Showing papers in "Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms in 2009"

Quantitative depth profiling of deuterium up to very large depths

Abstract: Quantitative depth profiles of deuterium up to very large depths are achieved from the energy spectra of protons created by the D( 3 He,p)α nuclear reaction at incident energies up to 6 MeV. The advantages of this method compared to the more often applied resonance method are discussed. For light target materials the achievable depth resolution is mainly limited by geometrical spread due to the finite size of the detector aperture, while for heavy materials the resolution is mainly limited by multiple small-angle scattering. A reasonable depth resolution throughout the whole analyzed depth can be obtained by using several different incident energies. Depth profiling up to 38 μm is demonstrated for a-C:D layers deposited on the limiter of Tore Supra, and up to 7.5 μm in tungsten coatings from the divertor of ASDEX Upgrade.

Characteristics comparison between a cyclotron-based neutron source and KUR-HWNIF for boron neutron capture therapy

Abstract: At Kyoto University Research Reactor Institute (KURRI), 275 clinical trials of boron neutron capture therapy (BNCT) have been performed as of March 2006, and the effectiveness of BNCT has been revealed. In order to further develop BNCT, it is desirable to supply accelerator-based epithermal-neutron sources that can be installed near the hospital. We proposed the method of filtering and moderating fast neutrons, which are emitted from the reaction between a beryllium target and 30-MeV protons accelerated by a cyclotron accelerator, using an optimum moderator system composed of iron, lead, aluminum and calcium fluoride. At present, an epithermal-neutron source is under construction from June 2008. This system consists of a cyclotron accelerator, beam transport system, neutron-yielding target, filter, moderator and irradiation bed. In this article, an overview of this system and the properties of the treatment neutron beam optimized by the MCNPX Monte Carlo neutron transport code are presented. The distribution of biological effect weighted dose in a head phantom compared with that of Kyoto University Research Reactor (KUR) is shown. It is confirmed that for the accelerator, the biological effect weighted dose for a deeply situated tumor in the phantom is 18% larger than that for KUR, when the limit dose of the normal brain is 10 Gy-eq. The therapeutic time of the cyclotron-based neutron sources are nearly one-quarter of that of KUR. The cyclotron-based epithermal-neutron source is a promising alternative to reactor-based neutron sources for treatments by BNCT.

The micro-imaging station of the TopoTomo beamline at the ANKA synchrotron light source

Abstract: The TopoTomo bending magnet beamline at the ANKA synchrotron facility in Karlsruhe (Germany) operates in the hard X-ray regime (above 6 keV). Recently, an X-ray micro-imaging station has been installed at TopoTomo. For typical imaging applications, a filtered white beam or from 2009 on a double-multilayer monochromator is used. In order to optimize the field of view and the resolution of the available indirect pixel detectors, different optical systems have been installed, adapted, respectively, to a large field of view (macroscope) and to high spatial resolution (microscope). They can be combined with different camera systems, ranging from 14-bit dynamic range CCDs to fast CMOS cameras. The spatial resolution can be brought substantially beyond the micrometer limit by using a Bragg magnifier. Due to the moderate flux of the beamline compared to insertion-device beamlines on third generation light sources, special emphasis has been put on the efficiency of the detectors via a dedicated scintillator concept. The layout of the beamline optics makes optimal use of the coherence properties. Thus, absorption contrast, phase-contrast and analyzer-based imaging can be applied. Additionally, white beam synchrotron topography is performed, using digital indirect X-ray pixel detectors as well as X-ray film.

Dose profile monitoring with carbon ions by means of prompt-gamma measurements

Abstract: A key point in the quality control of ion therapy is real-time monitoring and imaging of the dose delivered to the patient. Among the possible signals that can be used to make such a monitoring, prompt gamma-rays issued from nuclear fragmentation are possible candidates, provided the correlation between the emission profile and the primary beam range can be established. By means of simultaneous energy and time-of-flight discrimination, we could measure the longitudinal profile of the prompt gamma-rays emitted by 73 MeV/u carbon ions stopping inside a PMMA target. This technique allowed us to minimize the shielding against neutrons and scattered gamma rays, and to find a good correlation between the prompt-gamma profile and the ion range. This profile was studied as a function of the observation angle. By extrapolating our results to higher energies and realistic detection efficiencies, we showed that prompt gamma-ray measurements make it feasible to control in real time the longitudinal dose during ion therapy treatments.

