Ions Of Different Energies Research Articles

Fabrication of carbon nanostructures (nanodots, nanowires) by energetic ion irradiation

Carbon nanostructures were synthesized by energetic ion irradiation of Si-based gel films. These polymer-like films with different side groups and C concentrations were prepared by sol–gel chemistry and irradiated with Si or Au ions of different energies in the range 3 MeV–2 GeV. The shape and size of the formed carbon nanostructures was studied by energy filtered transmission electron microscopy. They exhibited a visible photoluminescence emission, due to their semiconducting nature and the confinement of excitons. The changes in the optical properties were correlated with the structural transformation of films, investigated by means of Fourier transformed infrared (FTIR) and Raman spectroscopies. The role of carbon concentration, structure and energy transferred by ions on the luminescence properties are discussed.

Implications of Nuclear Reactions for Single Event Effects Test Methods and Analysis

Simulation results for the full galactic cosmic ray environment demonstrate that current accelerator-based test methods using linear energy transfer as the engineering metric to characterize single event effects are not sufficient to capture the nuclear reaction portion of the response. Nuclear reactions contribute significantly to on-orbit single-event rates as compared to those from direct ionization induced by the primary ions. Based on these results, the applicability of current single-event test methods to predicting on-orbit event rates is examined and improved procedures are identified. For devices with critical charge values that are in the range where nuclear reactions may play a role in determining the event rate, ground-based tests should include irradiation with several types of ions of different energies to identify the contribution of these reactions to the measured SEE cross section

Tailoring of magnetic anisotropy in amorphous and nanocrystalline soft magnetic alloys using swift heavy ions

Amorphous films of Fe 0.85N 0.15 and Fe 73.9Cu 0.9Nb 3.1Si 13.2B 8.9 have been prepared by using ion-beam sputtering. Magneto-optic Kerr effect (MOKE) and Mössbauer measurement shows that the FeN film has a perpendicular magnetic anisotropy while the finemet film has a uniaxial in-plane anisotropy. The anisotropy in as-deposited state may be attributed to some quenched-in stresses present in the film during deposition. Films have been irradiated with Ag and Au ions of different energies. In both the films, irradiation results in gradual removal of anisotropy and a decrease in coercivity, which may be attributed to relaxation of internal stresses. This demonstrates that swift heavy ions can be used for controlled modification of magnetic properties of thin films.

Calculations of particle and heavy ion interactions with space shielding materials using the SHIELD-HIT transport code

Spectra of secondary particles produced by nucleus–nucleus interactions and heavy-ion interactions in the extended targets of interest for space research were calculated using the Monte Carlo code SHIELD-HIT. This code simulates the interactions of hadrons and atomic nuclei of arbitrary charge and mass number ( Z , A ) with complex extended targets in a wide energy range, from 10 GeV/ u down to 1 MeV/ u, and to thermal energies in the case of neutrons. Inelastic nuclear reactions in SHIELD-HIT are simulated using the Russian models of nuclear reactions. The total reaction cross sections evaluated by these models are discussed for proton and carbon interactions with different nuclei in a wide energy range. Production of secondary neutrons and charged secondary particles from the thick targets of lead, water and PMMA irradiated by 4He, 12C and 28Si ions of different energies was calculated and compared with the experimental data. The results obtained by SHIELD-HIT are in reasonable agreement with experiments and are promising for further applications in space research.

Ion beam enhanced etching of LiNbO3

Single crystals of z- and x-cut LiNbO3 were irradiated at room temperature and 15K using He+- and Ar+-ions with energies of 40 and 350keV and ion fluences between 5×1012 and 5×1016cm−2. The damage formation investigated with Rutherford backscattering spectrometry (RBS) channeling analysis depends on the irradiation temperature as well as the ion species. For instance, He+-irradiation of z-cut material at 300K provokes complete amorphization at 2.0dpa (displacements per target atom). In contrast, 0.4dpa is sufficient to amorphize the LiNbO3 in the case of Ar+-irradiation. Irradiation at 15K reduces the number of displacements per atom necessary for amorphization. To study the etching behavior, 400nm thick amorphous layers were generated via multiple irradiation with He+- and Ar+-ions of different energies and fluences. Etching was performed in a 3.6% hydrofluoric (HF) solution at 40°C. Although the etching rate of the perfect crystal is negligible, that of the amorphized regions amounts to 80nmmin−1. The influence of the ion species, the fluence, the irradiation temperature and subsequent thermal treatment on damage and etching of LiNbO3 are discussed.

