International Journal of Modern Physics E

We have studied the neutron-capture reactions ⁸Li($n,\gamma {)}^9$Li and its role in the primordial nucleosynthesis. The $n{+}^8\mathrm{\text{Li}}{\to }^9\mathrm{\text{Li}}+\gamma$ reaction has a significant astrophysical interest because it includes one of the variants of chain of primordial nucleosynthesis processes of the Universe and thermonuclear reactions in type II supernovae. Furthermore, we consider the ${}^9\mathrm{\text{Be}}{(p,\gamma )}^{10}\mathrm{\text{B}}$ reaction in the astrophysical energy range in the modified potential cluster model (MPCM) with splitting of orbital states according to Young tableaux and, in some cases, with forbidden states (FS). The reaction ${}^9\mathrm{\text{Be}}{(p,\gamma )}^{10}\mathrm{\text{B}}$ plays an important role in primordial and stellar nucleosynthesis of light elements in the $p$ shell. Hydrogen burning in second-generation stars occurs via the proton–proton (pp) chain and CNO cycle, with the ${}^9\mathrm{\text{Be}}{(p,\gamma )}^{10}\mathrm{\text{B}}$ reaction serving as an intermediate link between these cycles. Furthermore, the possibility of describing available experimental data for the total reaction cross-sections of neutron radiative capture on ${}^{10}$Be at thermal and astrophysical energies has been shown. This reaction is a part of one of the variants of the chain of primordial nucleosynthesis of the Universe due to which the elements with a mass of $A>11\text{–}12$ may be formed. The results in the field of study of thermonuclear proton-capture reaction on ${}^{10}\mathrm{\text{B}}$ at ultralow, i.e., astrophysical energies will be presented further. The possibility of description of the experimental data for the astrophysical $S$-factor of the proton radiative capture on ${}^{16}$O to the ground state (GS) of ${}^{17}$F was considered in the frame of the MPCM with FS and classification of the states according to Young tableaux. It was shown that on the basis of the $E1$ transitions from the states of $p^{16}$O scattering to the GS of ${}^{17}$F in the $p^{16}$O channel generally succeed to explain the value of measured cross-sections at astrophysical energies.

We review a large body of predictions obtained within the framework of relativistic meson theory together with the Dirac–Brueckner–Hartree–Fock approach to nuclear matter and finite nuclei. The success of this method has been largely related to its ability to take into account important three-body effects. Therefore, the overarching theme of this paper is the interpretation of the so-called “Dirac effects” as an effective three-nucleon force. We address the equation of state (EoS) of isospin symmetric and asymmetric nucleonic matter and related issues, ranging from proton and neutron density distributions to momentum distributions and short-range correlations. A central part of the discussion is devoted to the optical model potential for nucleon–nucleus scattering. We also take the opportunity to explore similarities and differences with predictions based on the increasingly popular chiral effective field theory.

The assumption that the production of quark–antiquark pairs and their sequential string-breaking takes place, likely as a tunneling process, through the event horizon of the color confinement determines the freezeout temperature and gives a plausible interpretation for the thermal pattern of elementary and nucleus–nucleus collisions. When relating the black-hole electric charges to the baryon-chemical potentials, it was found that the phenomenologically deduced parameters from the ratios of various particle species and the higher-order moments of net-proton multiplicity in the statistical thermal models and Polyakov linear-sigma model agree well with the ones determined from the thermal radiation from charged black hole. Accordingly, the resulting freezeout conditions, such as normalized entropy density $s/T^3=7$ and average energy per particle $〈E〉/〈N〉\simeq 1$GeV, are confirmed at finite chemical potentials as well. Furthermore, the problem of strangeness production in elementary collisions can be interpreted by thermal particle production from the Hawking–Unruh radiation. Consequently, the freezeout temperature depends on the quark masses. This leads to a deviation from full equilibrium and thus a suppression of the strangeness production in the elementary collisions. But in nucleus–nucleus collisions, an average temperature should be introduced in order to dilute the quark masses. This nearly removes the strangeness suppression. An extension to finite chemical potentials is introduced. The particle ratios of kaon-to-pion (${\mathrm{\text{K}}}^{+}/{\pi }^{+}$), phi-to-kaon ($\varphi /{\mathrm{\text{K}}}^{-}$) and antilambda-to-pion ($\bar{\mathrm{\Lambda }}/{\pi }^{-}$) are determined from Hawking–Unruh radiation and compared with the thermal calculations and the measurements in different experiments. We conclude that these particle ratios can be reproduced, at least qualitatively, as Hawking–Unruh radiation at finite chemical potential. With increasing energy, both ${\mathrm{\text{K}}}^{+}/{\pi }^{+}$ and $\varphi /{\mathrm{\text{K}}}^{-}$ keep their maximum values at low SPS energies. But the further energy decrease rapidly reduces both ratios. For $\bar{\mathrm{\Lambda }}/{\pi }^{-}$, there is an increase with increasing $\sqrt{s_{\mathrm{\text{NN}}}}$, i.e., no saturation is to be observed.

