Mass measurements on ${}^{33,34,42,43}\mathrm{Ar}$ were performed using the Penning trap mass spectrometer ISOLTRAP and a newly constructed linear Paul trap. This arrangement allowed us, for the first time, to extend Penning trap mass measurements to nuclides with half-lives below one second ( ${}^{33}\mathrm{Ar}$: $T_{1/2}=174\mathrm{}\mathrm{ms}$). A mass accuracy of about ${10}^{-7\mathrm{}}$ $\left(\delta m\approx 4\mathrm{keV}\right)$ was achieved for all investigated nuclides. The isobaric multiplet mass equation was checked for the $A=33\mathrm{}$, $T=3/2\mathrm{}$ quartet and found to be inconsistent with the generally accepted quadratic form.

The ground state band in ${}^{46}\mathrm{Cr}$ and the isospin $T=1\mathrm{}$ band in ${}^{46}\mathrm{V}$ have been delineated up to $I^{\pi }{=10\mathrm{}}^{+}$ (tentatively ${12}^{+}$). These observations complete the highest spin $T=1\mathrm{}$ isospin triplet known. Following the isobaric multiplet mass equation, a combination of level energies in ${}^{46}\mathrm{Cr}$, ${}^{46}\mathrm{Ti}$, and ${}^{46}\mathrm{V}$ are taken to highlight the angular momentum dependence of the isovector and isotensor parts of the interaction. The results are compared with full- $\mathrm{fp}$-space shell model calculations. The influence of the one-body and two-body contributions to the isovector energy difference are investigated.

Subpicosecond lifetimes of states in shears band 1 in ${}^{197}\mathrm{Pb}$ were measured by means of the recoil distance method employing Gammasphere and the New Yale Plunger Device. The extracted reduced matrix elements, $B\left(M1\mathrm{}\right)$, show a clear sensitivity to the crossing of different shears configurations reflecting the closing and reopening of the shears blades. The energies and $B\left(M1\mathrm{}\right)$ values in the band crossing region are successfully described in the framework of the semiclassical model of the shears bands. The relevance of core rotation contributions are shown. The results point to the existence of shears states with an angular momentum coupling angle larger than $90°$.

An experiment demonstrating the production of double- $\Lambda$ hypernuclei in $\left(K^{-}{,K}^{+}\right)$ reactions on ${}^9\mathrm{Be}$ was carried out at the D6 line in the BNL alternating-gradient synchrotron. The technique was the observation of pions produced in sequential mesonic weak decay, each pion associated with one unit of strangeness change. The results indicate the production of a significant number of the double hypernucleus ${}_{\Lambda \Lambda }^4\mathrm{H}$ and the twin hypernuclei ${}_{\Lambda }^4\mathrm{H}$ and ${}_{\Lambda }^3\mathrm{H}$. The relevant decay chains are discussed and a simple model of the production mechanism is presented. An implication of this experiment is that the existence of an $S=-2\mathrm{}$ dibaryon more than a few MeV below the $\Lambda \Lambda$ mass is unlikely.

Dipole excitations in highly excited energy regions of ${}^6\mathrm{He}$ and ${}^7\mathrm{He}$ nuclei were investigated via the ( ${}^7\mathrm{Li}{,}^7\mathrm{Be}$) reaction with an incident energy of $65A\mathrm{MeV}$ at forward scattering angles. The resonances at $Q\simeq -30\mathrm{}\mathrm{MeV}$ observed commonly for both ${}^6\mathrm{Li}$ and ${}^7\mathrm{Li}$ targets were found to be excited via both spin-flip and spin-nonflip transitions with $\Delta L=1\mathrm{}$. Based on the observed excitation energy, width, and cross section of each resonance, the relevant resonances are inferred to be analogs of the dipole resonances of $\alpha$ clusters in the ${}^6\mathrm{Li}$ and ${}^7\mathrm{Li}$ nuclei.

The ground state rotational bands of the $N=Z$ nuclei ${}^{72}\mathrm{Kr}$, ${}^{76}\mathrm{Sr}$, and ${}^{80}\mathrm{Zr}$ have been extended into the angular momentum region where rotation alignment of particles is normally expected. By measuring the moments of inertia of these bands we have observed a consistent increase in the rotational frequency required to start pair breaking, when compared to neighboring nuclei. ${}^{72}\mathrm{Kr}$ shows the most marked effect. It has been widely suggested that these “delayed alignments” arise from $\mathrm{np}$-pairing correlations. However, alignment frequencies are very sensitive to shape degrees of freedom and normal pairing, so the new experimental observations are still open to interpretation.

