Narrow Results

To confirm the quantitative accuracy of PIXE analysis instruments, we measured NIST SRM air particles on filter media using different types of PIXE analysis instrument: in-air micro-PIXE, in-air PIXE, in-vacuum PIXE, and in-vacuum micro-PIXE. Then, we compared the measured values with certified values and reference values of NIST SRM. We found that the quantitative values of the NIST SRM filter media measured with each PIXE instrument were within 90% to 110% of the NIST-certified and reference values for most elements. In particular, the quantitative values of major elements ranged from 90% to 110% for the in-air PIXE (Kyoto University), the in-vacuum PIXE, and the in-vacuum micro-PIXE at Tohoku University, and the relative errors are also small. These results will aid in determining the quantitative values of atmospheric particles on filter samples.

Chemical shifts of Kα_1,2 line of sulfur in marine sediments were measured with in-air high-resolution PIXE in order to examine the possibility of direct speciation of sulfur in such environmental substances. Change of chemical states of sulfur along the depth in the sediments was observed. Oxidation of the sediment samples by air was also examined. Problems to be improved for exact speciation are discussed.

A narrow entrance slit was attached to an in-air high-resolution PIXE system composed of a flat analyzing crystal and a position-sensitive proportional counter. Chemical shift measurements were carried out for Si, P and S Kα_1,2 lines from various sample targets. The precision of measurements is much improved compared with that obtained by the position-sensitive crystal spectrometer system without the entrance slit. The new system equipped with the entrance slit does not require exact sample positioning. It is applicable to non-flat targets. Chemical shift measurements are also possible while moving the targets.

The feasibility of RIKEN high-resolution PIXE system for direct chemical state analysis of 3d transition elements was examined. Kβ spectra of Cr and Fe from several compounds were measured in air at atmospheric pressure using a crystal spectrometer consisting of a position-sensitive proportional counter and a curved crystal in v. Hamos geometry. Fine structures which reflect the chemical states of Cr and Fe were well recognized with the measuring time of tens minutes.

Coins are important archaeological objects and analysis of metallic compositions of coins can provide valuable information regarding coin minting, methodology, classification, provenance, art, culture and economics of the minting time. In-air Proton Induced X-ray emission (PIXE) is a good scientific method for non-destructive analysis of coins preserved in museum. Selected ten Kushana copper coins (3^rd-4^th century A. D.) from the Orissa State Museum, Bhubaneswar have been analysed, for the first time as preliminary work, by using an external beam PIXE facility at Institute of Physics. Our study reveals that copper is the main constituent of the Kushana coins, with minor/trace elements like titanium, iron, and nickel, zinc, lead and bismuth.

Determination of proton charge during in-air PIXE experiments can be hampered when analysing thick non-conductive samples. Several arrangements may be used for overcoming this problem, while in studies of historical documents a variant employing X-ray yield measurements on Ar in air is often used. At compact geometry, with a small distance from the exit foil to the sample (10 mm or less), and also with close location of the X-ray detector to the sample to increase the detector solid angle, the uncertainties in the experimental geometry directly influence the accuracy of the PIXE analysis. The factors affecting the accuracy when using Ar yields are estimated. The advantage of the other technique, measuring X-ray radiation from the exit foil, is elaborated.

In order to confirm the availability of an in-air Helium ion induced X-ray emission method for multi-elemental analysis of polytetrafluoroetylene (PTFE) filter sample containing atmospheric particles, NIST urban particulate matter (SRM 1648) collected on PTFE filter using a special small chamber was analyzed by an in-air PIXE method with Helium ions and a proton beam. In addition, we analyzed 10 elements, mixing a standard solution with different concentrations to confirm detection sensitivity of characteristic X-ray peaks. As a result, it is suggested that 1) elements that are lighter than Zn and Pb can be satisfactorily measured using the in-air Helium ion induced X-ray emission method if the amount contained in the filter sample is at least 0.1 mg/L, i.e., 15 ng/cm², 2) the in-air Helium ion induced X-ray emission method is useful as a method for quantitatively analyzing the light elements such as Mg, Al, Si, S and Cl that are important for identifying the behavior and characteristics of atmospheric particles from the PTFE filter sample containing atmospheric particles, and 3) in the case of the PTFE filter sample containing atmospheric particles, it is possible to measure elements from Mg to Pb by means of analysis using Helium ions and protons.

We originally developed a preparation method for samples of automobile engine lubricating oil (liquid sample) specifically designed for in-air particle induced X-ray emission (PIXE) analysis with Helium ions. In the developed preparation method, target samples were fixed by making the oil sample sandwiches with 1% collodion solution based ethanol. With this analytical method, elements such as Al, Si, P, S, Cl, Ca and Zn can be detected from the oil samples, while Si, P, S, Ca and Zn were the elemental components of the oil additives.

In recent years, the self-sufficiency ratio of food in Japan has gradually decreased and 60% of foods are now imported from abroad. Japanese people rely strongly upon imported food and should take care of their safety, but what is happening now is that soil pollution in country of origin grows into a serious problem and can affect imported food. Umeboshi is one of the traditional pickled food in Japan and very popular. In the case of umeboshi, more than 65% of it is imported. We analyzed imported umeboshi and domestic ones by using in-air PIXE system and submili-PIXE camera at Tohoku University. In this experiment, the concentrations of toxic heavy metals such as As, Cd, Hg and Pb were lower than standard values given by a food hygiene law. Concentrations of elements heavier than Ca show similar trend among each sample. On the other hand, lighter elements than Ca show large differences, which is related to food coloring or processing technique.

