The Experts below are selected from a list of 84183 Experts worldwide ranked by ideXlab platform
A L Stepanov - One of the best experts on this subject based on the ideXlab platform.
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positron annihilation study of the juniperus communis based biomaterial nefrovil
2015Co-Authors: Taras Kavetskyy, Ya S Voloshanska, I V Komar, A L Stepanov, Ondrej ŠaušaAbstract:The results of positron annihilation lifetime (PAL) measurements of the Juniperus communis based biomaterial NEFROVIL are reported for the first time. Three- and four-component fittings were applied to deconvolute the PAL spectrum. In order to determine which fitting procedure is most suited, a maximum entropy lifetime (MELT) analysis was also performed. It was found that the nanovoid topology of this biomaterial is constructed by small and large free-volume holes identified by the Ortho-Positronium lifetime parameters in the most suitable four-component fitting procedure.
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structural defects and positronium formation in 40 kev b implanted polymethylmethacrylate
Journal of Physical Chemistry B, 2014Co-Authors: Taras Kavetskyy, Yoshinori Kobayashi, H. F. M. Mohamed, Ryoichi Suzuki, O Sausa, V M Tsmots, Atsushi Kinomura, V I Nuzhdin, V F Valeev, A L StepanovAbstract:Slow positron beam and optical absorption measurements are carried out to study structural defects and positronium formation in 40 keV B(+)-implanted polymethylmethacrylate (B:PMMA) with ion doses from 6.25 × 10(14) to 5.0 × 10(16) ions/cm(2). Detailed depth-selective information on defects in implanted samples was obtained by measuring of Doppler broadening of positron annihilation γ rays as a function of incident positron energy and these experimental results were compared with SRIM (stopping and range of ions in matter) simulation results. Two general processes, appearance of free radicals at lower ion doses ( 10(16) ions/cm(2)), are considered from the Doppler S-E and W-E dependences in the framework of the concept of defects formation during radiation damage of polymer structure. Probabilities of Ortho-Positronium (o-Ps) formation are analyzed using S-W plot and slow positron annihilation lifetime measurements. Dose dependence of o-Ps lifetime τ3 and intensity I3 at the incident positron energy of 2.15 keV correlates well with the dose dependence of S-parameter and seems to account for the existence of the expected two processes, i.e., scission of polymer chains and appearance of free radicals preceding the aggregation of the clusters resulting in the formation of network of conjugated bonds at lower ion doses and carbonization at higher ion doses. The increase of optical absorption observed with increasing ion implantation dose also suggests a formation of carbonaceous phase in the ion-irradiated PMMA.
D Varshalovich - One of the best experts on this subject based on the ideXlab platform.
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positron annihilation spectrum from the galactic centre region observed by spi integral revisited annihilation in a cooling ism
Monthly Notices of the Royal Astronomical Society, 2011Co-Authors: E Churazov, R Sunyaev, S Sazonov, S S Tsygankov, D VarshalovichAbstract:We analyse SPI/INTEGRAL data on the 511-keV line from the Galactic Centre, accumulated over ∼6 yr of observations. We decompose the X-ray and soft gamma-ray emission of the central part of the Milky Way into relatively compact ‘bulge’ and more extended ‘disc’ components and report their spectral properties. The bulge component shows a prominent 511-keV line and essentially no flux at 1.8 MeV, while the disc component on the contrary contains a prominent 1.8-MeV line and a very weak annihilation line. We show that the spectral shape of the annihilation radiation (the narrow 511-keV line and the associated Ortho-Positronium continuum) is surprisingly well described by a model of annihilation of hot positrons in a radiatively cooling interstellar medium (ISM). The model assumes that positrons are initially injected into a hot (∼10 6 K), volume-filling ISM, which is allowed to freely cool via radiative losses. The annihilation time in such a medium is longer than the cooling time for temperatures higher than a few 10 4 K. Thus, most of the positrons annihilate only after the gas has cooled down to ∼10 5 K, giving rise to annihilation emission
