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Surface damage produced by single MeV-GeV heavy ions impacting ultrathin polymer films has been shown to be weaker than those observed under bulk (thick film) conditions. The decrease in damage efficiency has been attributed to the suppression of long-range effects arising from excited atoms lying deeply in the solid. This raises the possibility that the substrate of the films itself may be relevant to the radiation effects seen at the top surface. Here, the role of the substrate on cratering induced by individual 1.1 GeV Au ions in ultrathin poly(methyl methacrylate) (PMMA) layers is investigated. Materials of different thermal and electrical properties (Si, SiO2, and Au) are used as substrates to deposit PMMA thin films of various thicknesses from ∼1 to ∼300 nm. We show that in films thinner than ∼40 nm craters are modulated by the underlying substrate to a degree that depends on the transport properties of the medium. Crater size in ultrathin films deposited on the insulating SiO2 is larger than in similar films deposited on the conducting Au layer. This is consistent with an inefficient coupling of the electronic excitation energy to the atomic cores in metals. On the other hand, the damage on films deposited on SiO2 is not very different from the Si substrate with a native oxide layer, suggesting, in addition, poor energy transmission across the film/substrate interface. The experimental observations are also compared to calculations from an analytical model based on energy addition and transport from the excited ion track, which describe only partially the results.

We report on the evaluation of iron content and biodistribution in zebrafish larvae (Danio rerio) exposed to dextran-coated superparamagnetic iron oxide nanoparticles (SPION-DX) using the micro-PIXE technique. We compare results of elemental 2D maps and Fe quantification obtained from two different sample preparation procedures: one using sagittal slices prepared by cryo-sectioning and another using entire dehydrated larvae. Independently of the preparation method used, the Fe content in the tissues of exposed animals is significantly higher than in the controls, but the increase is not proportional to the exposure level. In addition, 2D elemental maps show a somewhat homogeneous Fe distribution in the larvae, with some samples showing a slight enhancement in Fe content near the gut. From the PIXE data a curve correlating the exposure (nanoparticle concentration in the fish water) to the iron content in the body was obtained, which shows a saturation trend towards high exposure doses.

This chapter presents a specific reliability study of some GEANT4-DNA (version 10.02.p01) processes and models for proton transportation considering ultra-thin layers (UTL). The Monte Carlo radiation transport validation is fundamental to guarantee the simulation results accuracy. However, sometimes this is impossible due to the lack of experimental data and, it is then that the reliability evaluation takes an important role. Geant4-DNA runs in an energy range that makes impossible, nowadays, to perform a proper microscopic validation (cross-sections and dynamic diffusion parameters) and allows very limited macroscopic reliability. The chemical damage cross-sections reliability (experiment versus simulation) is a way to verify the consistency of the simulation results which is presented for 2 MeV incident protons beam on PMMA and PVC UTL. A comparison among different Geant4-DNA physics lists for incident protons beams from 2 to 20 MeV, interacting with homogeneous water UTL (2 to 200 nm) was performed. This comparison was evaluated for standard and five other optional physics lists considering radial and depth profiles of deposited energy as well as number of interactions and stopping power of the incident particle.

The influence of the charge state q on surface modifications induced by the impact of individual fast, heavy ions on muscovite mica was investigated. Beams of 593 MeV 197Auq+ with well-defined initial charge states over a relatively broad range of values (30 to 51) and at different irradiation geometries were used. At normal incidence, the impact features are rounded protrusions (hillocks) with ≳20 nm in diameter. At grazing angles, besides the hillocks, craters and elongated tails (up to 350 nm-long) extending along the direction of ion penetration are produced. It is shown that the impact features at normal incidence depend strongly on the initial charge state of the projectiles. This dependence is very weak at grazing angles as the ion reaches the equilibrium charge state closer to the surface. At normal ion incidence, the hillock volume scales with q3.3±0.6. This dependence stems largely from the increase in the hillock height, as a weak dependence of the diameter was observed.

The purpose of this in vitro study is to evaluate the effect of the incorporation of silanized and non-silanized silica nanoparticles (~ 160 nm) in mechanical properties and surface roughness of self-cured acrylic resins. Five groups of samples were produced (with six specimens each), following the ISO 20795-1:2013 specifications. In the control group (Ctrl), no particles were added in the resin composition. Non-silanized silica nanoparticles were added either into the polymer (0.7 wt%, group G1) or into the monomer (0.27 wt%, G2). Two equivalent groups were formed for composite resins with silanized nanoparticles (groups G3 with 0.7 wt% incorporated into the polymer and G4 with 0.27 wt% added into the monomer). Data were submitted to Shapiro-Wilk (α = 0.05) and ANOVA/Tukey (α = 0.05). Nanoparticle-loaded resins showed similar microhardness as the control and a reduced flexural strength (20–27%) which was neither dependent on the amount of filler added nor in the method of nanoparticle incorporation. Surface silanization caused no major improvement in the mechanical behavior of the nanoresins but appears to improve dispersibility, as indicated by a smaller surface roughness.

We report on the effect of different coatings (dextran, chitosan, polyethylene glycol, carboxy-silane, and silica) in the toxicity elicited by superparamagnetic iron oxide nanoparticles (SPIONs) in the developing zebrafish (Danio rerio). Animals were exposed to nanoparticle concentrations ranging from 0.125 to 8.0 mM of Fe during the first 5 days after fertilization. Embryotoxicity parameters (survival, hatching rate, and the incidence of anatomical malformations) and behavioral patterns (locomotion during the exploration of a new environment, thigmotaxis, and the escape response to an aversive stimulus) were evaluated. Exposed embryos hatched between 48 and 72 hpf, as expected for the species, but tendencies of either acceleration or delay were observed, depending on the nanoparticle coating. Malformations in exposed and control groups were similar, independent of the coating. Mortality rates were also not significantly affected by exposure to most of the coated SPIONs, except for animals treated with chitosan-coated nanoparticles, which induced 100% mortality at concentrations higher than 2 mM. A similar trend was observed in the behavioral parameters, in which significant adverse effects were mostly caused by chitosan-coated nanoparticles even at low concentrations. The higher toxicity observed for chitosan-coated particles raises concern and deserves further mechanistic investigations, considering the ample use of this compound in pharmaceutical and biomedical applications.