Modelling radiation effects using the ab-initio based tungsten and vanadium potentials

Abstract: The Embedded Atom Model (EAM) Derlet–Nguyen–Manh–Dudarev tungsten and vanadium potentials were modified to correctly reproduce the experimentally obtained defect threshold energies. This was done by letting the interactions at short distances be dictated by the universal screened Coulomb potential. Both the repulsive part and the electron density function of the potentials were modified. The potentials were then used in collision cascade simulations and the resulting defects were compared with the corresponding defects in iron. Based on this comparison, factors affecting the outcome of a cascade were identified.

Ion beam figuring for lithography optics

Abstract: Optical lithography is the key technology used for mass manufacturing of today’s semiconductor devices. The tremendous development pressure in the semiconductor industry, both in time-to-market and in design quality is best illustrated by “Moore’s Law” [G.E. Moore, Cramming more components on electronic circuits, Electronics 38 (1965) [1] ] according to which the number of transistors that can be inexpensively placed on an integrated circuit is doubling approximately every two years. Today, state-of-the-art microprocessors are produced with smallest structures of 0.045 μm width. Picometer tolerance requirements are already reality. Since the resolution of a lithography tool is determined by the performance of the imaging optics, it is obvious that the fabrication of such high-quality optics requires tremendous efforts. The following figure requirements have to be met both for spherical and for aspherical optical surfaces used in optical lithography tools to guarantee aberration control and contrast of the imaging optics: Figure Mid-Spatial-Frequency Roughness (MSFR) High-Spatial-Frequency Roughness (HSFR) This contribution focuses on the role of the ion beam figuring (IBF) technology in manufacturing of lens elements for lithography optics. An outline on past, present and future developments will be given.

A review of transmission electron microscopes with in situ ion irradiation

Abstract: Transmission electron microscopy (TEM) with in situ ion irradiation is unique amongst experimental techniques in allowing the direct observation of the internal microstructure of materials on the nanoscale whilst they are being subjected to bombardment with energetic particles. Invaluable insights into the underlying atomistic processes at work can be gained through direct investigation of radiation induced and enhanced effects such as: phase changes and segregation; mechanical and structural changes; atomic/layer mixing and chemical disorder; compositional changes; chemical reactions; grain growth and shrinkage; precipitation and dissolution; defect/bubble formation, growth, motion, coalescence, removal and destruction; ionisation; diffusion; and collision cascades. The experimental results obtained can be used to validate the predictions of computational models which in turn can elucidate the mechanisms behind the phenomena seen in the microscope. It is 50 years since the first TEM observations of in situ ion irradiation were made by D.W. Pashley, A.E.B. Presland and J.W. Menter at the Tube Investment Laboratories in Cambridge, United Kingdom and 40 years since the first interfacing of an ion beam system with a TEM by P.A. Thackery, R.S. Nelson and H.C. Sansom at the Atomic Energy Research Establishment at Harwell, United Kingdom. In that time the field has grown with references in the literature to around thirty examples of such facilities. This paper gives an overview of the importance of the technique, especially with regard to the current challenges faced in understanding radiation damage in nuclear environments; a description of some of the important construction elements and design considerations of TEMs with in situ ion irradiation; a brief history of the development of this type of instrument; a summary of the facilities built around the world over the last half century; and finally a focus on the instruments in operation today.

