Mean Free Path Research Articles

Radiation attenuation properties of transparent aluminum oxynitride: a comprehensive study

The investigation of radiation-durable materials with outstanding gamma shielding capabilities and lead-free alternatives remains a compelling area of research. This study fills a critical gap by exploring, for the first time, the radiation attenuation properties of the novel material aluminum oxynitride (AlON) and its shielding mechanism. Utilizing the XCOM database and Geant4 Monte Carlo simulation toolkit, we systematically examined AlON’s linear attenuation coefficient, mass attenuation coefficient, half-value layer, tenth-value layer, mean-free path, effective atomic number, and effective electron density. Comparing AlON to traditional shielding materials and glasses, including both lead-containing and lead-free compositions, our study suggests its superiority over concrete and lead-free glasses. At higher energies, AlON demonstrates comparability with lead-doped materials. These findings contribute valuable insights into the potential applications of AlON across diverse radiation shielding contexts. This research provides a foundational understanding of AlON’s radiation attenuation capabilities, paving the way for future exploration and practical applications in the field of gamma shielding.

Characterization and radiation shielding efficiency of MWCNT/shape memory ternary blend composite films

In this study, the structural, X-ray and gamma-ray, and neutron shielding properties of shape memory ternary blend/multi-walled carbon nanotube (MWCNT) composite films were investigated. The composition of the composite films was defined as (100-x) poly (ε-caprolactone) (PCL):polyethylene glycol (PEG):polyvinyl chloride (PVC) + xMWCNT, where x = 0, 1, 3, 5% (mole percentage). The ternary blend/MWCNT composite films were characterized using Attenuated Total Reflectance Infrared Spectroscopy (ATR-IR), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). Thermal results showed that the degradation temperatures of composite materials with two degradation curves increased with increasing MWCNT percentage. The appearance of the MWCNT signal along with the characteristic polymer signals in the XRD pattern may be evidence that MWCNT is homogeneously distributed in the polymer blend. The mass attenuation coefficients (MAC), half-value layer (HVL), mean free path (MFP), and effective atomic numbers (Z_eff) of the composite films were experimentally measured over an energy range of 8.04–383.85 keV. Additionally, the equivalent dose rates for fast neutrons were measured, and the exposure buildup factor (EBF) and fast neutron removal cross-section (Σ_R) were theoretically calculated. The proton and alpha shielding parameters of the ternary blend/MWCNT composite films were determined, revealing that the inclusion of higher amounts of MWCNTs in the composite structure significantly improved capability of the films in shielding against radiation and neutrons.

Radiative corrections for factorized jet observables in heavy ion collisions

I look at the renormalization of the medium structure function and a medium induced jet function in a factorized cross section for jet substructure observables in Heavy Ion collisions. This is based on the formalism developed in [1], which uses an Open quantum system approach combined with the Effective Field Theory (EFT) for forward scattering to derive a factorization formula for jet observables which work as hard probes of a long lived dilute Quark Gluon Plasma (QGP) medium. I show that the universal medium structure function that captures the observable independent physics of the QGP has both rapidity and UV anomalous dimensions that appear due to medium induced Bremsstrahlung. The resulting Renormalization Group (RG) equations correspond to the BFKL equation and the running of the QCD coupling respectively. I present the first results for the numerical impact of resummation using these RG equations on the mean free path of the jet in the medium. I also briefly discuss the prospects of extending this formalism for a short lived dense medium.