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positron annihilation spectrum from the galactic centre region observed by spi integral
Monthly Notices of the Royal Astronomical Society, 2005Co-Authors: E Churazov, R Sunyaev, S Sazonov, M Revnivtsev, D VarshalovichAbstract:The electron-positron annihilation spectrum observed by SPI/INTEGRAL during deep Galactic Centre region exposure is reported. The line energy (510.954±0.075 keV) is consistent with the unshifted annihilation line. The width of the annihilation line is 2.37 ± 0.25 keV (full width at half-maximum), while the strength of the Ortho-Positronium continuum suggests that the dominant fraction of positrons (94 ± 6 per cent) form positronium before annihilation. Compared to the previous missions, these deep INTEGRAL observations provide the most stringent constraints on the line energy and width. Under the assumption of an annihilation in a single-phase medium, these spectral parameters can be explained by a warm T e ∼ 7000 to 4 x 10 4 K gas with degree of ionization larger than a few 10 -2 . One of the widespread phases of the interstellar medium (ISM) - warm (T e ∼ 8000 K) and weakly ionized (degree of ionization ∼0.1) - satisfies these criteria. Other single-phase solutions are also formally allowed by the data (e.g. cold, but substantially ionized ISM), but such solutions are believed to be astrophysically unimportant. The observed spectrum can also be explained by annihilation in a multiphase ISM. The fraction of positrons annihilating in a very hot (T e ≥ 10 6 K) phase is constrained to be less than ∼8 per cent. Neither a moderately hot (T e ≥ 10 5 K) ionized medium nor a very cold (T e ≥ 10 3 K) neutral medium can make a dominant contribution to the observed annihilation spectrum. However, a combination of cold/neutral, warm/neutral and warm/ionized phases in comparable proportions could also be consistent with the data.
P Moskal - One of the best experts on this subject based on the ideXlab platform.
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feasibility study of the positronium imaging with the j pet tomograph
Physics in Medicine and Biology, 2019Co-Authors: P Moskal, D Kisielewska, C Curceanu, E Czerwinski, K Dulski, A Gajos, M Gorgol, Beatrix C Hiesmayr, B Jasinska, K KacprzakAbstract:A detection system of the conventional PET tomograph is set-up to record data from e+e- annihilation into two photons with energy of 511 keV, and it gives information on the density distribution of a radiopharmaceutical in the body of the object. In this paper we explore the possibility of performing the three gamma photons imaging based on Ortho-Positronium annihilation, as well as the possibility of positronium mean lifetime imaging with the J-PET tomograph constructed from plastic scintillators. For this purposes simulations of the Ortho-Positronium formation and its annihilation into three photons were performed taking into account distributions of photons' momenta as predicted by the theory of quantum electrodynamics and the response of the J-PET tomograph. In order to test the proposed Ortho-Positronium lifetime image reconstruction method, we concentrate on the decay of the Ortho-Positronium into three photons and applications of radiopharmaceuticals labeled with isotopes emitting a prompt gamma. The proposed method of imaging is based on the determination of hit-times and hit-positions of registered photons which enables the reconstruction of the time and position of the annihilation point as well as the lifetime of the Ortho-Positronium on an event-by-event basis. We have simulated the production of the positronium in point-like sources and in a cylindrical phantom composed of a set of different materials in which the Ortho-Positronium lifetime varied from 2.0 ns to 3.0 ns, as expected for Ortho-Positronium created in the human body. The presented reconstruction method for total-body J-PET like detector allows to achieve a mean lifetime resolution of ~40 ps. Recent Positron Annihilation Lifetime Spectroscopy measurements of cancerous and healthy uterine tissues show that this sensitivity may allow to study the morphological changes in cell structures.