Theoretical and experimental investigations of electron emission in C6+ + H2O collisions

Abstract: Theoretical differential and total cross sections for the direct ionization process of water vapour by 6 MeV/u C6+ ions are compared to new experimental measurements performed by the dedicated apparatus already used for measuring the energy and angular distributions of secondary electrons emitted from water vapour by fast heavy-ion impact [D. Ohsawa, H. Kawauchi, M. Hirabayashi, Y. Okada, T. Homma, A. Higashi, S. Amano, Y. Hashimoto, F. Soga, Y. Sato, Nucl. Instr. and Meth. B 227 (2005) 431]. In the present work, ab initio calculations have been carried out in the first Born approximation by using an accurate molecular wave function for describing the initial bound state of the target. The calculated cross sections exhibit good agreement with the present experimental measurements and compare relatively well to the existing semi-empirical results over the entire angular and energy ranges investigated here. Free from any adjustable parameter, the proposed theoretical approach describes in detail the complete kinematics of the water molecule ionization process by highly energetic carbon ions, and could therefore be easily used for modelling the heavy charged-particle transport in the biological matter.

Radiation damage in ZnO ion implanted at 15 K

Abstract: Commercial O-face (0 0 0 1) ZnO single crystals were implanted with 200 keV Ar ions. The ion fluences applied cover a wide range from 5 × 10 11 to 7 × 10 16 cm −2 . The implantation and the subsequent damage analysis by Rutherford backscattering spectrometry (RBS) in channelling geometry were performed in a special target chamber at 15 K without changing the target temperature of the sample. To analyse the measured channelling spectra the computer code DICADA was used to calculate the relative concentration of displaced lattice atoms. Four stages of the damage evolution can be identified. At low ion fluences up to about 2 × 10 13 cm −2 the defect concentration increases nearly linearly with rising fluence (stage I). There are strong indications that only point defects are produced, the absolute concentration of which is reasonably given by SRIM calculations using displacement energies of E d (Zn) = 65 eV and E d (O) = 50 eV. In a second stage the defect concentration remains almost constant at a value of about 0.02, which can be interpreted by a balance between production and recombination of point defects. For ion fluences around 5 × 10 15 cm −2 a second significant increase of the defect concentration is observed (stage III). Within stage IV at fluences above 10 16 cm −2 the defect concentration tends again to saturate at a level of about 0.5 which is well below amorphisation. Within stages III and IV the damage formation is strongly governed by the implanted ions and it is appropriate to conclude that the damage consists of a mixture of point defects and dislocation loops.

Determination of mass attenuation coefficients, effective atomic and electron numbers for Cr, Fe and Ni alloys at different energies

Abstract: The total mass attenuation coefficients ( μ m ), for Cr, Fe, Ni and Fe x Ni 1− x ( x = 0.8, 0.7, 0.6, 0.5, 0.4, 0.3 and 0.2), Fe x Cr y Ni 1−( x + y ) ( x = 0.7, y = 0.1; x = 0.5, y = 0.2; x = 0.4, y = 0.3; x = 0.3, y = 0.3; x = 0.2, y = 0.2 and x = 0.1, y = 0.2) and Ni x Cr 1− x ( x = 0.8, 0.6, 0.5, 0.4 and 0.2) alloys were measured at 22.1, 25.0, 59.5 and 88.0 keV photon energies. The samples were irradiated with 10 mCi Cd-109 and 100 mCi Am-241 radioactive point source using transmission arrangement. The γ- and X-rays were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. Total atomic and electronic cross-sections ( σ t and σ e ), effective atomic and electron numbers ( Z eff and N eff ) were determined experimentally and theoretically using the obtained mass attenuation coefficients for investigated 3d alloys. The theoretical mass attenuation coefficients of each alloy were estimated using mixture rule. The experimental values were compared with the calculated values for all samples.

Transmission of 4.5 keV Ar9+ ions through a single glass macro-capillary

Abstract: We present experimental studies of the transmission of slow 4.5 keV Ar 9 + ions through a single cylindrical-shaped glass capillary of macroscopic dimension with large aspect ratio. We show that an electric guiding field can also build-up inside a macro-scale single capillary, and thereby slow highly charged ions can be transmitted through the macro-capillary, keeping their initial charge state in a similar manner as for the case of nano-capillaries. Our results clearly indicate the existence of the guiding effect even in the case of large tilt angles.

