Synthesis and ESR Study of Transition from Ferromagnetism to Superparamagnetism in La_0.8Sr_0.2MnO₃ Nanomanganite

Electron spin resonance (ESR) spectroscopy was used to determine the magnetic state transitions of nanocrystalline La0.8Sr0.2MnO3 at room temperature, as a function of crystallite size. Ferromagnetic nanoparticles having an average crystallite size ranging from 9 to 57 nm are prepared by adopting the autocombustion method with two-step synthesis process. Significant changes of the ESR spectra parameters, such as the line shape, resonance field (Hr), g-factor, linewidth (∆Hpp), and the low-field microwave absorption (LFMA) signal, are indicative of the change in magnetic domain structures from superparamagnetism to single-domain and multi-domain ferromagnetism by increase in the crystallite size. Samples with crystallite sizes less than 24.5 nm are in a superparamagnetic state. Between 24.5 and 32 nm, they are formed by a single-domain ferromagnetic. The multi-domain state arises for higher sizes. In superparamagnetic region, the value of g-factor is practically constant suggesting that the magnetic core size is invariant with decreasing crystallite size. This contradictory observation with the core-shell model was explained by the phenomenon of phase separation that leads to the formation of a new magnetic state that we called multicore superparamagnetic state

Effect of gamma rays absorbed doses and heat treatment on the optical absorption spectra of silver ion-exchanged silicate glass

International audienceSamples of a commercial silicate glass have been subjected to ion exchange at 320 °C in a molten mixture of AgNO 3 and NaNO 3 with molar ratio of 1:99 and 5:95 for 60 min. The ion exchange process was followed by gamma irradiation in the dose range of 1–250 kGy and heating at the temperature of 550 °C for different time periods ranging from 10 to 582 min. The spectral absorption in UV–Vis range of the Ag–Na ion exchanged glass was measured and used to determine the states of silver prevailing in the glass during the ion exchange, the gamma irradiation and the heat treatment. The gamma irradiation induced holes and electrons in the glass structure leading to the creation of a brown colour, and silver ions trapped electrons to form silver atoms. We observed the first stage of aggregation after irradiation, as well as after heating. The silver atoms diffused and then aggregated to form nanoclusters after heating at 550 °C. A characteristic band at about 430 nm was induced. The surface Plasmon absorption of silver nanoclusters in the glass indicated that the nanoclusters radius grew between 0.9 and 1.43 nm with increasing of annealing time from 10 to 242 min and then saturated. We also found that the size of aggregates depends on the value of gamma radiation absorbed dose. Contrary to what was expected, we found that 20 kGy is the optimal absorbed dose corresponding to the larger size of the aggregates which decreases for absorbed doses above 20 kGy

CONTRIBUTION TO THE PHYTOCHIMIC STUDY AND THE ANTIOXIDANT ACTIVITY OF THE ESSENTIAL OIL OF THE WILD CARROT

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Insights into Ionizing-Radiation-Resistant Bacteria S-Layer Proteins and Nanobiotechnology for Bioremediation of Hazardous and Radioactive Waste

S-layers are crystalline arrays formed by proteinaceous subunits that cover the outer surface of many different kinds of microorganisms. This “proteinaceous cover” is particularly important in the case of ionizing-radiation-resistant bacteria (IRRB) that might be used in bioremediating hazardous and radioactive wastes (HRW). Despite the exponential growth in the number of comparative studies and solved proteic crystal structures, the proteic networks, diversity, and bioremediation-useful structural properties of IRRB S-layers remain unknown. Here, aided by literature, a tentative model of Deinococcus radiodurans R1 S-layer proteins (SLPs) and the network of its main constituents were proposed. The domain analysis of this network was performed. Moreover, to show the diversity of IRRB S-layers, comparative genomics and computer modeling experiments were carried out. In addition, using in silico modeling, assisted by previously published data, the outermost exposed segments of D. radiodurans SlpA (surface layer protein A) that were predicted to interact with uranium were mapped. The combination of data and results pointed to various prospective applications of IRRB S-layers in nanobiotechnology for bioremediation of radioactive waste

