Positron Annihilation Lifetime Spectroscopy Studies Research Articles

Synthesis of High Na+ Ion-Conducting NASICON-Based Electrolytes and Insights from Diffraction and Positron Annihilation Lifetime Spectroscopy Studies

Synthesis of High Na⁺ Ion-Conducting NASICON-Based Electrolytes and Insights from Diffraction and Positron Annihilation Lifetime Spectroscopy Studies

Improved mechanical and microstructural performance of high-density polyethylene–chitosan–hydroxyapatite composites as potential bone implant materials

High-density polyethylene (HDPE)–chitosan–hydroxyapatite hybrid composite series with varying concentration of hydroxyapatite were prepared and compared with its corresponding HDPE-chitosan binary composite. The microstructural and mechanical characterizations of the prepared composites were studied. A 12% increase for the composite system with 8 wt% hydroxyapatite (HA4) has been noted when compared with its corresponding binary system and has been optimized for further applications. The structural characterization and miscibility of the components in the composite system were studied by using Fourier transform infrared spectroscopy and X-ray diffractometry. Positron annihilation lifetime spectroscopy studies showed that the free holes are formed in the range of ∼115.8 Å3. Contact angle studies and sorption studies were further correlated with the biocompatibility analysis to study cell adhesion and protein absorption on the surface of the composites. MC3T3 E1 cell lines showed good cell proliferation on the optimized systems. The presence of micropores along with chitosan and hydroxyapatite promoted cell growth in the prepared composites. The current research study presents the development of an improved hybrid biocomposite material that has potential in biomedical implants.

Exploration of nano sized defects in Fe2O3 doped lead zirconium silicate glass ceramics by using positron annihilation lifetime spectroscopy

This work is focused on the evaluation of the free volume space and the concentration of nano-sized cavities trapped in Fe2O3 mixed lead zirconium silicate glass ceramics using positron annihilation lifetime spectroscopy (PALS) studies with 22Na (0.1MBq) positron source. Such imperfections are anticipated to have strong bearing on physical characteristics of the glass ceramic. The glasses of a particular composition viz., 36PbO–4ZrO2–(60–x)SiO2: xFe2O3 (0 ≤ x ≤ 0.5 in the intervals of 0.1) were synthesized by traditional melting and quenching techniques. The lifetime of the positrons measured in these samples is found to be strongly reliant on the content of Fe2O3. The results have suggested the increased fraction of free volume imperfections (fv), and radius of the cavities (R) with increase of Fe2O3 content from 0.2 to 0.5 mol%. The spectroscopic studies of these samples indicated that iron ions predominantly existed in Fe3+ state and occupied octahedral positions with FeO6 structural units, acted as modifiers and induced several imperfections. The estimated maximal concentration of imperfections in the glass ceramic sample F5 by PALS studies is attributed to such reasons. The inferences drawn from PALS studies regarding the concentration of defects in these samples are found to be in agreement with the results of third harmonic generation (THG) studies and conductivity studies.

The lifetimes for each state of $$l=0$$ levels of the para-positronium

We developed a model for a para-positronium system by taking into account the annihilation condition which requires $$l=0$$ . A para-positronium system composed by an electron-antielectron pair is an unstable system that decays predominantly into two gamma photons via self-annihilation process. This is because of the conservation of (overall) charge conjugation parity. Our $$2+1$$ -dimensional model was based on an exact solution of a two-body Dirac–Coulomb type equation (one-time). The resulting non-perturbative spectra were found to have a form of quasi-normal modes that naturally give proper and damping oscillations of the system. As a result, with a single equation, not only the binding energies and total annihilation energy transmitted by the annihilation photons but also the lifetimes, $$\tau \left( n,\alpha \right) \propto n^{3}/\alpha ^{3}$$ , for each state of $$l=0$$ levels of the para-positronium were obtained. With this unique presentation of above-mentioned characteristic of the system, we also calculated transition frequencies and transition times between differing n level of $$l=0$$ . This also gave us an opportunity to discuss the screening effect from electronic environment of the system. For this, the effective dielectric constant of the medium that surrounds the annihilation point was adapted into the calculated non-perturbative spectra. This may provide an important tool for the positron annihilation lifetime spectroscopy studies and for development of related techniques.

