Positron Annihilation Lifetime Research Articles

Chemical environment effects on the size of mono-vacancy in CrFeCoNi alloy

Atomic studies of mono-vacancy are crucial for comprehending the mechanisms governing the related macroscopic properties of materials. High-entropy alloys (HEAs) manifest unique properties arising from a complex, localized, disordered chemical environment and distinctive site lattice distortions. In this study, the effects of chemical environment on the size of vacancy point defects in equiatomic CrFeCoNi alloy are investigated using Density Functional Theory through positron annihilation lifetime (PL) calculations. To better understand the nature of local lattice distortion, a similar atomic environment method is employed for supercell construction. Our findings reveal a significant inverse relationship between the PL of single-vacancy in CrFeCoNi HEA and the number of its first nearest neighbor Cr atoms. The underlying mechanisms in the perspective of local atomic mismatch and electronic structures are discussed.

Innovative Mn3−xO4−y@NCA design: Leveraging Mn/O vacancies and amorphous architecture for enhanced sodium-ion storage

Manganese-based oxide electrode materials suffer from severe Jahn-Teller (J-T) distortion, leading to severe cycle instability in sodium ion storage. However, it is difficult to adjust the electron at d orbitals exactly to a low spin state to eliminate orbital degeneracy and suppress J-T distortion fundamentally. This article constructed concentration-controllable Mn/O coupled vacancy and amorphous network in Mn3O4 and coated it with nitrogen-doped carbon aerogel (Mn3−xO4−y@NCA). The existence of Mn/O vacancies has been confirmed by scanning transmission electron microscopy (STEM) and positron annihilation lifetime spectroscopy (PALS). Atomic absorption spectroscopy (AAS) and X-ray photoelectron spectroscopy (XPS) determine the most optimal ratio of Mn/O vacancies for sodium ion storage is 1:2. Density functional theory (DFT) calculations prove that Mn/O coupled vacancies with the ratio of 1:2 could exactly induce a low spin states and a d4 electron configuration of Mn, suppressing the J-T distortion successfully. The abundant amorphous regions can shorten the transport distance of sodium ions, increase the electrochemically active sites and improve the pseudocapacitance response. From the synergetic effect of Mn/O coupled vacancies and amorphous regions, Mn3−xO4−y@NCA exhibits an energy density of 37.5 W h kg−1 and an ultra-high power density of 563 W kg−1 in an asymmetric supercapacitor. In sodium-ion batteries, it demonstrates high reversible capacity and exceptional cycling stability. This research presents a new method to improve the Na+ storage performance in manganese-based oxide, which is expected to be generalized to other structural distortion.

Swift Au+9 ion irradiation-induced defects and alloy complexity effect on the mechanical hardness of NiCoCrFePd HEA and NiCoCrFe MEA

The outstanding radiation damage stability of an NiCoCrFePd high entropy alloy (HEA) as compared to conventional alloys poses the question for the mechanism of an ion–matter interaction. The positron annihilation lifetime spectroscopic and TEM (transmission electron microscopic) measurements are implemented to trace different kinds of defects produced by 120 MeV Au+9 ion irradiation and their evolution as a function of ion fluence. The variation of lifetimes and corresponding intensities with the ion fluence indicates the formation of dislocation-type defects at a lower ion fluence and vacancy clusters at a higher ion fluence caused by coalescence or agglomeration of dislocation defects. Formation of different types of defects in turn modulates the strain development inside the crystal. Additionally, the HR-TEM investigation of NiCoCrFePd HEA also exhibits the formation of dislocation and vacancy clusters with the average size of vacancy clusters increases from ∼2.9 ± 0.1 to ∼3.8 ± 0.1 nm with the increases in the ion fluence. Surprisingly, the average defect cluster size in NiCoCrFePd HEA is suppressed compared to NiCoCrFe MEA, thereby showing the enhanced radiation stability on Pd incorporation due to the high defect recombination caused by reduced thermal conductivity and high lattice distortion. Nano-indentation measurement shows that the radiation hardening behavior of the NiCoCrFePd HEA responded slowly owing to its damage suppression property as compared to the NiCoCrFe MEA. Additionally, softening behavior also appeared at an early fluence in NiCoCrFe MEA compared to the NiCoCrFePd HEA signifying its excellent resistance to defect accumulation.

