A. Turkin - Academia.edu (original) (raw)
Papers by A. Turkin
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2000
The dependencies of void formation and radiolytic sodium accumulation on the irradiation dose, do... more The dependencies of void formation and radiolytic sodium accumulation on the irradiation dose, dose rate, temperature and impurity content are analyzed within a framework of a theoretical model, which is based on a new mechanism of dislocation climb. The mechanism involves the production of V F centers (self-trapped hole neighboring a cation vacancy) as a result of the absorption of excess H centers at dislocation lines. Voids are shown to arise due to the reaction between F and V F centers at the surface of halogen bubbles. All reactions involved in the evolution of extended defects are controlled by the dierence between the absorption of H centers and F centers. This dierence is determined by the material speci®c parameters responsible for the bias factors of extended defects and by the mean concentration of point defects. The latter depends on the temperature and dose rate as described in the present paper. Impurities can facilitate or suppress radiation damage formation depending on their eect on the nucleation of extended defects under irradiation. This is demonstrated by comparing theoretical results obtained for dose dependence of colloid volume fraction at dierent dislocation densities with experimental data obtained in crystals doped with dierent impurities.
Defect and Diffusion Forum, 1997
Radiation Effects and Defects in Solids, 1999
physica status solidi (c), 2005
Take-down policy If you believe that this document breaches copyright please contact us providing... more Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
physica status solidi (c), 2005
A mechanism of radiation-induced emission of Schottky defects from extended defects proposed orig... more A mechanism of radiation-induced emission of Schottky defects from extended defects proposed originally for metals has recently been applied to ionic crystals, where it is based on interactions of excitons with extended defects such as dislocations and colloids. Exciton trapping and decay at colloids may result in the emission of F centers and consequent shrinkage of the colloid. In the present paper, the radiationinduced emission of F centers is taken into account in the modeling of nucleation and growth of sodium colloids and chlorine bubbles in NaCl exposed to electron or gamma irradiation. The evolution of colloid and bubble number densities and volume fractions with increasing irradiation dose is modeled in the framework of a modified rate theory and compared with experimental data. Experimental values of the colloid volume fractions and number densities have been estimated on the basis of latent heat of melting of metallic Na obtained with combined differential scanning calorimetry experiments and atomic force microscopy investigations of metallic clusters.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2002
A kinetic model is formulated for the chemical reaction between radiolytic sodium colloids and ga... more A kinetic model is formulated for the chemical reaction between radiolytic sodium colloids and gas bubbles, which are brought into contact with each other during the exposure to ionising radiation by the growing voids. The reaction starts with the evaporation of Na atoms into the void due to the localized heat release caused by reactions between chlorine molecules colliding with the colloid surface. It is shown that this exothermic and autocatalytic reaction leads to a sudden temperature increase inside the void, which gives rise to thermoelastic stresses in the surrounding matrix. Tangential stresses might exceed the threshold stress required for localized cleavage of the matrix resulting in crack formation and mechanical instability of NaCl under high dose irradiation.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2002
A kinetic model of zircon thermoluminescence (TL) has been constructed to simulate the processes ... more A kinetic model of zircon thermoluminescence (TL) has been constructed to simulate the processes and stages relevant to thermoluminescent dating such as: filling of electron and hole traps during the excitation stage both for natural and laboratory irradiation; the time dependence of fading after laboratory irradiation; TL experiments both after laboratory and natural irradiation. The goal is to inspect qualitative behavior of the system and to unravel the processes and determine the parameters controlling TL phenomena of zircon. The input parameters of the model, such as types and concentrations of the TL centers and energy distributions of the hole and electron traps, were obtained by analyzing the experimental data on fading of the TL-emission spectra of samples from different locations. EPR data were used to establish the nature of the TL centers. Glow curves and 3D TL emission spectra are simulated and compared with the experimental data on time-dependent TL fading. Theoretical dating curves for combined natural plus laboratory irradiation have been calculated for as-irradiated, faded and preheated samples.
