In this work we look at the low-lying nuclear structure properties of several $N=Z$ nuclei residing between the doubly magic nuclei ${}^{40}$Ca and ${}^{100}$Sn. Using large shell model codes, we calculate and discuss the systematics of energies. We show energy levels, $B\left(E2\right)$'s, static quadrupole moments, and $g$ factors of these $N=Z$ nuclei. In all cases, we compare the results of two different interactions which yield significantly different occupation numbers. We compare our shell model results with those of the rotational and vibrational models. By examining $B\left(E2\right)$'s and static quadrupole moments, we make associations with collective models and find that in the model space considered here, ${}^{88}$Ru is oblate. The quadrupole moment of the lowest 2${}^{+}$state of ${}^{92}$Pd is calculated to be very small. This would appear to support a vibrational picture and indeed recent measurements give equally spaced levels up to $J=6^{+}$ but the authors also point out that the $B\left(E2\right)$'s do not steadily increase as is required by such a model.

Based on the framework of the isospin-dependent quantum molecular dynamics (IQMD) model in which the initial neutron and proton densities are sampled according to the droplet model, the correlation between triton-to-${}^3$He yield ratio $[R\left(t{/}^3\mathrm{He}\right)=\mathrm{Yield}\left(t\right)/\mathrm{Yield}{(}^3\mathrm{He})$] and neutron skin thickness (${\delta }_{np}$) in neutron-rich projectile induced reactions is investigated. By changing the diffuseness parameter of neutron density distribution in the droplet model for the projectile to obtain different ${\delta }_{np}$, the relationship between ${\delta }_{np}$ and the corresponding $R$($t$/${}^3$He) in semiperipheral collisions is obtained. The calculated results show that $R$($t$/${}^3$He) has a strong linear correlation with ${\delta }_{np}$ for neutron-rich ${}^{50}$Ca and ${}^{68}$Ni nuclei. It is suggested that $R$($t$/${}^3$He) could be regarded as a good experimental observable to extract ${\delta }_{np}$ for neutron-rich nuclei because the yields of charged particles triton and ${}^3$He can be measured quite precisely.

Background: The ${}^{17}O(p,\gamma ){}^{18}F$ reaction affects the production of key isotopes (e.g., ${}^{18}F$ and ${}^{18}O$) in the explosive hydrogen burning that powers classical novae. Under these explosive conditions, the reaction rate is dominated by contributions from a narrow resonance at $E_{\mathrm{c}.\mathrm{m}.}=183\mathrm{keV}$ and by the combined contributions of direct capture and low-energy tails of broad resonances. At present, the astrophysical reaction rate is not well constrained because of the lack of data in the energy region appropriate to classical novae.

Purpose: This study aims at the measurement of the ${}^{17}O$$(p,\gamma ){}^{18}F$ reaction cross section in order to determine its reaction rate in the temperature region appropriate to explosive hydrogen burning in novae.

Method: The ${}^{17}O$$(p,\gamma ){}^{18}F$ reaction cross section was measured using both the prompt detection of the emitted $\gamma$ rays and an activation technique. Measurements were carried out at the Laboratory for Underground Nuclear Astrophysics (Gran Sasso, Italy) where the strongly reduced cosmic-ray-induced background allows for improved sensitivity compared to previous studies.

Results: The ${}^{17}O$$(p,\gamma ){}^{18}F$ reaction cross section was measured in the range $E_{\mathrm{c}.\mathrm{m}.}=160$ to $370\mathrm{keV}$. The strength of the $E_{\mathrm{c}.\mathrm{m}.}=183\mathrm{keV}$ resonance, $\omega \gamma =1.67\pm 0.12\mu \mathrm{eV}$, was determined with unprecedented precision. The total $S$ factor was obtained through a combined fit of prompt $\gamma$-ray and activation results. An overall global fit including other existing data sets was also carried out and a recommended astrophysical reaction rate is presented.

Conclusions: The reaction rate uncertainty attained in this work is now below the required precision for nova models. We verified, following a full set of hydrodynamic nova models, that the abundances of oxygen and fluorine isotopes obtained with the present reaction rate are determined with 10% precision and put firmer constraints on observational signatures of novae events.

A five-body calculation of ${}^{12}$C$+n+n+p+p$ is performed to take a step towards solving an outstanding problem in nuclear theory: the simultaneous and accurate description of the ground and first excited 0${}^{+}$ states of ${}^{16}$O. The interactions between the constituent particles are chosen consistently with the energies of bound subsystems, especially ${}^{12}$C$+n$, ${}^{12}$C$+p$, and the $\alpha$ particle. The five-body dynamics is solved with the stochastic variational method on correlated Gaussian basis functions. No restriction is imposed on the four-nucleon configurations except for the Pauli principle excluding the occupied orbits in ${}^{12}$C. The energies of both the ground and first excited states of ${}^{16}$O are obtained in excellent agreement with experiment. Analysis of the wave functions indicates a spatially localized $\alpha$-particle-like cluster structure for the excited state and a shell-model-like delocalized structure for the ground state.