Probing of CoO-induced nano-sized defects in Li2SO4–MgO–P2O5 glasses: Insights from positron annihilation lifetime spectroscopy

This study investigates the influence of CoO doping on concentration and characteristics of nano-sized cavities in Li₂SO₄-MgO-P₂O₅ glasses using positron annihilation lifetime spectroscopy (PALS). These defects are known to significantly impact the physical properties of glasses. Glasses with compositions of 20 Li₂SO₄-20MgO-(60-x) P₂O₅: x CoO (0 ≤ x ≤ 1.0 mol%), were prepared using melt-quench technique. PALS analysis revealed a strong dependence of positronium (e⁺- e⁻ pair) lifetime on CoO concentration. The analysis of the results further indicated that the fraction of free volume Δf/f0) and cavity radius (R) reached minimum values between 0.6 and 0.8 mol% CoO, but increased with further CoO doping. This suggests that cobalt ions prefer Oh sites, act as network modifiers, and create a larger concentration of free volume defects when CoO is increased beyond 0.8 mol%. Notably, the PALS-derived free volume defect concentration with CoO concentration is found to follow nearly same trend exhibited by the results of optical absorption and AC conductivity studies.

TDAE aromatic oil preference for polymer blends: An analysis of S-SBR, BR, and miscible S-SBR/BR systems

This study assesses the impact of Treated Distillate Aromatic Extract (TDAE) oil, at concentrations of 0–20 parts per hundred rubber (phr), on the glass transition temperature (Tg) of High Vinyl/Low Styrene Styrene-Butadiene Rubber (HVLSS-SBR), polybutadiene rubber (BR), and their blends with weight ratios of 70/30 and 50/50. Using Dynamic Mechanical Analysis, Broadband Dielectric Spectroscopy, and Positron Annihilation Lifetime Spectroscopy, we found that TDAE modifies Tg and fractional free volume (Fv) differently across materials. In HVLSS-SBR, TDAE reduced Tg by approximately 10 °C and increased Fv by 0.8 %. In BR, TDAE raised Tg by 5–7 °C without altering Fv. The 70/30 blend showed no Tg change but a 0.6 % Fv increase. For the 50/50 blend, one Havriliak-Negami equation indicated a Tg rise of 2–3 °C and a 0.4 % Fv increase. A two-equation analysis revealed a 6 °C Tg increase and 0.9 % Fv boost in the BR-rich phase, versus a 2 °C rise and 0.3 % Fv uptick in the HVLSS-SBR-rich phase. The sequence of compatibility, influenced by TDAE, is crystalline BR > amorphous BR > HVLSS-SBR >70/30 blend >50/50 blend. This study provides valuable insights into the behavior of TDAE oil in rubber blends and can serve as a basis for further research in this field.

Alkali Silicates Codoped with NIR-Emitting RE (Nd3+ and Yb3+) Ions for Thermometry Applications.

