In light of recent speculations on a potentially increased speed of the radioactive decay of $\alpha$-emitters embedded in a metallic matrix at very low temperature, four high-purity Cu disks deep-implanted with ${}^{209}\mathrm{Bi}$ were prepared. The disks were irradiated in a high-flux reactor to transmute the ${}^{209}\mathrm{Bi}$ into ${}^{210}\mathrm{Po}$. After the irradiation, the ${}^{210}\mathrm{Po}$ activity was measured for all four disks. While two of the disks were stored at room temperature, the other two disks were stored in a sealed container submerged in liquid helium ($T=4.2$ K) for approximately 200 days. After the storage time the ${}^{210}\mathrm{Po}$-activity measurements were repeated and the ${}^{210}\mathrm{Po}$ half-life was calculated for each sample. No difference between the half-lives for the four samples could be detected within the uncertainties of the measurements. In other words, the results of this study show no evidence for an increase of activity for $\alpha$ emitters embedded in a metallic matrix at very low temperature.

Correlations induced by quantum statistics are sensitive to the spatiotemporal extent as well as dynamics of particle-emitting sources in heavy-ion collisions. In addition, such correlations can be used to search for the presence of a coherent component of pion production. Two- and three-pion correlations of same and mixed charge are measured at low relative momentum to estimate the coherent fraction of charged pions in Pb-Pb collisions at $\sqrt{s_{{}_{\mathit{N}N}}}=2.76$ TeV at the CERN Large Hadron Collider with ALICE. The genuine three-pion quantum statistics correlation is found to be suppressed relative to the two-pion correlation based on the assumption of fully chaotic pion emission. The suppression is observed to decrease with triplet momentum. The observed suppression at low triplet momentum may correspond to a coherent fraction in charged-pion emission of $23\%\pm 8\%$.

We calculate, for the first time, differential distributions for double-${\rho }^0$-meson production in exclusive ultraperipheral, ultrarelativistic collisions via a double-scattering mechanism. The calculations are done in impact parameter space. The cross section for $\gamma A\to {\rho }^{0}A$ is parametrized based on an existing calculation. Smearing of ${\rho }^0$ masses is taken into account. The results of our calculations are compared at the Relativistic Heavy Ion Collider (RHIC) energy to the contribution of the two-photon mechanism discussed previously in the literature. The cross section for the double-scattering mechanism is found to be an order of magnitude larger at $M_{\rho \rho }<$ 2 GeV and more than two orders of magnitude at $M_{\rho \rho }>$ 3 GeV, than that for the photon-photon mechanism. Compared to the two-photon mechanism, the double-scattering mechanism populates somewhat larger ${\rho }^0{\rho }^0$ invariant masses and larger rapidity distances between the two ${\rho }^0$ mesons and gives a significant contribution to the $AA\to AA{\pi }^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}$ reaction. Some observables related to charged pions are presented too. We compare the results of our calculation with the STAR Collaboration results on four-charged-pion production. While the shape in invariant mass of the four-pion system is very similar to the measured one, the predicted cross section constitutes only 20% of the measured one. We discuss a possibility of identifying the double scattering mechanism at the Large Hadron Collider (LHC).

We consider two-photon exchange (TPE) in elastic electron-proton scattering and evaluate the effect of $\pi N$ (pion + nucleon) intermediate hadronic states. Among different $\pi N$ states, we concentrate on the $P_{33}$ channel; thus we effectively include $\Delta \left(1232\right)$ resonance with realistic width and shape and corresponding background as well. In agreement with the previous result, obtained for the zero-width resonance, we observe that the TPE correction to the electric form factor is the largest one; it grows with $Q^2$ and at $Q^2\gtrsim 2.5{\mathrm{GeV}}^2$ exceeds the corresponding elastic contribution.