We investigate the description of the pion-nucleon experimental data at low energy (i.e., below pion laboratory kinetic energy of 100MeV) on the basis of the current SAID solution (WI08). We demonstrate that, in a self-consistent analysis scheme, the scale factors of the fits based on the Arndt–Roper formula come out independent of the beam energy and ‘cluster’ around the expectation value of $1$. We report systematic effects in the low-energy behavior of the WI08 solution. These effects indicate that at least one of the three following assumptions, underlying the WI08 analysis, does not hold, namely that: (a) the bulk of the data is reliable, (b) the electromagnetic effects are correctly accounted for and (c) the isospin invariance in the strong interactions of the $\pi N$ system is valid.

Within the framework of Coulomb and proximity potential model (CPPM), the probable heavy particle decays from various isotopes of superheavy nuclei (SHN), $Z=125$, within the range $A=295$–$325$ have been studied using two versions of proximity potential; proximity 1977 and proximity 2000. The decay half lives evaluated using proximity 2000 is observed to be higher than the values obtained using proximity 1977. The effect of surface deformation on the decay half lives is studied using Coulomb and proximity potential for deformed nuclei (CPPMDN). As a result of the inclusion of deformation $({\beta }_2)$, the penetrability of the decays are observed to be increased and accordingly the decay half lives are reduced. The estimated values are compared with other theoretical models, Universal curve (UNIV), Universal Decay law (UDL) and the scaling law of Horoi. The odd–even staggering (OES) effect is observed in the emission of odd mass clusters. An intriguing aspect of the study is the effect of the magicity at $N=184$ which is confirmed from the plot of ${\mathrm{\text{log}}}_{10}{T}_{1/2}$ against the neutron number of the daughter nuclei. Almost all the predicted half lives are favorable for experimental measurements. The Geiger–Nuttall (GN) plots and the Universal curve have been studied for various cluster emissions from various superheavy isotopes with $Z=125$. Finally, the linearity of the GN plot and the Universal curve of the heavy particle emissions very well established the strength of CPPM.

An experiment in direct registration of neutron nuclei ($x\ge 6$) using a multineutron detector has been conducted for the first time. The results indicate the presence of hexaneutron and/or octaneutron emission in decay of ${}^{238}$U nuclei. The multineutron detector consisted of 20 ³He-filled counters placed in a polyethylene moderator. Samples (emitters) of uranium trioxide (UO₃) were used as sources of neutron nuclei. The experiment was conducted for a period of 112.66 days. Thus, the ratios of probabilities of hexaneutron and/or octaneutron emission by the ${}^{238}$U nuclei to the probabilities of $\alpha$-decay have been determined as upper bounds at a 90% confidence level: $\lambda {(}^{6}n)/{\lambda }_{\alpha }\le 9.3\times 10^{-9}$ and $\lambda {(}^{8}n)/{\lambda }_{\alpha }\le 3.6\times 10^{-10}$.