We report on surface modification of poly(methyl methacrylate) (PMMA) thin films deposited onto silicon wafers induced by fast ions in a wide range of electronic stopping powers [14 keV/nm (2.1 GeV Bi), 2.2 keV/nm (17 MeV Au) and 0.019 keV/nm (2 MeV H)]. Marked differences were observed on surface morphology induced by low and high dE/dx ions. The effect of the 2 MeV H beam on the PMMA surface was a weak smoothing, whilst for the heavier Bi and Au ions, pronounced roughening occurs with development of porosity and other surface features in a broad range of spatial frequencies. For the heavy ions, surface changes develop in basically two regimes. At the single ion regime at low fluences, most of the changes can be attributed to sputtering and flow of material in individual ion impacts. At the track overlap regime, porosity emerge in a pattern of holes, with an areal density not directly related to the ion fluence, but still spread uniformly across the film. A good correlation between the input of energy and the changes in surface morphology was obtained when (dE/dx)1.85 was used as the scaling factor.

This study investigated the effects of smooth and microgrooved membrane blends, with different polycaprolactone (PCL)/ poly(lactic-co-glycolic acid) (PLGA) ratios on the viability, proliferation, and adhesion of different mammalian cell types. The polymer matrices with and without microgrooves, obtained by solvent casting, were characterized by field-emission scanning electron microscopy, atomic force microscopy, contact angle and Young's modulus. Blend characterization showed an increase in roughness and stiffness of membranes with 30% PLGA, without any effect on the contact angle value. Pure PCL significantly decreased the viability of Vero, HaCaT, RAW 264.7, and human fetal lung and gingival fibroblast cells, whereas addition of increasing concentrations of PLGA led to a reduced cytotoxicity. Increased proliferation rates were observed for all cell lines. Fibroblasts adhered efficiently to smooth membranes of the PCL70/PLGA30 blend and pure PLGA, compared to pure PCL and silicone. Microgrooved membranes promoted similar cell adhesion for all groups. Microstructured membranes (15 and 20-μm wide grooves) promoted suitable orientation of fibroblasts in both PCL70/PLGA30 and pure PLGA, as compared to pure PCL. Neuronal cells of the dorsal root ganglion exhibited an oriented adhesion to all the tested microgrooved membranes. Data suggest a satisfactory safety profile for the microgrooved PCL70/PLGA30 blend, pointing out this polymer combination as a promising biomaterial for peripheral nerve regeneration when cell orientation is required. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1522-1534, 2018.

Quercetin is a flavonoid found in a great variety of foods such as vegetables and fruits. This compound has been shown to inhibit the proliferation of various types of cancer cells, as well as the growth of tumors in animal models. In the present study, we analyze morphological and mechanical changes produced by quercetin in T24 bladder cancer cells. Decreased cell viability and cell number were observed following quercetin treatment at 40 μM and 60 μM, respectively, as observed by the MTT assay and trypan blue exclusion test, supporting the hypothesis of quercetin anticancer effect. These assays also allowed us to determine the 40, 60, and 80 μM quercetin concentrations for the following analyses, Lactate Dehydrogenase assay (LDH); Nuclear Morphometric Analysis (NMA); and atomic force microscopy (AFM). The LDH assay showed no cytotoxic effect of quercetin on T24 cancer cells. The AFM showed morphological changes following quercetin treatment, namely decreased cell body, cytoplasmic retraction, and membrane condensation. Following quercetin treatment, the NMA evidenced an increased percentage of nuclei characteristic to the apoptotic and senescence processes. Cells also presented biophysical alterations consistent with cell death by apoptosis, as increased roughness and aggregation of membrane proteins, in a dose-dependent manner. Cellular elasticity, obtained through force curves, showed increased stiffness after quercetin treatment. Data presented herein demonstrate, for the first time, in a quantitative and qualitative form, the morphological and mechanical alterations induced by quercetin on bladder cancer cells.

The current application of nanotechnology in dentistry is limited to nanoparticles incorporated into adhesive systems and composite resins. Dental stone is a widely used material, and the incorporation of silica nanoparticles is still unexplored.The purpose of this in vitro study was to evaluate the mechanical properties of dental stone after the addition of silica nanoparticles in different concentrations.A total of 180 specimens were prepared, 90 for each dental stone (Durone and Fuji Rock). For the control group (CG), no silica particles were added, while test group TGnI had silica nanoparticles added to 1 wt%, and test group TGnV had silica nanoparticles added to 5 wt%. The roughness, diametral tensile strength (DTS), and compressive strength were measured 24 hours after the start of spatulation.The mean roughness values for Durone were 0.55, 0.36, and 0.28 μm for CG, TGnI, and TGnV; for Fuji Rock, the mean roughness values were 0.47 for CG, 0.31 for TGnI, and 0.35 μm for TGnV. The mean DTS values for Durone were 6.0, 5.1, and 5.0 MPa for CG, TGnI, and TGnV, respectively, and for Fuji Rock, the mean DTS values were 6.4, 5.2, and 4.5 MPa for CG, TGnI, and TGnV, respectively. The mean compressive strength values for Durone were 35.4, 32.7, and 32.4 MPa for CG, TGnI, and TGnV, respectively, and for Fuji Rock, the mean compressive strength values were 42.9, 31.2, and 29.8 MPa for CG, TGnI, and TGnV respectively.Surface roughness was statistically lower for the Durone and Fuji Rock stones (P.001) when silica nanoparticles were added. The addition of silica nanoparticles did not significantly affect the DTS and compressive strength of Durone compared with CG (P.05) but did affect the DTS of Fuji Rock when 5 wt% was added and the compressive strength in both concentrations (P.05).