Positron simulations of defects in tungsten containing hydrogen and helium

Abstract: An understanding of the behavior of defects containing hydrogen or helium in tungsten is an important issue. Here the properties of defects in tungsten containing hydrogen or helium atoms have been investigated by model positron lifetime quantum-mechanical simulations. The electron and positron wave functions have been obtained in the local density approximation to the two-component density-functional theory. The calculated values of the positron lifetime correlate with the magnitude of the electron density. The vacancy-clusters without hydrogen or helium are active positron traps. The lattice relaxation of atoms around vacancy reduces the effective vacancy volume and decrease the positron lifetime at a vacancy. The hydrogen and helium atoms are trapped in tungsten by lattice vacancies and nano-voids. It was established that positron lifetime depends on the density of gas atoms inside the nano-void. Hydrogen and helium presence in the larger nano-voids considerably decrease the positron lifetime.

Mechanisms of damage formation in semiconductors

Abstract: The damage accumulation in ion-implanted semiconductors is analysed using Rutherford backscattering spectrometry (RBS). When energetic ions are implanted in a material, they transfer their energy mainly into atomic collision processes (nuclear energy loss) and in electronic excitations (electronic energy loss). For a given material this primary energy deposition is determined by the mass and energy of the implanted ions and the ion fluence (number of ions per unit area). However, the damage concentration which is measured after implantation does not only depend on the primary energy deposition, but is strongly influenced by secondary effects like defect annealing and defect transformation. For the latter processes the target temperature and the ion flux (number of ions per unit area and time) play an important role. In this presentation the influence of the various parameters mentioned above on the damage accumulation is demonstrated for various materials. Simple empirical models are applied to get information about the processes occurring and to systematize the results for the various semiconductors.

Radiation effects on PbO–Al2O3–B2O3–SiO2 glasses by FTIR spectroscopy

Abstract: The infrared absorption spectra of PbO–Al2O3–B2O3–SiO2 glasses have been measured in the spectral range 600–4000 cm−1 before and after absorbed dose of 50 Gy, 4 kGy and 50 kGy to investigate the structural change due to irradiation The structural change due to composition has also been discussed The experimental results clearly indicate that after irradiation, a significant change in structure of lead alumino borosilicate glass network is observed It was shown that BO4 groups decreases and BO3 groups increases with the increase of Al2O3

Elemental analysis of edible grains by micro-PIXE: Common buckwheat case study

Abstract: The aim of this study was the adaptation of the micro-PIXE method for analysis of nutritionally relevant heavy elements in different tissues of the grain of common buckwheat (Fagopyrum esculentum), as a representative nutritionally interesting grain food source. At 57% of the buckwheat grain biomass, the endosperm was a modest nutrient source when compared to the cotyledons, at 17% of the biomass. These latter contained high concentrations of trace elements, representing 91% of the total grain Zn, 87% for P, 70% for S, 62% for Mg, 60% for K, 54% for Cu, 53% for Mn and 35% for Fe. The husk provided storage for 85% of the total Ca, 84% for Al, 83% for Si, 76% for Cl, 69% for Ti and 46% for Fe. Knowledge on these preferential elemental constitutions of the different grain tissues makes the possibility of designing target products with nutritionally optimal constitution more feasible. These data represent a basis for a more targeted approach to nutritional improvement of grains intended for human consumption.

Dual chamber laser ion source at LISOL

Abstract: A new type of gas cell for the resonance ionization laser ion source at the Leuven Isotope Separator On Line (LISOL) has been developed and tested under off-line and on-line conditions Two-step selective laser ionization is applied to produce purified beams of radioactive isotopes The selectivity of the ion source has been increased by more than one order of magnitude by separation of the stopping and laser ionization regions This allows the use of electrical fields for further ion purification

Cytocompatibility of Ar+ plasma treated and Au nanoparticle-grafted PE

Abstract: Polyethylene (PE) was irradiated with inert Ar plasma, and the chemically active PE surface was grafted with Au nanoparticles. The composition and the structure of the modified PE surface were studied using X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy (RBS). Changes in the surface wettability were determined from the contact angle measured in a reflection goniometer. The changes in the surface roughness and morphology were followed by atomic force microscopy (AFM). The modified PE samples were seeded with rat vascular smooth muscle cells (VSMC) or mouse NIH 3T3 fibroblasts, and their adhesion and proliferation were studied. We found that plasma discharge and Au grafting lead to dramatic changes in the surface morphology and roughness of PE. The Au nanoparticles were found not only on the sample surface, but also in the sample interior up to the depth of about 100 nm. In addition, plasma modification of the PE surface, followed with grafting Au-nanoparticles, significantly increased the attractiveness of the PE surface for the adhesion and growth of VSMC, and particularly for mouse embryonic 3T3 fibroblasts.

