In the modern description of nuclear forces based on chiral effective field theory, four-nucleon operators with unknown coupling constants appear. These couplings can be fixed by a fit to the low partial waves of nucleon-nucleon scattering. We show that the so-determined numerical values have a remarkable similarity to values extracted from phenomenological one-boson-exchange models in a low momentum expansion. We also extract these values from various modern high accuracy nucleon-nucleon potentials and find again the same similarity. This paves the way for estimating the low-energy constants of operators with more nucleon fields and/or external probes.

We have investigated the evolution of the shell structure of nuclei in going from the r-process path to the neutron drip line within the framework of the relativistic Hartree-Bogoliubov (RHB) theory. By introducing the quartic self-coupling of $\omega$ meson in the RHB theory in addition to the nonlinear scalar coupling of $\sigma$ meson, we reproduce the available data on the shell effects about the waiting-point nucleus ${}^{80}\mathrm{Zn}.$ With this approach, it is shown that the shell effects at $N=82\mathrm{}$ in the inaccessible region of the r-process path become milder as compared to the Lagrangian with the scalar self-coupling only. However, the shell effects remain stronger as compared to the quenching exhibited by the HFB+SkP approach. It is also shown that in reaching out to the extreme point at the neutron drip line, a terminal situation arises where the shell structure at the magic number is washed out significantly.

Nuclear transparency in ${(e,e}^{\prime }p)$ reactions is evaluated in a fully relativistic distorted wave impulse approximation model. The relativistic mean field theory is used for the bound state and the Pauli reduction for the scattering state, which is calculated from a relativistic optical potential. Results for selected nuclei are displayed in a $Q^2$ range between $0.3$ and $1.8(\mathrm{GeV}{/c)}^2$ and compared with recent electron scattering data. For $Q^2=0.3\mathrm{}(\mathrm{GeV}{/c)}^2$ the results are lower than data; for higher $Q^2$ they are in reasonable agreement with data. The sensitivity of the model to different prescriptions for the one-body current operator is investigated. The off-shell ambiguities are rather large for the distorted cross sections and small for the plane wave cross sections.

Nucleon-nucleon decoupled dibaryons below the pion emission threshold have been investigated by the $p\overrightarrow{d}\mathrm{pdX}$ and $p\overrightarrow{d}\mathrm{ppX}$ reactions at $E_p=300\mathrm{}\hspace{0.5em}\mathrm{MeV}.$ Such dibaryons are predicted to either decay into a deuteron or two nucleons by emitting a $\gamma$ ray and consequently have a very narrow width of less than 1 keV. The experiment was carried out at the Research Center for Nuclear Physics employing a two-arm magnetic spectrometer. A mass resolution of 0.95 MeV and background-free condition have been achieved. No resonance was found in either the $d+\gamma$ or $p+n+\gamma$ decay channels within the mass region of 1896–1914 MeV. Upper limits for the dibaryon production cross section are presented.

High-precision cross sections and analyzing powers have been measured for proton-proton bremsstrahlung at an incident energy of 190 MeV. A large part of the total reaction phase space has been covered in two separate measurements in which all reaction products were detected. Photon angular distributions for a number of proton angle combinations are presented and compared to theoretical models. The discrepancy between the experimental and theoretical values of the cross sections becomes larger at smaller values of relative energy of the two outgoing protons pointing to the fact that other effects such as those due to the Coulomb force should be investigated more thoroughly. The simplest photonuclear process remains to be fully understood.

The production of the ${}^{26}\mathrm{Al}$ radioisotope in astrophysical environments is not understood, in part, because of large uncertainties in key nuclear reaction rates. The ${}^{25}\mathrm{Al}(p,\gamma {)}^{26}\mathrm{Si}$ reaction is one of the most important, but its rate is very uncertain as a result of the lack of information on the ${}^{26}\mathrm{Si}$ level structure above the proton threshold. To reduce these uncertainties, we have measured differential cross sections for the ${}^{28}\mathrm{Si}{\mathrm{}(p,t)\mathrm{}}^{26}\mathrm{Si}$ reaction and determined excitation energies for states in ${}^{26}\mathrm{Si}.$ A total of 21 states in ${}^{26}\mathrm{Si}$ were observed, including ten above the proton threshold. One new state at 7019 keV was observed, the excitation energies of several states were corrected, and the uncertainties in the excitation energies of other states were significantly reduced. Spins and parities of several states above the proton threshold were determined for the first time through a distorted-wave Born approximation analysis of the angular distributions. These results substantially clarify the level structure of ${}^{26}\mathrm{Si}.$

The regions of neutron-proton and neutron-neutron quasifree scattering (QFS) have been investigated in the n-d breakup reaction at 26 MeV, measuring absolute cross sections with an accuracy of a few percent. The data were analyzed by means of detailed Monte Carlo simulations based on rigorous three-body calculations with realistic nucleon-nucleon potentials. For n-p QFS, good agreement between theory and experiment was found. In contrast, for n-n QFS the experimentally determined cross section is almost 20% larger than the theoretical predictions.

