International Journal of PIXE

Continuous X rays produced by highly charged heavy ion-atom collisions have been studied experimentally. 2–5.5 MeV/u F, Si, S and Cl ions with zero or one electron were bombarded with a thin gas target of H₂ and He. Emitted X-ray spectra were measured by using a Si(Li) X-ray detector at 90°. The characteristic X rays and radiative electron capture X rays were observed clearly, which were superimposed on the continuum X rays. The continuum X rays can be well explained by two types of radiative processes: mainly quasi-free electron bremsstrahlung (QFEB), and partly atomic bremsstrahlung (AB). It should be noticed that QFEB is predominant at low X-ray energy region and AB at high X-ray energy region in highly charged heavy ion-atom collision process.

The chemical effect on K-shell fluorescence yields for carbon compounds has been estimated in a simple model based on the discrete-variational Xα molecular orbital calculations and the statistical scaling method. The calculated results show that there is a relation between the fluorescence yield and the effective number of 2p electrons in carbon, n_2p. The behavior of the fluorescence yield as a function of n_2p is in qualitatively agreement with the experimental data by proton impact. The present values for fluorescence yields of carbon oxides agree with other theoretical values.

PIXE analysis opened to public was conducted as an event of an open school of the Atomic Energy Society of Japan, which is semiannually held in order to arouse public interest in the science of radiation and nuclear power. The experiment was performed using a vertical in air (Via) PIXE system at Tohoku university. Forty-seven people participated and enjoyed this open experiment.

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.

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.

The enrichment procedure of heavy metals (Fe³⁺, Co²⁺, and Hg²⁺) in water was examined in conjunction with in-air PIXE. The preconcentration step consisted of adsorption of dibenzyldithiocarbamate complexes of the metal ions onto dibenzylidene-D-sorbitol gels. The colloidal gels in solutions were then collected on a nuclepore membrane for direct irradiation by proton beams in a system of vertical beam type in-air PIXE. The amounts of the chemicals used in the enrichment were minimized to prepare thin target specimens with the homogeneous composition. The metal-recovery in the preconcentration step was confirmed to be quantitative in a wide range of the concentrations. The reproducibility and detection limit were shown and discussed for the present setup of PIXE analysis in our laboratory.

For the purpose of studying loss of elements through PIXE analysis, a target of modern Japanese paper with ancient red Chinese ink on was prepared and analyzed. Red Chinese ink includes mercury sulfide which has low melting point of 583 °C at 1 atm. In this study, two classes of 2 MeV proton beams of about 5 nA/mm² and 50 nA/mm² were used. A simple data taking system of multi-spectra was establised and X-ray spectra by proton-PIXE were consecutively obtained every 10 seconds for about 2 hours. The obtained multi-spectra were used for the loss of each element in the target. The results show that S, Hg and Pb in the target gradually decrease with time under 50 nA/mm² of a 2 MeV proton beam and the decreases start under about 25 nA/mm². These elements, however, don’t decrease under 5 nA/mm². Most of chlorine in modem Japanese paper was lost under 15 nA/mm².

Mate is a kind of tea popular in Central and South America. Trace elements contained in two types of Mate. green Mate and roast Mate. obtained from various districts were determined using PIXE technique comparing the results with those of other teas. Contents of Ca. Mn and Zn in Mate leaf were higher than those of the other tea leaves. Ca and Mn were exuded more easily from the Mate leaves than from the other tea leaves. Exudation amount of Zn was larger in the green Mate than in the roast Mate. It was suggested that Mate is a better supplier of trace elements than other teas.

A fundamental investigation of the PIXE method applied to the measurement of trace elements in wood samples, is described in this work. Yields of the elements added to a sugi (Cryptomeria japonica D. Don) specimen, were almost constant after they were bombarded with radiation up to 600µC. Yields of certain elements in the early wood and the late wood in the same annual ring of the sugi were compared. The yields of Ca, Cu, Zn, Rb and Sr in the late wood were the same or slightly higher than those in the early wood, but Fe and Mn yields in the late wood were higher than those in the early wood. The concentration profiles of Ca, Mn, Fe, Zn and Sr along a radial direction in the stem of the sugi were also determined.

Trace element concentrations in short necked clam Ruditapes philippinarum marked shells with iron rusting were determined by particle induced X-ray emission (PIXE) method. Element such as Ca, Mn, Fe, Zn, Sr, and Br were detected in the shells. The Fe/Ca X-ray intensity ratio decreased exponentially on the day after marking. It was concluded that the higher Fe concentration on marked clams was caused by attached iron rusting. The concentrations of Fe, Br, and Sr differed among the 3 stations (Kamaya, Shigaki, and Iwatani), suggesting that elemental concentrations may be related to the growth of clams.