Excitation functions for production of medically relevant radioisotopes in deuteron irradiations of Pr and Tm targets

Abstract: Activation cross sections of deuteron induced reaction on monoisotopic Tm (169Tm) and Pr (141Pr) were measured by stacked foil experiments. First measurements are presented for direct or cumulative production of 141Nd, 140Nd, 139mNd, 142Pr, 139Ce, 137mCe and 140La. Thick target yields and practical batch activity are derived from the fitted excitation curves for the medically relevant 140Nd and 139Pr (as decay product of 139mNd). For reactions on Tm targets previous published results up to 20 MeV are extended and confirmed up to 40 MeV for 169Yb, 167,168Tm while high energy values are presented for the first time for 166Yb. Values for the thick target yield (TTY) of 169Yb production are derived and the discussion of different production routes is in agreement with previous published results. A comparison of experimental values with different model codes shows that the upgraded versions of the ALICE and EMPIRE codes can give a better description of (d,pxn) reaction than older ones.

Characterization of some plant extracts by GC-MS

Abstract: Different types of herbs often used in pharmaceutical, cosmetic and food industry were extracted and then analyzed by gas chromatography and gas chromatography–mass spectrometry. The method validation parameters showed good linearity, precision and recovery for a standard mixture. Herbs from different zones of Romania were studied: melissa (Melissa officinalis), nettle (Urtica dioica, Lamium album), camomile (Matricaria chamomilla). The study was applied for fingerprint chromatograms to characterize the flavors extracted from herb plants of different sources. The identity and quantity of the measured active compounds was correlated with the expected therapeutic effects. The active principles content was determined for the same herb, and different amounts of the active principles were determined for plants of different origin.

Behavior of tungsten with exposure to deuterium plasmas

Abstract: Four kinds of tungsten (W) materials, i.e. (1) foil of 50 μm thick (f-W), (2) polycrystalline (Pc-W) with grain size of ∼3 μm, (3) recrystallized (Re-W) with grain size of ∼50 μm and (4) vacuum plasma spraying (VPS-W) coatings, were irradiated employing linear plasma generators, with fluxes ⩾1 × 10 22 D/m 2 /s and energies ⩽100 eV/D. Scanning electron microscopy (SEM) was used to observe blister formation at the surfaces. The SEM surface morphology and cross section observation indicates that blister formation is related to the microstructure and surface state of different material grades. Results of trapping and deuterium retention measured by thermal desorption spectroscopy (TDS) and nuclear reaction analysis (NRA) show also a close correlation between the retention and the microstructure and surface state.

Convolution approximation for the energy loss, ionization probability and straggling of fast ions

Abstract: In this work we describe an extension of the convolution approximation for the ionization probability and energy-loss straggling as a function of the impact parameter for swift ions. Analytical formulas for these quantities are derived and compared to full first-order Born calculations. The physical inputs of the model are the electron density and oscillators strengths of the target as well as the screening function of the projectile (in the case of dressed ions). A very good agreement is obtained for all impact parameters. In addition, we propose a general schema to add contributions from distant and close collisions. In this way physical processes arising from large and small impact parameters can be easily included into a single expression valid for all impact parameters. This model is then used to investigate the projectile-charge q dependence of ionization, stopping and straggling cross-sections.

