International Journal of PIXE

An aluminum target was bombarded with 1.5 MeV protons and continuous x-rays were measured at the angles of 45°, 90° and 135° with respect to the beam direction. By investigating the shape of the x-ray energy spectrum, it was recognized that, the continuous x-rays below 12 keV are atomic bremsstrahlung (AB) and those of above 12 keV are nuclear bremsstrahlung (NB), and AB and NB are mingled in the energy region of around 12 keV The x-ray energy dependence of angular distributions presented well a change from the process of AB to that of NB in the continuous x-ray spectrum. Interference between AB and NB were discussed on the basis of PWBA theory. Continuous x-ray production cross sections were calculated on the basis of PWBA BEA and a semi-classical theory and compared with the experimental results. The theoretical prediction reproduced well the experimental cross sections over the wide range of 6 orders in magnitude and of 2 keV – 35 keV in the energy except for the energy region mingled with AB and NB. The ratio of the theoretical cross sections to the experimental ones showed an interference effect between AB and NB in their mingled region.

For the purpose of obtaining basic data to understand the population dynamics of the Japanese flounder, Paralichthys olivaceus, inhabiting the Sanriku coastal waters, the concentration ratios of Ca and Sr in otoliths of juvenile fishes being cultivated for releasing to the regions, and those of adult fishes captured in both the Sanriku area (Aomori, Iwate and Miyagi) and Shizuoka prefecture coastal regions (as a comparison) were analysed using a particle induced X-ray emission (PIXE) technique.

The Sr/Ca ratios of otoliths taken from juvenile Japanese flounders had significant differences between Sanriku and Shizuoka sea-farming groups. The differences in otolith Sr/Ca ratios between Sanriku and Shizuoka sea-farming stations would thus differentiate flounder populations. No significant difference in otolith Sr/Ca ratios was observed among the Sanriku group. However, the values for Aomori group formed by small fishes in the Sanriku group seemed to be lower in proportion to their body size. Therefore, genetic characteristics of the juvenile Japanese flounder being reared at the sea-farming stations in Iwate and Miyagi prefectures are possibly different from those at an Aomori station.

On the other hand, statistically significant differences in the otolith Sr/Ca ratios among Aomori, Iwate, Miyagi and Shizuoka groups were found in the adult Japanese flounder. That is, higher values for the otolith Sr/Ca ratios were found in the groups inhabiting in the northern regions. The differences in otolith Sr/Ca ratios among these groups probably indicate that there are differences in the fish populations among these sample sites.

Lead pollution present in atmospheric aerosols in the city of Buenos Aires was measured in 1989, using Heavy Ion PIXE. Since then, environmental conditions have changed significantly. The usage of unleaded gasoline was introduced, and the utilisation of compressed natural gas as car fuel has increased. Recently, a new sampling campaign of atmospheric aerosols has started, partly in collaboration with the Greenpeace Foundation. The present studies reveal that lead pollution in Buenos Aires has significantly decreased since 1989. The concentrations of other elements are determined as well.

The work presents preliminary studies for the development of a Romanian national aerosol sampling network for the monitoring of air quality [1]. We made the sampling of aerosol particulate using mobile aerosol sampling pumps at a flow rate of about 41/min and 1 hour acquisition time at different locations in Romania. We used a stack filter unit using polycarbonate filters, PM-8 for coarse particles and PM-0.4 for fine particles.

The elemental analysis was performed using 2 MeV protons from the Van de Graaff accelerator located in Nagoya.

We try to give an interpretation of the results upon the geographical and economic particularities of these regions, to highlight the pollution contribution of each type of source and to identify it.

The aim of this work is the microelemental analysis of blood serum samples collected from healthy and ill cows (downer cow syndrome (DCS)). Today the origin of DCS is uncertain. At the beginning of our work, we assume some connections among the diminution of some nutritive elements from food, the activity of some enzymes and the origin of DCS. The samples were collected from cows at some animal farms on the neighbourhood of Targoviste city. To obtain a microelemental monitoring of these samples, we used a nuclear analysis method PIXE (Particle Induced X-Rays Emission) and a spectrometric one ICP (Induced Coupled Plasma). For Ca and P content of the analysed samples, we used PIXE based on the internal standard method. The ICP analysis method was used for Mg content determination. The determinations of phosphatase alkaline enzyme of analysed blood serum samples were made by a spectrometric analysis using Bessey-Lowry method. In studying diseases a significant variation in Ca, P, Mg and enzyme contents was observed. Those changes correlate with age, season of alimentation and type of disease.