In the present study, the synthesis of BaSrSiO4 co-doped Yb3+ and Nd3+ nanophosphors (NPs) was successfully achieved through the conventional sol-gel method, as confirmed by X-ray diffraction and SEM analysis, verifying the formation of pure NPs. The FTIR and Raman spectra analysis confirm the formation of silicates, as different modes and vibrations of Si-O and Si-O-Si were seen at 800-1000cm-1. The energy transfer (ET) mechanism between Nd3+ and Yb3+ ions was seen as the emission spectra showed a rise in intensity of one over another. PLE emission spectra showed transitions at 2F7/2-2F5/2 for Yb3+ and from 4F3/2 to (4I9/2, 4I11/2, and 4I13/2) for Nd3+ when excited at 785nm. All the samples record low activation energy, which shows that the rate of reaction will be higher in all the samples, and it will be highest for 1mol% Nd3+ and 1mol% Yb3+. An increasing value of τ was seen with increasing Yb3+ concentration, which confirms the increase in the population of trap centers. The positron annihilation lifetime (PAL) curve showed that 1mol% Yb3+ and 2mol Nd3+ have single vacancies or shallower positron traps, whereas 3mol% Yb3+ and 2mol% Nd3+ have larger defects like surface oxygen vacancy clusters. The other two samples have balance vacancies, which makes them best for thermometry applications. The fluorescence intensity ratio (FIR) was calculated to get sensitivity for thermometry application. 2.13% K-1 sensitivity achieved at 303-333K temperature.

Effect of the electric field on the free volume investigated from positron annihilation lifetime and dielectric properties of sulfonated PVC/PMMA

AbstractPolymer electrolyte membranes (PEMs) play a vital role in electrochemical devices, facilitating ion conduction while blocking gases and electrons. Their effectiveness is closely linked to their microstructural properties, especially the free volume, which impacts ionic conductivity, mechanical strength, and overall device performance. This study examines the behavior of PVC/PMMA/SSA blends under electric fields, using Positron Annihilation Lifetime Spectroscopy (PALS) to assess free volume and dielectric properties. The study involved preparing and characterizing membranes through x‐ray diffraction (XRD), thermogravimetric analysis (TGA), and PALS. XRD results indicated semi‐crystalline structures with changes in intensity due to temperature variations, while TGA highlighted changes in thermal stability under different electric fields. PALS measurements showed that free volume varied with temperature and electric field strength, influencing the material's dielectric and mechanical characteristics. The results revealed that higher electric fields reduced free volume while enhancing dielectric properties. The dielectric constant and loss were found to depend on frequency, which was affected by the polar SO3H groups. Impedance spectroscopy provided further insights into the electrical properties, showing increased dc conductivity with stronger electric fields. A correlation between the free volume investigated from PAL and the electrical properties was observed. This study emphasizes the significance of free volume and external electric field in optimizing PEMs for advanced energy applications.

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Heat capacities and role of defects in ion transfer of quinuclidinium hexafluorophosphate plastic crystal

To study the phase behavior and role of defects in the ion conduction of a well-investigated plastic crystal electrolyte, we measured the low-temperature heat capacities of quinuclidinium hexafluorophosphate ([HQ]PF6) plastic crystal and the defects of pure [HQ]PF6 and its mixtures containing lithium ions and chloride ions. The heat capacities of the pure material show two solid‒solid phase transitions at room temperature and a low temperature. Positron annihilation lifetime spectroscopy (PALS) revealed the phase dependence of the defect size for both the pure material and the mixtures. The defects in these two mixtures expand largely to approximately 2 (with Li+) and 2.5 (with Cl−) times larger than those in the pure material. The relationships between the ionic conductivity and vacancy volume of the pure material and the mixtures obey the Cohen−Turnbull free volume model, which is also phase dependent. This work help elucidate defect-assisted ion transfer in organic ionic plastic crystals.

Coordination Structure Modulation in Group-VIB Metal Doped Ag3PO4 Augments Active Site Density for Electrocatalytic Conversion of N2 to NH3.

