International Journal of PIXE

Since the Great East Japan Earthquake on 11 March 2011, we have seen a rapid increase of requests for soil analysis by PIXE. In the Nishina Memorial Cyclotron Center (NMCC), a powdered internal standard method with palladium on carbon powder has been adopted for soil sample preparation. However, the method can be heavily laborious when many samples need to be handled in a limited time. Here, we report an alternative to the method which takes a standard in the liquid form with a few drops of acetone to be homogenized with soil sample in an agate mortar. The applicability of the moist method was examined using some standard reference materials by comparing the analyzed results with those from the conventional method and with the certified values. The results were generally satisfactory, although further examination is needed to improve the accuracy and reliability of the new method.

Over the past 10 years, several thousand otoliths have been analyzed with PIXE (using 2.55 MeV protons) at LIBAF (Lund Ionbeam Analysis Facility, formerly LNMP Lund Nuclear Micro Probe). Over 40 elements have been identified in otoliths, many at levels suitable for PIXE analysis. Readily detectable elements in otoliths starting with Ca are: Ca (the matrix), Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Sr, Y, Zr, Mo, Cd, Sn (difficult), I, Ba (sometimes difficult), Pb (difficult). The detector system, used over this time period, is more sensitive than many other X-ray detector systems, since it consists of eight HPGE detector elements (100 mm² each), in an annular formation around the beam entrance. Using a thick absorber allows us to use quite high beam current, typically 12 nA, but sometimes up to 20 nA. This permits us to have low detection limits within short analysis times. Additionally, light stable isotope research is widespread in the sciences including ecology. Stable isotopes of N provide information about trophic level (“who eats who”), providing the opportunity to map out the switching of diets from one food type to another. Oxygen isotopes are useful as “environmental thermometers”. Currently, most of such analyses require destruction of the otolith, and nitrogen isotope analysis may require dissolving entire otoliths, thus losing all temporal information. We present new techniques using new types of detectors, double side silicon strip detector (DSSSD). The detectors, electronics and the laboratory setup are described in detail; for our analysis, a MeV proton and a deuterium microbeam at LIBAF is used. The analysis is performed immediately after the PIXE analysis, without moving the sample.

We report on the development of a high-current microbeam system for wavelength-dispersive X-ray micro particle-induced X-ray emission (WDX-$\mu$-PIXE) for chemical state mapping. The microbeam system is composed of two slits and a quadrupole doublet lens mounted on a heavy rigid support. The microbeam system is installed immediately after a switching magnet. A beam brightness of $2.4\text{pA}\cdot \mu {\text{m}}^{-2}\cdot {\text{mrad}}^{-2}\cdot {\text{MeV}}^{-1}$ is obtained at a half-divergence of 0.1 mrad. A beam current of more than 300 pA is obtained for object sizes of $40\times 10\mu {\text{m}}^2$ with a half-divergence of 0.2 mrad, which corresponds to a beam spot size of $1\times 1\mu {\text{m}}^2$. The calculated spot size of the beam was $1\times 1\mu {\text{m}}^2$ and the measured spot size was $1\times 1.5\mu {\text{m}}^2$. The WDX-$\mu$-PIXE system with the microbeam system is now operational.

In this paper, we have developed a wavelength dispersive X-ray spectrometer microparticle-induced X-ray emission (WDX-$\mu$-PIXE) system combining a microbeam system with high spatial resolution and wavelength dispersive X-ray (WDX) spectrometry with high-energy resolution for chemical state mapping. A Von Hamos geometry was used for the WDX system to achieve higher detection efficiency and energy resolution. The system consists of a curved crystal and a CCD camera. The WDX system was installed in a newly developed microbeam system. The energy resolution of the WDX system was 0.67 eV for $\text{Si-}{K}_{\alpha 1}$ (1740 eV). $\text{Si-}{K}_{\alpha 1,2}$ and $\text{Si-}{K}_{\beta }$ X-ray spectra from various Si compounds were measured and chemical shifts related to chemical states were clearly observed. The system was applied to the chemical state analysis of clay particles. After elemental mapping of the clay particles using a conventional $\mu$-PIXE system with a Si(Li) detector, particles to be analyzed were selected and analyzed sequentially with the WDX system. $\text{Si-}{K}_{\beta }$ spectra from clay particles were obtained. The microscopic spatial distribution of elements and chemical state of the clay particles were sequentially measured with high energy and spatial resolution using a microbeam.