Behavior of crystalline silicon under huge electronic excitations: A transient thermal spike description

Abstract: Recent experimental works devoted to the phenomena of mixing observed at metallic multilayers Ni/Si irradiated by swift heavy ions irradiations make it necessary to revisit the insensibility of crystalline Si under huge electronic excitations. Knowing that Ni is an insensitive material, such observed mixing would exist only if Si is a sensitive material. In order to extend the study of swift heavy ion effects to semiconductor materials, the experimental results obtained in bulk silicon have been analyzed within the framework of the inelastic thermal spike model. Provided the quenching of a boiling ( or vapor) phase is taken as the criterion of amorphization, the calculations with an electron-phonon coupling constant g(300 K) = 1.8 x 10(12) W/cm(3)/K and an electronic diffusivity D-e(300 K) = 80 cm(2)/s nicely reproduce the size of observed amorphous tracks as well as the electronic energy loss threshold value for their creation, assuming that they result from the quenching of the appearance of a boiling phase along the ion path. Using these parameters for Si in the case of a Ni/Si multilayer, the mixing observed experimentally can be well simulated by the inelastic thermal spike model extended to multilayers, assuming that this occurs in the molten phase created at the Ni interface by energy transfer from Si. (C) 2009 Elsevier B. V. All rights reserved.

Ion-irradiation-induced damage of steels characterized by means of nanoindentation

Abstract: Self-ion irradiation was used to simulate the damage caused by fast neutrons in the austenitic stainless steel SS 304 SA, the ferritic/martensitic steel Eurofer’97 and a Fe–9 at.%Cr model alloy. The irradiation-induced hardness change in the damage layer was evaluated by means of nanoindentation. Three-step irradiations were performed at room temperature and 300 °C up to 1 and 10 dpa. An irradiation-induced hardness change was shown for all materials. No influence of irradiation temperature could be resolved. Irradiation-induced hardening exhibits different fluence dependencies in Eurofer’97 and Fe–9 at.%Cr. While the data indicate a saturation-like behaviour for Fe–9 at.%Cr, an increase of hardness with fluence up to 10 dpa was found for Eurofer’97.

Effects of ion irradiation in metallic glasses

Abstract: Application of metallic glasses as structural materials has been limited by their poor ductility. To overcome brittle failure, nanocrystals are intentionally introduced to stabilize the glasses. In this study, we report on the application of ion irradiation to induce nanocrystalization in a Cu50Zr45Ti5 (CZT) alloy. Transmission electron microcopy, microindentation and nanoindentation have been used to characterize the CZT alloy irradiated with 140 keV He ions at room temperature. Hardness enhancement was observed near the projected range of the He ions, coinciding with the formation of nanocrystals. Such microstructural changes, however, were not observed in the near surface region, where the electronic stopping process is dominant.

Electron inelastic mean free paths in biological matter based on dielectric theory and local-field corrections

Abstract: The inelastic mean free path (IMFP) of electrons with energies up to a few keV is calculated from the dielectric electron-gas theory for densities corresponding to those of biological matter. The effect of the many-body local-field correction on the Lindhard dielectric response function is examined using some of the available analytical approximations to its static limit. We have tested the performance of several Hubbard-type local-field corrections along with the formula proposed by Corradini and co-workers [M. Corradini, R. Del Sole, G. Onida, M. Palumno, Phys. Rev. B 57 (1998) 14569] which is extensively used in connection with the exchange-correlation kernel of time-dependent density functional theory. It is shown that the Lindhard dielectric function provides reasonable estimates of electron IMFPs below about 50 eV, where the majority of semi-empirical dielectric calculations based on the extended-optical-data methodology fail. The use of LFC results in a sizeable reduction of the IMFP which, at low energies, may reach ∼20%.

Calculated depth-dose distributions for H + and He + beams in liquid water

Abstract: We have calculated the dose distribution delivered by proton and helium beams in liquid water as a function of the target-depth, for incident energies in the range 0.5–10 MeV/u. The motion of the projectiles through the stopping medium is simulated by a code that combines Monte Carlo and a finite differences algorithm to consider the electronic stopping power, evaluated in the dielectric framework, and the multiple nuclear scattering with the target nuclei. Changes in projectile charge-state are taken into account dynamically as it moves through the target. We use the MELF–GOS model to describe the energy loss function of liquid water, obtaining a value of 79.4 eV for its mean excitation energy. Our calculated stopping powers and depth-dose distributions are compared with those obtained using other methods to describe the energy loss function of liquid water, such as the extended Drude and the Penn models, as well as with the prediction of the SRIM code and the tables of ICRU.