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feasibility study of the positronium imaging with the j pet tomograph
arXiv: Instrumentation and Detectors, 2018Co-Authors: P Moskal, D Kisielewska, C Curceanu, E Czerwinski, K Dulski, A Gajos, M Gorgol, Beatrix C Hiesmayr, B Jasinska, K KacprzakAbstract:A detection system of the conventional PET tomograph is set-up to record data from e+ e- annihilation into two photons with energy of 511 keV, and it gives information on the density distribution of a radiopharmaceutical in the body of the object. In this paper we explore the possibility of performing the three gamma photons imaging based on Ortho-Positronium annihilation, as well as the possibility of positronium mean lifetime imaging with the J-PET tomograph constructed from plastic scintillators. For this purposes simulations of the Ortho-Positronium formation and its annihilation into three photons were performed taking into account distributions of photons' momenta as predicted by the theory of quantum electrodynamics and the response of the J-PET tomograph. In order to test the proposed Ortho-Positronium lifetime image reconstruction method, we concentrate on the decay of the Ortho-Positronium into three photons and applications of radiopharmaceuticals labeled with isotopes emitting a prompt gamma quantum. The proposed method of imaging is based on the determination of hit-times and hit-positions of registered photons which enables the reconstruction of the time and position of the annihilation point as well as the lifetime of the Ortho-Positronium on an event-by-event basis. We have simulated the production of the positronium in a cylindrical phantom composed of a set of different materials in which the Ortho-Positronium lifetime varied from 2.0 ns to 3.0 ns, as expected for Ortho-Positronium created in the human body. The presented reconstruction method for total-body J-PET like detector allows to achieve a mean lifetime resolution of about 40 ps. Recent Positron Annihilation Lifetime Spectroscopy measurements of cancerous and healthy uterine tissues show that this sensitivity may allow to study the morphological changes in cell structures.
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genuine multipartite entanglement in the 3 photon decay of positronium
Scientific Reports, 2017Co-Authors: Beatrix C Hiesmayr, P MoskalAbstract:The electron-positron annihilation into two photons is a standard technology in medicine to observe e.g. metabolic processes in human bodies. A new tomograph will provide the possibility to observe not only direct e + e - annihilations but also the 3 photons from the decay of Ortho-Positronium atoms formed in the body. We show in this contribution that the three-photon state with respect to polarisation degrees of freedom depends on the angles between the photons and exhibits various specific entanglement features. In particular genuine multipartite entanglement, a type of entanglement involving all degrees of freedom, is subsistent if the positronium was in a definite spin eigenstate. Remarkably, when all spin eigenstates are mixed equally, entanglement -and even stronger genuine multipartite entanglement- survives. Due to a "symmetrization" process, however, Dicke-type or W-type entanglement remains whereas GHZ-type entanglement vanishes. The survival of particular entanglement properties in the mixing scenario may make it possible to extract quantum information in the form of distinct entanglement features, e.g., from metabolic processes in human bodies.
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genuine multipartite entanglement in the 3 photon decay of positronium
arXiv: Quantum Physics, 2017Co-Authors: Beatrix C Hiesmayr, P MoskalAbstract:The electron-positron annihilation into two photons is a standard technology in medicine to observe e.g. metabolic processes in human bodies. A new tomograph will provide the possibility to observe not only direct $e^+ e^-$ annihilations but also the $3$ photons from the decay of Ortho-Positronium atoms formed in the body. We show in this contribution that the three-photon state with respect to polarisation degrees of freedom depends on the angles between the photons and exhibits various specific entanglement features. In particular genuine multipartite entanglement, a type of entanglement involving all degrees of freedoms, is subsistent if the positronium was in a definite spin eigenstate. Remarkably, when all spin eigenstates are mixed equally, entanglement --and even stronger genuine multipartite entanglement-- survives. Due to a "\textit{symmetrization}" process, however, $Dicke$-type of entanglement remains whereas $GHZ$-type of entanglement vanishes. The survival of particular entanglement properties in the mixing scenario may make it possible to extract quantum information in form of distinct entanglement features, e.g., from metabolic processes in human bodies.