Impacts of swift heavy ions of different energy loss in amorphous and crystalline Lennard-Jones (LJ) thin films (2–60 nm) were simulated using classical molecular dynamics to study cratering and sputtering in model molecular thin films. Crater size is determined mostly by evaporation and melt flow from the hot ion track, while rim size is determined both by melt flow and by coherent displacement of particles due to the large pressure developed in the excited region, with minor influence of particles from the substrate. Sputtering yields from both crystalline and amorphous samples are similar (including the scaling with energy loss), due to the extremely high temperature and disordered condition of the track region from where most ejected particles originate in the early stages of the track evolution. Cratering, however clearly depends on the crystallinity of the film. Craters and rims are much smaller in crystalline films mainly due to faster energy dissipation, higher stress threshold for plasticity and smaller free-volume in the ordered phase. We also found a large dependence of the induced surface effects on film thickness below a critical thickness value. The pressure pulse due to the ion impact is weaker and cooling of the excited track is more efficient in short tracks, both contributing to the decreased radiation damage efficiency on ultrathin layers. Despite the simplicity of the LJ model, the simulations in the amorphous films reproduce remarkably well several of the experimental features seen recently on polymer thin and ultrathin films irradiated by swift heavy ions. Fil: Gutierres, L. I.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Lima, N.W.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Thomaz, R. S.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Papaléo, R. M.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Bringa, Eduardo Marcial. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina

International audience; Abstract Damaged regions of cylindrical shapes called ion tracks, typically in nano-meters wide and tens micro-meters long, are formed along the ion trajectories in many insulators, when high energy ions in the electronic stopping regime are injected. In most cases, the ion tracks were assumed as consequences of dense electronic energy deposition from the high energy ions, except some cases where the synergy effect with the nuclear energy deposition plays an important role. In crystalline Si (c-Si), no tracks have been observed with any monomer ions up to GeV. Tracks are formed in c-Si under 40 MeV fullerene (C 60 ) cluster ion irradiation, which provides much higher energy deposition than monomer ions. The track diameter decreases with decreasing the ion energy until they disappear at an extrapolated value of ~ 17 MeV. However, here we report the track formation of 10 nm in diameter under C 60 ion irradiation of 6 MeV, i.e., much lower than the extrapolated threshold. The diameters of 10 nm were comparable to those under 40 MeV C 60 irradiation. Furthermore, the tracks formed by 6 MeV C 60 irradiation consisted of damaged crystalline, while those formed by 40 MeV C 60 irradiation were amorphous. The track formation was observed down to 1 MeV and probably lower with decreasing the track diameters. The track lengths were much shorter than those expected from the drop of S e below the threshold. These track formations at such low energies cannot be explained by the conventional purely electronic energy deposition mechanism, indicating another origin, e.g., the synergy effect between the electronic and nuclear energy depositions, or dual transitions of transient melting and boiling.

In this chapter, we review fundamental issues related to the damaging processes of PMMA films induced by high-energy ions with kinetic energies from a few keV to a few GeV, covering the regimes of energy deposition dominated by nuclear collisions and by electronic excitation. Emphasis is given to present an overview of the bond-breaking processes, the changes in the polymer chemical structure, and the corresponding modifications in selected macroscopic physical properties (optical, mechanical, and electrical).

In this work, we report a new approach to non-invasive imaging of the internal architecture of sedimentary deposits from turbidity currents in hydraulic tank simulations. A composite material based on polyester resin, barium sulphate particles and different dyes newly developed enhances and controls optical and x-ray contrast of the deposited sediments. The composites presented specific mass and settling velocity, which varied slightly with composition, but were similar to those of coal, a material that is commonly used for small-scale sedimentation simulations. The addition of 2% (w/w) of barium sulphate provides the opacity required for detection by x-ray microtomography and the presence of dyes of vivid colors gives a natural contrast for optical imaging. The developed nanocomposites present suitable hydraulic properties combined with tunable multimodal contrast properties for non-invasive visualization, making them useful materials in physical simulations of sedimentary deposits from experimental turbidity currents.

Investigations on the chemical modifications induced by swift heavy ions in PMMA thin films were carried out using beams of high d E /d x (2.2 GeV Bi, 14,090 eV/nm) and low d E /d x (2 MeV H, 19 eV/nm). The induced chemical modifications were monitored by XPS for films with initial thickness of 50 and 100 nm. For both beams, the irradiation decreased the amount of carbon atoms bound to oxygen (C O and C O C), with a larger decrease of the carboxyl moiety, as expected. However, the chemical changes induced by light and heavy ions were qualitatively different. For the same mean deposited energy density, proton irradiation induced a decrease of the relative intensity of the carbon–oxygen bonds up to ∼20% larger than the irradiation with Bi ions. This suggests a greater importance of particle ejection by unzipping of PMMA chains at high d E /d x , which tends to keep the O/C ratio closer to the pristine value.

Superparamagnetic iron oxide nanoparticles are suitable contrast agents for magnetic resonance imaging due to their effect on proton relaxation times, and excellent biocompatibility and biodistribution in tissue. In the present study, a ferrofluid formed by dextran-coated iron oxide nanoparticles was prepared by the coprecipitation method and with subsequent steps of crosslinking and addition of functionalizations on the nanoparticle's surface (amino groups and a fluorophore). The effect of differences in the synthesis route (ratio of dextran to iron salts and temperature of the reaction) on the physico-chemical characteristics of the nanoparticles and their performance as contrast agents for magnetic resonance imaging was investigated. Overall, the nuclear magnetic relaxation times of water protons in aqueous suspensions of the nanoparticles did not show major differences among different batches, with no significant effect due to the addition of the fluorophore or changes in the dextran fraction of up to 50%. Larger reductions in the ratio of dextran to iron salts resulted in particles with slightly larger sizes, higher saturation magnetization and distinct nuclear magnetic relaxation times.

