The recently observed resonance ( $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=32.5\mathrm{}$ MeV) in the $0_2^{+}-0_2^{+}$ channel of ${}_{}{}^{12}{}_{}{}^{}C+{}_{}{}^{12}{}_{}{}^{}C$ collisions is predicted to be a weakly coupled structure of two three- $\alpha$-particle states ( $0_2^{+}$ state of ${}^{12}$C). At the same time a well-known resonance ( $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=29\mathrm{}$ MeV) in the $0_1^{+}-0_2^{+}$ channel is explained as of three α particles plus ${}^{12}$C core structure. The band crossing model is shown to be valid also for inelastic scatterings to α-cluster states. A strong resonance is predicted in the $3_1^{-}-0_2^{+}$ channel in the same energy region. A relation to the linear chain configuration of six α particles is discussed.

Previously we have presented calculations for α-chain states using the Bloch-Brink model. Here we develop an approximate coupled channels model of a 6-α chain state. We consider the scattering of two lighter α-chain nuclei using double folded potentials. An analysis of these potentials shows that they can be approximated by a potential whose matrix elements are separable for the aligned configuration. The coupled equations are then solved approximately using an adiabatic approximation. We show that the model leads to resonances with properties similar to the configurations predicted by the Bloch-Brink model. We compare the calculated properties of these resonances with the known properties of the resonance observed in ${}^{12}\mathrm{C}{+}^{12}\mathrm{C}$ scattering at $E_{\mathrm{CM}}=32.5\mathrm{}\mathrm{MeV}$.

A many-particle operator that affects a transformation to the pseudospin basis in heavy nuclei is identified. Both mean-field and many-particle estimates demonstrate that in the helicity-transformed representation the nucleons move in a finite-depth nonlocal potential with a reduced spin-orbit strength. Because of the close relation between the helicity and chirality operations, the results suggest that the pseudospin symmetry in heavy nuclei yields to the chiral symmetry of massless hadrons in the high energy region.

We calculate the cross section for the thermal $n+p\to d+\gamma$ process in chiral perturbation theory to next-to-next-to-leading order using heavy-fermion formalism. The exchange current correction is found to be $(4.5\pm 0.3)\%$ in amplitude, and the chiral perturbation at one-loop order gives the cross section ${\sigma }_{\mathrm{th}}=334\mathrm{}\pm 2$ mb, which is in agreement with the experimental value $334.2\pm 0.5\mathrm{mb}$. Together with the axial-charge transitions, this provides a strong support for the power of chiral Lagrangians for nuclear physics.

The pionic deuterium $3P-1S$ x-ray transition was measured with a quartz crystal spectrometer in combination with a cyclotron trap and charge coupled device detectors. The strong interaction shift and total decay width of the $1S$ level are ${\epsilon }_{1S}\left(\mathrm{shift}\right)=2.48\mathrm{}\pm 0.10$ eV (repulsive), ${\gamma }_{1S}\left(\mathrm{width}\right)=1.02\mathrm{}\pm 0.21$ eV, where the statistical and systematic errors were added linearly. They yield the total pionic deuterium $S$-wave scattering length: $a_{{\pi }^{-}d}=-0.0264\mathrm{}(\pm 0.0011)+i0.0054\mathrm{}(\pm 0.0011)m_{\pi }^{-1\mathrm{}}$.

Rotational cascades observed in neutron-deficient nuclei with $Z\approx 51$ are described as the first examples of smoothly terminating bands in heavy nuclei, since they show a continuous transition from high collectivity to a noncollective state. Excellent agreement between experiment and calculations in the Nilsson-Strutinsky cranking model is obtained for the ${}_{51}^{109}{\mathrm{Sb}}_{58}$ nucleus.

