We present the first measurements of the Dalitz plot for ortho-positronium annihilation to three photons. Our measurements, accurate to about 3

Positron Annihilation Lifetime Spectroscopy (PALS) is a well-established non-destructive technique used for nanostructural characterization of porous materials. It is based on the annihilation of a positron and an electron. Mean positron lifetime in the material depends on the free voids size and molecular environment, allowing the study of porosity and structural transitions in the nanometer scale. We have developed a novel method enabling spatially resolved PALS, thus providing tomography of nanostructural characterization of an extended object. Correlating space (position) and structural (lifetime) information brings new insight in materials studies, especially in the characterization of the purity and pore distribution. For the first time, a porosity image using stationary positron sources for the simultaneous measurement of the porous polymers XAD4, silica aerogel powder IC3100, and polyvinyl toluene scintillator PVT by the J-PET (Jagiellonian Positron Emission Tomography) system is demonstrated.

This study presents in situ monitoring using positron annihilation lifetime spectroscopy (PALS) of the reduction process, at its very early stage, occurring on nickel oxide and ceria-based nickel catalyst designed for the steam reforming of ethanol. The PALS results show the formation of water on the surface of materials containing Ni species just after exposure to hydrogen at only 120 degrees C. For the first time, it has been presented that on the surface of both materials, water droplets exist in the form of plugs or bridges that can accommodate ortho-positronium bubbles of about 0.5 nm in diameter. The chemical composition and structure, and what follows, the availability of highly reactive oxygen species, affect the size of water droplets. The droplets are larger on the surface of NiO than on the catalyst (consisting of NiO dispersed on CeO2 and a solid solution of Ce1-X Ni X O2), which is characterized by the greater availability of reactive oxygen species.

The μPPET [mu(μ)on Probe with J-PET] project aims to investigate the “Muon Puzzle” seen in cosmic ray air showers. This puzzle arises from the observation of a significantly larger number of muons on Earth’s surface than that predicted by the current theoretical models. The investigated hypothesis is based on recently observed asymmetries in the parameters for the strong interaction cross-section and trajectory of an outgoing particle due to projectile–target polarization. The measurements require detailed information about muons at the ground level, including their track and charge distributions. To achieve this, the two PET scanners developed at the Jagiellonian University in Krakow (Poland), the J-PET detectors, will be employed, taking advantage of their well-known resolution and convenient location for detecting muons that reach long depths in the atmosphere. One station will be used as a muon tracker, while the second will reconstruct the core of the air shower. In parallel, the existing hadronic interaction models will be modified and fine-tuned based on the experimental results. In this work, we present the conceptualization and preliminary designs of μPPET.

The influence of organic-inorganic ureasil-based polymers containing sulfur on the bioanalytical properties of electrochemical biosensors was studied. The ureasil-As2S3 (0.1 g of As2S3) and ureasil-chalcogenide (0.066 and 0.198 g of S) composites were selected for research. Network properties (free volume) of the samples are rather similar as revealed by positron annihilation lifetime spectroscopy (PALS) measurements. At the same time, the effect of sulfur on the operational parameters of laccase biosensors was observed. In particular, the obtained results showed the differences in the sample responses in chronoamperometric measurements which most probably do not originate from differences in the structure of the samples at the nanoscale level. The results of this work support the earlier proposed topological and chemical mechanisms for effective enzyme immobilization using holding polymer matrixes.

In state-of-the-art positron emission tomography (PET), information about annihilation photon polarization is unavailable. Here, we present a PET scanner built from plastic scintillators, where annihilation photons primarily interact via the Compton effect, providing information about both photon polarization and propagation direction. Using this plastic-based PET, we determined the distribution of the relative angle between polarization planes of photons from positron-electron annihilation in a porous polymer. The amplitude of the observed distribution is smaller than predicted for maximally quantum entangled two-photon states but larger than expected for separable photons. This result can be well explained by assuming that photons from pick-off annihilation are not entangled, while photons from direct and parapositronium annihilations are maximally entangled. Our result indicates that the degree of entanglement depends on the annihilation mechanism in matter, opening avenues for exploring polarization correlations in PET as a diagnostic indicator.