Impact of Bi2O3 on the glass system B2O3 -TeO2–MgO–PbO on the purpose of radiation shielding efficacy

In this study, eight glass samples were prepared with the composition of [x Bi2O3-(75-x) B2O3–15TeO2 –5MgO–5PbO; where x = 0, 10, 20, 25, 30, 40, 50, and 60 mol%]. In the composition of those glass samples, various amountsof B2O3 were replaced by Bi2O3 to improve the glass material's radiation shielding capability. The mechanical properties of these glasses have been evaluated using densimeter and microhardness. The Vickers microhardness (Hv) slightly decreases as the amount of Bi2O3 increases due to the formation of Non-Bridging Oxygen (NBO). To evaluate the radiation shielding effectiveness of the prepared glass samples, we performed Monte Carlo simulations of several shielding parameters. The mass attenuation coefficients of the experimentally produced BTMPBi glass series were calculated using NIST and MCNP6, and reasonable agreement was found between the simulation and experimental results. The relative difference between NIST and MCNP6-based results was calculated, and the maximum deviation was 2.21% for the 1173 keV gamma ray incident in the BTMPBi60 glass sample. The value of the mean free path of those prepared glass samples maintained the following trend - BTMPBi0> BTMPBi10> BTMPBi20> BTMPBi25> BTMPBi30> BTMPBi40> BTMPBi50>BTMPBi60. The prepared glass sample BTMPBi0 showed a 2.6 times higher value of the mean free path at energy 1332 KeV compared with the prepared BTMPBi60. Analyzing the composition of the prepared glass samples, it is clear that the greater the amount of Bi2O3 the greater the value of linear attenuation coefficient (LAC) and effective atomic number. Based on the results, it can be concluded that the glass sample containing 60 mol % of Bi2O3 (BTMPBi60) exhibited the highest radiation shielding capability among all of the prepared samples.

Super-Suppression of Long-Wavelength Phonons in Constricted Nanoporous Geometries.

In a typical semiconductor material, the majority of the heat is carried by long-wavelength, long-mean-free-path phonons. Nanostructuring strategies to reduce thermal conductivity, a promising direction in the field of thermoelectrics, place scattering centers of size and spatial separation comparable to the mean free paths of the dominant phonons to selectively scatter them. The resultant thermal conductivity is in most cases well predicted using Matthiessen's rule. In general, however, long-wavelength phonons are not as effectively scattered as the rest of the phonon spectrum. In this work, using large-scale molecular-dynamics simulations, non-equilibrium Green's function simulations, and Monte Carlo simulations, we show that specific nanoporous geometries that create narrow constrictions in the passage of phonons lead to anticorrelated heat currents in the phonon spectrum. This effect results in super-suppression of long-wavelength phonons due to heat trapping and reductions in the thermal conductivity to values well below those predicted by Matthiessen's rule.

Rate-limiting factors in thin-film evaporative heat transfer processes

In this paper, we present a theoretical study aimed at investigating the rate-limiting factors in thin-film evaporative heat transfer processes, considering the finite-rate evaporation kinetics. The problems of evaporation of a flat thin-film in either pure vapours or vapour-inert-gas mixtures are analysed based on the non-dimensionalised macroscopic transport equations for continuum fluids, coupled with out-of-equilibrium kinetic boundary conditions. Both the full numerical solutions and asymptotic analytical solutions at slow evaporation limit are provided and applied to analyse thin water film evaporation. Existing solutions, assuming negligible heat transfer in the gas domain, or negligible temperature jump across the non-equilibrium kinetic layer, or more boldly a thermodynamically equilibrial interface (i.e. its temperature is at the saturation temperature), can be fully recovered from the more general solutions presented here. Our results show that while these assumptions hold in special cases, they can lead to significant errors in many conditions, especially when the film thickness δ is reduced to a few micrometers or thinner. We show that the conventional views that the rate-limiting factors in thin-film evaporative heat transfer is either the heat diffusion through the liquid film or the mass transfer in the gas domain only apply to thick film (i.e. δ≫λ where λ is the mean free path in the vapour phase). As δ decreases to a few micrometer or smaller (more precisely when the Knudsen number Kn increases beyond O(1) in an pure vapour environment or when the kinetic Peclet number Pe is reduced below O(1) in inert gases), the interfacial thermal resistance due to the evaporation kinetics can be on the same orders of magnitude as the thermal resistance in the liquid film. The analysis also allow us to compare the heat transfer processes during the evaporation of a thin-film in pure vapours to those in inert gases, providing deeper insight into the effectiveness of various strategies for exploring the evaporation process in practical thermal management.

