The $T=0\mathrm{}$ and $T=1\mathrm{}$ pairing correlations are discussed within the framework of two simple models: the SO(8) algebraic model and the single-$j$ model with a surface-$\delta$ interaction. The possibility of an approximate description of the ground-state wave functions in terms of correlated four-particle $T=0,$ $S=0\mathrm{}$ (α-like) structures is investigated. The overlap of the approximate and the exact wave functions is shown to be larger than $0.93$ for any relation between the $T=1\mathrm{}$ and $T=0\mathrm{}$ pairing strengths. The influence of the neutron-proton pairing interaction terms on the quadrupole sum rule and on the ground-state magnetic moments of the odd nuclei with $Z=N\pm 1$ is analyzed.

A fusion-evaporation reaction has been employed to search for isomeric states in the near-proton drip-line $N=77\mathrm{}$ isotones, ${}_{\hspace{0.5em}65}^{142}\mathrm{Tb}$ and ${}_{\hspace{0.5em}67}^{144}\mathrm{Ho}.$ The recoiling nuclei were implanted into a silicon detector at the focal plane of a gas-filled separator, where a recoil isomer tagging technique was employed to correlate prompt and delayed $\gamma$-ray transitions across isomeric states. New states were observed to be built upon a known $15-\mu \mathrm{s}$ isomer in ${}^{142}\mathrm{Tb}$ and the feeding and decay of a new $500\left(20\right)\mathrm{}-\mathrm{ns}$ isomeric state was established in ${}^{144}\mathrm{Ho}.$ This measurement represents the first observation of excited states in ${}^{144}\mathrm{Ho}.$ The behavior of the new states above the isomers suggests that they are built upon low-deformation configurations with significant triaxiality. This is in contrast to the lighter-mass proton emitters that were recently interpreted as being well-deformed, prolate, axially symmetric nuclei.

Cross sections for the ${}^{90,92,94}\mathrm{Zr}\mathrm{}(p,n)\mathrm{}$ reactions were measured at energies of 79.2 and 119.4 MeV. A phenomenological model was developed to describe the variation with bombarding energy of the position of the $L=1\mathrm{}$ peak observed in these and other $\mathrm{}(p,n)\mathrm{}$ reactions. The model yields the splitting between the giant dipole and giant spin-dipole resonances. Values of these splittings are obtained for isotopes of Zr and Sn and for ${}^{208}\mathrm{Pb}.$

Precise values of the normal-component spin observables $D_{{\mathrm{NN}}^{\prime }},$ P, and $A_y$ have been determined at an incident proton energy of 198 MeV for the $T=0\mathrm{}$ (12.71 MeV) and $T=1\mathrm{}$ (15.11 MeV) $1^{+}$ states in ${}^{12}\mathrm{C}$ for momentum transfers between 80 and 250 $\mathrm{MeV}/c,$ and for the $T=0\mathrm{}$ (17.78 and 19.81 MeV) and $T=1\mathrm{}$ (18.98 MeV) $4^{-}$ states in ${}^{16}\mathrm{O}$ for momentum transfers of 225–400 $\mathrm{MeV}/c.\mathrm{}$ The data are compared with distorted wave impulse approximation calculations in which a microscopic treatment of the nuclear medium has been used to obtain an effective nucleon-nucleon interaction. Nuclear binding and Pauli blocking effects, as well as those due to the strong scalar and vector mean field potentials that arise in covariant treatments of nuclear matter, are incorporated using a G-matrix approach. Our results suggest that while the isovector channel of the effective nucleon-nucleon interaction is reasonably well understood, pronounced discrepancies between theory and experiment for the isoscalar transitions point towards problems with the relative strengths of the spin-orbit and tensor components. For the ${}^{12}\mathrm{C}$ states, these discrepancies are more difficult to interpret due to ambiguities in the nuclear structure.

