Weak-interaction rates, including $\beta$ decay and electron capture, are studied in several odd-$A$ nuclei in the $pf$-shell region at various densities and temperatures of astrophysical interest. Special attention is paid to the relative contribution to these rates of thermally populated excited states in the decaying nucleus. The nuclear structure involved in the weak processes is studied within a quasiparticle random-phase approximation with residual interactions in both particle-hole and particle-particle channels on top of a deformed Skyrme Hartree–Fock mean field with pairing correlations. In the range of densities and temperatures considered, it is found that the total rates do not differ much from the rates of the ground state fully populated. In any case, the changes are not larger than the uncertainties due to the nuclear-model dependence of the rates.

Background: It was suggested that the shape of the barrier height distribution can be determined not only by strong reaction channels (collective excitations) but also by weak channels such as transfers and/or noncollective excitations.

Purpose: The study of the barrier height distributions for the ${}^{20}\mathrm{Ne}+{}^{58,60,61}\mathrm{Ni}$ systems requires information on transfer cross sections at near-barrier energies.

Methods: A measurement of the cross sections for various transfer channels at a backward angle (142 degrees), at a near-barrier energy was performed. Identification of products was based on time-of-flight and $\mathrm{\Delta }E\text{−}E$ methods. A measurement of the angular distribution of $\alpha$ stripping in the ${}^{20}\mathrm{Ne}+{}^{61}\mathrm{Ni}$ system was performed using a gas $\mathrm{\Delta }E\text{−}E$ telescope.

Results: For all three systems studied: ${}^{20}\mathrm{Ne}+{}^{58}\mathrm{Ni},{}^{60}\mathrm{Ni}$, and ${}^{61}\mathrm{Ni}$ total (sum of all transfer channels) cross sections are similar and dominated by $\alpha$ stripping.

Conclusions: The results, as well as coupled reaction channel calculations, suggest that transfer is not responsible for smoothing the barrier height distribution in ${}^{20}\mathrm{Ne}+{}^{61}\mathrm{Ni}$, supporting the hypothesis that barrier distribution shapes are influenced by noncollective excitations.

Total thermal radiative neutron cross sections have been measured on natural and enriched isotopic targets containing ${}^{6,7}\mathrm{Li},{}^9\mathrm{Be},{}^{10,11}\mathrm{B},{}^{12,13}\mathrm{C}$, and ${}^{14,15}\mathrm{N}$ with neutron beams from the Budapest Reactor. Complete neutron capture $\gamma$-ray decay schemes were measured for each isotope. Absolute transition probabilities have been determined by a least-squares fit of the transition intensities, corrected for internal conversion, to the $\left(n,\gamma \right)$ decay schemes. The $\gamma$-ray cross sections were standardized using stoichiometric compounds containing both the isotope of interest and another element whose $\gamma$-ray cross sections are well known. Total cross sections ${\sigma }_0$ were then determined for each isotope from the $\gamma$-ray cross sections and transition probabilities. For the ${}^{11}\mathrm{B}\left(n,\gamma \right){}^{12}\mathrm{B}$ reaction decay transition probabilities were determined for the $\gamma$ rays from ${}^{12}\mathrm{B}$ ($t_{1/2}=20.20$ ms) ${\beta }^{-}$ decay.

In this paper we present first results for prompt fission $\gamma$-ray spectra (PFGS) characteristics from the spontaneous fission (sf) of ${}^{240}\mathrm{Pu}$ and ${}^{242}\mathrm{Pu}$. For ${}^{242}\mathrm{Pu}\left(\mathrm{sf}\right)$ we obtained, after proper unfolding of the detector response, an average energy per photon ${\overline{\epsilon }}_{\gamma }=(0.843\pm 0.012)$ MeV, an average multiplicity ${\overline{M}}_{\gamma }=(6.72\pm 0.07)$, and an average total $\gamma$-ray energy release per fission ${\overline{E}}_{\gamma ,\mathrm{tot}}$ = ($5.66 \pm$ 0.06) MeV. The ${}^{240}\mathrm{Pu}\left(\mathrm{sf}\right)$ emission spectrum was obtained by applying a so-called detector-response transformation function determined from the ${}^{242}\mathrm{Pu}$ spectrum measured in exactly the same geometry. The results are an average energy per photon ${\overline{\epsilon }}_{\gamma }=(0.80\pm 0.07)$ MeV, the average multiplicity ${\overline{M}}_{\gamma }$ = ($8.2 \pm$ 0.4), and an average total $\gamma$-ray energy release per fission ${\overline{E}}_{\gamma ,\mathrm{tot}}$ = ($6.6 \pm$ 0.5) MeV. The PFGS characteristics for ${}^{242}\mathrm{Pu}\left(\mathrm{sf}\right)$ are in very good agreement with those from thermal-neutron-induced fission on ${}^{241}\mathrm{Pu}$ and scales well with the corresponding prompt neutron multiplicity. Our results in the case of ${}^{240}\mathrm{Pu}\left(\mathrm{sf}\right)$, although drawn from a limited number of events, show a significantly enhanced average multiplicity and average total energy, but may be understood from a different fragment yield distribution in ${}^{240}\mathrm{Pu}\left(\mathrm{sf}\right)$ compared to that of ${}^{242}\mathrm{Pu}\left(\mathrm{sf}\right)$.