Activated alumina is widely used in industry as an adsorbent. Its strong affinity toward water allows for the profound dehydration of gas streams. To optimize such processes, a deeper insight into water interaction with activated alumina is required. This knowledge can be obtained using positron annihilation lifetime spectroscopy, a sensitive tool that unravels previously unknown aspects of adsorption processes. Activated alumina (Compalox® AN/V-813) was subjected to such a study supported by detailed characterization using scanning electron microscopy, X-ray diffraction, and N2 adsorption–desorption. A complex porous structure of the material, consisting mainly of boehmite and η-Al2O3 or γ-Al2O3, was found. It is responsible for significant differences in adsorption and desorption. The course of adsorption is close to the classical layer-by-layer description. However, there are indications of initial water capture at active sites and final water reorganization consisting of filling the smallest free volumes that remain empty. The narrow mesopore inlets that keep water in the pores even at a relative vapor pressure of 0.4 are primarily responsible for the course of the desorption process. During adsorption, water is mainly maintained in the form of small clusters up to the highest pressures, whereas during desorption, it is continuous until narrow pore openings.

Discrete symmetries play an important role in particle physics with violation of CP connected to the matter-antimatter imbalance in the Universe. We report the most precise test of P, T and CP invariance in decays of ortho-positronium, performed with methodology involving polarization of photons from these decays. Positronium, the simplest bound state of an electron and positron, is of recent interest with discrepancies reported between measured hyperfine energy structure and theory at the level of 10-4 signaling a need for better understanding of the positronium system at this level. We test discrete symmetries using photon polarizations determined via Compton scattering in the dedicated J-PET tomograph on an event-by-event basis and without the need to control the spin of the positronium with an external magnetic field, in contrast to previous experiments. Our result is consistent with QED expectations at the level of 0.0007 and one standard deviation.

This paper presents the results of an experimental study on the impact of slide burnishing on surface roughness parameters (Sa, Sz, Sp, Sv, Ssk, and Sku), topography, surface layer microhardness, residual stress, and mean positron lifetime (τmean). In the study, specimens of X6CrNiTi18 stainless steel were subjected to slide burnishing. The experimental variables were feed and slide burnishing force. The slide burnishing process led to changes in the surface structure and residual stress distribution and increased the surface layer microhardness. After slide burnishing, the analyzed roughness parameters decreased compared with their pre-treatment (grinding) values. The slide burnishing of X6CrNiTi18 steel specimens increased their degree of strengthening e from 8.77% to 42.74%, while the hardened layer thickness gh increased after the treatment from about 10 µm to 100 µm. The maximum compressive residual stress was about 450 MPa, and the maximum depth of compressive residual stresses was gσ = 1.1 mm. The positron mean lifetime τmean slightly yet systematically increased with the increase in burnishing force F, while an increase in feed led to changes of a different nature.

Water confined in cylindrical pores of silica with a diameter of 2nm was studied by positron annihilation lifetime spectroscopy. Instead offreezing at 273 K, the glass-like transition through the viscous state to the solidphase was observed in the wide temperature range of 225-188 K. Reducing thevapor pressure over confined water allowed us to obtain the negative pressurepn=-164 MPa in liquid water, and the phase transition temperature rangechanged to 234-189 K. The temperature dependence of the ortho-positronium(o-Ps) lifetime in water underpnbecame consistent with the surface tension asin most liquids, as opposed to the anomalous temperature dependence in waterunder the saturated vapor pressure. This indicates a reduction in the number ofhydrogen bonds in confined water underpn. On this basis, to explain the anomalous temperature dependence, we propose ahypothesis of a partial energy transfer to distant water molecules via the OH-stretching modes instead of repelling the moleculessurrounding o-Ps. Our results indicate that thermally generated defects in the confined ice are accompanied by permanent defects,which predominate in the ice formed underpn. Both types of defects have the same volume of 70 A3, which is much greater than inhexagonal iceIh. We conjecture that the defects are larger due to the influence of the silanol groups on the structure of solid water.These observations imply that the structure of confined ice differs significantly from that of bulk ice and the vapor pressureinfluences its formation.

