It is shown that the use of a proper form factor in the study of the pygmy dipole resonance (PDR) is of paramount importance in order to determine the correct values for the relevant quantities characterizing these new modes. Form factors calculated within a microscopic model are compared with those provided by different macroscopic collective models. Their differences, shown in the shape and magnitude, are reflected on the calculated cross section and therefore jeopardize the extracted physical quantities.

Background: The fusion-evaporation reaction at energies around the Coulomb barrier is presently the only way to produce the heaviest elements. However, formation of evaporation residues is strongly hindered due to the competing fusion-fission and quasifission processes. Presently, a full understanding of these processes and their relationships has not been reached.

Purpose: This work aims to use new fission measurements and existing evaporation residue and fission excitation function data for reactions forming Cf isotopes to investigate the dependence of the quasifission probability and characteristics on the identities of the two colliding nuclei in heavy element formation reactions.

Method: Using the Australian National University's 14UD electrostatic accelerator and CUBE detector array, fission fragments from the ${}^{12}\mathrm{C}+{}^{235}\mathrm{U}$, ${}^{34}\mathrm{S}+{}^{208}\mathrm{Pb}$, ${}^{36}\mathrm{S}+{}^{206}\mathrm{Pb}$, ${}^{36}\mathrm{S}+{}^{208}\mathrm{Pb}$, and ${}^{44}\mathrm{Ca}+{}^{198}\mathrm{Pt}$ reactions were measured. Mass and angle distributions of fission fragments were extracted and compared to investigate the presence and characteristics of quasifission.

Results: Mass-angle-correlated fission fragments were observed for the ${}^{44}\mathrm{Ca}+{}^{198}\mathrm{Pt}$ reaction; no correlation was observed in the other reactions measured. Flat-topped fission-fragment mass distributions were observed for ${}^{12}\mathrm{C}+{}^{235}\mathrm{U}$ at compound-nucleus excitation energies from 28 to 52 MeV. Less pronounced flat-topped distributions were observed, with very similar shapes, for all three sulfur-induced reactions at excitation energies lower than 45 MeV.

Conclusions: A high probability of long-time-scale quasifission seems necessary to explain both the fission and evaporation residue data for the ${}^{34}\mathrm{S}+{}^{208}\mathrm{Pb}$ and ${}^{36}\mathrm{S}+{}^{206}\mathrm{Pb}$ reactions. Flat-topped mass distributions observed for ${}^{12}\mathrm{C}$- and ${}^{34,36}\mathrm{S}$-induced reactions are suggested to originate both from late-chance fusion-fission at low excitation energies and the persistence of shell effects at the higher energies associated with quasifission.

The dependence of the momentum-dependent symmetry potential on the nuclear collective flows produced in semicentral ${}^{197}\mathrm{Au}+{}^{197}\mathrm{Au}$ collisions at incident energies from 250 to 800A MeV has been investigated within the isospin-dependent quantum molecular dynamics model. It is found that the theoretical results overestimate the values of the experimental data on directed flow of protons in the domain of large rapidities but can reproduce well the one of mass-three cluster. Neutron-proton differential flows and difference of neutron-proton collective flows are sensitive to the momentum-dependent symmetry potential, especially in the domain of larger rapidities and momenta. This sensitivity becomes stronger with increasing cut of the transverse velocity and becomes smaller with increasing incident energies.

The possibilities of production of yet-undiscovered neutron-rich isotopes of Ca, Gd, Dy, Er, Yb, Hf, W, Os, Hg, Pb, and Th are explored in various multinucleon transfer reactions with stable and radioactive beams. The probable projectile-target combinations and bombarding energies to produce these neutron-rich isotopes are suggested for future experiments.

The ${}^{27}\mathrm{Al}\left(d,t\right)$ reaction has been studied to extract spectroscopic information for the odd-odd nucleus ${}^{26}\mathrm{Al}$. The excited states of ${}^{26}\mathrm{Al}$ up to 5.50 MeV have been analyzed using the local, zero range distorted wave Born approximation. A new set of optical model potential parameters was extracted from the measured elastic scattering angular distribution. The spectroscopic factors calculated for these states are found to be in good agreement with previously reported values for the same; they are also in agreement with those obtained from shell model predictions.