We investigate the precession motion of the exotic torus configuration in high-spin excited states of ${}^{40}$Ca. For this aim, we use the three-dimensional time-dependent Hartree-Fock (TDHF) method. Although the high-spin torus isomer is a unique quantum object characterized by the alignment of angular momenta of independent single-particle motions, we find that the obtained moment of inertia for rotations about an axis perpendicular to the symmetry axis is close to the rigid-body value. We also analyze the microscopic structure of the precession motion using the random-phase approximation (RPA) method for high-spin states. In the RPA calculation, the precession motion of the torus isomer is generated by coherent superposition of many one-particle–one-hole excitations across the sloping Fermi surface that strongly violates the time-reversal symmetry. By comparing results of the TDHF and the RPA calculations, we find that the precession motion obtained by the TDHF calculation is a pure collective motion well decoupled from other collective modes.

We explore the role of final-state interactions (FSIs) in inclusive deep-inelastic scattering from the deuteron. Relating the inclusive cross section to the deuteron forward virtual Compton scattering amplitude, a general formula for the FSI contribution is derived in the generalized eikonal approximation, utilizing the diffractive nature of the effective hadron-nucleon interaction. The calculation uses a factorized model with a basis of three resonances with mass $W<2$ GeV and a continuum contribution for larger $W$ as the relevant set of effective hadron states entering the final-state interaction amplitude. The results show sizeable on-shell FSI contributions for Bjorken $x\gtrsim 0.6$ and $Q^2\lesssim 10$ GeV${}^2$, increasing in magnitude for lower $Q^2$, but vanishing in the high-$Q^2$ limit because of phase-space constraints. The off-shell rescattering contributes at $x\gtrsim 0.8$ and is taken as an uncertainty on the on-shell result.

High precision measurements of the parity-violating asymmetry in polarized electron scattering from nuclei can be used to extract information on nuclear and nucleon structure or to determine standard model couplings and higher-order radiative corrections. To this end, low uncertainties are also required in the effects that inevitably arise from modeling the underlying nuclear structure. An experimental precision of a few tenths of a percent may be attainable for the asymmetry if the appropriate kinematic range is chosen, as will be discussed here for the case of ${}^{12}$C. And given this, the dual goal of ascertaining both the sizes of various nuclear structure related effects and of providing estimates of their uncertainties for this particular target will be discussed.

The influence of pairing correlations on the size of the nucleus and the development of nuclear halos is studied in the framework of relativistic continuum Hartree-Bogoliubov theory. It turns out that the contributions of weakly bounded orbits in the continuum with low orbital angular momenta $l$ play an essential role. Pairing correlations have a two-fold influence on the density distribution of the neutrons and therefore on the total nuclear size. First, they can change the root-mean-square radius of the individual weakly bound orbits and, second, they can change the occupation probabilities of these orbits in the nuclear system. Both effects are important, and finally the total radius is dominated by their competition.

Elastic scattering angular distribution measurements of the weakly bound ${}^{6,7}$Li projectiles on a ${}^{232}$Th target have been carried out at different bombarding energies close to the Coulomb barrier. The data have been analyzed for both systems using the optical model ecis code with phenomenological Woods-Saxon and Sao Paulo double-folding forms of the optical potentials. The energy dependence of the volume-type real and imaginary parts of the optical potentials are derived from the best fit of the experimental angular distribution data. The usual threshold anomaly has been observed for the ${}^7$Li + ${}^{232}$Th system, whereas there is an indication of a breakup threshold anomaly in case of the ${}^6$Li + ${}^{232}$Th system. Results on total reaction cross sections obtained from the optical model analysis for both systems have been interpreted to understand the role of projectile breakup on the reaction mechanism.

Prompt fission neutron spectra in the neutron-induced fission of ${}^{239}$Pu have been measured for incident neutron energies from 1 to 200 MeV at the Los Alamos Neutron Science Center. Mean energies deduced from the prompt fission neutron spectra (PFNS) lead to the observation of the opening of the second chance fission at 7 MeV and to indications for the openings of fission channels of third and fourth chances. Moreover, the general trend of the measured PFNS is well reproduced by the different models. The comparison between data and models presents, however, two discrepancies. First, the prompt neutron mean energy seems constant for neutron energy, at least up to 7 MeV, whereas in the theoretical calculations it is continuously increasing. Second, data disagree with models on the shape of the high energy part of the PFNS, where our data suggest a softer spectrum than the predictions.