Thin films of poly(methyl methacrylate) and poly(vinyl chloride) of different thickness are used to investigate the effect of spatial confinement on the efficiency of bond breaking induced by 2 MeV H^{+} and 2.1 GeV Bi ions. Effective cross sections for oxygen and chlorine loss are extracted for films down to a thickness of about 5 nm and are compared to theoretical estimations based on radial energy density profiles simulated with geant-dna. The cross sections are to a large extent thickness independent, indicating that bond breaking is dominated by short-range processes. This is in contrast to the strongly reduced efficiencies found recently for cratering induced by high-energy ions in similar ultrathin polymer films [Phys. Rev. Lett. 114, 118302 (2015)PRLTAO0031-900710.1103/PhysRevLett.114.118302].

We report on the modification of the structure and morphology of Bi nanowires of two different diameters (80 or 130 nm) exposed to beams of 400 keV and 1 MeV Au+ until complete wire degradation. For fluences up to ∼1 ion/nm2, the main effect was a slight roughening of the originally smooth surface and the appearance of a damaged zone at the wire edges. After an exposure to ∼2 ions/nm2, shallow (∼5-7 nm deep) but wide (up to 120nm) depressions are seen, giving the wires a “wavy” morphology. At the largest fluence tested (10 ions/nm2), the thickest nanowires present an amorphized structure containing an embedded dispersion of small spherical metallic crystallites, while the thinner wires collapse into large (∼50nm) nanoparticles composed of a crystalline core surrounded by a disordered oxidized shell. The observed morphologic modifications are discussed considering sputtering and radiation induced surface diffusion effects.We report on the modification of the structure and morphology of Bi nanowires of two different diameters (80 or 130 nm) exposed to beams of 400 keV and 1 MeV Au+ until complete wire degradation. For fluences up to ∼1 ion/nm2, the main effect was a slight roughening of the originally smooth surface and the appearance of a damaged zone at the wire edges. After an exposure to ∼2 ions/nm2, shallow (∼5-7 nm deep) but wide (up to 120nm) depressions are seen, giving the wires a “wavy” morphology. At the largest fluence tested (10 ions/nm2), the thickest nanowires present an amorphized structure containing an embedded dispersion of small spherical metallic crystallites, while the thinner wires collapse into large (∼50nm) nanoparticles composed of a crystalline core surrounded by a disordered oxidized shell. The observed morphologic modifications are discussed considering sputtering and radiation induced surface diffusion effects.

Iron oxide nanoparticles (IONPS) have been widely investigated as a platform for a new class of multifunctional theranostic agents. They are considered biocompatible, and some formulations are already available in the market for clinical use. However, contradictory results regarding toxicity of IONPs raise a concern about the potential harm of these nanoparticles. Changes in the nanoparticle (NP) physicochemical properties or exposure media can significantly alter their behavior and, as a consequence, their toxic effects. Here, behavior and two-step RT-qPCR were employed to access the potential toxicological effects of dextran-coated IONPs (CLIO-NH2) and uncoated IONPs (UCIO) in zebrafish larvae. Animals were exposed for 7 days to NP solutions ranging from 0.1–100 μg/mL directly mixed to the system water. UCIO showed high decantation and instability in solution, altering zebrafish mortality but showing no alterations in behavior and molecular expression analysis. CLIO-NH2 exposure did not cause significant mortality or changes in hatching rate of zebrafish larvae; however, behavior and expression profiles of the group exposed to lower concentration (1 μg/mL) presented a tendency to decrease the locomotor activity and apoptotic pathway activation.

In this paper are presenting a comparison by using experimental data about chemical damage for all possible physics list for Geant4-DNA (Geant4 version 10.02.p01) for protons incident beam interacting with homogeneous nano-layers of water. Associated to the chemical damage it were evaluated: radial profile of energy deposition, profile of energy deposition on depth, number of interactions, proportion among possible processes and stopping power of the incident particle. The application considers water ultra-thin layers of thicknesses from 2 nm to 200 nm with monodirectional and monochromatic (2 MeV to 20 MeV) protons impinging normally on its entrance surface. It was evoked the standard physics list (“G4EmDNAPhysics” class) and other 5 physics list available (names Opt 1 up to 5). Concerning the experimental data, the films were bombarded by 2 MeV H+ textbf in vacuum at a HVEE 3 MV Tandetron and Xray photoelectron spectroscopy was performed on the irradiated samples at Universite de Namur, Belgium. The preliminary results show that radial and depth profile of energy deposition to all physics lists evaluated presented as expected, with exception for the physics list Opt1. This physics list shows a peak of energy deposition at the end of the layer on depth profile. On radial profile it is clear that the secondaries electrons transported by Opt1 presented larger range than the presented by other evaluated physics list. It was observed for few simulations considering standard physics list that for thickness above $\sim 350$ nm the curve of depth profile achieve it “saturation” and stop the increasing on energy deposition with depth.

This study investigated the effects of smooth and microgrooved membrane blends, with different polycaprolactone (PCL)/ poly(lactic-co-glycolic acid) (PLGA) ratios on the viability, proliferation, and adhesion of different mammalian cell types. The polymer matrices with and without microgrooves, obtained by solvent casting, were characterized by field-emission scanning electron microscopy, atomic force microscopy, contact angle and Young's modulus. Blend characterization showed an increase in roughness and stiffness of membranes with 30% PLGA, without any effect on the contact angle value. Pure PCL significantly decreased the viability of Vero, HaCaT, RAW 264.7, and human fetal lung and gingival fibroblast cells, whereas addition of increasing concentrations of PLGA led to a reduced cytotoxicity. Increased proliferation rates were observed for all cell lines. Fibroblasts adhered efficiently to smooth membranes of the PCL70/PLGA30 blend and pure PLGA, compared to pure PCL and silicone. Microgrooved membranes promoted similar cell adhesion for all groups. Microstructured membranes (15 and 20-μm wide grooves) promoted suitable orientation of fibroblasts in both PCL70/PLGA30 and pure PLGA, as compared to pure PCL. Neuronal cells of the dorsal root ganglion exhibited an oriented adhesion to all the tested microgrooved membranes. Data suggest a satisfactory safety profile for the microgrooved PCL70/PLGA30 blend, pointing out this polymer combination as a promising biomaterial for peripheral nerve regeneration when cell orientation is required. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1522-1534, 2018.