It is important for maintenance and understanding of health to make inquiries into the biological defence mechanisms. Yonezawa et al. came across an induction of yet unknown defence mechanisms in mice which acquired two types of radioresistance (decrease in bone-marrow death rate after midlethal exposure): one occured 2 weeks after preirradiation with 0.3–0.5 Gy and the other 2 months after 0.05–0.10 Gy of X-rays. To elucidate the acquired radioresistance induced after preirradiation with 0.5 Gy (in a shorter time case). recovery of blood cell counts after sublethal irradiation were measured in mice of ICR strain. Contrary to the common knowledge on radiation protection. recovery of blood cell counts of thrombocytes. leukocytes and erythrocytes after sublethal irradiation were not stimulated by the preirradiation. This study was planned to find some keys to elucidate the mechanism for the acquired radioresistance. Eleven elements. Cl. K. Ca. Cr. Mn. Fe. Ni. Cu. Zn. Se and Br. were analysed clearly in mice sera by PIXE.

PIXE was adopted for analysis of trace elements in otoliths of anadromous fish, masu salmon Oncorhynchus masou masou and amago salmon O. masou ishikawae. Mn, Zn and Sr were detected in order of ppm. Two different types of spectra were obtained from masu salmon otoliths. The concentrations of Sr and Zn in the two types were quite different. The difference seems to be a result of the difference in periods when the individuals stayed in freshwater environment until they were caught. Amago salmon otoliths contain significantly less Sr than masu salmon otoliths. It is considered to be due to different migration pattern between the two subspecies. Anadromous fish generally experiences freshwater and sea water environment in its migration. Trace elemental concentrations in sea water is quite different from those in freshwater. The environment, which varies along with the migration, would affect the incorporation of trace elements into otoliths of anadromous fish.

Trace elements in the squid statoliths were analyzed by PIXE for following seven species distributing at offshore and inshore waters: Family Ommastrephidae, Ommastrephes bartrami, Todarodes pacificus; family Loliginidae, Loligo bleekeri, L. duvaucelii, L. chinensis, L. edulis and Sepioteuthis lessoniana. Statoliths of all seven species contained manganese, iron, capper, zinc and relatively high amount of strontium. Statoliths Sr concentration, an possible index for thermal history of the animal’s habitat, were the highest in O. bartrami that spends their entire life time at pelagic water, and secondly highest in T. pacificus living at the pelagic as well as the coastal waters. On the other hand, statoliths Sr concentration was relatively low in the five species of Loliginidae living at coastal waters, with following order: L. edulis >S. lessoniana >L. duvaucelii >L. bleekeri >L. chinensis. These observations may indicate that quantity of the statoliths trace elements are species specific in squids, thus would be a possible “key” to reconsidering about taxonomy and distribution in squid.

To evaluate a participatory role of environmental minerals in the pathogenesis of amyotrophic lateral sclerosis (ALS) in the Kii Peninsula of Japan, one of the three high-incidence foci, elemental and neuropathological investigations of lumbar spinal cord and hippocampal tissues were conducted, using particle-induced x-ray emission (PIXE) spectrometry and histomorphometric analysis. The PIXE analysis revealed extremely high contents of Al in both tissues of Kii ALS cases as compared with sporadic ALS and control cases. Morphometric analysis in the hippocampus showed abundant Alzheimer’s neurofibrillary tangles (NFTs) in the Kii ALS cases as compared with the other cases. Al content significantly correlated with the density of NFTs in all ALS cases (r=0.765, p < 0.0001). Interestingly, both Al content and density of NFTs in the hippocampus of all ALS cases significantly and negatively correlated with Ca and Mg contents in the birthplace area’s rivers. The extremely low Ca and Mg content in the focus rivers was confirmed along with the high ratio of Al₂O₃/CaO in the soil. Thus, Kii ALS patients may reflect the geochemical environment of their birthplace, i.e., long term Ca and Mg deficiencies and excess Al accumulation along with widespread NFT formation in the brain.

Praseodymium is one of the most important pigment materials for high-quality china and ceramics but its source minerals are not well known to geologists. Allanite, one of the REE-bearing minerals in nature, has a large coordination polyhedra for cations and favors the larger LREE ions such as praseodymium than other REE-bearing minerals that favor the smaller HREE. We have tested some allanite crystals by CSIRO’s micro-PIXE to examine its possibility as a praseodymium source. Our result showed that allanite incorporates praseodymium at the order of 4000 to 5000 ppm and thus it is one of the good host of this element. We conclude that micro-PIXE is a viable quantitative tool for determining REE in allanite and other conventional REE sources in spite of the relatively poor minimum detection limit compared to that for other elements.

For the purpose of establishing an effective exploration model of antimony deposit as a final goal. minor elements in stibnite (Sb₂S₃) were analyzed by micro-PIXE. Samples were taken from the largest antimony mine in the world. Xikuangshan. Hunan. China. Measurements were carried out using 1 MeV proton to avoid the problem where low energy tail of K X-ray peaks of antimony could mask small peaks of interest. As a result. arsenic at a concentration of around 0.2 wt % was successfully detected for the stibnite crystals that contact calcite but not those that contact quartz.