Doping is considered a promising material engineering strategy in electrochemical nitrogen reduction reaction (NRR), provided the role of the active site is rightly identified. This work concerns the doping of group VIB metal in Ag3PO4 to enhance the active site density, accompanied by d-p orbital mixing at the active site/N2 interface. Doping induces compressive strain in the Ag3PO4 lattice and inherently accompanies vacancy generation, the latter is quantified with positron annihilation lifetime studies (PALS). This eventually alters the metal d-electronic states relative to Fermi level and manipulate the active sites for NRR resulting into side-on N2 adsorption at the interface. The charge density deployment reveals Mo as the most efficient dopant, attaining a minimum NRR overpotential, as confirmed by the detailed kinetic study with the rotating ring disk electrode (RRDE) technique. In fact, the Pt ring of RRDE fails to detect N2H4, which is formed as a stable intermediate on the electrode surface, as identified from in-situ attenuated total reflectance-infrared (ATR-IR) spectroscopy. This advocates the complete conversion of N2 to NH3 on Mo/Ag3PO4-10 and the so-formed oxygen vacancies formed during doping act as proton scavengers suppressing hydrogen evolution reaction resulting into a Faradaic efficiency of 54.8% for NRR.

Investigating the impact of gamma irradiation and temperature on vacancy formation and recombination in ZrB2 ceramics using positron annihilation spectroscopy

In the presented work, the mechanism of evolution of defects in the crystalline structure after irradiation with 1500 kGy and 3000 kGy absorption dose at room temperature in a 60Co gamma source was studied, using 43 nm sized ZrB2 crystals. The crystals were characterized by a purity of 99.9%, a powder density of 0.23 g/cm3, a specific surface area of 80 to 120 m2/g, and a hexagonal P6/mmm spatial structure. The dose rate applied was 6.05 Gy/s, with 1.17 and 1.37 MeV energy lines. The effect of particles resulting from the decay of 22Naradioactive isotope β+ with an activity of 10.5 μCi, as well as gamma quanta with an energy of 1.27 MeV, on the core and valence electrons and vacancies in the crystal structure was studied using Positron Annihilation Lifetime Spectroscopy (PALS) and Doppler broadening analysis methods. Additionally, the changes in the S and W parameters, which characterize the distribution of defects within the volume of the ZrB2 crystal, were studied using the Doppler broadening method. For unannealed material, the positron lifetime τ1 component varied between 174±2 ps and 181±1 ps. After annealing, the positron lifetime component τ2 was decreased from 290±3 ps to 226±3 ps, and the intensity component I2 increased from 17.49% to 40% depending on the radiation dose. The calculated values of the positron lifetime τ for one boron vacancy from ABINIT and MIKA packages were found to be 172 ps and 145 ps, respectively. The material was observed to satisfy the necessary functional conditions at gamma doses not exceeding 3000 kGy.

Effects of Low-Temperature Heat Treatment on Mechanical and Thermophysical Properties of Cu-10Sn Alloys Fabricated by Laser Powder Bed Fusion.

This study investigated the impact of low-temperature heat treatments on the mechanical and thermophysical properties of Cu-10Sn alloys fabricated by a laser powder bed fusion (LPBF) additive manufacturing (AM) process. The microstructure, phase structure, and mechanical and thermal properties of the LPBF Cu-10Sn samples were comparatively investigated under both the as-fabricated (AF) condition and after low-temperature heat treatments at 140, 180, 220, 260, and 300 °C. The results showed that the low-temperature heat treatments did not significantly affect the phase and grain structures of the Cu-10Sn alloys. Both pre- and post-treatment samples displayed consistent grain sizes, with no obvious X-ray diffraction angle shift for the α phase, indicating that atom diffusion of the Sn element is beyond the detection resolution of X-ray diffractometers (XRD). However, the 180 °C heat-treated sample exhibited the highest hardness, while the AF samples had the lowest hardness, which was most likely due to the generation of precipitates according to thermodynamics modeling. Heat-treated samples also displayed higher thermal diffusivity values than their AF counterpart. The AF sample had the longest lifetime of ~0.19 nanoseconds (ns) in the positron annihilation lifetime spectroscopy (PALS) test, indicating the presence of the most atomic-level defects.