Journal of Physics: Condensed Matter, 2004
Journal of Nuclear Materials, 2005
We have performed numerical calculation of the capture efficiency of a dislocation loop in a fini... more We have performed numerical calculation of the capture efficiency of a dislocation loop in a finite toroidal reservoir, which is a more appropriate model for a dislocation loop than a spherical or cylindrical reservoir adopted in the previous models. It allows a direct evaluation of the capture efficiency and the bias for a loop of any size with a full account of the stress field in the loop region of influence. It is shown that the loop bias depends on the loop size, dislocation density and the interstitial to vacancy dilatation ratio. With increasing loop size its bias decreases or increases to the straight dislocation bias value if the dislocation density is low or high, respectively. The bias difference of loops of different sizes is shown to be the reason of a coexistence of vacancy and interstitial loops under irradiation. In the conventional case of the dislocation bias for interstitials, interstitial loops are expected to grow to larger sizes than vacancy loops, while in a special case of dislocation bias for vacancies, the opposite tendency is expected.
Journal of Nuclear Materials, 1995
A model of cascade-induced precipitate dissolution is formulated describing the effect of heavy i... more A model of cascade-induced precipitate dissolution is formulated describing the effect of heavy ion irradiation at low temperatures on the stability of the metastable coherent chromium phase in a Cu-based alloy. Both analytical and Monte Carlo simulation results are consistent with recent transmission electron microscopy observations [l] which showed that the strain contrast of these precipitates disappeared completely after irradiation to a fluence of 0.1 dpa at room temperature.
Journal of Nuclear Materials, 2006
The effect of coherency loss on the development of precipitate size distribution under cascade-pr... more The effect of coherency loss on the development of precipitate size distribution under cascade-producing irradiation is considered. The nucleation of coherent precipitates, their growth followed by coherency loss and cascade-induced dissolution of large incoherent precipitates can occur simultaneously resulting in formation of a quasi-stationary size distribution of semicoherent precipitates. To describe this process we consider co-evolution of a mixed population of coherent, semicoherent and incoherent precipitates. Mathematically, the problem is formulated as a set of discrete rate equations of nucleation kinetics (the Master equation approach) which is also used for later stages of evolution. To solve the corresponding large set of equations (typically, more than 10 5 equations) an efficient numerical method is developed. The simulation results obtained for material parameters and irradiation conditions typical for nuclear reactors show that the coherency loss affects considerably evolution of the precipitate population. Under certain irradiation conditions, both in solution-annealed alloys and in aged ones, the mean precipitate size and the number density during prolonged irradiation tend to steady state values, whereas the size distribution function of large precipitates narrows. The width of the quasi-stationary size distribution is controlled by cascade parameters. It was found that the asymptotic quasi-stationary state of the precipitate population may depend on initial state of the alloy.
Applied Physics A Solids and Surfaces, 1994
The interaction energy between point defects and dislocation patterns (such as the pileup of disl... more The interaction energy between point defects and dislocation patterns (such as the pileup of dislocation loops and the dislocation wall) is derived. The bias for interstitial absorption by a dislocation in a pattern is shown to be lower than that of an isolated dislocation. The dislocation patterning is proposed to be driven by the dependence of dislocation bias on the dislocation arrangement.
Journal of Physics: Condensed Matter, 2006
New experimental results are presented on low temperature irradiation (18 • C) of rock-salt sampl... more New experimental results are presented on low temperature irradiation (18 • C) of rock-salt samples which had been exposed to initial doses up to 320 GRad at 100 • C. Differential scanning calorimetry (DSC) shows that the latent heat of melting (LHM) of sodium colloids decreases during subsequent lowtemperature irradiation, whereas the stored energy (SE) increases slowly, indicating that the process of radiolysis continues. The decrease of the LHM is due to dissolution of large colloids, because the intensities of the melting peaks decrease during the second stage irradiation at low temperature. The model is formulated to describe the nucleation kinetics and the evolution of the size distribution of chlorine precipitates and sodium colloids in NaCl under high dose irradiation. It is shown that the mechanism of dissolution of large Na colloids during low temperature irradiation can be related to melting of sodium colloids.