The article demonstrates the series of silicas produced from various alkoxysilanes introduced into the Amberlite (R) XAD7HP and lyophilized agar, whose transformation took place in the presence of ammonia vapors as catalyst. The silicas have been investigated by the means of the up-to-date analytical methods for the full characterisation of produced solids including positronium annihilation lifetime spectroscopy. The morphology of the silica is the result of the specific conditions applied for precursors transformation. Usage of lyophilized agar as a template for the vapor-phase method does not lead to creation of highly porous silica. The same applies to SiO2 materials produced without any template, with one except for tetrapropoxysilane. On the contrary Amberlite (R) XAD7HP is a very effective template. This polymer used as a template allows to obtain porous silica (specific surface area > 300 m(2) g(-1)) in a form of microspheres from each of the employed precursors.

The J-PET tomograph is constructed from plastic scintillator strips arranged axially in concentric cylindrical layers. It enables investigations of positronium decays by measurement of the time, position, polarization and energy deposited by photons in the scintillators, in contrast to studies conducted so far with crystal and semiconductor based detection systems where the key selection of events is based on the measurement of the photons' energies. In this article we show that the J-PET tomograph system is capable of exclusive measurements of the decays of ortho-positronium atoms. We present the first positronium production results, its lifetime distribution measurements and discuss estimation of the influence of various background sources. The tomograph's performance demonstrated here makes it suitable for precision studies of positronium decays including entanglement of the final state photons, positron annihilation lifetime spectroscopy plus molecular imaging diagnostics.

The paper presents the results of experimental studies on the impact of impulse shot peening parameters on surface roughness (Sa, Sz, Sp, Sv), surface layer microhardness, and the mean positron lifetime (τmean). In the study, samples made of the Inconel 718 nickel alloy were subjected to impulse shot peening on an originally designed stand. The variable factors of the experiment included the impact energy, the diameter of the peening element, and the number of impacts per unit area. The impulse shot peening resulted in changes in the surface structure and an increase in surface layer microhardness. After the application of impulse shot peening, the analyzed roughness parameters increased in relation to post-milling values. An increase in microhardness was obtained, i.e., from 27 HV 0.05 to 108 HV 0.05 at the surface, while the maximum increase the microhardness occur at the depth from 0.04 mm to 0.08 mm. The changes in the physical properties of the surface layer were accompanied by an increase in the mean positron lifetime τmean. This is probably related to the increased positron annihilation in point defects. In the case of small surface deformations, the increase in microhardness was accompanied by a much lower increase in τmean, which may indicate a different course of changes in the defect structure consisting mainly in modification of the dislocation system. The dependent variables were subjected to ANOVA analysis of variance (it was one-factor analysis), and the effect of independent variables was evaluated using post-hoc tests (Tukey test).

Research conducted in the framework of the Jagiellonian-PET (J-PET) project aims to develop a cost-effective total-body positron emission tomography scanner. As a first step on the way to construct a full-scale J-PET tomograph from long strips of plastic scintillators, a 24-strip prototype was built and tested. The prototype consists of detection modules arranged axially forming a cylindrical diagnostic chamber with the inner diameter of 360 mm and the axial field-of-view of 300 mm. Promising perspectives for a low-cost construction of a total-body PET scanner are opened due to an axial arrangement of strips of plastic scintillators, which have a small light attenuation, superior timing properties, and the possibility of cost-effective increase of the axial field-of-view. The presented prototype comprises dedicated solely digital front-end electronic circuits and a triggerless data acquisition system which required the development of new calibration methods including time, thresholds, and gain synchronization. The system and elaborated calibration methods, including first results of the 24-module J-PET prototype, are presented and discussed. The achieved coincidence resolving time equals to ${\mathrm {CRT}}=490\pm 9$ ps. This value can be translated to the position reconstruction accuracy $\sigma (\Delta l) =18$ mm, which is fairly position independent.

Positron annihilation lifetime spectroscopy was used to examine grown-in defects in Cd1–x Zn x Te mixed crystals as a function of Zn content (x = 0, 0.07, 0.11, 0.49, 0.9, 0.95, 1) and measuring temperature. All samples were prepared using the high-pressure modified vertical Bridgman–Stockbarger method. The crystal structure and material phase were characterized by X-ray diffraction. The positron lifetime spectra reveal the presence of both open volumes and shallow traps regardless of the sample composition. In particular, both average and bulk lifetimes are found to be much higher in ternary alloys (CdZnTe) than those in binary systems (CdTe and ZnTe). This originates from distinct differences in average electron densities and the nature of open-volume defects between binary and ternary samples. Competition in positron trapping with increasing Zn content is observed between defects characteristic for both structural systems. Moreover, a clear correlation is shown between defects and the lattice thermal conductivity of studied samples. The applicability of the positron trapping model to CdTe-based materials is discussed.

