Size-fractionated aerosol composition during an intensive 1997 summer field campaign in northern Finland

A 12-stage small deposit area low pressure impactor (SDI) was used to collect size-fractionated aerosol samples during an intensive 1997 summer field campaign in northern Finland. The samples were analyzed for over 20 elements by PIXE, and some “difficult” elements such as As and Se could be quantified. The sea-salt and crustal elements had essentially a unimodal coarse size distribution with geometric mean aerodynamic diameter (GMAD) of about 4–5 μm. In one third of the samples, S showed only one mode in the fine size range, with GMAD of 0.4–0.5 μm. In the other samples, this fine S mode broke up into two modes, with GMADs of 0.3 and 0.6 μm, respectively. V, Zn, As, Se and Pb were mainly present in a single submicrometer mode, with GMAD of 0.4–0.5 μm for V and Se, and slightly larger (i.e., 0.6 μm) for the other three elements. The highest concentrations of S, V, Ni, Cu, Zn, As, Se and Pb were encountered in the SDI sample which had been collected in the period 14–16 July. During this sampling, the air masses came in from the west, but had recirculated over northern Scandinavia and passed over the Kola peninsula.     

Study of particulate emissions near a steel plant in Genova by continuous sampling and PIXE hourly analysis

The particulate emissions near a large steel plant located in a densely inhabited suburb of the town of Genova (Italy) have been studied for a period of six months. We have used two-stage continuous streaker samplers and subsequent PIXE analysis with hourly resolution, to follow both seasonal and daily trends. The first streaker sampler remained installed very close to the plant cokery and furnaces, while another sampler was moved to different locations. Samples have been analysed by PIXE, deducing concentrations for elements from Na to Pb. During part of the campaign, the aerosol fractions with aerodynamic diameter (D_ae) < 2.5 μm (fine fraction) and with 2.5 < D_ae < 10 μm (coarse fraction) have been separately collected. We have measured and analysed about 8500 PIXE spectra: the steel plant emissions have been identified to some extent and resolved from other aerosol sources.     

Analysis of lichen thin sections by PIXE and STIM using a proton microprobe

In order to better understand the distribution pattern of mineral elements in lichen tissues, thin sections (15 μm) of the foliose, vagrant soil lichen Xanthoparmelia chlorochroa were examined using proton microprobe Particle induced X-ray emission (PIXE). This technique was used to make two-dimensional scans, with 5 μm resolution, across tissue cross sections of the test species. Element maps for Si, P, S, Cl, K, Ca, Ti, Mn, Fe, Cu, Zn, and As have been prepared. Several elements are strongly localized in the element maps. PIXE data are complimented with STIM, light micrographs, and SEM images. Preliminary data suggest that nuclear microprobe techniques may be useful in elucidating element absorption and transport mechanisms in lichens.     

Aerosol composition and source apportionment in Santiago de Chile

Santiago de Chile, São Paulo and Mexico City are Latin American urban areas that suffer from heavy air pollution. In order to study air pollution in Santiago area, an aerosol source apportionment study was designed to measure ambient aerosol composition and size distribution for two downtown sampling sites in Santiago. The aerosol monitoring stations were operated in Gotuzo and Las Condes during July and August 1996. The study employed stacked filter units (SFU) for aerosol sampling, collecting fine mode aerosol (dp<2 μm) and coarse mode aerosol (210 mass of particles smaller than 10 μm) and black carbon concentration were also measured. Particle-Induced X-ray Emission (PIXE) was used to measure the concentration of 22 trace elements at levels below 0.5 ng m⁻³. Quantitative aerosol source apportionment was performed using Absolute Principal Factor Analysis (APFA). Very high aerosol concentrations were observed (up to 400 μg/m³ PM₁₀). The main aerosol particle sources in Santiago are resuspended soil dust and traffic emissions. Coarse particles account for 63% of PM₁₀ aerosol in Gotuzo and 53% in Las Condes. A major part of this component is resuspended soil dust. In the fine fraction, resuspended soil dust accounts for 15% of fine mass, and the aerosols associated with transportation activities account for a high 64% of the fine particle mass. Sulfate particle is an important component of the aerosol in Santiago, mainly originating from gas-to-particle conversion from SO₂. In the Gotuzo site, sulfates are the highest aerosol component, accounting for 64.5% of fine mass. Direct traffic emissions are generally mixed with resuspended soil dust. It is difficult to separate the two components, because the soil dust in downtown Santiago is contaminated with Pb, Br, Cl, and other heavy metals that are also tracers for traffic emissions. Residual oil combustion is observed, with the presence of V, S and Ni. An aerosol components from industrial emissions is also present, with the presence of several heavy metals such as Zn, Cu and others. A factor with molybdenum, arsenic, copper and sulfur was observed frequently, and it results from emissions of copper smelters.     

