supplies very accurate analytic formulas for the universal nuclear proximity force and potential functions $\phi$ and $\Phi .$ This does away with the need to consult the tables published in 1977.