Charged lepton system symmetry under combined charge, parity, and time-reversal transformation (CPT) remains scarcely tested. Despite stringent quantum-electrodynamic limits, discrepancies in predictions for the electron-positron bound state (positronium atom) motivate further investigation, including fundamental symmetry tests. While CPT noninvariance effects could be manifested in non-vanishing angular correlations between final-state photons and spin of annihilating positronium, measurements were previously limited by knowledge of the latter. Here, we demonstrate tomographic reconstruction techniques applied to three-photon annihilations of ortho-positronium atoms to estimate their spin polarisation without magnetic field or polarised positronium source. We use a plastic-scintillator-based positron-emission-tomography scanner to record ortho-positronium (o-Ps) annihilations with single-event estimation of o-Ps spin and determine the complete spectrum of an angular correlation operator sensitive to CPT-violating effects. We find no violation at the precision level of 10-4, with an over threefold improvement on the previous measurement.

We present results on CPT symmetry tests in decays of positronium performed with the precision at the level of 10${^{-4}}$, and positronium images determined with the prototype of the J-PET tomograph. The first full-scale prototype apparatus consists of 192 plastic scintillator strips readout from both ends with vacuum tube photomultipliers. Signals produced by photomultipliers are probed in the amplitude domain and are digitized by FPGA-based readout boards in triggerless mode. In this contribution we report on the first two- and three-photon positronium images and tests of CPT symmetry in positronium decays.

The research describes systematic approach to the novel synthesis and formation of a potential organic-inorganic drug carriers. The poly(trimethylolpropane trimethacrylate) and polymer-silica composites based on SBA-3 or SBA-15 mesoporous silica were fabricated by the suspension-emulsion polymerization method in the form of small micrometric porous beads (specific surface area approx. 500 m(2)/g). The type of organic templates filling silica pores has proved to be crucial in the synthesis of the composites. The introduction of diclofenac sodium via solvent diffusion method into the polymer and composites resulted in the solid drug dispersions. The composites have greater effectiveness in the drug desorption (90% of the release) in comparison with the pure polymer (20% of the release after 7 h). Both, however, suffer from the burst effect. This downside can be overcome by functionalization of the solid drug dispersions with (3-aminopropyl)triethoxysilane. The functionalized solid drug dispersions do not desorb the diclofenac sodium in an acidic medium (the desorption rate is less than 6% during 2 h contact), which makes them attractive for oral multiparticulate formulations of modified release. The presented solids were characterized with modern analytical methods and the relation between the material structure and desorption rate were discussed.

Vacuum chambers are necessary for the physics experiments planned to be carried out with the use of the J-PET detector. Two chambers manufactured and used for particular runs of experiments had generally cylindrical shapes, while the radioactive source was placed in the center of each chamber. The highly porous material, used as a target in which positrons/positronium atoms annihilate, was placed in the immediate vicinity of the source. Such orientation ensures the axially symmetrical response of J-PET scintillators and allows to carry out correct calibration. The variation of material used for manufacturing of the chambers (aluminum/plastic), allows to observe the detector response with various rates of absorption and scattering of annihilation quanta. Such determination is necessary for proper analysis of multi-quanta annihilation, which will be needed for planned experiments.

In this paper we introduce a semi-analytic algorithm for 3-dimensional image reconstruction for positron emission tomography (PET). The method consists of the back-projection of the acquired data into the most likely image voxel according to time-of-flight (TOF) information, followed by the filtering step in the image space using an iterative optimization algorithm with a total variation (TV) regularization. TV regularization in image space is more computationally efficient than usual iterative optimization methods for PET reconstruction with full system matrix that use TV regularization. The efficiency comes from the one-time TOF back-projection step that might also be described as a reformatting of the acquired data. An important aspect of our work concerns the evaluation of the filter operator of the linear transform mapping an original radioactive tracer distribution into the TOF back-projected image. We obtain concise, closed-form analytical formula for the filter operator. The proposed method is validated with the Monte Carlo simulations of the NEMA IEC phantom using a one-layer, 50 cm-long cylindrical device called Jagiellonian PET scanner. The results show a better image quality compared with the reference TOF maximum likelihood expectation maximization algorithm.