The $A/Z$ dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at SIS. A stable beam of ${}^{124}\mathrm{Sn}$ and radioactive beams of ${}^{124}\mathrm{La}$ and ${}^{107}\mathrm{Sn}$ at 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. Chemical freeze-out temperatures are found to be nearly invariant with respect to the $A/Z$ of the produced spectator sources, consistent with predictions for expanded systems. Small Coulomb effects ($\Delta T\approx 0.6\mathrm{MeV}$) appear for residue production near the onset of multifragmentation.

The results of measurements of the production of neutron-rich nuclei by the fragmentation of a ${}^{76}\mathrm{Ge}$ beam are presented. The cross sections were measured for a large range of nuclei including 15 new isotopes that are the most neutron-rich nuclides of the elements chlorine to manganese (${}^{50}\mathrm{Cl}$, ${}^{53}\mathrm{Ar}$, ${}^{55,56}\mathrm{K}$, ${}^{57,58}\mathrm{Ca}$, ${}^{59,60,61}\mathrm{Sc}$, ${}^{62,63}\mathrm{Ti}$, ${}^{65,66}\mathrm{V}$, ${}^{68}\mathrm{Cr}$, ${}^{70}\mathrm{Mn}$). The enhanced cross sections of several new nuclei relative to a simple thermal evaporation framework, previously shown to describe similar production cross sections, indicates that nuclei in the region around ${}^{62}\mathrm{Ti}$ might be more stable than predicted by current mass models and could be an indication of a new island of inversion similar to that centered on ${}^{31}\mathrm{Na}$.

Time-resolved Schottky mass spectrometry has been applied to uranium projectile fragments which yielded the mass value for the ${}^{208}\mathrm{Hg}$ ($Z=80$, $N=128$) isotope. The mass excess value of $\mathrm{ME}=-13265(31)\mathrm{keV}$ has been obtained, which has been used to determine the proton-neutron interaction strength in ${}^{210}\mathrm{Pb}$, as a double difference of atomic masses. The results show a dramatic variation of the strength for lead isotopes when crossing the $N=126$ neutron shell closure, thus confirming the empirical predictions that this interaction strength is sensitive to the overlap of the wave functions of the last valence neutrons and protons.

In ultraperipheral relativistic heavy-ion collisions, a photon from the electromagnetic field of one nucleus can fluctuate to a quark-antiquark pair and scatter from the other nucleus, emerging as a ${\rho }^0$. The ${\rho }^0$ production occurs in two well-separated (median impact parameters of 20 and 40 F for the cases considered here) nuclei, so the system forms a two-source interferometer. At low transverse momenta, the two amplitudes interfere destructively, suppressing ${\rho }^0$ production. Since the ${\rho }^0$ decays before the production amplitudes from the two sources can overlap, the two-pion system can only be described with an entangled nonlocal wave function, and is thus an example of the Einstein-Podolsky-Rosen paradox. We observe this suppression in 200 GeV per nucleon-pair gold-gold collisions. The interference is $87\%\pm 5\%(\mathrm{stat}.)\pm 8\%(\mathrm{syst}.)$ of the expected level. This translates into a limit on decoherence due to wave function collapse or other factors of 23% at the 90% confidence level.

We report on the $g$-factor measurement of the first isomeric state in ${}_{16}{}^{43}\mathrm{S}_{27}$ [$E_x=320.5(5)\mathrm{keV}$, $T_{1/2}=415(5)\mathrm{ns}$, and $g=0.317(4)$]. The $7/2^{-}$ spin-parity of the isomer and the intruder nature of the ground state of the nucleus are experimentally established for the first time, providing direct and unambiguous evidence of the collapse of the $N=28$ shell closure in neutron-rich nuclei. The shell model, beyond the mean-field and semiempirical calculations, provides a very consistent description of this nucleus showing that a well deformed prolate and quasispherical states coexist at low energy.

We study the effect of the QCD critical point on non-Gaussian moments (cumulants) of fluctuations of experimental observables in heavy-ion collisions. We find that these moments are very sensitive to the proximity of the critical point, as measured by the magnitude of the correlation length $\xi$. For example, the cubic central moment of multiplicity $⟨(\delta N{)}^3⟩\sim {\xi }^{4.5}$ and the quartic cumulant $⟨(\delta N{)}^4{⟩}_c\sim {\xi }^7$. We estimate the magnitude of critical point contributions to non-Gaussian fluctuations of pion and proton multiplicities.

