International Journal of Modern Physics E

Tensor target spin asymmetries $T_{2M}$ ($M$=0,1,2) in the reaction $\gamma d\to {\pi }^{-}pp$ are studied for photon energies from $\pi$-threshold up to 1.5GeV with inclusion of rescattering effects. It is shown that the influence of rescattering effects on the tensor target spin asymmetries is sizable in the energy region near $\pi$-threshold. At higher energies, much smaller influence of rescattering effects is seen. The sensitivity of the obtained results to the elementary pion photoproduction operator is investigated and a considerable dependence is found, in particular at forward pion angles. In addition, a comparison with results of other theoretical models is also given. The extracted spin asymmetries are compared with available experimental data and a qualitative agreement is obtained. The predictions presented here may be useful to interpret the recent measurements from the VEPP-3 electron storage ring.

The strong interactions are charge independent. If we limit ourselves to the strong interactions, we have the isospin $T$ as a good quantum number. Here, we consider the lack of level repulsion of states of different isospin and how this effect manifests in nearest neighbor spacing (NNS) histograms, which provide a visual and statistical context in which to study distributions of energy level spacings. In particular, we study nucleons in the $f-p$ model space for the nucleus ${}^{44}\mathrm{\text{Ti}}$. We also compare NNS distributions produced in the isospin formalism to distributions produced in the proton–neutron formalism.

A comparable study of the quantum van der Waals (QvdW) and Walecka models of nuclear matter is presented. Each model contains two parameters which characterize the repulsive and attractive interactions between nucleons. These parameters are fixed in order to reproduce the known properties of the nuclear ground state. Both models predict a first-order liquid-gas phase transition and a very similar behavior in the vicinity of the critical point. Critical exponents of the QvdW model are studied both analytically and numerically. There are important differences in the behavior of the thermodynamical functions of the considered models at large values of the nucleon number density. At the same time, both models fall into the universality class of mean-field theory.

It is shown that the random-phase approximation (RPA) method with its nonlinear higher generalization, which was previously considered as approximation except for a very limited case, reproduces the exact solutions of the Lipkin model. The nonlinear higher RPA is based on an equation nonlinear on eigenvectors and includes many particle-many hole components in the creation operator of the excited states. We demonstrate the exact character of solutions analytically for the particle number $N=2$ and, numerically, for $N=8$. This finding indicates that the nonlinear higher RPA is equivalent to the exact Schrödinger equation, which opens up new possibilities for realistic calculations in many-body problems.

This work systematically analyzed the fusion dynamics of the projectile-target combinations involving stable and loosely bound systems within the view of the energy-dependent Woods–Saxon potential model (EDWSP model) and the coupled channel approach. The different projectiles are bombarded onto series of Sm-isotopes, which possess the dominance of the different kinds of the nuclear structure degrees of freedom and with the increase of the neutron richness, the Sm-isotopes gradually shift from spherical shape to a statically deformed shape. In the fusion of ${}_6^{12}\mathrm{\text{C}}{+}_{62}^{144}\mathrm{\text{Sm}}$ reaction, the impacts of vibrational degrees of freedom of the colliding nuclei are dominant while in the case of ${}_6^{12}\mathrm{\text{C}}{+}_{62}^{152,154}\mathrm{\text{Sm}}$ systems, the rotational states of the deformed target isotopes have a strong impression on the below-barrier fusion data. The heavier target isotopes (${}_{62}^{152,154}\mathrm{\text{Sm}})$ also exhibit the higher order deformation such as ${\beta }_4$, ${\beta }_6$-deformation parameter in its ground state and couplings to such channels must be incorporated in theoretical calculations in order to achieve close agreement with the sub-barrier fusion data. However, in the case of the loosely bound systems, the projectile breakup channel significantly affects the fusion excitation functions in the domain of the Coulomb barrier. To ensure the role of the projectile breakup channel, the fusion of the different loosely bound projectiles (${}_3^{6,7}\mathrm{\text{Li}}$ and ${}_4^9\mathrm{\text{Be}})$ with Sm-isotopes are investigated, wherein the above-barrier fusion data of these reactions are suppressed with reference to the coupled channel calculations. This hindrance is the result of the projectile breakup effects that occur as a consequence of the breakup of the projectile before reaching the fusion barrier due to its low binding energy. However, in the EDWSP model calculations the magnitude of the hindrance of the above-barrier fusion data of ${}_4^9\mathrm{\text{Be}}{+}_{62}^{144}\mathrm{\text{Sm}}$ and ${}_3^{6,7}\mathrm{\text{Li}}{+}_{62}^{144,152}\mathrm{\text{Sm}}$ reactions is reduced by a factor varying from 7% to 13% with respect to a value reported in the literature. In contrast to this, the sub-barrier fusion enhancement of ${}_4^9\mathrm{\text{Be}}{+}_{62}^{144}\mathrm{\text{Sm}}$ and ${}_3^{6,7}\mathrm{\text{Li}}{+}_{62}^{144,152}\mathrm{\text{Sm}}$ reactions is the result of the dominance of the nuclear structure degrees of freedom of the colliding systems.

The reaction ${}^{27}$Al($d$,³He) at 25 MeV beam energy has been utilized to study the states in even–even nucleus ${}^{26}$Mg. The spectroscopic factors have been extracted for the states of ${}^{26}$Mg up to 7.50MeV excitation energy using local, zero-range distorted wave Born approximation. The extracted spectroscopic factors have been compared with the previously reported values. The present results were also compared with the predictions from a theoretical shell model and rotational model.