Poisson-like statistical fluctuations, which are caused by the finite number of produced particles, are estimated for the cumulants of conserved charges, i.e., net baryon, net electric, and net strangeness. They turn out to be the same as those baselines derived from the hadron resonance gas model. The energy and centrality dependence of net-proton cumulants at the Relativistic Heavy-Ion Collider (RHIC) are demonstrated to be mainly caused by statistical fluctuations. By subtracting the statistical fluctuations, the dynamical kurtosis of net- and total-proton cumulants from two versions of a multi-phase transport model and the ultra-relativistic quantum molecular dynamics model at current RHIC collision energies are presented. It is found that the observed sign change of the dynamical kurtosis of the net-proton cumulant cannot be reproduced by these three transport models. There is no significant difference between the net- and total-proton kurtosis in model calculations, in contrast to the data at RHIC.

In recent years, the $N=90$ isotones have been investigated to a large extent in relation to studies of quantum phase transitions. In this paper, we use the mean field approach with pairing-deformation self-consistent total Routhian surface (TRS) calculations to study the $N=90$ isotones and neighboring nuclei. The important probes, such as moments of inertia, quadrupole moments, the energy ratio of $E\left(4_1^{+}\right)/E\left(2_1^{+}\right)$, and octupole and hexadecapole degrees of freedom are considered and the calculated results are compared with the available experimental data. From a microscopic point of view, the $N=90$ isotones characterize the onset of the deformed region and are very well described by mean field calculations. The results are compared with those from other studies in beyond mean field approximations. Shape coexistence phenomena in the region of interest are discussed.

Background: Models based on using perturbative polarization corrections and mean-field blocking approximation give conflicting results for masses of odd nuclei.

Purpose: We systematically investigate the polarization and mean-field models, implemented within self-consistent approaches that use identical interactions and model spaces, to find reasons for the conflicts between them.

Methods: For density-dependent interactions and with pairing correlations included, we derive and study links between the mean-field and polarization results obtained for energies of odd nuclei. We also identify and discuss differences between the polarization-correction and full particle-vibration-coupling (PVC) models. Numerical calculations are performed for the mean-field ground-state properties of deformed odd nuclei and then compared to the polarization corrections determined using the approach that conserves spherical symmetry.

Results: We have identified and numerically evaluated self-interaction (SI) energies that are at the origin of different results obtained within the mean-field and polarization-correction approaches.

Conclusions: Mean-field energies of odd nuclei are polluted by the SI energies, and this makes them different from those obtained using polarization-correction methods. A comparison of both approaches allows for the identification and determination of the SI terms, which then can be calculated and removed from the mean-field results, giving the self-interaction-free energies. The simplest deformed mean-field approach that does not break parity symmetry is unable to reproduce full PVC effects.

The new neutron-deficient isotope ${}^{205}$Ac was synthesized in the complete-fusion reaction ${}^{169}$Tm(${}^{40}$Ca, $4n$)${}^{205}$Ac. The evaporation residues were separated in-flight by the gas-filled recoil separator SHANS in Lanzhou and subsequently identified by the $\alpha$-$\alpha$ position and time correlation method. The $\alpha$-decay energy and half-life of ${}^{205}$Ac were determined to be 7.935(30) MeV and 20${}_{-9}^{+97}$ ms, respectively. Previously reported decay properties of the ground state in ${}^{206}$Ac were confirmed.

We present a fully self-consistent computational framework composed by Hartree-Fock plus random-phase approximation where the spin-orbit and Coulomb terms of the interaction are included in both steps of the calculations. We study the effects of these terms of the interaction on the random-phase approximation calculations, where they are usually neglected. We carry out our investigation of excited states in spherical nuclei of oxygen, calcium, nickel, zirconium, tin, and lead isotope chains. We use finite-range effective nucleon-nucleon interactions of Gogny type. The size of the effects we find is, usually, of a few hundred keV. There are not simple approximations which can be used to simulate these effects since they strongly depend on all the variables related to the excited states, angular momentum, parity, excitation energy, isoscalar, and isovector characters. Even the Slater approximation developed to account for the Coulomb exchange terms in the Hartree-Fock approximation is not valid in random-phase approximation calculations.

The nucleus ${}^{35}S$ has been studied by in-beam $\gamma$-ray spectroscopy using the ${}^{24}$Mg(${}^{14}$N,$3p$) fusion-evaporation reaction at $E_{\mathrm{lab}}=40$ MeV. A level scheme extended up to $J^{\pi }=17/2^{+}$ at 8023 keV and $J^{\pi }=13/2^{-}$ at 6352 keV has been established. Lifetimes of six excited states have been determined by applying the Doppler shift attenuation method. The experimental data have been compared with the results of large-scale shell model calculations performed using different effective interactions and model spaces allowing particle-hole excitations across the $N=Z=20$ shell gap.