The method of quantitative analysis of oil samples in in-air PIXE has been developed on the basis of a standard-free method. The components of the continuous X-rays originated from air and backing film can be exactly subtracted using a blank spectrum after normalization by the yields of Ar K-α X-rays. The method was developed using nine oil samples including standard oils and its accuracy was confirmed by comparing the results with those obtained by the internal-standard method. Validity of the method for practical oil samples was confirmed for various kinds of oils such as engine, machine and cooking oils. It was found that the method is effective for various kinds of oils whatever elements we designate as an index element.

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.

NABESHIMA-DANTSU is the name of the first Japanese-made carpets which have been produced in the Nabeshima domain (Saga Prefecture) since the later Edo period. The NABESHIMA-DANTSU carpets have been woven from one kind of cotton, and have been dyed with various dyes and color fixatives. We analyzed pieces of the NABESHIMA-DANTSU carpets stored in the Saga Prefectural Museum and the Saga Prefectural Art Museum, by using PIXE method in order to detect dyeing methods used in them. We also analyzed dyes, color fixatives and cotton used in the traditional Japanese dyeing method. From the NABESHIMA-DANTSU carpets, small amounts of dyed and non-dyed samples were picked up and were analyzed by in-air PIXE system at Tohoku University. It was found that Fe and Cu are related to the parts dyed orange, and Al is related to the parts dyed green. The analysis of cotton dyed by the traditional Japanese method shows the similar results. It means that both colors in the NABESHIMA-DANTSU carpets were dyed by the traditional Japanese method which uses natural dyes. From literature documentation, it is considered that synthetic dyes were mainly used during the Taisho era. The present result shows that natural dyes might have been used in the Taisho era. In this research the PIXE method has proved to be very effective for the analysis of dyeing methods.

To understand the elemental characteristics of the exhaust particles from a jet aircraft, we performed an element analysis using an in-air PIXE system of the different lubrication oils of a jet engine (Mobil Jet Oil II, Mobil Jet Oil 254 and Eastman Turbo Oil 2380) and the jet fuel (JET A-1) to determine the effects on the exhaust particles. A high concentration (1,400–2,500 wt.-ppm) of P was detected from the analyzed three oil samples. The high concentration of P is probably due to the tricresyl phosphate (TCP: C${}_{21}$H${}_{21}$O₄P) contained in the oil samples. The S concentrations of the JET A-1 fuel samples with different collection dates were in the range of $<$10 to 530 wt.-ppm. These results aid in determining the component features of nanoparticles emitted from an aircraft.

Trace elements in soy sauce have been measured by means of in-air PIXE. Six kinds of trace elements were detected, such as Mn, Fe, Ni, Zn, Cu and Br. Concentrations of Mn, Fe, Zn and Br which were observed in all samples, have been determined. Bach analyzed sample contained considerable amount of Br about 160 ppm. Comparison of Br content of the imported raw materials with those of the domestic ones suggested that the large amount of Br was the residual fumigation chemicals in the imported raw materials.

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.

Trace elements in five kinds of flour which were made in Japan. America and Canada, have been measured by means of in-air PIXE. Twelve kinds of trace elements were detected, such as Cl, K, Ca, Sc, Cr, Mn, Fe, Co, Ni, Cu, Zn and Br. The concentration of these elements varied depending on the place where they were made. In order to check the target preparation procedure, two types of sample preparation have been used, such as wet ashing by nitric acid in a microwave oven and making a paste by an internal standard solution. Comparisons of the results of both samples ensures that bromine was not lost during micro-wave oven heating. Analytic fitting of PIXE spectra by a personal computer and a commercial apllication software was successfully used.

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.

Elemental composition of living cells and tissues reflects their physiological function and status. However, it has been difficult to know in-situ elemental distribution by conventional analytical methods. In-air PIXE seems suitable for surface analysis of living cells and tissues because any treatment (e.g. freeze drying, digestion) is not required before and during measurement. We applied Via (vertical-beam in-air) PIXE to surface analysis of plant roots exposed to aluminum (Al). Aluminum stress is a major factor that limits elongation of plant roots in acid soils. We previously reported decrease in atomic ratio of potassium to phosphorus (K/P ratio) of dried root-tip of alfalfa (Medicago sativa L.) under Al stress using in-vacuum PIXE. In Via PIXE, 5 to 7-minute irradiation by 3 MeV proton beams of 200 pA was sufficient to obtain X-ray spectra without drying root samples. Decrease in K/P ratio in surface cells of root-tips was observed by short-term (6-8 h) exposure of root to Al. Via PIXE is recognized as a powerful tool for in-situ surface analysis of plant material.

We have installed a new in-air PIXE system which has been connected after an existing in-vacuum PIXE course at NMCC (Nishina Memorial Cyclotron Center). Some samples which cannot be placed under a vacuum condition: A living plant and samples of engine oil were measured successfully using the in-air PIXE. The in-air PIXE system as well as the results of the experiments are described.