Johannes H. Sterba

Geochemical fingerprints by activation analysis of tephra layers in Lake Van sediments, Turkey

We discuss geochemical and sedimentological characteristics of 12 tephra layers, intercalated within the finely laminated sediments of Lake Van. Within the about 15kyr long sediment record studied, volcanic activity concentrated in the periods 2.6-7.2 and 11.9-12.9kyr B.P. Concentrations of 25 elements provide the geochemical fingerprint of each tephra layer and allow comparison to literature values of potential source volcanoes such as Mts. Nemrut and Süphan. The youngest two tephra layers (and probably also the other three ashes from the 2.6-7.2kyr B.P. eruptions) originate from the Nemrut volcano. The source of the older tephra (11.9-12.9kyr B.P.), however, remains unidentified.

Prospects for measuring the 229Th isomer energy using a metallic magnetic microcalorimeter

The Thorium-229 isotope features a nuclear isomer state with an extremely low energy. The currently most accepted energy value, 7.8±0.5 eV, was obtained from an indirect measurement using a NASA x-ray microcalorimeter with an instrumental resolution 26 eV. We study, how state-of-the-art magnetic metallic microcalorimeters with an energy resolution down to a few eV can be used to measure the isomer energy. In particular, resolving the 29.18 keV doublet in the γ-spectrum following the α-decay of Uranium-233, corresponding to the decay into the ground and isomer state, allows to measure the isomer transition energy without additional theoretical input parameters, and increase the energy accuracy. We study the possibility of resolving the 29.18 keV line as a doublet and the dependence of the attainable precision of the energy measurement on the signal and background count rates and the instrumental resolution.

The successful "recipe" for a long-lasting tradition: Nubian ceramic assemblages from Sai Island (northern Sudan) from prehistory to the New Kingdom

Abstract Sai Island, in the Nile in northern Sudan, has a series of settlement sites spanning the entire period from the eighth millennium BC through to the Eighteenth Dynasty of the Egyptian New Kingdom. This long sequence provides an excellent opportunity to study continuity and discontinuity in long-term pottery traditions. Ceramics from the varying cultural phases of the occupation reflect changing dynamics between broader regional social identities, notably Kerma to the south and Egypt to the north. Combining studies of petrography with trace element composition and chaîne opératoire analysis, the authors present the first diachronic study of ceramic manufacture throughout the extended cultural history of Nubia, highlighting the varying manifestations of change and continuity.

Feasibility study for production of 99mTc by neutron irradiation of MoO3 in a 250 kW TRIGA Mark II reactor

The subject of this paper is to explore the possibility to obtain 99mTc from activation of 98Mo, using the TRIGA Mark II low flux research reactor (Vienna, Austria). Irradiation of both natural and enriched in 98Mo molybdenum oxides was compared. Aims of this work included the determination of neutron fluxes and 98Mo(n, γ)99Mo reaction effective cross section in the TRIGA Mark II reactor irradiation channels, calculation of 99Mo specific activities, determination of optimal irradiation conditions for the subsequent 99mTc separation from MoO3 targets using concentrating technologies.

Feasibility study of measuring the Th 229 nuclear isomer transition with U 233 -doped crystals

We propose a simple approach to measure the energy of the few-eV isomeric state in Th-229. To this end, U-229 nuclei are doped into VUV-transparent crystals, where they undergo alpha decay into Th-229, and, with a probability of 2%, populate the isomeric state. These Th-229m nuclei may decay into the nuclear ground state under emission of the sought-after VUV gamma, whose wavelength can be determined with a spectrometer. Based on measurements of the optical transmission of U:CaF2 crystals in the VUV range, we expect a signal at least 2 orders of magnitude larger compared to current schemes using surface-implantation of recoil nuclei. The signal background is dominated by Cherenkov radiation induced by beta decays of the thorium decay chain. We estimate that, even if the isomer undergoes radiative de-excitation with a probability of only 0.1%, the VUV gamma can be detected within a reasonable measurement time.

Investigation of the isotopic ratio 129I/I in petrified wood.

In fossil specimens, measurements of the natural isotopic ratio (129)I/I may provide a method to estimate the age of sample. The motivation for measuring the isotopic composition ((129)I/I) of petrified wood samples collected from Austria was to check this feasibility. Alkaline fusion together with anion exchange was used to extract iodine from the sample. Typical sample size for this study was 10-90 g. An atomic ratio as low as 10(-14) was determined using accelerator mass spectrometry (AMS). Uranium concentrations measured by instrumental neutron activation analysis (INAA) and α-spectrometry were found to be less than 3 mg kg(-1), therefore the contribution from fissiogenic (129)I was small and an estimation of ages was based on the decrease of the initial ratio (due to decay of the cosmogenic (129)I in a closed system) after subtraction of the fissiogenic (129)I. The value of the prenuclear ratio is crucial for the use of the (129)I system for dating purposes in the terrestrial environment. From the preanthropogenic (initial) ratio of 1.5 × 10(-12) of the hydrosphere and the results of the present study for the samples from Altenburg (1.05 × 10(-12)) and Fuerwald (6.16 × 10(-13)), respective ages of 8 ± 2.2 and 20.2 ± 2.2 million years were derived. Since samples were collected from a stratum deposited in the Upper Oligocene/Ergerien period (~25-30 million years ago), it can be concluded that these isotopic ratios do not show ages but an elapsed time since fossil wood was isolated from mineral rich water. Paleontological investigation shows that samples from Altenburg had mixed characteristics of old and modern Tertiary plants, thus an origin from a younger stratum re-sedimented with Oligocene cannot be excluded. However, the sample from Drasenhofen reflects that the (129)I/I system might not always be suitable for the dating of petrified wood sample due to fixation of anthropogenic (129)I into surface fractures.