In-stack particle size and composition transformations during circulating fluidized bed combustion of willow and forest residue

The in-stack transformations of the particle size and composition of the fly ash were studied experimentally during combustion of forest residue and willow in a 35 MW circulating fluidized bed co-generation plant. Samples of the in-stack fly ash were taken with 11-stage Berner low pressure impactors (BLPIs) at two locations in the flue gas stream, i.e., downstream of the circulating cyclone at a temperature of 810–850°C and downstream of the convective back pass at a temperature of 150–160°C. The mass size distribution of the fly ash was derived from weighing the BLPI substrate films. For obtaining the multielemental composition of the fly ash as a function of particle size, the BLPI films were analyzed by both particle-induced X-ray emission (PIXE) and instrumental neutron activation analysis (INAA).     

Use of the nuclear microprobe at the University of Arizona for the study of heavy metal deposition in rabbit renal tissue

Industrial wastes consigned to disposal sites frequently contain substantial amounts of heavy metals. We have successfully applied proton induced X-ray emission analysis (PIXE) in the conduct of heavy metal (Hg, Cd, Cr, As) toxicity studies using precision cut rabbit renal cortical slices. The large beam diameter (4000 μm) of the proton macroprobe at The University of Arizona Ion Beam Analysis facility allowed an overall concentration of the metal(s) of interest in the samples to be determined, but lacked the ability to resolve point concentrations in the tissue. The ability to locate these areas has now been made available to us with the addition of a rastering microprobe (μ-PIXE) to the facility. Studies now being conducted in our laboratory using this micro-technique include analysis of renal tissue taken from rabbits injected intraperitoneally with HgCl₂, K₂Cr₂O₇, and NaAsO₂. The small beam size (3 μm) and the ability to raster this beam over areas of up to 125 μm × 125 μm has allowed regional mapping of endogenous and non-endogenous metal concentrations and revealed trends in heavy metal deposition in in vivo treated renal tissue, significantly increasing the amount of information obtained from these animal studies using PIXE alone. The combination of small beam size, high resolution, and multi-element detection makes μ-PIXE a powerful tool for investigating the impact of non-endogenous metals on the kidney.     

The external beam microprobe facility in Florence: Set-up and performance

An external beam microprobe facility, based on a quadrupole doublet supplied by Oxford Microbeam Ltd, has been installed on a new beamline at the 3 MV single-ended Van de Graaff accelerator in Florence. The goal was to obtain a beam with a spot size on target of 10–20 μm and a current in the order of at least 1 nA, in order to allow PIXE, PIGE and RBS elemental analysis in air or in a helium atmosphere. The beam was extracted from the vacuum lines through a 0.1 μm thick Si₃N₄ window to minimise lateral straggling. The design goals have been successfully achieved; the measurements of the beam spot characteristics in vacuum as well as in air and in helium atmosphere, are here reported.     

On the accuracy of element concentrations and masses of micron sized samples determined with the Heidelberg proton microprobe

We have already tested the reliability of element-normalized PIXE (Proton Induced X-ray Emission) data on small (10–100 μm) particles that we routinely obtain with the Heidelberg proton microprobe. Thus, we here discuss the accuracy of quantitative results, i.e., absolute concentrations inferred from PIXE analyses of such particles. We investigated and reduced the effects of mechanical vibrations and of the instability of the electronic devices on the achievable minimum beam spot. We implemented into our computer code a mapping software for qualitative element distributions (PIXE) and quantitative mass images using STIM (Scanning Transmission Ion Microscopy). The STIM images determine the area density required to calculate from PIXE spectra the absolute element concentrations in thin samples. The accuracy of absolute PIXE concentrations is tested by measurements on 15 μm soda lime glass microspheres. Finally, the complete results of PIXE and STIM analyses of an interplanetary dust particle (IDP) are described.     

WDX-PIXE analysis of low energy X-rays using a microbeam

A high-energy resolution PIXE system developed at a heavy ion microbeam line was used to analyze low energy X-rays below 1 keV. The system is equipped with a plane crystal spectrometer with a gas flow position sensitive proportional counter (PSPC), which enables high-energy resolution PIXE analysis using a microbeam. In order to improve the detection efficiency for the low energy X-rays, the X-ray entrance window of the PSPC was replaced with a thin polymer film supported by a metal grid. As the result, the detectable energy range was extended to carbon K X-rays and chemical effect in Fe and Cu L X-rays could be detected. A preliminary result of high-energy resolution PIXE mapping of Cu mesh (#500) showed that it is possible to obtain the Cu L mapping image using a 2 MeV proton microbeam with the size of 20 × 20 μm.     