The ground state hyperfine splitting of ${}^7\mathrm{Be}^{+}$ has been measured by laser-microwave double-resonance spectroscopy in the online rf trap of RIKEN’s slow RI-beam facility. Be ions produced by projectile fragmentation of ${}^{13}\mathrm{C}$ at $\approx 1\mathrm{GeV}$ were thermalized in a rf ion guide gas cell and subsequently laser cooled in the ion trap to $\approx 1\mu \mathrm{eV}$. This ${10}^{15}$-fold reduction of the kinetic energy allows precision spectroscopy of these ions. A magnetic hfs constant of $A=-742.77228(43)\mathrm{MHz}$ was measured for ${}^7\mathrm{Be}^{+}$, from which a nuclear magnetic moment of ${\mu }_I=-1.39928(2){\mu }_N$ was deduced.

A general new technique to solve the two-center problem with arbitrarily oriented deformed realistic potentials is demonstrated, which is based on the powerful potential separable expansion method. As an example, molecular single-particle spectra for ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}\to {}^{24}\mathrm{Mg}$ are calculated using deformed Woods-Saxon potentials. These clearly show that nonaxial symmetric configurations play a crucial role in molecular resonances observed in reaction processes for this system at low energy.

Reaction mechanism analyses performed with a $4\pi$ detector for the systems ${}^{208}\mathrm{Pb}+\mathrm{Ge}$, ${}^{238}\mathrm{U}+\mathrm{Ni}$ and ${}^{238}\mathrm{U}+\mathrm{Ge}$, combined with analyses of the associated reaction time distributions, provide us with evidence for nuclei with $Z=120$ and 124 living longer than ${10}^{-18}\mathrm{s}$ and arising from highly excited compound nuclei. By contrast, the neutron deficient nuclei with $Z=114$ possibly formed in ${}^{208}\mathrm{Pb}+\mathrm{Ge}$ reactions have shorter lifetimes, close to or below the sensitivity limit of the experiment.

Forming the same heavy compound nucleus with different isotopes of the projectile and target elements allows nuclear structure effects in the entrance channel (resulting in static deformation) and in the dinuclear system to be disentangled. Using three isotopes of Ti and W, forming ${}^{232}\mathrm{Cm}$, with measurement spanning the capture barrier energies, alignment of the heavy prolate deformed nucleus is shown to be the main reason for the broadening of the mass distribution of the quasifission fragments as the beam energy is reduced. The complex, consistently evolving mass-angle correlations that are observed carry more information than the integrated mass or angular distributions, and should severely test models of quasifission.

The generalized two-center cluster model, which can treat static structures and dynamical reactions in excited states, is applied to the light neutron-rich system, ${}^{12}\mathrm{Be}=\alpha +\alpha +4N$. We discuss the change of the neutrons’ configuration around two $\alpha$ cores from the covalent structure to the ionic one. We show that, in the unbound region above particle-decay thresholds, the ionic configurations appear as the molecular resonances of $\alpha +{}^8\mathrm{He}$, ${}^6\mathrm{He}+{}^6\mathrm{He}$, and ${}^5\mathrm{He}+{}^7\mathrm{He}$. A new type of superdeformation is possible, and we find here a covalent superdeformation with a hybrid configuration of both the covalent and ionic structures. The excitation of these exotic structures through the two-neutron transfer reaction is also discussed.

We present shell model calculations for the beta decay of ${}^{14}\mathrm{C}$ to the ${}^{14}\mathrm{N}$ ground state, treating the states of the $A=14$ multiplet as two $0p$ holes in an ${}^{16}\mathrm{O}$ core. We employ low-momentum nucleon-nucleon ($NN$) interactions derived from the realistic Bonn-B potential and find that the Gamow-Teller (GT) matrix element is too large to describe the known lifetime. By using a modified version of this potential that incorporates the effects of Brown-Rho scaling medium modifications, we find that the GT matrix element vanishes for a nuclear density around 85% that of nuclear matter. We find that the splitting between the $(J^{\pi },T)=(1^{+},0)$ and $(J^{\pi },T)=(0^{+},1)$ states in ${}^{14}\mathrm{N}$ is improved using the medium-modified Bonn-B potential and that the transition strengths from excited states of ${}^{14}\mathrm{C}$ to the ${}^{14}\mathrm{N}$ ground state are compatible with recent experiments.

We report on the first measurement of the ${\beta }^{+}$ and orbital electron-capture decay rates of ${}^{140}\mathrm{Pr}$ nuclei with the simplest electron configurations: bare nuclei, hydrogenlike, and heliumlike ions. The measured electron-capture decay constant of hydrogenlike ${}^{140}\mathrm{Pr}^{58+}$ ions is about 50% larger than that of heliumlike ${}^{140}\mathrm{Pr}^{57+}$ ions. Moreover, ${}^{140}\mathrm{Pr}$ ions with one bound electron decay faster than neutral ${}^{140}\mathrm{Pr}^{0+}$ atoms with 59 electrons. To explain this peculiar observation one has to take into account the conservation of the total angular momentum, since only particular spin orientations of the nucleus and of the captured electron can contribute to the allowed decay.