Neste artigo fazemos uma breve revisão da ultrassonografia na perspectiva da física médica. Iniciamos apresentando uma visão resumida dos princípios físicos mais fundamentais em imagens por ultrassom e alguns parâmetros importantes na aferição da qualidade de imagem e do desempenho geral dos ecógrafos que derivam desses princípios. Na segunda parte, apresentamos uma contextualização histórica do controle da qualidade (CQ) em ultrassonografia na prática profissional da física médica e as dificuldades associadas à falta de legislação governamental e à contínua evolução da tecnológica. Esforços para sistematizar e implementar protocolos de CQ para ultrassonografia no Brasil são feitos há mais de 20 anos. Porém, que nível de inserção nesse mercado tão amplo foi atingido pelos serviços e empresas de física médica desde então? Fazemos uma breve reflexão sobre essa questão a partir da experiência no estado do Rio Grande do Sul, buscando, ao final, extrapolar para o cenário nacional e avaliar as perspectivas futuras do CQ no mercado da física médica.

In this work, morphological characterization of microstructures produced by focused 3 MeV H + beams and chemical etching on poly(ethylene terephthalate) foils was investigated by on- and off-axis scanning transmission ion microscopy (STIM). STIM images were obtained from different energy regions of the transmitted energy spectra. STIM performance was compared to scanning electron microscopy (SEM) used as a reference. STIM and SEM images provided similar morphological information. The deviations observed between the measured dimensions obtained from both techniques were within the uncertainties of the experiment. Moreover, the scaling of the structures’ size versus etching time (i.e. the etching rates) extracted from STIM and SEM data were equivalent. Prolonged etching times of up to 60 min were performed to check the effect of the irradiation on the non-bombarded vicinity of the structured lines. STIM images clearly revealed a distribution of cavities and porosity along the structured walls for etching times above 20 min. This is attributed to thermal effects and outgassing during the proton beam writing, which probably create voids that are enlarged by the long exposure to the etching solution.

The presence of impurities in polymers makes them electroactive. When immersed in electrolytes, polymers can incorporate additional ions, thus changing their electronic properties. The aim of the present work is to characterize the electronic behavior of polymers with microstructures obtained from proton irradiation and etching. To that end, polyethylene terephthalate foils were irradiated with a 2.0 × 2.0 μm2 proton beam of 3 MeV. Subsequently, the foils were submitted to an etching procedure with NaOH, leading to microstructures of the order of 1000 μm2. Finally, the polymers were immersed in a solution of NaCl and submitted to an AC voltage from a function generator. The results show that the etching procedure after proton irradiation leads to buried structures in the polymers. Pristine and microstructured foils show an Ohmic behavior for frequencies below 1 kHz and a capacitive behavior above this frequency up to 1 MHz. This behavior is independent of the foil thickness and the area of the structures.

In this paper, the surface effects of individual heavy ions impacting thin polymerlike films were investigated, using molecular dynamics simulations with the finite extensible nonlinear elastic (FENE) potential to describe the molecular chains. The perturbation introduced by the ions in the lattice was modeled assuming that the initial excitation energy in the ion track is converted into an effective temperature, as in a thermal spike. The track was heated only within the film thickness h, leaving a nonexcited substrate below. The effect of decreasing thickness on cratering and sputtering was evaluated. The results were compared to experimental data of thin polymer films bombarded by MeV-GeV ions and to simulations performed with the Lennard-Jones potential. While several qualitative results observed in the experiments were also seen in the simulations, irrespective of the potential used, there are important differences observed on FENE films. Crater dimensions, rim volume, and sputtering yields are substantially reduced, and a threshold thickness for molecular ejection appears in FENE simulations. This is attributed to the additional restrictions on mass transport out of the excited track region imposed by interchain interactions (entanglements) and by the low mobility of the molten phase induced by the spike. Fil: Lima, N. W.. Universidade Católica Do Rio Grande Do Sul; Brasil Fil: Gutierres, L. I.. Universidade Católica Do Rio Grande Do Sul; Brasil Fil: Gonzalez, R. I.. Universidad de Chile; Chile Fil: Müller, S.. Universidade Católica Do Rio Grande Do Sul; Brasil Fil: Thomaz, R. S.. Universidade Católica Do Rio Grande Do Sul; Brasil Fil: Bringa, Eduardo Marcial. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Papaléo, R.M.. Universidade Católica Do Rio Grande Do Sul; Brasil

In this work, we investigate the influence of ion fluence on the development of microstructures produced by 2.2 MeV H+ impinging on 12-μm-thick poly(ethylene terephthalate) (PET, Mylar®) foils. Several lines of 1 × 100 pixels corresponding to approximately 2.5 × 101.5 µm2 were patterned on PET foils using different ion fluences (from 1012 to 1017 H+/cm2) and etching times (from 1 to 60 min). We observe the presence of three different behaviors according to the ion fluence. Long etching times are necessary to open the structure in the low fluence regime, while moderate fluences require shorter etching times. In the high fluence regime, a more complex scenario emerges where short etching times lead to structures either fully or partially developed.

Excited-state intramolecular proton transfer (ESIPT) is a particularly well known reaction that has been very little studied in magnetic environments. In this work, we report on the photophysical behavior of a known ESIPT dye of the benzothiazole class, when in solution with uncoated superparamagnetic iron oxide nanoparticles, and when grafted to silica-coated iron oxide nanoparticles. Uncoated iron oxide nanoparticles promoted the fluorescence quenching of the ESIPT dye, resulting from collisions during the lifetime of the excited state. The assembly of iron oxide nanoparticles with a shell of silica provided recovery of the ESIPT emission, due to the isolation promoted by the silica shell. The silica network gives protection against the fluorescence quenching of the dye, allowing the nanoparticles to act as a bimodal (optical and magnetic) imaging contrast agent with a large Stokes shift.