Background: In electron-capture decay, a second $K$-shell vacancy is eventually created with a small probability. Measurements of the double-vacancy creation probability per $K$-shell electron capture $P_{KK}$ of various nuclei undergoing electron-capture decays have already been performed, but the statistical accuracy of $P_{KK}$ of several nuclides is still not satisfying.

Purpose: The purpose of this experiment was to improve the statistical error of $P_{KK}$ in the decay of ${}^{55}\mathrm{Fe}$ and to demonstrate the possibility of detecting double-vacancy creation events with position resolving pixel detectors. This enables angle resolved measurements.

Method: For the first time, two active-pixel detectors (A,B) were used to detect satellite- and hypersatellite-line photons in coincidence either both in two clusters of triggered pixels in only one detector (A,B) or in both detectors $(\text{A}\wedge \text{B})$. $P_{KK}$ was determined for the two detectors regarded as one single, larger detector ($P_{KK}$), for each detector separately (single-sided analysis: $P_{KK,\text{A}⊻\text{B}}$), and for both detectors in coincidence (double-sided analysis: $P_{KK,\text{A}\wedge \text{B}}$).

Results: The result of the experiment is $P_{KK}=(1.531\pm 0.079)\times {10}^{-4}$ with a systematic error of ${\left(\Delta P_{KK}\right)}_{\text{syst}}=\pm 0.023\times {10}^{-4}$. This value is in agreement with the value previously measured by Campbell et al. of $P_{KK}=(1.3\pm 0.2)\times {10}^{-4}$. The discrepancy in literature between $P_{KK}$ of ${}^{54}\mathrm{Mn}$ to the expected value extrapolated from ${}^{55}\mathrm{Fe}$ almost vanished with our result. The asymmetry between the result of the single-sided analysis ($P_{KK,\text{A}⊻\text{B}}$) and the double-sided analysis ($P_{KK,\text{A}\wedge \text{B}}$) is consistent with zero: $(P_{KK,\text{A}⊻\text{B}}-P_{KK,\text{A}\wedge \text{B}})/(P_{KK,\text{A}⊻\text{B}}+P_{KK,\text{A}\wedge \text{B}})=-0.003\pm 0.051$. This supports the assumption that angular correlations between the two photons are negligible within the achieved level of statistical accuracy for the given angular acceptance of our detectors.

Conclusions: One can conclude that hybrid photon counting pixel detectors can be used to measure angular correlations between the directions of emission of satellite and hypersatellite photons. Our result supports the suspicion that the reported discrepancy between $P_{KK}$ measured for the electron-capture decays of ${}^{54}\mathrm{Mn}$ and ${}^{55}\mathrm{Fe}$ was probably due to statistical fluctuations in the measurements. Furthermore, the $Z^{-2}$ dependence of $P_{KK}$ predicted by Primakoff and Porter is supported. The improved statistical error of our measurements underlines the previously reported discrepancy between $P_{KK}$ expected for ${}^{65}\mathrm{Zn}$ if an extrapolation is carried out from our result on ${}^{55}\mathrm{Fe}$. Thus, our result strengthens the need for triple coincidence measurements of $P_{KK}$ on ${}^{65}\mathrm{Zn}$.

We derive expressions for $\mathrm{core}+N+N$ overlap integrals starting from microscopic wave functions obtained in the ab initio no-core shell model. These overlap integrals correspond to three-body channel form factors and can be used to investigate the clustering of many-body systems into a core plus two nucleons. We consider the case when the composite system and the core are described in Slater determinant, harmonic oscillator bases, and we show how to remove spurious center-of-mass components exactly in order to derive translationally invariant overlap integrals. We study in particular the Borromean ${}^6$He nucleus using realistic chiral nuclear interactions, and we demonstrate that the observed clusterization in this system is a Pauli focusing effect. The inclusion of three-body forces has a small effect on this structure. In addition, we discuss the issue of absolute normalization for spectroscopic factors, which we show is larger than one. As part of this study we also perform extrapolations of ground-state observables and investigate the dependence of these results on the resolution scale of the interaction.

We use the ultrarelativistic quantum molecular-dynamics model to simulate Pb + Pb collisions. In the freeze-out geometry of noncentral Pb + Pb collisions we observe a tilt of the particle emission zone in the collision plane away from the beam axis. We find that the magnitude of this tilt depends on the scale at which the distribution is measured. We quantify this “twisting” behavior with a parametrization and propose to measure it experimentally via azimuthally sensitive Hanbury-Brown–Twiss (HBT) correlations. Additionally we show that the twist is related to the emission of particles from different times during the evolution of the source. A systematic comparison between the theoretically observed twist in the freeze-out position distribution and a mock experimental analysis of the model calculations via HBT correlations is shown.