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potential of the j pet detector for studies of discrete symmetries in decays of positronium atom a purely leptonic system
Acta Physica Polonica B, 2016Co-Authors: P Moskal, C Curceanu, E Czerwinski, A Gajos, M Gorgol, D Alfs, T Bednarski, P Bialas, B Glowacz, Beatrix C HiesmayrAbstract:The Jagiellonian Positron Emission Tomograph (J-PET) was constructed as a prototype of the cost-effective scanner for the simultaneous metabolic imaging of the whole human body. Being optimized for the detection of photons from the electron-positron annihilation with high time- and high angular-resolution, it constitutes a multi-purpose detector providing new opportunities for studying the decays of positronium atoms. Positronium is the lightest purely leptonic object decaying into photons. As an atom bound by a central potential it is a parity eigenstate, and as an atom built out of an electron and an anti-electron it is an eigenstate of the charge conjugation operator. Therefore, the positronium is a unique laboratory to study discrete symmetries whose precision is limited in principle by the effects due to the weak interactions expected at the level of (~10$^{-14}$) and photon-photon interactions expected at the level of (~10$^{-9}$). The J-PET detector enables to perform tests of discrete symmetries in the leptonic sector via the determination of the expectation values of the discrete-symmetries-odd operators, which may be constructed from the spin of Ortho-Positronium atom and the momenta and polarization vectors of photons originating from its annihilation. In this article we present the potential of the J-PET detector to test the C, CP, T and CPT symmetries in the decays of positronium atoms.
Taras Kavetskyy - One of the best experts on this subject based on the ideXlab platform.
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positron annihilation study of the juniperus communis based biomaterial nefrovil
2015Co-Authors: Taras Kavetskyy, Ya S Voloshanska, I V Komar, A L Stepanov, Ondrej ŠaušaAbstract:The results of positron annihilation lifetime (PAL) measurements of the Juniperus communis based biomaterial NEFROVIL are reported for the first time. Three- and four-component fittings were applied to deconvolute the PAL spectrum. In order to determine which fitting procedure is most suited, a maximum entropy lifetime (MELT) analysis was also performed. It was found that the nanovoid topology of this biomaterial is constructed by small and large free-volume holes identified by the Ortho-Positronium lifetime parameters in the most suitable four-component fitting procedure.
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structural defects and positronium formation in 40 kev b implanted polymethylmethacrylate
Journal of Physical Chemistry B, 2014Co-Authors: Taras Kavetskyy, Yoshinori Kobayashi, H. F. M. Mohamed, Ryoichi Suzuki, O Sausa, V M Tsmots, Atsushi Kinomura, V I Nuzhdin, V F Valeev, A L StepanovAbstract:Slow positron beam and optical absorption measurements are carried out to study structural defects and positronium formation in 40 keV B(+)-implanted polymethylmethacrylate (B:PMMA) with ion doses from 6.25 × 10(14) to 5.0 × 10(16) ions/cm(2). Detailed depth-selective information on defects in implanted samples was obtained by measuring of Doppler broadening of positron annihilation γ rays as a function of incident positron energy and these experimental results were compared with SRIM (stopping and range of ions in matter) simulation results. Two general processes, appearance of free radicals at lower ion doses ( 10(16) ions/cm(2)), are considered from the Doppler S-E and W-E dependences in the framework of the concept of defects formation during radiation damage of polymer structure. Probabilities of Ortho-Positronium (o-Ps) formation are analyzed using S-W plot and slow positron annihilation lifetime measurements. Dose dependence of o-Ps lifetime τ3 and intensity I3 at the incident positron energy of 2.15 keV correlates well with the dose dependence of S-parameter and seems to account for the existence of the expected two processes, i.e., scission of polymer chains and appearance of free radicals preceding the aggregation of the clusters resulting in the formation of network of conjugated bonds at lower ion doses and carbonization at higher ion doses. The increase of optical absorption observed with increasing ion implantation dose also suggests a formation of carbonaceous phase in the ion-irradiated PMMA.
D Kaminska - One of the best experts on this subject based on the ideXlab platform.
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novel j pet scanner combined with positron annihilation lifetime spectroscopy technique as a tool for morphometric imaging
Physica Medica, 2016Co-Authors: E Kubicz, E Czerwinski, A Gajos, M Gorgol, B Jasinska, D Alfs, T Bednarski, P Bialas, B Glowacz, D KaminskaAbstract: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.