Engineering defect clusters in distorted NaMgF3 perovskite and their important roles in tuning the emission characteristics of Eu3+ dopant ion.

An attempt has been made to explore various new defect clusters in distorted NaMgF3 perovskite and their important role in tuning optical properties. We have tried to tailor the defect clusters and to understand the impact on the luminescence of the lanthanide, for example the Eu3+ ion. Defect engineering has been carried out by doping aliovalent dopant ions to create a charge imbalance in the matrix, which in turn led to the creation of various mono-, di- and new cluster vacancies. Such vacancies have been characterized by Electron Para-magnetic Resonance (EPR), Positron Annihilation Lifetime Spectroscopy (PALS) and Photoluminescence (PL) studies. The PALS data of both undoped and Eu3+ doped compounds confirmed that in addition to Mg mono vacancies, cluster vacancies with different configurations comprising Mg, Na and F atom vacancies also exist in the matrix. The PL study revealed that depending on the surrounding defect structure, three different types of Eu3+ components can be created. The position of the Eu3+ ion with respect to these cluster vacancies determines the respective emission profiles and the decay kinetics. It has been found that when Li+ ions are co-doped with Eu3+, there is a sudden change in the decay kinetics and the emission profiles. The PALS study revealed that Li+ co-doping modified the configuration of the vacancy clusters, which in turn changes the emission characteristics. The EPR study confirmed the presence of different types of F-centers (F, F2, etc.) which are responsible for the host emission. Overall, this new study will be very helpful for a detailed understanding of the defect structures, in particular the cluster vacancies in distorted NaMgF3 perovskite, which have a direct or indirect impact on many physical properties.

Chitosan modified Ti-PILC supported PdOx catalysts for coupling reactions of aryl halides with terminal alkynes

Biopolymer of chitosan (CS) and titanium pillared clays (Ti-PILCs) have been combined in a hybrid as advanced supports for immobilization of PdOx=0,1 species to prepare novel PdOx=0,1@Ti-PILC/CS nano-composite catalysts. The Ti-PILC materials showed high specific surface areas and abundant meso-porous structure with many irregular pore channels caused by collapses of layered structure of clay during Ti pillaring process. Both CS chains and sub-nano sized PdOx particles were successfully incorporated into the pore channels of Ti-PILC, resulting in a decrease in both the specific surface areas and uniform distribution of pore size. Besides conventional methods characterizations, the strong interactions between PdOx species and Ti-PILC/CS support were further evidenced with positron annihilation lifetime spectroscopy studies. The resultant PdOx@Ti-PILC/CS catalyst was highly active for the coupling reactions of aryl halides with phenyl acetylenes. It was recyclable and gave excellent yield up to 13 runs with low leaching of Pd species.

Free volume estimation in Au and Ag mixed sodium antimonate glass ceramics by means of positron annihilation

Earlier, we have reported the results of quantitative studies on structural and a variety of physical properties (that include non-linear optical, piezo-optical and electrical characteristics) of Na2O-Sb2O3:Ag2O/Au2O3 glass ceramics. In continuation of these studies, this part of the investigation is devoted to estimate the concentration of the defects and the free volume space (up to the nano scale) entrenched in the titled glass ceramics (as functions of the concentrations of dopant noble metal ions) by means of positron annihilation lifetime spectroscopy (PAS) technique. Such defects are predicted to have tremendous influence on above mentioned physical properties of these glass ceramics. Glasses of the composition (40-x) Na2O–60 Sb2O3: xAg2O/Au2O3 (x = 0.025–0.15 mol% for Ag2O glasses and x = 0.025–0.1 mol% for Au2O3 glasses) were prepared by melt quenching and subsequent heat-treatment for prolonged times. PAS studies were performed using 22Na positron source of strength 0.1 MBq. The results of these studies indicated significant influence of the concentrations Ag2O and Au2O3 on positron annihilation lifetime in the samples. In both the series of the samples, the third component of intensity, I3 (among the three components) is observed to be the longest-lived component. Further, for Ag2O doped glass ceramics, the value of I3 is found to be the maximal, whereas the life time component τ3, concentration of nano sized free volume defects and their volume fraction (fv), cavity radius (R) are found to be minimal for the samples doped with 0.1 mol% Ag2O and for the Au2O3 doped glass ceramics, these parameters have exhibited continuous decreasing trend with increase of Au2O3 concentration. Such decrease of defect concentration is attributed to the increasing degree of participation of antimony ions in the glass network forming with Sb(V)O4 structural units. Overall, information obtained regarding the dependence of free volume defect concentration on the contents of dopants is well in accordance with conclusions drawn from various macroscopic properties of these materials presented in our earlier reports.

