H.C. Kaufmann

REX - A Computer Programme for PIXE Analysis

The implementation of a physics-based model for non-linear least-squares analysis of proton-induced X-ray emission spectra via a Fortran programme REX is discussed. The modelling of distinct spectral components and of the physical effects involved is briefly discussed. Results are presented in graphical and tabular form. The limitations of the present model are discussed and future refinements indicated.

Tree-ring analysis by pixe for a historical record of soil chemistry response to acidic air pollution

Tree cores have been analyzed intact in 1 mm steps, corresponding to time intervals in the rings as short as half a growing season, providing a chronological record of 16 elemental concentrations extending over thirty years back to 1950. Samples were collected in a forested region of western Canada in sandy soil which was impacted by acid-forming gases released by a sulfur recovery sour natural gas plant. Tree core samples of the hybrid lodgepole-Jack pine (Pinns contorta Loud. × Pinus banksiana Lamb.) were taken in five ecologically similar locations between 1.2 and 9.6 km from the gas plant stacks. Concentrations of some elements showed patterns suggesting that the annual rings preserved a record of changing soil chemistry in response both to natural environmental conditions and to deposition from sulfur gas emissions, commencing after plant start-up in 1959 and modified by subsequent modifications in plant operating procedures. These patterns were most pronounced nearest the gas plant. Certain other elements did not exhibit these patterns, probably reflecting greater importance of biological than of soil chemical properties. The high time resolution of tree-ring analysis, which can be achieved by PIXE, demonstrates that the rings preserve a historical record of elemental composition which may reflect changes in soil chemistry during plant growth as it may be affected by both natural ecological processes and acidic deposition from the atmosphere.

Non-Linear Least Squares Analysis of Proton-Induced X-Ray Emission Data

A Fortran program for analysis of spectra obtained in proton induced x-ray emission spectroscopy is under development. The first version is working and some results are shown. The program uses a model which describes the physics involved in the analysis. The continuum is described by an exponentially decreasing function representing secondary electron induced bremsstrahlung and a constant approximating different Compton scattering processes. Absorption effects are also included. All parameters in the model are fitted simultaneously. About 100 test runs have been made with good results. The continuum was accurately fitted for each spectrum. Other advantages are reliability, speed, and the fact that the program is easily adaptable to a small computer with 16K memory. (Less)

Advances In The Use Of Pixe And Pesa For Air-Pollution Sampling

Abstract Proton induced X-ray emission (PIXE) and proton elastic scattering analysis (PESA) are complementary ion beam techniques well suited to giving total elemental analysis of small samples. Air particulate samplers designed to yield ideal small samples have been developed at Florida State University to give size and time distributions of the particulates. The two methods are discussed using samples taken mostly at Kawecki Berylco Industries.

Thick target elemental analysis of organic and inorganic materials by PIXE using thin film standards

Abstract Modification of a mathematical procedure developed by Reuter et al. in 1975 allows the use of thin target reference standards to compute thick target elemental concentrations. The computer program is used in conjunction with the HEX program for X-ray spectrum resolution, and it takes account of both proton energy loss and X-ray attenuation by the target as they depend on target composition. These are determined by the target mass which includes the elements measured by PIXE and an additional low Z component which is calculated from observed X-ray line intensities. The sum of concentrations is constrained to equal 100%. The procedure has been applied to the PIXE analysis of a set of US Environmental Protection Agency polymer film elemental standards and of three US National Bureau of Standards standard reference materials irradiated as pressed pellets for 15 min at 1.58 and 2.52 MeV proton beam energy. The resulting composite spectra are resolved for elemental concentrations down to 1 ppm with good agreement with certified values.

PIXE calibration and absorption corrections with the aid of proton scattering

Abstract The computer programme HEX (a modification of programme REX) is a nonlinear, least squares, matrix minimization code for evaluation of Si(Li) detector X-ray spectra induced by charged particle bombardment. Correction to the Gaussian areas to allow for low energy tailing of peaks and secondary fluorescence has been included in the calculation. For our detector, this correction is largest (9%) for phosphorous and decreases with X-ray energy to less than 1% for copper. Since our present range of energies observed extends from 0.6–40 keV, absorption errors are usually large for the softer X-rays. Inclusion of L X-ray line intensities (down to 0.897 keV, Z = 28) into the fitting process allows for evaluation of absorption. In addition, the amount of absorption correction for sodium in air particulate field samples (where particle size effects dominate) has been assessed by comparison with results from the proton scattering (PESA) method.