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a feasibility study of ortho positronium decays measurement with the j pet scanner based on plastic scintillators
European Physical Journal C, 2016Co-Authors: D Kaminska, C Curceanu, E Czerwinski, K Dulski, A Gajos, D Alfs, T Bednarski, P Bialas, B Glowacz, N GuptasharmaAbstract:We present a study of the application of the Jagiellonian positron emission tomograph (J-PET) for the registration of gamma quanta from decays of Ortho-Positronium (o-Ps). The J-PET is the first positron emission tomography scanner based on organic scintillators in contrast to all current PET scanners based on inorganic crystals. Monte Carlo simulations show that the J-PET as an axially symmetric and high acceptance scanner can be used as a multi-purpose detector well suited to pursue research including e.g. tests of discrete symmetries in decays of Ortho-Positronium in addition to the medical imaging. The gamma quanta originating from o-Ps decay interact in the plastic scintillators predominantly via the Compton effect, making the direct measurement of their energy impossible. Nevertheless, it is shown in this paper that the J-PET scanner will enable studies of the \(\text{ o-Ps }\rightarrow 3\gamma \) decays with angular and energy resolution equal to \(\sigma (\theta ) \approx {0.4^{\circ }}\) and \(\sigma (E) \approx 4.1\,{\mathrm{keV}}\), respectively. An order of magnitude shorter decay time of signals from plastic scintillators with respect to the inorganic crystals results not only in better timing properties crucial for the reduction of physical and instrumental background, but also suppresses significantly the pile-ups, thus enabling compensation of the lower efficiency of the plastic scintillators by performing measurements with higher positron source activities.
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a feasibility study of ortho positronium decays measurement with the j pet scanner based on plastic scintillators
arXiv: Instrumentation and Detectors, 2016Co-Authors: D Kaminska, C Curceanu, E Czerwinski, K Dulski, A Gajos, D Alfs, T Bednarski, P Bialas, B Glowacz, N GuptasharmaAbstract:We present a study of the application of the Jagiellonian Positron Emission Tomograph (J-PET) for the registration of gamma quanta from decays of Ortho-Positronium (o-Ps). The J-PET is the first positron emission tomography scanner based on organic scintillators in contrast to all current PET scanners based on inorganic crystals. Monte Carlo simulations show that the J-PET as an axially symmetric and high acceptance scanner can be used as a multi-purpose detector well suited to pursue research including e.g. tests of discrete symmetries in decays of Ortho-Positronium in addition to the medical imaging. The gamma quanta originating from o-Ps decay interact in the plastic scintillators predominantly via the Compton effect, making the direct measurement of their energy impossible. Nevertheless, it is shown in this paper that the J-PET scanner will enable studies of the o-Ps$\to3\gamma$ decays with angular and energy resolution equal to $\sigma(\theta) \approx 0.4^{\circ}$ and $\sigma(E) \approx 4.1$ keV, respectively. An order of magnitude shorter decay time of signals from plastic scintillators with respect to the inorganic crystals results not only in better timing properties crucial for the reduction of physical and instrumental background, but also suppresses significantly the pileups, thus enabling compensation of the lower efficiency of the plastic scintillators by performing measurements with higher positron source activities.
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trilateration based reconstruction of ortho positronium decays into three photons with the j pet detector
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2016Co-Authors: A Gajos, E Czerwinski, M Gorgol, B Jasinska, D Alfs, T Bednarski, P Bialas, B Glowacz, D Kaminska, ł KaplonAbstract:Abstract This work reports on a new reconstruction algorithm allowing us to reconstruct the decays of Ortho-Positronium atoms into three photons using the places and times of photons recorded in the detector. The method is based on trilateration and allows for a simultaneous reconstruction of both location and time of the decay. Results of resolution tests of the new reconstruction in the J-PET detector based on Monte Carlo simulations are presented, which yield a spatial resolution at the level of 2 cm (FWHM) for X and Y and at the level of 1 cm (FWHM) for Z available with the present resolution of J-PET after application of a kinematic fit. Prospects of employment of this method for studying angular correlations of photons in decays of polarized ortho -positronia for the needs of tests of CP and CPT discrete symmetries are also discussed. The new reconstruction method allows for discrimination of background from random three-photon coincidences as well as for application of a novel method for determination of the linear polarization of ortho -positronium atoms, which is also introduced in this work.