Narrow Results

In PIXE analysis system and Tandem Accelerator facility (PASTA) of NIRS, we are using Scanning Transmission Ion Microscopy (STIM) method and solid track detector to diagnose the spatial resolution of scanning microbeam PIXE analysis system. These methods are widely used by many microbeam facilities.

A microbeam analysis system has been developed at Tohoku University for biological applications. Spatial resolution of less than 1 μm has been achieved with a beam current of ~40 pA. In microbeam analysis of biological specimens, simultaneous measurement of structural and elemental properties is very important. Our system is applicable to simultaneous in-air/vacuum PIXE, RBS and STIM analyses. Typical results of biological application are shown.

A microbeam system has been developed for the analysis of single aerosol particles. Combination of PIXE, RBS and off-axis STIM methods enabled simultaneous analysis for hydrogen to metal elements. Aerosol particles were collected on thin polycarbonate film (~0.3 μm) resulting in good signal-to-noise ratio. Quantitative elemental correlation was measured for single aerosol particles. A total of 270 particles were analyzed and clustered into 4 groups. The analysis system reveals the chemical composition of aerosol particles and is a powerful tool for source identification.

A program was started to create a new medical scientific field, which involves radiation oncology and nuclear medicine, utilizing advanced accelerator and ion beam technology. An in-air micro-PIXE analyzer system, which is among the most important technical aspects of the program, was upgraded to improve the accuracy of elemental mapping for samples with thickness variation in the scope of microbeam scanning. In order to address important bio-medical problems in cancer, the intracellular dynamics of trace elements according to the development mechanism of diseases were studied using this system. This paper outlines the program, showing correction of micro-PIXE elemental map by STIM analysis and the preliminary application results.

We developed a new microbeam scanning system for efficient local area analyses and also for micro fabrication. The system accomplished a pattern-to-pattern spacing procedure, in which the microbeam was just scanned with a corresponding pattern of the analyzing sample area or of the fabrication form. Between the patterns, the beam was moved with the fastest responsive scanning speed. In order to set patterns of the analyzing sample in the scanning system, an image of the sample was previously obtained with a scanning transmission ion microscopy (STIM). As the result, analyzing time was greatly reduced for the cell sample in which cells are not distributed all over. To demonstrate the scanning system for micro fabrication, such as proton beam writing (PBW). Patterns which were translated from bitmap data including color scale were inscribed on thin films.

Particulate matter (PM) such as chromium compound (PbCrO₄) is highly cytotoxic and carcinogenic. Several hexavalent chromium, compounds, Cr (VI), compounds are known to generate hydroxyl radical with in the cell and contribute to tissue damage. The way that theses compounds interact with human bodies at a cellular level is still unknown. To investigate the intracellular mechanism of chromium compounds, the 3D imaging techniques at the micro level are needed. In this paper, we report on the improvement of the PIXE-µ-CT system which was developed at Tohoku University and measured intracellular distribution images of PbCrO_4.particles on human lung cell.

Wall thinning of piping made of carbon steel when exposed to high temperature water flow and va-por is a common problem in all types of these plants. Oxide layer formation and dissolution should be related to the mechanism of corrosion. In order to understand the mechanism of corrosion, characterization of oxide layer including elemental concentration in the localized area is indispensable. In this study, simultaneous μ-PIXE/RBS/SEM analysis system was developed to obtain elemental characterization on oxide layer in localized area as well as to obtaining surface condition. Carbon steel samples were oxidized dynamically for 1100 hours and analyzed by the system. The oxide layer is not uniform even in the localized area of 30 × 30 μm². In the chromium content of 0.003 wt%, oxide layer thickness varied from 0.71 to 1.2 mg/cm². While accumulation of chromium is seen in the map, accumulation is not related to the iron distribution. Chromium and iron ratio in the accumulated region is more than five times higher than that of the other area. The higher chromium and iron ratio indicates that chromium migrate from substrate to oxide layer. In the chromium content of 1.01 wt%, oxide layer thickness varies from 1.4 to 3.9 mg/cm². Oxide layer is thicker than that in the chromium content of 1.01 wt%, which is opposite to the result in the static condition. Large variation of X-ray yield of iron indicates that dissolution of the oxide layer might occur during long exposure to the water flow. These results of this experiment obviously show the simultaneous μ-PIXE/RBS and SEM analysis system to be useful for better understanding of the corrosion mechanism.