A quark propagating through the quark gluon plasma and scattering off the thermal gluons can radiate photons in states with definite angular momentum and magnetic helicity. These states, known as the Chandrasekhar-Kendall states, are eigenstates of the curl operator and have a nontrivial topology. I compute the spectrum of these states in the ultrarelativistic limit and study its properties.

In central Au-Au collisions at top RHIC energy, two-particle correlation measurements with identified hadron trigger have shown attenuation of near-side proton triggered jetlike yield at intermediate transverse momentum $\left(p{}_T\right),2<p{}_T<6\mathrm{GeV}/\mathit{c}$. The attenuation was attributed to the anomalous baryon enhancement observed in the single inclusive measurements at the same $p{}_T$ range. The enhancement was found to be in agreement with the models invoking coalescence of quarks as a mechanism of hadronization. Baryon enhancement was also observed at LHC in the single inclusive spectra. We study the consequence of such an enhancement on two-particle correlations at LHC energy within the framework of a multiphase transport (AMPT) model that implements quark coalescence as a mode of hadronization. In this paper we have calculated the proton over pion ratio and the near side per trigger yield associated with pion and proton triggers at intermediate $p{}_T$ from the string melting (SM) version of AMPT. Results obtained are contrasted with the AMPT default (Def.) which does not include coalescence. Baryon enhancement was observed in AMPT SM at intermediate $p{}_T$. Near-side jetlike correlated yield associated with baryon (proton) trigger in the momentum region where baryon generation is enhanced is found to be suppressed as compared to the corresponding yields for the meson (pion) trigger in most central Pb-Pb events. No such effect was found in the default version of AMPT.

The mass splitting of elliptic anisotropy $\left(v_2\right)$ at low transverse momentum is considered as a hallmark of hydrodynamic collective flow. We investigate a multiphase transport (AMPT) model where the $v_2$ is mainly generated by an anisotropic escape mechanism, not of the hydrodynamic flow nature, and where mass splitting is also observed. We demonstrate that the $v_2$ mass splitting in AMPT is small right after hadronization (especially when resonance decays are included); the mass splitting mainly comes from hadronic rescatterings, even though their contribution to the overall charged hadron $v_2$ is small. These findings are qualitatively the same as those from hybrid models that combine hydrodynamics with a hadron cascade. We further show that there is no qualitative difference between heavy ion collisions and small system collisions. Our results indicate that the $v_2$ mass splitting is not a unique signature of hydrodynamic collective flow and thus cannot distinguish whether the elliptic flow is generated mainly from hydrodynamics or the anisotropic parton escape.

Polarization observables in neutron-deuteron scattering are calculated to next-to-next-to-next-to-leading order $({\mathrm{N}}^3\mathrm{LO})$ in pionless effective field theory $\left({\mathrm{EFT}}_{\neg \pi }\right)$. At ${\mathrm{N}}^3\mathrm{LO}$ the two-body $P$-wave contact interactions are found to be important contributions to the neutron vector analyzing power, $A_y\left(\theta \right)$, and the deuteron vector analyzing power, $i{T}_{11}\left(\theta \right)$. Extracting the two-body $P$-wave ${\mathrm{EFT}}_{\neg \pi }$ coefficients from two-body scattering data and varying them within the expected ${\mathrm{EFT}}_{\neg \pi }$ theoretical errors provides results that are consistent (at the ${\mathrm{N}}^3\mathrm{LO}$ level) with $A_y$ experimental data at low energies. Cutoff dependence of the ${\mathrm{N}}^3\mathrm{LO}$ correction of the doublet $S$-wave $nd$ scattering amplitude suggests the need for a new three-body force at ${\mathrm{N}}^3\mathrm{LO}$, which is likely one that mixes Wigner-symmetric and Wigner-antisymmetric three-body channels.