We consider the collinear ternary fission which is a sequential ternary decay with a very short time between the ruptures of two necks connecting the middle cluster of the ternary nuclear system and outer fragments. In particular, we consider the case where the Coulomb field of the first massive fragment separated during the first step of the fission produces a lower pre-scission barrier in the second step of the residual part of the ternary system. In this case, we obtain a probability of about ${10}^{-3}$ per binary fission for the yield of massive clusters such as ${}^{70}\mathrm{Ni},{}^{80-82}\mathrm{Ge},{}^{86}\mathrm{Se}$, and ${}^{94}\mathrm{Kr}$ in the ternary fission of ${}^{252}\mathrm{Cf}$. These products appear together with the clusters having mass numbers of $A=132–140$. The results show that the yield of a heavy cluster such as ${}^{68-70}\mathrm{Ni}$ would be followed by a product of $A=138–148$ with a large probability as observed in the experimental data obtained with the FOBOS spectrometer at the Joint Institute for Nuclear Research. The third product is not observed. The landscape of the potential-energy surface shows that the configuration of the $\mathrm{Ni}+\mathrm{Ca}+\mathrm{Sn}$ decay channel is lower by about 12 MeV than that of the $\mathrm{Ca}+\mathrm{Ni}+\mathrm{Sn}$ channel. This leads to the fact that the yield of $\mathrm{Ni}$ and $\mathrm{Sn}$ is large. The analysis on the dependence of the velocity of the middle fragment on mass numbers of the outer products leads to the conclusion that, in the collinear tripartition channel of ${}^{252}\mathrm{Cf}$, the middle cluster has a very small velocity, which does not allow it to be found in experiments.

Sub-barrier fusion cross sections for reactions involving stable and very neutron-rich nuclei, which may be important in determining the composition and heating of the crust of accreting neutron stars, are calculated using internuclear potentials derived from the microscopic Brueckner $G$-matrix and Skyrme SKM* and SLy4 energy density functionals. Microscopic Skyrme-Hartree-Fock proton and neutron density distributions are used. No parameters have been fit to fusion data. Calculations are performed for the isotopic reactions ${}^{16}\mathrm{O}+{}^{16}\mathrm{O},{}^{16}\mathrm{O}+{}^{24}\mathrm{O},{}^{16}\mathrm{O}+{}^{28}\mathrm{O},{}^{24}\mathrm{O}+{}^{24}\mathrm{O},{}^{12}\mathrm{C}+{}^{16}\mathrm{O},{}^{12}\mathrm{C}+{}^{24}\mathrm{O}$, and ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$, which are of great astrophysical importance for the understanding of the time scale and the nucleosynthesis during late stellar evolution. The coupling to the low lying excited states is considered through the ccfull code. I compare my results with the time-dependent-Hartree-Fock calculations and with the São Paulo model as well as the experimental data. I found a remarkable agreement with the fusion cross sections for stable nuclei.

We present a method to select events with a specific initial configuration, namely, the body-tip, in heavy-ion collisions using deformed uranium nuclei. We propose to use asymmetry in spectator neutron numbers to filter out these body-tip events from the unbiased configurations in U + U collisions. We have used a variable $S_{\eta }$ to differentiate between the body-tip and unbiased configurations. We have calculated the second-order azimuthal anisotropy, namely, elliptic flow $v_2$, for this body-tip configuration in the framework of a transport model and found it to be consistently lower compared to that in unbiased configurations as we expected. The purity of selecting such events in a real experiment is also discussed.

We propose a mechanism for the damping of density oscillations in multicomponent compact stars. The mechanism is the periodic conversion between different phases, i.e., the movement of the interface between them, induced by pressure oscillations in the star. The damping grows nonlinearly with the amplitude of the oscillation. We study in detail the case of r-modes in a hybrid star with a sharp interface, and we find that this mechanism is powerful enough to saturate the r-mode at very low saturation amplitude, of order ${10}^{-10}$, and is therefore likely to be the dominant r-mode saturation mechanism in hybrid stars with a sharp interface.

A triaxial shape-constrained Skyrme-Hartree-Fock mean-field model, employing a density-dependent pairing interaction and the $\mathrm{NSC}89 N\Lambda$ interaction, is used to investigate the potential energy surfaces of the $\Lambda$ hypernuclei ${}_{\Lambda }{}^{13}\mathrm{C},{}_{\Lambda }{}^{21}\mathrm{Ne},{}_{\Lambda }{}^{25,27}\mathrm{Mg}$, and ${}_{\Lambda }{}^{27,29}\mathrm{Si}$. Angular momentum projection and particle number projection techniques are applied to the axially deformed mean-field states to restore the symmetries lost in the mean-field calculation, and the energy spectra and $E2$ transition probabilities of several (hyper)nuclei are studied, demonstrating the shrinkage effect of the $\Lambda$, which is analyzed in detail.