Ion-Beam-Induced Luminescence (IBIL) spectra and images for the chemical states and crystal structures of micrometer-sized mineral targets were obtained by wavelength-dispersive IBIL analysis. A wavelength resolution of approximately 2 nm was achieved with a remote-controlled compact monochromator installed on an IBIL analysis system using a 3 MeV H⁺ microbeam. Several particulate mineral targets and aerosol samples were prepared on a carbon-plate sample holder that was selected to reduce the background noise and achieve a high S/N ratio in both the IBIL and Particle-Induced X-ray Emission (PIXE) analyses. The chemical composition of small targets that could not be well determined using micro-PIXE analysis was successfully visualized by the proposed IBIL analysis.

In this paper, we measured the concentrations and spatial distributions of aluminum and manganese with the growing period of a tea leaf. Both elemental concentrations increased with the growing period and showed a rapid increase between five and six months. Aluminum showed clear localization in the epidermis with the growing period. Manganese did not show clear localization like aluminum throughout the growing period. The spatial correlation between aluminum and manganese were not observed.

The microbeam system at Tohoku University has various applications. Recently higher spatial resolution down to several hundred nm and higher beam current with the resolution of several μm were required. To meet these requirements, a triplet lens system was installed. While the triplet system has higher demagnification, the chromatic aberration is much larger than in the doublet system. To achieve better performance in the triplet system, improvements in the energy resolution of the accelerator are required. Various sources of accelerator voltage ripples were investigated. The high voltage generating circuit was symmetrized and the noise components were reduced to minimize the voltage ripple. The voltage ripple of the accelerator for low-frequency components was reduced to around 70 V. The voltage ripple of the 120-kHz component was 140 V_p-p.

The microbeam system at Tohoku University was upgraded to a triplet lens system aiming at applying to the analysis of sub-micron features. The triplet lens system has a higher demagnification than the existing doublet system. However, the introduction of the triplet system also resulted in larger chromatic and spherical aberration coefficients. To overcome these problems, the energy resolution of the accelerator was improved by developing a terminal voltage stabilization system. The energy resolution of the accelerator was improved to 1 × 10⁻⁵ ΔE/E, which resulted in an increase in the brightness of the beam. The beam brightness was 2.3 pA Δ μm⁻² Δ mrad⁻² Δ MeV⁻ and was higher in the central region. The effects of the increased chromatic and spherical aberration were mitigated by restricting the divergence angle without reducing the beam current. A beam spot size of 0.6 × 0.8 μm² was obtained with a beam current of 150 pA.

Over the past 10 years, several thousand otoliths have been analyzed with PIXE (using 2.55 MeV protons) at LIBAF (Lund Ionbeam Analysis Facility, formerly LNMP Lund Nuclear Micro Probe). Over 40 elements have been identified in otoliths, many at levels suitable for PIXE analysis. Readily detectable elements in otoliths starting with Ca are: Ca (the matrix), Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Sr, Y, Zr, Mo, Cd, Sn (difficult), I, Ba (sometimes difficult), Pb (difficult). The detector system, used over this time period, is more sensitive than many other X-ray detector systems, since it consists of eight HPGE detector elements (100 mm² each), in an annular formation around the beam entrance. Using a thick absorber allows us to use quite high beam current, typically 12 nA, but sometimes up to 20 nA. This permits us to have low detection limits within short analysis times. Additionally, light stable isotope research is widespread in the sciences including ecology. Stable isotopes of N provide information about trophic level (“who eats who”), providing the opportunity to map out the switching of diets from one food type to another. Oxygen isotopes are useful as “environmental thermometers”. Currently, most of such analyses require destruction of the otolith, and nitrogen isotope analysis may require dissolving entire otoliths, thus losing all temporal information. We present new techniques using new types of detectors, double side silicon strip detector (DSSSD). The detectors, electronics and the laboratory setup are described in detail; for our analysis, a MeV proton and a deuterium microbeam at LIBAF is used. The analysis is performed immediately after the PIXE analysis, without moving the sample.