Faisceaux exotiques par méthode ISOL (développements pour l'ionisation par laser et l'ionisation de surface)

Ces travaux s'inscrivent dans le cadre du programme de R&D PARRNe (Production d'Atomes Radioactifs Riches en Neutrons). Ce programme vise d'une façons générale à déterminer les conditions optimales pour produire d'intenses faisceaux d'isotopes riches en neutrons. Cette thèse traite des multiples aspects techniques liés à la production d'isotopes radioactifs séparés en ligne (ISOL). Elle porte principalement sur le développement de l'ensemble cible-source qui est l'élément clé pour les projets comme SPIRAL-2 ou EURISOL.La première partie présente les différentes méthodes utilisant la fission comme réaction exploitée en ligne ainsi que leur comparaison: fission thermique, fission induite par des neutrons rapides et photofission. L'expérience faite au CERN a permis de valider la photofission comme mode prometteur pour la production d'ions radioactifs, c'est pour cela que l'IPN d'Orsay a décidé de construire un Accélérateur Linéaire d'électrons auprès du Tandem d'Orsay (ALTO).La deuxième partie de cette thèse a porté sur le développement de cibles d'uranium. Des techniques d'analyse comme la diffraction X et la Microscopie Electronique à Balayage ont été utilisées. Elles ont permis de déterminer les caractéristiques chimiques et structurales de cibles de carbure d'uranium portées à différentes températures de chauffage. Après la production, le processus d'ionisation est étudié. Deux types de sources ont été mises en œuvre : La première est une source à ionisation de surface et la deuxième est une source basée sur l'ionisation résonante par laser. Ces deux types de sources seront utilisées pour le projet ALTO.The works were carried out in the framework of the R&D program PARRNe (Production d'Atomes Radioactifs Riches en Neutrons). This program aims to determine optimal conditions to produce intense beams of neutron-rich isotopes. This thesis treats multiple technical aspects related to the production of separate radioactive isotopes in line (ISOL). It deals mainly with the development of the target-source unit which is the key element for projects such as SPIRAL-2 or EURISOL.The first part presents the various methods using fission as production mode and compares them: fission induced by thermal neutrons, induced by fast neutrons and photofission. The experiment carried out at CERN validated the interest of the photofission as a promising production mode of radioactive ions. That is why IPN of Orsay decided to build a linear electron accelerator at the Tandem d'Orsay (ALTO).The second part of this thesis deals with the development of uranium targets. The X-rays diffraction and Scanning Electron Microscopy have been used as analyisis techniques. They allowed to determine the chemical and structural characteristics of uranium carbide targets as function of various heating temperatures. After the production, the process of ionization has been studied. Two types of ion source have been worked out: The first one is a surface ion source and the second one is a source based on resonant ionization by laser. These two types of sources will be used for the ALTO project.STRASBOURG-Bib.Central Recherche (674822133) / SudocORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Surface Disinfection to Protect against Microorganisms: Overview of Traditional Methods and Issues of Emergent Nanotechnologies

Sterilization methods for individuals and facilities are extremely important to enable human beings to continue the basic tasks of life and to enable safe and continuous interaction of citizens in society when outbreaks of viral pandemics such as the coronavirus. Sterilization methods, their availability in gatherings, and the efficiency of their work are among the important means to contain the spread of viruses and epidemics and enable societies to practice their activities almost naturally. Despite the effective solutions given by traditional methods of surface disinfection, modern nanotechnology has proven to be an emergent innovation to protect against viruses. On this note, recent scientific breakthroughs have highlighted the ability of nanospray technology to attach to air atoms in terms of size and time-period of existence as a sterilizer for renewed air in large areas for human gatherings. Despite the ability of this method to control the outbreak of infections, the mutation of bactericidal mechanisms presents a great issue for scientists. In recent years, science has explored a more performant approach and techniques based on a surface-resistance concept. The most emergent is the self-defensive antimicrobial known as the self-disinfection surface. It consists of the creation of a bacteria cell wall to resist the adhesion of bacteria or to kill bacteria by chemical or physical changes. Besides, plasma-mediated virus inactivation was shown as a clean, effective, and human healthy solution for surface disinfection. The purpose of this article is to deepen the discussion on the threat of traditional methods of surface disinfection and to assess the state of the art and potential solutions using emergent nanotechnology

