Publikační činnost Katedry fyziky / Department of Physics (480)

Permanent URI for this collectionhttp://hdl.handle.net/10084/122994

Kolekce obsahuje bibliografické záznamy publikační činnosti (článků) akademických pracovníků Katedry fyziky (480) v časopisech registrovaných ve Web of Science od roku 2018 po současnost.
Do kolekce jsou zařazeny:
a) publikace, u nichž je v originálních dokumentech jako působiště autora (adresa) uvedena Vysoká škola báňská-Technická univerzita Ostrava (VŠB-TUO),
b) publikace, u nichž v originálních dokumentech není v adrese VŠB-TUO uvedena, ale autoři prokazatelně v době jejich zpracování a uveřejnění působili na VŠB-TUO.

Bibliografické záznamy byly původně vytvořeny v kolekci Publikační činnost akademických pracovníků VŠB-TUO, která sleduje publikování akademických pracovníků od roku 1990.

Záznamy vytvořené před rokem 2018 se nacházejí v této kolekci.

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Now showing 1 - 20 out of 104 results

Bloch surface wave fast ellipsometric sensor utilizing a polarization camera with an improved detection limit
(Elsevier, 2024) Kaňok, Roman; Abuleil, Marwan; Hlubina, Petr; Abdulhalim, Ibrahim
In the field of optical sensing, one-dimensional photonic crystals (1DPhC) are of great interest and seem to be a promising alternative to plasmonic sensors. In this paper, a fast ellipsometric sensor based on the Bloch surface wave (BSW) is demonstrated. The Kretschmann configuration and a pixelated micro -grid polarization camera are used, allowing real-time observation of ellipsometric parameters tan psi and cos Delta. Moreover, this method is improved by utilizing another 1DPhC acting as a spectral filter, leading to the deepening of the BSW dip in the angular domain. Furthermore, ratios between the different measured intensities from the four pixels are shown to reveal a deep narrow dip which can also be used for sensing with high figure of merit. This new approach is experimentally confirmed using a 1DPhC comprising of 6 bilayers of TiO 2 /SiO 2 and a termination layer of TiO 2 . Sensors based on this concept have the potential to be used in many applications, including real-time chemical or biological analytes detection.
Highly stabilized fiber Bragg grating accelerometer based on cross-type diaphragm
(Optica Publishing Group, 2024) Wei, Heming; Zhuang, Changquan; Che, Jiawei; Zhang, Dengwei; Zhu, Mengshi; Pang, Fufei; Caucheteur, Christophe; Hu, Xuehao; Nedoma, Jan; Martinek, Radek; Marques, Carlos
A fiber Bragg grating (FBG) accelerometer based on cross-type diaphragm was proposed and designed, in which the cross-beam acts as a spring element. To balance the sensitivity and stability, the accelerometer structure was optimized. The experimental results show that the designed device has a resonant frequency of 556 Hz with a considerable wide frequency bandwidth of up to 200 Hz, which is consistent with the simulation. The sensitivity of the device is 12.35 pm/g@100 Hz with a linear correlation coefficient of 0.99936. The proposed FBG accelerometer has simple structure and strong anti-interference capability with a maximal cross-error less than 3.26%, which can be used for mechanical structural health monitoring.
The role of smart optical biosensors and devices on predictive analytics for the future of aquaculture systems
(Elsevier, 2024) Soares, Maria Simone; Singh, Ragini; Kumar, Santosh; Jha, Rajan; Nedoma, Jan; Martinek, Radek; Marques, Carlos
Recirculating aquaculture systems (RAS) have been rising quickly in the last decade, representing a new way to farm fish with sustainable aquaculture practices. This system is an environmentally and economically sustainable technology for farming aquatic organisms by reusing the water in production. RAS present some benefits compared with other aquaculture methods, for instance, allows the minimization of water usage and disease occurrence, the absence of antibiotics in these systems, shortens the production cycle, functions as a water treatment system, allows the improvement of the feed conversion, and a reduction in the alteration of coastal habitat, among others. However, this is a complex system with complex interactions between the number of fish and water quality parameters, which can compromise the fish welfare. Currently, there is a huge gap in the global aquaculture sector in terms of smart sensors for cortisol (stress hormone), bacteria, water pollutants, volatile organic compounds and micro/nano-plastics assessment. This sector does not measure such critical parameters which brings a weak understanding of the wellbeing of fish. Therefore, it is crucial to implement point of care (POC) sensors for those critical parameters' assessment via multiparameter solution and predictive analytic capabilities for data supply. This work presents an overall introduction about the impact of the RAS on fish production and its necessity as protein as well as the actual solutions for those problems. Additionally, it reviews the actual state of the art in terms of potential multiparameter POC sensors and predictive analytical approaches that have been investigated in recent years for future application in aquaculture with the aim to guide the researchers on the sector's needs. Additionally, future perspectives are also described in order to digitize the aquaculture sector with novel optical systems and biosensing elements.
