International Journal of PIXE

As a part of epidemiological study on the effects of the chemical composition of airborne particulate matter (PM) and ozone on asthma attacks, we carried out size-resolved sampling of PM in Himeji City, Japan and elemental and ionic composition analyses of the PM samples. Size-resolved PM was collected using a 3-stage NLAS impactor (Tokyo Dylec Co., Ltd.; particle cut size at sampling stages was 10, 2.5 and 1.0 $\mu$m for a flow rate of 3 L/min) with a 1-week sampling interval from November 2009 to May 2012. Concentrations of several elemental and ionic species in the PM samples were determined by PIXE and ion chromatography analysis, respectively. In addition, source apportionment analysis of the PM was performed by positive matrix factorization (PMF) model using the analytical data of size-resolved particles. The research results are important for the physicochemical characterization of PM in the atmosphere, enabling evaluation of various PM emission sources and atmospheric processes. Of particular note is that the PM₁₀ consisted mainly of ${NO}_3^{\mathrm{-}}$ and ${SO}_4^{2-}$, and PM_2.5 consisted only of ${SO}_4^{2-}$. This is believed to suggest the different formation processes of ${NO}_3^{\mathrm{-}}$ and ${SO}_4^{2-}$. Based on the results from the PMF model analysis, the particles larger then PM_2.5 were estimated to have been from soil and sea salt particles. On the other hand, the particles smaller than PM_2.5 were estimated to have been from soot, smoke and secondary particles. In particular, the majority of particle smaller than PM_1.0 were estimated to be secondary sulfate particles.

We used micro-PIXE to investigate the distribution of Cs and Rb in rice grains. We succeeded, for the first time, in measuring the elemental distributions in entire rice grains (with dimensions of 6.25 mm $\times$ 6.25 mm) at micrometer spatial resolution. We found that Cs and Rb accumulated in the bran and germ of the rice. The distributions of P, K, Rb and Cs were similar within the rice grain. The concentrations of Cs and Rb in the rice were proportional to those in the soil, as well as to the exposure time. The uptake of Rb was significantly larger than that of Cs. Furthermore, the behavior of Rb was similar to that of Cs in the micrometer-scale regions in plants. It follows that the distribution of Rb can be used to investigate the behavior of radioactive Cs in plants.

A lot of radiocesium had been deposited onto pastures and grasslands following Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. More radiocesium was accumulated in root-mat horizon than in both above ground plant bodies and mineral soils. In this study, factors causing higher radiocesium concentrations in root-mat horizon were evaluated by the addition of stable cesium solution and particle-induced X-ray emission (PIXE) analysis. Results suggest that adsorption onto root surfaces played a significant role in Cs accumulation in root-mat horizon. Furthermore, absorption of Cs was key to its long-term preservation. The adsorption of Cs by clay minerals also contributed to its retention. A slow water infiltration rate may also affect the enrichment of radiocesium in root-mat horizon. Based on these results, it is concluded that both biotic and abiotic factors contributed to the effective retention of radiocesium in root-mat horizons following the FDNPP accident.

The concentrations of alkali elements in Japanese green tea leaves were evaluated using particle-induced X-ray emission (PIXE) analysis combined with an internal standard method to investigate the elution of radioactive cesium into green tea using potassium and rubidium. The concentrations of potassium and rubidium of used tea leaf samples were lower than those of unused samples, whereas no significant differences in the concentrations of the other elements were observed between them. In addition, we found a similarity in the relative concentrations between potassium and rubidium although the other elements showed different aspects. These results suggest that it is possible to investigate the elution of radioactive cesium into green tea using potassium and rubidium as substitutes of cesium.

We report an elemental analysis of murine solid tumors treated with cisplatin-incorporated polymeric micelles (NC-6004) to evaluate the concentration of the drug in the tumor tissue using conventional particle-induced X-ray emission (PIXE) analysis, as well as the spatial distribution in the tumor section using sub-millimeter PIXE analysis. The results reveal that the platinum concentration in the tumor treated with NC-6004 was higher than in that treated with cisplatin, whereas no significant difference was found in platinum concentration between NC-6004 and cisplatin samples in the normal tissue. This suggests that NC-6004 can both provide therapeutic efficacy and reduce the side effects caused by conventional treatment using cisplatin. These results show that PIXE analysis is a powerful tool for research into drug delivery systems.

Development of a number of diseases like cardiovascular diseases and cancer has been related with abnormalities of certain trace elements in some tissues. The purpose of this study was to investigate the levels of trace elements in breast cancer patients in comparison with healthy controls. Particle induced X-ray emission (PIXE) technique was employed to measure the hair trace element concentrations in 30 cancer patients and 30 healthy controls. A 2.2 MeV proton beam was employed to excite the biological samples. The concentrations of Fe and Cu ($p<0.05$) in the hair of cancer patients were found to be higher compared to those of healthy controls, while the concentration of Zn ($p<0.05$) was found to be lower. No significant difference was observed for sulfur concentration between the two groups. Also, no meaningful difference was observed in the concentrations of K, Ca, Ti as well as ratios of Cu/Zn and Cu/Fe in the hair of the two groups ($p<0.05$). These abnormalities could potentially be used as a means of breast cancer screening in women.

The effects of the vascular disrupting agent AVE8062 on tumor and normal tissue samples were investigated by particle-induced X-ray emission (PIXE) analysis using quantum dots (QDs). We investigated fibrosarcoma tumors in mice, and used kidney tissue as a control. Non-targeted QDs were used to characterize the tissue regions where blood flow is interrupted by AVE8062. We found that the concentration of the QDs in the tumors and kidneys exposed to AVE8062 was lower than that of the control group. Sub-millimeter PIXE analysis (with a beam size of 0.5 $\times$ 0.5 mm²) was used to investigate the spatial distribution of QDs in the tissue samples. We found that the QDs were accumulated in localized regions of the kidney section of the AVE8062-treated group whereas the QDs were uniformly distributed in the control kidney. This suggests that AVE8062 caused blood flow interruption not only in the tumor samples but also in the normal blood vessels in the kidneys.

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.