Ivan Callegari

A new FSA approach for in situ γ ray spectroscopy.

An increasing demand of environmental radioactivity monitoring comes both from the scientific community and from the society. This requires accurate, reliable and fast response preferably from portable radiation detectors. Thanks to recent improvements in the technology, γ spectroscopy with sodium iodide scintillators has been proved to be an excellent tool for in-situ measurements for the identification and quantitative determination of γ ray emitting radioisotopes, reducing time and costs. Both for geological and civil purposes not only (40)K, (238)U, and (232)Th have to be measured, but there is also a growing interest to determine the abundances of anthropic elements, like (137)Cs and (131)I, which are used to monitor the effect of nuclear accidents or other human activities. The Full Spectrum Analysis (FSA) approach has been chosen to analyze the γ spectra. The Non Negative Least Square (NNLS) and the energy calibration adjustment have been implemented in this method for the first time in order to correct the intrinsic problem related with the χ(2) minimization which could lead to artifacts and non physical results in the analysis. A new calibration procedure has been developed for the FSA method by using in situ γ spectra instead of calibration pad spectra. Finally, the new method has been validated by acquiring γ spectra with a 10.16 cm × 10.16 cm sodium iodide detector in 80 different sites in the Ombrone basin, in Tuscany. The results from the FSA method have been compared with the laboratory measurements by using HPGe detectors on soil samples collected particular, the (137)Cs isotopes has been implemented in the analysis since it has been found not negligible during the in-situ measurements.

Calibration of HPGe detectors using certified reference materials of natural origin

The feasibility of using certified reference materials for the full energy efficiency calibration of p-type coaxial high-purity germanium detectors for the determination of radioactivity in environmental samples is discussed. The main sources of uncertainty are studied and the contributions to the total uncertainty budget for the most intense gamma lines are presented. The correction factors due to self-absorption and true coincidence summing effects are discussed in detail. The calibration procedure is validated for natural and artificial radionuclide determination in different matrices through an internal cross-validation and through the participation in a world-wide open proficiency test.

A multivariate spatial interpolation of airborne γ-ray data using the geological constraints

In this paper we present maps of K, eU, and eTh abundances of Elba Island (Italy) obtained with a multivariate spatial interpolation of airborne γ-ray data using the constraints of the geologic map. The radiometric measurements were performed by a module of four NaI(Tl) crystals of 16 L mounted on an autogyro. We applied the collocated cokriging (CCoK) as a multivariate estimation method for interpolating the primary under-sampled airborne γ-ray data considering the well-sampled geological information as ancillary variables. A random number has been assigned to each of 73 geological formations identified in the geological map at scale 1:10,000. The non-dependency of the estimated results from the random numbering process has been tested for three distinct models. The experimental cross-semivariograms constructed for radioelement-geology couples show well-defined co-variability structures for both direct and crossed variograms. The high statistical correlations among K, eU, and eTh measurements are confirmed also by the same maximum distance of spatial autocorrelation. Combining the smoothing effects of probabilistic interpolator and the abrupt discontinuities of the geological map, the results show a distinct correlation between the geological formation and radioactivity content. The contour of Mt. Capanne pluton can be distinguished by high K, eU and eTh abundances, while different degrees of radioactivity content identify the tectonic units. A clear anomaly of high K content in the Mt. Calamita promontory confirms the presence of felsic dykes and hydrothermal veins not reported in our geological map. Although we assign a unique number to each geological formation, the method shows that the internal variability of the radiometric data is not biased by the multivariate interpolation.