The asymptotic normalization coefficients of the bound states $J^{\pi }=(0_1^{+},2_1^{+},4_1^{+},2_2^{+})$ in ${}^{18}\text{O}$ are extracted from the peripheral neutron transfer reaction ${}^{13}\text{C}$$({}^{17}\text{O}$$,{}^{18}\text{O}$$){}^{12}\text{C}$. They are then converted to their mirror states in ${}^{18}\text{Ne}$, which are further used to evaluate the astrophysical $S$ factor for the proton capture reaction ${}^{17}\text{F}$($p$,$\gamma$)${}^{18}\text{Ne}$. The elastic-scattering cross sections have been measured in both incoming and outgoing channels in order to extract the optical potentials needed for distorted-wave-Born-approximation calculations. The $S$ factor is found to be $S_{1-17}\left(0\right)=2.17\pm 0.37$ keV b. The contribution of the direct capture rate to this reaction is estimated, and its consequences on the production of ${}^{18}\text{F}$ at stellar energies in ONe novae are discussed.

The Gallagher-Moszkowski rule in the spectroscopy of odd-odd nuclei imposes a new spin constraint on the energy functionals for self-consistent mean field theory. The commonly used parametrization of the effective three-body interaction in the Gogny and Skyrme families of energy functionals is ill suited to satisfy the spin constraint. In particular, the Gogny parametrization of the three-body interaction has the spin dependence opposite to that required by the observed spectra. The two-body part has a correct sign, but in combination the rule is violated as often as not. We conclude that a new functional form is needed for the effective three-body interaction that can take into better account the different spin-isospin channels of the interaction.

Background: Effective interactions, either derived from microscopic theories or based on fitting selected properties of nuclei in specific mass regions, are widely used inputs to shell-model studies of nuclei. The commonly used unperturbed basis functions are given by the harmonic oscillator. Until recently, most shell-model calculations have been confined to a single oscillator shell like the $sd$ shell or the $pf$ shell. Recent interest in nuclei away from the stability line requires, however, larger shell-model spaces. Because the derivation of microscopic effective interactions has been limited to degenerate models spaces, there are both conceptual and practical limits to present shell-model calculations that utilize such interactions.

Purpose: The aim of this work is to present a novel microscopic method to calculate effective nucleon-nucleon interactions for the nuclear shell model. Its main difference from existing theories is that it can be applied not only to degenerate model spaces but also to nondegenerate model spaces. This has important consequences, in particular for intershell matrix elements of effective interactions.

Methods: The formalism is presented in the form of a many-body perturbation theory based on the recently developed extended Kuo-Krenciglowa method. Our method enables us to microscopically construct effective interactions not only in one oscillator shell but also for several oscillator shells.

Results: We present numerical results using effective interactions within (i) a single oscillator shell (a so-called degenerate model space) like the $sd$ shell or the $pf$ shell and (ii) two major shells (nondegenerate model space) like the $sd{f}_7{p}_3$ shell or the $pf{g}_9$ shell. We also present energy levels of several nuclei that have two valence nucleons on top of a given closed-shell core.

Conclusions: Our results show that the present method works excellently in shell-model spaces that comprise several oscillator shells, as well as in a single oscillator shell. We show, in particular, that the microscopic intershell interactions are much more attractive than has been expected by degenerate perturbation theory. The consequences for shell-model studies are discussed.

Background: The scissors mode is a rotational mode of isovector character in deformed nuclei. Together with the isoscalar rotation, it is the prominent collective mode at low excitation energies.

Purpose: We use a simple field theory model to investigate the role of the nucleon spin for the magnetic sum rules associated with the low-lying scissors mode. Special emphasis is put on the coupling of the spin part of the $M1$ operator to the scissors mode.

Methods: We apply the mean-field approximation and random phase approximation to a model Hamiltonian based on a simple quadrupole-quadrupole interaction. The effects of the spin-orbit interaction are included in the mean-field Hamiltonian. Ward-Takahashi relations are used to derive the $M1$ sum rules.