The nucleon density distributions were usually described by the two-parameter Fermi shape formula. In this work, the isospin effects in the nucleon density distributions are considered, and a three-parameter formula is proposed and modified by simultaneously considering the experimental data of 885 root-mean-square (rms) charge radii and neutron skin thickness of 26 stable nuclei. The improved nucleon density formula is physically reasonable and achieves a good agreement for the charge radii and neutron skin thickness calculated with the new nucleon density formula comparing the available experimental data.

The partial inelasticity coefficients of baryon fragments of oxygen nuclei and pions were investigated and the full inelasticity coefficient was determined for the first time in ${}^{16}\mathrm{\text{O}}p$ collisions at $3.25A\mathrm{\text{GeV}}/c$. The fraction of kinetic energy of incident proton in ${}^{16}\mathrm{\text{O}}p$ collisions at $3.25A\mathrm{\text{GeV}}/c$ spent on formation of all the baryon fragments and production of charged and neutral pions was found. The experimental results were compared with those obtained in other experiments at high energies. The experimental full inelasticity coefficient in ${}^{16}\mathrm{\text{O}}p$ collisions at $3.25A\mathrm{\text{GeV}}/c$ was reproduced well by calculations within the framework of Glauber model of multiple scatterings in hadron–nucleus collisions.

The nonlinear behavior in electron–nucleus collisions for nuclei with mass number $A=56,108,208$ and 265 at very small $x$ regime $(1E-8<x<0.1)$ with low and moderate $Q^2$ is studied. The charm and bottom heavy quarks contributions to the reduced cross-section and ratio of structure functions $F_L^{H-A}$ to $F_2^{H-A}$ are investigated by using the Kharzeev–Levin–Nardi phenomenological ansatz at LO and NLO analyses.

In previous studies, we provided a novel systematization of $\alpha$-decaying even–even and even–odd nuclei starting with the classically adopted mechanism [T. Yarman et al., Eur. Phys. J. A 52 (2016) 140; Eur. Phys. J. A 53 (2017) 4]. Knowing beforehand the measured decay half-life, we had taken as a parameter the probability of the $\alpha$-particle as being first born in a unit period of time, within the parent nucleus before it is emitted out. We thence developed a scaffold based on shell properties of families composed of “alike nuclei”. Along the same line, we now present a systematization of odd–even (OE) as well as odd–odd (OO) nuclei. We apply our approach further to the investigation of the effect of pairing (e.g., the effect when the number of nucleons is increased by one neutron), and that of unpairing (e.g., the effect when the number of nucleons is decreased by one neutron); thus it becomes an even number for the case of odd–even nuclei $($Case OE$)$, and an odd number in the case of odd–odd nuclei $($Case OO$)$. For the first case $($OE$)$, we pick the exemplar set ${}^{161}$Re, ${}^{217}$Fr, ${}^{243}$Bk, ${}^{263}$Db; where we delineate by, respectively, Re, Fr, Bk, and Db all of the odd–even or odd–odd isotopes that neighbor the four mentioned odd–even isotopes on the proposed scaffold. We proceed in the same way for the second case $($OO$)$. Thus, we choose the exemplar set of odd–odd nuclei ${}^{172}$Ir, ${}^{218}$Ac, ${}^{244}$Es. We then gather all of the Ir, Ac, and Es odd–odd and odd–even isotopes that neighbor the three mentioned odd–odd isotopes on the proposed scaffold. We show that, in the former case, pairing, as expected, generally increases stability of the given nucleus; and in the latter case, unpairing works in just the opposite direction — i.e., it generally increases instability. We disclose “stability peaks” versus $Z$ for both sets of nuclei, we tackle here. Furthermore, we present a study to highlight an outlook of “odd-A nuclei” at hand. Contrary to the general expectation, we unveil no systematic on that.

The alpha decay half-lives of even–even and even–odd Platinum (Pt) nuclei have been studied within the Coulomb and proximity potential model (CPPM). The present study is restricted to even–even nuclei with $A=166$–198. The results are compared with other calculations such as the Semi-empirical formula (SemFIS) from Poenaru et al. based on fission theory of alpha decay, the Viola–Seaborg (VS), Royer (R) and Brown formulae. Also, the alpha decay half-lives have been calculated using the Scaling law of Brown (SLB), the Universal Decay Law (UDL) of Qi et al., the Scaling Law of Horoi et al. (SLH), and Akrawy–Dorin formula (ADF) of Akrawy and Poenaru, which are the Royer modified formula for alpha decay half-live by adding asymmetry term.

In this paper, a transitional interacting boson model (IBM) Hamiltonian in both sd-(IBM) and sdg-IBM versions based on affine $SU(1,1)$ Lie algebra is employed to describe deviations from the gamma-unstable nature of Hamiltonian along the chain of Xe isotopes. sdg-IBM Hamiltonian proposed a better interpretation of this deviation which cannot be explained in the $sd$-boson models. The nuclei studied have well-known $\gamma$ bands close to the $\gamma$-unstable limit. The energy levels, $B(E2)$ transition rates and signature splitting of the $\gamma$ -vibrational band are calculated via the affine SU(1,1) Lie algebra. An acceptable degree of agreement was achieved based on this procedure. It is shown that in these isotopes the signature splitting is better reproduced by the inclusion of sdg-IBM. In none of them, any evidence for a stable, triaxial ground state shape is found.