The Miocene successions of the Fiora Hills: considerations about the development of the minor basins of Southern Tuscany

The Miocene sequences of Southern Tuscany represent the first post-nappe sedimentary record of the Northern Apennines, and are linked with the opening of the Tyrrhenian Sea. The sequences are located in several basins, characterizing the hinterland of the orogen. They are settled on a stack that is composed of deformed tectonic units and are capped by Plio-Pleistocene deposits. The respective basins have been strongly controlled by tectonics, which have remarkably forced the sedimentation. The Fiora Hills represent the southernmost area of Tuscany, where there are some minor but significant examples of these basins. In particular, they are the Fiora and the Tafone basins, the infillings of which are characterized by Miocene successions subdivided into several depositional units separated by unconformity or correlative conformity surfaces. This study deals with the stratigraphic features of such Miocene basinal infillings, with the aim being to define the depositional architecture and the tectonic-sedimentation interplays. Moreover, the collected data also enables there to be a discussion of some of the aspects of the basins’ structuring that are linked with the Miocene evolution of the hinterland of the Northern Apennines. The entire Miocene succession of the Fiora Hills spans from the Langhian up to the late Messinian, with there being minor differences between the Fiora-Tafone basins and with the nearby Albegna Basin. In general, we recognize: the basal Ponsano P Unit (middle Miocene), which is referable to coastal-shallow marine environment; the Lignitiferous T Unit (late Tortonian-early Messinian), which is referable to fan-delta and lacustrine systems; the Acquabona-Spicchiaiola M1 Unit (early Messinian), which is referable to lagoonal fan-deltaic environment; the Castelnuovo M2 Unit (early Messinian), which is referable to shallow marine environment; and the “Lago-Mare” M3 Unit (late Messinian), which is referable to fan-deltaic lacustrine systems. The Miocene succession is overlaid by Plio-Pleistocene marine to continental succession. The Miocene basins have settled on deformed Ligurian allochthonous units, which are markedly structured in tectonic depressions and highs and coherently so with the “crustal lateral segmentation” model. The development of the Miocene sedimentation in this sector of the chain appears to be strictly connected to the tectonic evolution of the Tyrrhenian Sea rifting. The middle Miocene deposits may in fact be related to the first syn-rift shallow-marine basins, marking the beginning of the post-nappe phase. During late Tortonian-early Messinian, important lacustrine-fan-delta systems dominated in the basins and represented the development of the middle Miocene stages. They evolved during the early Messinian in lagoonal fan-deltaic systems and then in shallow-marine systems. The transition to the upper Messinian deposits is marked by a significant unconformity, which is marked locally by angularity, thus noting an intramessinian deformative episode. This characterizes the lacustrine fan-deltaic systems that are linked to the Messinian salinity crisis for the paleo-Mediterranean Sea. The stratigraphic differences between the Fiora Hills’ basins are therefore linked to the somewhat different basinal sedimentary evolution, which is connected to the development of morphological/tectonic ridges.

First characterisation of natural radioactivity in building materials manufactured in Albania

This study focuses on the radiological characterisation of building materials manufactured in Albania by using a high-resolution gamma-ray spectrometer. The average activity concentrations of (40)K, (226)Ra and (232)Th were, respectively, 644.1±64.2, 33.4 ± 6.4 and 42.2 ± 7.6 Bq kg(-1) in the clay brick samples and 179.7 ± 48.9, 55.0 ± 5.8 and 17.0 ± 3.3 Bq kg(-1) in the cement samples. The calculated activity concentration index (ACI), varied from 0.48±0.02 to 0.63±0.04 in the clay brick samples and from 0.29±0.03 to 0.37±0.02 in the cement samples. Based on the ACI, all of the clay brick and cement samples were categorised as A1 materials. The authors can exclude (at 3σ level) any restriction of their use as bulk materials.

Total natural radioactivity, Tuscany, Italy

In this paper, we report an extensive survey of the natural radioactive content of rocks of the Tuscany Region (Italy): this permitted the first total natural radioactivity map of the region. The sampling was planned using the geological map of Tuscany at scale 1:250,000, which contains 45 distinct geological groups recognized by tectonic and stratigraphic features. Each geological group was characterized for the total activity by measuring the activity concentrations of 40K, 238U and 232Th in 865 samples using a high-purity germanium (HPGe) gamma-ray spectrometer. The average areal distribution of samples is approximately one sample per 25 km2. The radiometric map was constructed through the reclassification of each geological formation based on the median value of the total activity. Seven classes of total activity are identified by choosing percentiles almost evenly spread across the range of values. This map represents the starting point for future studies on natural background radiation, geochemical processes and epidemiological investigations.