Upon increasing significantly the nuclear elongation, the $\beta$-decay energy grows. This paper investigates within a simple yet partly microscopic approach, the transition rate of the ${\beta }^{-}$ decay of the ${}^{252}\mathrm{Cf}$ nucleus on the way to scission from the exit point for a spontaneous fission process. A rather crude classical approximation is made for the corresponding damped collective motion assumed to be one dimensional. Given these assumptions, we only aim in this paper at providing the order of magnitudes of such a phenomenon. At each deformation the energy available for ${\beta }^{-}$ decay, is determined from such a dynamical treatment. Then, for a given elongation, transition rates for the allowed (Fermi) $0^{+}⟶0^{+} \beta$ decay are calculated from pair correlated wave functions obtained within a macroscopic-microscopic approach and then integrated over the time corresponding to the whole descent from exit to scission. The results are presented as a function of the damping factor (inverse of the characteristic damping time) in use in our classical dynamical approach. For instance, in the case of a descent time from the exit to the scission points of about ${10}^{-20}$ s, one finds a total rate of $\beta$ decay corresponding roughly to 20 events per year and per milligram of ${}^{252}\mathrm{Cf}$. The inclusion of pairing correlations does not affect much these results.

In the standard Big-Bang nucleosynthesis (BBN) model, the primordial ${}^7\mathrm{Li}$ abundance is overestimated by about a factor of 2 to 3 compared to astronomical observations; this is the so-called pending cosmological lithium problem. The ${}^7\mathrm{Be}(n,\alpha ){}^4\mathrm{He}$ reaction was regarded as the secondary important reaction in affecting the ${}^7\mathrm{Li}$ abundance by destructing the ${}^7\mathrm{Be}$ nucleus in BBN. However, the reaction rate of ${}^7\mathrm{Be}(n,\alpha ){}^4\mathrm{He}$ has not been well studied so far. This reaction rate was first estimated by Wagoner in 1969, which has been primarily adopted in the current BBN simulations. This simple estimate involved only a direct reaction contribution, but the resonant component should also be considered according to the later experimental results. In the present work, we revised this rate based on the indirect cross-section data available for the ${}^4\mathrm{He}(\alpha ,n){}^7\mathrm{Be}$ and ${}^4\mathrm{He}(\alpha ,p){}^7\mathrm{Li}$ reactions by applying the charge symmetry and the principle of detailed balance. Our new result shows that the previous rate (acting as an upper limit) is overestimated by about a factor of ten. The BBN simulation shows that the present rate leads to a 1.2% increase in the final ${}^7\mathrm{Li}$ abundance compared with the result using the Wagoner rate and, hence, the present rate even worsens the ${}^7\mathrm{Li}$ problem. By the present estimation, the role of ${}^7\mathrm{Be}(n,\alpha ){}^4\mathrm{He}$ in destroying ${}^7\mathrm{Be}$ is weakened from the second most importance to the third and, in turn, the ${}^7\mathrm{Be}(d,p)2{}^4\mathrm{He}$ reaction becomes of secondary importance in destroying ${}^7\mathrm{Be}$.

The neutron drip transition in the dense matter constituting the interior of neutron stars generally refers to the appearance of unbound neutrons as the matter density reaches some threshold density ${\rho }_{\mathrm{drip}}$. This transition has been mainly studied under the cold catalyzed matter hypothesis. However, this assumption is unrealistic for accreting neutron stars. After examining the physical processes that are thought to be allowed in both accreting and nonaccreting neutron stars, suitable conditions for the onset of neutron drip are derived and general analytical expressions for the neutron drip density and pressure are obtained. Moreover, we show that the neutron drip transition occurs at lower density and pressure than those predicted within the mean-nucleus approximation. This transition is studied numerically for various initial composition of the ashes from x-ray bursts and superbursts using microscopic nuclear mass models.

The levels structure and electromagnetic transitions of ${}^{84,85}\mathrm{Ge},{}^{86,87}\mathrm{Se}$, and ${}^{88,89}\mathrm{Kr}$ isotopes have been investigated in the interacting boson model (IBM-2), including the interacting boson-fermion model (IBFM-2), as a first application of the model. In the calculation, the fermions are allowed to excite to the $2d_{5/2},1g_{7/2},2d_{3/2},3s_{1/2}$, and $1h_{11/2}$ single-particle orbitals. The results of the model calculation have been found to be in good agreement with both shell-model and available experimental data. Also the strong staggering of the yrast band has been found to be well described.