Nature of the Positron State in CdSe Quantum Dots.

Previous studies have shown that positron-annihilation spectroscopy is a highly sensitive probe of the electronic structure and surface composition of ligand-capped semiconductor quantum dots (QDs) embedded in thin films. The nature of the associated positron state, however, whether the positron is confined inside the QDs or localized at their surfaces, has so far remained unresolved. Our positron-annihilation lifetime spectroscopy studies of CdSe QDs reveal the presence of a strong lifetime component in the narrow range of 358-371ps, indicating abundant trapping and annihilation of positrons at the surfaces of the QDs. Furthermore, our abinitio calculations of the positron wave function and lifetime employing a recent formulation of the weighted density approximation demonstrate the presence of a positron surface state and predict positron lifetimes close to experimental values. Our study thus resolves the long-standing question regarding the nature of the positron state in semiconductor QDs and opens the way to extract quantitative information on surface composition and ligand-surface interactions of colloidal semiconductor QDs through highly sensitive positron-annihilation techniques.

On the empirical determination of positron trapping coefficient at nano-scale helium bubbles in steels irradiated in spallation target

In the present work, the specific positron trapping rate of small helium bubbles was empirically derived from positron annihilation lifetime spectroscopy (PALS) and transmission electron microscopy (TEM) studies of Fe9Cr martensitic steels. Both techniques are well known to be sensitive to nanometer-sized helium-filled cavities induced during irradiation in a mixed proton-neutron spectrum of spallation target. Complementary TEM and PALS studies show that positrons are being trapped to these defects at a rate of 1.2 ± 0.8 × 10−14 m3s−1. This suggests that helium bubbles in ferritic/martensitic steels are attractive traps for positrons comparable to mono-vacancies and quantitative analysis of the bubbles by PALS technique is plausible.

In situ investigation of the kinetics and microstructure during photopolymerization by positron annihilation technique and NIR-photorheology.

The microstructural free volume evolution during a photopolymerization process was studied on a commercial photopolymer (SPOT LV) in situ by positron annihilation lifetime spectroscopy (PALS) and concomitant NIR-photorheology. Analysis of the positron lifetime spectra revealed a high sensitivity of the PALS technique to the different phases of photopolymerization associated with different reaction rates as well as to the evolution of microstructural free-volume shrinkage, which was described at the molecular level by the Kohlrausch–Williams–Watts equation. The in situ PALS study of microstructural changes in photopolymerization was related to the vitrification (gel point) accompanied by shrinkage stress registered via NIR-photorheology. The simultaneous NIR measurements yield information on the monomer conversion of SPOT LV, which can be correlated to the occurrence of the gel point and the evolution of the microstructural free volume. This combined study allows us to see deeper into the crosslinking process and its influence on the resulting material characteristics.