Physical properties of MnFeAl-based alloys affected by Mn content and annealing
(Elsevier, 2024) Životský, Ondřej; Szurman, Ivo; Gembalová, Lucie; Alexa, Petr; Uhlář, Radim; Čegan, Tomáš; Malina, Ondřej; Čížek, Jakub; Veverka, Miroslav; Goraus, Jerzy
The present study is devoted to the Mn 2.4 Fe 0.8 Al 0.8 and Mn 2 FeAl alloys prepared by induction melting and studied in their original and subsequently annealed states. The annealing was carried out at 773 K/100 h and 1073 K/100 h in the argon atmosphere. The microstructure, phase composition, magnetic properties, and atom arrangement are followed with regard to Mn content and annealing conditions. The scanning electron microscopy completed by the energy dispersive X-ray spectroscopy and neutron activation analysis has detected single-phase alloys with compositions close to the nominal ones. Their structure, analyzed by X-ray diffraction, was found to be primitive cubic beta -Mn with the lattice parameters of 0.6359(2) nm for Mn 2.4 Fe 0.8 Al 0.8 and 0.6339(1) nm for Mn 2 FeAl. The coherent potential approximation calculations and positron annihilation spectroscopy have allowed obtaining an overview to the arrangement of Mn, Fe, and Al atoms in the beta -Mn structure and formation of the open volume defects. It is shown that Mn atoms occupy predominantly 8c Wyckoff sites and remaining Mn, Fe and Al atoms occupy 12d sites in equal 1/3 proportion. The open volume defects, vacancies and vacancy clusters, occur in both alloys and both annealed states in a very low concentration. From the magnetic viewpoint, both alloys in the as -prepared state and after annealing at 773 K/ 100 h are paramagnetic at room temperature with transition to antiferromagnetic state at about 30 - 40 K. The ac susceptibility measurements have indicated spin glass nature of the Mn 2 FeAl alloys. The annealing at a higher temperature, 1073 K/100 h, has affected mainly Mn 2.4 Fe 0.8 Al 0.8 alloy manifesting a weak ferro-/ferrimagnetic contribution at room temperature contributing to a strong magnetic ordering below 42 K.
Magnetite/ceria-based composites for effective adsorption of pharmaceuticals and pesticides in water
(Elsevier, 2024) Ederer, Jakub; Ryšánek, Petr; Vrtoch, Ľuboš; Neubertová, Viktorie; Henych, Jiří; Životský, Ondřej; Janoš, Pavel; Adamec, Slavomír; Kolská, Zdeňka
Contamination of water sources by pharmaceuticals and agricultural pollutants has become an urgent environmental issue. A magnetic cerium oxide composite (FeCe oxides) was synthesized and used as an effective adsorbent for the removal of 2,4-dichlorophenoxyacetic acid (2,4-D) and cephalexin (CEF) from aqueous solution. The magnetic core of FeCe composite was prepared from commercial chemicals (common food additives or flocculants) or the commercial pigment was used directly as a magnetic core without further purification. The adsorption kinetics and mechanism governing the removal of CEF and 2,4-D by FeCe composites were studied in detail. The measured data were fitted by the commonly used isotherms (Langmuir, Langmuir-Freundlich, Freundlich and Temkin). The results showed that the adsorption of 2,4-D and CEF followed Freundlich and Langmuir-Freundlich isotherm with the maximum adsorption capacity of 55.7 mg/g (2,4-D) and 110.7 mg/g (CEF), respectively. Also, 2,4-D and CEF adsorption on the composite follow pseudo-second-order kinetics. The study showed that the FeCe composites have high efficacy in eliminating 2,4-D and CEF from aqueous solution with the added benefit of simple separation of the used composites. Therefore, they can be considered as promising and effective tools for water purification.