Defect dynamics studies during heat treatments in plastically deformed metals predicted for nuclear applications

We report on defects dynamics during heat treatment in plastically deformed metallic materials using positron annihilation lifetime spectroscopy carried out on the intense pulsed positron beam. The conducted experiment allowed us to observe the changes in the concentration and sizes of vacancy-like defects observed during in situ annealing. We monitored heat treatments up to 300 °C in hydrostatic extruded Ti and cavitation peened V–4Cr–4Ti alloy. We were able to track the recovery processes in Ti and redistribution of large voids at the surface of cavitation peened V–4Cr–4Ti alloy. The relaxation time during recovery was about 20 min. Performed experiments show that in cold-worked metallic materials significant changes in vacancy clusters concentrations occur at mildly elevated temperatures. The presented results give opportunity to the application of in situ observation of defects dynamic to similar problems related to thermomechanical processing of metallic materials.Graphical abstract

Investigating the Free Volumes as Nanospaces in Human Stratum Corneum Lipid Bilayers Using Positron Annihilation Lifetime Spectroscopy (PALS).

This work is the first one that provides not only evidence for the existence of free volumes in the human stratum corneum but also focuses on comparing these experimental data, obtained through the unique positron annihilation lifetime spectroscopy (PALS) method, with theoretical values published in earlier works. The mean free volume of 0.269 nm was slightly lower than the theoretical value of 0.4 nm. The lifetime τ3 (1.83 ns with a coefficient of variation CV of 3.21%) is dependent on the size of open sites in the skin. This information was used to calculate the free volume radius R (0.269 nm with CV 2.14%), free volume size Vf (0.081 nm3 with CV 4.69%), and the intensity I3 (9.01% with CV 10.94%) to estimate the relative fractional free volume fv (1.32 a.u. with CV 13.68%) in human skin ex vivo. The relation between the lifetime of o-Ps (τ3) and the radius of free volume (R) was formulated using the Tao-Eldrup model, which assumes spherical voids and applies to sites with radii smaller than 1 nm. The results indicate that PALS is a powerful tool for confirming the existence of free volumes and determining their size. The studies also focused on describing the probable locations of these nanospaces in SC lipid bilayers. According to the theory, these play an essential role in dynamic processes in biological systems, including the diffusion of low-molecular-weight hydrophobic and moderately hydrophilic molecules. The mechanism of their formation has been determined by the molecular dynamics of the lipid chains.

High adsorption of Cu(II) in novel thiacalix[4]arene/acrylic polymer/diatomite fast fabricated by electron beam irradiation: Controllable microstructures, adsorption performance and mechanism

Chemical grafting of calix[4]arene is a common method to prepare high-performance calix[4]arene adsorbents for heavy metals, however, the chemical grafting process consumes much time and a large amount of heating energy due to the tedious steps. Herein, a thiacalix[4]arene/acrylic polymer/diatomite (TC4A/PAA/diatomite) adsorbent was fast fabricated by electron beam irradiation induced grafting, polymerization and crosslinking technique only in one-pot for the removal of Cu(II) as an important form of heavy metal pollution. Characterization by Fourier transform infrared (FTIR) spectra, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), diffuse reflectance UV–visible spectra and positron annihilation lifetime spectra (PALS) disclosed that the eco-friendly and low-cost TC4A/PAA/diatomite irradiated at 90 kGy namely TC4A/PAA/diatomite (90 kGy) with strong complexing ability owing to many functional groups such as carboxyl, hydroxyl etc in it. The effects of electron beam irradiation dose, initial solution pH, and initial concentration of Cu(II) on the adsorption performance of TC4A/PAA/diatomite were investigated. The isotherm adsorption data of Cu(II) in TC4A/PAA/diatomite (90 kGy) are more suitable for the Langmuir model with the maximum adsorption capacity of 123.30 mg/g. In addition, the bifunctional TC4A/PAA/diatomite (90 k Gy) can efficiently remove Cu(II) and display excellent reusability properties. The adsorption mechanism was further analyzed by FTIR, SEM, X-ray photoelelctron spectroscopy (XPS), diffuse reflectance UV–visible spectra and PALS. This study provides a fast, efficient and eco-friendly synthesis method of calix[4]arene adsorbent, conducing to the design of material innovation. Meanwhile, TC4A/PAA/diatomite (90 kGy) has potential application prospects in the treatment of practical Cu(II) contaminated wastewater.