We report on the development of a high-current microbeam system for wavelength-dispersive X-ray micro particle-induced X-ray emission (WDX-$\mu$-PIXE) for chemical state mapping. The microbeam system is composed of two slits and a quadrupole doublet lens mounted on a heavy rigid support. The microbeam system is installed immediately after a switching magnet. A beam brightness of $2.4\text{pA}\cdot \mu {\text{m}}^{-2}\cdot {\text{mrad}}^{-2}\cdot {\text{MeV}}^{-1}$ is obtained at a half-divergence of 0.1 mrad. A beam current of more than 300 pA is obtained for object sizes of $40\times 10\mu {\text{m}}^2$ with a half-divergence of 0.2 mrad, which corresponds to a beam spot size of $1\times 1\mu {\text{m}}^2$. The calculated spot size of the beam was $1\times 1\mu {\text{m}}^2$ and the measured spot size was $1\times 1.5\mu {\text{m}}^2$. The WDX-$\mu$-PIXE system with the microbeam system is now operational.

We report imaging of human lung epithelial cells exposed to cobalt oxide (${Co}_3{\mathrm{O}}_4$) microparticles using three-dimensional (3D) particle-induced X-ray emission microcomputed tomography ($PIXE\mu CT$). The use of energy-selectable quasi-monochromatic low-energy X-rays generated via proton microbeam bombardment led to high-quality images. We also carried out two-dimensional (2D) micro-PIXE imaging. The 3D $PIXE\mu CT$ imaging data are complementary with 2D micro-PIXE images and the CT value ratios of the cells show that the strong absorption stems from ${Co}_3{\mathrm{O}}_4$. The 2D micro-PIXE analysis provides projection images of the elemental distribution, and this in combination with the 3D $PIXE\mu CT$ imaging revealed details of the internal distribution of ${Co}_3{\mathrm{O}}_4$, and hence provides insight into the mechanisms of ${Co}_3{\mathrm{O}}_4$ toxicity via intracellular perinuclear accumulation.

A microbeam system called MB-I was developed at the Dynamitron laboratory at Tohoku University in 2002 for use in biological applications. Although the system was designed to achieve a submicron beam spot size, parasitic field contamination from tungsten carbide slit chips and an annular Si surface barrier detector have limited the beam spot size to $\text{2}\times \text{2}\mu m^2$. By replacing these components, parasitic field contamination of the system was reduced and the performance of the microbeam system was remarkably improved. A measured beam spot size of $\text{0}\text{.4}\times \text{0}\text{.4}\mu m^2$ at a beam current of several tens of pA has been achieved. MB-I has been used for simultaneous in-air/in-vacuum particle-induced X-ray emission (PIXE), Rutherford backscattering spectroscopy (RBS), secondary electron (SE), scanning transmission ion microscopy (STIM) analyses, and three-dimensional PIXE micron computed tomography (PIXEμCT), with applications in various fields. To obtain a higher spatial resolution of several hundred nm and a higher beam current with a resolution of several μm, a triplet lens system was designed and installed in MB-I. The triplet system has a larger demagnification than the existing system; however, it also has larger chromatic and spherical aberration coefficients. Therefore, stricter requirements are imposed on the accelerator performance, particularly the beam brightness and energy stability. In addition to the microbeam, the Dynamitron accelerator was also upgraded to obtain a higher beam brightness. The beam brightness is $2.3\text{pA}\cdot \mu \text{m}{}^{-2}\cdot \text{mrad}{}^{-2}\cdot \text{MeV}{}^{-1}$, with a half-divergence of 0.07 mrad. The energy resolution of the accelerator was improved by developing a terminal voltage stabilization system (TVSS), to achieve an energy resolution of $\text{1}\times {10}^{-5}\Delta E/E$. Thus, the effects of the increased chromatic and spherical aberration were mitigated by restricting the divergence angle, without reducing the beam current. A beam spot size of $\text{0}\text{.6}\times \text{0}\text{.8}\mu m^2$ was obtained with a beam current of 150 pA. While the analysis system of MB-I can be used for simultaneous in-air/vacuum PIXE, RBS and STIM analyses, as well as 3D PIXEμCT, without changing the target chamber, changes are required in the experimental setup for these techniques, which is time-consuming, Thus, a new microbeam system, MB-II, was developed. The MB-II is a doublet system and is not equipped with a high-resolution energy analysis system. It is connected to a switching magnet. The beam brightness is $2.4\text{pA}\cdot \mu \text{m}{}^{-2}\cdot \text{mrad}{}^{-2}\cdot \text{MeV}{}^{-1}$ at a half-divergence of 0.1 mrad and this does not decrease as the beam divergence increases. This property is matched to obtain a higher beam current using the doublet system. With a current of 300 pA, the MB-II provides a higher beam current for a $\text{1}\times \text{1}\text{.5}\mu m^2$ beam spot size than is achievable with the MB-I. At present, both microbeam systems are in routine operation at the Dynamitron laboratory.

