G. Momose

MICRON-CT USING PIXE WITH MICRO-BEAMS

We developed a micron-CT consisting of micro-beam system and X-ray CCD camera (Hamamatsu photonics C8800X), whose element size is 8μm×8μm and a total number of image elements 1000×1000 gives an image size of 8mm×8mm. The sample is placed in a tube of a small diameter, which is rotated by a stepping motor. The transmission data through the sample are taken with characteristic Ti-K-X-rays (4.558 keV) produced by 3MeV proton and α particle micro-beams. After image reconstruction using an iteration method, 3D-images of small objects namely, hair and small ants were obtained with a spatial resolution of ~5μm. It is expected that our micron-CT can provide cross sectional images of in-vivo cellular samples with high resolution and can be applied to a wide range of research in biology and medicine.

Microbeam Analysis at Tohoku University for Biological Studies

A microbeam analysis system at Tohoku University has been improved in detection efficiency for application to single cell analysis. The system is applicable to STIM analysis and to simultaneous PIXE and RBS analysis. Sample preparation methods suitable for non-adhesive single cell analysis were developed and first results with the improved analysis system are shown.

MICROBEAM ANALYSIS OF SINGLE AEROSOL PARTICLES AT TOHOKU UNIVERSITY

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.

In-Vivo Elemental Analysis by PIXE-μ-CT

We have developed “micron-CT”, using micro-PIXE for in-vivo imaging. This system comprises an X-ray CCD camera (Hamamatsu photonics C8800X9) with high resolution (pixel size: 8×8μm2, number of pixels: 1000×1000) and an X-ray-point-source with a spot size of 1.5×1.5μm2 which is generated by irradiation of a microbeam on a pure metal target. Thus we can acquire projection data with high resolution. The sample is placed in a small diameter tube and is rotated by a stepping motor. The 3D images were reconstructed from the obtained projection data by using cone-beam CT reconstruction algorithm. X-ray spectra produced by heavy charged particle bombardment, exhibit a much smaller continuous background compared to electron bombardment. Therefore, X-rays produced by ion beam can be used as a monochromatic and low energy X-ray source. The feature is very effective to investigate small insects. Moreover we can get elemental distribution image of object by choosing appropriate characteristic X-rays corresponding to the absorption edge. On the other hand, the conventional X-ray CT, in which continuous X-rays are used, provides images of the electron density in the object. Using this system, we were able to get 3D images of a living ants head with 6 μm spatial resolution. By using Fe-K-X-rays (6.40 keV) and Co-K-X-rays (6.93 keV), we can investigate the 3D distribution of Mn (K-absorption edge = 6.54 keV) in an ants head.

Development of an In-air on/off Axis STIM System for Quantitative Elemental Mapping

We have developed an in-air on/off axis STIM for simultaneous density mapping with PIXE and RBS, which will be useful for damage-monitoring in cell analysis and for yield correction based on the thickness distribution of X-ray self-absorption in samples. The in-air on/off axis STIM system provides a mass concentration map in the cell analysis. In the system, a thin scattering foil is placed downstream of the sample and scattered protons are detected by a Si-PIN photodiode set at 30 degrees with respect to the beam axis. These components are set in a He-gas-filled chamber to reduce energy loss, scattering and sample damage. Using this system, areal density mapping is carried out for RBL-2H3 cells simultaneously with PIXE and RBS. Correction for self-absorption is performed and areal density map of elements is converted into a mass-concentration map using the measured matrix density. The areal density distribution of P corresponds to that of matrix and mass concentration of P is uniform in the cell region. On the other hand, Br is concentrated in the nucleus, even in the mass concentration map. The Br accumulation in the nucleus is first confirmed in mass concentration using the on/off axis STIM and PIXE system. The in-air on/off STIM system will be effective for monitoring changes in cell density during beam irradiation.

ANALYSIS OF LACQUERWARE USING IN-AIR SUBMILLI-PIXE CAMERA

Pigments used in lacquerware pieces excavated from the Edo-period stratum at the southern part of Kawauchi campus of Tohoku University are analyzed using an in-air submilli-PIXE camera. That area is located at the former secondary citadel area of Sendais Aoba Castle. The lacquerware pieces were analyzed as elemental images without sample degradation and without sample preparation. Pigments used in the red lacquer resin were cinnabar and Bengala. This analytical method, which uses images, was effective for discrimination of contaminant elements through comparison with the decoration. Results show that PIXE analysis using the in-air submilli-PIXE camera is an effective tool for use in archeological studies.

PIXE ANALYSIS OF WATER LEAKAGE FROM A LANDFILL SITE OF INDUSTRIAL WASTE GENERATING HYDROGEN SULFIDE

The aim of this study is to develop a method for monitoring water pollution caused by dissolved sulfides and other harmful elements by means of PIXE offering the advantage of multielemental nature, high sensitivity and speed of analysis for a wide variety of samples. Sulfide ions dissolved in an aqueous sample were converted to insoluble CuS compounds and then collected on a thin organic filter suitable as a backing foil for PIXE measurements. The standard method for scavenging CuS precipitate is founded on an investigation of the pH-dependence of the recovery of dissolved sulfides and the calibration curve covering the concentration range from 10 to 1000 ppb. The recovery-factor of CuS showed a maximum value at around pH 8 although it changed with the intrinsic pH of samples. The recovery factor for pH adjusted to 7.50 was kept constant in a wide concentration range of sulfide ions from 10 to 1000 ppb. The concentration of tens of ppm sulfur compound was detected in both drain water from the industrial waste disposal and in peripheral agricultural water, but the fraction of dissolved sulfide was only about 1%. The low concentration of dissolved sulfides was discussed from the viewpoint of the oxidation condition originated from the soluble and insoluble components detected in samples by PIXE analysis.

DEVELOPMENT OF MICROBEAM SCANNING SYSTEM

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.

IDENTIFICATION OF OXIDATION STATES OF TRACE-LEVEL ARSENIC IN ENVIRONMENTAL WATER SAMPLES USING PIXE

An enhanced sample preparation method for PIXE analysis is described allowing to separate and concentrate arsenic ions of different oxidation states in water samples. Arsenate ions are separated from arsenite ions by co-precipitating into 10 ppm indium hydroxide colloids that are generated at pH 4.0 in a 25 ml solution containing 1 ppm phosphate ions and 25 ppm sulfate ions. Arsenite ions are oxidized to the pentavalent state with permanganate ions and adsorbed by indium hydroxide colloids generated afterwards in solution. The standard procedure for collecting the colloids adsorbing arsenic ions on Nuclepore filter of 0.2 μm pores is based on an investigation of the pH-dependence of the recovery of dissolved arsenic ions and the obtained standard calibration curve covers the concentration range from 1 to 100 ppb for arsenic ions. The prepared targets were examined for 5 to 10 minutes by 3 MeV proton beam (0.7-4 nA beam currents). The lower detection limit of arsenic in a 25 ml aquatic sample is 0.3 ppb for the arsenic-precipitated targets based on the 3σ error of background counts integrated over the FWHM of arsenic peak in the PIXE spectrum. This sample preparation technique was then applied to analyze concentrations and oxidation states of arsenic in a river basin where hot springs are located upstream being possible sources for releasing arsenic in the river.