Gamma rays from the $N=Z-2\mathrm{}$ nucleus ${}^{50}\mathrm{Fe}$ have been observed, establishing the rotational ground state band up to the state $J^{\pi }{=11\mathrm{}}^{+}$ at 6.994 MeV excitation energy. The experimental Coulomb energy differences, obtained by comparison with the isobaric analog states in its mirror ${}^{50}\mathrm{Cr}$, confirm the qualitative interpretation of the backbending patterns in terms of successive alignments of proton and neutron pairs. A quantitative agreement with experiment has been achieved by exact shell model calculations, incorporating the differences in radii along the yrast bands, and properly renormalizing the Coulomb matrix elements in the $\mathrm{pf}$ model space.

We report a particle source imaging analysis based on two-pion correlations in high multiplicity $\mathrm{Au}+\mathrm{Au}$ collisions at beam energies between $2A$ and $8A\mathrm{GeV}$. We apply the imaging technique introduced by Brown and Danielewicz, which allows a model-independent extraction of source functions with useful accuracy out to relative pion separations of about 20 fm. The extracted source functions have Gaussian shapes. Values of source functions at zero separation are almost constant across the energy range under study. Imaging results are found to be consistent with conventional source parameters obtained from a multidimensional Hanburg-Brown–Twiss analysis.

Measurements, with the BRAHMS detector, of the antiproton-to-proton ratio at midrapidities and forward rapidities, are presented for $\mathrm{Au}+\mathrm{Au}$ reactions at $\sqrt{s_{\mathrm{NN}}}=130\mathrm{}\mathrm{GeV}$, and for three different collision centralities. For collisions in the $0\%–40\%$ centrality range, we find $N\left(\overline{p}\right)/N\left(p\right)=0.64\mathrm{}\pm {0.04}_{\left(\mathrm{stat}\right)}\pm {0.06}_{\left(\mathrm{syst}\right)}$ at $y\approx 0$, $0.66\pm 0.03\pm 0.06$ at $y\approx 0.7$, and $0.41\pm 0.04\pm 0.06$ at $y\approx 2$. The ratios are found to be nearly independent of collision centrality and transverse momentum. The antiproton and proton rapidity densities vary differently with rapidity, and indicate a significant degree of collision transparency, although a net-baryon free midrapidity plateau (Bjorken limit) is not yet reached.

Two-particle interferometry of positive kaons is studied in $\mathrm{Pb}+\mathrm{Pb}$ collisions at mean transverse momenta $〈p_T〉\approx 0.25$ and $0.91\mathrm{GeV}/c$. A three-dimensional analysis was applied to the lower $p_T$ data, while a two-dimensional analysis was used for the higher $p_T$ data. We find that the source-size parameters are consistent with the $m_T$ scaling curve observed in pion-correlation measurements in the same collisions, and that the duration time of kaon emission is consistent with zero within the experimental sensitivity.

We suggest the variation of charmonium production rate with Feynman $x_F$ in heavy ion collisions as a novel and sensitive probe for the properties of the created matter. Final state interactions with the comoving matter create a minimum at $x_F=0\mathrm{}$, which is especially deep and narrow if a quark-gluon plasma is formed. While a strong effect is predicted at SPS, at the RHIC energy it overlaps with the expected peak formed by shadowing effects and needs comparison with pA data. We predict a steep dependence on centrality and suggest that this new probe is complementary to the dependence on transverse energy, and is more sensitive to a scenario of final state interactions.

The minimum-bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons ( $h^{-}$) in $\mathrm{Au}+\mathrm{Au}$ interactions at $\sqrt{s_{\mathrm{NN}}}=130\mathrm{}\mathrm{GeV}$. The multiplicity density at midrapidity for the $5\%$ most central interactions is ${\mathrm{dN}}_{h^{-}}/d\eta {|}_{\eta =0\mathrm{}}=280\mathrm{}\pm 1\left(\mathrm{stat}\right)\pm 20\left(\mathrm{syst}\right)$, an increase per participant of $38\%$ relative to $p\overline{p}$ collisions at the same energy. The mean transverse momentum is $0.508\pm 0.012\mathrm{GeV}/c$ and is larger than in central $\mathrm{Pb}+\mathrm{Pb}$ collisions at lower energies. The scaling of the $h^{-}$ yield per participant is a strong function of $p_{\perp }$. The pseudorapidity distribution is almost constant within $|\eta |<1\mathrm{}$.

The charged-particle pseudorapidity density ${\mathrm{dN}}_{\mathrm{ch}}/d\eta$ has been measured for $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=130\mathrm{}\mathrm{GeV}$ at RHIC, using the PHOBOS apparatus. The total number of charged particles produced for the $3\%$ most-central $\mathrm{Au}+\mathrm{Au}$ collisions for $|\eta |\le 5.4$ is found to be $4200\pm 470$. The evolution of ${\mathrm{dN}}_{\mathrm{ch}}/d\eta$ with centrality is discussed, and compared to model calculations and to data from proton-induced collisions. The data show an enhancement in charged-particle production at midrapidity, while in the fragmentation regions, the results are consistent with expectations from $\mathrm{pp}$ and $\mathrm{pA}$ scattering.