Microstructural PALS study of regulated dimethacrylates: Thiol‐ versus β‐allyl sulfone‐based networks

ABSTRACTRadical photocuring of multifunctional (meth)acrylates is lacking control over the irregular chain growth process yielding highly crosslinked, inhomogeneous networks. Chain transfer agents (CTAs, e.g., thiols or β‐allyl sulfones) have been widely used to modify this curing process, thus reducing shrinkage stress and increasing the toughness of the formed photopolymers. Resulting photopolymer networks exhibit higher bulk density, lower crosslinking density, and narrow glass transitions. Consequently, a more homogeneous network structure was postulated for those networks. Whereas macroscopic properties of the modified final materials have already been studied, herein the microstructural arrangement of such modified networks has also been evaluated with the help of positron annihilation lifetime spectroscopy (PALS). A more homogenous network structure with a decreased average free‐volume void size was confirmed for CTA‐based dimethacrylate networks. A sharper distribution of the ortho‐positronium (o‐Ps) lifetime, mainly for the β‐allyl sulfone‐based photopolymers, hints toward a more regulated network structure. Moreover, the combination of PALS, DMTA, density and swelling experiments elucidates relations between void formation, crosslinking density and macroscopic characteristics such as shrinkage stress and mechanical properties. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2476–2484

Subnanoscopic inhomogeneities in model end-linked PDMS networks probed by positron annihilation lifetime spectroscopy and their effects on thermomechanical properties

The subnanoscopic free volume hole properties of model poly(dimethylsiloxane) (PDMS) networks with unimodal and bimodal distribution of chain lengths between the cross-links were determined using positron annihilation life time spectroscopy (PALS). Wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) studies were carried out to further understand the structural inhomogeneities of the networks at different length scales. The networks were prepared by end-linking combinations of sufficiently longer (Mn = 18,952) and shorter (Mn = 4323) precursor PDMS chains relative to entanglement spacing (Me). The macroscopic properties of the networks were studied by tensile testing, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), as well as equilibrium swelling measurements. Through PALS studies it was possible to delineate the subtle variations in the elementary mesh sizes, a measure of the segmental spacing, of the unimodal short and long chain networks influenced by cross-links or entanglements. The intersegmental spacing of the unimodal PDMS networks at a length scale of few angstroms obtained from WAXD measurements were found to be almost in quantitative agreement with the free volume hole sizes obtained from PALS. SAXS measurements on solvent swollen PDMS networks from short and long chain precursors were used to obtain correlation length of the networks at a higher length scale of a few nanometers. Further, the studies revealed that the enhanced mechanical properties seen in certain bimodal elastomer networks are connected with topological features of the networks. A noteworthy finding from PALS studies was that the bimodal composition with 20 wt% short chain, which showed the best combination of mechanical properties with a feature of stress-upturn in tensile testing, exhibited the least free volume size and relatively lower dispersion in its size distribution among the networks. These fundamental studies are expected to provide new insights into the network structure of model elastomers at a molecular scale and its possible connection with macroscopic properties.

Novel J-PET scanner combined with positron annihilation lifetime spectroscopy technique as a tool for morphometric imaging

Positron Annihilation Lifetime Spectroscopy (PALS) allows examining structure of materials at nano and sub-nanometer level. This technique is based on the lifetime and production intensity of ortho-positronium atoms in free volumes of given structures. It is mostly used for studies of organic materials. However there exist also few results, e.g. by groups of Y. C. Jean and R. Pietrzak, showing that morphology of cells is correlated with the PALS parameters. Jagiellonian Positron Emission Tomograph (J-PET) is a multi-purpose detector which will be used for investigations with positronium atoms in life-sciences as well as for medical diagnostics. Such prototype based on plastic scintillators and fully compatible with MRI is currently being developed at the Jagiellonian University in Krakow, Poland. In this talk results of the first experiments conducted by the J-PET collaboration will be presented. We performed PALS studies of well known structures such as silica and of some model micro-organisms, e.g. Saccharomyces cerevisiae both with dry and aqueous samples allowing to determine the correlation between hygroscopicity of the cell and PALS parameters. As a result, we proved that PALS can be successfully used for studies of living organisms their dynamics and its relation to the cells morphology. This result opens perspective for simultaneous determination of early and advanced stages of carcinogenesis by observing changes in biomechanical parameters between normal and tumour cells and standard PET examination. J-PET detection system combined with PALS technique will be more accurate and affordable for cancer diagnostics. Disclosure Authors disclose any relationship that may bias the presentation.

