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As a part of research project for food risk assesment in Asian countries, we have collected a variety of samples including dairy products from Mongolia for PIXE analysis. However, some kinds of milk products or fats such as butter, margarine, mayonnaise and cream are often hard to be homogenized with internal standards because of their viscosity and oiliness, which makes their sample preparation a tiresome work. We have tried to develop efficient preparation and measurement methods for in-air PIXE analysis of those samples. For butter and margarine, liquid internal standard method was taken after melting them with water bath. Pasty samples like mayonnaise and cream were mixed with liquid standard in agate mortar. The applicability of these methods was examined by checking homogeneity of so prepared samples on the basis of Ca concentration. Along with the internal standard methods, a standard-free method has also been worked out for those fatty samples. The obtained results have been fairly satisfactory and we have applied the methods to the Mongolian dairy samples.

Since the Great East Japan Earthquake on 11 March 2011, we have seen a rapid increase of requests for soil analysis by PIXE. In the Nishina Memorial Cyclotron Center (NMCC), a powdered internal standard method with palladium on carbon powder has been adopted for soil sample preparation. However, the method can be heavily laborious when many samples need to be handled in a limited time. Here, we report an alternative to the method which takes a standard in the liquid form with a few drops of acetone to be homogenized with soil sample in an agate mortar. The applicability of the moist method was examined using some standard reference materials by comparing the analyzed results with those from the conventional method and with the certified values. The results were generally satisfactory, although further examination is needed to improve the accuracy and reliability of the new method.

Internal Standard Method, which has been widely used for quantitative analysis of general bio-samples, requires certain skill in sample preparation since it sometimes accompanies a noticeable error due not only to inaccuracy of weight measurement both of a sample and of an internal standard but also to nonuniformity of the internal standard in the target. In this work, a standard-free method of quantitative analysis, based on the fact that the total yield of continuous x-rays from the sample approximately corresponds to effective weight of the sample, has been developed and applied to some typical bio-samples (NIST Bovine liver, a rat liver and a human serum). As a result, values of concentration obtained by the present method present good agreement with those obtained by the internal standard method. Further, in a case where target preparation is performed by unskilled person, the present method gives better results than those obtained by the internal standard method. It is also found that this method is applicable to almost all soft-tissue samples and, moreover, to targets prepared by a different method.

A metal-preconcentration procedure, which consists of a combination of chelation by dibenzyldithiocarbamate ions with subsequent condensation into dibenzylidene-D-sorbitol gels, has been reformed by using Zr as an internal standard. The colloidal gels formed in solutions were collected on a nuclepore filter for direct irradiation by 3 MeV proton beams in a system of vertical beam type in-air PIXE. The methodology was tested for simultaneous determination of the concentrations of seven metals (Fe, Co, Ni, Cu, Cd, Hg, Pb) in 25 ml of an aqueous sample. A good linear relationship was obtained between the nominal concentration and the elemental X-ray yields normalized with Zr-K_α ones. Absolute values of concentration in the sample solutions can be determined with an experimental error less than ±14 % in the 5-100 ppb range by employing published data pertinent to the inner shell ionization and subsequent X-ray emission of the heavy metals.

The purpose of this study is to analyze quantitatively trace elements in human organs without decomposing samples. A palladium thin layer was deposited onto a sample on carbon adhesive tape using a metal ion sputtering equipment. The Pd film was used as an internal standard to determine concentrations of trace elements in human liver. Bovine Liver was applied as the reference standard. Five elements Cu, Zn, Mn, Se and Fe were measured by this method. The values of Copper, Zinc and iron concentrations determined by PIXE using this method agree well with those by ICP-AES. It can he asserted that this method is quite useful in the study of non-destructive PIXE analysis.

A method of quantitative analysis which is capable of analyzing powdered samples consisting of high-Z elements, such as ash, soil and aerosol, is developed. It is confirmed that an internal standard method using a powdered internal standard, which has almost the same particle size as that of a sample, gives quantitative values of concentration with satisfactory accuracy and reproducibility. It was successfully applied to standard samples such as NIST-Urban particulate matter (1648), GBW-Tibet soil (08302), BCR-City waste incineration ash (0497) and also to a practical fly-ash sample. As a result, it is found that the effect of self-absorption in the target is not negligible even for samples whose particle size is less than 4 μm, and a method of correcting it is established. Firstly, the effective thickness for self-absorption is estimated by comparing peak yields of a certain element for two measuring conditions of beam irradiation from the surface and from the back of the target. The correction factors can be estimated by using the effective thickness, values of concentration of principal elements and their photon absorption cross sections. For practical samples whose compositions are unknown, it is confirmed that accurate correction coefficients can be derived by carrying out an iterative calculation until a self-consistent solution between values of concentration of the main constituents and the correction factors is obtained.

Availability of a powdered internal standard method developed in the previous report has been investigated in detail for geological, mineralogical, environmental and biological samples. It is found that this method is effective for various powdered samples composed of high-Z elements. A computer program for correcting self-absorption of x-rays, which is based on the method we previously reported, was developed and it has been applied to soil samples of varied thickness. As a result, it is found that the method is quite effective even for a pretty thick target where particles overlap with each other. Moreover, the method was applied to several rock samples, which were prepared by grinding and consist of particles of divergent size, and found to be applicable. Lastly, the powdered internal standard method was applied to a biological sample and found to be almost satisfactory, too. These results demonstrate the availability of the powdered internal standard method combined with the method of x-ray-absorption correction for samples in many research fields.