Charge-changing transitions play a significant role in stellar weak-decay processes. The fate of the massive stars is decided by these weak-decay rates including lepton (positron and electron) captures rates, which play a consequential role in the dynamics of core collapse. As per previous simulation results, weak interaction rates on nickel (Ni) isotopes have significant influence on the stellar core vis-à-vis controlling the lepton content of stellar matter throughout the silicon shell burning phases of high mass stars up to the presupernova stages. In this paper, we perform a microscopic calculation of Gamow–Teller (GT) charge-changing transitions, in the $\beta$-decay and electron capture (EC) directions, for neutron-rich Ni isotopes (${}^{66-71}$Ni). We further compute the associated weak-decay rates for these selected Ni isotopes in stellar environment. The computations are accomplished by employing the deformed proton–neutron quasiparticle random phase approximation (pn-QRPA) model. A recent study showed that the deformed pn-QRPA theory is well suited for the estimation of GT transitions. The astral weak-decay rates are determined over densities in the range of 10–10${}^{11}$g/cm³ and temperatures in the range of 0.01$\times 10^9$–30$\times 10^9$K. The calculated lepton capture rates are compared with the previous calculation of Pruet and Fuller (PF). The overall comparison demonstrates that, at low stellar densities and high temperatures, our EC rates are bigger by as much as two orders of magnitude. Our results show that, at higher temperatures, the lepton capture rates are the dominant mode for the stellar weak rates and the corresponding lepton emission rates may be neglected.

Concepts from statistical mechanics and ensemble theory are applied to study the characteristic properties of charged particle production in hadron–nucleus collisions at high energy. In the present study we utilize the predictions from different approaches using statistical mechanics. The Tsallis q-statistics is used to study the regularity in multiplicity distributions in hadron–nucleus collisions at high energies as one of the interesting options. Gamma distributions and a possible microcanonical generalization of Tsallis distribution have also been exploited to describe the data.

$K^0{\bar{K}}^0$ transitions in a medium followed by decay and regeneration of $K_S^0$-component are considered by means of perturbation theory. It is shown that in the previous calculations the problem different from regeneration is solved.

The accurate calculations of the cluster formation model (CFM) have been extended to determine the alpha cluster preformation probability for the three even–even superheavy isotopes (Hs, Ds and Cn) with atomic number $Z=108,110$ and 112 and neutron numbers $144\le N\le 188$ in the mass region from 252 to 300. According to the hypothesized CFM, the calculations of the formation energy and surface energy, which depended on differences of binding energies are crucial for determining the realistic values of the preformation probability. Our results showed reasonable agreement with the results of previous work for the heavy nuclei. In addition, realistic values of the preformation probability certified that CFM can successfully be used to calculate the alpha cluster preformation probability for other wide range of superheavy nuclei.

The quark saturation behavior at low $Q^2$ is shown in a numeric solution of the DGLAP equation with parton recombination corrections, which resembles the widely discussed JIMWLK saturation of gluons. Our calculation suggests that the partonic saturation can be interpreted as a dynamical balance between the splitting and the fusion processes of partons, without any other condensation mechanisms added. The nuclear shadowing saturation at small $x$ resulted from the proposed quark saturation is also discussed.

The dissipation phenomenon has been studied by simulating the reaction ${}^{129}\mathrm{\text{Xe}}{+}^{129}\mathrm{\text{Sn}}$ with Isospin-dependent Quantum Molecular Dynamics (IQMD) model. The evolution of the isotropic ratio with bombarding energy for the free protons moving forward in the center of mass system in the final state of the reactions, drawn from the experimental measurements by INDRA collaboration, is reproduced with the model in the energy region near and slightly higher than the Fermi energy. Comparison of the data with the simulation obtained using the IQMD model in the cases of different combinations of in-medium effects in two-body collisions, i.e., medium modification of nucleon–nucleon cross-section and Pauli-blocking effect, indicates that the Pauli exclusion principle is indispensable in the microscopic model and the Pauli-blocking in binary interactions dominates the in-medium effects in the heavy-ion reactions in the energy range, even below the Fermi energy. Based on such comparisons, an energy-dependent effective factor responsible for the Pauli-blocking in the binary collisions in heavy-ion collisions in the Fermi energy domain has been extracted.