Results: The presence of the spin-orbit interaction leads to interference terms in the inverse energy weighted sum rule. It is shown that the low-lying scissors mode, which is generated by the isovector combination of proton and neutron total angular momenta, gives the main contribution to the spectral sum for this case.

Conclusions: The basic concept of the scissors mode as an isovector vibrational rotation remains valid in the presence of the nucleon spin. The inverse energy weighted sum rule, however, receives nontrivial modifications because of interference terms.

We study the dinucleon (dineutron and diproton) correlation of the ground states of ${}^9\mathrm{Li}$, ${}^{10}$Be, and ${}^{9,10}\mathrm{C}$. We assume an $\alpha +t$ core for ${}^9\mathrm{Li}$, an $\alpha +\alpha$ core for ${}^{10}$Be and ${}^{10}\mathrm{C}$, and an $\alpha {+}^3$He core for ${}^9\mathrm{C}$, and investigate the effect of core structure changes on the degree of dineutron formation and spatial expansion from the core. For ${}^9\mathrm{Li}$, $t$ cluster breaking in the core significantly enhances the dineutron component inside the nuclei. Moreover, its component markedly depends on the strength of the spin-orbit interaction since a dineutron is fragile and dissociates readily due to the spin-orbit interaction. Compared with ${}^9\mathrm{Li}$, the dineutron of ${}^{10}$Be dissociates largely due to the stronger spin-orbit attraction from the $\alpha +\alpha$ core than the $\alpha +t$ core. We also investigate diproton features in ${}^{9,10}\mathrm{C}$, the mirror nuclei of ${}^9\mathrm{Li}$ and ${}^{10}$Be, respectively, and compare them with the dineutron features of ${}^9\mathrm{Li}$ and ${}^{10}$Be. No qualitative difference is observed between diprotons and dineutrons in the degree of formation at the surface, but a quantitative difference may exist in the degree of dinucleon-size change far from the core.

Excited states and decay properties of ${}^{175}$Pt have been investigated using the ${}^{92}$Mo${(}^{86}\mathrm{Sr},2pn)$ fusion-evaporation reaction. The JUROGAM I $\gamma$-ray spectrometer and the GREAT spectrometer were used in conjunction with the gas-filled recoil separator RITU for the measurement of the radiation at the target and focal plane positions, respectively. Two new band structures, assigned to be based on the $I^{\pi }=\left({{}^7{/}_2}^{-}\right)$ ground state in ${}^{175}$Pt, have been established and the known yrast band has been extended up to $I^{\pi }=\left({{}^{49}{/}_2}^{+}\right)$. Rotational properties of the excited states in ${}^{175}$Pt have been investigated within the cranked shell-model formalism. The low-frequency changes in the alignments of the positive- and negative-parity bands are interpreted as a sign of proton-pair excitations in the rotating core. Furthermore, the $\alpha$-decay measurements reveal a candidate for a fourth $\alpha$-decay branch in ${}^{175}$Pt, feeding a non-yrast state in ${}^{171}$Os.

We report a leading-order calculation of radiative ${}^7\mathrm{Li}$ neutron captures to both the ground and first excited state of ${}^8\mathrm{Li}$ in the framework of a low-energy effective field theory (halo-EFT). Each of the possible final states is treated as a shallow bound state composed of both $n+{}^7\mathrm{Li}$ and $n+{}^7{\mathrm{Li}}^{*}$ (core excitation) configurations. The ab initio variational Monte Carlo method is used to compute the asymptotic normalization coefficients of these bound states, which are then used to fix couplings in our EFT. We calculate the total and partial cross sections in the radiative capture process using this calibrated EFT. Fair agreement with measured total cross sections is achieved and excellent agreement with the measured branching ratio between the two final states is found. In contrast, a previous halo-EFT calculation [Rupak and Higa, Phys. Rev. Lett. 106, 222501 (2011)] assumes that the $n$-${}^7\mathrm{Li}$ couplings in different spin channels are equal, fits the $P$-wave “effective-range” parameter to the threshold cross section for ${}^7\mathrm{Li}+n\to {}^8\mathrm{Li}+\gamma$, and assumes the core excitation is at high enough energy scale that it can be integrated out.