PALS and physico-chemical study of swift heavy ions and gamma radiation irradiated polyamide nylon 66 polymer

Polyamide nylon 66 (PA-66) polymer samples after being irradiated with 100 MeV O7+ ions and gamma radiation were studied for modifications in free volume properties by using positron annihilation lifetime spectroscopy (PALS) technique. The results obtained from PALS experiment were analysed in terms of hole radius, available free volume and fractional free volume. Both, ion irradiation as well as gamma exposure showed modifications in the size of available free volume and fractional free volume but the effectiveness of gamma radiation exposure was more pronounced than that of ion irradiation. The modifications produced in optical, structural and chemical properties of the PA-66 samples were studied by UV–visible (UV–vis) spectroscopy, X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy respectively. UV–vis studies showed a shift in absorption edge towards the visible region and a decrease in band gap energy (Eg). An increase in the crystalline nature of the polymer at higher fluence as a result of decrease in the peak width of XRD patterns was observed. The FTIR studies showed insignificant modifications in the chemical structure of irradiated polymer samples. Increase in surface roughness and cracks were observed in SEM results of ion and gamma exposed samples respectively.

Structure at Interphase of Poly(vinyl alcohol)–SiC Nanofiber Composite and Its Impact on Mechanical Properties: Positron Annihilation and Small-Angle X-ray Scattering Studies

The interphase structure of poly(vinyl alcohol) (PVA)–SiC nanofiber polymer nanocomposites has been investigated using positron annihilation lifetime spectroscopy (PALS) and small-angle X-ray scattering (SAXS). The interphase region in polymer nanocomposites extends from nanofillers’ surface to bulk polymer matrix. PVA–SiC nanocomposite films with varying concentration of SiC nanofiber (0.1, 0.2, 0.5, and 1.0 wt %) were prepared using solvent casting method. PALS studies indicated the rearrangement of hydrogen bonded structure of PVA and the creation of an interphase layer with larger size nanoholes. SAXS measurements also confirmed the modification of semicrystalline structure of PVA through lamellae structure parameters. The crystallinity of the nanocomposite films have been determined using X-ray diffraction. The observed changes in the polymer nanocomposite structure are resultant of weak interaction between hydrophilic PVA and hydrophobic SiC nanofiber. The mechanical properties of the nanocomposites...

Positron annihilation lifetime spectroscopy study on the structural relaxation of phenylmethylsiloxane-modified epoxy hybrids at different aging temperatures

The cured network conformations and structural relaxation behaviours of the diglycidyl ether of bisphenol A (DGEBA)-methylhexahydrophthalic anhydride (MHHPA) modified with phenylmethylsiloxane-modified epoxy (PMSE) at different aging temperatures were studied using dynamic mechanical analysis (DMA) and positron annihilation lifetime spectroscopy (PALS). The DMA results revealed that the cured PMSE network can insert into the cured DGEBA network to form interpenetrating polymer networks (IPNs). The structural relaxation behaviours of DGEBA–PMSE-0.4 produced using DGEBA, PMSE, and MHHPA at a ratio of 0.6:0.4:1 by equivalent weight were studied using PALS at 150 °C and 55 °C. The aging-induced free volume relaxation parameters of DGEBA–PMSE-0.4 at 150 °C and 55 °C were investigated using the double additive exponential model and the Kohlrausch–Williams–Watts exponential model. For double additive exponential model, only one relaxation time (ζ) of 584.5 h was found at 150 °C; By contrast, there were two separate relaxation times of 37.4 h (ζ1) and 753.6 h (ζ2) at 55 °C. The ζ1 of the IPNs hybrid can be attributed to the network relaxation of PMSE, and the ζ2 can be attributed to the network relaxation of DGEBA at 55 °C. The results suggested the double additive exponential model can effectively predict DGEBA–PMSE hybrid relaxation behaviours.

