Brazilian Journal of Physics最新文献

The carbon-nitrogen-oxygen (CNO) cycle is fundamental to the process of hydrogen burning in stars, serving as a pivotal mechanism. At its core, the primary reaction involves the radiative capture of a proton by ( ^{12}textrm{C} ), which crucially influences the isotopic ratio of ( ^{12}textrm{C} ) to ( ^{13}textrm{C} ) observed in celestial bodies, including our Solar System. To address this, we applied the astrophysical (R)-matrix approach to extrapolate low-energy cross sections and S-factors, thereby improving the precision of nuclear reaction rates. At a proton energy of around 25 keV (C.M. system), the extrapolated value of the astrophysical S-factor is determined to be ( 1.34 pm 0.10 , mathrm {keV , barn} ). Our investigation sheds light on its implications for nuclear reaction rates, suggesting that at low temperatures in hydrogen-burning sites, the conversion of ( ^{12}textrm{C} ) to ( ^{13}textrm{C} ) via proton capture is relatively slow, thereby influencing the abundance ratios in the cosmic environment. This slow conversion affects stellar nucleosynthesis and isotopic evolution, particularly in low-mass stars ((M le 2 , M_odot )) where hydrogen burning proceeds at relatively low temperatures. Unlike previous analyses with large uncertainties at low energies, our approach refines the S-factor determination by incorporating improved ANC (Asymptotic Normalization Constant) values, reducing extrapolation uncertainties.

At a deuteron energy of 14.5 MeV, the ¹⁰B(d,³He)⁹Be reaction was examined. A series of experiments were carried out to investigate the reaction dynamics and excitation properties of the ⁹Be nucleus. In particular, measurements of cross-sections for transitions to its ground state (3/2⁻) and an excited state at an energy of 2.429 MeV (5/2⁻) were conducted. Using the coupled channel method for angular distributions analysis, the derived spectroscopic amplitude values were SA = 0.71 ± 0.15 and SA = 0.82 ± 0.15. These results align well with prior theoretical and experimental outcomes, considering the inherent uncertainties in the data. Additionally, investigations of the (d, t) reaction on ¹⁰B revealed that transitions to the ⁹B nucleus at corresponding energy levels yield spectroscopic amplitude values of SA = 0.67 ± 0.1 for its ground state and SA = 0.94 ± 0.2 for an excited state at 2.361 MeV (5/2⁻). The congruence the results of the analysis the mirror (d, ³He) and (d, t) reactions emphasizes the charge-independent nature of their mechanisms.

This study investigates the complex dynamics of dust ion-acoustic waves (DIAWs) in a non-Maxwellian plasma, comprising stationary negatively charged dust grains, dynamical positive ions, and inertialess hot Maxwellian electrons and cold generalized (r, q)-distributed electrons. Our investigation is motivated by observations of the Cassini spacecraft in Saturn’s magnetosphere. We aim to analyze the formation and interaction of multiple solitons within this plasma system by employing the reductive perturbation method (RPM) to reduce the fluid equations to the Gardner equation (GE). Subsequently, Hirota’s bilinear method is applied to obtain the multiple soliton solutions for the GE. This study is the first to explore the existence of multiple soliton solutions within the GE framework in a plasma context. Consequently, it will gain a commendable standing among several researchers studying fluids, explicitly focusing on plasma physics. Furthermore, we examine the influence of the nonthermal population of electrons on soliton propagation and their interaction. The findings presented in this paper provide valuable insights into the behavior of dust ion-acoustic (DIA) Gardner solitons in space plasmas and offer a comprehensive analysis of their interaction dynamics. This study is anticipated to pave the way for other researchers to investigate the dynamical scenario of the propagation and interaction of multiple soliton waves in various plasma systems.

In the present study, the combined impacts of self-generated and non-uniform magnetic fields on the acceleration of plasma electrons using circularly polarized laser pulses propagating in plasma are theoretically studied under a strongly relativistic regime. Analytical and mathematical formulations for analyzing laser pulse propagation through plasma medium with consideration of the self-generated and non-uniform magnetic fields have been obtained. The simulation results show that in comparison to without a non-uniform magnetic field, electron energy increases with an increasing δ-parameter. Additionally, it is recognized that the existence of both non-uniform as well as self-generated magnetic fields simultaneously increases electron transverse momentum, which increases energy. Furthermore, it is observed that when the plasma is only dominated via the self-generated magnetic fields consisting of azimuthal and axial magnetic fields, plasma electrons accelerate much less than when a non-uniform magnetic field is employed. It is also shown that higher laser intensity results in a rise in electron energy, depending on the optimal laser field and self-consistent magnetic field. Moreover, it is realized that the amounts of the slope parameter and the magnetic field can be adjusted to control electron energy gain.