Variation of Elemental Composition with Particle Size in the St. Louis Aerosol

Detailed particle size distribution of elemental constituents have been determined in the St. Louis aerosol by sampling with cascade impactors for particles >0.25 μm aerodynamic diameter and by analyzing using proton-induced X-ray emission, PIXE, for S, Cl, K, Ca, Ti, Mn, Fe, Zn, Br, and Pb. Two rooftop sites were selected for intensive sampling in industrial and residential locations in St. Louis during February 1974, every 12 h for a 7 d period which included clear, rainy, and snowy weather regimes. The data could be compared with the results of a similar study of the St. Louis aerosol during August 1973 when the weather was generally warm and without rain. Both data sets could also be compared with results of studies of Tallahassee, situated in coastal north Florida, and the north Atlantic marine atmosphere of Bermuda. Although variation in elemental concentrations and their size distributions were observed which could be associated with local weather conditions during the February sampling period, the data set was sufficiently large for meaningful average characteristics to be computed. As examples, two elements of pollution importance, sulfur and iron, show the following comparison between St. Louis and the Florida and Atlantic locations: Sulfur in all data sets was most abundant in the smallest particle size classes. Winter and summer concentration in St. Louis air were the same within a factor of two but generally exceeded north Florida concentrations. Bermuda concentrations were intermediate between St. Louis and north Florida, except for largest particles where sea spray derived material was present. The results reflect the importance of gas phase conversion to particulate forms of sulfur, e.g. sulfate, in all three locations. Iron concentrations in St. Louis generally exceeded those in north Florida for smallest particles and to a lesser extent for larger sizes. Concentrations in Bermuda were about 10-fold lower than in St. Louis for all particle sizes. The results reflect the terrestrial dust origin of iron and also suggest that iron is partially pollution-derived in the St. Louis atmosphere, especially in smaller size ranges. (Less)

Aerosol lead and associated elements in Beijing, China

The relative importance of local and regional sources of lead and associated elements in fine and coarse aerosol particles of an urban atmosphere was assessed by means of a two-day study, July 20 and 30, 1980 in Beijing, China. Five near-ground locations were selected for aerosol sampling by cascade impactors and elemental analysis by proton induced X-ray emission (PIXE): the imperial palace courtyard, a park, near two streets, and a mid-street traffic island. These sites, ranked in order of increasing traffic intensity and fugitive surface dust, showed that concentrations of major dust constitutents, represented by coarse particle (>2 μm diameter) Si, Al, and Ca, increased correspondingly. Pb, as well as Zn, As, and Cu, were present mainly in fine (<2 μm) particles; their concentrations were unrelated to traffic, indicating they resulted mainly from regional combustion or other sources. However, these elements also were present in coarse particles at concentrations that varied with the major dust elements and were relatively enriched, compared to average earth crust rock material, by factors of more than 100 (Pb), 50 (Zn), and 10 (Cu). Nonurban Beijing shows much smaller coarse aerosol enrichments of Pb, Zn, and Cu, indicating urban contamination of surface dust. Published data from St. Louis, USA show both fine and coarse aerosol Pb and Zn. Compared with Beijing, fine and coarse concentrations in St. Louis are similar for Pb, but lower for Zn, Ca, and Fe. Both Pb and Zn are enriched relative to earth crust composition to a greater degree in St. Louis than Beijing in both fine and coarse particle size ranges. The results suggest that heavy metals from combustion occur in the air as fine particles and, after deposition on the surface, as reentrained coarse particles of fugitive dust. Both many contribute to human exposures of these heavy metals.

The use of PIXE in generating evidence for primordial superheavy elements

Abstract The physical and chemical nature of the monazite inclusions studied through PIXE in the search for superheavy elements sharply constrained the nature of the analysis and set strict limits on the nature fo the ion beam and X-ray detection techniques.

Beryllium analysis of simulated aerosol samples by proton scattering

Abstract Proton scattering analysis is demonstrated to be suitable for assessment of the beryllium content of aerosols. Cross sections are such that the method could be applied over a wide range of bombarding energies. The method may be applied in coniunction with other methods such as proton induced X-ray emission analysis.