Applied Radiation and Isotopes, 2021
A nondestructive iterative method for uranium-bearing material characterization with HRGS develop... more A nondestructive iterative method for uranium-bearing material characterization with HRGS developed earlier in Burdeinyi et al. (2020) is applied to determine matrix densities, uranium mass fraction and uranium isotope masses of uranium ore, UO2 and U3O8 powders, fuel elements in the form of UO2 microspheres, uranium metal and uranium alloys. It is shown that U3O8 powders with uranium mass fraction of about 84% can be distinguished from the powders of UO2 with uranium mass fraction of about 87%; uranium products in the form of liquid or loose powder with matrix density of 0.5-2.0g/cm3 can be distinguished from uranium products in the form of compacted fuel elements with matrix density of 6.0-10.0g/cm3 and from pure metal uranium and uranium alloys with matrix density of 14.0-19.0g/cm3. In fuel microspheres based on UO2 the uranium mass fraction 88.02% measured by HRGS is consistent, within the measurement uncertainties, with the results of isotope dilution mass spectrometry 87.76±0.64% and also is confirmed by X-ray diffraction technique. The uranium mass fraction of the uranium ore estimated as 0.08% by HRGS is consistent, within the measurement uncertainties, with the value 0.09±0.01% determined with WDXRF. Densities of two different uranium metal samples, estimated as 18.42g/cm3 and 19.33g/cm3 by HRGS are consistent with values 18.24±0.55g/cm3 and 18.86±0.59g/cm3, respectively, obtained by the gas pycnometry technique.
Applied Radiation and Isotopes, 2020
Background: Treating patients with hepatocellular carcinoma (HCC) remains a challenge, especially... more Background: Treating patients with hepatocellular carcinoma (HCC) remains a challenge, especially when the disease presents at an advanced stage. The aim of this retrospective study was to determine the efficacy of liver resection in patients who fulfil or exceed University of California San Francisco (UCSF) criteria by assessing longterm outcome. Methods: Between 2002 and 2008, 59 patients with large HCC (>5 cm) underwent hepatectomy. Thirty-two of these patients fulfilled UCSF criteria for transplantation (group A) and 27 did not (group B). Disease-free survival and overall survival rates were compared between the two groups after resection and were critically evaluated with regard to patient eligibility for transplant. Results: In all patients major or extended hepatectomies were performed. There was no perioperative mortality. Morbidity consisted of biliary fistula, abscess, pleural effusion and pneumonia and was significantly higher in patient group B. Disease-free survival rates at 1, 3 and 5 years were 66%, 37% and 34% in group A and 56%, 29% and 26% in group B, respectively (P < 0.01). Survival rates at 1, 3 and 5 years were 73%, 39% and 35% in group A and 64%, 35% and 29% in group B, respectively (P = 0.04). The recurrence rate was higher in group B (P = 0.002). Conclusions: Surgical resection, if feasible, is suggested in patients with large HCC and can be performed with acceptable overall and disease-free survival and morbidity rates. In patients eligible for transplantation, resection may also have a place in the management strategy when waiting list time is prolonged for reasons of organ shortage or when the candidate has low priority as a result of a low MELD (model for end-stage liver disease) score.
Journal of Alloys and Compounds, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Thin Solid Films, 2019
In general, fundamental understanding of radiation resistance of high surface density nanoporous ... more In general, fundamental understanding of radiation resistance of high surface density nanoporous materials and nanoporous coatings is severely lacking. In this contribution ion-induced bending phenomena are studied in freestanding nanoporous Au cantilevers with thickness in the range of 100 to 200 nm. Experiments were performed in a Tescan Lyra dual beam system with Ga + ion irradiation normal to the sample surface up to a maximum fluence of~3 × 10 19 m −2. Cantilevers bend towards the incident ion beam. It was found that the sensitivity of nanoporous Au samples to radiation-induced bending is substantially higher in comparison to the solid bulk counterparts. The process is described in terms of ion-induced coarsening of the structure top layers, which generates a volume contraction responsible for the bending moment. Therefore it is concluded that radiationinduced coarsening/sintering leads to negative swelling. Radiation-modified effective Young's modulus of the top layers was shown to influence essentially the fluence dependence of bending curvature. Model predictions agree well with our experimental findings showing that inhomogeneous radiation-induced coarsening of nanoporous structure results in bending and that nanoporous materials are less suitable for coatings in nuclear applications under the test conditions.
