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Balance of essential elements in organisms might be changed by environmental stresses. Small teleost fish, Medaka, was burdened with X-ray irradiation (total dose: 17Gy) and salty water (70% NaCl of sea water). These stresses are not lethal dose. Essential elements in various organs in the fish were measured by PIXE method and compared with a control fish to determine the effect of two types of the burdens on the elemental contents. P, K, Ca and Br are examined in brain, eye, liver, ovary, spleen and intestine. P and K did not change their concentrations with both of the stresses. Ca concentrations increased under both stresses in the brain, eye, liver and spleen, and decreased in the intestine and ovary. Br concentrations of the organs largely changed in the case of salty water breeding. Micro-beam scanning PIXE provided elemental mapping of thin section of Medaka eye with STIM imaging.

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 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.

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.

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.

In this study, we applied ML-EM (maximum likelihood expectation maximization) iterative algorithm and STIM-CT to a three dimension imaging technique of PIXE -CT for cellular analysis using 3 MeV proton microbeam with a diameter of 1 μm at TIARA (Takasaki Ion Accelerators for Advanced Radiation Application). The algorithm had been applied to tomography such as SPECT (Single Photon Emission Computed Tomography). It is also possible and suitable to apply the algorithm to PIXE-CT because the algorithm can be used to project images taking into account errors due to rare events. Energy loss of incident particles and absorption of X-rays, however, affect quantitative values dramatically in the case of PIXE -CT. We estimated those effects from density distribution of major elements measured by STIM-CT in this work. In order to show the appropriateness of this method, X-ray yield and absorption were calculated using density distribution of two-dimensional Shepp phantom. The PIXE-CT experiments were carried out using a dried unicellulate as a test sample placed on an automatic rotation stage, which made a full turn by rotating 360° at each step of 18° in vacuum. The results of those simulation and experiments have proved that this method is effective.

During PIXE analyses of biomedical samples often great damage of the sample occurs. This damage is always combined with mass loss and strong alterations of the initial structure. The loss of mass can be explained by the loss of volatile elements, mainly the major elements Hydrogen, Carbon, Nitrogen, and Oxygen. This results in a charge dependency of the element contents and has to be corrected during the data reduction. Here we describe measurements of different samples that monitor the mass loss and the charge dependency of the trace element concentrations. A model was developed to give the correct concentrations after the PIXE analyses. Additionally first results of PIXE analyses of gum tissue are reported. They give direct hints for amalgam residues inside the tissue in pathologically altered areas.