Chalcogenides represent a versatile class of materials with diverse properties, enabling their application in a broad range of technologies, including solar cells, LEDs, superconductors, magneto-resistive devices, and topological insulators. In this study, the structural, electronic, optical, phononic, and radiation-related properties of XAl₂S₄ (X = Eu, Fe, Rh) compounds were investigated using first-principles density functional theory (DFT). The electronic properties reveal a semiconducting nature with bandgaps in the range of 1.2–3.4 eV. The computed negative formation energy and phonon calculations confirm phase stability. Analysis of the density of states highlights the specific electronic states contributing to the band structure. The density of states (DOS) analysis for XAl₂S₄ (X = Eu, Fe, Rh) compounds identifies the electronic states contributing to the band structure. The valence band is mainly influenced by S-3p orbitals and X-d states, while the conduction band is predominantly shaped by Al-3p and X-d orbitals. The interaction between X-d and S-3p states plays a significant role in defining the bandgap and electronic transitions. These findings highlight the key contributions of localized and hybridized states in determining the semiconducting nature of these materials, with bandgaps ranging from 1.2 to 3.4 eV. Optically, the reflectivity remains around 30% below 12.0 eV and reaches a maximum of 32% at approximately 13.0 eV. The compounds demonstrate strong potential for radiation shielding, attributed to their high-density elements and effective absorption properties. Notably, the strong optical anisotropy of these materials suggests their potential for polarization-sensitive photodetector applications. The Seebeck coefficient is positive, indicating the properties of a p-type semiconductor with the highest power factor is approximately 2.0 × 10¹¹ W m⁻¹ K⁻². At 600 K, the thermoelectric figure of merit ZT reaches its maximum value of 1.2. These findings indicate that XAl₂S₄ compounds are promising candidates for optoelectronic devices and LED technologies, particularly as green phosphors for energy applications. Radiation shielding analysis reveals that the EuAl₂S₄ compound achieves a mass attenuation coefficient of 0.145 cm²/g at 1 MeV, surpassing conventional materials like lead-based shields in low-energy regimes.

Eu³⁺-doped TiO₂ nanophosphors were synthesized using the co-precipitation method and characterized for structural, optical, and thermoluminescent (TL) properties. X-ray diffraction (XRD) analysis confirmed the anatase phase with crystallite sizes ranging from 19.47 to 28.05 nm. UV–Vis spectroscopy revealed a redshift on doping Eu³⁺ which causes a decrease in the optical band gap from 3.73 eV (pure TiO₂) to 3.44 eV (Eu-doped samples) as defect states introduced by europium ions. Raman and FTIR spectroscopy confirmed the structural integrity and vibrational modifications induced by Eu³⁺ doping. Thermoluminescence studies exhibited a prominent glow peak at 287 °C for TiO₂ doped with 3 mol % Eu³⁺, with quenching at higher doping levels due to the saturation of trapping centres. The activation energy of TL glow peaks is calculated using peak shape methods, ranging from 0.732 to 0.818 eV, indicating the presence of deep trap levels. The frequency factor varied between 2.78 × 10⁷ s⁻¹ and 1.68 × 10⁸ s⁻¹, suggesting a thermally stable trapping mechanism. The relatively low activation energy highlights the potential of Eu³⁺-doped TiO₂ as a rapid-response sensor material, suitable for radiation dosimetry and optoelectronic applications. These findings demonstrate that controlled Eu³⁺ doping can enhance the luminescence efficiency and thermal stability of TiO₂ nanophosphors, making them promising candidates for advanced sensing and display application.

