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 have studied calculated collective contributions to nuclear binding and separation energies and find that there is a deeper and much more sensitive link to nuclear structure than previously recognized or expected, especially near midshell in medium mass and heavy nuclei. As a consequence, measured masses may help understand the structure of well-deformed nuclei (e.g., intrinsic excitations). Conversely, future structure calculations must consider their implications for binding energies.

Within an isospin- and momentum-dependent hadronic transport model, it is shown that the recent FOPI data on the ${\pi }^{-}/{\pi }^{+}$ ratio in central heavy-ion collisions at SIS/GSI energies [Willy Reisdorf et al., Nucl. Phys. A 781, 459 (2007)] provide circumstantial evidence suggesting a rather soft nuclear symmetry energy $E_{\mathrm{sym}}(\rho )$ at $\rho \ge 2{\rho }_0$ compared to the Akmal-Pandharipande-Ravenhall prediction. Some astrophysical implications and the need for further experimental confirmations are discussed.

Nuclear charge radii of ${}^{7,9,10,11}\mathrm{Be}$ have been determined by high-precision laser spectroscopy. On-line measurements were performed with collinear laser spectroscopy in the $2s_{1/2}\to 2p_{1/2}$ transition on a beam of ${\mathrm{Be}}^{+}$ ions. Collinear and anticollinear laser beams were used simultaneously, and the absolute frequency determination using a frequency comb yielded an accuracy in the isotope-shift measurements of about 1 MHz. Combining this with accurate calculations of the mass-dependent isotope shifts yields nuclear charge radii. The charge radius decreases from ${}^7\mathrm{Be}$ to ${}^{10}\mathrm{Be}$ and then increases for the halo nucleus ${}^{11}\mathrm{Be}$. When comparing our results with predictions of ab initio nuclear-structure calculations we find good agreement. Additionally, the nuclear magnetic moment of ${}^7\mathrm{Be}$ was determined to be $-1.3995(5){\mu }_N$ and that of ${}^{11}\mathrm{Be}$ was confirmed with an accuracy similar to previous $\beta$-NMR measurements.

We have extracted 565 neutron spectroscopic factors of $sd$ and $fp$ shell nuclei by systematically analyzing more than 2000 measured ($d$, $p$) angular distributions. We are able to compare 125 of the extracted spectroscopic factors to values predicted by large-basis shell-model calculations and evaluate the accuracies of spectroscopic factors predicted by different shell-model interactions in these regions. We find that the spectroscopic factors predicted for most excited states of $sd$-shell nuclei using the latest USDA or USDB interactions agree with the experimental values. For $fp$ shell nuclei, the inability of the current models to account for the core excitation and fragmentation of the states leads to considerable discrepancies. In particular, the agreement between data and shell-model predictions for Ni isotopes is not better than a factor of 2 using either the GXPF1A or the XT interaction.

Three-particle azimuthal correlation measurements with a high transverse momentum trigger particle are reported for $pp$, $d+\mathrm{Au}$, and $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ by the STAR experiment. Dijet structures are observed in $pp$, $d+\mathrm{Au}$ and peripheral $\mathrm{Au}+\mathrm{Au}$ collisions. An additional structure is observed in central $\mathrm{Au}+\mathrm{Au}$ data, signaling conical emission of correlated charged hadrons. The conical emission angle is found to be $\theta =1.37\pm 0.02(\mathrm{stat}{)}_{-0.07}^{+0.06}(\mathrm{syst})$, independent of $p_{\perp }$.

The ABC effect—a puzzling low-mass enhancement in the $\pi \pi$ invariant mass spectrum, first observed by Abashian, Booth, and Crowe—is well known from inclusive measurements of two-pion production in nuclear fusion reactions. Here we report on the first exclusive and kinematically complete measurements of the most basic double-pionic fusion reaction $pn\to d{\pi }^0{\pi }^0$ at beam energies of 1.03 and 1.35 GeV. The measurements, which have been carried out at CELSIUS-WASA, reveal the ABC effect to be a $(\pi \pi {)}_{I=L=0}$ channel phenomenon associated with both a resonancelike energy dependence in the integral cross section and the formation of a $\Delta \Delta$ system in the intermediate state. A corresponding simple $s$-channel resonance ansatz provides a surprisingly good description of the data.