Applied Surface Science, 2018
This contribution concentrates on ion-induced bending phenomena which may serve as a versatile to... more This contribution concentrates on ion-induced bending phenomena which may serve as a versatile tool to manufacture nanostructured devices. In particular bending was studied in free standing Au cantilevers. The preparation and irradiation of the cantilevers were performed using a TESCAN LYRA dual beam system. Cantilevers with thicknesses ranging between 90 and 200 nm were irradiated with 30 keV Ga ions normal to the sample surface up to a maximum fluence of $3 Â 10 20 Ga/m 2. The bending of the cantilevers towards the incident beam is discussed in terms of local volume change due to accumulation of radiation-induced vacancies and substitutional Ga atoms in the Ga implantation layer, as well as due to accumulation of interstitial type clusters in the region beyond the Ga penetration range. A model is proposed to explain the observations, based on a set of rate equations for concentrations of point defects, i.e. vacancies, self-interstitials and implanted Ga atoms. The influence of preexisting defects is also discussed. The work shows that an in-depth understanding the ion-beam bending can play a predictive role in a quantitative control in for the micro-and nanofabrication of small-sized products.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999
Results of experimental and theoretical investigations are presented on heavily irradiated natura... more Results of experimental and theoretical investigations are presented on heavily irradiated natural and synthetic NaCl crystals in the temperature range where anion defects are mobile. They give a strong evidence for the formation of vacancy voids, which cannot be explained by the Jain±Lidiard model used up to date for description of metal colloids and dislocation loops formed in ionic crystals during earlier stages of irradiation. We consider an additional set of reactions between experimentally observed extended defects (metal colloids, gas bubbles and voids) and point defects. The latter include F and H centers that are the primary defects produced by irradiation, and cation vacancies (with a trapped hole) that are secondary defects, produced in the process of dislocation climb due to absorption of extra H centers. We show that highly overpressurized bubbles of¯uid halogen are strongly biased for absorption of H centers, which makes them grow via punching out interstitial dislocation loops. The loops grow and produce cation vacancies that are subsequently trapped at the incoherent colloids together with extra F centers giving rise to the colloid±void transition. Elastic interaction between extended defects and point defects is shown to play a major role, since it determines the bias factors of extended defects, which is a major driving force of the microstructural evolution under irradiation. A quantitative comparison of the new model for radiation damage in NaCl with experimental data is presented. Mean sizes and volume fractions of all types of observed defects are calculated. It is shown that voids formed due to agglomeration of F centers and cation vacancies can grow to the dimensions exceeding the mean distance between colloids and bubbles, eventually absorbing them, hence, bringing the halogen gas and metal to a back reaction. Impurities play a major role in the void development with increasing irradiation dose, which strongly aects the radiation stability of NaCl.
Materials Science Forum, 1992
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2000
The dependencies of void formation and radiolytic sodium accumulation on the irradiation dose, do... more The dependencies of void formation and radiolytic sodium accumulation on the irradiation dose, dose rate, temperature and impurity content are analyzed within a framework of a theoretical model, which is based on a new mechanism of dislocation climb. The mechanism involves the production of V F centers (self-trapped hole neighboring a cation vacancy) as a result of the absorption of excess H centers at dislocation lines. Voids are shown to arise due to the reaction between F and V F centers at the surface of halogen bubbles. All reactions involved in the evolution of extended defects are controlled by the dierence between the absorption of H centers and F centers. This dierence is determined by the material speci®c parameters responsible for the bias factors of extended defects and by the mean concentration of point defects. The latter depends on the temperature and dose rate as described in the present paper. Impurities can facilitate or suppress radiation damage formation depending on their eect on the nucleation of extended defects under irradiation. This is demonstrated by comparing theoretical results obtained for dose dependence of colloid volume fraction at dierent dislocation densities with experimental data obtained in crystals doped with dierent impurities.
