We observed the bound-state ${\beta }^{-}$ decay of fully ionized ${}^{187}$Re nuclei circulating in a storage ring. With two independent methods the time dependent growth of hydrogenlike ${}^{187}$Os ions has been measured and a half-life of $32.9\pm 2.0\mathrm{yr}$ for bare ${}^{187}$Re nuclei could be determined, to be compared with 42 Gyr for neutral ${}^{187}$Re atoms. With the resulting $\log \mathrm{ft}$ value of $7.87\pm 0.03$ the half-life of ${}^{187}$Re ions in any ionization state can be calculated. Thus one can correct the ${}^{187}$Re${-}^{187}$Os galactic chronometer calibration, by taking account of the ${\beta }^{-}$ decay enhancement in stellar interiors, which will lead to a more accurate estimate of the galactic age.

The spectroscopic quadrupole moments of the neutron deficient radioactive Ir isotopes ${}^{184}$Ir, ${}^{186}$I${\mathrm{r}}^{\mathit{g}}$, ${}^{186}$I${\mathrm{r}}^{\mathit{m}}$, ${}^{187}$Ir, ${}^{188}$Ir, and ${}^{189}$Ir were measured with the technique of quadrupole-interaction-resolved NMR on oriented nuclei. The ratio of quadrupole moments of the $2^{-}$ isomeric state ${}^{186}$I${\mathrm{r}}^{\mathit{m}}$ and the $5^{+}$ ground state ${}^{186}$I${\mathrm{r}}^{\mathit{g}}$ points to different nuclear deformations in these states. In addition, we present a new method for the unambiguous measurement of ground state spins.

Distributions of parallel and transverse momenta for ${}^7$Be fragments formed in the breakup of ${}^8$B have been measured at $41A\mathrm{MeV}$. The $p_{\parallel }$ distributions are narrow ( $81\pm 4$ and $62\pm 3\mathrm{MeV}/c$ FWHM for Be and Au targets, respectively), comparable to those of neutron halo nuclei. Reaction mechanisms influence the ${}^7$Be momentum distributions, so they do not directly reflect the valence proton momentum wave function. We present reaction models that reproduce the distributions.

The effect of parity nonconservation (PNC) averaged over compound resonances is considered using a semiclassical approximation. We demonstrate that the result of averaging depends crucially on the properties of the residual strong nucleon-nucleon interaction. The way to elucidate this problem would be to investigate experimentally the PNC spin rotation $\psi$ or the longitudinal polarization $a$ of a nonmonochromatic neutron beam: $E\sim \Delta E\sim 1\mathrm{MeV}$. The magnitude of the effect can reach $\psi \sim a\sim {10}^{-5\mathrm{}}–{10}^{-4\mathrm{}}$ per mean free path.

Fission fragment angular distributions have been measured for fission following full momentum transfer in ${}^{11}\mathrm{B}$, ${}^{12}\mathrm{C}$, ${}^{16}\mathrm{O}$, and ${}^{19}\mathrm{F}{+}^{232}\mathrm{Th}$ systems from above barrier to below sub-barrier energies. The fragment anisotropies $\left[W\right(0^{\circ }\left)/W\right({90}^{\circ }\left)\right]$ are found to exhibit an anomalous peaklike structure below the fusion barrier in all the systems. This structure has a universal behavior independent of the entrance channel mass asymmetry. With some refinement in the quasifission hypothesis it is possible to explain qualitatively the experimental results reasonably well.

Subthreshold $K^{+}$ production cross sections have been measured in symmetric $\mathrm{Ne}+\mathrm{NaF}$, $\mathrm{Ni}+\mathrm{Ni}$, and $\mathrm{Au}+\mathrm{Au}$ collisions at $1.0A\mathrm{GeV}$. The mass dependence is strong, close to $A^2$. The angular distributions are nonisotropic in the center-of-mass system. Introducing rescattering seems to explain this effect to a large extent.

We report on an extensive on-line nuclear orientation study of the angular distribution of $\alpha$ particles emitted in the favored decay of neutron deficient At and Rn nuclei near the $N=126\mathrm{}$ shell closure. Surprisingly large anisotropies were observed, showing pronounced changes from one isotope to another. Comparing these data with several theoretical models shows that anisotropic $\alpha$ emission in favored decays from near-spherical nuclei can well be explained within the shell model, implying that it is mainly determined by the structure of the decaying nucleus.