We investigate the fragmentation mechanism reflecting the cluster structure of the ${}^{19}\mathrm{B}$ nucleus. We perform antisymmetrized molecular dynamics (AMD) calculations of ${}^{19}\mathrm{B}{+}^{14}\mathrm{N}$ and ${}^{13}\mathrm{B}{+}^{14}\mathrm{N}$ reactions, and compare ${}^{19}\mathrm{B}$ fragmentation with ${}^{13}\mathrm{B}$ fragmentation. The neutron drip-line nucleus ${}^{19}\mathrm{B}$ has been predicted to have a well-developed cluster structure in its ground state while the neutron closed-shell nucleus ${}^{13}\mathrm{B}$ has no clustering features in its structure. The clustering structure of ${}^{19}\mathrm{B}$ is reflected in its fragmentation as the dynamical cluster breakup into He and Li isotopes, depending on the incident energy. In the low-incident-energy region around 30 MeV/nucleon, dynamical cluster breakup of ${}^{19}\mathrm{B}$ occurs and brings about an abundance of He and Li isotopes in ${}^{19}\mathrm{B}$ fragmentation compared with those in ${}^{13}\mathrm{B}$ fragmentation. In the high-incident-energy region above 50 MeV/nucleon, dynamical cluster breakup of ${}^{19}\mathrm{B}$ hardly occurs and the cluster structure of the ${}^{19}\mathrm{B}$ nucleus is not reflected in its fragmentation. We suggest here the coincident experiment between He and Li isotopes as an experimental way to confirm whether the ${}^{19}\mathrm{B}$ nucleus has a cluster structure in its ground state or not.

The formation and subsequent decay of nuclei excited via the annihilation of 1.22-GeV antiprotons have been investigated at the low energy antiproton ring (LEAR). Both neutrons and charged products, from protons up to fission fragments and heavy residues, were detected over a solid angle of $4\pi$ by means of the Berlin neutron ball (BNB) and the Berlin silicon ball (BSiB), respectively. All events associated with an inelasticity greater than 10 MeV were recorded, a condition fulfilled for 100% of the annihilation events. The distributions of excitation energy ${(E}^{*})$ of the transient hot nuclei have been investigated for a large range of target nuclei, $E^{*}$ being determined event by event from the total multiplicity of light particles. The average excitation energies are about twice as large as for annihilations at rest, and range from 2.5 MeV/nucleon for the Cu target to 1.5 MeV/nucleon for the U target, in good agreement with the predictions of an intranuclear-cascade model. The distributions extend to $E^{*}>8\mathrm{}$ MeV/nucleon for Cu and $E^{*}>5\mathrm{}$ MeV/nucleon for Au, with cross sections exceeding 1% of ${\sigma }_{\mathrm{reac}}.$ Thanks to the capability of determining $E^{*}$ for all events, largely irrespective of their mass partitions, the probabilities of the different decay channels at play could be estimated as a function of $E^{*}.$ The data show the prevalence of fission and evaporation up to $E^{*}=4\mathrm{}–5$ MeV/nucleon for Au and U. The fission probability $P_{\mathrm{fis}}$ was measured for the first time over the full range of $E^{*}.$ The reproduction of the data by statistical models is reasonable, provided that the ratio $a_f{/a}_n$ is adjusted for the different targets and a transient time shorter than $1\times {10}^{-21}$ s is considered. The experiment has allowed the fission probability to be investigated as functions of the associated neutron and light-charged particle multiplicities. The intermediate-mass fragment multiplicities rise smoothly with $E^{*}$ up to about 1 unit at $E^{*}=1\mathrm{}$ GeV for Au and U, with no indication of significant contribution from another process than evaporation. Heavy residues have been measured quite abundantly at the highest $E^{*},$ with most of their kinetic energy arising from the recoil effects in the evaporation stage. Overall, the data allow a coherent picture to be established, consistent with the hot nucleus retaining conventional decay properties.