Inelastic and multinucleon transfer reactions between a ${}^{238}U$ beam, accelerated at 6.14 MeV/u, and a ${}^{12}C$ target were used for the production of neutron-rich, fissioning systems from U to Cm. A Si telescope, devoted to the detection of the targetlike nuclei, provided a characterization of the fissioning systems in atomic and mass numbers, as well as in excitation energy. Cross sections and angular and excitation-energy distributions were measured for the inelastic and transfer channels. Possible excitations of the targetlike nuclei were experimentally investigated for the first time, by means of $\gamma$-ray measurements. The decays from the first excited states of ${}^{12}C$, ${}^{11}B$, and ${}^{10}\mathrm{Be}$ were observed with probabilities of 0.12–0.14, while no evidence for the population of higher-lying states was found. Moreover, the fission probabilities of ${}^{238}U$, ${}^{239}\mathrm{Np}$ and ${}^{240,241,242}$Pu and ${}^{244}\mathrm{Cm}$ were determined as a function of the excitation energy.

The production cross sections of superheavy nuclei in hot fusion reactions are investigated systematically. In hot fusion reactions, the capture cross section can be obtained by calculating the weighted average of the transmission probability for different orientations of deformed colliding nuclei. An analytical formula for calculating the value of the fusion probability is proposed, which is suitable for both hot and cold fusion reactions. The orientation effects are considered empirically in calculating the fusion probability. The method proposed in the present work reproduces the measured evaporation residue (ER) cross sections in hot fusion reactions acceptably well. The formula also gives reasonable results for fusion probability in cold fusion reactions. Using this method the evaporation residue cross sections for synthesizing $Z=119$ and 120 are predicted. It is found that for hot fusion reaction's larger maximal ER cross section of the $4n$ channel corresponds to lower optimal incident energy.

Partial contributions of elliptic $v_2$ and triangular $v_3$ flows to the hexagonal $v_6$ flow are studied within the hydjet$++$ model for Pb+Pb collisions at $\sqrt{s}=2.76$ TeV. Scaling of the ratio $v_6^{1/6}\left\{{\Psi }_2\right\}/v_2^{1/2}\left\{{\Psi }_2\right\}$ in the elliptic flow plane, ${\Psi }_2$, is predicted in the range $1\le p_t\le 4$  GeV/$c$ for semicentral and semiperipheral collisions. Jets increase this ratio by about 10% and also cause its rise at $p_t\ge 3.5$ GeV/$c$. The part of $v_6$ coming from $v_2$ is instantly increasing as the reaction becomes more peripheral, whereas the contribution of $v_3$ to $v_6$ drops. This behavior explains the experimentally observed increase of correlations between second and sixth harmonics and the decrease of correlations between third and sixth harmonics with rising impact parameter $b$. Our study favors the idea that basic features of the hexagonal flow can be understood in terms of the interplay of elliptic and triangular flows.

Methods for building a consistent interface between hydrodynamic and Boltzmann modules is presented. These methods account for the backflow across the hydrodynamic-Boltzmann hypersurface. The algorithms are efficient, relatively straight-forward to implement, and exactly satisfy conservation laws across the hypersurface. The methods also account for the interactions between particles in the backflow and other particles by following the subsequent impact of such particles. Since the number of altered trajectories grows exponentially in time, a cutoff is built into the procedure so that the effects of the backflow are ignored beyond a certain number of collisions.

