International Journal of PIXE

A proton microbeam system is under construction for a 2.5 MV Van de Graaff in Hiroshima University. We have prepared and tested a proto-type target chamber, a beam scanning system, a secondary electron detection system and software for scanner control and data acquisition. The minimum beam spot size obtained so far is 3.0 µm×2.7 µm (FWHM) for 2 MeV protons.

In the past two decades the utilization of dental and orthopaedic implants in reconstructive surgery has been spread widely. Most of these implants are inserted in the corrosive environment of the human body for long periods of time. The level of dissolution, release, and transport of metal ions as a result of corrosion of these materials are not fully known at present. We report the results of application of micro ion beam PIXE spectroscopy to detect release of titanium from titanium and titanium alloy implants inserted in the tibiae of rabbits for three months. It was found that titanium ions could be detected in the surrounding tissues, with high precision, as a gradient from the implant surface and in higher amounts in the bone tissue as compared with the soft tissues. It is concluded that application of micro ion beam PIXE spectroscopy for detection of metal ion release, and distribution of the released material around the implants with high special resolution and accuracy may be used to further investigate the mechanism of metal release, and the relation between surface micromorphology and corrosion resistance of the implant materials.

The construction of a new Nuclear Microprobe at the Livermore multi-user 10 MV FN tandem Laboratory has recently been completed. The facility is primarily used for PIXE, PIGE and Proton energy loss tomography (PELT) in a broad range of multi-disciplinary sciences. Details of the new facility and current applications/programs are discussed.

We investigated the elemental composition of mouse blood plasma with PIXE method. We measured quantitative X-ray yields of S, Cl, K and Ca by changing sample volume from 1.25 to 15.0 µl to find the most profitable volume of plasma for elemental analysis. Linear relationships were confirmed between the applied volume (1.25^~5.0 µl) and the counts of X-ray from each element. Some elements showed, however, saturated curves over 5.0 µl. Five μl was enough to analyze some important elements of blood plasma and used in the present analysis. We propose 5.0 µl as a standard amount of sample in plasma analysis. We found differences in the elemental ratio of X-ray counts in plasma among five mouse strains used in the present experiment. This result suggests that the strain differences in the elemental constitution of mouse blood plasma are related to those of physiological states such as the number of blood cells and the radio sensitivity.

Typical elements in PET bottled mineral water and in running water of public waterworks near by our cyclotron center was investigated by PIXE. We can detect typical elements in water sample using only a pipette. After water sample was preserved in a brown-glass vessel or a clear-glass vessel, Ba and Ti consisting in the vessels were detected in water samples. Concentration of typical elements in running water is found to be equal to that in PET bottled mineral water.

Trace elements in four kinds of soybean and three kinds of salt have been measured by means of in-air PIXE. In soybeans, which were made in Japan, America, Canada and China, six kinds of trace elements were detected, such as Mn, Fe, Ni, Cu, Zn and Br. The concentration of these elements varied depending on the place they were made. American soybean showed characteristic feature compared with other soybeans. As to the bromine concentration, American soybean contains ten times as much as Japanese one. In salts Br and Sr were detected.

In-air PIXE was used to analyze trace elements in otoliths from several species of teleost fish in order to examine the correlation between the trace elements concentrations and environmental conditions. Mn, Fe, Zn and Sr were detected accurately in the order of ppm by using the in-air PIXE. It seemed that concentrations of Sr and Zn in red sea bream otoliths increased in proportion to higher seawater temperature. In addition, there were significant differences in trace element composition between that of reared red sea bream and rockfish and that of wild ones. Preliminary results indicate that the PIXE is a powerful technique to investigate fish otoliths.

A new technique of spectrum analysis for PIXE based on the linear associative neural network has been developed. The network has high capability in the association of almost all elements across the periodic table in samples, in the quantification with wide dynamic range of the concentrations, and in the analysis speed.

The influence of Compton tail background on the PIXE detection limit is discussed in the case of human serum as an example of biological samples containing sodium element. The PIXE spectrum of the human serum for 3 MeV proton bombardment was measured with a Si(Li) x-ray detector and the Compton tail edge of 440keV γ-rays from ²³Na in the serum was observed at the x-ray energy of 278.4 keV. The spectrum of the Compton tail was measured for the 511 keV γ-rays from a ²²Na source and compared with a theoretical one. It is found that the intensity of the experimental Compton tail below 35 keV is two~three times larger than the theoretical one. Minimum detection limits for the elements of Z=35~55 in the human serum were estimated by using experimental Compton tail background.

We have constructed a vertical beam line for in situ liquid analysis. Details of this beam line, the analytical results of milk and tea, and the detection limits of this beam line for 8-MeV He⁺ ion beam are described.

Two standard samples for the PIXE calibration were prepared using the standard solution for Atomic Absorption Spectrophotometry (AAS). Both standard samples contained six elements each. The mixed and diluted AAS solutions were dropped on the non-hole Nuclepore film and dried. Standard sample B consisting of Ca, Cr, Co, Cu, Se and Sr had close agreement between the experimental and theoretical values. According to the theoretical study about the effects of thick samples on the accuracy of the PIXE analysis, the reduction of X-ray yields in the thick sample can not be neglected for the sample thicker than 100 µg/cm².

A new method has been developed to determine absorption curves which are needed to derive quantitative values in PIXE analysis. In this method two spectra obtained with absorbers of different thickness are divided by each other after background subtraction and the absorption curve can be obtained immediately. Absorption curves for a 50 and a 200 µm-thick Mylar films and that for a Cr foil of 2500 µg/cm² were determined experimentally. These curves are in good agreement with the absorption values derived from peak areas of characteristic x-rays. This method enables one to obtain absorption curves for any kind of absorber accurately and quickly.

A new method has been developed for determining detection efficiency of a Si(Li) detector, which is one of the most important quantities in PIXE analysis. In this method, targets prepared by smashing crystals of several chemical compounds into fine pieces and by sprinkling them onto a thin polypropylene film are measured in same experimental condition as in PIXE analysis, and relative efficiency curves are obtained for two Si(Li) detectors. These results are compared with those from theoretical calculations. New efficiency curves are obtained by regarding thickness of the Be window, the Si dead layer, the gold contact and ice layer as variable parameters and practical thicknesses of them are estimated. It is found that these efficiency curves give quantitatively fairly accurate values when they are used for data analysis from NIST bovine liver even in cases of Na and Mg.

The characterization of the single crystal of type 304 stainless steels was performed by using particle induced x-ray emission and Rutherford backscattering spectroscopy with channeling technique (PIXE-C and RBS-C). They proved that the solution annealing process is absolutely necessary for production of a good single crystal of stainless steels.

They are also shown that the positions of P atoms before He irradiation were mostly substitutional sites of fcc structure and that MeV He ion irradiation induced segregation of Si and S atoms to the (110) surface.