International Journal of PIXE

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.

We developed and reported standard-free methods for various samples such as hair, nail, urine, serum, sweat, snivel, tear and saliva, and they have been confirmed to be effective for addressing global environmental issues. It is expected that analyses of beard samples give us useful information about daily changes of elemental concentration in the body in comparison with the other samples. In this work, a quantitative method for untreated beard analysis based on the standard-free method has been developed. By means of the method, it becomes possible to quantitatively analyze extremely small quantity of beard samples, which are daily taken with ordinary electric shaver. The optimum conditions of washing samples have also been examined. It is found that some elements such as potassium, calcium and chlorine are lost by washing in distilled water and it is better to wash the sample in acetone. As a result, the standard-free method for beard samples has been successfully established and good accuracy and reproducibility were achieved.

We developed and reported a standard-free method for beard (including mustache and whiskers) samples that enables us to quantitatively analyze powdered beard samples of extremely small quantity. In order to investigate intake of essential elements and also exposure to toxic elements, daily changes of elemental concentration in the body give us essential information. Firstly, we have measured dependence of elemental concentration in beard, mustache and whiskers on the collecting regions in the face. Then, daily changes of elemental concentration in the body, which reflect daily ingestion of foods and waters, have been estimated by means of quantitative analyses of beard samples. These beard samples were taken from three persons everyday over successive 7, 14 and 33 days, respectively. As a result, some elements show long-term changes and a few toxic elements such as arsenic and lead exhibit changes in a period of a few days. We have also measured daily changes of elemental concentration in urine and beard taken from the same person at the same time every half day over 10 days, and clear correlation of daily changes of the arsenic concentration between urine and beard samples was observed. It is found that the standard-free method is quite effective for beard samples of very small quantities, and that beard analyses are quite suited to studies on daily changes of elemental concentration in the human body in comparison with the other samples depending on the elements.

PIXE analysis has been performed at NMCC (Nishina Memorial Cyclotron Center) as a common utilization in Japan since 1993. In order to cope with a variety of samples, various sample-preparation methods have been developed at NMCC. In order to make uniform hair samples of large quantity, a method of powdering in liquid nitrogen was carried out. A powdered-internal-standard method was applied to the powdered hair sample thus prepared and the results were compared with those obtained by a standard- free method for untreated hairs and with those by an internal-standard method combined with the chemical ashing method. As a result, good agreement was obtained for the principal elements such as sulfur, calcium and zinc. Moreover, good reproducibility was achieved in the results obtained by repeated measurements, and it is found that uniformity of the powdered sample and the powdered- internal standard (palladium-carbon) was almost satisfactory.

Total suspended particulate (TSP) samples were collected from three areas (commercial, residential and agricultural) in and near Akita City in northern Japan, October 1996 (rice straw burning period), over three days with a one-hour sampling interval for each area. The elemental composition and particle shape of TSP samples were determined and/or observed by PIXE and a Scanning Electron Microscope (SEM) combined with Energy Dispersive X-ray (EDX) analysis. In the hourly TSP samples collected during the rice straw burning period, values of 24 elements were determined for each area, and Na, Mg, Al, Si, S, K, Ca and Fe were the major components. Comparing the arithmetic means of elemental concentrations in TSP for the rice straw burning and non-snow-clad period (May – June 1996), in the residential and agricultural areas the Si concentration in the rice straw burning period was approximately two times that in the non-snow-clad period, and K and Ca concentrations in the rice straw burning period were a little higher than those in the non-snow-clad period. In the residential and agricultural areas, change in SPM concentration and change in Si, K and Ca concentrations were in relative agreement during the hours that smoke from rice straw burning was present in the atmospheric space. With the aid of SEM- EDX analysis, many cubic particles were observed for almost all hourly TSP samples. The cubic particles were of the silicon-rich type, and their morphology was rice straw fragments or aggregation of fragments.

We have measured concentration of multi elements in vegetables on the market and a wild plant gathered around Nishina Memorial Cyclotron Center in Iwate prefecture by means of PIXE. Elemental concentration in vegetables cultivated by spraying mineral-rich waters was also analyzed. As a result, it is found that the mineral-supplying vegetables abundantly contain essential elements for body such as K, Ca, Fe, Cu and Zn in comparison with ordinary ones. With regard to a wild plant, concentration of essential elements such as Ca, Cu and Zn shows no clear difference in comparison with that in commercially available one of the same kind, while that of toxic elements such as Cr and Pb is relatively higher. Moreover, it is suggested that the wild plant has a certain property of concentrating a specific element depending on its growing period. The relation between elemental concentration in the plants and that in their growing environment, such as water and soil, was also examined. It is also suggested that elemental concentration in vegetables reflects elemental constituent not only of the soil but also of the sprayed water as well as of the fertilizer.

Elemental analyses were carried out for the seabed sludge collected from Uranouchi bay (Kochi, Japan) using Particle Induced X-ray Emission (PIXE). Seabed-sludge contamination with heavy metals as well as toxic elements becomes one of the most serious environmental problems. The aim of the present study is to investigate the polluted areas in the bay by heavy and toxic elements. As a results of analyses of samples collected from eleven different places in the bay, seventeen elements including toxic ones were detected. The results suggest that the center region of the bay is seriously contaminated by heavy and toxic elements in comparison with the other areas in the bay.

We have investigated the nitrogen lattice location in MOVPE grown Ga_1-xIn_xN_yAs_1-y with x = 0.07 and y = 0.025 by means of ion beam channeling technique. In this system, the lattice constant of the Ga_1-xIn_xN_yAs_1-y film is equal to GaAs lattice. Therefore, we can grow apparently no strain, high quality and very thick GaInNAs film on GaAs substrate. The quality of the films as well as the lattice location of In and N were characterized by channeling Rutherford backscattering spectrometry and nuclear reaction analysis using 3.95 MeV He²⁺ beam. The fraction of substitutional nitrogen in the film was measured using the ¹⁴N(α,p)¹⁷O endothermic nuclear reaction. Our results indicate that more than 90% of In and N atoms are located the substitutional site, however, N atoms are slightly displaced by ~0.2 Å from the lattice site. We suggest that the GaInNAs film has a local strain or point defects around the N atoms.