Directional-sensitive wide field-of-view monitoring of high-intensity proton beams by spectral tracking of scattered particles with scattering foil and miniaturized radiation camera
(IOP Publishing, 2024) Granja, C.; Uhlář, Radim; Poklop, Dušan; Alexa, Petr; Zach, V.; Oancea, C.; Marek, L.
Monitoring and characterization of particle beams in wide -range is often necessary in research and many applications with particle accelerators. The quantitative measurement evaluation of composition especially of high -intensity beams are limited and can become a challenge with conventional methods especially with simplified instrumentation for ease of deployment. For purpose, we developed a novel technique based on high -resolution spectral -sensitive tracking of single particles scattered from the beam path by a thin foil. We use a compact radiation camera equipped with the semiconductor pixel detector Timepix3 together with dedicated Monte -Carlo simulations. Particle -event type discrimination and directional information are produced by the detector spectral tracking response together with particle -type resolving power derived from experimental calibrations. Directional- and spectral -sensitive components can be resolved in wide field -of -view. Quantification of the primary beam intensity is extrapolated by numerical calculations. Demonstration and evaluation of the technique are provided by measurements with 33 MeV protons from a light ion cyclotron accelerator. Scattered particles originating from the thin foil, the accelerator beam nozzle, and air space along the beam path are detected and evaluated.
Microscopic study of ground–state binding energies in Z = 52 − 70 neutron–rich nuclei
(Elsevier, 2024) Abolghasem, Mojgan; Alexa, Petr
We investigate 15 different Skyrme-interaction parametrizations and apply them to the chains of Te, Xe, Ba, Ce, Nd, Sm, Gd, Dy, Er, and Yb isotopes beyond N = 78 to calculate theoretical binding energies within the mean -field approach based on density functional theory. Results of calculations are compared with available experimental data on binding energies and quadrupole deformation with the aim to find out which interaction is the most convenient for shape and structure studies of these isotopic chains.
Low-temperature antiferromagnetism in quaternary Mn2FeSi0.5Al0.5 alloys
(AIP Publishing, 2024) Životský, Ondřej; Gembalová, Lucie; Skotnicová, Kateřina; Szurman, Ivo; Čegan, Tomáš; Juřica, Jan; Malina, Ondřej; Čížek, Jakub
In this work, the quaternary Mn2FeSi0.5Al0.5 alloys are prepared for the first time in the form of cylinder-shaped ingots by traditional induction melting technique followed by homogenization annealing at 773 K for 100 h. The microstructural and magnetic properties of as-cast and annealed Mn2FeSi0.5Al0.5 samples are analyzed in detail and compared to the Mn2FeSi and Mn2FeAl ternary alloys. The Mn2FeSi0.5Al0.5 ingots are two-phase both before and after annealing, and their diffractograms correspond to the primitive cubic beta-Mn structure. Obtained lattice constant of 0.6274 nm is only slightly lower than that of Mn2FeAl alloy (0.6339 nm) and different from Mn2FeSi (0.5672 nm). The existence of both phases enriched in Si at the expense of Al and Mn was confirmed by differential thermal analysis showing two endothermic and exothermic peaks at temperatures of 1363 K and 1407 K. The magnetic properties of both quaternary samples studied in wide temperature range from 5 K to 573 K indicate paramagnetic behavior at room and elevated temperatures. The annealed system has the values of Curie temperature and effective paramagnetic moment comparable to the ternary Mn2FeAl alloy. The transition to antiferromagnetic state occurring at Neel temperatures of 34 K (as-cast sample) and 37 K (annealed sample) is caused by strong geometric frustration of beta-Mn structure. The magnetic transitions observed in both samples between Neel and room temperature are discussed in terms of the existence of Griffiths phase.
