International Journal of PIXE

The two methods, which enable us to observe changes in concentration of heavy elements in living plants and to perform quantitative analysis of all elements heavier than aluminum in in-air PIXE with two detectors, simultaneously, were successfully applied to studies on movement of light elements in plants. It was found that light elements including silicone, phosphorus and sulfur in leaves of living plants can be quantitatively analyzed. Accuracy of the method for light elements could be confirmed by comparing the results with those obtained by an internal-standard method. It was also confirmed that changes in elemental concentration with elapsed time after starting irradiation could be observed for silicone, phosphorus, sulfur and chlorine together with heavier elements at the same time. Interesting changes in elemental concentration with elapsed time were observed for phosphorus and sulfur together with heavier elements such as potassium, calcium and manganese. Moreover, quite interesting changes of concentration of some light elements were clearly observed after supplying water-soluble manure containing phosphorus acid and potassium to the plant.

A method of quantitative elemental analysis of mosquitoes which convey serious infectious diseases, such as Japanese encephalitis and Dengue fever, has been developed in order to clarify their mode of life and sphere of action. The method was developed on the basis of a standard-free method for biological samples. The method enables us to perform quantitative analysis of untreated mosquito. Moreover, the method was successfully applied to quantitative analysis of each part of mosquito's body such as head and chest, abdomen, leg and wing. It was found that there are clear differences among parts in the body of mosquito, and also among different species such as Culex tritaeniorhynchus and Aedes albopictus. The method was successfully applied to quantitative analysis of small fly belonging to Sciaridae (Bradysia.praecox) whose size is smaller than that of mosquito. It was also confirmed that the method is applicable to other kind of bio-samples of small quantities such as a grain of egg of Alaska pollock whose dry weight is less than 100 μg.

Water and tailings from lead-mining area in Kanchanaburi, Thailand were analyzed by PIXE to study how serious the alleged pollution was. Eleven water samples were collected in the field and were sealed in the tube after the pH < 2 was attained by ultrapure nitric acid. All of the samples were transported to Nishina Memorial Cyclotron Center of Japan Radioisotope Association and analyzed by its vacuum PIXE. The result showed that the water contains up to 25 ppb Pb with an average value 12 ppb. The value is lower than the environmental norm in Thailand (0.05 mg/L) but higher than that of WHO (10 μg/L = 0.01 mg/L). Tailings contain high amount of lead. Since resumption of mining is being considered to deliver the economic expectation of local people, it should be invested in treatment or containment within storage facilities. Also discharge of treated process water should be regularly monitored by competent agencies.

The concentration and distribution of fluorine in mature leaves of Camellia sinensis were determined using micro-PIGE. The elemental concentration was measured as 2210 ± 450 ppm. Fluorine showed clear localization in the epidermis. Fluorine was distributed uniformly in the upper epidermis, suggesting that fluorine was localized in the cytoplasm. On the other hand, extremely concentrated areas of fluorine were observed in the lower epidermis.

Whether fluorine penetrated from material completely incorporates into tooth mineral is a matter of debate, although it is well known that the fluoride from material penetrates directly into tooth structures. The purpose of this study is to determine tooth-bound fluoride uptake from fluoride-containing materials using PIGE/PIXE system at the Wakasa Wan Energy Research Center. Class V cavities in buccal surfaces of eighteen extracted human teeth were drilled and filled with six fluoride-containing materials. After being stored in distilled water for one year, a longitudinal section including materials was obtained from each tooth. Fluorine and calcium distribution of specimens were evaluated using PIGE/PIXE system. After evaluation, the specimens were immersed in 10 mL of 1M KOH solution and were agitated at room temperature for 24 h to remove a KOH soluble fluoride. The specimens were washed with 200 mL distilled water and left to dry. Again, to estimate tooth-bound fluorine (KOH-insoluble fluoride) uptake, the same portion of the specimens after KOH treatment were evaluated using PIGE/PIXE system. It was confirmed that fluorine penetrated from material partly incorporated into tooth mineral. This tooth-bound fluoride have the potential to prevent dental caries after loss of the bond between the filling material and tooth structure.