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 structure of neutron-rich isotopes ${}^{60}\mathrm{Cr}$ and ${}^{62}\mathrm{Cr}$ was studied via proton inelastic scattering in inverse kinematics. The deformation lengths ($\delta$) for ${}^{60}\mathrm{Cr}$ and ${}^{62}\mathrm{Cr}$ were extracted as 1.12(16) and 1.36(14) fm, respectively, providing evidence for enhanced collectivity in these nuclei. An excited state at 1180(10) keV in ${}^{62}\mathrm{Cr}$ was identified for the first time. We adopted $4^{+}$ as its spin and parity, leading to the rapid increase of the $E_x(4^{+})/E_x(2^{+})$ ratio, which indicates the development of large deformation in ${}^{62}\mathrm{Cr}$ near $N=40$. Importance of the admixture of the $gd$-shell component above $N=40$ is also discussed by comparing with a modern shell model calculation.

We report the first measurement of an angular correlation parameter in neutron $\beta$ decay using polarized ultracold neutrons (UCN). We utilize UCN with energies below about 200 neV, which we guide and store for $\sim 30\mathrm{s}$ in a Cu decay volume. The interaction of the neutron magnetic dipole moment with a static 7 T field external to the decay volume provides a 420 neV potential energy barrier to the spin state parallel to the field, polarizing the UCN before they pass through an adiabatic fast passage spin flipper and enter a decay volume, situated within a 1 T field in a $2\times 2\pi$ solenoidal spectrometer. We determine a value for the $\beta$-asymmetry parameter $A_0=-0.1138\pm 0.0046\pm 0.0021$.

The $\Sigma (1385)$ resonance, or ${\Sigma }^{*}$, is well known as part of the standard baryon decuplet with spin $J=\frac{3}{2}$. Measurements of the reaction $\gamma p\to K^{+}{\Sigma }^{*0}$ are difficult to extract due to overlap with the nearby $\Lambda (1405)$ resonance. However, the reaction $\gamma n\to K^{+}{\Sigma }^{*-}$ has no overlap with the $\Lambda (1405)$ due to its charge. Here we report the first measurement of cross sections and beam asymmetries for photoproduction of the ${\Sigma }^{*-}$ from a deuteron target. The cross sections at forward angles range from 0.4 to $1.2\mu \mathrm{b}$, with a broad maximum near $E_{\gamma }\simeq 1.8\mathrm{GeV}$. The beam asymmetries are negative, in contrast with positive values for the $\gamma n\to K^{+}{\Sigma }^{-}$ reaction.

A new reaction mechanism of violent reseparation of a heavy nucleus-nucleus system, ${}^{197}\mathrm{Au}+{}^{197}\mathrm{Au}$, into three or four massive fragments in collisions at $15\mathrm{MeV}/\mathrm{\text{nucleon}}$ has been observed. After reseparation, the fragments are almost exactly aligned, thus showing a very short time scale of the reseparation process, of about $70–80\mathrm{fm}/c$.

High-precision mass measurements on neutron-rich zinc isotopes ${}^{71m,72–81}\mathrm{Zn}$ have been performed with the Penning trap mass spectrometer ISOLTRAP. For the first time, the mass of ${}^{81}\mathrm{Zn}$ has been experimentally determined. This makes ${}^{80}\mathrm{Zn}$ the first of the few major waiting points along the path of the astrophysical rapid neutron-capture process where neutron-separation energy and neutron-capture $Q$-value are determined experimentally. The astrophysical conditions required for this waiting point and its associated abundance signatures to occur in $r$-process models can now be mapped precisely. The measurements also confirm the robustness of the $N=50$ shell closure for $Z=30$.

High-precision mass and charge radius measurements on ${}^{17–22}\mathrm{Ne}$, including the proton-halo candidate ${}^{17}\mathrm{Ne}$, have been performed with Penning trap mass spectrometry and collinear laser spectroscopy. The ${}^{17}\mathrm{Ne}$ mass uncertainty is improved by factor 50, and the charge radii of ${}^{17–19}\mathrm{Ne}$ are determined for the first time. The fermionic molecular dynamics model explains the pronounced changes in the ground-state structure. It attributes the large charge radius of ${}^{17}\mathrm{Ne}$ to an extended proton configuration with an $s^2$ component of about 40%. In ${}^{18}\mathrm{Ne}$ the smaller radius is due to a significantly smaller $s^2$ component. The radii increase again for ${}^{19–22}\mathrm{Ne}$ due to cluster admixtures.