The $\beta$ decay and $\beta$-delayed neutron emission of ${}^{102}\mathrm{Rb}$ have been studied using the $8\pi$ spectrometer at TRIUMF-ISAC. The level scheme of ${}^{102}\mathrm{Sr}$ has been expanded from results of a $\gamma -\gamma$ coincidence analysis, including the identification of the $(4^{+})$ member of the ground-state band. The $\beta$-delayed neutron branching ratio of ${}^{102}\mathrm{Rb}$ was found to be significantly larger than previously reported. This larger value has the potential to modify the results of $r$-process calculations and motivates further measurements as well as refinements of theoretical models.

The low-spin structure of the ${}^{210}\mathrm{Bi}$ nucleus was investigated in the neutron capture experiment ${}^{209}\mathrm{Bi}\left(n,\gamma \right){}^{210}\mathrm{Bi}$ performed at ILL Grenoble at the PF1B cold-neutron facility. By using the EXILL multidetector array, consisting of 46 high-purity germanium crystals, and $\gamma \gamma$-coincidence technique, 64 primary $\gamma$ rays were observed (40 new) and a total number of 70 discrete states (33 new) were located below the neutron binding energy in ${}^{210}\mathrm{Bi}$. The analysis of the angular correlations of $\gamma$ rays provided information about transitions multipolarities, which made it possible to confirm most of the previously known spin-parity assignments and helped establish new ones. The obtained experimental results were compared to shell-model calculations involving one-valence-proton, one-valence-neutron excitations outside the ${}^{208}\mathrm{Pb}$ core. It has been found that while up to the energy of $\sim 2$ MeV each state observed in ${}^{210}\mathrm{Bi}$ has its calculated counterpart; at higher excitation energies some levels cannot be described by the valence particle couplings. These states may arise from couplings of valence particles to the $3^{-}$ octupole phonon of the doubly magic ${}^{208}\mathrm{Pb}$ core and may serve as a testing ground for models which describe single particle-phonon excitations.

The electromagnetic structure of ${}^{140}\mathrm{Sm}$ was studied in a low-energy Coulomb excitation experiment with a radioactive ion beam from the REX-ISOLDE facility at CERN. The $2^{+}$ and $4^{+}$ states of the ground-state band and a second $2^{+}$ state were populated by multistep excitation. The analysis of the differential Coulomb excitation cross sections yielded reduced transition probabilities between all observed states and the spectroscopic quadrupole moment for the $2_1^{+}$ state. The experimental results are compared to large-scale shell model calculations and beyond-mean-field calculations based on the Gogny D1S interaction with a five-dimensional collective Hamiltonian formalism. Simpler geometric and algebraic models are also employed to interpret the experimental data. The results indicate that ${}^{140}\mathrm{Sm}$ shows considerable $\gamma$ softness, but in contrast to earlier speculation no signs of shape coexistence at low excitation energy. This work sheds more light on the onset of deformation and collectivity in this mass region.

Background: Time-dependent density functional theory is widely used to describe excitations of many-fermion systems. In its many applications, three-dimensional (3D) coordinate-space representation is used, and infinite-domain calculations are limited to a finite volume represented by a spatial box. For finite quantum systems (atoms, molecules, nuclei, hadrons), the commonly used periodic or reflecting boundary conditions introduce spurious quantization of the continuum states and artificial reflections from boundary; hence, an incorrect treatment of evaporated particles.

Purpose: The finite-volume artifacts for finite systems can be practically cured by invoking an absorbing potential in a certain boundary region sufficiently far from the described system. However, such absorption cannot be applied in the calculations of infinite matter (crystal electrons, quantum fluids, neutron star crust), which suffer from unphysical effects stemming from a finite computational box used. Here, twist-averaged boundary conditions (TABC) have been used successfully to diminish the finite-volume effects. In this work, we extend TABC to time-dependent modes.

Method: We use the 3D time-dependent density functional framework with the Skyrme energy density functional. The practical calculations are carried out for small- and large-amplitude electric dipole and quadrupole oscillations of ${}^{16}\mathrm{O}$. We apply and compare three kinds of boundary conditions: periodic, absorbing, and twist-averaged.

