The new $\beta$-delayed proton precursor ${}^{121}$Ce was synthesized in the reaction ${}^{92}$Mo${(}^{32}$S,$3n)$ and first identified in $p$-$\gamma \mathrm{}\left(X\right)\mathrm{}$ coincidence measurements with a helium-jet recoil fast-moving tape-transport system. The half-life of the ${}^{121}$Ce decay was determined to be 1.1$\pm$0.1 s. Its $\beta$-delayed proton spectrum was observed and the $\beta$-delayed proton branching ratio for ${}^{121}$Ce decay was estimated to be $\sim$1%.

Inclusive photons of low transverse momenta have been measured in 200 GeV/nucleon ${}^{32}$S+Au collisions at the CERN SPS. Data were taken in the WA93 experiment using a small acceptance BGO detector with longitudinal segmentation. The results are compared to WA80 measurements for the same system and results from hadron decay calculations. An excess of soft photons over the expectations from neutral meson decays is observed.

We have performed an additional analysis to clarify the interpretation of two candidate events which were the result of a search for an $H$ dibaryon.

Electromagnetic fission cross sections for the reactions U + (Be, C, Al, Cu, In, Au, U) at $E/A$ = 0.6 and 1.0 GeV are compared to theoretical calculations using recently proposed quantum-mechanical equivalent-photon spectra. In contrast to semiclassical calculations, systematically lower cross sections are obtained that cannot reproduce the experimental results. Since electromagnetic fission cross sections are virtually independent of the excitation of the double giant dipole resonance (DGDR), this conclusion is not influenced by the strength of the DGDR.

For a $Q\cdot Q$ interaction the energy-weighted sum rule for isovector orbital magnetic dipole transitions is proportional to the difference $\sum B(E2,\mathrm{isoscalar})-\sum B(E2,\mathrm{isovector})$, not just to $\sum B(E2,\mathrm{physical})$. This fact is important in ensuring that one gets the correct limit as one goes to nuclei, some of which are far from stability, for which one shell (neutron or proton) is closed.

The differential elastic scattering cross section of a few heavy-ion systems, in the energy range 8–100 MeV/nucleon, has been studied in the framework of the Coulomb-modified Glauber model. Ingredients in this formalism are the densities of the colliding ions and the elementary nucleon-nucleon scattering amplitude. The only free parameter ${\alpha }_{\mathrm{NN}},$ the ratio of the real to imaginary part of the forward nucleon-nucleon scattering amplitude, is varied to fit the data. Elastic scattering angular distributions using the realistic two-parameter Fermi densities and the surface-matched Gaussian densities agree reasonably well with each other.

Within the Skyrme energy density formalism, an analytical formula for the spin density part of the heavy ion interaction potential is obtained for $1s-0d$ shell nuclei by using the shell model density consistently. Comparisons are made with similar results for the parametrized Fermi density distribution which are useful for their later use in the calculations of fusion cross sections.

The consistency of the BCS approach in treating proton-neutron pairing correlations is examined. Generalized BCS transformations, which combine proton and neutron states, are used to extract the pairing gap parameter. This procedure gives energy gains due to the inclusion of proton-neutron pairing correlations, but the effect is found to be restricted to small values of the neutron excess $\left(N-Z\right)$.

The neutron-deficient and neutron-rich zirconium nuclei are studied using statistical theory. The deformation dependence of occupation numbers of the neutron orbitals in these nuclei near the Fermi level is investigated. The preference of the neutrons to occupy or vacate a particular orbital is found to contribute a particular shape to the nucleus.

Commenting on a recent investigation of the effect of in-medium corrections to the pion dispersion relation, we point out that the description (hence the conclusions) might be affected if a more refined (and consistent) $\Delta N^{-1}$ model was employed, primarily due to the appearance of two pionic modes (rather than only one) whose character $(\pi$ or $\Delta N^{-1})$ changes with momentum.

The energy of pions in nuclei as a function of momentum and density (and temperature) is an important ingredient, e.g., for pion production in heavy ion collisions. In spite of many efforts over the last 25 years one is not yet able to calculate reliably this dispersion relation from first principles. At the moment it seems best to use this relation determined by experiments (at least at lower energies and densities).

Nuclear-polarizability corrections that go beyond unretarded-dipole approximation are calculated analytically for hydrogenic (atomic) $S$ states. These retardation corrections are evaluated numerically for deuterium and contribute $-0.68$ kHz, for a total polarization correction of 18.58(7) kHz. Our results are in agreement with one previous numerical calculation, and the retardation corrections completely account for the difference between two previous calculations. The uncertainty in the deuterium polarizability correction is substantially reduced. At the level of 0.01 kHz for deuterium, only three primary nuclear observables contribute: the electric polarizability ${\alpha }_E,$ the paramagnetic susceptibility ${\beta }_M,$ and the third Zemach moment $〈r^3{〉}_{\mathrm{}\left(2\right)\mathrm{}}.$ Cartesian multipole decomposition of the virtual Compton amplitude and its concomitant gauge sum rules are used in the analysis.