Defect and Diffusion Forum, 1997
Radiation Effects and Defects in Solids, 1999
physica status solidi (c), 2005
Take-down policy If you believe that this document breaches copyright please contact us providing... more Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
physica status solidi (c), 2005
A mechanism of radiation-induced emission of Schottky defects from extended defects proposed orig... more A mechanism of radiation-induced emission of Schottky defects from extended defects proposed originally for metals has recently been applied to ionic crystals, where it is based on interactions of excitons with extended defects such as dislocations and colloids. Exciton trapping and decay at colloids may result in the emission of F centers and consequent shrinkage of the colloid. In the present paper, the radiationinduced emission of F centers is taken into account in the modeling of nucleation and growth of sodium colloids and chlorine bubbles in NaCl exposed to electron or gamma irradiation. The evolution of colloid and bubble number densities and volume fractions with increasing irradiation dose is modeled in the framework of a modified rate theory and compared with experimental data. Experimental values of the colloid volume fractions and number densities have been estimated on the basis of latent heat of melting of metallic Na obtained with combined differential scanning calorimetry experiments and atomic force microscopy investigations of metallic clusters.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2002
A kinetic model is formulated for the chemical reaction between radiolytic sodium colloids and ga... more A kinetic model is formulated for the chemical reaction between radiolytic sodium colloids and gas bubbles, which are brought into contact with each other during the exposure to ionising radiation by the growing voids. The reaction starts with the evaporation of Na atoms into the void due to the localized heat release caused by reactions between chlorine molecules colliding with the colloid surface. It is shown that this exothermic and autocatalytic reaction leads to a sudden temperature increase inside the void, which gives rise to thermoelastic stresses in the surrounding matrix. Tangential stresses might exceed the threshold stress required for localized cleavage of the matrix resulting in crack formation and mechanical instability of NaCl under high dose irradiation.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2002
A kinetic model of zircon thermoluminescence (TL) has been constructed to simulate the processes ... more A kinetic model of zircon thermoluminescence (TL) has been constructed to simulate the processes and stages relevant to thermoluminescent dating such as: filling of electron and hole traps during the excitation stage both for natural and laboratory irradiation; the time dependence of fading after laboratory irradiation; TL experiments both after laboratory and natural irradiation. The goal is to inspect qualitative behavior of the system and to unravel the processes and determine the parameters controlling TL phenomena of zircon. The input parameters of the model, such as types and concentrations of the TL centers and energy distributions of the hole and electron traps, were obtained by analyzing the experimental data on fading of the TL-emission spectra of samples from different locations. EPR data were used to establish the nature of the TL centers. Glow curves and 3D TL emission spectra are simulated and compared with the experimental data on time-dependent TL fading. Theoretical dating curves for combined natural plus laboratory irradiation have been calculated for as-irradiated, faded and preheated samples.
Journal of Physics: Condensed Matter, 2004
Journal of Nuclear Materials, 2005
We have performed numerical calculation of the capture efficiency of a dislocation loop in a fini... more We have performed numerical calculation of the capture efficiency of a dislocation loop in a finite toroidal reservoir, which is a more appropriate model for a dislocation loop than a spherical or cylindrical reservoir adopted in the previous models. It allows a direct evaluation of the capture efficiency and the bias for a loop of any size with a full account of the stress field in the loop region of influence. It is shown that the loop bias depends on the loop size, dislocation density and the interstitial to vacancy dilatation ratio. With increasing loop size its bias decreases or increases to the straight dislocation bias value if the dislocation density is low or high, respectively. The bias difference of loops of different sizes is shown to be the reason of a coexistence of vacancy and interstitial loops under irradiation. In the conventional case of the dislocation bias for interstitials, interstitial loops are expected to grow to larger sizes than vacancy loops, while in a special case of dislocation bias for vacancies, the opposite tendency is expected.
Journal of Nuclear Materials, 1995
A model of cascade-induced precipitate dissolution is formulated describing the effect of heavy i... more A model of cascade-induced precipitate dissolution is formulated describing the effect of heavy ion irradiation at low temperatures on the stability of the metastable coherent chromium phase in a Cu-based alloy. Both analytical and Monte Carlo simulation results are consistent with recent transmission electron microscopy observations [l] which showed that the strain contrast of these precipitates disappeared completely after irradiation to a fluence of 0.1 dpa at room temperature.
Journal of Nuclear Materials, 2006
The effect of coherency loss on the development of precipitate size distribution under cascade-pr... more The effect of coherency loss on the development of precipitate size distribution under cascade-producing irradiation is considered. The nucleation of coherent precipitates, their growth followed by coherency loss and cascade-induced dissolution of large incoherent precipitates can occur simultaneously resulting in formation of a quasi-stationary size distribution of semicoherent precipitates. To describe this process we consider co-evolution of a mixed population of coherent, semicoherent and incoherent precipitates. Mathematically, the problem is formulated as a set of discrete rate equations of nucleation kinetics (the Master equation approach) which is also used for later stages of evolution. To solve the corresponding large set of equations (typically, more than 10 5 equations) an efficient numerical method is developed. The simulation results obtained for material parameters and irradiation conditions typical for nuclear reactors show that the coherency loss affects considerably evolution of the precipitate population. Under certain irradiation conditions, both in solution-annealed alloys and in aged ones, the mean precipitate size and the number density during prolonged irradiation tend to steady state values, whereas the size distribution function of large precipitates narrows. The width of the quasi-stationary size distribution is controlled by cascade parameters. It was found that the asymptotic quasi-stationary state of the precipitate population may depend on initial state of the alloy.