Effect of gamma radiation on the photocatalytic properties of Cu doped titania nanoparticles

International audienceThe aim of this paper is to study the effect of gamma-rays on structural, physicochemical, optical and photocatalytic performance of TiO 2 nanoparticles doped with different concentrations of copper ranging from 0 to 6 at.%. The powders have been prepared by sol-gel technique and annealed at 400 °C. They were irradiated by gamma-rays with doses varying from 14 to 60 KGy. These investigations confirm the formation of anatase TiO 2 nanoparticles and Cu 2+ ion substitution for Ti 4+ sites within the TiO 2 structure. This study also shows that, once the TiO 2 structure is saturated with copper, a metallic copper segregation is formed at the crystallite surfaces. After gamma irradiation, samples present a crystalline core and a disordered shell structure as a result of the formation of oxygen vacancies. Such oxygen vacancies at the TiO 2 nanocrystal surface lead to a remarkable enhancement of the photocatalytic activity of Cu-doped TiO 2 catalysts

Effect of γ-radiation on free radicals formation, structural changesand functional properties of wheat starch

Wheat starch was treated by different γ-radiation doses (3, 5, 10, 20, 35 and 50 kGy). The effects of γ-radiation on structural, thermal, physicochemical, morphological and rheological properties of wheat starch were studied. The presence of free radicals after γ-radiation treatment, which number decreased with time was confirmed. Structural analysis revealed decreases in the intensities of the O–H and C–H stretches and glycosidic linkages indicating the depolymerization of amylose and probably amy-lopectin into shorter chain molecules, but showed that γ-radiation treatment did not affect the crystalline structure. Differential scanning calorimetric (DSC) thermograms showed the absence of significant differences in the gelatinization temperatures, as well as the corresponding transition enthalpies since the DSC parameters are related to the crystalline ordering within the granules. Apparent amylose content decreased linearly with increasing irradiation dose leading to an increase in water solubility index. Anincrease in the swelling power was observed after irradiation treatment until 20 kGy, followed by a rapiddecrease at higher doses. Microscopic observations showed that the effect of γ-radiation was more visible on starch pastes than on starch granules. Rheological properties of the starch pastes decreased within creasing irradiation dose as a result of glycosidic bond cleavage

Gamma radiation induced modifications of tapioca starch

peer reviewedThe effect of gamma radiation (3, 5, 10, 20, 35 and 50 kGy) on the morphological, structural, physicochemical, pasting and thermal properties of tapioca starch was studied. Microphotographs of scanning electron microscopy and polarized light microscopy revealed the absence of morphological changes induced by gamma radiation. The X-ray diffraction spectra showed that irradiation treatment did not influence the shape and intensity of X-ray diffraction peaks. The presence of free radicals in the irradiated tapioca starch was confirmed by electron spin resonance spectrometry. Fourier transform infrared spectroscopy showed that the irradiated starch displayed a significant decrease in the intensity of the O–H and C–H stretches, bending modes of water and glycosidic linkages. Irradiation improved the water solubility index of starch granules and depressed the apparent amylose content. An increase in the swelling power was observed after irradiation treatment until 20 kGy, followed by a decrease at higher doses. Brabender viscoamylograph test showed that the maximal consistency of the starch paste decreased significantly with increasing irradiation dose. There was no significant difference in the gelatinization temperatures, as well as the corresponding transition enthalpies among native and irradiated tapioca starch samples, as shown in the differential scanning calorimetry thermograms