Optimized film thicknesses for maximum refractive index sensitivity and figure of merit of a bimetallic film surface plasmon resonance sensor
(Springer Nature, 2024) Chylek, Jakub; Ciprian, Dalibor; Hlubina, Petr
In this paper, a simple surface plasmon resonance (SPR) optical sensor with a bimetallic gold-silver film is proposed and its parameters are optimized based on reflectance spectra analysis. In comparison with most SPR sensors, which use single gold films, the evanescent field of this bimetallic configuration at the analyte-metal interface enables the sensing with substantially enhanced refractive index (RI) sensitivity and figure of merit (FOM). The proposed structure comprising a BK7 glass substrate, an adhesion layer of chromium, a gold-silver plasmonic layer, and a protective layer of silicon dioxide is employed in the Kretschmann configuration for liquid analyte sensing. In order to achieve the best sensing properties, the gold-silver layer thickness ratio is varied, and a thorough analysis of reflectance spectra is performed based on RI sensitivity and FOM. For this purpose, a liquid analyte of aqueous solutions of NaCl is employed for angles of incidence 63 degrees and 64 degrees, respectively. Moreover, based on the analysis, an optimized gold-silver layer thickness ratio is selected, and a sensitivity of 41,592 nm per RI unit (RIU) and FOM of 424 RIU-1 are reached. The designed bimetallic SPR structure proves to be advantageous compared to single-gold-film structures employed for sensing applications.
Differential isotropic model of ferromagnetic hysteresis
(American Physical Society, 2023) Pytlík, Jan; Luňáček, Jiří; Životský, Ondřej
This paper presents an alternative isotropic model of magnetization curves in ferromagnetic materials. It is based on the well-known Jiles-Atherton model, but significantly modifies its assumptions to be consistent with fundamental physical principles. As a result, the number of model parameters has been reduced to four. The differential model couples the volume energy density of the sample with the external magnetic field and includes the process of rigid and flexible overcoming of the pinning sites in the law of energy density conservation. The magnetic moment magnitude is connected with coherent regions called magnetic clusters, which are smaller than magnetic domains. The commonly used concept of anhysteretic magnetization, based on the Langevin function, is modified by a parameter 𝛽, which represents the average mutual interaction among magnetic clusters. The model was successfully tested on two isotropic materials: amorphous Fe77.5⁢Si7.5⁢B15 alloy and powdered magnetite. The main advantages compared with previous models are the simpler model equation and a much more convenient numerical and fitting procedure.
From Bloch surface waves to cavity-mode resonances reaching an ultrahigh sensitivity and a figure of merit
(Optica Publishing Group, 2023) Gryga, Michal; Ciprian, Dalibor; Hlubina, Petr
We report on a new sensing concept based on resonances supported by a one-dimensional photonic crystal (1DPhC) microcavity resonator in the Kretschmann configuration. For a 1DPhC comprising six bilayers of TiO2/SiO2 with a termination layer of TiO2 employed to form a microcavity, we show that when the angle of incidence is changed, the Bloch surface waves (BSWs) can be transformed into cavity -mode resonances exhibiting an ultrahigh sensitivity and a figure of merit. Using wavelength interrogation, we demonstrate that Bloch surface TE wave excitation shows up as a sharp dip in the reflectance spectrum with a sensitivity and a figure of merit (FOM) of 70 nm per refractive index unit (RIU) and 19.5 RIU-1, respectively. When the angle of incidence decreases, cavity-mode resonances for both TE and TM waves are resolved for RI in a range of 1.0001-1.0005. The sensitivity and FOM can reach 52,300 nm/RIU and 402,300 RIU-1 for the TE wave, and 14,000 nm/RIU and 2154 RIU-1 for the TM wave, respectively. In addition, resonances are confirmed experimentally for a humid air with a sensitivity of 0.073 nm per percent of the relative humidity (%RH) for BSW resonance and is enhanced to 1.367 nm/%RH for the TM cavity-mode resonance. This research, to the best of the authors' knowledge, is the first demonstration of a new BSW-like response that can be utilized in a simple sensing of a wide range of gaseous analytes.