This paper shows the comparison among experimental, theoretical published data and data generated by the Geant4 toolkit to determine X-ray transmission curves in an energy range suitable for radiology as well a study of the influence of spectra and shielding composition on transmission data. The objectives of this work were: to compare the differences on transmission data considering different shielding material composition, to validate the application for Geant4 and to calculate transmission curves for new material based on the proposed methodology. Transmission curves and fitting equations for lead, concrete, barited concrete and barited mortar were obtained as a function of shielding thickness and X-ray polychromatic spectra. The simulated transmission curves for lead showed to be statistically the same when compared to published reference. Good agreement was calculated between the experimental data and the data simulated using Geant4. For the other composite materials no comparable reference data is available, but the spread in the transmission values is below 10% for the range of the thicknesses used in real shielding. The results showed that changes in composition for the studied materials can have some impact on the transmission data. The X-ray transmission was sensitive to changes in the incoming beam energy spectra for a fixed acceleration voltage. The simulation application developed in this work can be used, associated to a shielding composition elemental analysis, to customize transmission curves for different composite materials and X-ray spectra.

We report on the effect of light-ion irradiation on the size distribution of etched tracks produced by medium energy heavy-ions in polycarbonate. Makrofol KG polycarbonate foils were treated with 2 MeV H+ ions at different fluences φ either before or after a short irradiation with 18 MeV Au7+. The heavy ion irradiation was used to produce the latent tracks in the foils and the proton beam acted as a perturbation to the matrix. The proton irradiation causes initially a decrease in the mean etched pore size, as compared to samples only bombarded by Au ions, reaching a minimum at H+ fluences around 2–5×1013 cm−2, while at higher φ the pore size starts to grow again. This effect is attributed to the action of two competitive processes that dominate in different fluence regimes. The decrease in the pore radii at low fluences is attributed to an increase in crystallinity induced by the proton beam. As the total dose builds up, this effect is surpassed by chain scission and amorphization that grow at a lower rate and cause the pore radii to increase again.

Modifications of the structure and mechanical properties in LiF crystals irradiated with MeV-energy Au ions have been studied using nanoindentation, atomic force microscopy and optical spectroscopy. The nanostructuring of crystals under a high-fluence irradiation (above 1013 ions/cm2) was observed. Nanoindentation tests show a strong ion-induced increase of hardness (up to 150–200%), which is related to the high volume concentration of complex color centers, defect aggregates, dislocation loops and grain boundaries acting as strong barriers for dislocations. From the depth profiling of the hardness and energy loss it follows that both nuclear and electronic stopping mechanisms of MeV Au ions contribute to the creation of damage and hardening. Whereas the electronic stopping is dominating in the near-surface region, the effect of elastic displacements prevails in deeper layers close to the projectile range.

O câncer de mama é o tipo de câncer mais comum entre as mulheres no Brasil e no mundo. A mamografia é o exame considerado padrão ouro para rastreamento de câncer de mama e, tanto a ressonância magnética quanto a ultrassonografia, são utilizadas como complemento. Atualmente, existe um crescimento na quantidade de requerimentos médicos da ressonância como método de rastreamento de lesão, acompanhamento de tumores malignos e em casos de pacientes que possuam histórico familiar de câncer de mama. Este trabalho teve como objetivo comparar o desempenho das imagens por ressonância magnética com a mamografia e ecografia de mamas no diagnóstico de lesões mamárias malignas e benignas, utilizando a biópsia como padrão ouro. Foi feito um comparativo entre variáveis que quantificam características de desempenho, tais como sensibilidade, especificidade, valor preditivo positivo e negativo. Essas informações foram obtidas dos laudos médicos da biopsia e dos três métodos de aquisição de imagem. Os parâmetros de sensibilidade e especificidade para as lesões benignas foram de 91% e 63% para mamografia/ecografia e 77% e 100% para ressonância magnética. Em relação às lesões malignas, a sensibilidade e especificidade encontradas foram de 57% e 100% para a mamografia e ecografia, respectivamente. Concluiu-se que a ressonância magnética é um bom exame para avaliação de lesões benignas, devido aos altos parâmetros de desempenho. Para as lesões malignas não foi possível obter os parâmetros, visto que os valores não foram válidos para o estudo.

In the present work, the relaxation behavior of nanometer-sized deformations produced by single ion impacts on the surface of monodisperse (Mw = 60,000 u) polycarbonate thin films was investigated at temperatures close to and below the glass transition. The relaxation functions for the length, height and width of the deformations were well described by a stretched exponential law, with characteristic relaxation times τ strongly dependent on temperature. For T > 100 °C, the temperature dependence of τ obeys a Vogel–Fulcher law, but for lower temperatures it becomes less steep and tends to an Arrhenius-type behavior.

Creation of color centers in LiF under irradiation with 3–12-MeV Au ions was studied. Comparison of experimental data of color center creation with computer simulation of the energy deposition and elastic atomic displacements reveals the role of elastic collisions in defect creation by these ions, which have comparable magnitudes of electronic and elastic stopping. The experimentally measured efficiency of color center creation and that predicted by the simulation of elastic displacements have a similar dependence on the projectile energy. Thus, the color center creation is mainly associated with the elastic collisions, despite the relatively large values of the electronic stopping power for these ions.

The peculiarities of defect creation in LiF crystals by irradiation with 5- and 10-MeV Au ions have been studied using optical spectroscopy. The crystals were irradiated at room temperature with fluences from 1 × 10 12 to 2 × 10 14 ions/cm 2 at various beam current densities (1–200 nA/cm 2 ). The short ion range in LiF allowed measurements for higher absorbed energy densities and high defect volume concentration. The efficiency of single F center and F n and larger aggregate creation depends drastically both on ion fluence and flux (beam current). Color center creation is less effective for 5-MeV Au ions than for 10-MeV Au ions, which produce δ electrons with energies sufficient for creation of cation excitons (∼62 eV). The peculiarities of color center accumulation in LiF crystals under MeV Au ion irradiation are considered taking into account the nonlinear kinetics of interstitials (H centers).

