Narrow Results

Quantitative analysis of powder sample, soil, ash and so on, which consists of rich heavy metal elements that are not decomposed easily with acid or alkali was attempted. Usually, powder sample was ground with an agate mortar, mixed with binding material cellulose and pelletized for quantitative PIXE analysis. However, the resulting pellet target is thick. Accordingly, when heavy elements are included in sample, it gives effect on PIXE spectrum. Namely, matrix effect arises on it. So firstly, a fixed quantity of molybdenum was added into sample and mixed as standard material in order to determine the concentration of the most typical element, iron included in sample. Then the mixed powder were pelletized and analyzed to determine the concentration of iron. Next, original powder sample was pushed on a backing film to make thin target, and the thin target was analyzed as internal standard of determined iron by ordinary PIXE analysis method. In the result, concentrations of major elements of powder sample were determined quantitatively.

An unknown bone was analyzed by PIXE at the Nishina Memorial Cyclotron Center. The head bone had a normal area, a rotted area and the green colored area on its surface. An extremely small amount of powder was cut from each area. Each powder sample was fixed on a backing film with a small amount of collodion liquid. The concentrations of sodium and chlorine are relatively high compared with that of other elements in all powder samples. The concentrations of copper and zinc in the colored area are higher than that in the other areas. The analytical results by PIXE agreed with other investigated results. We describe one of the applications of PIXE to archaeology field.

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.