Results: Calculations employing absorbing boundary conditions (ABC) and TABC are superior to those based on periodic boundary conditions. For low-energy excitations, TABC and ABC variants yield very similar results. With only four twist phases per spatial direction in TABC, one obtains an excellent reduction of spurious fluctuations. In the nonlinear regime, one has to deal with evaporated particles. In TABC, the floating nucleon gas remains in the box; the amount of nucleons in the gas is found to be roughly the same as the number of absorbed particles in ABC.

Conclusion: We demonstrate that by using TABC, one can reduce finite-volume effects drastically without adding any additional parameters associated with absorption at large distances. Moreover, TABC are an obvious choice for time-dependent calculations for infinite systems. Since TABC calculations for different twists can be performed independently, the method is trivially adapted to parallel computing.

A novel method for calculating spectroscopic properties of medium-mass and heavy atomic nuclei with an odd number of nucleons is introduced, based on the framework of nuclear energy density functional theory and the particle-core coupling scheme. The deformation energy surface of the even-even core, as well as the spherical single-particle energies and occupation probabilities of the odd particle(s), are obtained in a self-consistent mean-field calculation determined by the choice of the energy density functional and pairing interaction. This method uniquely determines the parameters of the Hamiltonian of the boson core, and only the strength of the particle-core coupling is specifically adjusted to selected data for a particular nucleus. The approach is illustrated in a systematic study of low-energy excitation spectra and transition rates of axially deformed odd-mass Eu isotopes.

Background: Models describing nuclear fragmentation and fragmentation fission deliver important input for planning nuclear physics experiments and future radioactive ion beam facilities. These models are usually benchmarked against data from stable beam experiments. In the future, two-step fragmentation reactions with exotic nuclei as stepping stones are a promising tool for reaching the most neutron-rich nuclei, creating a need for models to describe also these reactions.

Purpose: We want to extend the presently available data on fragmentation reactions towards the light exotic region on the nuclear chart. Furthermore, we want to improve the understanding of projectile fragmentation especially for unstable isotopes.

Method: We have measured projectile fragments from ${}^{10,12-18}\mathrm{C}$ and ${}^{10-15}\mathrm{B}$ isotopes colliding with a carbon target. These measurements were all performed within one experiment, which gives rise to a very consistent data set. We compare our data to model calculations.

Results: One-proton removal cross sections with different final neutron numbers $\left(1pxn\right)$ for relativistic ${}^{10,12-18}\mathrm{C}$ and ${}^{10-15}\mathrm{B}$ isotopes impinging on a carbon target. Comparing model calculations to the data, we find that the epax code is not able to describe the data satisfactorily. Using abrabla07 on the other hand, we find that the average excitation energy per abraded nucleon needs to be decreased from 27 MeV to 8.1 MeV. With that decrease abrabla07 describes the data surprisingly well.

Conclusions: Extending the available data towards light unstable nuclei with a consistent set of new data has allowed a systematic investigation of the role of the excitation energy induced in projectile fragmentation. Most striking is the apparent mass dependence of the average excitation energy per abraded nucleon. Nevertheless, this parameter, which has been related to final-state interactions, requires further study.

The mass, charge, isotopic, and kinetic-energy distributions of fission fragments are studied within an improved scission-point statistical model in the reactions ${}^{235}\mathrm{U}+n$ and ${}^{239}\mathrm{Pu}+n$ at different energies of the incident neutron. The charge and mass distributions of the electromagnetic- and neutron-induced fission of ${}^{214,218}\mathrm{Ra},{}^{230,232,238}\mathrm{U}$ are also shown. The available experimental data are well reproduced and the energy-dependencies of the observable characteristics of fission are predicted for future experiments.

We present calculations of dilepton and photon spectra for the energy range $E_{\text{lab}}=2A\text{to}35A\mathrm{GeV}$ which will be available for the Compressed Baryonic Matter (CBM) experiment at the future Facility for Antiproton and Ion Research (FAIR). The same energy regime will also be covered by phase II of the beam-energy scan at the Relativistic Heavy-Ion Collider (RHIC-BES). Coarse-grained dynamics from microscopic transport calculations of the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model is used to determine temperature and chemical potentials, which allows for the use of dilepton and photon-emission rates from equilibrium quantum-field-theory calculations. The results indicate that nonequilibrium effects, the presence of baryonic matter, and the creation of a deconfined phase might show up in specific manners in the measurable dilepton invariant-mass spectra and in the photon transverse-momentum spectra. However, as the many influences are difficult to disentangle, we argue that the challenge for future measurements of electromagnetic probes will be to provide a high precision with uncertainties much lower than in previous experiments. Furthermore, a systematic study of the whole energy range covered by CBM at FAIR and RHIC-BES is necessary to discriminate between different effects, which influence the spectra, and to identify possible signatures of a phase transition.