Gamma ray Shielding Properties of the 57.6TeO2-38.4ZnO-4NiO system

The radiation shielding is important for human health as it is hazardous for cell. New material development is under research for alternative shielding materials. Thus 57.6TeO2–38.4ZnO–4NiO system was developed and its shielding capacity were inspected. The variation of the linear attenuation coefficient (LAC) and some other parameters such as half value length (HVL), mean free path (mfp), effective atomic number (Zeff) and Effective electron density (Neff) were studied. The Phy-X/PSD program was utilized for this purpose

Presheath-like structures and effusive particle losses for biased probes at and near I–V electron saturation

A theory for presheath-like structures near probes biased at and above the plasma potential is developed for collisionless plasmas with an electron-neutral mean free path on the order of the chamber scale. The theory predicts presheath-like perturbations to the plasma that result from the free streaming of electrons and an effusion loss process from the chamber at the electrode. For these situations, a loss-cone-like velocity distribution function for electrons is predicted where the loss angle of the depletion region corresponds to the angular size of the electrode at a specified distance. The angle of the loss cone becomes 180° at the sheath edge. In comparison with a previous collisional electron presheath model that required electrons satisfy a Bohm criterion at the sheath edge [Scheiner et al., Phys. Plasmas 22, 123520 (2015)], the present work suggests that no such condition is needed for collisionless low pressure plasmas in the ≲10 mTorr range. The theory predicts the generation of a density depletion of roughly 0.5ne and an electron velocity moment of tens of percent of the electron thermal speed by the sheath edge in a presheath with a potential drop of less than Ti/e. The range of this presheath perturbation is determined by the electrode geometry instead of the collisional mean free path. These predictions are tested against previously published particle in cell simulations and are found to be in good agreement.

Radiation attenuation properties of yttrium lithium borate glasses

As the glass is used in a variety of fields, it is vital to test it on radiation shielding purposes. In this article, the radiation attenuation properties of examined glasses by replacing Li2O for Y2O3 have been investigated. The samples formulated as 72B2O3–(28-x)Li2O–xY2O3 (where x = 0,2,4,8,12 mol%). The parameters of linear absorption coefficients (LAC) and other parameters of half value layer (HVL), mean free path (MFP), tenth value layer (TVL) and effective atomic numbers were calculated. It was found that when Li2O is replaced to Y2O3, the radiation shielding properties of glasses increment.

Proximity-induced gapless superconductivity in two-dimensional Rashba semiconductor in magnetic field

Two-dimensional semiconductor-superconductor heterostructures form the foundation of numerous nanoscale physical systems. However, measuring the properties of such heterostructures, and characterizing the semiconductor in-situ is challenging. A recent experimental study by [Phys. Rev. Lett. 128, 107701 (2022)] was able to probe the semiconductor within the heterostructure using microwave measurements of the superfluid density. This work revealed a rapid depletion of superfluid density in semiconductor, caused by the in-plane magnetic field which in presence of spin-orbit coupling creates so-called Bogoliubov Fermi surfaces. The experimental work used a simplified theoretical model that neglected the presence of non-magnetic disorder in the semiconductor, hence describing the data only qualitatively. Motivated by experiments, we introduce a theoretical model describing a disordered semiconductor with strong spin-orbit coupling that is proximitized by a superconductor. Our model provides specific predictions for the density of states and superfluid density. Presence of disorder leads to the emergence of a gapless superconducting phase, that may be viewed as a manifestation of Bogoliubov Fermi surface. When applied to real experimental data, our model showcases excellent quantitative agreement, enabling the extraction of material parameters such as mean free path and mobility, and estimating gg-tensor after taking into account the orbital contribution of magnetic field. Our model can be used to probe in-situ parameters of other superconductor-semiconductor heterostructures and can be further extended to give access to transport properties.