The nature of the nonrelativistic nucleon-nucleon potential in the large-$N_c$ limit is discussed. In particular, we address the consistency of the meson-exchange picture of nucleon interactions. It is shown that the nonrelativistic nucleon-nucleon potential extracted from the Feynmann graphs up to and including two-meson-exchange diagrams satisfies the spin-flavor counting rules of Kaplan and Savage and of Kaplan and Manohar, provided the nucleon momenta is of order $N_c^0.$ The key to this is a cancellation of the retardation effect of the box graphs against the contributions of the crossed-box diagram. The consistency requires including $\Delta$ as an intermediate state.

We have studied the excitation mechanism of $d^{*},$ a bound state of two deltas $\left(\Delta \right),$ in proton-deuteron collisions. In our model for the mechanism of $d^{*}$ excitation in this reaction, the incident proton interacts with both nucleons of the deuteron, exciting each one of them to the $\Delta$ state in sequence. The $V_{N\overrightarrow{N}N\Delta }$ transition potential is described by the one-pion exchange, parameters of which are fixed taking guidance from studies on $p\overrightarrow{p}N\Delta$ reaction. The results presented here are for angular distribution, mass distribution, t distribution, and the excitation function. We find that the position of the peak in the mass distribution is directly related to the strength of the $\Delta -\Delta$ binding potential. The excitation function peaks between 300- and 550-MeV beam energy for binding potentials between 500 and 350 MeV. The angular distribution peaks around $55°–60°.$

The influence of $\Delta$ isobar components on the ground-state properties of nuclear systems is investigated for nuclear matter as well as finite nuclei. Many-body wave functions, including isobar configurations and binding energies, are evaluated employing the framework of the coupled-cluster theory. It is demonstrated that the effect of isobar configurations depends in a rather sensitive way on the model used for the baryon-baryon interaction. As examples for realistic baryon-baryon interactions with explicit inclusion of isobar channels we use the local $\mathrm{}\left(V28\mathrm{}\right)\mathrm{}$ and nonlocal meson-exchange potentials $\left({\mathrm{Bonn}}_{2000}\right)$ but also a model recently developed by the Salamanca group, which is based on a quark picture. The differences obtained for the nuclear observables are related to the treatment of the interaction, the π-exchange contributions in particular, at high momentum transfers.

Reactions of ${}^7\mathrm{Li}{+}^7\mathrm{Li}$ at $E_{\mathrm{lab}}=34\mathrm{}\hspace{0.5em}\mathrm{MeV},$ which lead to charged particle decaying excited states of ${}^{10}\mathrm{Be},$ have been studied by use of a detection system sensitive to decay energies of a few hundred keV. The α-particle branching fractions in ${}^{10}{\overrightarrow{{\mathrm{Be}}^{*}}}^4\mathrm{He}{+}^6\mathrm{He}$ have been measured for excited states at $E_x=7.542\mathrm{}$ and $\sim 9.6\hspace{0.5em}\mathrm{MeV}.$ For the 7.542 MeV state an unusually large separation radius is required to explain the observed branching fraction of ${\Gamma }_{\alpha }/\Gamma =(3.5\mathrm{}\pm 1.2)\times {10}^{-3}.$ This result is interpreted in terms of the energy level structure of ${}^{10}\mathrm{Be}$ as related to analogous states in ${}^{12}\mathrm{C}$ and to the recent molecular orbital calculations. A new $J^{\pi }{=0\mathrm{}}^{-}$ state is observed in the decay ${}^{10}{\overrightarrow{{\mathrm{Be}}^{*}}}^7{\mathrm{Li}}^{*}\left(0.478\mathrm{}\hspace{0.5em}\mathrm{MeV}\right)+t.\mathrm{}$

