Attila Stopic

Evaluation of relative comparator and k 0 -NAA for characterization of Aboriginal Australian ochre

Ochre is a significant material in Aboriginal Australian cultural expression from ceremonial uses to its application on many types of artifacts. However, ochre is a complex material, with associated surrounding minerals potentially challenging the overall analysis. In recent literature several studies have attempted to characterize ochre by a variety of techniques to understand procurement and trade. However, ochre is difficult to differentiate on major elemental or mineralogical composition and requires a detailed analysis of its geochemical “fingerprint”. Neutron activation analysis (NAA) provides the high sensitivity (sub-ppm), precision and accuracy in multi-elemental analysis required for ochre. The elements of interest for ochre generally include rare earth elements (REEs) and certain transition metal elements as well as arsenic and antimony. Data from relative comparator NAA (MURR, University of Missouri, USA) is compared with data from k0-NAA OPAL (ANSTO, Lucas Heights, Australia). A discussion of the two methods will be examined for their utility in “fingerprinting” the provenance of ochre. The continuing importance of NAA to archaeometry will also be discussed.

Ceramics, trade, provenience and geology: Cyprus in the Late Bronze Age

The island of Cyprus was a major producer of copper and stood at the heart of east Mediterranean trade networks during the Late Bronze Age. It may also have been the source of the Red Lustrous Wheelmade Ware that has been found in mortuary contexts in Egypt and the Levant, and in Hittite temple assemblages in Anatolia. Neutron Activation Analysis (NAA) has enabled the source area of this special ceramic to be located in a geologically highly localised and geochemically distinctive area of western Cyprus. This discovery offers a new perspective on the spatial organisation of Cypriot economies in the production and exchange of elite goods around the eastern Mediterranean at this time.

Purity of 28Si-Enriched Silicon Material Used for the Determination of the Avogadro Constant

At present, counting atoms in a one-kilogram sphere made of (28)Si-enriched silicon allows the determination of the Avogadro constant with the 2.0 × 10(-8) relative standard uncertainty required for the realization of the definition of the new kilogram. With the exception of carbon, oxygen, boron, nitrogen, and hydrogen, the claimed uncertainty is based on the postulation that the silicon material used to manufacture the sphere was above a particular level of purity. Two samples of the silicon were measured using instrumental neutron activation analysis to collect experimental data to test the purity assumption. The results obtained in two experiments carried out using different research reactor neutron sources are reported. The analysis confirmed that the silicon material was of sufficient purity by quantifying the ultratrace concentration of 12 elements and determining the detection limits of another 54 elements.

Evaluation of Westcott g(T n )-factors used in k 0-NAA for “non-1/v” (n,γ) reactions

Abstract The Westcott convention was introduced in the early 1990s in k0-NAA to allow the analysis of nuclides whose thermal neutron capture cross-sections do not follow the “1/v”-law, so called “non-1/v” nuclides. Most affected nuclides are Lu-176, Eu-151 and Yb-169. Westcott introduced a neutron temperature dependent “g(Tn)-factor” for the activation by thermal neutrons. Recently the extended Høgdahl convention was introduced in k0-NAA for “non-1/v” nuclides using the same factor, emphasizing the interest in the analysis using these nuclides. This paper reviews most publications on “g(Tn)-factors” for NAA and provides new factors based on the most recent evaluated nuclear database ENDF/B-VII.1.

Establishing a basis for nuclear archaeometry in Australia using the 20 MW OPAL research reactor

The k0-method of standardisation for instrumental neutron activation analysis (INAA) has been used at the OPAL research reactor to determine the elemental composition of three certified reference materials: coal fly ash (SRM 1633b), brick clay (SRM 679) and Montana soil (SRM 2711). Of the 41 certified elements in the three materials, 88 percent were within five percent of the certified values and all determinations were within 15 percent of the certified values. The average difference between the measured and certified values was 0.1 percent, with a standard deviation of 4.1 percent. Since these reference materials are widely used as standards in the analysis of archaeological ceramics by INAA, it has been concluded that the INAA facility in Australia is particularly well-suited for nuclear archaeometry.

Irradiation pneumatic system fine-tuning using accelerometers

The OPAL research reactor is fitted with short-residence pneumatic irradiation systems to facilitate neutron activation analysis using short-lived isotopes. Irradiation timing information as reported by the control system was found to be inaccurate. Two independent methods were employed to understand the behaviour of the system, the first using activation methods while the second method involved sending irradiation cans fitted with self-contained logging accelerometers in and out of the reactor. Results from these tests were used to correct errors in the control system parameters and enable further process optimisation of the pneumatic system.

Porous ZrC-carbon microspheres as potential insoluble target matrices for production of 188W/188Re

New microsphere sorbents are reported, which could find application in demanding radiation environments and especially as targets for the production of nuclear medicines by neutron irradiation. An easily-synthesized Zr anionic complex was introduced into quaternary amine-functionalised polystyrene-divinylbenzene-based anion-exchange resins by batch adsorption. Upon carbothermal reduction, the precursors were converted to porous carbon matrices containing particles of ZrC and ZrO2 polymorphs. The most phase-pure material, ZrAX-1, possessed high surface area, multi-scale porosity and high mechanical strength. Adsorption of Re and W was investigated and its possible deployment as a reusable host for the production of 188W/188Re is discussed.

Measurement of the 30Si Mole Fraction in the New Avogadro Silicon Material by Neutron Activation and High-Resolution γ-Spectrometry

The use of new silicon single crystals highly enriched in 28Si recently produced for the upcoming redetermination of the Avogadro constant requires knowledge of their molar masses. The isotopic composition data are collected independently in different laboratories but all using the virtual element technique with multicollector inductively coupled plasma mass spectrometers. In this framework, the comparison of the results with an independent measurement of the amount of at least one of the depleted isotopes is useful to limit hidden systematic errors. To this aim, the 30Si mole fraction of a sample of the new material was measured using a relative measurement protocol based on instrumental neutron activation analysis. The protocol is similar to that previously applied with the AVO28 silicon material used for the last determination of the Avogadro constant value with the exception that unknown and standard samples are not coirradiated. The x(30Si) = 5.701 × 10-7 mol mol-1 estimate is close to the expected one and is given with a standard uncertainty of 8.8 × 10-9 mol mol-1. This value, if adopted, gives a contribution to the relative standard uncertainty of the Avogadro constant of 6.3 × 10-10.

Impurities in a 28Si-Enriched Single Crystal Produced for the Realization of the Redefined Kilogram

The practical realization of the unit of mass is possible by manufacturing a perfect one-kilogram sphere from a 28Si-enriched single crystal. The mass of the sphere can be determined in terms of a fixed value of the Planck constant by counting the number of silicon atoms in the core of the single crystal. To reach the target 2.0 × 10-8 relative standard uncertainty, the mass of the surface layer and the mass deficit due to point defects such as impurities and vacancies must be investigated and corrected for. A sample of a 28Si-enriched single crystal produced to test the possibility of obtaining material at a scale useful to the dissemination of mass standards was measured by instrumental neutron activation analysis to check the purity with respect to a large number of possible contaminant elements. The results collected in a neutron activation experiment performed with the high thermal neutron flux available at the 20 MW OPAL research reactor are described. The data collected in this study showed that the produced material has a purity level never achieved with silicon used to manufacture previous one-kilogram spheres.

The robustness of k0-NAA in large multi-purpose research reactors

The challenges and opportunities associated with performing k0-NAA in high-powered, multi-purpose research reactors are examined and recommendations are made concerning the conditions that need to be met in such facilities in order to allow the potential for this method of elemental analysis to be fully realised.