The transverse momentum ${(p}_t)$ dependence of hadron flow at SPS energies is studied. In particular, the nucleon and pion flow in S+S and Pb+Pb collisions at $160A$ GeV is investigated. For simulations the microscopic quark-gluon string model is applied. It is found that the directed flow of pions $v_1(y,\Delta p_t)$ changes sign from a negative slope in the low-$p_t$ region to a positive slope at $p_t>~0.6\hspace{0.5em}\mathrm{GeV}/c$ as recently observed experimentally. The change of the flow behavior can be explained by early emission times for high-$p_t$ pions. We further found that a substantial amount of high-$p_t$ pions are produced in the very first primary nucleon-nucleon collisions at the surface region of the touching nuclei. Thus, at SPS energies high-$p_t$ nucleons seem to be a better probe for the hot and dense early phase of nuclear collisions than high-$p_t$ pions. Both in the light and in the heavy system the pion directed flow $v_1{(p}_t,\Delta y)$ exhibits large negative values when the transverse momentum approaches zero, as also seen experimentally in Pb+Pb collisions. It is found that this effect is caused by nuclear shadowing. The proton flow, on the contrary, shows the typical linear increase with rising $p_t.$

A search for the H dibaryon has been conducted at the Brookhaven National Laboratory AGS, using a 1.8 GeV/c $K^{-}$ beam. ${\Xi }^{-}$ hyperons were produced in a liquid-hydrogen target via the reaction $K^{-}+\overrightarrow{p}{K}^{+}+{\Xi }^{-}.$ The hyperons were slowed in degraders and those most likely to stop in an adjacent liquid-deuterium target were tagged by silicon detectors. Monoenergetic neutrons were sought as the signature for H formation in $({\Xi }^{-}{,d)}_{\mathrm{atom}}\to H+n.\mathrm{}$ The experiment was designed for optimal sensitivity to a loosely-bound H, complementing recent ${(K}^{-}{,K}^{+})$ measurements on nuclear targets. In addition, the experiment’s sensitivity was independent of lifetime and of decay modes of the H. No statistically significant evidence for H formation was seen. Upper limits on the branching ratio for H formation in the above reaction have been set in a mass range extending from slightly above $\Lambda \Lambda$ threshold to $\sim 100$ MeV of binding and are compared with a corresponding theoretical prediction.

The low-lying baryon spectrum predicted by a chiral constituent quark model is examined within an exact Faddeev approach. The reliability of the solutions provided by a truncated hyperspherical harmonic calculation is discussed. We demonstrate that the obtained spectrum is quite reasonable and compatible with the description of the $\mathrm{NN}$ phenomenology in the presence of a standard one-gluon exchange force.

We study the four channels associated with neutrino-deuteron breakup reactions at next-to-next-to-leading order in effective field theory. We find that the total cross section is indeed converging for neutrino energies up to 20 MeV, and thus our calculations can provide constraints on theoretical uncertainties for the Sudbury Neutrino Observatory. We stress the importance of a direct experimental measurement to high precision in at least one channel, in order to fix an axial two-body counterterm.

Levels in ${}^{22}\mathrm{Mg}$ between 4 and 7 MeV excitation energy have been populated in a high-resolution study of the ${}^{24}\mathrm{Mg}{\mathrm{}(p,t)\mathrm{}}^{22}\mathrm{Mg}$ reaction. Two new states have been observed at energies $E_x=5090\mathrm{}$ and 6323 keV, while two states were observed at 5962 and 6046 keV. The precision in measured excitation energies for several other ${}^{22}\mathrm{Mg}$ levels has been improved substantially. In addition, a new state at 8141 keV was observed in ${}^{23}\mathrm{Mg}.$ Using spin and parity restrictions from the present and previous work, we discuss $T=1\mathrm{}$ analog state assignments of $A=22\mathrm{}$ nuclei below 7 MeV excitation energy. The implications for the rate of the stellar reaction ${}^{21}\mathrm{Na}(p,\gamma {)}^{22}\mathrm{Mg}$ which takes part in hydrogen burning during nova outbursts are presented.