We have annually held an open experiment of PIXE analysis since 1996 to get people's understanding on nuclear technology and radiation science. Up to the present, more than 270 participants joined and enjoyed the open experiments. This year, we demonstrated performance of a submilli-PIXE camera and had sixty-nine participants in the open experiment of PIXE. Elemental spatial distribution images gave deep impression to the participants. Half of the participants were high school students since the open experiment of PIXE was held during the period of open campus of Tohoku University. About ten percents of the participants were junior high school students. Our open experiment of PIXE was very effective to arouse public interest in radiation science and nuclear technology.

Degradation of paper caused by beam irradiation was investigated from a viewpoint of discoloration in PIXE analysis and its application to the paper samples of archaeology. Two types of paper (Japanese paper and fine quality paper) were tested in in-air PIXE analysis with 3 MeV protons. The degree of discoloration was quantitatively measured by the use of a calorimeter. The degree of discoloration was different for each tested paper and corresponded to the radiation dose of ions. It is resulted that even the in-air PIXE analysis should be carefully applied to archaeological treasures. Because discoloration of all tested paper decreased gradually at first but then increased after a few weeks. However, this phenomenon can be used to develop a technique of funny coloration.

Aerosols were continuously collected for 2 or 3 hours during the periods of 4-27 August 1997 and of 23 March-2 April 1998 at a suburb of Sendai City (east 10 km from Sendai), and meteorological data such as wind directions, wind velocities, etc were measured at the same time. The collected aerosol samples were analyzed by the particle-induced X-ray emission (PIXE) method. Fourteen elements (S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Hg and Pb) were contained in these samples. The elemental concentrations increased in the daytime and decreased at night. It coincided with the time variation of people movement. The concentrations of Mn, Fe, Zn and Pb elements depended strongly on the direction of wind and their distributions for wind directions reflected to the position of aerosol sources. This result suggests that the position of aerosol source can be determined by measuring aerosols and wind directions at the many positions.

Elemental images of rice leaves with lesion parts were taken with an in-air submilli-PIXE camera at Tohoku University. The rice leaves were analyzed in vivo and it resulted that the elements of Ca and Mn are accumulated in the lesion parts. It was confirmed by checking the intactness of cells that the living leaves were not seriously damaged. The surface of japan bowls (the Edo period), Japanese vessels (Shigaraki wares, the Edo period) and wooden tablets (the Meiji period) were directly surveyed by submilli-beams (3 MeV protons). Japanese vessels and wooden tablets were not discolored by the beam irradiation. Shigaraki vessels were discolored first, but their color disappeared after 10 days from the irradiation. It is concluded that such samples are not seriously deteriorated in in-air PIXE analysis.

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.

A method has been developed and tested for PIXE analysis of soluble and insoluble constituents in a variety of water samples in our surroundings. Insoluble components were filtered on a Nuclepore filter of 0.4-μm pores. For soluble fractions, a target of major components was made from a 0.15-ml filtrate evaporated on a user-made polycarbonate film, and in turn heavy metals in trace amounts were preconcentrated in a PIXE-target through the use of a combination of dibenzyldithiocarbamate-chelation with subsequent condensation into dibenzylidene-D-sorbitol gels. These three kinds of targets were analyzed with a PIXE system of 3-MeV proton beams. The widespread concentrations (several tenths of ppb to a few tens of ppm) of ~24 elements from Na to Pb were determined simultaneously in a precision sufficient to reveal the elemental distribution between the soluble and insoluble fractions of various aqueous samples such as river water, rain water and water leaking from disposal sites of industrial wastes. Hence, the methodology for preparing three types of targets promotes the PIXE analysis to a truly effective means for monitoring a water-pollution problem in our surroundings.