Instrumental neutron absorption activation analysis

We present and discuss a modification of instrumental neutron activation analysis (INAA) that is sensitive for nuclides that do not yield (suitable) activation products but have high cross sections for neutron absorption. Their presence in a sample may thwart INAA by neutron flux suppression inside the sample, but they remain undetected and thus unnoticed by the analyst. In particular, this refers to Li, B, Cd and Gd. The proposed method—instrumental neutron absorption activation analysis (INAAA)—takes advantage of the flux depression inside the sample caused by the neutron absorbers. It is made visible by addition of an activatable nuclide (indicator). The concentration of the neutron absorber (analyte) causes a decrease in activity of the indicator. The activity difference between a mixed sample (sample plus indicator) and the pure indicator carries the analytical information. The calibration curve hence follows a reciprocal exponential function. In a proof-of-principle experiment, the applicability for the quantification of boron was exemplified. In presence of only one neutron absorber (whose nature is known), INAAA can be applied easily for quantification of the analyte in powdered or liquid samples. Although INAAA is no trace sensitive method, it has the potential to increase the reliability of INAA analyses by fast and straightforward quality control (even in presence of two or more neutron absorbing nuclides). It is especially suited for research reactors that do not operate a prompt gamma neutron activation analysis (PGNAA) station.

Raising the temper—μ-spot analysis of temper inclusions in experimental ceramics

Provenancing of ancient ceramics is a highly important scientific tool for archaeological studies. In general, ceramics are not made from the original clay as it is found in deposits. To produce the needed physical properties in the finished product, the clay has to be either tempered by adding sands or biological materials, or levigated, to remove the coarse fraction. Thus, the chemical composition of the finished ceramic differs from the composition of the original clay bed. To overcome this obfuscation, any information that can be gained about the temper is useful. In a small series, several pieces of ceramic were produced from known clay and tempers and the resulting ceramics analysed by neutron activation analysis (NAA). As many attempts to physically separate the temper from the clay matrix have failed, μ-spot analysis of temper inclusions was performed at the microbeam particle induced X-ray Emission (μ-PIXE) facility in Rossendorf and with laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS) at the Aberystwyth University in Wales. It could be shown that from a small number of measurements, a general impression of the temper used could be gained. Furthermore the μ-spot methods and the bulk data gained from INAA are highly comparable, extending the set of elements that can be measured. With this information, the influence of the temper on the bulk composition of the finished product can be estimated, which potentially adds crucial information to subsequent dilution calculations.

On the geochemistry of the Kyra eruption sequence of Nisyros volcano on Nisyros and Tilos, Greece

The Kyra sequence is a volcanic eruption sequence originating from the eastern flank of Nisyros volcano, Greece. Its eruptions products can be found not only on Nisyros itself but also on the nearby non-volcanic island of Tilos. In an extensive sampling campaign, outcrops of the Kyra eruption products on Nisyros were sampled and corresponding samples on Tilos were taken. The clear stratigraphical relationship between the different units within in the individual outcrops, combined with the chemical information gained by the application of instrumental neutron activation analysis (INAA) to the samples, made a detailed chemo-stratigraphy of the complete eruption sequence possible. It can be shown that the sequence is separated into eight distinguishable eruptions. Furthermore, no eruption products of the caldera-forming eruptions from Nisyros (Lower- and Upper Caldera Pumice) or from Santorin were found on Tilos.

A workflow for neutron activation analysis of archaeological ceramics at the Atominstitut in Vienna, Austria

The main focus for neutron activation analysis (NAA) at the Atominstitut in Vienna has moved to the analysis of archaeological ceramics. The workflow for NAA has been adapted for this material and the elemental spectrum quantified has been expanded for compatibility with international databases. Statistical methods for the grouping of the archaeometric data have been implemented, following the methods applied by Mommsen et al. in Bonn (Archaeometry 30(1):47–57, 1988). Limits of detection specific for ceramics have been calculated and are at the ng/g level. High reproducibility as necessary for archaeometric analysis can be shown by comparative measurements of an internal quality control sample.