Electron-capture delayed fission was observed in 26-min ${}^{248}\mathrm{Es}$ and 7.7-min ${}^{246}\mathrm{Es},$ which were produced at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron via ${}^{249}\mathrm{Cf}\mathrm{}(p,2n)\mathrm{}$ and ${}^{249}\mathrm{Cf}\mathrm{}(p,4n)\mathrm{}$ reactions at proton energies of 18 and 37 MeV on target, respectively. The delayed fission probabilities were determined to be $(3.5\mathrm{}\pm 1.8)\times {10}^{-6}$ for ${}^{248}\mathrm{Es}$ and ${(3.7\mathrm{}}_{-3.0}^{+8.5\mathrm{}})\times {10}^{-5}$ for ${}^{246}\mathrm{Es}.$ These values were determined in separate experiments using our automated rotating wheel online collection and measurement system. Collection and measurement times were optimized for the isotope being measured. The measured delayed fission probabilities are consistent with the experimentally observed trend of increasing delayed fission probability with increasing Q value for electron capture.

A simulation is performed of the recently reported data from PHOBOS at energies of $\sqrt{s}=56,130\mathrm{}A$ GeV using the relativistic heavy ion cascade LUCIFER which had previously given a good description of the NA49 inclusive spectra at $\sqrt{s}=17.2A$ GeV. The results compare well with these early measurements at RHIC.

The latest measurements of the atomic level width in $\Sigma$-hyperonic Pb atoms offer the most accurate datum in the region of low-energy $\Sigma$-hyperon physics. Atomic widths are due to the $\Sigma N$-$\Lambda N$ conversion which in high-angular-momentum states is dominated by one-pion exchange. A joint analysis of the ${\Sigma }^{-}\overrightarrow{p}\Lambda n$ scattering data and atomic widths allows us to extract the pion-hyperon coupling constant $f_{\pi \Lambda \Sigma }^2/4\mathrm{}\pi =0.048\mathrm{}\pm 0.005$ (stat) $\pm 0.004$ (syst) or $G_{\pi \Lambda \Sigma }^2=13.3\mathrm{}\pm 1.4$ (stat) $\pm 1.1$ (syst).

We discuss a working approximation scheme to a recently developed formulation of the coupled $\pi \mathrm{NNN}-\mathrm{NNN}$ problem. The approximation scheme is based on the physical assumption that, at low energies, the 2N-subsystem dynamics in the elastic channel is conveniently described by the usual 2N-potential approach, while the explicit pion dynamics describes small, correction-type effects. Using the standard separable-expansion method, we obtain a dynamical equation of the Alt-Grassberger-Sandhas (AGS) type. This is an important result, because the computational techniques used for solving the normal AGS equation can also be used to describe the pion dynamics in the 3N system once the matrix dimension is increased by one component. We have also shown that this approximation scheme treats the conventional 3N problem once the pion degrees of freedom are projected out. Then, the 3N system is described with an extended AGS-type equation where the spin-off of the pion dynamics (beyond the 2N potential) is taken into account in additional contributions to the driving term. These new terms are shown to reproduce the diagrams leading to modern 3N-force models. We also recover two sets of irreducible diagrams that are commonly neglected in 3N-force discussions, and conclude that these sets should be further investigated.

We have studied electric dipole $\mathrm{}\left(E1\mathrm{}\right)\mathrm{}$ strength distribution in neutron and proton drip line nuclei ${}_{\hspace{0.5em}4}^{12}{\mathrm{Be}}_8,$ ${}_{\hspace{0.5em}4}^{14}{\mathrm{Be}}_{10},$ and ${}_{\hspace{0.5em}8}^{13}{\mathrm{O}}_5$ by large scale shell model calculations with the effect of loosely-bound single particle wave functions. Large $E1\mathrm{}$ strength is found in the low excitation energy region below $E_x=3\mathrm{}\hspace{0.5em}\mathrm{MeV}$ in both ${}_{\hspace{0.5em}4}^{12}{\mathrm{Be}}_8$ and ${}_{\hspace{0.5em}8}^{13}{\mathrm{O}}_5,$ while strong $E1\mathrm{}$ strength is found only in high excitation energy region above $E_x=7\mathrm{}\hspace{0.5em}\mathrm{MeV}$ in ${}_{\hspace{0.5em}4}^{14}{\mathrm{Be}}_{10}.$ The effect of extended wave functions and the coherence in the transition amplitudes enhance significantly the $E1\mathrm{}$ strength in the low energy region. A manifestation of melting of the shell magicity at $N=8\mathrm{}$ and $Z=8\mathrm{}$ is pointed out in the systematics of $E1\mathrm{}$ transitions in Be and O isotopes.