A microbeam system at the Wakasa Wan Energy Research Center is presented. A magnetic quadrupole doublet is used for the focusing of ion beams from a 5 MV tandem accelerator. Micro-PIXE and micro-PIGE measurements both in the vacuum and air are applicable with this system. Examples of the measurements for tooth and tea leaves are also presented.

We developed a terminal voltage stabilization system (TVSS) to improve the high-voltage properties of the Dynamitron accelerator in microbeam experiments. However, a voltage deviation of ca. 1 Hz increased gradually over time because of power variation in the oscillation tube. The deviation was caused by feedback phase delay and the low sensitivity of the generating voltage meter (GVM). By optimizing the feedback parameters, the voltage deviation was greatly reduced, even when old oscillation tubes were used. The optimum parameters were strongly dependent on tube conditions. By combining gain-adjustable proportional-integral (PI) and proportional (P) circuits in the feedback system, the parameters can be changed, even during accelerator operation, and remain adjustable over a long period. The low sensitivity of the GVM prohibits voltage regulation at $<$100 V. We developed a slit feedback system to compensate for this weakness. The voltage ripple became ca. $20{\mathrm{\text{V}}}_{pp}$ at $<$1 Hz even using old oscillation tubes. Although the ripple $>$1 Hz was difficult to validate because of vibration of the high-voltage terminal, the ripple at $<$10 Hz was greatly reduced with use of this mode. The modified TVSS is now used routinely during microbeam experiments.

Scanning nuclear microprobes using Rutherford backscattering (RBS) and particle-induced X-ray emission (PIXE) with light ions have been formed using variable objective slits and a magnetic quadrupole doublet. Beam optics, focusing techniques, factors limiting the minimum beam-spot size, and data acquisition systems are discussed. Two- and three-dimensional RBS mapping and channeling contrast mapping of processed semiconductor layers such as multilayered wiring and focused ion-implanted layers are demonstrated. Problems with microbeam analysis such as radiation damages due to the probe beams are discussed.

Human nails were analyzed by PIXE measurements using focused 3MeV Si²⁺ and 2MeV proton beams. It was found that the 3MeV Si²⁺ ions have a higher sensitivity for sodium and aluminium, on the other hand, 2MeV protons have a higher sensitivity for sulfur, potassium and calcium in nails. By using 3MeV Si²⁺ microprobe, it was observed that the sodium is distributed uniformly with some depletion areas and that aluminium segregates in grains. It shows an advantage of a heavy ion microprobe over a proton microprobe.

A external microbeam system using polyimide windows has been developed for PIXE (Particle Induced X-ray Emission) analysis in air. A beamline consists of a magnetic quadrupole-doublet lens, cylindrical objective slits and double-deflection scanning coils. Polyimide films with a thickness of 3.5 μm or 7.5 μm were used for the exit windows. Spot sizes in air were measured by beam-induced fluorescence of CsI scintillation plates. A minimum spot size obtained was about 10 μm for a 1.5 MeV proton beam. PIXE-mapping images of a Cu grid were successfully obtained in air.