PESA as a complementary tool to PIXE at CTU Prague

Proton Elastic Scattering Analysis (PESA) is a simple convenient method for hydrogen analysis in thin samples. A Proton Induced X-ray Emission (PIXE) target chamber was equipped with a PIPS detector for detection of forward-scattered protons. One of the objectives was to perform PIXE and PESA analyses of air particulate targets simultaneously. Tests and calibrations were fulfilled mainly with Mylar foils 1.5–6.5 μm thick in the proton energy region between 1.35 and 2.3 MeV. The energy dependence of scattering cross section is different from the Rutherford formula. Comparison of PIXE/PESA analysis with the Guelph Scanning Proton Microprobe Laboratory at the University of Guelph, Canada on seven aerosol samples was carried out. The intercomparison results validated our PESA/PIXE quality assurance protocol. In addition, repeated measurements of Gelman Teflo^TM filters indicated a gradual increase of hydrogen content by 1 ng/cm² per 1 μC/cm² proton dose.     

Air quality work at Guelph: GAViM and a traffic tunnel study

The Guelph Aerosol and Visibility Monitoring (GAViM) program presently runs three monitoring sites: two rural sites compatible with the IMPROVE protocol and one urban site mostly for special comparison studies. Fine aerosol is analyzed by the Laser Integrated Plate Method (LIPM), Proton Elastic Scattering Analysis (PESA), Proton Induced X-ray Emission (PIXE) and gravimetric analysis. Air quality data from the presently running sites and from two rural sites operated in the past are available through the WWW. The Guelph Scanning Proton Laboratory also participates in other aerosol programs: PIXE was employed to determine the composition of the ambient aerosol in a Vancouver traffic tunnel, to identify the main emission sources and to make estimates of vehicle emission factors. The PIXE facility was also modified for analysis of size-fractionated samples from the PIXE International Cascade Impactor (PCI) sampler. Significant improvement in detection limits for light elements due to the two-detector PIXE system used in Guelph, was justified particularly because of low air particulate loadings in case of PCI.     

Study by PIXE method of trace elements transferred from prostheses to soft tissues and organs

Some metallic prostheses inserted in human hip undergo physico-chemical modification, a few years after their implantation. Tissues surrounding these prostheses are damaged by metallic element transfer. Surgeons in Clermont-Ferrand Hospital (France) recover tissues of abnormal coloration that were in contact with metallic implants. PIXE technique (particles induced X-ray emission) with a 400 μm proton beam and 3 MeV of energy is an efficient technique to analyze these tissues and to detect elements, which are transferred from prosthesis to tissues. PIXE analyses were carried at the CERI-CNRS Laboratory. We have applied this method to determine qualitatively and quantitatively trace elements migration from metallic implants to surrounding tissues and organs, like kidney, spleen, liver, lymphatic gland and lung.     

Analysis of metallic pigments by ion microbeam

Metallic paints consist of metallic flakes dispersed in a resinous binder, i.e. a light-element polymer matrix. The spatial distribution and orientation of metallic flakes inside the matrix determines the covering efficiency of the paint, glossiness, and its angular-dependent properties such as lightness flop or color flop (two-tone). Such coatings are extensively used for a functional (i.e. security) as well as decorative purpose. The ion microbeam analysis of two types of silver paint with imbedded metallic flakes has been performed to determine the spatial distribution of the aluminum flakes in paint layer. The average sizes of the aluminum flakes were 23 μm (size distribution 10–37) and 49 μm (size distribution 34–75), respectively. The proton beam with the size of 2×2 μm² at Ljubljana ion microprobe has been used to scan the surface of the pigments. PIXE mapping of Al K map shows lateral distribution of the aluminum flakes, whereas the RBS slicing method reveals tomograms of the flakes in uppermost 7 μm of the pigment layer. The series of point analysis aligned over the single flake reveal the flake angle in respect to the polymer matrix surface. The angular sensitivity is well below 1 angular degree.     

Nuclear microprobe analysis of U-doped (Bi,Pb)2Sr2Ca2Cu3Oy/Ag superconducting tapes

Superconducting (Bi,Pb)₂Sr₂Ca₂Cu₃O_y/Ag tapes are doped with uranium compounds to introduce flux pinning defects from neutron-induced fission. The composition and distribution of elements in cross sections of the tapes were probed with a scanned 3 MeV proton microbeam using proton induced X-ray emission (PIXE). Distributions of the constituent elements were found to be heterogeneous on a scale of 10 μm. By combining the PIXE analysis with Rutherford backscattering spectrometry, the stoichiometry of the superconductor within the tape was measured, including oxygen from elastic scattering, revealing a departure from the desired 2223 composition. In one of the tapes, PIXE elemental maps of the Ag distribution showed diffusion of Ag into the superconductor from the enclosing jacket. Crystals of the same material, not fabricated into tapes, did not contain the contaminants and had a more ideal stoichiometry. Correlation maps between the constituent elements, deduced from the elemental maps, indicate the presence of secondary or unreacted phases.     

