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.     

PIXE analysis of sand and soil from Ulaanbaatar and Karakurum, Mongolia

Twenty-one sand and soil samples were collected at the surface from 22 to 25 June 2007 at sampling sites from Ulaanbaatar to Karakurum, Mongolia. The sand samples were collected from constantly changing sand dunes which may still contain salt from prehistoric oceans. The dry sand and soil samples were processed for PIXE and PIGE analyses. A clear division between soils and sand become apparent in the silicon results. Concentrations of all bulk elements in human habitation samples and of Si, Al, K and Fe in dry lake/flood plain samples are similar to those in the soils and sands. Among elements which could be regarded as being at trace concentrations the average S concentration in the soils is 0.9 g kg⁻¹ whereas it is not detected in the sand samples. Zinc and Cu concentrations are both higher in the soils than the sands and are strongly correlated. A surprising presence of uranium at a concentration of 350 mg kg⁻¹ was detected in the PIXE measurement on one of the dry lake samples. Gamma spectrometry confirmed the presence of U in this sample and also at a lower level in a sample from the lake shore, but in none of the other samples. Further, the gamma spectrometry showed that ²³⁸U decay products were present only at a level corresponding to about 3 mg kg⁻¹ U for a system in radioactive equilibrium, a figure which is typical for U in the earth’s crust. Disequilibria between ²³⁸U and its decay products occur naturally but such a high degree of separation at high concentration would be unique if confirmed. PIXE and PIGE measurements of these samples highlight the difficulty in correlating trace element measurements with occurrence of indicators of sea salt in air particulate samples.     

Analysis of C, N and O in aerosol collected on an organic backing using internal blank measurements and variable beam size

A method with low MDL (minimum detection limit) was developed for analysis of carbon (C), nitrogen (N) and oxygen (O) in aerosol samples collected on an organic backing. An accelerator-produced beam of protons interacting with the sample and the detection of elastically scattered protons (PESA; particle elastic scattering analysis) and emitted X-rays (PIXE; particle-induced X-ray emission) were the basic components of the setup. The method is based on measurement of internal blank concentrations, i.e. measurement of the blank concentration outside the aerosol deposit in each sample, and the use of two sizes of the beam in order to improve the MDL of the analysis. Large beam size covering the entire aerosol deposit was used to obtain quantitative analysis with PIXE. Small beam was used to obtain relative elemental concentrations with PESA and PIXE, which were transformed to absolute values by the aid of large-beam analysis. The small-size-beam served two purposes: to make internal blank measurements feasible and to improve the signal ratio of aerosol-deposit to backing. Compared with the traditional way of analysis, using a beam that is larger than the deposit and specially prepared blank samples, the new method reduced the MDL of C, N and O by a factor of 130, 70 and 90, respectively. The new method was applied to aerosol samples collected in the upper troposphere and the lowermost stratosphere from the CARIBIC platform. As far as the authors know, these measurements are the first quantitative determinations of C, N and O in the aerosol of this part of the atmosphere. The results show that these elements together with sulfur are major components of the aerosol.     

PIXE analysis of trace pollutants in Chaliyar river water in Malabar,India

Analysis of trace elemental concentration in the Chaliyar river water has been carried out using the Proton Induced X-ray Emission (PIXE) spectroscopic technique. Water samples were collected from different locations along the course of the river during summer and rainy seasons. Samples were prepared by a preconcentration method. The PIXE analysis was carried out using 2 MeV protons. The details of the measurements and the results are presented in this paper.     

Use of rutherford scattering on a secondary carbon target for correcting intermediate thickness sample PIXE measurements

A method is presented for correcting PIXE measurements on intermediate thickness targets. The correction deals with the X-ray attenuation and the incident proton energy loss. It is based on the simultaneous acquisition of the PIXE spectrum along with the energy distribution of protons elastically scattered by a thin secondary carbon foil located behind the PIXE target. These measurements allowed a linear correlation between the proton energy loss ΔE and the correcting factor for X-ray absorption XF to be demonstrated.The validity of these simplifying linear approximations is discussed. The method is applicable to inhomogeneous thickness samples like aerosol impactor stages.     