Annealing temperature induced micro-structural, opto-electronic, electrical and fluorescence properties of the sol–gel synthesized CdO nanoparticles through the analytical study of vacancy-type defects

Cadmium oxide (CdO) nanoparticles (NPs) have been synthesized through the simple sol–gel route using cadmium nitrate tetrahydrate and aqueous ammonium hydroxide as precursors. Synthesised products were annealed at different temperatures in the range of 250 °C–500 °C. The annealed samples were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), Selected area electron diffraction (SAED), Field emission scanning electron microscopy (FESEM), UV–visible absorption (UV–Vis), room temperature Fluorescence (FL) measurements, Positron annihilation lifetime spectroscopic measurements (PALS) and resistivity measurements. Through the utilization of XRD method, it was shown that the particle size varies from 15 nm to 35 nm and unit cell volume exhibit an increase, while the lattice strain decreases as the annealing temperature is raised. The interplanar distance reduces as temperature increases, and the presence of defects can explain the minimal fluctuation in lattice characteristics. There is an inverse relationship between lattice strain and dislocation density of the pristine CdO NPs. The Williamson-Hall (W-H) analysis demonstrated a decrease in compressive lattice strain as particle sizes increased. The TEM and FESEM techniques were used to analyze the nearlyspherical morphological characteristics of CdO NPs, and thesize-related XRD results were further supported by the histogram plots from TEM. UV–Vis spectroscopy revealed that the band gap energy drops from 4.02 eV to 3.33 eV as the particle size increases, which may be attributed to the quantum confinement effect and the presence of defect states in the energy band gap. The distinct emission peaks of CdO NPs are detected in the fluorescence spectra at the wavelengths 488 nm, 529 nm and 584 nm. These findings indicate a modest correlation between the emission bands and the energy band gap. The strength of the emission peaks has been amplified as the annealing temperature increases, indicating a higher concentration of oxygen vacancies with increase in annealing temperatures. PALS shows the concentration of vacancy-clusters are reduced with the increase in temperature, which justifies the decrease in resistivity (from ∼ 1 × 102 to 2 × 10−2 Ω cm) with rise in annealing temperature as measured by the standard four-probe method. These characteristics of the NPs can be utilized in various optoelectronic and energy storage applications.

Comparative analysis of parent and modified ZSM-5 zeolites: Insights from positron annihilation lifetime spectroscopy

Modified zeolite ZSM-5 samples were prepared by synthesis in the presence of the organics acting as mesoporogens: cationic surfactant, hexadecyltrimethylammonium bromide (CTAB) and cationic polymer, polydiallyldimethylammonium chloride (PDADMAC), as well as by alkali etching of the parent zeolite. Properties of modified zeolites were compared to the parent ZSM-5 zeolite. X-ray diffractograms demonstrate that the obtained modified zeolite ZSM-5 samples in all cases have preserved parent crystalline zeolite framework of the MFI-type. However, scanning electron micrographs of the same samples show morphology variations of the modified samples as compared to the starting zeolite. Thermogravimetric analyses show distinct weight loss curves of the samples. Differences have been also noted in the hydroxyl stretching range of the infrared spectra, and in the results of positron annihilation lifetime spectroscopy (PALS) measurements, which indicated dissimilarities by probing free volume in parent and modified zeolite ZSM-5 samples. In that way, PALS as scarcely used technique in zeolite studies, proved its applicability in structural investigation of this kind.

Insights into the LiMn2O4 Cathode Stability in Aqueous Electrolytes.