Applied Physics A Solids and Surfaces, 1994
The interaction energy between point defects and dislocation patterns (such as the pileup of disl... more The interaction energy between point defects and dislocation patterns (such as the pileup of dislocation loops and the dislocation wall) is derived. The bias for interstitial absorption by a dislocation in a pattern is shown to be lower than that of an isolated dislocation. The dislocation patterning is proposed to be driven by the dependence of dislocation bias on the dislocation arrangement.
Journal of Physics: Condensed Matter, 2006
New experimental results are presented on low temperature irradiation (18 • C) of rock-salt sampl... more New experimental results are presented on low temperature irradiation (18 • C) of rock-salt samples which had been exposed to initial doses up to 320 GRad at 100 • C. Differential scanning calorimetry (DSC) shows that the latent heat of melting (LHM) of sodium colloids decreases during subsequent lowtemperature irradiation, whereas the stored energy (SE) increases slowly, indicating that the process of radiolysis continues. The decrease of the LHM is due to dissolution of large colloids, because the intensities of the melting peaks decrease during the second stage irradiation at low temperature. The model is formulated to describe the nucleation kinetics and the evolution of the size distribution of chlorine precipitates and sodium colloids in NaCl under high dose irradiation. It is shown that the mechanism of dissolution of large Na colloids during low temperature irradiation can be related to melting of sodium colloids.
Applied Radiation and Isotopes, 2021
A nondestructive iterative method for uranium-bearing material characterization with HRGS develop... more A nondestructive iterative method for uranium-bearing material characterization with HRGS developed earlier in Burdeinyi et al. (2020) is applied to determine matrix densities, uranium mass fraction and uranium isotope masses of uranium ore, UO2 and U3O8 powders, fuel elements in the form of UO2 microspheres, uranium metal and uranium alloys. It is shown that U3O8 powders with uranium mass fraction of about 84% can be distinguished from the powders of UO2 with uranium mass fraction of about 87%; uranium products in the form of liquid or loose powder with matrix density of 0.5-2.0g/cm3 can be distinguished from uranium products in the form of compacted fuel elements with matrix density of 6.0-10.0g/cm3 and from pure metal uranium and uranium alloys with matrix density of 14.0-19.0g/cm3. In fuel microspheres based on UO2 the uranium mass fraction 88.02% measured by HRGS is consistent, within the measurement uncertainties, with the results of isotope dilution mass spectrometry 87.76±0.64% and also is confirmed by X-ray diffraction technique. The uranium mass fraction of the uranium ore estimated as 0.08% by HRGS is consistent, within the measurement uncertainties, with the value 0.09±0.01% determined with WDXRF. Densities of two different uranium metal samples, estimated as 18.42g/cm3 and 19.33g/cm3 by HRGS are consistent with values 18.24±0.55g/cm3 and 18.86±0.59g/cm3, respectively, obtained by the gas pycnometry technique.
Applied Radiation and Isotopes, 2020
Background: Treating patients with hepatocellular carcinoma (HCC) remains a challenge, especially... more Background: Treating patients with hepatocellular carcinoma (HCC) remains a challenge, especially when the disease presents at an advanced stage. The aim of this retrospective study was to determine the efficacy of liver resection in patients who fulfil or exceed University of California San Francisco (UCSF) criteria by assessing longterm outcome. Methods: Between 2002 and 2008, 59 patients with large HCC (>5 cm) underwent hepatectomy. Thirty-two of these patients fulfilled UCSF criteria for transplantation (group A) and 27 did not (group B). Disease-free survival and overall survival rates were compared between the two groups after resection and were critically evaluated with regard to patient eligibility for transplant. Results: In all patients major or extended hepatectomies were performed. There was no perioperative mortality. Morbidity consisted of biliary fistula, abscess, pleural effusion and pneumonia and was significantly higher in patient group B. Disease-free survival rates at 1, 3 and 5 years were 66%, 37% and 34% in group A and 56%, 29% and 26% in group B, respectively (P < 0.01). Survival rates at 1, 3 and 5 years were 73%, 39% and 35% in group A and 64%, 35% and 29% in group B, respectively (P = 0.04). The recurrence rate was higher in group B (P = 0.002). Conclusions: Surgical resection, if feasible, is suggested in patients with large HCC and can be performed with acceptable overall and disease-free survival and morbidity rates. In patients eligible for transplantation, resection may also have a place in the management strategy when waiting list time is prolonged for reasons of organ shortage or when the candidate has low priority as a result of a low MELD (model for end-stage liver disease) score.