Combining PIXE and XRF with gamma-ray transmission to get accurate analysis of archaeological bronzes

A method that combines PIXE and XRF measurements with gamma-ray transmission has been developed. This method allows the measurement of the bulk composition of corroded bronze samples, which cannot be done with PIXE or XRF alone because these are near-surface techniques. The method is applied to several archaeological bronzes of the Final Bronze Age and First Iron Age of the region around Sevilla, Spain.     

Total elemental composition analysis of soil samples using the PIXE technique

The determination of major and trace element contents in soils was developed by acid digestion method combined with particle-induced X-ray emission spectrometry (PIXE). The digestion of soils was achieved by using nitric acid (HNO₃), hydrochloric acid HCl and hydrogen peroxide (H₂O₂) with repeated additions. A 20 μL aliquot from the digested samples was evaporated on the Nuclepore Track-Etch Membrane and irradiated by the 2.5 MeV proton beam from the single-end type Van de Graaff accelerator. The accuracy of this methodology was estimated based on series of measurements done for a reference material of soil CRM 023-050. The proposed experimental procedure was shown to have good reproducibility of the experimental results. The corresponding limits of detection (LODs) for Na, Mg, Al, P, S, Cl, K, Cr, Mn, Fe, Ni, Cu, Zn, As, Sr, Mo and Cd were estimated. Other soil characteristics such as total carbon (TC) and nitrogen (TN) content, pH and electrical conductivity (EC) were also measured.     

PIXE and XRF analysis of particulate matter samples: an inter-laboratory comparison

PIXE and XRF are very effective techniques in atmospheric aerosol investigation, therefore they are extensively used by the authors. In this work an inter-laboratory comparison of the results obtained analysing several samples (collected on different substrata) with both techniques is presented: the samples were analysed by PIXE (in Florence, at the 3 MV Tandetron accelerator of LABEC laboratory) and by XRF (in Genoa and Milan, where two Oxford XRF instruments are operational). The results of the three sets of measurements are in good agreement for all the analysed samples.The aim of this work was also to compare PIXE and XRF performance in atmospheric aerosol analysis with the routine set-up currently in use at the three laboratories, to determine the best technique to be applied depending on the substratum used for aerosol sampling and the main elements of interest for each specific research project. Results of the comparison between the minimum detection limits of both techniques will be shown for all the measured elements, for different substrata (Teflon, polycarbonate and cellulose mixed esters).     

GIC4117串列加速器外束PIXE/PIGE分析系统

本文介绍在北京师范大学GIC4117串列加速器上建立的外束PIXE/PIGE分析系统,和基于此系统的薄样品外束PIXE/PIGE定量分析方法。给出了2010年Teflon滤膜采集的361个气溶胶样品外束PIXE分析得到的各元素平均探测限和最低探测限,并同真空PIXE分析探测限进行了比较。利用标准样品给出了激发曲线不同坪区薄样品外束PIGE分析F和Na的探测限,通过测定¹⁹F(p, p′γ)¹⁹F激发的197 keV γ射线得到的F的探测限可达73.9 ng•cm^-2,Na的探测限可达198.9 ng•cm^-2。     

Monitoring of chromium, copper and arsenic in contaminated soils using thick-target PIXE

Soil contamination by toxic metal ions is one of the most serious environmental problems today. In this work soil samples from an area where a wood preservation plant has been active were studied. Chromium, copper and arsenic (CCA) are the main metal ions used in preservation of lumber. For the monitoring of these metal ions and of other elements in soil, thick-target PIXE (TTPIXE) has been proved to be a successful method. About 20 elements were quantitatively determined in the soil samples from the contaminated area and from a reference area. The reliability of the results was evaluated by analysing geochemical certified reference materials (CRMs) of chemical compositions similar to the soil samples.     

