LABEC Laboratory Research Articles

External micro-PIXE analysis of fluid inclusions: Test of the LABEC facility on samples of quartz veins from Apuan Alps (Italy)

Fluid inclusions are small portions, usually smaller than 100μm, of fluid trapped within minerals during or after growth. Their characteristics provide therefore fundamental information on nature and evolution of fluids present in the past in different geological environments. At the LABEC laboratory in Firenze, high-salinity fluid inclusions in quartz crystals, coming from the Apuan Alps metamorphic complex, were analysed at the external scanning microbeam. Results, although still preliminary, have already provided us with hints on fluid-rock interaction processes during the metamorphism of the Apuan Alps.

Use of silicon drift detectors for the detection of medium-light elements in PIXE

In order to fully exploit in PIXE the superior performance of silicon drift detectors especially for the detection of low- and medium-energy X-rays, avoiding in particular the negative effects of backscattered particles, we developed a custom spectrometer based on a 10mm2 chip with a thermoelectric Peltier cooler and home-designed front-end electronics, coupled to a weakly focusing polycapillary lens.This paper briefly describes the detector+lens assembly and reports the results of first tests carried out at an external beam line of the LABEC laboratory in Florence. Excellent energy resolution is achieved under real operating conditions in a PIXE run (measured FWHM at 1keV is 81eV with a count-rate of 480cps) and also the lineshapes are very good (FW1/10M over FWHM ratio is 2.1). As a whole, our preliminary tests gave encouraging results and also helped to point out some aspects which it is worthwhile to investigate further (e.g. how X-ray peak intensity ratios may be affected by inaccurate lens alignment), in order to profit fully from such a good performance of the spectrometer.

The pulsed beam facility at the Tandetron accelerator in Florence

An electrostatic chopper has been installed in the LABEC laboratory (Sesto Fiorentino) along one of the beamlines of the new Tandetron accelerator. The chopper allows us the creation of a pulsed beam, from a continuous one, with a variable and finely controllable number of particles in each pulse. The facility can be tuned to obtain an average of one ion per pulse. This feature allows us the study of the basic processes of particle–target interactions, useful when performing ion beam analysis. Increasing the beam current, bunches up to thousands of ions can be obtained with a total energy being always an integer multiple of the one of the single ion. This configuration can be employed e.g. in a detector energy calibration.

Micro‐PIXE determination of Zr in rutile: an application to geothermometry of high‐P rocks from the western Alps (Italy)

AbstractThe Western Alps of Northern Italy mostly consist of lithotectonic units which re‐crystallised and were metamorphosed at high depth in a subduction zone. During their exhumation to shallow crustal levels, however, the high‐pressure (high‐P) mineral assemblages were pervasively re‐equilibrated under low‐pressure (low‐P) conditions, making difficult to estimate the metamorphic thermal peak.Rutile [TiO2] is a typical high‐P mineral, occurring as relict phase in low‐P re‐equilibrated metamorphic rocks. Recent studies suggest that, in thermodynamic systems buffered by the occurrence of quartz and zircon in the rock, Zr content in rutile is a temperature–dependent function that can be modelled quantitatively.An application of rutile Zr‐geothermometer to continental and oceanic rocks of the Western Alps, pervasively re‐equilibrated under low‐P conditions, is presented.The selected rutile crystals were analysed by PIXE using a microbeam set‐up at the LABEC laboratory of INFN in Florence. The PIXE spectra and maps were processed by Geopixe software package. Micro‐PIXE analyses allowed determining the concentration and the distribution of Zr.Results obtained by applying the rutile Zr‐geothermometer gave a more precise indication about the temperatures of the metamorphic conditions suffered by Alpine metamorphic rocks with respect to phase relations and conventional geothermometry, showing that determination of Zr concentration by micro‐PIXE technique is a useful tool to reconstruct metamorphic events.The continental units, outcropping in separate zones of Western Alps, show two slightly different thermal peaks (Tmean = 530 ± 10 °C and Tmean = 555 ± 10 °C) for the same metamorphic event. The oceanic units provide Tmean estimates of 575 ± 10 °C slightly higher than the continental units. Copyright © 2008 John Wiley & Sons, Ltd.

Recent developments of ion beam induced luminescence at the external scanning microbeam facility of the LABEC laboratory in Florence

A new ionoluminescence (IL) apparatus has been successfully installed at the external scanning microbeam facility of the 3 MV Tandetron accelerator of the INFN LABEC in Firenze; the apparatus for photon detection has been fully integrated in the existing ion beam analysis (IBA) set-up, for the simultaneous acquisition of IL and PIXE/PIGE/BS spectra and maps.The potential of the new set-up is illustrated in this paper by some results extracted by the analysis of art objects and advanced semiconductor materials. In particular, the adequacy of the new IBA set-up in the field of cultural heritage is pointed out by the coupled PIXE/IL micro-analysis of a lapis lazuli stone; concerning applications in material science, IL spectra from a N doped diamond sample were acquired and compared with CL analyses to evaluate the relevant sensitivities and the effect of ion damage.