Dispersion and interaction of graphene oxide in amorphous and semi-crystalline nano-composites: a PALS study

The influence of dispersion and interaction of Graphene Oxide (GO) in semicrystalline Polyhydroxy butyrate (PHB) and glassy amorphous Poly(tBP-oda) is explored by Positron Annihilation Lifetime Spectroscopy (PALS). The ortho-Positronium lifetimes which represent the main free volume hole size of both polymers are mainly affected by the large differences in internal stresses built up by the shrinkage of the polymers during their preparation, restricted by the platelet structure of GO. The ortho-Positronium intensities, which represent the ortho-Positronium formation probabilities, suggest a strong dependency of on the dispersion of the nano-particles and their aspect ratio.

Investigation of in-depth and surface properties of polyethyleneterephthalate thin films after SHI and gamma radiation treatment by means of PALS and AFM studies

Positron annihilation lifetime spectroscopy (PALS) and atomic force microscopy (AFM) analyses were adopted for in-depth (at the nanoscale level) and surface (at the microscale level) understanding of the swift heavy ions (SHI) irradiated and radiation exposed polymer films. Polyethyleneterephthalate (PET) polymer films were irradiated by 70 MeV C5+ ions to the fluences ranging from 1 × 1011 to 5 × 1012 ions/cm2. The other set of PET films were exposed to gamma radiation emitted by 60Co source at various doses ranging from 250 to 1250 kGy. The Tao-Eldrup model was used to calculate the value of hole radius (R), free volume (FV) and fractional free volume (FFV) from the lifetime and intensity values of ortho-positronium (o-Ps) as obtained from the PALS spectra. These parameters (R, FV and FFV) were analyzed to study the in-depth modification of the polymer after ion beam and gamma radiation treatment. The AFM studies reveal the surface modifications in the ions irradiated and gamma radiation exposed polymer films. In addition to these studies; the structural, optical and chemical properties were studied by X-ray diffraction (XRD), UV–visible (UV–vis) and Fourier transform infrared (FTIR) spectroscopy respectively. The XRD spectra showed improved crystalline nature of the polymer after ion beam irradiation as well as gamma radiation exposure. The optical absorption spectra showed a shift in the absorption edge towards higher wavelength side. The band gap energy was calculated using Tauc's relation, which indicated a significant decrease in the value of band gap of the polymer films in both the cases (C5+ ions and gamma radiation). The FTIR spectra obtained after irradiation exhibits increment of the intensities of the typical vibrational bands.

Characterization of Neutron Transmutation Doped (NTD) Ge for low temperature sensor development

Development of NTD Ge sensors has been initiated for low temperature (mK) thermometry in The India-based TIN detector (TIN.TIN). NTD Ge sensors are prepared by thermal neutron irradiation of device grade Ge samples at Dhruva reactor, BARC, Mumbai. Detailed measurements have been carried out in irradiated samples for estimating the carrier concentration and fast neutron induced defects. The Positron Annihilation Lifetime Spectroscopy (PALS) measurements indicated monovacancy type defects for all irradiated samples, while Channeling studies employing RBS with 2MeV alpha particles, revealed no significant defects in the samples exposed to fast neutron fluence of ∼4×1016/cm2. Both PALS and Channeling studies have shown that vacuum annealing at 600°C for ∼2h is sufficient to recover the damage in the irradiated samples, thereby making them suitable for the sensor development.

Low-temperature positron annihilation study of B+-ion implanted PMMA

Temperature dependent positron annihilation lifetime spectroscopy (PALS) measurements in the range of 50–300 K are carried out to study positronium formation in 40 KeV B+-ion implanted polymethylmethacrylate (B:PMMA) with two ion doses of 3.13 × 1015 and 3.75 × 1016 ions/cm2. The investigated samples show the various temperature trends of ortho-positronium (o-Ps) lifetime τ3 and intensity I3 in PMMA before and after ion implantation. Two transitions in the vicinity of ∼150 and ∼250 K, ascribed to γ and β transitions, respectively, are observed in the PMMA and B:PMMA samples in consistent with reference data for pristine sample. The obtained results are compared with room temperature PALS study of PMMA with different molecular weight (Mw) which known from literature. It is found that B+-ion implantation leads to decreasing Mw in PMMA at lower ion dose. At higher ion dose the local destruction of polymeric structure follows to broadening of lifetime distribution (hole size distribution).