S. Yamauchi

Improvement of the energy stability of the Tohoku Dynamitron accelerator for microbeam and nanobeam applications

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 Vp-p.

PIXE STUDY ON THE GROWTH ENVIRONMENT OF PLANTS

Growth environment of plants was investigated by analyzing the elemental concentration in leaves of the plants. Camellia was selected as the sample and the leaves of the camellias were collected from Miyagi and Chiba prefectures. The species of elements and their concentrations in the leaves were measured by the in-air PIXE system at Tohoku University. More than 10 elements were detected from the leaves. The concentrations of Mn, Fe, and Rb in the leaves were strongly affected by the place where the tree grew. On the other hand, the concentration of P, S, K, and Ca were less affected by the place of the tree. The determination of the place of the tree was also performed by evaluating the similarity of the elemental concentration in the leaves quantitatively. The difference due to the place was clearly identified and the sampling place was successfully determined by using the elemental concentrations in the leaves.

Effects of a vascular disrupting agent for cancer treatment on normal tissue evaluated by PIXE analysis using quantum dots

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 × 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.

Evaluating radiocesium retention ability of root-mat horizon using micro-PIXE analysis

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.