Empirical average proton-neutron interaction energies, $\delta V_{\mathit{pn}}$, between the last nucleons can be isolated using double differences of masses. We have examined the systematic behavior of $\delta V_{\mathit{pn}}$ throughout the mass surface using the 2003 mass table that includes many new and improved experimental masses. The results are especially revealing for self-conjugate nuclei and in regions of strong shell closures in heavy nuclei. In the former the large $p\text{−}n$ interaction strength can be interpreted as a consequence of the $\mathrm{T}=0$ interaction between protons and neutrons in spatially similar orbitals. In the latter, the bifurcated systematic can be understood in terms of the evolution of proton and neutron orbital overlaps in regions surrounding a shell closure. In regions between shells, anomalies are sometimes encountered that are not fully understood. They might reflect structural effects or could arise from one or more erroneously measured masses. A scheme based on fractional shell filling is presented that may serve as a signature of shell structure in exotic nuclei. A link between empirical $p\text{−}n$ interactions and growth rates of collectivity is pointed out. Finally, our analysis is used to identify candidates for future mass measurements and their needed levels of accuracy, many of which will require new exotic beam facilities.

The double-folding model with an M3Y effective nucleon-nucleon (NN) interaction was applied to obtain the angle-dependent bare nucleus-nucleus potential for heavy-ion fusion reactions involving deformed target nuclei. The angular dependence with a zero-range exchange NN interaction is almost identical to that with a finite-range interaction, allowing quick calculations of the fusion cross sections and corresponding barrier distributions $D(E_{c.m.})$. Since in the literature the experimental $D(E_{c.m.})$ have been analyzed usually using a Woods-Saxon shape for the nuclear part of the nucleus-nucleus potential, we fitted the spherical double-folding potentials at the barrier radii with a Woods-Saxon (WS) form. The calculated $D(E_{c.m.})$ with this fitted WS potential, but now accounting for the deformation of the target nuclei, are significantly different from the $D(E_{c.m.})$ calculated directly using the double-folding potential. This indicates that the finite size effects are substantial and should not be ignored in the analysis of experimental fusion cross sections and barrier distributions for reactions with statically deformed nuclei.

We study the coupling of the $\Lambda (1520)\equiv {\Lambda }^{*}$ resonance to the ${\overline{K}}^{*}$ vector meson and nucleon. This coupling is not directly measured from the resonance decay, but is expected to be important in hyperon production reactions, in particular for the exotic ${\Theta }^{+}$ production. We compute the coupling in two different schemes, one in the chiral unitary model where the ${\Lambda }^{*}$ is dominated by the quasibound state of mesons and baryons, and the other in the quark model where the resonance is a p-wave excitation in the three valence quarks. Although it is possible to construct both models such that they reproduce the $\overline{K}N$ and $\pi \Sigma$ decays, there is a significant difference between the ${\Lambda }^{*}{\overline{K}}^{*}N$ couplings in the two models. In the chiral unitary model $\left|g_{{\Lambda }^{*}{\overline{K}}^{*}N}\right|~1.5$, while in the quark model $\left|g_{{\Lambda }^{*}{\overline{K}}^{*}N}\right|~10$. The difference of the results stems from the different structure of the ${\Lambda }^{*}$ in both models, and hence, an experimental determination of this coupling would shed light on the nature of the resonance.

Microsecond isomers of neutron-rich nuclei in the mass $A=95$ chain were investigated at the ILL reactor in Grenoble. These nuclei were produced by thermal-neutron induced fission of ${}^{241}\mathrm{Pu}$. The detection is based on time correlation between fission fragments selected by the Lohengrin mass spectrometer and the γ rays from the isomers. In this article, the decay scheme of an isomer of half-life 1.4(2) $\mu$s in ${}^{95}\mathrm{Kr}$ is reported. It is the first time that excited states of this nucleus have been measured. These data show that this neutron-rich $N=59$ isotone is spherical at low excitation energy.