Monte Carlo Simulation of Water Radiolysis for Low-energy Charged Particles

The paper describes the development of chemical modules simulating the prechemical and chemical stages of charged particle tracks in pure liquid water. These calculations are based on our physical track structure codes for electrons and ions (KURBUC, LEPHIST and LEAHIST) which provide the initial spatial distribution of H2O+, H2O* and subexcitation electrons at approximately 10(-15) s. We considered 11 species and 26 chemical reactions. A step-by-step Monte Carlo approach was adopted for the chemical stage between 10(-12) s and 10(-6) s. The chemistry codes enabled to simulate the non-homogeneous chemistry that pertains to electron, proton and alpha-particle tracks of various linear energy transfers (LET). Time-dependent yields of chemical species produced by electrons and ions of different energies were calculated. The calculated primary yields (G values at 10(-6) s) of 2.80 for OH and 2.59 for e(aq)- for 1 MeV electrons are in good agreement with the published values. The calculated G values at 10(-6) s for a wide range LETs from of 0.2 to 235 keV microm(-1) were obtained. The calculations show the LET dependence for OH and H2O2. The electron penetration ranges were calculated in order to discuss the role of low energy electrons.

Threshold temperatures of heavy ion-induced nucleation in superheated emulsions

The threshold temperatures of nucleation in superheated emulsions were investigated with self-made superheated emulsions using R114 as sensitive liquid irradiated with a number of heavy ion species at several hundred megaelectron volt per nucleon. Calculations were made to estimate the threshold temperatures of nucleation for heavy ions of different energies. The calculation shows that the response of the emulsion increases near threshold temperature and then saturates to a value corresponding to the drop size of the superheated liquid. The nucleation rates were observed as a function of the operating temperature of the superheated emulsions for different heavy ion species and energies, and a comparison is made with the calculation.

DNA DSB induced by iron ions in human fibroblasts: LET dependence and shielding efficiency

This paper reports on DNA DSB induction in human fibroblasts by iron ions of different energies, namely 5, 1 GeV/u, 414 and 115 MeV/u, in absence or presence of different shields (PMMA, Al and Pb). Measure of DNA DSB was performed by calibrated Pulsed Field Gel Electrophoresis using the fragment counting method. The RBE–LET relationships for unshielded and shielded beams were obtained both in terms of dose average LET and of track average LET. Weak dependence on these parameters was observed for DSB induction. The shielding efficiency, evaluated by the ratio between the cross sections for unshielded and shielded beams, depends not only on the shield type and thickness, but also on the beam energy. Protection is only observed at high iron ions energy, especially at 5 GeV/u, where PMMA shield gives higher protection compared to Al or Pb shields of the same thickness expressed in g/cm 2.

Ion velocity, charge state and substrate dependent electronic sputtering of fullerene

In order to understand electronic sputtering phenomenon, a systematic study is performed by bombarding fullerene (C 60) thin films deposited on Si and glass substrates with Au and Ag ions of different energies. The incident ion velocity, charge state and substrate dependent electronic sputtering yield (sputtered atoms/ion) of C is measured on-line by elastic recoil detection analysis (ERDA) technique in the three different sets of studies. The salient features observed in these experiments are that the yield is quite high (∼10 3 atoms/ion and above), which is influenced by the above-mentioned three physical parameters. Slower ion having same electronic energy deposition ( S e) as compared to its high velocity counterpart erodes more. C 60 films deposited on more insulating substrate (electrically and thermally: glass) shows higher sputtering yield as compared to those deposited on Si substrate. However, no charge state effect was observed in the electronic sputtering yield within the detection limit of the set up.

Computation of etched track profiles in CR-39 and comparison with experimental results for light ions of different kinds and energies

Computation of etched track profiles needs the knowledge of the variable track etch rates along the ion trajectories. Using the depth-dependent track etch rates experimentally determined for perpendicularly incident protons, deuterons and alpha particles as well as 7 Li , 11 B , 12 C , 14 N and 16 O ions of different energies simulations of the track development were performed. Two models of track etching were applied for that purpose recently published in literature. Although the models are based on the same physical fundamentals the results are slightly different. The reasons of the discrepancies were found by analysing the algorithms in detail. Comparison of the calculated track profiles with those determined experimentally from longitudinal sections of the etch pits showed good agreement for non-overetched as well as overetched tracks. The consistency of the whole experimental data set was checked by analysing the correlation of the track etch rates with geometric track parameters for all kinds of ions and etching times covered by the experiments.