An angular correlation analysis of the breakup fragments from the ${}^{12}\mathrm{C}{(}^{24}\mathrm{Mg}{,}^{12}\mathrm{C}{}^{16}\mathrm{O}{)}^8\mathrm{Be}$ and ${}^{12}\mathrm{C}{(}^{24}\mathrm{Mg}{,}^{12}\mathrm{C}{}^{12}\mathrm{C}{)}^{12}\mathrm{C}$ reactions is presented. For the ${}^{12}\mathrm{C}{+}^{16}\mathrm{O}$ breakup of ${}^{28}\mathrm{Si},$ spins of ${13}^{-},$ $8^{+}{(10\mathrm{}}^{+}),$ and ${\mathrm{}(12,14)\mathrm{}}^{+}$ are assigned to states at excitation energies of 28.0, 33.4, and 34.5 MeV, respectively. The results are compared to the resonances observed in ${}^{12}\mathrm{C}{+}^{16}\mathrm{O}$ scattering studies and to the predictions of nuclear models. For the ${}^{12}\mathrm{C}{+}^{12}\mathrm{C}$ breakup of ${}^{24}\mathrm{Mg},$ previous spin assignments are verified and new assignments of ${(2\mathrm{}}^{+}),$ $6^{+}{(8\mathrm{}}^{+}),$ ${(6\mathrm{}}^{+}),$ and $8^{+}$ are proposed for states at 20.5, 23.8, 25.1, and 26.4 MeV, respectively.

The g factors of the $2_1^{+}$ states of the stable, even-even Mo isotopes ${}^{92,94,96,98,100}\mathrm{Mo}$ were measured using the transient field method. While ${}^{92}{\mathrm{Mo}}_{50}$ has a g factor consistent with that of the $\pi g_{9/2}^2$ configuration, the g factor of ${}^{94}\mathrm{Mo}$ is about 60% of the hydrodynamic model value, $Z/A.\mathrm{}$ As further pairs of neutrons are added, the heavier isotopes ${}^{96,98,100}\mathrm{Mo}$ show a monotonic increase in ${g(2\mathrm{}}^{+})$ to values that exceed $Z/A$ for ${}^{98}\mathrm{Mo}$ and ${}^{100}\mathrm{Mo}.$ The systematic behavior of the ${g(2\mathrm{}}_1^{+})$ values for the Mo isotopes, as one moves away from the neutron shell closure at $N=50,$ is compared with the shell model, a collective model with pairing corrections and IBM-2 calculations.

The Faddeev technique is employed to address the problem of describing the influence of both particle-particle and particle-hole phonons on the single-particle self-energy. The scope of the few-body Faddeev equations is extended to describe the motion of two-hole–one-particle (two-particle–one-hole) excitations. This formalism allows one to sum both particle-particle and particle-hole phonons, obtained separately in the random phase approximation. The appearance of spurious solutions for the present application of the Faddeev method is related to the inclusion of a consistent set of diagrams. The formalism presented here appears practical for finite nuclei and achieves a simultaneous inclusion of particle-particle and particle-hole phonons to all orders while the spurious solutions are properly eliminated.

The path and termination point for the rapid proton-capture (rp) process above ${}^{56}\mathrm{Ni}$ is uncertain due to a lack of knowledge of nuclear properties, especially masses, near the proton drip line. To address this need we have begun a program to measure masses along the rp-process path in the $A\sim 60–80$ region using β-γ coincidence spectroscopy. $Q_{\mathrm{EC}}$ values derived from ${\beta }^{+}$ spectrum end points were used to calculate mass excess values for ${}^{70}\mathrm{Se},$ ${}^{71}\mathrm{Se},$ ${}^{72}\mathrm{Br},$ and ${}^{73}\mathrm{Br}.$ The results are compared to predictions of mass models and to estimates based on systematic trends in this region.