Regeneration possibilities and application of magnetically modified biochar for heavy metals elimination in real conditions
(Elsevier, 2023) Tokarčíková, Michaela; Peikertová, Pavlína; Čech Barabaszová, Karla; Životský, Ondřej; Gabor, Roman; Seidlerová, Jana
Although new types of composites with magnetic properties and high adsorption capacity for potentially toxic elements elimination are studied by researcherers, the information about the reusability, stability and removal efficiency of composites is still scarce or absent. Therefore, the aim of our work was applicate the sorbent to eliminate Zn(II), Cd(II) and Pb(II) ions from in dustrial waste leachates, and moreover, study the composite reusability and magnetic separation efficiency. Magnetically modified biochar was prepared from the fermentation residue of maise hybrid by a simple two-step method with microwave assistance. Composite properties, as well as the adsorption efficiency and magnetic response are depend on the extraction agent. The alkaline extraction agent showed the best properties for reusability and had no influence on Fe releasing from the composite, the adsorption efficiency was higher than 90% even in the 5th recycling cycle, and the composite remained magnetically active. The separation efficiency of composite from an aqueous environment by a magnet was higher than 95% within 15 min. Magnetically modified biochar proved to be an effective sorbent for metal ions elimination from wastewater.
Experimental and stochastic application of an elastic foundation in loose material transport via a sandwich belt conveyor - Part 2
(MDPI, 2023) Čepica, Daniel; Frydrýšek, Karel; Hrabovský, Leopold; Nikodým, Marek
This article serves as a continuation of our previously published work and focuses on loose material transport via sandwich belt conveyors. Experimental, analytical, stochastic, and numerical approaches are used to obtain and utilize the moduli of a bilateral Winkler elastic foundation that represent a loose material, which is wheat (Triticum aestivum) that is free of bran in this case. The solutions were obtained for a uniformly and nonuniformly distributed loose material. The task of the conveyor with loose material is simplified into a symmetric task, i.e., a beam on an elastic bilateral Winkler foundation, for an analytical solution and stochastic solution (Anthill and Matlab sw). In a numerical approach, this is considered a plane strain problem within the finite element method (Ansys and MSC.Marc sw). The experimental data are evaluated and used to obtain the functions of Winkler elastic foundation moduli, which are further considered in the numerical solution. The finite element method mainly serves as a verification tool. The acquired histograms of the elastic foundation moduli can be further applied in various scientific and research fields.
Effect of rapid solidification in Mn2FeSi alloy formation and its physical properties
(Elsevier, 2023) Životský, Ondřej; Jirásková, Yvonna; Buršík, Jiří; Janičkovič, Dušan; Čížek, Jakub
The structure and magnetic properties of Mn2FeSi alloy as a prospective Heusler material are studied from the viewpoint of the rapid solidification technology used for its preparation. The planar flow casting leads due to fast cooling of the melted material to formation of ribbons with different structural and physical properties. In present study, the crystalline ribbon-type samples are produced and subjected to detail analysis using electron microscopy, positron annihilation spectroscopy, X-ray diffraction, as well as magnetic and Mössbauer measurements. It is shown that the as-prepared Mn2FeSi ribbon is paramagnetic at room temperature and adopts a cubic structure with lattice parameter of 0.567 nm and Néel temperature of antiferromagnetic/paramagnetic transition around 45 K. The presence of other phase(s) observed at low temperatures is reflected also in changes of the structural and physical properties after sample annealing at 773 K for 100 h. The results of microstructure, magnetic, and phase composition observations are completed by the positron life time measurements suggesting single vacancies as the main defects in which the positrons are trapped.
Measurement of dosimetrical cross sections with 14.05 MeV neutrons from compact neutron generator
(Elsevier, 2023) Košt́ál, Michal; Czakoj, Tomáš; Alexa, Petr; Šimon, Jan; Zmeškal, Marek; Schulc, Martin; Krechlerová, Alena; Peltán, Tomáš; Mravec, Filip; Cvachovec, František; Rypar, Vojtěch; Uhlář, Radim; Harkut, Ondřej; Matěj, Zdeněk
This paper deals with the measurement of the differential dosimetry cross sections using a small compact D-T neutron generator with 14.05 ± 0.08 MeV neutron emission (1 × 108 n/s into 4π). In spite of low neutron flux, it is possible to get measurable gamma-ray activities by irradiating a larger amount of target material placed in close geometry. The experimentally determined cross sections are in good agreement with the cross sections in the IRDFF-II dosimetry library. The comparison with other nuclear data libraries was performed as well. It is worth noting that the mean standard deviation in IRDFF-II library is about 4 %, while in the case of other data libraries they are from 5.5 % to 7.5 %. This result can be understood as a validation of IRDFF-II using 14.05 MeV neutrons and also a confirmation of the applicability of small compact generators in the measurement of activation cross sections.