A systematic investigation of the shears mechanism in silver isotopes has been carried out. Lifetimes have been measured by means of the Doppler-shift attenuation method for states in two magnetic dipole ($M1$) bands in ${}^{105}\mathrm{Ag}$ and one each in ${}^{103}\mathrm{Ag}$ and ${}^{106}\mathrm{Ag}$. Experimental total angular momenta and reduced transition strengths for these bands have been compared with the predictions of the tilted axis cranking (TAC) model with configurations involving one $g_{9/2}$ proton and quasineutrons from the $h_{11/2}$ and $g_{7/2}$ or $d_{5/2}$ orbitals. There is good overall agreement for both the total angular momenta and reduced transition strengths. The deduced $B(M1)$ strengths, which are a sensitive probe of magnetic rotation, show a decrease consistent with TAC predictions for one $M1$ band in ${}^{105}\mathrm{Ag}$ and in ${}^{106}\mathrm{Ag}$, confirming the shears mechanism as the means of excitation. Furthermore, the staggering in the transition energies in ${}^{103}\mathrm{Ag}$ and absence of regular sequences of $M1$ transitions for $N\le 56$ suggest that $N=56$ is the lower boundary for the appearance of the shears mechanism in this mass region.

We measured evaporation residue (ER) cross sections of the fusion reactions ${}^{86}\mathrm{Kr}+{}^{134,138}\mathrm{Ba}$ to investigate the effect of the shell structure of the interacting nuclei on the fusion process. The measured ER cross sections for the reaction ${}^{86}\mathrm{Kr}+{}^{138}\mathrm{Ba}$ have a sizable component, 37 nb, at the excitation energy ($E_{\mathrm{ex}}$) of 12.1 MeV. However, there is no evaporation residue for the reaction ${}^{86}\mathrm{Kr}+{}^{134}\mathrm{Ba}$ below the energy $E_{\mathrm{ex}}=24.7$ MeV. This result suggests that the neutron shell closure ($N=82$) of ${}^{138}\mathrm{Ba}$ plays a crucial role in the formation of the compound nucleus.

In the framework of the ab-initio no-core shell model (NCSM), we describe the longitudinal-longitudinal distribution function, part of the inclusive $(e,e^{\text{'}})$ longitudinal response. In the two-body cluster approximation, we compute the effective operators consistent with the unitary transformation used to obtain the effective Hamiltonian. When short-range correlations are probed, the results display independence from the model space size and length scale. Long-range correlations are more difficult to model in the NCSM and they can be des-cribed only by increasing the model space or increasing the cluster size. In order to illustrate the model space independence for short-range observables, we present results for a large set of model spaces for ${}^4\mathrm{He}$, and in $0-4\hslash \Omega$ model spaces for ${}^{12}\mathrm{C}$.

We show that the new experimental data reported by Galaviz et al. [Phys. Rev. C 71, 065802 (2005)] can be used to improve a previous optical potential global parameter set, employing the corresponding former local parameter basis as well as the parameter sets obtained through a similar analysis of the new data.

A simultaneous measurement of the cross sections of the ${}^3\mathrm{He}$($\gamma ,p$)D and ${}^3\mathrm{He}$($\gamma ,\mathit{pp}$)n reactions has been performed for the first time using monoenergetic pulsed γ-rays at $\langle E_{\gamma }\rangle =$10.2 and 16.0 MeV. Charged fragments from the reactions were detected with an efficiency of 100% using a 4π time projection chamber containing ${}^3\mathrm{He}$ gas as an active target. The incident γ-ray flux was measured by a γ-ray detector. Both the track and energy loss signals of charged fragments were obtained in an off-line analysis and used to clearly identify the reaction channel. Thus, the ($\gamma ,p$) and ($\gamma ,\mathit{pp}$) cross sections have been determined with small uncertainty. A comparison of the new data to current theory based on the AV18+Urbana IX nuclear forces including π- and ρ-like meson exchange currents shows a severe discrepancy at 10.2 MeV, while at 16.0 MeV data and theory agree within about 12%. Three-nucleon force effects are small, but in general shift the theory in the correct direction.

