Search Results (107)

Pulsar wind nebulae (PWNe), formed when the wind originating from a rapidly rotating neutron star flows out into its surroundings, have now been observed across the electromagnetic spectrum from the radio to the PeV gamma-ray regime. For most of these sources, leptonic processes, where electrons interacting with background photon fields produce high-energy photons through inverse Compton scattering, are believed to be the origin of associated very-high-energy gamma-ray emission. As such, these objects cannot contribute significantly to the galactic hadronic cosmic ray flux at ∼TeV-PeV energies. However, in a handful of cases, the possibility for an energetically sub-dominant hadron population being accelerated and producing very to ultra-high energy gamma-rays through pion decay has not yet been comprehensively excluded. Such scenarios have received renewed attention in the light of recent results from the Large High Altitude Air Shower Observatory (LHAASO). In this review, we explore the theoretical background positing hadronic acceleration in galactic PWNe, considering cases where the hadrons escape from the pulsar surface and/or are accelerated in the wind, as well as potential ‘shock mixing’ scenarios. We also explore current and future possible constraints on a hadronic component to PWNe from observations. Full article

This review serves as a conceptual and practical introduction to strong-field quantum electrodynamics (SFQED), written from the standpoint of experimental physicists. Rather than providing a comprehensive theoretical review, the paper focuses on the core ideas, terminology, and challenges in SFQED that are most relevant to experimental design and interpretation. The review serves as a first point of contact with the subject, bridging the gap between foundational theory and hands-on experimental investigations, and complementing more formal literature in the field. Full article

We propose a novel theoretical framework for describing photon–electron interactions and electron collision processes in a unified manner within quantum electrodynamics. Specifically, we develop a method to construct the Dirac operator in curved spacetime using only matrix representations rooted in the basis structure of four-dimensional gamma matrix algebra, without introducing vierbeins (tetrads) or independent spin connections. We realize 16 gamma matrices with two indices as $256\times 256$ matrices and embed the spacetime metric directly into the matrix elements. This reduces geometric operations such as covariantization, connection-like operations, and basis transformations to matrix products and trace calculations, yielding a unified and transparent computational scheme. The spacetime dimension remains as four, and the number “16” represents the number of basis elements of four-dimensional gamma matrix algebra ($2^4=16$). Based on the extended QED Lagrangian, vertex rules, propagators, spin sums, and traces can be handled uniformly, making it suitable for automation. As validation of this method, we analyzed four fundamental scattering processes in atomic and particle physics: (i) Compton scattering (photon–electron scattering), (ii) muon pair production ($e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$), (iii) Møller scattering (electron–electron collision), and (iv) Bhabha scattering (electron–positron collision). In the flat spacetime limit, we confirmed the exact reproduction of standard quantum electrodynamics (QED) results including the Klein–Nishina formula. Furthermore, trial calculations using a metric with off-diagonal components show systematic deviations from flat results near scattering angle $\theta \approx {90}^{\circ }$, suggesting that metric-induced angular dependence could in principle serve as an observable signature. The matrix representation developed in this work enables unified pipeline execution of theoretical calculations for photon interactions and charged particle collision processes, with expected applications to precision calculations in atomic and particle physics. Full article

This work presents a simulation study of a Timepix3 telescope composed of nine detectors for use as a Compton scatter polarimeter in the energy range of 35–100 keV. Four detectors carry 1 mm thick silicon (Si) sensors and five detectors carry 1 mm thick cadmium telluride (CdTe) sensors. The modulation factor for 100% linearly polarized X-ray beams was found to be ${\mu }_{100}>70\%$ in the energy range of 55–80 keV. The quality factor of the polarimeter has its maximum 12.8% at the energy 75 keV. The comparison of quality factors and the calculations of a hypothetical observation of the Crab nebula show that this multilayer Timepix3 approach is competitive with contemporary X-ray polarimeters. Full article