Modeling energetic particle injections in dynamic pulse fields with varying propagation speeds

Dispersionless injections are a ubiquitous characteristic of substorms. They are defined as simultaneous enhancements in the fluxes of electrons and ions of different energies, and they are often observed near or inside geosynchronous orbit. We model dispersionless electron injections by considering the interaction of an earthward propagating electromagnetic pulse with the preexisting electron population. Such simulations have been performed previously [Li et al., 1993, 1998]; however, they assumed a constant propagation velocity for the transient fields. Observations have shown that substorm injections and associated magnetic signatures do not propagate at constant velocities, but rather slow down as they approach the inner magnetosphere. Between 4.5 and 6.6 RE the injection propagation speeds reach surprisingly low values, of the order of 24 km/s. Nonetheless, the injections still remain dispersionless [Reeves et al., 1996]. In our simulation we vary the pulse speed with the radial distance from the Earth to match the reported propagation speeds and demonstrate that dispersionless injections are achievable under such low propagation speeds. In particular, we simulate the dispersionless injections of 12 February 1991 measured at two radially displaced spacecraft (CRRES and LANL 1990–095), when they were both around local midnight.

Mechanism of H release from Si-based polymers under ion irradiation

The release of H from Si-based polymers under irradiation by He, C, Si, Cu, Ag and Au ions of different energies has been studied. The ions and energies have been chosen in such a way that they cover a wide range of electronic and nuclear energy loss values. Results are analysed in the frame of three different models. A model of track percolation leading to an exponential decay of the H concentration as a function of ion fluence fits the kinetics of H evolution only on a limited range of fluence. An explanation is proposed in the second model, assuming that the radiolytic efficiency in the core of tracks changes when the tracks overlap. A better agreement is found however with a model implying the diffusion of molecular hydrogen in the material after combination of two radicals formed within a critical recombination volume.

Interdiffusion in direct ion beam deposited isotopic Fe/Si trilayers

Interdiffusion and intermixing have been examined in Fe/Si trilayers prepared with ions of different energies, using the direct ion beam deposition technique. Isotope-pure layers were deposited and spin-polarized neutron reflectivity used to determine the role of Fe diffusion in iron silicide formation. It was found that a nonmagnetic iron silicide was formed that contained Fe from both the top and bottom layers in the trilayer, suggesting complete diffusion across the spacer region. Electron microscopy observations revealed the presence of an iron silicide phase and crystalline interface layers in films prepared with low energy ions (30 eV), while mixed and amorphous-like regions were found at higher ion energies (100 eV).

Low-dose hypersensitivity of V79 cells under exposure to γ-rays and 4 He ions of different energies: survival and chromosome aberrations

Purpose : To examine the low-dose sensitivity of V79 cells under exposure to γ-rays and 4 He ions of different energies. Materials and methods : Cell survival and cytogenetic analysis using the Giemsa technique were studied following irradiation to doses of 0-3 Gy at the INFN-LNL facilities. Results : Low-dose hyper-radiosensitivity (HRS) of V79 was demonstrated after irradiation with γ-rays and α -particles of various linear energy transfers (LET) (58.9, 79.3 and 101.7 keV μ m -1) . Cytogenetic analysis showed an LET dependence of aberrations at a dose of 1Gy; the frequency of chromatid fragments appeared to vary with the number of α -particles traversing the cell nucleus. The results of both studies fit together to give a better understanding of so-called 'induced radioresistance' phenomenon. Conclusions : The mechanism of induced cellular radioresistance appears to be initiated after a certain amount of energy is deposited in the cell nucleus. This amount depends on both radiation quality and the number of particles traversing the cell.

Assessment of DNA damage induced by high-LET ions in human lymphocytes using the comet assay

The alkaline single-cell gel electrophoresis assay (comet assay) was used to analyze DNA damage induced in human lymphocytes by irradiation with high linear energy transfer (LET) ions. Our aim was to measure DNA breaks and to demonstrate the heterogeneity of the damage levels in a lymphocyte population irradiated with ions of different energies and LETs. Four experiments with heavy ions (Ar, C and U), as well as γ-ray exposure, were conducted to enable comparisons. We demonstrated that the comet assay is able to assess the variability in DNA damage induced at the single cell level. The amount of DNA damage and its heterogeneity increased with particle fluence and LET, but saturated at high LETs. However, when expressed in terms of the mean dose, γ-rays were more efficient than most of the ions used. The comet assay also allowed the detection of highly damaged cells (HDC), which were previously described as cells in late apoptotic stages. The rapid emergence of HDC in this study suggests that they were generated following ion irradiation-induced creation of DNA break clusters induced by ion exposure. Another clue was that the proportion of HDC increased with LET and fluence. We hypothesized that the LET threshold observed and the higher efficiency of low-LET radiation might be linked to the impossibility of measuring small DNA fragments in HDC.