Geological map of the Chianti Mts (Northern Apennines, Italy)

A detailed stratigraphical-structural survey combined with classical geological mapping has been performed in the northern Chianti Mts, part of the Northern Apennines Orogen (central Italy). The study area can be subdivided in different tectonic and depositional units: (i) the widely outcropping Tuscan Nappe (middle/late Lias–earliest Miocene), thrusted to the west by (ii) Ligurian units (Cretaceous–Eocene) and unconformably covered by (iii) post-nappe deposits (Pliocene–Pleistocene). The Chianti Mts are structured as a mega-antiformal fold, dissected by WSW-ENE transversal lines and by NNW-SSE normal faults linked with the exhumation of the Northern Apennines Range, developing a basin/ridge structure. As results, (i) a new improved stratigraphic frame is here proposed; (ii) several tectonic and stratigraphic domains have been newly recognised; (iii) a large area characterised by severe internal deformation has been recognised and mapped as an imbricate fan thrust system, linked with transversal lines.

Reference worldwide model for antineutrinos from reactors

correction to the reference reactor spectra associated with the long-lived isotopes and we estimate a 2.4% increase of the unoscillated event rate in the geoneutrino energy window due to the storage of spent nuclear fuels in the cooling pools. We predict that the research reactors contribute to less than 0.2% to the commercial reactor signal in the investigated 14 sites. We perform a multitemporal analysis of the expected reactor signal over a time lapse of 10 years using reactor operational records collected in a comprehensive database published at www.fe.infn.it/antineutrino.

Total natural radioactivity, Veneto (Italy)

We present the first detailed map of the terrestrial natural radioactivity of the Veneto Region (Italy), a 18,264 km2 densely populated area, previously investigated through indoor radon surveys. The activity concentration in 709 representative samples of the main Alpine lithostratigraphic units was measured by using a high-purity germanium (HPGe) γ-ray spectrometer to characterize the radioactivity content of the 41 cartographic units of the Veneto Lithostratigraphic map at 1:250,000 scale. An area accounting for 61% of the territory, comprising alluvial plains was investigated through airborne γ-ray measurements. The large-volume NaI detectors were mounted on an ultralight aircraft, flying a 7000 km line. The data were interpolated using Ordinary Kriging, and a distribution model of the radioactivity content was produced. The result of the data analysis is a total natural radioactivity map of Veneto at 1:250,000 scale in which the activity concentration of the territory is visualized in seven classes, according to the percentile values calculated on the total dataset of measurements.

Uranium distribution in the Variscan Basement of Northeastern Sardinia

ABSTRACT We present a detailed map of uranium distribution and its uncertainties in the Variscan Basement of Northeastern Sardinia (VBNS) at a scale of 1:100,000. An area of 2100 km2 was investigated by means of 535 data points obtained from laboratory and in situ gamma-ray spectrometry measurements. These data volume corresponds to the highest sampling density of the European Variscides, aimed at studying the genetic processes of the upper crust potentially triggered by an enrichment of radiogenic heat-producing elements. For the first time, the Kriging with Variance of Measurement Error method was used to assign weights to the input data which are based on the degree of confidence associated with the measurements obtained using different gamma-ray spectrometry techniques. A detailed tuning of the model parameters for the adopted Experimental Semi-Variogram led to the identification of a maximum distance of spatial variability coherent to the observed tendency of the experimental data. We demonstrate that the obtained uranium distribution in the VBNS, characterized by several calc-alkaline plutons emplaced within migmatitic massifs and amphibolite-facies metamorphic rocks, is an excellent benchmark for the study of ‘hot’ collisional chains. The uranium map of VBNS, and in particular the Arzachena minor pluton, confirms the emplacement model based on the recognition of the different petrological associations characterizing the Variscan magmatic processes in the Late Paleozoic. Furthermore, the presented model of the uranium content of the geological bedrock is a potential baseline for future mapping of radon-prone areas.