The accuracy of current theoretical descriptions of nuclear masses is studied. Ten theoretical models of various kinds are taken for the study: the macroscopic-microscopic, purely microscopic (self-consistent), and models of other natures. Some of them are traditional, but still widely used, while the others are very recent. The most recently evaluated experimental masses of 2012 are taken for the test of the models. Much attention is given to the dependence of the accuracy on the region of nuclei described by the models. The macroscopic-microscopic approaches are still found to be the most accurate in the description of atomic masses. However, the recently developed purely microscopic models (the Hartree-Fock-Bogoliubov approach) reach comparable accuracy. A strong dependence of the accuracy on the region of nuclei described is found, knowledge of which is crucial for a realistic description of specific nuclei.

Background: The measurement and analysis of excitation functions may be used as an important tool to understand incomplete fusion reaction dynamics.

Purpose: Several studies have been carried out to study incomplete fusion reactions at low energies, but a clear picture of incomplete fusion reaction processes at energies below 6 MeV/nucleon has yet to emerge. Further, there is no theoretical model which may give a good representation of incomplete fusion processes.

Method: Off-line $\gamma$-ray spectrometry has been used to measure the excitation functions in the ${}^{16}\text{O}+{}^{130}\text{Te}$ system at energies $\approx 3$–6 MeV/nucleon.

Results: Excitation functions for five reaction products populated via complete and/or incomplete fusion processes in the ${}^{16}\mathrm{O}$ + ${}^{130}\mathrm{Te}$ system have been measured. Measured cross-sections have been compared with the predictions of the statistical model code pace4. A significant enhancement in the measured excitation functions compared to theoretical predictions for $\alpha$-emitting channels has been observed and is attributed to incomplete fusion processes. The relative strength of incomplete fusion has been found to increase with projectile energy. In the case of the ${}^{133}\mathrm{Xe}$($3\alpha n$) channel, the isomeric cross-section ratios have been deduced and found to increase rapidly with beam energy, indicating the importance of imparted angular momentum. The angular momentum at different energies has also been calculated. The analysis of the data indicates that incomplete fusion is associated even for angular momentum values smaller than the critical angular momentum for complete fusion. The results have been discussed in terms of the $\alpha$-cluster structure of the projectile for various fusion reactions.

Conclusions: It may be concluded that, apart from complete fusion, incomplete fusion processes are of greater importance even at energies as low as $\approx$3-6 MeV/nucleon, where fusion evaporation channels are expected to be dominant. The measured isomeric cross-section ratio for the dominant incomplete fusion channel is found to increase with energy. Analysis of the data indicates that the incomplete fusion contribution becomes significant even for values of imparted angular momentum $\ell <{\ell }_{\mathrm{critical}}$ also, contrary to SUMRULE model predictions.

I review the models suggested to date as an explanation for the so-called “ridge” phenomenon: an elongation in rapidity of two-particle correlations seen at energies of the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider. I argue that these models can be divided into two phenomenologically distinct classes: “$\text{Hotspot}+\text{flow}$”-driven correlations, where initial-state correlations created by structures local in configuration space are collimated by transverse flow, and models where the azimuthal correlation is created through local partonic interactions in a high-gluon-density initial state. I argue that the measurement of a strong double ridge in $pA$ and $dA$ collisions allows a good opportunity to understand the ridge's origin because it allows us to see if a common Knudsen number scaling, which is expected if the ridge has a hydrodynamic origin, can be used to understand all data. I show that current data present evidence that this scaling is lacking, which presents a challenge to the hydrodynamic models. On the other hand, particle-identified correlations are a particularly promising way of testing the assumption that distinguishes the two models; namely, of whether the correlation is formed initially in the partonic phase, or as a final-state effect. Assuming fragmentation occurs “as in vacuum” can be used to predict scaling trends which are generally broken by models, such as hydrodynamics, where the ridge is created as a final-state effect. While evidence is again not fully conclusive, data do seem to follow a scaling compatible with hydrodynamics [Phys. Rev. Lett. 111, 172303 (2013)]. I close by discussing experimental observables capable of clarifying the situation.