LiMn2O4 (LMO) cathodes present large stability when cycled in aqueous electrolytes, contrasting with their behavior in conventional organic electrolytes in lithium-ion batteries (LIBs). To elucidate the mechanisms underlying this distinctive behavior, we employ unconventional characterization techniques, including variable energy positron annihilation lifetime spectroscopy (VEPALS), tip-enhanced Raman spectroscopy (TERS), and macro-Raman spectroscopy (with tens of μm-size laser spot). These still rather unexplored techniques in the battery field provide complementary information across different length scales, revealing previously hidden features. VEPALS offers atomic-scale insights, uncovering cationic defects and subnanometer pores that tend to collapse with cycling. TERS, operating in the nanometric range at the surface, captured the presence of Mn3O4 and its dissolution with cycling, elucidating dynamic changes during operation. Additionally, TERS highlights the accumulation of SO4 2- at grain boundaries. Macro-Raman spectroscopy focuses on the micrometer scale, depicting small changes in the cathode's long-range order, suggesting a slow but progressive loss of crystalline quality under operation. Integrating these techniques provides a comprehensive assessment of LMO cathode stability in aqueous electrolytes, offering multifaceted insights into phase and defect evolution that can help to rationalize the origin of such stability when compared with conventional organic electrolytes. Our findings advance the understanding of LMO behavior in aqueous environments and provide guidelines for its development for next-generation LIBs.

Optimization study of a new β +-γ coincidence positron annihilation lifetime spectrometer using Geant4

Positron annihilation lifetime (PAL) spectroscopy is a unique method for characterizing atomic-scale defects and ultramicropores in materials. The conventional PAL spectrometer adopts the γ-γ coincidence principle, and its performance, especially the coincidence counting rate (CCR), can hardly be further increased. Another coincidence principle, β +-γ coincidence, has the potential to simultaneously improve the CCR and coincidence time resolution (CTR) of PAL spectrometers. However, early β +-γ coincidence PAL spectrometers have not been widely applied due to the considerable room for improvement in their performance. In this work, we proposed a new β +-γ coincidence PAL spectrometer utilizing silicon photomultiplier (SiPM) array as the positron detector and conducted a comprehensive optimization of its structure with the aim of achieving a breakthrough in performance. The effects of start signal threshold and structure parameters on its CTR, CCR, and proportion of source contribution (P SC) were studied using Geant4. The simulation results show that, with a 68Ge positron source of 30 μCi, the optimized β +-γ coincidence PAL spectrometer can achieve an extremely high CCR exceeding 10000 counts per second (cps) and an outstanding CTR below 160 picoseconds (ps) while maintaining a low P SC below 12%. This study provides valuable guidance for constructing high-performance β +-γ coincidence PAL spectrometers.

Isosorbide-based Poly(arylene ether) biopolymer membranes for gas separation

Efforts to utilize biopolymer membranes to diminish the carbon footprint of separation processes are ongoing. Herein, we report the fabrication of isosorbide (ISB)-based poly(arylene ether) biopolymer membranes, including ISB-based poly(arylene ether sulfone) (I-PAES) and ISB-based poly(arylene ether ketone) (I-PAEK) for gas separation. The robust mechanical properties and amorphous nature of ISB-based biopolymers allow for their application to gas separations. Both positron annihilation lifetime spectroscopy (PALS) and free volume analysis using density measurements reveal that replacing bisphenol A (BPA) in polysulfone (PSF) with ISB results in a significant reduction in free volume owing to the absence of bulky dimethyl groups and the presence of polar aliphatic ether groups. Substituting the sulfone group for a ketone group further decreased free volume. Solid-state CP/MAS 13C NMR analysis discloses that substituting ISB and replacing sulfonyl moieties with carbonyl groups restricts the rotational motion of internal rings, resulting in inhibited gas diffusion. Consequently, the I-PAEK membrane exhibited H2/CO2 and H2/CH4 selectivities more than three times and five times higher, respectively, compared to the PSF counterpart. Our present study demonstrates the feasibility of ISB-based poly(arylene ether) biopolymer membranes for gas separation.