This paper investigates the radiation pressure-driven linear magneto-gravitational instability in finitely conducting strongly coupled quantum plasma within the framework of the generalized hydrodynamic fluid model. The radiation pressure assists in the dynamic behavior of the plasmas by modifying the dispersion properties of the gravitational instability. Normal mode analysis is applied to the linearized perturbation equations to derive the general dispersion relation. The dispersion relations are discussed in the hydrodynamic and kinetic limits in the transverse and longitudinal propagation modes. The Jeans instability criterion and Jeans length are significantly modified due to radiation pressure, quantum corrections, and strong coupling effects. The viscoelastic compression mode in the kinetic limit has been coupled with quantum diffraction and Alfvén mode. It is also observed that the radiation pressure, quantum effects, and viscoelastic parameters suppress the growth rates; thus, these have stabilizing effects on the gravitational instability. The effects of various parameters on the growth rate of the instability are calculated numerically, and the outcomes are represented graphically.

The Southern Wide-field Gamma-ray Observatory, an experiment under development since 2019 with critical Brazilian contribution and leadership, is the most recent proposal for a ground-based gamma-ray detector in the Southern Hemisphere. When fully completed, it is expected to be the most sensitive particle detector array in the world, capable of measuring gamma rays from high- to ultra-high energies from a still-unexplored region of the sky including the Galactic Center. Over half a century of developments trace the history of Astroparticle Physics in South America, since the pioneering works of Cesar Lattes, that inaugurated experimental activities, first in Brazil, and across the region as a consequence. The Cherenkov Telescope Array Observatory (CTAO) is another global facility in planning for the continent, marking the next stage in a new era of large Latin-American astroparticle experiments inaugurated 25 years ago with the Pierre Auger Observatory, in Argentina, and later followed by the High-Altitude Water-Cherenkov (HAWC) Observatory, in Mexico. This contribution will introduce some of the general context and present the latest developments and perspectives for ground-based gamma-ray astronomy in Latin America, whose history testifies and pays tribute to the work and enduring legacy of Cesar Lattes.

In this paper, we investigate the influence of oscillating electric field radiation on the properties of a polaron in semiconductor quantum dot (SCQD). Using the Lee-Low-Pines-Huybrecht (LLPH) method, we derive the ground and first excited state energy of polaron. The superposition of these two energy states forms a two levels system (TLS) which is considered a quantum bit, allowing us to evaluate the probability density. The capacitance and the conductance of the SCQD are also investigated using the Drude model. Our results indicate that the electric field has pronounced effects on the properties of the polaron in SCQD. Some of these effects include, but are not limited to: (i) the variation of the probability density with respect to the x and y planar coordinates; (2i) the periodical modification of the probability density with electric field frequency, and its dependence on longitudinal optical (LO)-phonon coupling strength constant; (3i) both positive and negative values for the energy of the system, indicating the formation of free and couple polaronic entities. In particular, we found that the ground state energy of the polaron is predominant in gallium arsenide (GaAs) SCQD. Our results also suggest that oscillating electric field radiation leads to both coherent population transfer from the first excited to the ground states and to the scattering phenomenon. Therefore, investigating the interaction of an oscillating polaron-electric field (laser radiation) is especially relevant for gallium arsenide (GaAs).

The propagation of high-frequency positron-acoustic cnoidal waves (PACWs) is investigated in four-component plasmas consisting of inertialess non-Maxwellian electrons and hot positrons adhering to the Kaniadakis distribution, together with inertial fluid cold positrons and stationary ions. Using the reductive perturbation approach (RPA), the quadratic planar Korteweg-de Vries (KdV) equation is derived, and its cnoidal wave (CW) solution is reported. Additionally, at a critical plasma composition, such as the hot positron concentration, the modified-KdV (mKdV) equation is derived, and its CW solution is investigated. Subsequently, to examine the distinctive behavior of the fractional PACWs, both the integer KdV and mKdV equations are transformed into their fractional counterparts, namely the fractional KdV (FKdV) and fractional mKdV (FmKdV) equations. The Laplace novel iterative method (LNIM) is utilized to solve both FKdV and FmKdV equations and derive high-accuracy approximations for the two equations for modeling the characteristic behavior of FKdV-PACWs and KmKdV-PACWs. The influence of several associated physical parameters on the profile (amplitude and width) of both KdV-PACWs and mKdV-PACWs is numerically examined. Additionally, the impact of the fractionality on the profile of both FKdV-PACWs and FmKdV-PACWs is investigated. Moreover, the absolute error of the derived approximations is estimated and discussed numerically. Furthermore, the potential applications of the current study are discussed, and the obtained results are valuable for investigating the cosmic ray spectrum and the plasma environment surrounding stars.