Ionization layer with collision-free atoms at the edge of partially to fully ionized plasmas

When a hot arc spot has just formed on the cathode surface, e.g. in the course of arc ignition on a cold cathode, a significant part of the current still flows in the glow-discharge mode to the cold surface outside the spot. The near-cathode voltage continues to be high at all points of the cathode surface. The mean free path for collisions between the atoms and the ions within the plasma ball near the spot is comparable to, or exceeds, the thickness of the ionization layer, which is a part of the near-cathode non-equilibrium layer where the ion current to the cathode is generated. The evaluation of the ion current to the cathode surface under such conditions is revisited. A fluid description of the ion motion in the ionization layer is combined with a kinetic description of the atom motion. The resulting problem admits a simple analytical solution. Formulas for the evaluation of the ion current to the cathode for a wide range of conditions are derived and the possibilities of using these formulas to improve the accuracy of existing methods for modeling high-pressure arc discharges in relation to glow-to-arc transitions are discussed.

A comprehensive study of the shielding ability from ionizing radiation of different mortars using iron filings and bismuth oxide

The current work discusses the radiation attenuation capability and different shielding characteristics of different mortar samples. The samples were prepared by replacing different percentages of fine aggregate with iron filling and replacing different percentages of hydrated lime with Bi2O3 (0–50 wt.%). The prepared mortar samples are coded as CHBFX where X = 0, 10, 30, and 50 wt.%. The mass and linear attenuation coefficient was determined experimentally using a narrow beam technique, where a high purity germanium detector, and different point gamma-ray sources (such as Am-241, Cs-137, and Co-60). The linear attenuation coefficient was also calculated using the Monte-Carlo simulation code and the online Phy-X/PSD software. The comparison of the three methods showed a good agreement in the results. The linear attenuation coefficient drops from 19.821 to 0.053 cm−1 for CHBF0, from 27.496 to 0.057 cm−1 for CHBF10, from 42.351 to 0.064 cm−1 for CHBF30, and from 55.068 to 0.071 cm−1 for CHBF50 at photon energy range from 0.015 to 15 MeV. The half-value layer thickness, tenth-value layer thickness, and mean free path of the prepared mortar composites were also calculated photon energy ranged from 0.015 to 15 MeV. The fast neutron removal cross-section of the prepared CHBFX mortar samples have values of 0.096 cm−1, 0.098 cm−1, 0.103 cm−1, and 0.107 cm−1 for the mortar samples CHBF0, CHBF10, CHBF30, and CHBF50, respectively. The results showed that the mortar sample with the highest iron filing concentration, CHBF50, provides the best protection against gamma rays and fast neutrons which could be used in the nuclear and medical fields.

Energy Dissipation of Fast Electrons in Polymethylmethacrylate: Toward a Universal Curve for Electron-Beam Attenuation in Solids between ∼0 eV and Relativistic Energies.

Spectroscopy of correlated electron pairs was employed to investigate the energy dissipation process, as well as the transport and the emission of low-energy electrons on a polymethylmethacrylate surface, providing secondary electron spectra causally related to the energy loss of the primary. Two groups are identified in the cascade of slow electrons, corresponding to different stages in the energy dissipation process. The characteristic lengths for attenuation due to collective excitations and momentum relaxation are quantified for both groups and are found to be distinctly different: λ_{1}=(12±2) Å and λ_{2}=(62±11) Å. The results strongly contradict the commonly employed model of exponential attenuation with the electron inelastic mean free path as characteristic length, but they essentially agree with a theory used for decades in astrophysics and neutron transport, albeit with characteristic lengths expressed in units of angstroms rather than light-years.