The $\beta$-decay properties of the $N=Z$ nuclei ${}^{96}\mathrm{Cd}$, ${}^{98}\mathrm{In}$, and ${}^{100}\mathrm{Sn}$ have been studied. These nuclei were produced at the National Superconducting Cyclotron Laboratory by fragmenting a $120\mathrm{MeV}/\mathrm{\text{nucleon}}$ ${}^{112}\mathrm{Sn}$ primary beam on a Be target. The resulting radioactive beam was filtered in the A1900 and the newly commissioned Radio Frequency Fragment Separator to achieve a purity level suitable for decay studies. The observed production cross sections of these nuclei are lower than predicted by factors of 10–30. The half-life of ${}^{96}\mathrm{Cd}$, which was the last experimentally unknown waiting point half-life of the astrophysical $rp$ process, is ${1.03}_{-0.21}^{+0.24}\mathrm{s}$. The implications of the experimental $T_{1/2}$ value of ${}^{96}\mathrm{Cd}$ on the abundances predicted by $rp$ process calculations and the origin of $A=96$ isobars such as ${}^{96}\mathrm{Ru}$ are explored.

We measure directed flow ($v_1$) for charged particles in $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ collisions at $\sqrt{s_{NN}}=200$ and 62.4 GeV, as a function of pseudorapidity ($\eta$), transverse momentum ($p_t$), and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all available model implementations, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to $v_1$ in different collision systems, and investigate possible explanations for the observed sign change in $v_1(p_t)$.

How does the scattering cross section change when the colliding bound-state fragments are allowed particle-emitting resonances? This question is explored in the framework of a multichannel algebraic scattering method of determining nucleon-nucleus cross sections at low energies. Two cases are examined, the first being a gedanken investigation in which $n+{}^{12}\mathrm{C}$ scattering is studied with the target states assigned artificial widths. The second is a study of neutron scattering from ${}^8\mathrm{Be}$, a nucleus that is particle unstable. Resonance character of the target states markedly varies evaluated cross sections from those obtained assuming stability in the target spectrum.

For $\mathrm{Au}+\mathrm{Au}$ collisions at 200 GeV, we measure neutral pion production with good statistics for transverse momentum, $p_T$, up to $20\mathrm{GeV}/c$. A fivefold suppression is found, which is essentially constant for $5<p_T<20\mathrm{GeV}/c$. Experimental uncertainties are small enough to constrain any model-dependent parametrization for the transport coefficient of the medium, e.g., $⟨\widehat{q}⟩$ in the parton quenching model. The spectral shape is similar for all collision classes, and the suppression does not saturate in $\mathrm{Au}+\mathrm{Au}$ collisions.

We demonstrate that abundant quantities of short-lived $\beta$ unstable ions can be trapped in a novel transparent Paul trap and that their decay products can directly be detected in coincidence. Low energy ${}^6\mathrm{He}^{+}$ (807 ms half-life) ions were extracted from the SPIRAL source at GANIL, then decelerated, cooled, and bunched by means of the buffer gas cooling technique. More than ${10}^8$ ions have been stored over a measuring period of six days, and about ${10}^5$ decay coincidences between the beta particles and the ${}^6\mathrm{Li}^{++}$ recoiling ions have been recorded. The technique can be extended to other short-lived species, opening new possibilities for trap assisted decay experiments.

Coulomb excitation of the exotic neutron-rich nucleus ${}^{26}\mathrm{Ne}$ on a ${}^{208}\mathrm{Pb}$ target was measured at $58\mathrm{MeV}/u$ in order to search for low-lying $E1$ strength above the neutron emission threshold. This radioactive beam experiment was carried out at the RIKEN Accelerator Research Facility. Using the invariant mass method in the ${}^{25}\mathrm{Ne}+n$ channel, we observe a sizable amount of $E1$ strength between 6 and 10 MeV excitation energy. By performing a multipole decomposition of the differential cross section, a reduced dipole transition probability of $B(E1)=0.49\pm 0.16e^2{\mathrm{fm}}^2$ is deduced, corresponding to $4.9\pm 1.6\%$ of the Thomas-Reiche-Kuhn sum rule. For the first time, the decay pattern of low-lying strength in a neutron-rich nucleus is measured. The extracted decay pattern is not consistent with several mean-field theory descriptions of the pygmy states.