E. Clayton

A discussion of PIXAN and PIXANPC: The AAEC PIXE analysis computer packages

Abstract After an experimental PIXE spectrum has been measured, two steps are necessary to estimate the concentration of elements in the sample giving rise to the spectrum. Firstly, one must analyse the spectrum and evaluate the areas of all characteristic peaks in the spectrum. Secondly, these peak areas must be utilised to derive element concentration data from these areas and a knowledge of the expected X-ray yield for that element. In this paper we describe two programs, BATTY and THICK which we have developed at the AAEC as the package PIXAN to perform these analysis steps. These programs have also been developed for running on IBM PC look alike computers as the package PIXANPC. Typical running times and use are discussed.

Proton induced γ-ray yields

Abstract To extend the information available for prompt nuclear analysis and to investigate discrepancies between published data, measurements were made of the γ-ray yields from proton induced nuclear reactions in F, Na, Mg, Al, Si, Cr, Mn, Fe, Cu and other elements. A large volume Ge(Li) detector was used with pure element or compound targets. Measurements were made at proton energies of 2.0 and 2.5 MeV. Thick target angular distributions are usually isotropic, but departures from isotropy can be observed when the yield is dominated by a large resonance near the incident energy. Integral calculations were made to obtain the stopping power correction factors necessary to derive pure element yields from measurements on compound and mixture targets.

Thick target pixe analysis and yield curve calculations

Abstract Four computer programs used for thick target proton induced X-ray emission (PIXE) research at the Australian Atomic Energy Commission are discussed. Different techniques of spectrum analysis are considered and a description is given of the spectrum synthesis code PUCK used in our analysis. Attention is focused on the use of theoretical thick target yield curves as a means of obtaining quantitative information on trace element concentration. Finally, several applications indicating the versatility of thick target PIXE analysis are mentioned.

PIXE-PIGME studies of artefacts

Abstract A system is described for simultaneous measurements of proton induced X-rays (PIXE) and gamma rays (PIGME) as an automated analysis system. Complete artefacts are mounted so as to minimize variations in position and angle of the irradiated surface, but no other special preparation is necessary. More than 20 elements are determined from X-ray and γ-ray intensities and the results are field for statistical tests and comparisons with appropriate source material. Measurements on obsidian, pottery, metal and other material show that the data are useful for sample characterization provided that weathering and other surface anomalies are not too severe.

A database for thick target PIXE

Abstract In order to convert peak areas from PIXE spectra into sample concentrations, a large database is needed. This database must be reliable and cover the widest possible range of targets, ions and energies. It need not be unique: several different databases may produce similar end results. Our database includes ionisation cross sections, ion stopping powers, X-ray mass attenuation coefficients, fluorescence yields, Coster-Kronig transition rates, X-ray line intensities and transition rates, together with a good knowledge of the detection efficiency. It covers both proton (PIXE) and helium ion (HIXE) bombardment from 100 keV to 10 MeV for all targets composed of elements from hydrogen to uranium for both K and L shell X-rays. We have tested it successfully on a wide variety of samples. We present this database together with polynomial fits to some of the key parameters so others may use it.

Provenance studies of New Zealand obsidian artefacts

Abstract A large scale obsidian analysis program at the AAEC Research Establishment uses an automated facility with a multisample capacity and simultaneous PIXE and PIGME measurement. A pinhole filter in front of the PIXE detector ensures that up to 20 element concentrations can be obtained from the samples in a 5 min irradiation. Spectrum analysis and data handling procedures have been set up together with a variety of parametric and non-parametric statistical procedures. The clustering programs have been used with data from a previously measured S.W. Pacific and New Zealand obsidian source collection to identify the origin of artefact material. The example used to illustrate this provenancing program is of obsidian artefacts from the Kermadec and Chatham Islands.

PIXE analysis of thick target biological samples in vacuum

Abstract Analysis of thick target biological samples in vacuum is beset with several difficulties. The major problem is that the measured peak areas for the analysed trace elements increase with increasing current density. In this paper we show that powdering the sample and mixing with yttrium spiked graphite overcomes this problem and also removes charging difficulties. When calculating thick target yields for PIXE analysis we need to know the major components of carbon, nitrogen, oxygen and hydrogen. The use of techniques such as deuteron and proton induced gamma ray emission and non-Rutherford backscattering for determining these elements is discussed.

Recent ion beam analysis studies on archaeology and art

Abstract Recent ion beam analysis studies of archaeological and art material, which have been carried out at the AAECs Lucas Heights Research Laboratories, are described and the facilities available briefly discussed. Techniques used in the studies include particle induced X-ray emission (PIXE) with both protons and alpha particles as the incident ions, proton induced gamma-ray emission (PIGME), Rutherford backscattering (RBS) and forward recoil analysis. The materials studied include obsidian, pottery and desert varnish, and both provenance and dating studies are discussed. A brief description of data analysis and the use of statistical assessments for data interpretation is also included.

Ion beam analysis studies of desert varnish

Abstract The components of “desert varnish” cover on rock surfaces from western New South Wales have been investigated by a number of ion beam techniques. The elemental data obtained so far show significant changes in composition of F, Na, K, Ti, Ba and Mn when varnish is present on the rock surface.

The use of PIXE for the measurement of thorium and uranium at μgg−1 levels in thick ore samples

Abstract Proton induced X-ray emission (PIXE) techniques have been used to estimate the concentrations of trace quantities of thorium and uranium in pelletised powdered rock and ore samples. A variety of naturally occurring ores with uranium and thorium concentrations in the range 10–10 000 μg g −1 have been studied. The lower level detection limit with no adjacent element interference was 3–4 μg g −1 per 100 μC. To verify the PIXE technique for thorium and uranium determination, the same batch of samples was measured by delayed neutron activation for uranium concentrations, and neutron activation analysis for thorium concentrations. They were in excellent agreement.