Multifragment decays of central collisions in ${}^{84}\mathrm{Kr}{+}^{197}\mathrm{Au}$ at $E/A=70\mathrm{}\mathrm{MeV}$ are studied. By utilizing a technique sensitive to the emission order of fragments, it is deduced that carbon fragments are emitted prior to beryllium fragments when these fragments have the same velocity. This observation is consistent with the cooling of a thermally decaying source.

The first measurement of the elementary process ${\mu }^{-}p\to {\nu }_{\mu }n\gamma$ is reported. A photon pair spectrometer was used to measure the partial branching ratio $(2.10\pm 0.22)\times {10}^{-8\mathrm{}}$ for photons of $k>\mathrm{}60\mathrm{}\mathrm{MeV}$. The value of the weak pseudoscalar coupling constant determined from the partial branching ratio is $g_p\left(q^2{=-0.88m}_{\mu }^2\right)=(9.8\pm 0.7\pm 0.3)g_a\left(0\right)$, where the first error is the quadrature sum of statistical and systematic uncertainties and the second error is due to the uncertainty in ${\lambda }_{\mathrm{op}}$, the decay rate of the ortho to para $p\mu p$ molecule. This value of $g_p$ is $\sim 1.5$ times the prediction of partial conservation of axial current and pion-pole dominance.

Relativistic Hartree-Bogoliubov theory in coordinate space is used to describe the chain of lithium isotopes reaching from ${}^6$Li to ${}^{11}$Li. Pairing correlations are taken into account by a density dependent force of zero range. In contrast to earlier investigations within a relativistic mean field theory and a density dependent Hartree-Fock theory, where the halo in ${}^{11}$Li could only be reproduced by an artificial shift of the ${1p}_{1/2}$ level close to the continuum limit, the halo is now reproduced in a self-consistent way, without further modifications, using the scattering of Cooper pairs to the ${2s}_{1/2}$ level in the continuum. Excellent agreement with recent experimental data is observed.

The energies and $B({E2;0\mathrm{}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{+}\to 2_1^{+})$ values for the lowest $J^{\pi }{=2\mathrm{}}^{+}$ states in the neutron-rich radioactive nuclei ${}^{38,40,42}\mathrm{S}$ and ${}^{44,46}\mathrm{Ar}$ were measured via intermediate-energy Coulomb excitation. The results for ${}^{40,42}\mathrm{S}$ provide the first evidence of moderate deformation near $N=28\mathrm{}$, while the effects of the $N=28\mathrm{}$ shell closure persist in the $Z=18\mathrm{}$ nucleus ${}^{46}\mathrm{Ar}$.

It is shown that the critical threshold for percolation of the overlapping strings exchanged in heavy ion collisions can naturally explain the sharp strong suppression of $J/\psi$ shown by the experimental data on central Pb-Pb collisions, which does not occur in central O-U and S-U collisions.

Sidewards directed fragment flow has been extracted for ${}^{84}\mathrm{Kr}{+}^{197}\mathrm{Au}$ collisions at $E/A=200\mathrm{}\mathrm{MeV}$, using techniques that are free of reaction plane dispersion. The fragment flow per nucleon increases with mass, following a thermal or coalescencelike behavior, and attains roughly constant limiting values at $4\le A\le 12$. Comparisons of the impact parameter dependences of the measured coalescence-invariant proton flow to Boltzmann-Uehling-Uhlenbeck calculations clearly favor a momentum dependent nuclear mean field.

Prompt $\gamma$-ray cascades in neutron-rich nuclei around doubly magic ${}^{132}\mathrm{Sn}$ have been studied at Eurogam II using a ${}^{248}\mathrm{Cm}$ fission source. Yrast states to above 5.5 MeV in the two- and three-proton $N=82\mathrm{}$ isotones ${}^{134}\mathrm{Te}$ and ${}^{135}\mathrm{I}$ are reported. They are interpreted in terms of valence proton and particle-hole core excitations with the help of shell model calculations employing empirical nucleon-nucleon interactions from both ${}^{132}\mathrm{Sn}$ and ${}^{208}\mathrm{Pb}$ regions. A serious inconsistency in the accepted masses of $N=82\mathrm{}$ isotones near ${}^{132}\mathrm{Sn}$ is discovered but not resolved.