Numerical analysis of a gas flow in a square cavity driven by spanwise lid motion on the basis of kinetic theory: Behavior of the gas near a sharp corner

A gas flow in a square cavity driven by a lid sliding in the direction of its line of contact with the cavity wall is considered. The steady behavior of the gas is numerically investigated based on the linearized Bhatnagar–Gross–Krook kinetic equation and the diffuse reflection boundary condition. When one applies the Stokes equation and the no-slip boundary condition to the system considered here, the flow velocity becomes multivalued at the corner between the lid and the cavity wall, and the shear stress diverges at the corner inversely proportionally to the distance from there, which is known as the so-called corner singularity. In the present work, the behavior of the gas near the corner is examined based on numerical results obtained from the kinetic theory. Although the range of the flow velocity value in the kinetic solution is limited due to the significant velocity slip near the corner, the flow velocity is, nevertheless, multivalued at the corner. The shear stress varies inversely proportionally to the distance from the corner up to the position that is a few tens of mean free paths away from there. The increase in the stress is suppressed at positions closer to the corner and its magnitude remains bounded. Thus, the total forces acting on the lid and the side cavity walls are bounded as well. Due to the distinctive behavior of the stress near the corner, the resulting nondimensional total forces behave with an unconventional rate Kn ln Kn for small Knudsen numbers Kn.

Radiation and nuclear shielding performance of tellurite glass system containing Li2O and MoO3: XCOM and FLUKA Monte Carlo

This study investigates the radiation attenuation properties of tellurite-based glasses with the chemical formula 75TeO2-(24-x)Li2O-(x)MoO3–1V2O5 (TLMV), where x = 0, 12, 24 mol%. The research focuses on important radiation protection values, such as the linear attenuation coefficient (μ), mass attenuation coefficient (μ/ρ), effective atomic number (Zeff), effective electron density (Neff), mass energy-absorption coefficient (MEAC), specific gamma-ray constants (Γ), gamma dose rate (Dr), mean free path (λ), half value layer (d1/2), and removal of fast neutrons (∑R). The gathered results indicate that changing Li2O and MoO3 mol% concentrations significantly impact shielding effectiveness. Additionally, this study compares the radiation shielding of TLMV glasses with commercial glasses, providing a comprehensive analysis for applications in healthcare, industrial, and related fields and exploring the potential usage of TLMV glasses in various shielding scenarios.

Exploring the Power of Language in Persuasion and Communication through the Lens of Ella Minnow Pea and The Unbearable Lightness of Being

Cognitive structures embody mental concepts and direct our thinking about the world. In addition, semantic approaches reveal the conceptual structures involved in organizing the meaning of a word in light of the frames by which the meanings of words are understood. To understand the most prominent cognitive theories and semantic concepts, one must rely and refer to the cognitive model consisting of the frame theory which is a cognitive theory that seeks to embody the mental concepts derived from the linguistic structure. Frames are the mental structures underlie the lexical unit and draw its paths of meaning and define its embodied frame. They also translate the process of interaction between language and the human mind in creating new meanings and conceptual concepts. Among the scholars who developed this theory is the American linguistic Charles Fillmore (1929-2014) who had a strong presence in the field of behavioral psychology through his structural and lexical semantic researches. He was one of the founders of mental and cognitive linguistics along with George Lakoff and others. Fillmore insisted on the great importance of semantics and its value in explicating different morphological and syntactic phenomena.

Advancing mechanical durability and radiation shielding properties in Silicon dioxide (SiO2) glasses through various incorporations: A comparative analysis

Silicon dioxide (SiO2) glasses, known for their high thermal stability, excellent optical transparency, and substantial mechanical strength, are crucial in numerous technological applications, including radiation shielding. This research explores the impact of compositional variations in SiO2-based glasses on their mechanical and radiation shielding properties, particularly focusing on the inclusion of heavy metal oxides (HMO) and rare earth elements (REE) like neodymium (Nd). Through the systematic investigation of fifteen distinct glass samples with varying concentrations of specific oxides and elements, we investigate the compositional changes and their influence on physical properties and their effectiveness in attenuating radiation. Our findings demonstrate that the incorporation of Nd significantly enhances the glass's radiation shielding capabilities. Glasses doped with Nd exhibited higher effective atomic numbers and electron densities, which translate to superior attenuation characteristics at lower photon energies. This is highlighted by the exceptional performance of the 20Nd sample, showing the lowest exposure build-up factors (EBF) at 10 mean free paths (mfp), indicating its potential as a premier candidate for shielding applications against various energy levels of radiation. Moreover, the variation in the Elastic Modulus of the glass samples underscores the significant impact of the glass matrix composition on its mechanical properties, suggesting a delicate balance between network formers and modifiers in determining the glass properties. It can be concluded that the neodymium-doped SiO2-based glasses may be considered as targeted compositions in fine-tuning material properties to meet specific application requirements. As the demand for efficient radiation shielding materials grows across medical, industrial, and space exploration sectors, our findings provide a solid foundation for the development of new glass formulations tailored for enhanced mechanical properties and superior radiation protection levels.