Lightweight, lead-free polymer–mineral composites have attracted increasing interest as radiation-attenuating materials for applications where reduced mass and environmental compatibility are required. In this work, the $\gamma$-ray attenuation behavior of poly(ether ether ketone) (PEEK) reinforced with natural palygorskite and pumice was evaluated at filler concentrations of 10–40 wt%. Photon interaction parameters, including the linear attenuation coefficient ($\mu$), half-value layer (HVL), mean free path ($\lambda$), and effective atomic number ($Z_{\mathrm{eff}}$), were computed over the energy range 15 keV–15 MeV using the Phy-X/PSD platform and validated through full Geant4 Monte Carlo transmission simulations. At 15 keV, $\mu$ increased from $1.46{\mathrm{cm}}^{-1}$ for pure PEEK to $4.21{\mathrm{cm}}^{-1}$ and $8.499{\mathrm{cm}}^{-1}$ for the 40 wt% palygorskite- and pumice-filled composites, respectively, reducing the HVL from 0.69 cm to 0.24 cm and 0.11 cm. The corresponding $Z_{\mathrm{eff}}$ values increased from 6.5 (pure PEEK) to 9.4 (40 wt% palygorskite) and 15.3 (40 wt% pumice), reflecting the influence of higher-Z oxide constituents in pumice. At higher photon energies, the attenuation curves converged as Compton scattering became dominant, although pumice-filled PEEK retained marginally higher $\mu$ and shorter $\lambda$ up to the MeV region. These findings demonstrate that natural mineral fillers can enhance the photon attenuation behavior of PEEK while retaining the known thermal stability and mechanical performance of the polymer matrix as reported in the literature, indicating their potential use as lightweight, secondary radiation-attenuating components in medical, industrial, and aerospace applications. Full article

This study evaluates lead-free high-density polyethylene (HDPE) composites reinforced with high-Z oxides (Bi₂O₃, WO₃, Gd₂O₃, TeO₂, and a Bi₂O₃/WO₃ hybrid) as lightweight materials for gamma-ray and fast-neutron shielding. A hybrid computational framework combining Phy-X/PSD with Geant4 Monte Carlo simulations was used to obtain key shielding parameters, including the linear and mass attenuation coefficients (μ, μ/ρ), half-value layer (HVL), mean free path (MFP), effective atomic number (Z_eff), effective electron density (N_eff), exposure and energy-absorption buildup factors (EBF, EABF), and fast-neutron removal cross section (Σ_R). The incorporation of heavy oxides produced a pronounced improvement in gamma-ray attenuation, particularly at low energies, where the linear attenuation coefficient increased from below 1 cm⁻¹ for neat HDPE to values exceeding 130–150 cm⁻¹ for Bi- and W-rich composites. In the intermediate Compton-scattering region (≈0.3–1 MeV), all oxide-reinforced systems maintained a clear attenuation advantage, with μ values around 0.12–0.13 cm⁻¹ compared with ≈0.07 cm⁻¹ for pure HDPE. At higher photon energies, the dense composites continued to outperform the polymer matrix, yielding μ values of approximately 0.07–0.09 cm⁻¹ versus ≈0.02 cm⁻¹ for HDPE due to enhanced pair-production interactions. The Bi₂O₃/WO₃ hybrid composite exhibited attenuation behavior comparable, and in some regions slightly exceeding, that of the single-oxide systems, indicating that mixed fillers can effectively balance density and shielding efficiency. Oxide addition significantly reduced exposure and energy-absorption buildup factors below 1 MeV, with a moderate increase at higher energies associated with secondary radiation processes. Fast-neutron removal cross sections were also modestly enhanced, with Gd₂O₃-containing composites showing the highest values due to the combined effects of hydrogen moderation and neutron capture. The close agreement between Phy-X/PSD and Geant4 results confirms the reliability of the dual-method approach. Overall, HDPE composites containing about 60 wt.% oxide filler offer a practical compromise between shielding performance, manufacturability, and environmental safety, making them promising candidates for medical, nuclear, and aerospace radiation-protection applications. Full article