Effect of Ag modification on TiO2 and melem/g-C3N4 composite on photocatalytic performances
(Springer Nature, 2023) Michalska, Monika; Matějka, Vlastimil; Pavlovský, Jiří; Praus, Petr; Ritz, Michal; Serenčíšová, Jana; Gembalová, Lucie; Kormunda, Martin; Foniok, Kryštof; Reli, Martin; Simha Martynková, Gražyna
Here, the comparison of two diferent semiconductor materials is demonstrated, TiO2 and melem/g C3N4 composites—modifed with balls of approximately 5 nm Ag nanoparticles (NPs) as photocatalysts for the degradation of the model dye acid orange 7 (AO7). The melem molecule synthesized here is one of a series of organic compounds consisting of triazine ring compounds with a structure similar to that of melam and melamine. The photodegradation process of AO7 was carried out to examine all powder materials as a potential photocatalyst. Additionally, two diferent lamps of wavelengths 368 nm (UV light) and 420 nm (VIS light) were applied to compare the photodegradation tests. A new synthesis route for the acquisition of Ag NPs (Ag content 0.5, 1.0 and 2.5 wt%), based on a wet and low temperature method without the use of reducing reagents was proposed. The best photocatalytic performances under UV and VIS light were obtained for both, TiO2 and melem/g-C3N4 materials (new synthesis route) modifed with a very low Ag content—0.5 wt%. The photodegradation activities using UV lamp (3 h, 368 nm irradiation) for samples with 0.5 wt% of Ag: TiO2 and melem/g-C3N4, in excess of 95 and 94%, respectively, were achieved. The highest photoactive materials melem/g C3N4 with 0.5 and 1 wt% Ag revealed 98% of activity under the VIS lamp after 3 h long irradiation. Our work demonstrates a novel, environmentally acceptable, and cost-efective chemical strategy for preparation of photocatalysts suitable for degradation of organic contaminants in wastewater treatment.
Influence of domain walls thickness, density and alignment on Barkhausen noise emission in low alloyed steels
(Springer Nature, 2023) Neslušan, Miroslav; Pitoňák, Martin; Minárik, Peter; Tkáč, Michal; Kollár, Peter; Životský, Ondřej
This study deals with the characterization of low alloyed steels of diferent yield strengths (varying in the range of 235–1100 MPa) via Barkhausen noise emission. The study investigates the potential of this technique to distinguish among the low alloyed steels and all signifcant aspects contributing to Barkhausen noise, such as the residual stress state, microstructure expressed in terms of dislocation density, grain size, prevailing phase, as well as associated aspects of the domain wall substructure (domain wall thickness, energy, their spacing and density in the matrix). Barkhausen noise in the rolling as well as transversal direction grows along with the yield strength (up to 500 MPa) and the corresponding grain refnement of ferrite. As soon as the martensite transformation occurs in a high strength matrix, this evolution saturates, and remarkable magnetic anisotropy is developed when Barkhausen noise in the transversal direction grows at the expense of the rolling direction. The contribution of residual stresses as well as the domain wall thickness is only minor, and the evolution of Barkhausen noise is driven by the density of the domain walls and their realignment.
Experimental and stochastic application of an elastic foundation in loose material transport via sandwich belt conveyors
(MDPI, 2023) Frydrýšek, Karel; Čepica, Daniel; Hrabovský, Leopold; Nikodým, Marek
This article deals with the problem of loose materials, i.e., wheat grain, when transported by belt conveyors with cover belts. For the purpose of further research, experimental measurements of the deflections of a conveyor belt with loose material were carried out on a self-built laboratory test device. The mechanical contact between the wheat and the belt could be suitably approximated using an elastic foundation. The measured data were evaluated and used to obtain functional relationships for the compressibility moduli of the bilateral Winkler elastic foundation. The obtained relationships were further stochastically processed using the Monte Carlo method.