In this paper, we developed a technique for analyzing individual PM_2.5 particles using micro-PIXE. PM_2.5, a designation for extremely small particulate matter (PM) in the air, has recently become the center of attention because high levels of PM_2.5 were recorded in parts of western Japan, especially Fukuoka Prefecture, in January 2013. For a better understanding of their formation mechanism, analysis of individual particles is indispensable. We collected PM_2.5 on a $4\mu \text{m}$ thick Prolene foil using a multi-nozzle cascade impactor at Fukuoka Women’s University, Fukuoka, Japan. Its elemental analysis was carried out using a micro-PIXE system at Tohoku University. Although elemental concentration ratios of scanned areas were similar, those of individual particles were quite different from each other. Elemental concentration ratios for individual particles were categorized into five groups, indicating that the PM_2.5 particles came from at least five different sources. Although elemental concentrations obtained by averaging over single particles formed in different processes will lose detailed information, we were able to derive comprehensive elemental compositions of individual PM_2.5 particles using our novel technique. The individual particle analysis technique for PM_2.5 will provide important information to identify pollution sources and particle formation mechanisms.

The Fukushima Daiichi nuclear power plant accident caused radioactive pollution by ¹³¹I, ¹³⁴Cs and ¹³⁷Cs. The surface of the ground was contaminated at a volume of 3 × 10⁷ m³. The government has mandated that the top 5 cm of the contaminated soil be removed and stored, in this way, it is desirable to reduce its volume. Soil samples were collected from a mountain, a rice field and a vegetable field in northern Japan, and the silt was extracted from the muddy water by washing the soil. Next, the silt was sprayed with a solution of cesium carbonate (Cs₂CO₃). We determined the amounts of Al, Si, K and Cs in the silt particles using micro-particle-induced X-ray emission (micro-PIXE) analysis. The silt particles from a vegetable field, a rice field and a mountain were mainly formed from smectite or vermiculite, which absorbs Cs atoms. The measurements at multiple detection angles confirmed that Cs atoms were uniformly absorbed within silt particles less than $10-30\mu \text{m}$ in diameter. This resulted that the radioactive Cs atoms were adsorbed in silt particles within $10-30\mu \text{m}$ of the surface.

In this paper, we used microcapsules releasing liposome-protamine-hyaluronic acid nanoparticles (LPH-NP) with/without carboplatin in response to radiation to image and treat MM48 breast cancer in C₃He/N mice in two radiation sessions. The micro-particle-induced X-ray emission (PIXE) camera and quantitative PIXE were used to image and measure the release of nanoparticles from the microcapsules. In session one, iopamiron and computed tomography (CT)-detectable microcapsules containing P-selectin and LPH-NP were mixed with a solution of alginate, hyaluronate, ascorbate, and P-selectin. This solution was sprayed into an FeCl₂ solution containing VEGFR-1/2 antibodies (Abs). The microcapsules obtained were injected intravenously into mice, and after 9 h, the mice were exposed to 10 or 20 Gy (140 keV) of X-ray radiation. Anti-VEGFR-1/VEGFR-2 microcapsules accumulated around tumors and released P-selectin and the iopamiron-labeled LPH-NP in response to the first radiation. The iopamiron-containing nanoparticles were detected by CT, allowing detection of MM48 tumors by CT. In the second session, the microcapsules released LPH-NH that delivered carboplatin into the tumor cells. This treatment had a significant antitumor effect $(P<0.05)$. The micro-PIXE camera and quantitative PIXE successfully imaged and measured the release of contents from microcapsules. Our results indicate that targeted nanoparticles allow for accurate detection and treatment of tumors.

Lead poisoning is one of the environmental problems affecting human health. In Indonesia, leaded gasoline was completely phased out since July 2006. As part of an air pollution study, Pb monitoring was carried out from 2005 to 2012 in Bandung to assess the impact of the use of unleaded gasoline on the Pb level in the ambient air in Indonesia. Airborne particulate samples were collected using a Gent stacked filter unit sampler in two size fractions of $<2.5\mu \text{m}$ (fine) and 2.5 to $10\mu \text{m}$ (coarse). Black carbon (BC) was determined by reflectance and elemental analysis was performed using particle induced X-ray emission (PIXE). The results showed that the annual averages of lead concentrations in the fine particulate matter in 2005, 2006, 2007, 2008, 2009, 2010, 2011 and 2012 were 44.53, 27.06, 22.21, 17.75, 17.21, 16.24, 19.25 and 12.69 $\text{ng}\cdot {\text{m}}^{-3}$, respectively. The airborne lead concentrations showed a declining trend over the years after implementation of the government policy of phasing out leaded gasoline. After six years of monitoring, the lead concentration in PM2.5 was decreased by over 70% compared to samples collected before July 2006. The average of PM mass, BC and elemental concentrations are also presented and discussed. The significant decrease of Pb concentration in the ambient air of Bandung is a great success story of the phase out of leaded gasoline in Indonesia.

We developed and reported standard-free methods for various bio-samples in both invacuum and in-air PIXE and they have been applied to quantitative analyses of traces of bio-samples whose weights are less than 0.1 mg. In this study, we established a method of quantitative analysis for bio-samples of nearly $1\mu \text{g}$ in in-vacuum PIXE. In order to improve sensitivity and accuracy of analysis for smaller samples on the basis of the standard-free method, which makes use of continuous X-rays emitted from the sample, it is essential to design appropriate backing materials for supporting the sample. In the present study, we have examined various backing materials such as thinner and threadlike backings. As a result, it was found that a thread-like backing made of extended adhesive, which contains almost no impurity, is the most suitable for bio-samples of extremely small quantities, since it produces no large amount of continuous X-rays. The method has been applied to quantitative analyses of small insects and plants. Moreover, the method was applied to analyses of small marine organisms such as opossum shrimps and squilla shrimps which play important roles in a food chain in marine ecosystem. The results gave us valuable information about regeneration of marine ecosystem in the Sanriku district attacked by the huge tsunami that occurred on 11 March 2011.