Rare earth tantalate coating materials for thermal and oxidation protection of carbon-carbon composites

To protect carbon/carbon composites against thermal corrosion and high-temperature oxidation, the thermal/oxygen barrier properties and static oxidation behavior of rare earth tantalates (YbTaO4 and LuTaO4) are investigated here. Both samples with the m' phase are successfully fabricated. The formation of oxygen vacancies benefits from atomic substitution and valence variation and the widths of the domain boundaries (18–23 nm) are close to the phonon mean free path. Low thermal conductivity is caused by Umklapp phonon-phonon scattering, oxygen vacancies and domain walls, with LuTaO4 having a value of 1.903 W m−1 K−1 at 900 °C. Furthermore, LuTaO4 has decreased oxygen-ion conductivity due to a high activation energy and immobile vacancies. A LuTaO4/Si coating can efficiently prevent the oxidation of C/C composites at 1100 °C for 15 h. The coating failure results from oxygen penetrating along the microscopic cracks and mismatch of the thermal expansion coefficients.

Thermal conductivity reduction due to phonon geometrical scattering in nano-engineered epitaxial germanium

Nano-engineering crystalline materials can be used to tailor their thermal properties. By adding new nanoscale phonon scattering centers and controlling their size, one can effectively decrease the phonon mean free path, hence the thermal conductivity of a fully crystalline material. In this Letter, we use the 3ω method in the temperature range of 100–300 K to experimentally report on the more than threefold reduction of the thermal conductivity of an epitaxially grown crystalline germanium thin film with embedded polydispersed crystalline Ge3Mn5 nano-inclusions with diameters ranging from 5 to 25 nm. A detailed analysis of the structure of the thin film coupled with Monte Carlo simulations of phonon transport highlights the role of the nano-inclusions volume fraction in the reduction of the phononic contribution to the thermal conductivity, in particular its temperature dependence, leading to a phonon mean free path that is set by geometrical constraints.

Fabrication, Structural Characterization, and Photon Attenuation Efficiency Investigation of Polymer-Based Composites.

Experiments have assessed various polymer composites for radiation shielding in diverse applications. These composites are lighter and non-toxic when compared to lead (Pb), making them particularly effective in diagnostic imaging for shielding against low-energy photons. This study demonstrates the fabrication of four composites by combining a base material, specifically a high-density polyethylene (HDPE) polymer, with 10% and 20% silicon (Si) and silicon carbide (SiC), respectively. Additionally, 5% molybdenum (Mo) was incorporated into the composites as a heavy metal element. The composites obtained were fabricated into 20 disks with a uniform thickness of 2 mm each. Discs were exposed to radiation from a low-energy X-ray source (32.5-64.5 keV). The chemical and physical properties of composites were assessed. The shielding ability of samples was evaluated by determining the linear and mass attenuation coefficients (μ and μm), radiation protection efficiency (RPE), half-value layer (HVL), and mean free path (MFP). According to our findings, supplementing HDPE with additives improved the attenuation of beams. The μm values showed that composite X-ray shielding characteristics were enhanced with filler concentration for both Si and SiC. Polymer composites with micro-molecule fillers shelter X-rays better than polymers, especially at low energy. The HVL and MFB values of the filler are lower than those of the pure HDPE sample, indicating that less thickness is needed to shield at the appropriate energy. HC-20 blocked 92% of the incident beam at 32.5 keV. This study found that increasing the composite sample thickness or polymer filler percentage could shield against low-energy radiation.