Results of single-neutron knockout experiments from ${}^{34,35}\mathrm{Si}$ at $73A\hspace{0.5em}\mathrm{MeV}$ and from ${}^{37}\mathrm{S}$ at $69A\hspace{0.5em}\mathrm{MeV}$ on a Be target are reported. The final states in the reaction residues have been identified by measuring $\gamma$ rays in coincidence with the $\left(A-1\right)$ fragments. The results are compared with predictions based on the many-body shell model combined with eikonal and transfer-to-the-continuum reaction models. For the ${}^9\mathrm{Be}{(}^{34}\mathrm{Si}{,}^{33}\mathrm{Si}+\gamma )X$ reaction, the measured parallel-momentum distributions of the reaction residues demonstrate the orbital-angular-momentum assignments l=2, 0, 2 to levels at 0, 1.010, and 4.32 MeV (adopted values). The measured absolute spectroscopic factors exhaust a large fraction of the sum rules for a full $\mathrm{}(N=20\mathrm{})\mathrm{}\hspace{0.5em}\mathrm{sd}$ shell. We also give results for the absolute and relative positions of the parallel-momentum distributions and present experimental and theoretical results for the complex spectra of the ${}^9\mathrm{Be}{(}^{35}\mathrm{Si}{,}^{34}\mathrm{Si}+\gamma )X$ reaction. The measured inclusive cross section of 106(19) mb agrees well with the theoretical value of 98 mb, but more detailed conclusions are not possible. For the inclusive reaction ${}^9\mathrm{Be}{(}^{37}\mathrm{S}{,}^{36}\mathrm{S})X$ a cross section of 99(12) mb is found compared to the theoretical prediction of 85 mb where only final states with spectroscopic factors greater than 0.03 have been included.

Excited states in neutron-rich ${}^{133}\mathrm{Te}$ have been identified with the Gamma sphere array by measuring three- and higher-fold prompt coincidence events following spontaneous fission of ${}^{252}\mathrm{Cf}.$ Four types of particle-hole bands built on the known 334.3 keV isomer in ${}^{133}\mathrm{Te}$ are identified. The yrast and near yrast particle-hole states observed up to 6.2 MeV in ${}^{133}\mathrm{Te}$ have characteristics quite similar to those in ${}^{134}\mathrm{Te}.$ These states are interpreted as a result of coupling a neutron $\nu h_{11/2}$ hole to the ${}^{134}\mathrm{Te}$ core. The group of states observed above 5.214 MeV is the result of a neutron particle-hole excitation of the double magic core nucleus ${}^{132}\mathrm{Sn},$ and is a candidate for a tilted rotor band. Shell-model calculations considering ${}^{132}\mathrm{Sn}$ as a closed core have been performed and have provided guidance to the interpretation of the levels below 4.3 MeV. Very good agreement between theory and experiment is obtained for these states.

The lifetimes of excited states in the yrast band in ${}^{158}\mathrm{Er}$ up to $I^{\pi }{=20\mathrm{}}^{+}$ have been measured to high precision by means of the Gammasphere spectrometer using the coincidence recoil distance technique. The reaction ${}^{122}\mathrm{Sn}{(}^{40}\mathrm{Ar},4n)$ at a beam energy of 185 MeV was used. The data were analyzed using the differential decay-curve method and transition quadrupole moments were extracted. The quadrupole moment was found to gradually increase by 15% of its $2^{+}$ value before the first $\nu i_{13/2}$ alignment, after which it drops to a constant level 90% of the $2^{+}$ value. Detailed comparisons are made with previous measurements and Ultimate Cranker calculations.

The structure of nucleon self-energy in nuclear matter is evaluated for various realistic models of the nucleon-nucleon $\mathrm{}\left(\mathrm{NN}\right)\mathrm{}$ interaction. Starting from the Brueckner-Hartree-Fock approximation without the usual angle-average approximation, the effects of hole-hole contributions and a self-consistent treatment within the framework of the Green function approach are investigated. Special attention is paid to the predictions for the spectral function originating from various models of the $\mathrm{NN}$ interaction, which all yield an accurate fit for the $\mathrm{NN}$ phase shifts.

