P. Duerden

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.

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.

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.

Depth profiles and microtopology

Abstract Depth profiling by ion beam techniques, including Rutherford backscattering and nuclear reaction methods, is affected by the presence of surface microtopology. This is especially true in glancing angle measurements which involve enhanced depth resolution. Such effects have been previously investigated for samples of uniform composition but basic ambiguities appear in the interpretation of measurements of non-uniform depth profiles when roughness is present. Measurements at a number of angles can provide information on the influence of both these uniformity and roughness factors on observed energy spectra.

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.

The problems and potential of ion beam techniques in archaeology and art: nuclear reaction analysis

Abstract The main features of nuclear reaction analysis techniques are compared with other ion beam techniques in the context of their usefulness in archaeometry. A new approach to equipment layout is proposed for dedicated use in measurements on artefacts and art objects.

Variability in pottery analysis

Abstract The PIXE/PIGME method has been used to obtain concentrations of 22 elements in samples of ancient pottery which had previously been analysed by (n, p) and (n, α) spectrometry. Some of the samples show similarities in composition although they are by no means identical. Others are completely different with some elements changing by at least an order of magnitude. Many factors can contribute to an explanation of the observed variability and each needs to be studied carefully in order to establish evidence for a specific hypothesis concerning grouping or the significance of variation.