A microscopic description of the $\alpha$ decay to intruder $0_2^{+}$ states of Pb isotopes in terms of proton-neutron pairing vibrations is performed. The calculated hindrance factors with respect to $\alpha$ transitions into the ground state are in good agreement with the available experimental data. Predictions for further measurements are given. Hindrance factors corresponding to the decay towards Po, Hg, and Pt isotopes are calculated within a simple model. The calculated quantities agree well with the experimental data, indicating that $\alpha$ decay is a powerful tool to precisely determine the transition from spherical to deformed shapes in the region around $Z=82\mathrm{}$.

The isoscalar $E2\mathrm{}$ giant resonance in ${}^{40}\mathrm{Ca}$ has been calculated within a microscopic approach which takes into account, in addition to the random-phase-approximation configurations, one-particle–one-hole (1p1h) $\otimes$phonon configurations and the continuum. We reproduce the observed shift of a considerable part of the $E2\mathrm{}$ strength to lower energies which gives rise to a nearly uniform distribution. If we add the $E0\mathrm{}$ strength calculated within the same approach, then we obtain good agreement with a recent electron scattering experiment, which is a further strong indication for low-lying $E0\mathrm{}$ strength.

We have analyzed low-energy pion-nucleon data for isospin invariance by comparing charge-exchange amplitudes derived from charge-exchange data with those predicted from recent ${\pi }^{\pm }p$ elastic data through the application of isospin invariance. A discrepancy of the order of 7% is observed beyond the contributions of the ${\pi }^{\pm }p$ Coulomb interaction and the hadronic mass differences.

The isospin dependence of the spin-orbit potential is investigated for an effective Skyrme-like energy functional suitable for density dependent Hartree-Fock calculations. The magnitude of the isospin dependence is obtained from a fit to experimental data on finite spherical nuclei. It is found to be close to that of relativistic Hartree models. Consequently, the anomalous kink in the isotope shifts of Pb nuclei is well reproduced.

The strength function and the angular distribution of the high energy γ rays emitted by the giant dipole resonance (GDR) in hot rotating ${}^{109,110}$Sn nuclei have been measured at temperature $T=1.8\mathrm{}\mathrm{MeV}$ and at four values of the angular momentum $I$. The GDR width is $\approx 2$ times larger than at $T=0\mathrm{}$ and increases by $\approx 20\%$ as $I$ goes from 40 to $54ħ$. The $a_2\left(E_{\gamma }\right)$ increases by a factor of $\approx 2$. Based on these two facts and on the comparison with theory we conclude that large deformations driven by $I$ and combined with shape and orientation fluctuations are responsible for the measured increases. Collisional damping is constant and practically equal to the $T=0\mathrm{}$ case.

We present novel low-energy theorems for the $P$-wave multipoles ${2M}_{1+}{+M}_{1-}$, $M_{1+}{-M}_{1-}$, $E_{1+}$, and $L_{1\pm }$ for neutral pion electroproduction off protons. These should be very useful for the analysis of existing or future threshold data.

Multifragmentation of ${}^{\mathrm{nat}}$Ag and ${}^{197}$Au nuclei induced by a 4.8-GeV${\mathrm{}}^3$He ions has been studied with the Indiana Silicon Sphere $4\pi$ detector array. Rapidity and moving source analyses are consistent with thermal emission from a source in approximate kinetic equilibrium. For the most dissipative collisions, the spectral Coulomb peaks are broadened to very low energies, indicative of emission from an extended nuclear system. Predictions of a model with an intranuclear cascade and an expanding, emitting source compare well with experimental multiplicity distributions and the evolution of fragment spectral shapes.

We have measured angular distributions for the ${}^{15}\mathrm{N}{(}^6\mathrm{Li},d{)}^{19}$F and ${}^{16}\mathrm{O}{(}^6\mathrm{Li},d{)}^{20}$Ne reactions at a bombarding energy of 22 MeV. Distorted-wave Born-approximation and Hauser-Feshbach calculations were used to analyze the data. Ratios of $\alpha$-transfer cross sections in ${}^{19}\mathrm{F}$ and ${}^{20}$Ne, plus isospin invariance, provide ratios of $\alpha$ widths in ${}^{19}$Ne and ${}^{20}$Ne. Using ${}^{20}$Ne ( $1^{-}$, 5.788 MeV) as a standard allows the determination of the $\alpha$-particle width for the state at 4.033 MeV in ${}^{19}$Ne, and hence the resonant rate for the ${}^{15}$O $(\alpha ,\gamma {)}^{19}$Ne reaction, contributed from the 504 keV, ${\frac{3}{2}}^{+}$ resonance, at temperatures of astrophysical interest.