Analysis of atmospheric aerosols by PIXE: the importance of real time and complementary measurements

Particle-Induced X-ray Emission (PIXE) has been used for more than 30 yr in many urban and background air pollution studies. The technique has certainly contributed to the understanding of source-receptor relationship for aerosol particles as well as to aerosol physics and chemistry. In the last few years, where aerosol issues were strongly linked to global climate change through the relationship between aerosol and atmospheric radiation points to new challenges in atmospheric sciences, where PIXE could play an important role. Also the recognition for the inter-relationship between aerosol and liquid and gas phases in the atmosphere makes important to integrate PIXE aerosol analysis with other complementary measurements. The use of Nephelometers and Aethalometers to measure scattering and absorption of radiation by aerosol particles can be done in parallel with particle filter collection for PIXE analysis. Parallel measurements of trace gases using traditional monitors as well as with new techniques such as Differential Optical Absorption Spectroscopy (DOAS) that can provide concentration of O₃, SO₂, NO₃, NO₂, HCHO, HNO₃, Benzene, Toluene, and Xylene, is also important for both urban and remote aerosol studies. They provide information that allows a much richer interpretation of PIXE data. Recently developed instruments that provide real time aerosol data such as the Tapered Element Oscillating Microbalance (TEOM) PM₁₀ monitor and automatic real time organic and elemental carbon analyzers provide extremely useful data to complement PIXE aerosol analysis. The concentrations of trace elements measured by PIXE comprise only 10–30% of the aerosol mass, leaving the organic aerosol characterization and measurement with an important role. The aerosol source apportionment provided by PIXE analysis can be extended with other aerosol measurements such as scattering and absorption, estimating for example, the radiative impact of each discriminated aerosol source. The aerosol bulk PIXE measurements can be complemented with soluble concentrations provided by Ion Chromatography (IC) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Recent developments in remote sensing techniques and products also enhance significantly regional aerosol studies. Three-dimensional air mass trajectories should be integrated in aerosol studies for urban and remote areas. The applications of these techniques to study urban aerosols from São Paulo and Santiago de Chile have broadened extensively the scientific scope of these studies.     

PIXE as a complement to trace metal analysis of sediments by ICP-OES

The adverse effects of metal contamination in sediments require methods that can quickly and accurately assess the extent of environmental pollution. Particle induced X-ray emission spectrometry (PIXE) is demonstrated to be a viable alternative to an established method, which consists of acid digestion and Inductively coupled plasma-optical emission spectrometry (ICP-OES) to measure trace metals in sediment. The analysis of trace metal composition by both techniques on a NIST Standard Reference Material mud gives results that are consistent with the certified values for fourteen measured metals, seven of which are common to both methods. A comparison study conducted on a sediment core from a freshwater lake with a known chromium contamination in Muskegon County, MI also shows a good correlation between the methods for transition metals of environmental interest over a wide range of metal concentrations. Total sample preparation and analysis time for the PIXE measurements is roughly one third that of acid digestion and ICP-OES. Also, the acid digestion step does not elute all the metal, while the nondestructive PIXE approach is a total metals analysis method. However the PIXE method generally has higher limits of detection for many environmental metal contaminants. By combining the two techniques, the acid digestion elution factor can be quantified by running PIXE on an original sample and on the residue resulting from acid digestion.     

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.     

Micro-crystalline inclusions analysis by PIXE and RBS

A characteristic feature of the nuclear microprobe using a 3 MeV proton beam is the long range of particles (around 70 μm in light matrices). The PIXE method, with EDS analysis and using the multilayer approach for treating the X-ray spectrum allows the chemistry of an intra-crystalline inclusion to be measured, provided the inclusion roof and thickness at the impact point of the beam (Z and e, respectively) are known (the depth of the inclusion floor is Z + e). The parameter Z of an inclusion in a mineral can be measured with a precision of around 1 μm using a motorized microscope. However, this value may significantly depart from Z if the analyzed inclusion has a complex shape. The parameter e can hardly be measured optically. By using combined RBS and PIXE measurements, it is possible to obtain the geometrical information needed for quantitative elemental analysis. This paper will present measurements on synthetic samples to investigate the advantages of the technique, and also on natural solid and fluid inclusions in quartz. The influence of the geometrical parameters will be discussed with regard to the concentration determination by PIXE. In particular, accuracy of monazite micro-inclusion dating by coupled PIXE-RBS will be presented.     