Radiocarbon Dating in Late-Roman and Medieval Contexts: An Archaeological Excavation in the Center of Florence, Italy

A series of samples for radiocarbon dating were collected in 2005 from the Biblioteca Magliabechiana archaeological excavation area in the center of Florence, Italy, in a project directed by the Dipartimento di Archeologia e Storia delle Arti of the University of Siena, in cooperation with the Soprintendenza per i Beni Architettonici e per il Paesaggio per le province di Firenze e Prato. This area is located near the Uffizi Galleries, close to the Roman town, the Arno River and one of its former tributaries. The area is peculiar for the Florentine urban context because it was free from urban development until the 12th century AD. The exposed stratigraphy showed the presence of several layers composed of natural sediments, partly the result of historical floods. Here, we report a series of 14C measurements on charcoal and seed samples collected on this excavation. 14C dating has been performed in the LABEC laboratory in Florence, on the accelerator mass spectrometry (AMS) beam line of the AMS-IBA 3MV Tandetron accelerator. We also had the opportunity to compare the 14C dates obtained with several series of samples previously collected in nearby archaeological areas. Results were consistent with the data obtained previously and, moreover, offer interesting new aspects to the interpretation of the archaeological findings.

Hourly elemental composition and source identification of fine and coarse PM10 in an Italian urban area stressed by many industrial activities

A project is in progress to study the environmental problems of Taranto, an industrial town in the South of Italy. Within this framework we studied the atmospheric aerosol composition by means of continuous sampling and PIXE measurements. Particulate matter (PM) was collected simultaneously in two sampling sites during winter and summer 2004 by two streaker samplers, which separate the fine and coarse aerosol modes. Hourly concentrations of elements from Na to Pb were measured at the new 3MV Tandetron accelerator of the LABEC laboratory of INFN in Florence.

The new external beam facility for environmental studies at the Tandetron accelerator of LABEC

At the new 3MV Tandetron accelerator of the LABEC laboratory of INFN in Florence, an external beam facility fully dedicated to measurements of elemental composition of atmospheric aerosol has been installed. The experimental set-up hitherto used for this kind of applications has been upgraded with the introduction of a silicon drift detector and of a beam current monitor system based on the backscattering of protons on the extraction window. The new facility will be presented, together with some methodological results obtained so far for the analysis of airborne particulate matter samples collected on quartz fiber filters.

External Micro-PIXE Measurements: Preliminary Results on Volcanic Rocks from Nyiragongo Volcano

The external microbeam facility at the 3 MV Tandetron accelerator of the LABEC Laboratory of INFN in Florence has been used to determine, by PIXE, major, minor and trace element abundances of minerals and groundmass in the lavas from the active Nyiragongo Volcano (Democratic Republic of Congo), which is well known for its lava lake intra-crateric activity [e.g. 1, 2]. During the last eruption of this volcano (January, 2002), two main flows entered the Goma town producing major devastation, forcing the rapid exodus of about 300,000 people and causing the death of 150 persons [3]. After this eruption, the interest of the scientific community on this volcanic area suddenly increased. In this respect, determination of major and trace element abundances in mineral phases and groundmass of lavas may allow to constrain the evolution of magma within the volcanic system from a quantitative view point, thus helping to better understand the way this volcano works.

Study on sleep-waking rhythm and sleep architecture under absolute bed rest conditions for one week : T. Ohta, K. Ohara, S. Endo, T. Yamamoto, T. Kobayashi and H. Fukuda (Hamamutsu and Tokyo, Japan)

At the 3 MV Tandetron accelerator of the LABEC laboratory of INFN in Florence, an external beam facility is fully dedicated to measurements of elemental composition of atmospheric aerosol. The experimental set-up hitherto used for this kind of applications has been upgraded with the replacement of a traditional Si(Li) detector for the detection of medium–high Z elements with a silicon drift detector (SDD) with a big active area (80 mm2) and 450 μm thickness, with the aim of obtaining better minimum detection limits (MDL) and reduce measuring times. The Upilex extraction window has been replaced by a more resistant one (Si3N4). A comparison between the old Si(Li) and the new SDD for aerosol samples collected on different substrata like Teflon, Kapton and Nuclepore evidenced the better performances of the SDD. It allows obtaining better results (higher counting statistics, lower MDLs) even in shorter measuring times, thus allowing very fast analysis of both daily and hourly samples.