RBE for carbon track-segment irradiation in cell lines of differing repair capacity

Purpose: The LET position of the RBE maximum and its dependence on the cellular repair capacity was determined for carbon ions. Hamster celllines of differing repair capacity were irradiated with monoenergetic carbon ions. RBE values for cell inactivation at different survival levels were determined and the differences in the RBE-LET patterns were compared with the individual sensitivity to photon irradiation of the different cell lines. Material and methods: Three hamster cell lines, the wild-type cell lines V79 and CHO-K1 and the radiosensitive CHO mutant xrs5, were irradiated with carbon ions of different energies (2.4-266.4MeV/u) and LET values (13.7-482.7keV/mum) and inactivation data were measured in comparison to 250kV x-rays. Results: For the repair-proficient cell lines a RBE maximum was found at LET values between 150 and 200keV/mum. For the repair-deficient cell line the RBE failed to show a maximum and decreased continuously for LET values above 100keV/mum. Conclusions: The carbon RBE-LET relationship for inactivation is shifted to higher LET values compared with protons and alpha -particles. RBE correlated with the repair capacity of the cells.

A semi-quantitative study of disorder in argon ion-bombarded crystalline silicon using Auger lineshape analysis

It is important to have a means of determining the effect that various degrees of disorder (amorphousness) have on the valence band densities of states in thin film amorphous semiconducting materials. Crystalline silicon has been bombarded with Ar + ions of different energies to produce a surface analogous to amorphous material with varying degrees of disorder. X-ray excited Si L 2,3-VV and L 1-L 2,3V spectra have been obtained and numerically treated to obtain an indication of the valence band densities of states (DOS) for different degrees of surface disorder. A method based on the simplex algorithm has been applied to these spectra to decompose them into their component (pp-, sp- and ss-like) contributions. Changes in these components, before and after inducing differing degrees of disorder, have been compared in order to semi-quantitatively probe the effect of disorder on the surface DOS. It is shown that both the Si L 2,3-VV and Si L 1-L 2,3V Auger lines may be used to differentiate between an ordered and a disordered surface and the L 1-L 2,3V line can also be used to semi-quantitatively monitor different degrees of disorder. It is also shown that, despite it being initially counter-intuitive, increasing the bombarding ion energy results in less disorder on the surface.

Computer Simulation of Channeling Profile Analysis of Implantation Damage

ABSTRACTChanneling profile analysis is simulated using the dynamic binary collision code Crystal- TRIM. A good agreement between theoretical and experimental data is found for silicon targets which were predamaged by Si+ ions of different energies and analyzed by 140 keV B+ ions. For each example the depth profile of the defects relevant for the dechanneling of the analyzing ions is given. An estimate of the annealing of such defects is obtained by comparison of results for as-implanted and annealed samples.

Calculation of Radial Dose Distributions for Heavy Ions by a New Analytical Approach

With the new analytical method recently developed for calculation of radially restricted LET, radial dose distributions are calculated for protons and heavy ions of different energies. In the entire range of radial distance, the results agree well with the results of comprehensive Monte Carlo simulations and with experimental data. A comparison with other models of radial dose distribution demonstrates the advantages of the new analytical approach.

Calibration of CN and CR-39 track detectors for measurements of fast deuterons and nitrogen ions

The paper reports on the analysis of responses of CN-type films and CR39-plastic nuclear track detectors (NTDs) to fast deutrons and nitrogen ions emitted from high-current Plasma-Focus (PF) facilities, as operated at SINS and INFIP. In order to separate the deutrons and nitrogen ions of different energy, the use was made of a Thomson-type mass-spectrometer adapted to measurements within dense plasma streams. Deutron and ion parabolaen were registered the CN-80 and CN-LR115 films as well as with the CR39 plastic NTDs, which were undergone routine etching procedures. On the basisof known characteristics of the spectrometer applied energy- and mass-scales for the obtained ion paraboale were determined. Using an optical microscope, a detailed analysis of track dimensions was performed in chosen points along the registered parabolae, and the calibration diagrams (i.e. a track diameter for the chosen ion energy and different etching times) were determined. Results of the calibration procedure, after comparing with other calibration data obtained with conventional particle accelerators, may be applicable for measurements of fast deutrons (i.g., in nuclear fusion experiments) and energetic nitrogen ions (i.g., in some plasma- and ion-facilities used for technological applications).