We investigate the effects of nuclear absorption on the population of intrinsic vibrational states in scattering processes involving heavy ions. It is found that at the classical level the removal of flux assumes a qualitatively different form in the regular or chaotic regimes. Specifically, it is shown how certain reaction channels turn out to be—in the latter case—relatively insensitive to the strength of the absorptive potential. This realization has a counterpart at the quantum level where, at the chaotic layer, conditions of selective transparency in the nuclear system are enforced.

We propose a model-independent method to extract a linear combination of the $s$-wave $\pi -\pi$ scattering lengths by measuring the $\gamma \gamma$ decay branching ratio for a tagged sample of ${\pi }^{+}{\pi }^{-}$ atoms (pionium). In the first experimental search for an appropriate tagging reaction, we observed ${\sigma }_{\mathrm{tot}}=76\mathrm{}\pm 21\pm 11\mathrm{pb}$ for free pion pair production in $\mathrm{pd}{\to }^3\mathrm{He}{\pi }^{+}{\pi }^{-}$ 1.0 MeV above threshold. This result suggests a pionium production cross section $\lesssim 1\mathrm{pb}$.

Based on measured correlations between experimental observables in the ${}^{209}\mathrm{Bi}{+}^{136}\mathrm{Xe}$ reaction at $E/A=28\mathrm{MeV}$, it is shown that multiple intermediate-mass fragment (IMF) production is a dynamical process driven by the energy of relative motion of projectilelike and targetlike fragments. This kinetic energy is converted into thermal energy of the system, until a certain “saturation” value of approximately 3 MeV/nucleon is reached. From this point on, this “conventional” dissipation mechanism is replaced by dynamical IMF production, constituting a new mode of energy dissipation.

The feasibility of shell-model calculations is radically extended by the quantum Monte Carlo diagonalization method with various essential improvements. The major improvements are made in the sampling for the generation of shell-model basis vectors, and in the restoration of symmetries such as angular momentum and isospin. Consequently the level structure of low-lying states can be studied with realistic interactions. After testing this method on ${}^{24}\mathrm{Mg}$, we present first results for energy levels and $E2\mathrm{}$ properties of ${}^{64}\mathrm{Ge}$, indicating its large and $\gamma$-soft deformation.

Evidence for electron capture of ${}^{123}$Te from the K shell has been obtained in an experiment performed underground with an array of four 340 g Te${\mathrm{O}}_2$ thermal detectors. This is the first real proof of the decay of this isotope. In our thermal approach, unlike in previous experiments, the Te${\mathrm{O}}_2$ bolometer acts at the same time as source and detector of the ${}^{123}$Te decay and its resolution allows to discriminate between the lines produced by background x ray excitation and electron capture. In addition anticoincidence with the nearby detectors reduces the signal of x rays produced by excitation of Tellurium. The partial width for K electron capture of ${}^{123}$Te is the smallest one ever measured for a single beta process and lower by six orders of magnitude with respect to the previously reported one for this decay. An analysis based on the expected fraction of electron captures accompanied by internal bremsstrahlung allows to set a stringent limit, independent on the decay channel, for the lifetime of ${}^{123}$Te.

A primary beam of ${}^{58}$Ni at 600 MeV/nucleon from the SIS synchrotron at GSI was used to produce proton-rich isotopes in the titanium-to-nickel region by projectile fragmention on a beryllium target. The fragments were separated by a projectile-fragement separator and unambiguously identified. We report here the first observation of the $T_z=-7/2\mathrm{}$ nuclei ${}^{45}$Fe and ${}^{49}$Ni, the most proton-rich nuclei ever synthesized with an excess of seven protons. In addition, the new isotope ${}^{42}$Cr $(T_z=-3\mathrm{})$ was identified. According to commonly used mass predictions, these isotopes are all unbound with respect to two-proton emission from their ground states. From the nonobservation of ${}^{38}$Ti $(T_z=-3\mathrm{})$ in this experiment, an upper limit of 120 ns is deduced for the half-life of this isotope.