As part of a biomonitoring study of atmospheric particles for the development of a biological and environmental monitoring system in the beech (Fagus crenata Blume) forest ecosystem, we carried out elemental content and two-dimensional analysis of beech leaves by conventional PIXE and micro-PIXE. The beech leaves were collected from natural beech forests at eight locations in Japan. For conventional PIXE analysis of beech leaf samples, 27 elements were determined in total. Mg, P, S, K, Ca, Mn, Fe, Cu and Zn were found to be the important nutrient elements for plants at all sampling sites. According to radar chart analysis results for element (Mg, P, S, K, Ca, Mn, Fe, Cu and Zn) concentrations at each sampling site, K and P, Fe and Ca, and Zn and Cu showed relatively similar patterns. However, elements with a pattern similar to that of Mg, S, and Mn were not found. These elemental concentrations were largely different at beech leaf sampling sites. For micro-PIXE analysis of beech leaf samples from seven sampling sites (Soebetsu beech forest was excluded), scanning transmission ion microscopy (STIM) images and maps of Mg, Si, P, S, K, Ca, Mn and Fe were similar. In samples from Soebetsu beech forest, portions missing from the element distribution were observed. In particular, maps of Mg, Si, P, S, K and Ca were conspicuous. These analysis results may be important information for understanding the mechanism of plant metabolism.

We developed an X-ray pinhole camera using a radio-isotope source that emits only X-rays.We investigated the performance of this system using a ⁵⁵Fe source with phantom samples. We then applied it to investigate the movement of a ⁵⁵Fe tracer in Japanese mustard spinach. We obtained X-ray images of the ⁵⁵Fe tracer in the spinach samples, and found that ⁵⁵Fe accumulated in the plant.

The spatial distributions of potassium and rubidium in Lentinula edodes mushrooms contaminated with radioactive cesium were measured using particle-induced X-ray emission (PIXE) analysis by a beam scanning technique with a submillimeter sized proton beam to study relationships in elemental concentration in the mushrooms between radioactive cesium and other alkali elements. The results of PIXE analysis were compared with the spatial distribution of radioactive cesium in the samples measured by an autoradiographic method. Radioactive cesium was not uniformly distributed and strongly concentrated in the peripheral region of pileus of the mushroom while the elemental maps evaluated from PIXE analysis showed that potassium and rubidium are highly accumulated in the same area as radioactive cesium. The present results suggest a common mechanism of the accumulation of alkali elements including radioactive cesium in Lentinula edodes mushrooms.

While traditional proton induced X-ray emission (PIXE) analytical technique is based on the energy dispersive solid state detectors used to collect the X-ray fluorescence from the sample, wavelength dispersive X-ray (WDX) spectrometers are applied in high energy resolution PIXE (HR-PIXE) analysis. The main drawback of the WDX spectroscopy is the relatively low efficiency making it less applicable for trace element PIXE analysis. However, the efficiency was enhanced significantly in modern spectrometers employing cylindrically or even spherically curved crystals combined with position sensitive X-ray detectors. The energy resolution of such a spectrometer may exceed the resolution of the energy dispersive detector by two orders of magnitude while keeping the efficiency at a high enough level to perform trace element analysis. In this paper, the recent history and the development of HR-PIXE spectroscopy at the J. Stefan Institute in Ljubljana is presented. Our current setup based on in-vacuum Johansson-type crystal spectrometer is presented in more details followed by some most recent applications.

In order to maintain homeostasis and consequent optimal cell functioning and integrity and/or to avoid toxicity, proper allocation of elements at organ, tissue, cellular and subcellular level is needed. Studies of element localization are therefore crucial to reveal the mechanisms of element trafficking and also tolerance and toxicity. Moreover, studies of localization and speciation of trace elements in grains of staple crops are also of high applicative value, allowing one to determine major and trace element concentrations in different grain tissues without possible contamination.

In the last decade, a remarkable progress has been made in the development and application of different 2D imaging techniques in complex biological systems, especially in the sense of improved lateral resolution and sensitivity. The superiority of micro-PIXE over other 2D imaging techniques lies in its wide elemental range (from sodium (Na) to uranium (U)), high elemental sensitivity below micron spatial resolution and fully quantitative element concentration analysis.

The aim of this review is to summarize the latest development of micro-PIXE for imaging of the distribution of major and trace elements in crop plants with emphasis on sample preparation methodologies and post-imaging analysis. Case studies of element localization in the grains of major crop plants are also presented.