Quadrupole-doublet with permanent magnets for proton beam focussing

For PIXE studies on inhomogeneous samples with medium spatial resolution of about 50 μm two quadrupole doublets with Co₅Sm pole pieces for focussing 2.0 and 2.5 MeV proton beams, respectively, have been designed and tested. Technical data and first results are presented.     

Quantitative analysis of cascade impactor samples – revisited

Concentrations of aerosols collected in Singapore during the three months long haze period that affected the whole South-East Asian region in 1997 are reported. Aerosol samples were continuously collected by using a fine aerosol sampler (PM2.5) and occasionally with a single orifice cascade impactor (CI) sampler. Our results show that in the fine fraction (<2.5 μm) the concentrations of two well-known biomass burning products, i.e. K and S were generally increased by a factor 2–3 compared to the non-hazy periods. However, a discrepancy was noticed, at least for elements with lower atomic number (Ti and below) between the results obtained by the fine aerosol sampler and the cascade impactor. Careful analysis by means of Nuclear Microscopy, in particular by the Scanning Transmission Ion Microscopy (STIM) technique, revealed that thicknesses of the lower CI stages exceeded thick target limits for 2 MeV protons. Detailed depth profiles of all CI stages were therefore measured using the STIM technique and concentrations corrected for absorption and proton energy loss. After correcting results for the actual sample thickness, concentrations of all major elements (S, Cl, K, Ca) agreed much better with the PM2.5 results. The importance of implementing thick target corrections in analysis of CI samples, especially those collected in the urban environments, is emphasized. Broad beam PIXE analysis approach is certainly not adequate in these cases.     

Study of individual atmospheric aerosol particles at the Debrecen ion microprobe

Aerosol samples collected in outside and indoor environments with a 9-stage PI cascade impactor were analysed using PIXE, STIM (on and off-axis) and RBS ion beam analytical techniques at the Debrecen ion microprobe. Elemental composition, size and morphology of single aerosol particles were determined.Since the quantitative determination of light element concentrations requires a support material with small or no light element content, impactor surfaces made of different materials were tested in order to optimize the sampling and analysis. Thin polymer and Al foils were found to be possibly adequate substrate materials.     

Suitable test structures for submicron ion beam analysis

For the precise determination of the sizes of submicron beam spots test structures with an excellent edge definition are required. For this purpose a semiconductor heterostructure consisting of an 1.62 μm GaInP epi-layer grown on (0 0 1) GaAs has been made, which provides atomically sharp edges for beam spot size measurements. Since the sample has been thinned down by standard transmission electron microscope (TEM) preparation techniques, it can be used for both PIXE and STIM. The sample has been investigated with a TEM and the ion nanoprobe LIPSION. A one-dimensional beam profile in the low current mode was determined by a STIM measurement using 2 MeV protons and yielded a FWHM of (41±4) nm, which is the smallest value reported so far for high energy nuclear micro- and nanoprobes. Furthermore we present nickel nanowhiskers produced at the GSI Darmstadt by electrochemical preparation of etched ion track membranes that have been used to obtain two-dimensional images of the shapes of submicron beam spots. For these measurements a scan over a single nickel nanowhisker having a diameter of 220 nm and a height of about 6 μm was performed.     

Nuclear muscopy — Elemental mapping using high-energy ion beam techniques

Using a scanned, focused MeV ion beam, the techniques of ion beam analysis can be used to obtain images showing two-dimensional elemental distributions. This technique of nuclear muscopy is important in applications where the distribution of elements within a sample must be related to optical or electron images showing the structure or functional organisation of the sample. With the techniques available at present, spatial resolutions of 0.5 μm can be achieved at currents allowing PIXE analysis of trace elements at the ppm level. The simultaneous use of particle backscattering analysis and secondary-electron imaging allows the light elements and the surface topography of the sample to be determined. In some cases, nondestructive three-dimensional elemental analysis can be carried out. This paper reviews the techniques and describes two applications in semiconductor physics and microbiology carried out using the facility at Oxford.     

Elemental analysis of agricultural soil samples by particle induced X-ray emission (PIXE) technique

In agriculture, elements essential to vital processes are also called nutrients. A suitable and reliable particle induced X-ray emission (PIXE) methodology for content determination of essential nutrients in soil samples was developed and its effectiveness proved. The PIXE method is applied to intermediate thickness samples, whose mass per area unit are smaller than 1 μg/cm². Precision and accuracy of the method was estimated after repeated measurements of a single reference material: CRM PACS-2 (estuarine sediment) with a matrix quite similar to the soil samples measured. This paper reports the results of elemental measurements in soil samples. A discussion of agricultural soil sample preparation for PIXE analysis is also presented.