Journal of Alloys and Compounds, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Thin Solid Films, 2019
In general, fundamental understanding of radiation resistance of high surface density nanoporous ... more In general, fundamental understanding of radiation resistance of high surface density nanoporous materials and nanoporous coatings is severely lacking. In this contribution ion-induced bending phenomena are studied in freestanding nanoporous Au cantilevers with thickness in the range of 100 to 200 nm. Experiments were performed in a Tescan Lyra dual beam system with Ga + ion irradiation normal to the sample surface up to a maximum fluence of~3 × 10 19 m −2. Cantilevers bend towards the incident ion beam. It was found that the sensitivity of nanoporous Au samples to radiation-induced bending is substantially higher in comparison to the solid bulk counterparts. The process is described in terms of ion-induced coarsening of the structure top layers, which generates a volume contraction responsible for the bending moment. Therefore it is concluded that radiationinduced coarsening/sintering leads to negative swelling. Radiation-modified effective Young's modulus of the top layers was shown to influence essentially the fluence dependence of bending curvature. Model predictions agree well with our experimental findings showing that inhomogeneous radiation-induced coarsening of nanoporous structure results in bending and that nanoporous materials are less suitable for coatings in nuclear applications under the test conditions.
Applied Surface Science, 2018
This contribution concentrates on ion-induced bending phenomena which may serve as a versatile to... more This contribution concentrates on ion-induced bending phenomena which may serve as a versatile tool to manufacture nanostructured devices. In particular bending was studied in free standing Au cantilevers. The preparation and irradiation of the cantilevers were performed using a TESCAN LYRA dual beam system. Cantilevers with thicknesses ranging between 90 and 200 nm were irradiated with 30 keV Ga ions normal to the sample surface up to a maximum fluence of $3 Â 10 20 Ga/m 2. The bending of the cantilevers towards the incident beam is discussed in terms of local volume change due to accumulation of radiation-induced vacancies and substitutional Ga atoms in the Ga implantation layer, as well as due to accumulation of interstitial type clusters in the region beyond the Ga penetration range. A model is proposed to explain the observations, based on a set of rate equations for concentrations of point defects, i.e. vacancies, self-interstitials and implanted Ga atoms. The influence of preexisting defects is also discussed. The work shows that an in-depth understanding the ion-beam bending can play a predictive role in a quantitative control in for the micro-and nanofabrication of small-sized products.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999
Results of experimental and theoretical investigations are presented on heavily irradiated natura... more Results of experimental and theoretical investigations are presented on heavily irradiated natural and synthetic NaCl crystals in the temperature range where anion defects are mobile. They give a strong evidence for the formation of vacancy voids, which cannot be explained by the Jain±Lidiard model used up to date for description of metal colloids and dislocation loops formed in ionic crystals during earlier stages of irradiation. We consider an additional set of reactions between experimentally observed extended defects (metal colloids, gas bubbles and voids) and point defects. The latter include F and H centers that are the primary defects produced by irradiation, and cation vacancies (with a trapped hole) that are secondary defects, produced in the process of dislocation climb due to absorption of extra H centers. We show that highly overpressurized bubbles of¯uid halogen are strongly biased for absorption of H centers, which makes them grow via punching out interstitial dislocation loops. The loops grow and produce cation vacancies that are subsequently trapped at the incoherent colloids together with extra F centers giving rise to the colloid±void transition. Elastic interaction between extended defects and point defects is shown to play a major role, since it determines the bias factors of extended defects, which is a major driving force of the microstructural evolution under irradiation. A quantitative comparison of the new model for radiation damage in NaCl with experimental data is presented. Mean sizes and volume fractions of all types of observed defects are calculated. It is shown that voids formed due to agglomeration of F centers and cation vacancies can grow to the dimensions exceeding the mean distance between colloids and bubbles, eventually absorbing them, hence, bringing the halogen gas and metal to a back reaction. Impurities play a major role in the void development with increasing irradiation dose, which strongly aects the radiation stability of NaCl.
Materials Science Forum, 1992