In this work, microsecond isomers of the three neutron hole nuclei ${}^{129}\mathrm{Sn}$ and ${}^{130}\mathrm{Sb}$ were investigated. These nuclei were produced by the thermal neutron induced fission of ${}^{239}\mathrm{Pu}$ and ${}^{241}\mathrm{Pu}.$ The detection is based on time correlation between fission fragments selected by the LOHENGRIN spectrometer at ILL (Grenoble) and the $\gamma$ rays or conversion electrons from the isomers. The results include the identification of the $\nu {(h}_{11/2}^{-2}{d}_{3/2}^{-1}{)23/2\mathrm{}}^{+}$ aligned isomer in the odd ${}^{129}\mathrm{Sn}$ and the $\left[\pi g_{7/2}\nu {(h}_{11/2}^{-2}{d}_{3/2}^{-1}\right)]{13}^{+}$ isomer in the odd-odd ${}^{130}\mathrm{Sb}$ and their decay schemes. The interpretation of the level schemes is mainly based on a truncated shell model calculation using empirical two-body interactions. Several new $B\left(E2\mathrm{}\right)\mathrm{}$ strengths of isomeric transitions were measured and are discussed in the paper.

The nuclei ${}^{91}\mathrm{Sr}$ and ${}^{92}\mathrm{Sr}$ were produced at high spin as fission fragments following the fusion reaction ${}^{36}\mathrm{S}{+}^{159}\mathrm{Tb}$ at 165 MeV. $\gamma$ rays were detected with the Gammasphere array. The level schemes of ${}^{91}\mathrm{Sr}$ and ${}^{92}\mathrm{Sr}$ were extended up to $E\approx 6\hspace{0.5em}\mathrm{MeV}$ and $E\approx 8\hspace{0.5em}\mathrm{MeV},$ respectively. Level structures in ${}^{91}\mathrm{Sr}$ and ${}^{92}\mathrm{Sr}$ were interpreted in shell-model calculations performed in the configuration space ${(0f}_{5/2}{,1p}_{3/2}{,1p}_{1/2}{,0g}_{9/2})$ for the protons and ${(1p}_{1/2}{,0g}_{9/2}{,1d}_{5/2})$ for the neutrons. Negative-parity states in the yrast sequences are described in these calculations by coupling $3^{-}$ proton excitations to the unpaired ${1d}_{5/2}$ neutrons. A possible reduction of the gap between the proton ${1p}_{3/2}$ and ${1p}_{1/2}$ orbitals in ${}^{92}\mathrm{Sr}$ is discussed.

An enhanced population of the ${}^{149}\mathrm{Gd}$ yrast superdeformed band has been observed in the reaction ${}^{124}\mathrm{Sn}{(}^{31}P,p5n)$ using the EUROBALL IV multidetector associated with an inner ball. This effect is explained as the consequence of a higher probability of trapping residual nuclei into the superdeformed well whose depth has been increased due to favorable temperature and of total energy and angular momentum selection with the inner ball.

The deviation of the energy-weight sum rule (EWSR) and the energy shift for the two-phonon state from the prediction of the independent-phonon picture (the harmonic limit) are studied within the exactly solvable Lipkin-Meskov-Glick model. The exact results are used to compare with the estimations given within the random-phase approximation (RPA) and the renormalized RPA (RRPA). The analysis of the numerical results shows that the source of the “enhancement” of the two-phonon ESWR compared to the value given by the harmonic limit is the violation of the condition $[\mathrm{D̂},[\mathcal{V},\mathrm{D̂}\left]\right]=0\mathrm{}$ for the interaction part $\mathcal{V}$ of the model Hamiltonian and the operator $\mathrm{D̂}$ generating the electromagnetic transition. As a result, the EWSR for the two-phonon excitation exceeds its value in the harmonic limit by a factor of $\sim 1.8$ at $N\simeq 136$ and $\chi =\mathrm{0.8.}\mathrm{}$ It is also shown that the energy shift of the two-phonon energy compared to its value in the harmonic limit decreases with increasing the particle number N following a power law, which is more complicated than the simple approximation $\sim N^{-x}.$ The RPA and RRPA underestimate the exact EWSR of the two-phonon excitation by about $30\%$ at a given interaction in the region where the RPA is valid.

We investigate the mean energy, strength, and width of triple giant dipole resonance using sum rules. We point out that the transition operator for the triple giant dipole resonance must be modified from the naive choice $D^3.$ With the modified transition operator, the strength and mean energy calculated in the Tomonaga model agree with the harmonic limit, and the width is larger than $\sqrt{3}$ times that of the giant dipole resonance. Had we adopted the naive choice, we would have obtained unphysical results for these quantities. Assuming the absence of a charge-exchange component in the nuclear interaction, we derive model-independent relationships between the mean energies and strengths of multiple giant dipole resonances, which are an extension of relations derived previously for the double giant dipole resonance.