Analysis of atmospheric aerosols by particle-induced X-ray emission, instrumental neutron activation analysis, and ion chromatography

Particle-induced X-ray emission (PIXE), ion chromatography (IC), and occasionally also instrumental neutron activation analysis (INAA) were used in combination for the analysis of atmospheric aerosol samples that were collected on Nuclepore polycarbonate filters. A comparison of the results enabled us to evaluate the matrix effects (i.e., particle size effects) of the PIXE analysis for the light elements and to assess the water-solubility and/or speciation of a number of elements (e.g., S, K, Ca). Results are presented from several measurement campaigns at urban and forested sites in Europe, whereby PM10 or PM2.5 filter samples were taken. From the PIXE and IC results for a 2003 summer campaign at the K-puszta site in Hungary, it was estimated that organosulphates could be responsible for 20% of the total sulphur concentration and 30% of the organic aerosol in PM10. The comparison of the IC and PIXE data for K and Ca from the various sites indicated that most of the Ca was water-soluble (the mineral dust Ca was presumably mostly present as calcite, and perhaps also in part as gypsum); in contrast, for K, only half of it was typically water-soluble, indicating that it was to a large extent associated with insoluble mineral dust. Exceptions, with almost fully water-soluble K, were found for samples that were substantially impacted by biomass burning.     

Particle induced X-ray emission (PIXE) analyses on metal samples with structured surfaces

The X-ray yields obtained in PIXE measurements from metal samples with bent or relief surface have been investigated experimentally and by a computer simulation. It was found, that in the fundamental parameter method correct analytical results will be obtained, if two conditions are fulfilled: (1) the inclination of the tangential plane of the bent surface at the point where the ion beam hits this surface has to be known; and (2) the radius of curvature of the surface structure must be larger than 3 to 4 times the ion beam radius used.     

Pige coupled with PIXE for sodium determination in atmospheric aerosol samples

Experimental conditions are described for sodium detection on aerosol samples with a shielded NaI(Tl) gamma probe during PIXE measurements. The detection limit is approximately 50 ng.     

Subcellular trace element distribution in Geosiphon pyriforme

Geosiphon pyriforme is a unique endosymbiotic consortium consisting of a soil dwelling fungus and the cyanobacterium Nostoc punctiforme. At present this symbiosis becomes very interesting because of its phylogenetic relationship to the arbuscular mycorrhizal (AM) fungi. Geosiphon pyriforme could be an important model system for these obligate symbiotic fungi, which supply 80–90% of all land plant species with nutrients, in particular phosphorous and trace elements. Combined PIXE and STIM analyses of the various compartments of Geosiphon give hints for the matter exchange between the symbiotic partners and their environment and the kind of nutrient storage and acquisition, in particular related to nitrogen fixation and metabolism. To determine the quality of our PIXE results we analysed several geological and biological standards over a time period of three years. This led to an overall precision of about 6% and an accuracy of 5–10% for nearly all detectable elements. In combination with the correction model for the occurring mass loss during the analyses this holds true even for biological targets.     

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.     

An external sub-milliprobe optimized for PIXE analysis of archaeological samples

A simple and compact electrostatic quadrupole triplet lens has been designed and fabricated as part of the dedicated beam line for analysis of archaeological samples. A Fortran based ion optics program has been developed to simulate the beam line and lens parameters to achieve a focused sub-millimeter beam spot. The results of simulations are utilized to design and fabricate beam-line elements. The beam spot was measured by wire scanning method to be 0.3 mm for the object-slit width of 1 mm at a distance of 15 mm from the exit window. The improved Ion Beam Analysis setup allows accelerated PIXE analysis of samples whose details are comparable with the beam probe in size. The PIXE spectrum obtained by external analysis of a historical enameled ceramic sample with a sub-millimeter beam is compared with that obtained by in-vacuum standard PIXE analysis.