The spectroscopy of neutron-rich ${}^{109,110,111,112}\mathrm{Ru}$ nuclei was studied by measuring the prompt $\gamma$ rays that originate from fission fragments, produced by the ${}^{238}\mathrm{U}$($\alpha ,f)$ fusion-fission reaction, in coincidence with the detection of both fragments. For ${}^{109,111}\mathrm{Ru}$, both the negative-parity ($h_{11/2}$ orbitals) and $K=5/2$ positive-parity (mainly $g_{7/2}$ and $d_{5/2}$ orbitals) bands were extended to substantially higher spin and excitation energy than known previously. The ground-state and $\gamma$-vibrational bands of ${}^{110,112}\mathrm{Ru}$ also were extended to higher spin, allowing observation of the second band crossing at the rotational frequency of $\approx 450$ keV in ${}^{112}\mathrm{Ru}$, which is $\approx 50$ keV above the first band crossing. At a similar rotational frequency, the first band crossing for the $h_{11/2}$ band in ${}^{111}\mathrm{Ru}$ was observed, which is absent in ${}^{109}\mathrm{Ru}$. These band crossings most likely are caused by the alignment of the $g_{9/2}$ proton pair. This early onset of the band crossing for the aligned $\pi g_{9/2}$ orbitals may be evidence of a triaxial shape transition from prolate to oblate occurring in ${}^{111}\mathrm{Ru}$. The data together with a comparison of cranked shell‐model predictions are presented.

We perform a systematic study on the surface property of nucleus-nucleus potential in heavy-ion reactions using large-angle quasielastic scattering at energies well below the Coulomb barrier. At these energies, the quasielastic scattering can be well described by a single-channel potential model. Exploiting this fact, we point out that systems which involve spherical nuclei require the diffuseness parameter of around 0.60 fm in order to fit the experimental data, while systems with a deformed target between 0.8 and 1.1 fm.

We describe a semiclassical treatment of nuclear fusion reactions involving weakly bound nuclei. In this treatment, the projectile-target relative motion is approximated by a classical trajectory while the intrinsic dynamics is handled by time-dependent quantum mechanics. The complete fusion probabilities are approximated by products of two factors: A tunneling probability and the probability that the system is in its ground state at the strong absorption radius. We investigate the validity of the method in a schematic two-channel application, where the continuum is represented by a single effective state with finite lifetime. Coupling effects below the Coulomb barrier are included through an analytical continuation of the time. Comparisons with full coupled-channels calculations are performed. The agreement between semiclassical and fully quantal calculations is quite good, suggesting that the procedure may be extended to more sophisticated discretizations of the continuum.

The single-nucleon potential in hot nuclear matter is investigated in the framework of the Brueckner theory by adopting the realistic Argonne $V_{18}$ or Nijmegen 93 two-body nucleon-nucleon interaction supplemented by a microscopic three-body force. The rearrangement contribution to the single-particle potential induced by the ground state correlations is calculated in terms of the hole-line expansion of the mass operator and provides a significant repulsive contribution in the low-momentum region around and below the Fermi surface. Increasing temperature leads to a reduction of the effect, while increasing density makes it become stronger. The three-body force suppresses somewhat the ground state correlations due to its strong short-range repulsion, increasing with density. Inclusion of the three-body force contribution results in a quite different temperature dependence of the single-particle potential at high enough densities as compared to that adopting the pure two-body force. The effects of three-body force and ground state correlations on the nucleon effective mass are also discussed.

A quasiparticle-phonon model calculation is revised in the attempt of providing a satisfactory microscopic description of the extensive data on energies and electromagnetic decays of low-lying states in ${}^{92}\mathrm{Zr}$ obtained in a recent $(n,n^{\text{'}}\gamma )$ experiment. The new calculation reproduces satisfactorily most of the data, supports the conclusions drawn by a restricted shell model analysis about the nature of the two lowest $2^{+}$, and, partly, the lowest $3^{+}$ states, but suggests a different structure for the $4^{+}$ states.

In this work, we examine critically the relation between orbital magnetic dipole (scissors mode) strength and quadrupole deformation properties. Assuming a simple $K=0$ ground-state band in an even-even nucleus, the quantities $Q(2_1^{+})$ (i.e., the static quadrupole moment) and $B(E2){}_{0_1\to 2_1}$ both are described by a single parameter—the intrinsic quadrupole moment $Q_0$. In the shell model, we can operationally define $Q_0(\mathrm{static})$ and $Q_0(\mathit{BE}2)$ and see if they are the same. Following a brief excursion to the sd shell, we perform calculations in the fp shell. The nuclei we consider (${}^{44,46,48}\mathrm{Ti}$ and ${}^{48,50}\mathrm{Cr}$) are far from being perfect rotors, but we find that the calculated ratios $Q_0(\mathrm{static})/Q_0(\mathit{BE}2)$ with an FPD6 interaction are often very large (very close to unity) and far from the simple vibrational limit of zero. The experimental ratios for ${}^{46}\mathrm{Ti}$ and ${}^{48}\mathrm{Ti}$ are somewhat smaller ($~0.75$), but the ${}^{50}\mathrm{Cr}$ value is larger, exceeding unity. We also discuss the quadrupole collectivity of orbital magnetic dipole transitions. We find that the large orbital $B(M1)$ strength in ${}^{44}\mathrm{Ti}$ relative to ${}^{46}\mathrm{Ti}$ and ${}^{48}\mathrm{Ti}$ cannot be explained by simple deformation arguments.