Experimental information has been derived from the neutron-proton correlation function in order to deduce the time sequence of neutrons and protons emitted at $45°$ in the $E/A=45\mathrm{}\mathrm{MeV}$ ${}^{58}\mathrm{Ni}{+}^{27}\mathrm{Al}$ reaction.

The first measurements of the $d(\gamma ,p)n$ differential cross section at forward angles and photon energies above 4 GeV were performed at the Thomas Jefferson National Accelerator Facility (JLab). The results indicate evidence of an angular dependent scaling threshold. Results at ${\theta }_{\mathrm{cm}}=37\mathrm{}°$ are consistent with the constituent counting rules for $E_{\gamma }\gtrsim 4\mathrm{GeV}$, while those at $70°$ are consistent with the constituent counting rules for $E_{\gamma }\gtrsim 1.5\mathrm{GeV}$.

We have measured the ratios of antiparticles to particles for charged pions, kaons, and protons near mid-rapidity in central $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=130\mathrm{}\mathrm{GeV}$. We observe $〈{\pi }^{-}〉/〈{\pi }^{+}〉=1.00\mathrm{}\pm 0.01\left(\mathrm{stat}\right)\pm 0.02\left(\mathrm{syst}\right)$, $〈K^{-}〉/〈K^{+}〉=0.91\mathrm{}\pm 0.07\left(\mathrm{stat}\right)\pm 0.06\left(\mathrm{syst}\right)$, and $〈\overline{p}〉/〈p〉=0.60\mathrm{}\pm 0.04\left(\mathrm{stat}\right)\pm 0.06\left(\mathrm{syst}\right)$. The $〈K^{-}〉/〈K^{+}〉$ and $〈\overline{p}〉/〈p〉$ ratios give a consistent estimate of the baryo-chemical potential ${\mu }_B$ of $45\mathrm{MeV}$, a factor of 5–6 smaller than in central $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=17.2\mathrm{}\mathrm{GeV}$.

Experimental search for ${}^5\mathrm{H}$ using a secondary beam of ${}^6\mathrm{He}$ has been performed. The transfer reaction ${}^1\mathrm{H}{(}^6\mathrm{He}{,}^2\mathrm{He}{)}^5\mathrm{H}$ was studied by detecting two protons emitted from the decay of ${}^2\mathrm{He}$. A peak consistent with a ${}^5\mathrm{H}$ resonance at $1.7\pm 0.3\mathrm{MeV}$ above the $n+n+t$ threshold was observed, with a width of $1.9\pm 0.4\mathrm{MeV}$. The angular distribution of the ${}^1\mathrm{H}{(}^6\mathrm{He}{,}^2\mathrm{He}{)}^5\mathrm{H}$ reaction was measured as well as the energy correlation of the two protons.

Two-pion correlation functions in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=130\mathrm{}\mathrm{GeV}$ have been measured by the STAR (solenoidal tracker at RHIC) detector. The source size extracted by fitting the correlations grows with event multiplicity and decreases with transverse momentum. Anomalously large sizes or emission durations, which have been suggested as signals of quark-gluon plasma formation and rehadronization, are not observed. The Hanbury Brown–Twiss parameters display a weak energy dependence over a broad range in $\sqrt{s_{\mathrm{NN}}}$.

The magic numbers in exotic nuclei are discussed, and their novel origin is shown to be the spin-isospin dependent part of the nucleon-nucleon interaction in nuclei. The importance and robustness of this mechanism is shown in terms of meson exchange, G-matrix, and QCD theories. In neutron-rich exotic nuclei, magic numbers such as $N=8\mathrm{}$, 20, etc. can disappear, while $N=6\mathrm{}$, 16, etc. arise, affecting the structure of the lightest exotic nuclei to nucleosynthesis of heavy elements.

The differences between neutron and proton density distributions at large nuclear radii in stable nuclei were determined. Two experimental methods were applied: nuclear spectroscopy analysis of the antiproton annihilation residues one mass unit lighter than the target mass and the measurements of strong-interaction effects on antiprotonic x rays. Assuming the validity of two-parameter Fermi neutron and proton distributions at these large radii, the conclusions are that the two experiments are consistent with each other and that for neutron rich nuclei it is mostly the neutron diffuseness which increases and not the half-density radius. The obtained neutron and proton rms radii differences are in agreement with previous results.