Sull'origine delle terre rosse in Sardegna: gli elementi in traccia nella caratterizzazione di suoli e rocce madri

The trace elements in the characterization or red soils and parent rocks. The genesis of red soils (Terre Rosse) formed on limestone or dolomite rock bed is yet an unsolved question. A theory suggests that these soils are the final step of an intense decarbonation process of the parent rock followed by the change of the materials in the insoluble residue into iron oxides and clay minerals. A number of trace elements, most1y transition metals, was determined in Sardinian Terre Rosse and parent rocks by instrumental neutron activation analysis performing different irradiations in the TRIGA Mark II nuclear reactor of the University of Pavia. Induced radioactivity measurement was carried out by gamma-ray spectrometry using a High Purity germanium detector coupled to an analyzer-computer system. The same elements were also determined in some standard reference rocks, released by United States Geological Survey, in order to evaluate the accuracy of the employed analytical method. Average values of the trace element content in the Terre Rosse and in the parent rocks are presented and discussed, together with the evaluation of precision and accuracy. Trace element profiles at different horizons are reported as well. A comparison of trace element distribution among soils belonging to the same geological era is also presented

Increasing data (INAA) on Ecuadorian obsidian artifacts: preliminary provenance and a clue for pre-Columbian eastward trade.

In this work we carried out INAA major (Na, K, Ca and Fe %) and trace (ppm) elements (plus Mn by FAAS analysis) of 15 obsidian samples (waste flakes) coming from an unknown archaeological site (14C-AMS age of 1425 AD) located on the south-eastern flank of the back-arc Sumaco volcano, in the Sub-Andean Ecuador (to the east of the Cordillera Real) and from two already known pre-Columbian archaeological localities: La Florida (Quito) and Milan (Cayambe). Literature compositional data of the Ecuadorian obsidian outcrops (Bigazzi et al., 1992, Asaro et al., 1994, Bellot-Gurlet et al., 1999, 2008) provide some constraints on the provenance of the analyzed waste flakes, even though different methods of analyses make comparisons a difficult task. Concerning the obsidian artifacts of La Florida and Milan, they come from the well known Sierra de Guamanì obsidian sources (Cordillera Real). By contrast, the obsidian fragments of the Sumaco settlement show Mn-rich, U- Th-poor compositions and relatively high Nb/Zr ratios, these characters being compatible with obsidian erratic pebbles recently discovered by Bellot-Gurlet et al. (2008) in some river banks of the Amazonian foothills draining the easternmost flanks of the Antisana volcano in the Cordillera Real as well. In this way, the obsidian artifacts found at the Sumaco site reinforce the opinion of Bellot-Gurlet et al. (2008) that Ecuadorian source inventory is not yet exhaustive. These preliminary inferences of provenance for the Sumaco obsidian findings would however need to be furtherly tested with the same analytical methods on both artifacts and sources. The Antisana volcano, located 30 km to WNW of the Amazonian foothills, seems to be the best candidate to find out additional primary outcrops of obsidian sources. Obsidian ancient trade was well established in Ecuador among the Andean people of the Cordillera Real and between them and people of the Pacific coast, whereas an eastward trade toward the rainforest people was never documented. In this framework, the archaeometric study of the obsidian samples of the 1425 AD site of Sumaco, located well eastward of the Cordillera Real, is of paramount importance in tracing the ancient routes of the obsidian trade toward the Amazonian region. It can not be also excluded that sub-Andean and Amazonian people direcly took advantage from obsidian secondary sources (i.e. within the river banks of the Amazonian foothills) rather than procurements from primary outcrops in the Cordillera Real

Neutron activation analysis of the 30Si content of highly enriched 28Si: proof of concept and estimation of the achievable uncertainty

We investigated the use of neutron activation to estimate the 30Si mole fraction of the ultra-pure silicon material highly enriched in 28Si for the measurement of the Avogadro constant. Specifically, we developed a relative method based on Instrumental Neutron Activation Analysis and using a natural-Si sample as a standard. To evaluate the achievable uncertainty, we irradiated a 6 g sample of a natural-Si material and modeled experimentally the signal that would be produced by a sample of the 28Si-enriched material of similar mass and subjected to the same measurement conditions. The extrapolation of the expected uncertainty from the experimental data indicates that a measurement of the 30Si mole fraction of the 28Si-enriched material might reach a 4% relative combined standard uncertainty