We propose a simplified model to directly take into account the contribution of the tensor interaction (SMT) for light nuclei by extending the α-cluster model. In ${}^8\mathrm{Be}$, the energy curve with respect to the relative distance between the two ${}^4\mathrm{He}$ clusters suggests that the cluster structure persists even though the tensor interaction contributes strongly. In addition to SMT, a simplified method to take into account the strong spin-orbit contribution is introduced and the coupling effects of these two models is shown to be important in ${}^{12}\mathrm{C}$, in contrast to ${}^8\mathrm{Be}$.

Level densities for ${}^{93-98}\mathrm{Mo}$ have been extracted using the (${}^3\mathrm{He}$,$\alpha \gamma$) and (${}^3\mathrm{He}$,${}^3\mathrm{He}$${}^{\text{'}}\gamma$) reactions. From the level densities thermodynamical quantities such as temperature and heat capacity can be deduced. Data have been analyzed by utilizing both the microcanonical and the canonical ensemble. Structures in the microcanonical temperature are consistent with the breaking of nucleon Cooper pairs. The $\mathsf{S}$ shape of the heat capacity curves found within the canonical ensemble is interpreted as consistent with a pairing phase transition with a critical temperature for the quenching of pairing correlations at $T_c~0.7-1.0$MeV.

A method allowing studies of the hadronic matter at the early evolution stage in A+A collisions is developed. It is based on an interferometry analysis of approximately conserved values such as the averaged phase-space density (APSD) and the specific entropy of thermal pions. The plateau found in the APSD behavior vs collision energy at Super Proton synchroton (SPS) level is associated, apparently, with the deconfinement phase transition at low SPS energies; a saturation of this quantity at the energies available at BNL's-Relativistic Heavy Ion Collider (RHIC) indicates the limiting Hagedorn temperature for hadronic matter. It is shown that if the cubic power of the effective temperature of pion transverse spectra grows with energy similarly to the rapidity density (which is roughly consistent with experimental data), then the interferometry volume is inversely proportional to the pion APSD, which is nearly constant because of the limiting Hagedorn temperature. This sheds light on the Hanbury-Brown–Twiss puzzle.

The influence of time-dependent medium modifications of low-mass vector mesons on dilepton production is investigated within a nonequilibrium quantum field-theoretical description on the basis of the Kadanoff-Baym equations. Time scales for the adaption of the spectral properties to changing self-energies are given, and, under use of a model for the fireball evolution, nonequilibrium dilepton yields from the decay of ρ and ω mesons are calculated. In a comparison of these yields, those from calculations that assume instantaneous (Markovian) adaption to the changing-medium quantum-mechanical memory effects turn out to be important.

The implications of the empirical signatures for the positivity of the strangeness magnetic moment ${\mu }_s$ and the negativity of the strangeness contribution to the proton spin ${\Delta }_s$ on the possible $\mathit{uuds}\overline{s}$ configurations of five quarks in the proton are analyzed. The empirical signs for the values for these two observables can only be obtained in configurations where the uuds subsystem is orbitally excited and the $\overline{s}$ antiquark is in the ground state. The configurations in which the $\overline{s}$ is orbitally excited, including the conventional $K^{+}{\Lambda }^0$ configuration, with the exception of that in which the uuds component has spin 2, yield negative values for ${\mu }_s$. Here, the strangeness spin ${\Delta }_s$, strangeness magnetic moment ${\mu }_s$, and axial coupling constant $G_A^s$ are calculated for all possible configurations of the $\mathit{uuds}\overline{s}$ component of the proton. In the configuration with $[4]{}_{\mathit{FS}}[22]{}_F[22]{}_S$ flavor-spin symmetry, which is likely to have the lowest energy, ${\mu }_s$ is positive and ${\Delta }_s\simeq G_A^s\simeq -1/3{\mu }_s$.