The root-mean-square (rms) nuclear charge radius of ${}^8\mathrm{He}$, the most neutron-rich of all particle-stable nuclei, has been determined for the first time to be 1.93(3) fm. In addition, the rms charge radius of ${}^6\mathrm{He}$ was measured to be 2.068(11) fm, in excellent agreement with a previous result. The significant reduction in charge radius from ${}^6\mathrm{He}$ to ${}^8\mathrm{He}$ is an indication of the change in the correlations of the excess neutrons and is consistent with the ${}^8\mathrm{He}$ neutron halo structure. The experiment was based on laser spectroscopy of individual helium atoms cooled and confined in a magneto-optical trap. Charge radii were extracted from the measured isotope shifts with the help of precision atomic theory calculations.

We have measured the nuclear transparency of the $A(e,e^{\prime }{\pi }^{+})$ process in ${}^2\mathrm{H}$, ${}^{12}\mathrm{C}$, ${}^{27}\mathrm{Al}$, ${}^{63}\mathrm{Cu}$, and ${}^{197}\mathrm{Au}$ targets. These measurements were performed at the Jefferson Laboratory over a four momentum transfer squared range $Q^2=1.1$ to $4.7(\mathrm{GeV}/c{)}^2$. The nuclear transparency was extracted as the super-ratio of (${\sigma }_A/{\sigma }_H$) from data to a model of pion-electroproduction from nuclei without $\pi \mathrm{\text{−}}N$ final-state interactions. The $Q^2$ and atomic number dependence of the nuclear transparency both show deviations from traditional nuclear physics expectations and are consistent with calculations that include the quantum chromodynamical phenomenon of color transparency.

New measurements of fusion cross sections at deep sub-barrier energies for the reactions ${}^{16}\mathrm{O}+{}^{204,208}\mathrm{Pb}$ show a steep but almost saturated logarithmic slope, unlike ${}^{64}\mathrm{Ni}$-induced reactions. Coupled channels calculations cannot simultaneously reproduce these new data and above-barrier cross-sections with the same Woods-Saxon nuclear potential. It is argued that this highlights an inadequacy of the coherent coupled channels approach. It is proposed that a new approach explicitly including gradual decoherence is needed to allow a consistent description of nuclear fusion.

The decay of extremely neutron-deficient ${}^{45}\mathrm{Fe}$ has been studied in detail by means of a novel type of a gaseous detector employing digital imaging to record tracks of charged particles. The two-proton radioactivity channel was clearly identified. For the first time, the angular and energy correlations between two protons emitted from the nuclear ground state were determined, indicating the genuine three-body character of this decay. The half-life of ${}^{45}\mathrm{Fe}$ was found to be $2.6\pm 0.2\mathrm{ms}$ and the observed $2p$ decay branching ratio is $70\pm 4\%$.

Triggering of long-lived nuclear isomeric states via coupling to the atomic shells in the process of nuclear excitation by electron capture (NEEC) is studied. NEEC occurring in highly charged ions can excite the isomeric state to a triggering level that subsequently decays to the ground state. We present total cross sections for NEEC isomer triggering considering experimentally confirmed low-lying triggering levels and reaction rates based on realistic experimental parameters in ion storage rings. A comparison with other isomer triggering mechanisms shows that, among these, NEEC is the most efficient.

The existence of the ${}^7\mathrm{H}$ nuclear system was investigated via a one-proton transfer reaction with a ${}^8\mathrm{He}$ beam at $15.4\mathrm{A}\mathrm{MeV}$ and a ${}^{12}\mathrm{C}$ gas target. The experimental setup was based on the active-target MAYA which allowed a complete reconstruction of the reaction kinematics. The existence of the ${}^7\mathrm{H}$ was confirmed with the identification of seven events where the system was formed with a resonance energy of ${0.57}_{-0.21}^{+0.42}\mathrm{MeV}$ above the ${}^3\mathrm{H}+4n$ threshold and a resonance width of ${0.09}_{-0.06}^{+0.94}\mathrm{MeV}$. This study represents an unambiguous proof of the existence of the most neutron-proton unbalanced system presently found.

Gamma-ray transitions have been identified for the first time in the extremely neutron-deficient ($N=Z+2$) nucleus ${}^{110}\mathrm{Xe}$, and the energies of the three lowest excited states in the ground-state band have been deduced. The results establish a breaking of the normal trend of increasing first excited $2^{+}$ and $4^{+}$ level energies as a function of the decreasing neutron number as the $N=50$ major shell gap is approached for the neutron-deficient Xe isotopes. This unusual feature is suggested to be an effect of enhanced collectivity, possibly arising from isoscalar $n\mathrm{\text{−}}p$ interactions becoming increasingly important close to the $N=Z$ line.