The importance of $n$-$p$ radiative capture, utilizing polarized cold neutrons, as a means of measuring the weak pion coupling constant is reviewed. Parity conserving processes of the form ${\mathbf{k}}_{\gamma }\cdot ({\mathbf{s}}_n\times {\mathbf{k}}_n)$ can contribute to the ${\mathbf{s}}_n\cdot {\mathbf{k}}_{\gamma }$ photon asymmetry in any such experiment, if the apparatus is not perfectly symmetric. For an incident laboratory neutron energy of 0.003 eV a value of $A_{\gamma }^{\mathrm{PC}}=0.67\mathrm{}\times {10}^{-8}$ is obtained for two different potential models (Argonne AV14 and Nijmegen Reid93). Serving as an extreme test case, the Reid soft core potential yields $0.61\times {10}^{-8}$, close to the result of the contemporary forces. Implications for extracting the weak pion coupling constant and for monitoring the beam polarization are discussed.

Results are presented for a combined analysis of the reactions $\mathrm{pp}\to pp,\pi d\to \pi d$, and $\pi d\to \mathrm{pp}$ over the $\sqrt{s}$ interval from the pion threshold to approximately 2.4 GeV. These results for $\pi d\to \mathrm{pp}$ and $\pi d$ elastic scattering are superior to our previous analyses of these reactions. In particular, the overall phase in $\pi d\to \mathrm{pp}$ has now been determined. Comparisons are made with previous (separate and combined) analyses of this two-nucleon system.

The normalization condition for the relativistic three nucleon Bethe-Salpeter and Gross bound state vertex functions is derived, for the first time, directly from the three-body wave equations. It is also shown that the relativistic normalization condition for the two-body Gross bound state vertex function is identical to the requirement that the bound state charge be conserved, proving that charge is automatically conserved by this equation.

Nucleon-deuteron scattering is cast into the form of an optical potential formalism. Two forms of an optical potential are given. The resulting integral equations for the optical potentials are approximated by the first two leading terms. Our numerical results demonstrate that even at intermediate energies these approximations are insufficient to cover all of the angular range. Rescattering terms of higher order in the nucleon-nucleon ($\mathrm{NN}$) $t$ matrix are needed. If one focuses on forward scattering, low-order approximations in the $\mathrm{NN}$ $t$ matrix can be sufficient, depending on energy, and observable.

We work in a chiral invariant quark model, with a condensed vacuum, characterized by only one parameter. Bound state equations for the nucleon and Δ are solved in order to obtain an updated value of their radii and masses. Nucleon-nucleon $S$-wave scattering is studied in the resonating group method framework both for isospin $T=1\mathrm{}$ and $T=0.\mathrm{}$ The phase shifts are calculated and an equivalent local potential, which is consistent with $K-N$ scattering, is derived. The result is a reasonable microscopic short range repulsion in the nucleon-nucleon interaction.

We investigate in detail the effect of making the range of the “contact” interaction used in effective field theory (EFT) calculations of $\mathrm{NN}$ scattering finite. This is done in both an effective field theory with explicit pions, and one where the pions have been integrated out. In both cases we calculate $\mathrm{NN}$ scattering in the ${}^1{S}_0$ channel using potentials which are second order in the EFT expansion. The contact interactions present in the EFT Lagrangian are made finite by use of a square-well regulator. We find that there is an optimal radius for this regulator, at which second-order corrections to the EFT are identically zero; for radii near optimal these second-order corrections are small. The cutoff EFT’s which result from this procedure appear to be valid for momenta up to about $100–150\mathrm{MeV}/c.\mathrm{}$ We also find that the radius of the square well cannot be reduced to zero if the theory is to reproduce both the experimental scattering length and effective range. Indeed, we show that, if the $\mathrm{NN}$ potential is the sum of a one-pion-exchange piece and a short-range interaction, then the short-range piece must extend out beyond 1.05 fm, regardless of its particular form.

In this paper we review the present status of the $\pi \mathrm{NNN}$-$\mathrm{NNN}$ problem. In particular, we reconsider the chain-labeled approach recently proposed by us, and identify a class of graphs, previously overlooked, which prevents the kernel of the corresponding $\pi \mathrm{NNN}$-$\mathrm{NNN}$ equations from being connected. We propose some approximate schemes, yielding connected-kernel equations. A generalization of the residue method allows us to relate the transition amplitudes for the coupled $\pi \mathrm{NNN}$-$\mathrm{NNN}$ system to the chain-labeled formalism. The quasiparticle approach is extended to the present situation, where emission/absorption of particles is allowed. The open problems for the $\pi \mathrm{NNN}$-$\mathrm{NNN}$ system in light of the present and of previous approaches are finally discussed.