Studies on tunable electronically anisotropic material on semiconductor, “TEAMS”, with a polysilane layer spin-coated onto a silicon wafer and then contacted on both top and rear sides, are reported in the present paper. This structure was irradiated with swift heavy ions, and its electrical characteristics were studied both during and after irradiation. It was found that the current/voltage characteristics depend on the ion fluence, the time of voltage application, the gating voltage, the ambient pressure, light, and the post-annealing temperature of the samples. Under specific conditions, a negative differential resistance was also exhibited. The observations are indicative of a peculiar conduction mechanism.

We show direct experimental evidence that radiation effects produced by single MeV heavy ions on a polymer surface are weakened when the length of the ion track in the material is confined into layers of a few tens of nanometers. Deviation from the bulk (thick film) behavior of ion-induced craters starts at a critical thickness as large as ∼40nm, due to suppression of long-range additive effects of excited atoms along the track. Good agreement was found between the experimental results, molecular dynamic simulations, and an analytical model. Fil: Papaléo, R. M.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Thomaz, R.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Gutierres, L.I.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: De Menezes, V.M.. Universidade Federal Da Fronteira Sul; Brasil Fil: Severin, D.. GSI Helmholtz Centre; Alemania Fil: Trautmann, C.. GSI Helmholtz Centre; Alemania. Universitat Technische Darmstadt; Alemania Fil: Tramontina Videla, Diego Ramiro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Bringa, Eduardo Marcial. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Grande, P. L.. Universidade Federal do Rio Grande do Sul; Brasil

We report on measurements of relaxation times of craters and rims induced by 20 MeV Au ions bombarding PMMA targets at temperatures near the glass transition. PMMA thin films were bombarded at grazing angles and at low fluences (∼10 9 cm −2 ). The targets were kept at the irradiation temperature for a certain period of time before quenching to room temperature, where imaging of the surface was performed ex situ by scanning force microscopy (SFM). The average dimensions of the craters and rims as a function of annealing time t were extracted from SFM images and fitted to an exponential law [∝ exp(− t / τ )], where τ is identified as a characteristic relaxation time. Values of τ for the hillock tails were around 33 ± 7 s at 94 °C and increased to around 18 h at 76 °C, reflecting the great changes in viscosity near the glass transition temperature of the polymer. Some parts of the rims surrounding the middle of craters and the crater walls relax much more slowly, because of the severe chemical modification of the chains in the core of the impact.

In the last years, concepts have been developed to use etched ion tracks in insulators, such as polymer foils or silicon oxide layers as hosts for nano- and microelectronic structures. Depending on their etching procedure and the thickness of the insulating layer in which they are embedded, such tracks have typical diameters between some 10 nm and a few μm and lengths between some 100 nm and some 10 μm. Due to their extremely high aspect ratios, and due to the possibility to cover very large sample areas, they exceed the potential of nanolithography.In this paper, the strategies of etched ion track manipulation are briefly outlined, that lead to the formation of nanotubules, nanowires, or tubular arrangements of nanoclusters. Examples where nanoelectronic structures are based on single ion tracks, are nanocondensors or sensors for temperature, light, pressure, humidity and/or alcohol vapor. By combination of ion track metallization and conducting track-to-track connections on the foil surface, micromagnets, microtransformers and microcondensors could be formed within polymer foils.Finally, we present our new "TEMPOS" (Tunable Electronic Material with Pores in Oxide on Silicon) concept where nanometric pores, produced by etching of tracks in silicon oxide on silicon wafers, are used as charge extraction (or injection) channels. In comparison with the metal oxide semiconductor field effect transistors (MOS-FETs), the TEMPOS structures have a number of additional parameters (such as the track diameter, density, and shape, and the material embedded therein and its spatial distribution) which makes these novel structures much more complex. This eventually leads to higher compactation of the TEMPOS circuits and to unexpected electronic properties. TEMPOS structures can overtake the function of tunable resistors, condensors, photocells, hygrocells, diodes, sensors, and other elements. As an example, some corresponding current/voltage relations and TEMPOS circuits are presented. In this work we concentrate on TEMPOS structures with fullerene and phthalocyanine. Though not yet verified, TEMPOS structures could, in principle, be scaled down to nanometer sizes.

In this work, crater formation by single 20 MeV Au ions on ultra-thin poly(methyl methacrylate) (PMMA) films was systematically investigated as a function of the thickness t of the layers (2 nm

The impact of swift heavy ions onto silicon oxide and silicon oxynitride on silicon creates etchable tracks in these insulators. After their etching and filling-up with highly resistive matter, these nanometric pores can be used as charge extraction or injection paths towards the conducting channel in the underlying silicon. In this way, a novel family of electronic structures has been realized. 1 The basic characteristics of these “TEMPOS” (=tunable electronic material with pores in oxide on silicon) structures are summarized. Their functionality is determined by the type of insulator, the etch track diameters and lengths, their areal densities, the type of conducting matter embedded therein, and of course by the underlying semiconductor and the contact geometry. Depending on the TEMPOS preparation recipe and working point, the structures may resemble gatable resistors, condensors, diodes, transistors, photocells, or sensors, and they are therefore rather universally applicable in electronics. TEMPOS structures are often sensitive to temperature, light, humidity and organic gases. Also light-emitting TEMPOS structures have been produced. About 37 TEMPOS-based circuits such as thermosensors, photosensors, humidity and alcohol sensors, amplifiers, frequency multipliers, amplitude modulators, oscillators, flip-flops and many others have already been designed and successfully tested. Sometimes TEMPOS-based circuits are more compact than conventional electronics.