Lightweight and lead-free radiation shields are increasingly developed to overcome the toxicity and handling challenges associated with conventional heavy-metal-based materials. In this study, the $\gamma$-ray attenuation behavior of polymer–zeolite composites was examined by reinforcing high-density polyethylene (HDPE) and polylactic acid (PLA) with natural clinoptilolite zeolite at concentrations of 10–40 wt%. Photon-interaction parameters, including the linear attenuation coefficient ($\mu$), half-value layer (HVL), mean free path ($\lambda$), and effective atomic number ($Z_{\mathrm{eff}}$), were evaluated over 15 keV–15 MeV using the Phy-X/PSD platform. Zeolite incorporation consistently enhanced photon attenuation, particularly at low energies dominated by the photoelectric effect. At 15 keV, the HVL decreased from 0.60 cm to 0.08 cm for HDPE and from 0.043 cm to 0.033 cm for PLA as the zeolite loading increased to 40 wt%. Correspondingly, $Z_{\mathrm{eff}}$ increased from 2.7 to 4.3 for HDPE and from 6.5 to 11.6 for PLA, while $\mu$ reached approximately 41 cm⁻¹ and 56 cm⁻¹ at 15 keV for the respective 40 wt% composites. Beyond about 1 MeV, differences between compositions became minimal as Compton scattering dominated. PLA–zeolite composites exhibited higher $\mu$ and lower HVL than HDPE–zeolite, whereas HDPE maintained an advantage in mixed-field environments owing to its hydrogen-rich matrix. The results confirm that zeolite-reinforced polymers are safe, low-cost, and lightweight materials suitable for radiation shielding in medical, nuclear, and aerospace applications. Full article

Lead halide perovskites, including single-cation (MAPbI₃, FAPbI₃, CsPbI₃) and mixed-cation (Cs_0.12FA_0.88PbI₃, Cs_0.1MA_0.15FA_0.75PbI₃) compositions, are promising for both space photovoltaics and γ-ray detection due to their tunable optoelectronic properties. However, their response to high-energy radiation remains critical for reliable operation. We performed Monte-Carlo simulations using GEANT4 to investigate photon interactions (0.1–90 MeV) with perovskites of varying composition and thickness (1 cm to 1 μm). Results indicate that heavy atoms (Pb, I) dominate photoelectric absorption and scattering, broadly similar absorbed energies and event rates across compositions. Cs-containing perovskites exhibit slightly higher absorption and ionization, whereas FA- and MA-rich compositions show reduced photoelectric and Rayleigh scattering. Layer thickness strongly influences the radiation response: ultrathin films display fewer interactions with higher per-event energy, while millimeter-scale layers achieve efficient absorption and enable pair-production events at MeV energies. The sequence of dominant processes follows the expected energy dependence: photoelectric effect at low energies, Compton and Rayleigh scattering at intermediate energies, and pair production at high energies. These findings demonstrate that perovskite γ-interaction is primarily governed by heavy-atom content, with A-site cations fine-tuning the process balance, and that device performance for detection or photovoltaics depends critically on layer thickness. Full article

The Klein–Nishina formula is used to calculate and investigate the electronic cross-section, atomic cross-section, and Compton mass attenuation coefficients for the human blood, breasts, eye lens, ovaries, and testis, using X-rays in the 0.1–20 MeV energy range. The effects of radiation energy, tissue effective charge number, tissue density, and tissue electronic density on these parameters were studied. The results show that the electronic cross-section and atomic cross-section decrease with increasing radiation energy. These parameters are found to be linearly increasing when the density and electron density of a tissue increase. This increase is more rapid with a bigger slope when the electron density increases as compared to the density of each tissue. A complex relationship between these coefficients and the effective charge number Z_eff of tissues is observed because Z_eff changes with the energy and linear attenuation coefficient of a tissue. The Compton mass attenuation coefficient is found to be dependent on the effective charge number to mass number ratio Z_eff/A_eff instead of just the effective charge number. This increase in the Compton mass attenuation coefficient with increasing Z_eff/A_eff is rapid for the lower values of Z_eff/A_eff. However, for a higher Z_eff/A_eff ratio, the increase is very slow and becomes almost constant for X-ray energies above 10 MeV. The calculated parameters are useful in determining radiation dose for the investigated tissues and their response to low and high-energy X-rays. The results and outcomes are also very useful in shielding and protecting tissues from the hazards of radiation. These parameters are also helpful in determining the scattered and optimum doses to improve image quality and treatment options in radiology and radiation therapy to offer the best care. Full article