We have been developing microcapsules that release anticancer drugs in response to radiation with an aim of targeted delivery and increasing the efficacy of anticancer drugs by a combination of these drugs with radiation. The aim of this study was to micronize microcapsules by adding carbonated water to the core material of microcapsules, which releases the anticancer drugs in response to radiation. The core material of microcapsules was prepared by mixing 0.1 g of hyaluronic acid and 0.2 g of alginate into 5 mL of carbonated water. The mixture was sprayed onto a 0.3 mmoL/L solution of calcium chloride (CaCl₂) and ferrous chloride (FeCl₂) using an ultrasound disintegrator. The vibration of the ultrasound disintegrator generated microbubbles in the carbonated water, which micronized the microcapsules. Intravenous injection of the micronized microcapsules to tumor-bearing mice showed that the micronized microcapsules passed more efficiently through the capillaries of lungs or kidneys, which resulted in increased delivery of microcapsules to the tumors and increased the anticancer effect.

Particle-induced X-ray emission (PIXE) analysis of Lentinula edodes mushrooms (Shiitake mushrooms) contaminated with radioactive cesium was performed to study relationships between concentrations of alkali elements in the shiitake mushroom samples and their radioactive cesium levels. The shiitake mushrooms were cultivated using radiocontaminated hard wood logs due to the nuclear power plant accident in Fukushima. The significant localization of radioactive cesium was found in the pileus region of the shiitake mushroom from autoradiographic observation. The concentrations of alkali elements in the shiitake sample were measured by PIXE analysis. The PIXE analysis has shown that the concentrations and transfer coefficients of potassium and rubidium in the pileus are much higher than the other parts of the shiitake sample as is the case of radioactive cesium. It is suggested that radioactive cesium is transferred into shiitake mushrooms in a manner similar to potassium and rubidium. The results of this work have shown the possibility to be able to use rubidium as an elemental tracer for radioactive cesium.

Perfluorinated chemicals (PFCs) have been widely used in various household products. Because of inactive C–F bond within its structure, most PFCs cannot be biologically degraded and tend to accumulate in the ecosystems once discharged into the environment through sewage effluent etc., necessitating low-cost treatment technologies for PFCs. We have worked on the electrolysis method in which PFCs in water are decomposed at moderate cost, and found that perfluorooctane sulfonate, considered to be the most recalcitrant chemical among PFCs, can be decomposed by electrolysis. The decomposition products, however, remained unknown although we used various advanced analytical techniques (mass spectrometry for analysis of organic substances in liquid and gas samples, and combustion-ion chromatography for total fluorine analysis) to identify the products. The emanation of volatile low-molecular fluorine compounds was suspected. The present report summarizes our trial to identify the unknown decomposition products by analytical instruments cited above, and the application of PIXE/PIGE analysis to track the fluorine compounds lost from the solution by concentrating the gaseous compounds in low temperature (–100°C) activated charcoal.

The microbeam system at Tohoku University was upgraded to a triplet lens system aiming at applying to the analysis of sub-micron features. The triplet lens system has a higher demagnification than the existing doublet system. However, the introduction of the triplet system also resulted in larger chromatic and spherical aberration coefficients. To overcome these problems, the energy resolution of the accelerator was improved by developing a terminal voltage stabilization system. The energy resolution of the accelerator was improved to 1 × 10⁻⁵ ΔE/E, which resulted in an increase in the brightness of the beam. The beam brightness was 2.3 pA Δ μm⁻² Δ mrad⁻² Δ MeV⁻ and was higher in the central region. The effects of the increased chromatic and spherical aberration were mitigated by restricting the divergence angle without reducing the beam current. A beam spot size of 0.6 × 0.8 μm² was obtained with a beam current of 150 pA.