International Journal of PIXE

A physical method of quantitative analysis for in-air PIXE has been established. Among the three parameters required for performing physical analysis, X-ray production cross sections were recalculated by using the effective energy of the proton beam after losing its energy through a Kapton foil and in air. Detection efficiencies of the Si(Li) detector have been determined according to our method established for in vacuum system, where effects of absorption of X-rays in air are incorporated into the detection efficiencies. As a result, it is confirmed that the present method gives us accurate results in the analyses of standard samples as well as actual samples such as soil and ash. It becomes possible to perform quantitative analysis of various samples by optimizing the measuring conditions depending on the samples.

Characteristic-line radiation from heavy metal targets bombarded by MeV proton beams has been tested as an X-ray source for dual-energy K-edge subtraction imaging for human angiography (blood vessel imaging) based on iodinated contrast media. To utilize the strong absorption by iodine (Z = 53) at its K-absorption edge (33.2 keV), we used K_α-line of La (lanthanum, Z = 57) at 33.4 keV. As a reference, also K_αX emission of Sn (tin, Z = 50) at 25.2 keV was employed. Metallic plates of La and Sn were irradiated by 7-MeV protons to produce these characteristic X-rays. Energy-subtraction method was tested using Lucite phantoms which contain aqueous solutions of KI (potassium iodide) with different concentrations. Also Ca(H₂PO₄)₂ powder was stuffed in these phantoms to simulate bones. The transmission images of the phantoms were recorded on imaging plates. During the exposure, the energy spectra of the X-rays were monitored by a CdTe detector. We found that the contrast of images of iodide solutions taken with La X-rays was higher than that with Sn X-rays. Also the energy subtraction procedure was successfully applied to reduce the graphical noise due to the bones and inhomogeneity of the soft tissue. However, to apply the present method to actual clinical use, the X-ray intensity must be increased by several orders of magnitude. Also the transmission of the “lower-energy” photons has to be a few orders higher for imaging of objects as thick as human chest.

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.

Microcapsules comprising alginate and hyaluronic acid that can be decomposed by radiation are under development. Previously, we observed that radiation efficiently decomposes microcapsules comprising alginate and hyaluronic acid in the ratio 2:1 by weight. In this study, Yttrium (Y) was added to these microcapsules to improve their decomposition by radiation.

Hyaluronic acid solutions (0.1% weight/volume) were mixed into 0.2% alginate solution, and carboplatin (0.2 mmol) was added; the resultant was used for capsule preparation. Capsules were prepared by spraying the material into mixtures of 4.34% CaCl₂ solution supplemented with Y at final concentrations from 0 to 1.0 × 10⁻²%.

These capsules were irradiated by a single dose of 0.5, 1.0, 1.5, or 2 Gy with ⁶⁰Co γ-rays. Immediately after irradiation, we observed the release of the core contents of the microcapsule using a micro Particle Induced X-ray Emission (PIXE) camera.

The mean diameter of the microcapsules was 37.3 ± 7.8 μm. Maximum content of radiation-induced release was observed for liquid-core microcapsules prepared by polymerization in a 4.34% CaCl₂ solution supplemented with 5.5 × 10⁻³% Y.

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 ant's 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 ant's head.

Eighty-nine wild birds were found dead in Ogata Village in northern Japan in March 2006. Eighty-eight of the birds were rooks (Corvus Frugilegus Pastinator), which are migratory birds. Since the use of rodenticide (thallium sulfide and zinc phosphide) in the area around where the birds had been found was revealed by a survey, etiological and pathological examinations including elemental analysis by means of particle induced X-ray emission (PIXE) were conducted. Elemental analysis showed high concentrations (56–365 dry-μg/g) of thallium in the lungs, gastric contents, intestines, livers and kidneys. Histopathological examination revealed vacuolar degeneration of hepatic cells and granular and/or hyaline droplet degeneration of renal tubular epithelia. The results suggest that the mass deaths were caused by thallium poisoning.

We have constructed a network system which enables one to access and analyze environmental data obtained at different and distant laboratories. As a preliminary feasibility test of the system, we studied the elements in the water of the Tesio River using PIXE and ion chromatography. Students used the data online to carry out analysis via internet. We found two factors with different features in calcium from the factor analysis. The comparison of the specific result and relevant geology information has revealed a remarkable presence of Ca²⁺ which might come from dissolution of limestone in the upper Tesio River. PIXE data gave crucial information to draw such a conclusion. The present system has been found useful in environmental education in universities, online sharing of PIXE data in particular.

This is a preliminary report for “the joint investigation between Japan and Egypt on Tutankhamun's golden mask”. This experiment was performed in the Egyptian Museum in Cairo using an XRDF (X-Ray Diffractometer equipped with x-ray Fluorescence spectrometer) setup invented by one of the authors (M. U.) and improved here. A diffraction pattern and a fluorescence spectrum can be obtained by the XRDF setup in the air from one and the same small area (1–2 mm in diameter) on a specimen.

The face and neck, and the other parts of the Tutankhamun's golden mask were composed of 23.2–23.5 K matrix covered with an 18 K Au-Ag-Cu thin layer, whitish gold in color, and with a 22.5 K Au-Ag-Cu thin layer, gold in color, respectively.

A dark blue material used for the nemes (headdress) was characterized with a new kind of glass paste which includ main components of Amarna blue and Egyptian blue, and is named here as Tutankhamun blue. A grayish blue material used for a false beard had a similar chemical composition to the dark blue one. Pectoral red and green beads were made of carnelian and amazonite, respectively.

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 Sendai's 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.