High-spin states in the odd-odd nucleus ${}^{136}\mathrm{La}$, which is located close to the $\beta$-stability line, have been investigated in the radioactive-beam-induced fusion-evaporation reaction ${}^{124}\mathrm{Sn}({}^{17}\mathrm{N},5n)$. The use of the radioactive beam enabled a highly sensitive and successful search for a new isomer [${14}^{+},T_{1/2}=187\left(27\right)$ ns] in ${}^{136}\mathrm{La}$. In the $A=130$–140 mass region, no such long-lived isomer has been observed at high spin in odd-odd nuclei. The ${}^{136}\mathrm{La}$ level scheme was revised, incorporating the ${14}^{+}$ isomer and six new levels. The results were compared with pair-truncated shell model (PTSM) calculations which successfully explain the level structure of the $\pi h_{11/2}\otimes \nu h_{11/2}^{-1}$ bands in ${}^{132}\mathrm{La}$ and ${}^{134}\mathrm{La}$. The isomerism of the ${14}^{+}$ state was investigated also by a collective model, the cranked Nilsson-Strutinsky (CNS) model, which explains various high-spin structures in the medium-heavy mass region. It is suggested that a new type of collective structure is induced in the PTSM model by the increase of the number of $\pi g_{7/2}$ pairs, and/or in the CNS model by the configuration change associated with the shape change in ${}^{136}\mathrm{La}$.

The heavy quark collisional scattering on partons of the quark gluon plasma (QGP) is studied in a quantum chromodynamics medium at finite temperature and chemical potential. We evaluate the effects of finite parton masses and widths, finite temperature $T$, and quark chemical potential ${\mu }_q$ on the different elastic cross sections for dynamical quasiparticles (on- and off-shell particles in the QGP medium as described by the dynamical quasiparticle model “DQPM”) using the leading order Born diagrams. Our results show clearly the decrease of the $qQ$ and $gQ$ total elastic cross sections when the temperature and the quark chemical potential increase. These effects are amplified for finite ${\mu }_q$ at temperatures lower than the corresponding critical temperature $T_c\left({\mu }_q\right)$. Using these cross sections we, furthermore, estimate the energy loss and longitudinal and transverse momentum transfers of a heavy quark propagating in a finite temperature and chemical potential medium. Accordingly, we have shown that the transport properties of heavy quarks are sensitive to the temperature and chemical potential variations. Our results provide some basic ingredients for the study of charm physics in heavy-ion collisions at Beam Energy Scan at RHIC and CBM experiment at FAIR.

The pasta phase in core-collapse supernova matter (finite temperatures and fixed proton fractions) is studied within relativistic mean-field models. Three different calculations are used for comparison: the Thomas–Fermi, the coexisting phases, and the compressible liquid drop approximations. The effects of including light clusters in nuclear matter and the densities at which the transitions between pasta configurations and to uniform matter occur are also investigated. The free energy, pressure, entropy, and chemical potentials in the range of particle number densities and temperatures expected to cover the pasta region are calculated. Finally, a comparison with a finite-temperature Skyrme–Hartree–Fock calculation is drawn.

Elastic-scattering measurements have been performed for the ${}^6\mathrm{Li}+p$ system in inverse kinematics at the energies of 16, 20, 25, and 29 MeV. The heavy ejectile was detected by the large acceptance MAGNEX spectrometer at the Laboratori Nazionali del Sud in Catania, Italy. The results are considered in a Jeukenne-Lejeune-Mahaux and a continuum discretized coupled-channel calculation framework.

Within schematic models based on the Tamm-Dancoff approximation and the random-phase approximation with separable interactions, we investigate the physical conditions that may determine the emergence of the pygmy dipole resonance in the $E1$ response of atomic nuclei. By introducing a generalization of the Brown-Bolsterli schematic model with a density-dependent particle-hole residual interaction, we find that an additional mode will be affected by the interaction, whose energy centroid is closer to the distance between two major shells and therefore well below the giant dipole resonance (GDR). This state, together with the GDR, exhausts all the transition strength in the Tamm-Dancoff approximation and all the energy-weighted sum rule in the random-phase approximation. Thus, within our scheme, this mode, which could be associated with the pygmy dipole resonance, is of collective nature. By relating the coupling constants appearing in the separable interaction to the symmetry energy value at and below saturation density we explore the role of density dependence of the symmetry energy on the low-energy dipole response.

The fragmentation of excited hypernuclear systems formed in heavy ion collisions has been described by the canonical thermodynamical model extended to three-component systems. The multiplicity distribution of the fragments has been analyzed in detail and it has been observed that the hyperons tend to get attached to the heavier fragments. Another important observation is the phase coexistence of the hyperons, a phenomenon which is linked to the liquid-gas phase transition in strange matter.