We consider the theoretical possibility of generating a narrow resonance in the 4-neutron system as suggested by a recent experimental result. To that end, a phenomenological $T=3/2$ 3-neutron force is introduced, in addition to a realistic $NN$ interaction. We inquire what the strength should be of the $3n$ force to generate such a resonance. The reliability of the 3-neutron force in the $T=3/2$ channel is examined, by analyzing its consistency with the low-lying $T=1$ states of ${}^4\mathrm{H},{}^4\mathrm{He}$, and ${}^4\mathrm{Li}$ and the ${}^3\mathrm{H}+n$ scattering. The ab initio solution of the $4n$ Schrödinger equation is obtained using the complex scaling method with boundary conditions appropriate to the four-body resonances. We find that to generate narrow $4n$ resonant states a remarkably attractive $3N$ force in the $T=3/2$ channel is required.

The excitation of the dynamical dipole mode along the fusion path was investigated for the first time in the formation of a heavy compound nucleus in the $A\sim 190$ mass region. The compound nucleus was formed at identical conditions of excitation energy and spin from two entrance channels: the charge-asymmetric ${}^{40}\mathrm{Ca}+{}^{152}\mathrm{Sm}$ and the nearly charge-symmetric ${}^{48}\mathrm{Ca}+{}^{144}\mathrm{Sm}$ at $E_{\text{lab}}=11$ and 10.1 MeV/nucleon, respectively. High-energy $\gamma$ rays and light charged particles were measured in coincidence with evaporation residues by means of the MEDEA multidetector array (Laboratori Nazionali del Sud, Italy) coupled to four parallel plate avalanche counters. The charged particle multiplicity spectra and angular distributions were used to pin down the average excitation energy, the average mass, and the average charge of the compound nucleus. The $\gamma$-ray multiplicity spectrum and angular distribution related to the nearly charge-symmetric channel were employed to obtain new data on the giant dipole resonance in the compound nucleus. The dynamical dipole mode excitation in the charge-asymmetric channel was evidenced, in a model-independent way, by comparing the $\gamma$-ray multiplicity spectra and angular distributions of the two entrance channels with each other. Calculations of the dynamical dipole mode in the ${}^{40}\mathrm{Ca}+{}^{152}\mathrm{Sm}$ channel, based on a collective bremsstrahlung analysis of the reaction dynamics, are presented. Possible interesting implications in the superheavy-element quest are discussed.

A systematic study of the pseudorapidity dependence of elliptic flow parameter using transport models (e.g., a multiphase transport model, AMPT, and ultrarelativistic quantum molecular dynamics, UrQMD) has been presented. We have observed that while at mid-pseudorapidity the elliptic flow measured using the event-plane method differs significantly from that measured by actual reaction plane method, both the event-plane and reaction-plane methods give the same elliptic flow for far forward and backward pseudorapidity. This indicates that the magnitude of measured $v_2$ around midrapidity strongly depends on the analysis method. Therefore, one should use the same procedure (as used in data analysis) in model calculations while comparing model results and experimental data. We find the shape of $v_2\left(\eta \right)$ measured by the PHOBOS experiment is not reproduced by using actual $v_2$ (i.e., measured with respect to the reaction plane) from AMPT and UrQMD models. The shape and magnitude of measured $v_2\left(\eta \right)$ can be explained by the AMPT model with string-melting mode only if one uses the same procedure as used in data analysis. Magnitude of elliptic flow can be reproduced for all pseudorapidity range by taking the parton-parton interaction cross section to be 3 mb at $\sqrt{s_{NN}}=62.4$ and 200 GeV. This implies that the partonic interactions are necessary to reproduce data at $\sqrt{s_{NN}}=62.4$ and 200 GeV and the strength of partonic interactions at far forward and backward rapidity is as strong as at midrapidity. Both UrQMD and AMPT with default mode fail to explain the data.