Structural phase transition in ZrO2 induced by swift heavy ion irradiation at high-pressure

Abstract: Exposing pressurized crystals to GeV heavy ions reveals unexpected structural changes. Irradiated at ambient conditions, natural zirconia ( ZrO 2 ) transforms from the monoclinic structure to its tetragonal (high-temperature) phase. For this process the required fluence must exceed 5 × 10 12 ions / cm 2 for Pb and U and becomes even significantly higher for lighter ions. If samples are pressurized during irradiation using diamond anvil cells, the required fluence drops at least by one order of magnitude. The efficiency of the monoclinic to tetragonal phase transition becomes larger with increasing pressure.

A microfocus X-ray tube based on a microstructured X-ray target

Abstract: We present a novel concept to develop a microfocus X-ray tube based on a microstructured X-ray target that is irradiated with a nonfocused electron beam. X-ray emissions from the microstructured targets with various morphologies were studied using Monte-Carlo simulation code MCNP5. The calculations revealed that the microstructured targets are quite capable of minimizing the effective X-ray spot size compared with those of conventional transmission-type X-ray targets. Based on the simulation results of X-ray brightness, optimum geometric parameters were derived for the microstructured targets with different morphologies. Moreover, the stability of the microstructured target against heat loads delivered by an electron beam was also investigated under both the continuous and pulsed operation modes. From the analysis, the limitations of the maximum allowable electron beam currents for the stable operation of the X-ray targets are presented. The combination of the microstructured targets and nonfocused electron beam allows the miniaturization of a microfocus X-ray tube by eliminating the needs for massive and complex focusing devices.

Studies on effective atomic numbers, electron densities from mass attenuation coefficients in TixCo1−x and CoxCu1−x alloys

Abstract: The total mass attenuation coefficients ( μ / ρ ), for pure Ti, Co, Cu and Ti x Co 1 - x and Co x Cu 1 - x (x = 0.8, 0.7, 0.6, 0.5, 0.4, 0.3 and 0.2) alloys were measured at 22.1, 25.0, 59.5 and 88.0 keV photon energies. The samples were irradiated with 109Cd and 241Am radioactive point source using transmission arrangement. The X- and γ-rays were counted by a Si(Li) detector with resolution of 160 eV at 5.9 keV. Total atomic and electronic cross-sections ( σ t and σ e ), effective atomic numbers (Zeff) and electron densities (Nel) were determined using the obtained μ / ρ values for investigated 3d alloys. The theoretical mass attenuation coefficients were estimated using mixture rule and the experimental values of investigated parameters were compared with the calculated values.

Changes in metal nanoparticle shape and size induced by swift heavy-ion irradiation

Abstract: Changes in the shape and size of Co, Pt and Au nanoparticles induced by swift heavy-ion irradiation (SHII) have been characterized using a combination of transmission electron microscopy, small-angle X-ray scattering and X-ray absorption near-edge structure. Elemental nanoparticles of diameters 2-15 nm were first formed in amorphous SiO by ion implantation and thermal annealing and then irradiated at room temperature with 27-185 MeV Au ions as a function of fluence. Spherical nanoparticles below a minimum diameter (4-7 nm) remained spherical under SHII but progressively decreased in size as a result of dissolution into the SiO matrix. Spherical nanoparticles above the minimum diameter threshold were transformed to elongated rods aligned with the ion beamdirection. The nanorod width saturated at an electronic energy deposition dependent value, progressively increasing from 4-6 to 7-10 nm (at 5-18 keV/nm, respectively) while the nanorod length exhibited a broad distribution consistent with that of the unirradiated spherical nanoparticles. The threshold diameter for spherical nanoparticle elongation was comparable to the saturation value of nanorod width. We correlate this saturation value with the diameter of the molten track induced in amorphous SiO by SHII. In summary, changes in nanoparticle shape and size are governed to a large extent by the ion irradiation parameters.