We report on a systematic scanning force microscope study of crater formation induced by swift heavy ions as a function of angle of incidence. PMMA films were bombarded with 197Au (20 MeV), 209Bi (2320 MeV) and 238U (2640 MeV) ions at angles θ varying from 0° to 84° to the surface normal. In all cases, the length of the craters as well as rim height and length scale with (cosθ)−1. Crater width showed a much weaker (cosθ)−0.3 dependence. Similar angular dependences were observed for the different ion species and energies used. The experimental data is compared to molecular dynamics simulations of crater formation in a model solid. The simulations show a (cosθ)−1 dependence for the crater length, but no dependence for the crater width, unless a wide initial track of excitation is used.

Scanned beams of 0.1 MeV/u 197Au ions were employed for the bombardment of silicon oxide films thermally grown on silicon (1 0 0) substrates. Subsequently the films were etched in aqueous HF solution (1% and 4%) for various times and at different temperatures. Scanning force microscopy and transmission electron microscopy images of etched films reveal conical holes with diameters from 20 to 350 nm, depending on the HF concentration and etching time. For a fixed etching temperature, hole size increased roughly linearly with etching time, and for a fixed etchant concentration, it varied exponentially with etching temperature. These porous surfaces were tested for trapping of nano-particles, as templates for deposition of porous films, and for localized etching of the Si substrate.

Ion bombardment of surfaces at an angle with respect to the surface normal produces surface modification with more varied and rich features than normal incidence bombardment. This allows more possibilities for nanopatterning and surface processing. Megaelectronvolt ion bombardment of insulators can create a track of electronic excitations which can decay non-radiatively and couple to the lattice, leading to sputtering and crater creation. Using molecular dynamics simulations we present a systematic study of the craters produced by a cylindrical track of excitations with its axis at several angles with respect to the surface normal (in the range Θ =0–80°). We also use different energy densities inside the track, from 0.5 nU to 12.5 nU , where n is the density of the material and U its binding energy. Crater length is found to vary as cos −1 Θ .

The morphology and the dimensions of nanometer-sized craters and crater rims induced by individual MeV heavy ions impacting polymer surfaces have been systematically investigated by means of scanning force microscopy. We demonstrate that the morphology of the surface tracks varies systematically with temperature, molecular weight ( M w ) and tacticity of polymer thin films. Such parameters influence chain mobility and the characteristic relaxation times of the polymer, which appear to be key factors determining the final shape and size of observed holes and hillocks. Because of the correlation of the impact features with the thermal and rheological properties of polymers, the problem can be inverted and the surface track morphology may be used to identify physical parameters of the targets. This procedure has been applied to model polymer films. It was possible to identify a critical target temperature above which a sharp change in crater morphology is observed in the scanning force microscopy images. We propose this temperature to be the glass transition temperature. Also, crater size decreases steeply with increasing molecular weight up to a critical M w above which crater dimensions change very little. The transition region is around M c ′ , the critical molecular weight at which entanglement coupling of macromolecular chains becomes important.

Poly(methyl methacrylate) (PMMA) thin films maintained at temperatures from −196 up to 150 °C are bombarded at grazing angles by 20 MeV Au ions at very low fluences. Immediately after the irradiation, the samples are cooled down at two distinct rates. Scanning force microscopy (SFM) images of the bombarded targets after cooling reveal nanometer-sized craters and/or raised regions (hillocks) around the point of each ion impact. The size of the craters is independent of the temperature for −196 ° C ° C , but for higher temperatures, crater dimensions increase steeply and no hillock is observed behind the crater. The temperature above which the hillocks disappear is sensitive to the cooling rate and for rapidly cooled targets it is near the tabulated value for the glass transition temperature, Tg, of the polymer. Since the variation of the morphology of ion-induced defects occurs over a narrow temperature range and depends on the cooling rate of the targets, single ion bombardment coupled to SFM may be used as an alternative method to estimate Tg and relaxation rates of nanodeformations in thin polymer films. The post-irradiation thermal annealing of the surface tracks produced at room temperature is also discussed.

Thermal properties and recrystallization ability of commercial grade poly(para-phenylene sulphide) (PPS) and poly(ethylene terephthalate) (PET) thin foils, bombarded with 380 keV He + ions, were studied by Differential Scanning Calorimetry (DSC) and X-ray Diffractometry (XRD). The following phenomena are observed on bombarded targets: a) decrease of the enthalpy of fusion (ΔH f ) and recrystallization (ΔH rc ) and b) decrease of the onset of the melting and recrystallization temperature. This behaviour indicates amorphisation of crystalline phases, increase of imperfections in the remaining crystallites, and loss of the recrystallization ability of the amorphous zones upon repeated thermal cycles. The amorphisation fluence, for which no crystalline regions were detected by DSC and XRD, is 2 × 10 14 He + /cm 2 for PPS and 10 14 He + /cm 2 for PET. However, the irradiated targets lose their ability to recrystallize at much lower fluences, around 4 × 10 13 He + /cm 2 for PPS and 2 × 10 13 He + /cm 2 for PET. The loss of crystallization ability is attributed to the presence of reactive defects on the bombarded targets which may generate crosslinks (and chain scissions) during the heating stage of the DSC run.

Recent results obtained in our group on surface tracks (cratering and plastic deformation) induced by MeV heavy-ion impacts on polymers are briefly summarized in this paper. The morphology and dimensions of the surface tracks are monitored by scanning force microscopy (SFM) as a function of polymer molecular weight, monomer structure and irradiation temperature. 20 MeV 197Au ions from the Porto Alegre 3 MV Tandem accelerator were used to bombard the surface of different polymer films. Craters are observed on all irradiated polymers and are a manifestation of the surface erosion induced by the MeV ions. The volume of the craters give the total mass sputtered by each MeV ion impact which varied from (1.3 ± 0.4) × 105 u/ion to (2.7 ± 1.0) × 105 u/ion for polystyrene targets of different molecular weights with ions incident at a grazing angle (79°). This figure varies slightly depending on the nature of the macromolecules. Hillocks, plastically deformed zones around the point of ion impact, may also be present on the surface of irradiated films. The appearance or not of such features and the extent of the permanent deformation are found to be dependent on the molecular weight of a given polymer and the irradiation temperature.