The isotope shift of the $2^3{S}_1-2^3{P}_0$ transition in helium has been measured using laser excitation of an atomic beam, yielding 33 668.074(5) MHz. This value, combined with atomic theory and the ${}^4$He nuclear charge radius, gives a ${}^3$He radius of 1.9506(14) fm. This result is over an order of magnitude more precise than previous determinations. It agrees with two recent theoretical values 1.958(6) and 1.954(7) fm from realistic nucleon-nucleon potentials and the ${}^3$He binding energy. Our result provides both a confirmation and a sensitive test of the nuclear theory of few-nucleon systems.

Experimental excitation functions for the emission of complex fragments from compound nuclei are analyzed to search for atomic number $Z$ and energy $E$ dependent deviations from transition-state-method predictions. No $Z$ and/or $E$ dependent effects that could be attributed to an increased collectivity with increasing mass (charge) of the emitted fragment and associated with transient or stationary solutions of Kramers' diffusion equation are visible. Over seventy excitation functions, for complex fragments from four different compound nuclei, can be collapsed into a single universal straight line that is rigorously consistent with the transitions-state predictions.

The double-differential coincidence cross section for the reaction ${}^1\mathrm{H}\left({e,e}^{\prime }p\right){\pi }^0$ has been measured at $Q^2=0.1(\mathrm{GeV}/c{)}^2$ in a range in the invariant mass of 2–14 MeV above threshold. From the angular dependence of the data values of the pion $s$-wave multipoles $E_{0+}$ and $L_{0+}$ have been extracted. The results are compared to predictions from chiral perturbation theory and models based on an effective Lagrangian. None of the models is able to describe both the $E_{0+}$ and the $L_{0+}$ multipoles.

We explore the possibility of observing color transparency effects in incoherent diffractive electroproduction of $s\overline{s}$ mesons off nuclear targets in the energy range expected to be available at the Continuous Electron Beam Accelerator Facility. The $Q^2$, energy, and target mass dependences of the $\phi$ and ${\phi }^{\prime }$ transparency ratios have been studied within a theoretical approach in which the propagation of the $s\overline{s}$ pair through the nuclear medium is described in terms of the quantum mechanical evolution operator. In spite of the subasymptotic values of $Q^2$ and $\nu$, we find a complex pattern of color transparency induced effects.

We have measured the longitudinal momentum distribution of ${}^{18}\mathrm{C}$, ${}^{17}\mathrm{C}$, and ${}^{16}\mathrm{C}$ after the one-neutron breakup of ${}_{}{}^{19}{}_{}{}^{}C$, ${}^{18}\mathrm{C}$, and ${}^{17}\mathrm{C}$, respectively, using the A1200 fragment separator as an energy-loss spectrometer. The observed narrow width of $44.3\pm 5.9\mathrm{MeV}/c$ for the ${}^{18}\mathrm{C}$ fragments indicates that ${}^{19}\mathrm{C}$ is a new example of a one-neutron halo, so far the heaviest ever observed. The consequences of the obtained results on the structure of the three isotopes ${}^{19,18,17}\mathrm{C}$ are discussed together with shell-model calculations.

The staggering recently observed in some superdeformed rotational bands could be explained by a collective model including two quantized quantities. One of the latter being the angular momentum $I$, we propose for the other the Kelvin circulation $J$ associated with an intrinsic uniform vortical motion. This explanation is consistent with the observed strong $E2\mathrm{}$ intraband transitions. Some preliminary qualitative assessment of the relevant mass parameters is made.