Compton backscattering is a versatile non-destructive technique for material characterization and structural evaluation in reinforced concrete. This methodology enables a single-sided inspection of large structures—which is particularly useful where only one side of the material is accessible for examination—is relatively inexpensive, and can be made portable for field applications. This study aims to assess the influence of basaltic coarse aggregates on the accurate localization and dimensioning of rebar in reinforced concrete using the gamma-ray Compton backscattering technique at two distinct incident photon energies—59.5 keV and 1170 keV. The analysis was performed through Monte Carlo simulations using the FLUKA code, providing insights into the feasibility and limitations of this non-destructive method for structural evaluation. Both photon energies successfully detected the rebar embedded at a 3 cm depth in mortar, achieving a good spatial resolution and contrast, despite the presence of a significant amount of iron oxide within the aggregate. Among the evaluated sources, ⁶⁰Co yielded the highest contrast and count values, demonstrating its potential for rebar detection at greater depths within concrete structures. The single-sided Compton scattering technique proved to be effective for the investigated application and presents a promising alternative for the non-destructive assessment of real-world reinforced concrete structures. Full article

State-of-the-art 2D sensitive semiconductor detectors developed within the SPARC collaboration can be utilized as dedicated Compton polarimeters in the hard X-ray regime. We report on the technique of Compton polarimetry utilizing such a detector and present a method to determine the linear polarization of an analyzed hard X-ray beam by means of Monte-Carlo-simulated data sets. Full article

High-sensitivity fiber scintillator detectors are the key to achieving high signal-to-noise ratio and high contrast imaging in X-ray Compton backscattering technology. We established a simulation model of wavelength-shifting fiber (WSF) scintillator detectors based on Geant4. The influences of ray source energy, detection area, number of WSFs, and coupling mechanism on detection efficiency were simulated. By using the epoxy resin coupling method, the transmission efficiency between the WSF and scintillator was increased from 4.56% to 19.79%. Based on the simulation data, we developed an X-ray WSFs scintillator detector, built an X-ray backscattering imaging experimental system, obtained high-contrast backscattering images, and verified the performance of the detector. Full article

In this work, we present updated models of the spectral energy distributions (SEDs) for two high-frequency-peaked BL Lac objects (HBLs), that is, 1ES 0414+009 and 1ES 1959+650. The hard gamma-ray spectra observed during their flaring states suggest the presence of an additional emission component beyond the standard synchrotron self-Compton (SSC) scenario. We explore the possibility that this hard gamma-ray emission arises from inverse Compton (IC) scattering by Bethe–Heitler pairs produced along the line of sight, pointing to a more complex high-energy emission mechanism in these sources. Full article

Although photon–photon scattering does not exist at the tree level, this is no longer the case at loop order and was first calculated by Euler and Heisenberg. The existence of this phenomenon has now been confirmed experimentally by the ATLAS collaboration and plays a small but important role in the calculation of $g_{\mu }$-2. We show how the low-energy form of the $\gamma \gamma$ scattering amplitude can be determined via causal (on-shell) methods using Compton scattering helicity amplitudes as input for the case of charged S = 0, S = $1/2$, and S = 1 intermediate state fields. Full article

Understanding the interaction of charged particles with polymers is crucial for applications in materials science, radiation physics, and electron spectroscopy. This study investigates the differences in the elastic scattering spectra of electrons and positrons in polyethylene, focusing on the underlying mechanisms that influence the spectral features. The analysis isolates key factors such as recoil energy, Doppler broadening, and the interplay between elastic and inelastic mean free paths. Using Monte Carlo simulations, we analyze the effects of the elastic and inelastic mean free paths on the intensity of the elastic peaks in an energy range from 1000 eV to 3000 eV. The results show that the elastic peaks are consistently more intense for electrons than for positrons, correlating with the differences in the respective elastic scattering cross sections. In addition, we evaluate the effects of different inelastic mean free path models on spectral variations and compare the simulated data showing how variations in inelastic mean free path values affect the intensity of elastic peaks and the elastic reflection coefficient of polyethylene. The percentage difference in the elastic reflection coefficients of electrons and positrons in polyethylene decreases from 49% to 24% when the incident particle energy increases from 1000 eV to 3000 eV. These findings contribute to a refined understanding of the interactions of electrons and positrons with polymers, improve the accuracy of Monte Carlo simulations, and promote methods for material characterization. Full article