Microstructural and magnetic properties of Mn2FeSi and Mn2FeAl alloys prepared in bulk form
(Elsevier, 2023) Životský, Ondřej; Gembalová, Lucie; Jirásková, Yvonna; Szurman, Ivo; Čegan, Tomáš; Malina, Ondřej; Kuriplach, Jan; Čížek, Jakub
Microstructural and magnetic properties of the Mn2FeSi and Mn2FeAl alloys prepared in the bulk form have been investigated. Cylinder-shaped ingots produced by induction melting technique were analyzed in as-quenched state and additionally annealed at 773 K for 5 days in the protective argon atmosphere. The results show that Si and Al have different effects on the microstructural and magnetic properties of the alloys. The Mn2FeAl ingots are single-phase both before and after annealing, and their diffractograms surprisingly correspond not to the Heusler (L21 or XA) but to the primitive cubic β-Mn structure. Conversely, Mn2FeSi alloys show a two-phase behavior in the as-quenched state. From results of X-ray diffraction it was not possible to judge whether Mn2FeSi alloy has the inverse-Heusler (XA) or full Heusler (L21) structure. Annealing of Mn2FeSi leads to the formation of multiple phases. The EDX chemical area analyses resulted in only slight deviations of compositions compared to the nominal ones. The lattice parameters of 0.5672 nm and 0.6339 nm were estimated for the Mn2FeSi and Mn2FeAl samples from X-ray diffraction measurements. From the magnetic viewpoint, all samples are paramagnetic at room temperature and transform into antiferromagnetic state at the N é el temperatures about 50 K and 36 K for Mn2FeSi and Mn2FeAl, respectively. The negative Curie temperatures determined at all samples by Curie-Weiss law indicate an antiferromagnetic ordering of spins. Positron annihilation investigations revealed that Mn2FeSi contains a high concentration of vacancies. The local chemical environment of vacancies characterized by coincidence Doppler broadening is compatible with L21 rather than with XA structure. In contrast vacancy concentration in Mn2FeAl is very low and almost all positrons are annihilated in the free state.
Detection of fast neutrons with the pixel detector Timepix3
(IOP Publishing, 2023) Granja, C.; Uhlář, Radim; Chuprakov, I.; Alexa, Petr; Sansarbayar, E.; Gledenov, Y. M.; Poklop, Dušan; Olšanský, V.; Marek, L.; Vuolo, M.; Pacik, J.
We examined the response of the pixel detector Timepix3 with silicon sensor to well-defined fast neutron fields. Part of the pixel detector silicon sensor was additionally equipped with a neutron mask of distinct converter regions. The mask consists of separate thermal and fast neutron regions using 6LiF and hydrogen (plastic) converters, respectively. Measurements were performed with mono-energetic fast neutrons produced at D-D and D-T sources from a Van de Graaff accelerator and a neutron generator, respectively. Data were collected with low background including measurements with moderator material to provide a thermalized neutron component. All the signals produced in the detector were analyzed and decomposed in terms of the spectral -tracking response of the pixel detector. The effect of the fast and thermal components of the neutron converter were determined and compared with direct interactions in the silicon sensor which are significant and can be dominant for fast neutrons. We identify and classify the neutron-induced tracks in terms of the broad-type particle-event track classes. A partial overlap is unavoidable with tracks from direct detection of other radiations in particular protons and low-energy light ions as well as X rays. This will limit the neutron-event discrimination in mixed-radiation fields. The detection response according sensor-mask region was examined and calibrated for the investigated neutron fields. The neutron detection efficiency is selectively derived for the detector particle-event classes. This approach enables to enhance the neutron-discrimination and suppress background and unwanted events. This work enables to extend the response matrix of the detector for broad-type radiations to include neutrons both fast and thermal. The results serve to enhance the sensitivity and determine the neutron component in unknown and mixed-radiation fields such as outer space and particle radiotherapy environments.

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