Hard X-ray polarimetry using scintillators

The linear polarization of the radiation from celestial sources can be investigated by studying the angular distribution of Compton scattered photons in a detection device. In this contribution we present the design of a Compton polarimeter based on the technology of fiber-shaped scintillators. A total geometric area of 1000 cm2 or more could be obtained by repeating a basic polarimeter composed by several fiber-like scintillators, some of them of low Z, acting as active scatterers, and others of high Z, acting as detectors. Polarimetric measurements can thus be carried out by searching for coincidences between a scatterer fiber and an absorber one. Monte Carlo simulations of the performances of such a device, when employed onboard a stratospheric balloon, are compared with other kinds of X-ray polarimeters

Broad band X-ray spectral properties of Gamma-ray bursts with BeppoSAX

In about one year, five gamma-ray bursts were simultaneously observed with the Wide Field Cameras and Gamma Ray Burst Monitor aboard the BeppoSAX satellite. From some of them X-ray afterglow emission has been clearly detected with the same satellite. In order to understand how GRB emission is related to the X-ray afterglow, we are performing a systematic study of the spectral properties of these events. We report here preliminary results of this study.Comment: 5 pages, 3 figures. To appear in the Proceedings of the 4th Huntsville Gamma-ray Burst Symposiu

The Tor Caldara CO2 Diffuse Degassing Structure (DDS): 222Rn/220Rn output before and after the August, 22, 2005 Anzio Earthquake (Mw=4.6).

Soon after a 222Rn and 220Rn survey in soil gases, performed (June 2005) in the frame of the Diffuse Degassing in Italy risk assessment project, a moderate earthquake (Mw=4.6) occurred in the Anzio offshore, on August, 22, 2005, only 5 miles from the Tor Caldara Diffuse Degassing Structure (DDS onward). Having available the pre-earthquake 222Rn and 220Rn grid-map on around 50 soil-gas points and being 222Rn both a stress-pathfinder and a discriminative component of activated-faults, a mirrorlike survey was repeated on the same 50 sites, soon after the close earthquake. Later, during a quiescent-aseismic period (December, 2005), a CO2 flux survey was performed for the same 50 sites, adding detailed measurements (more than 100 sites) for the highest flux sectors. The aim of this survey was both to have an overall picture of the background CO2 flux and to calculate the total budget of CO2 flux throughout the DDS, to better interpret the 222Rn and 220Rn areal surveys before and after the seismic event. Herewith, we distinguish the contribution of organic, diffusive and advective CO2 flux. Hints of convection and strong degassing linked to the fracture field, inside the DDS, have been envisaged on selected points, where continuous monitoring stations could be strategic, for seismic, volcanic and NGH surveillance. Despite we found higher 222Rn values in soils after the earthquake, suggesting an enhanced local degassing probably linked to a stress signal throughout the DDS as a whole, the results highlight an unmodified shape and location of the 222Rn anomalies before and after the earthquake. This evidence excludes both that the activated seismogenic segment has affected in some ways both the DDS degassing patterns and that fracture field changed. A similar result could be expected if the activated fault was oriented along the DDS itself and reached the surface. This evidence is well correlated with the reconstructed focal mechanism of the earthquake, pertaining to the transfer structure of the Ardea Graben , located along a peripheral sector of the degassing Alban Hills volcano and intersecting the DDS Tor Caldara itself. The shape and location of 222Rn anomalies inside the DDS for both the surveys are strictly inversely correlated with the areal CO2 flux data. The geometry of the degassing pathways is probably linked to the barrier action (sealing power) of the clays cropping out in the study area. These clays are generated by the strong leaching of the outcropping sedimentary Pleistocene rocks due to the huge flux of volcanic gas -rich fluids

A Geant4 simulation code for simulating optical photons in SPECT scintillation detectors

Geant4 is an object oriented toolkit created for the simulation of High-Energy Physics detectors. Geant4 allows an accurate modeling of radiation sources and detector devices, with easy configuration and friendly interface and at the same time with great accuracy in the simulation of physical processes. While most Monte Carlo codes do not allow the simulation of the transport and boundary characteristics for optical photons transport generated by scintillating crystal, Geant4 allows the simulation of the optical photons. In this paper we present an application of the Geant4 program for simulating optical photons in SPECT cameras. We aim to study the light transport within scintillators, photomultiplier tubes and coupling devices. To this end, we simulated a detector based on a scintillator, coupled to a photomultiplier tube through a glass window. We compared simulated results with experimental data and theoretical models, in order to verify the good matching with our simulations. We simulated a pencil beam of 140 keV photons impinging the crystal at different locations. For each condition, we calculated the value of the Pulse Height Centroid and the spread of the charge distribution, as read out by the anode array of the photomultiplier. Finally, the spatial and the energy resolutions of the camera have been estimated by simulated data. In all cases, we found that simulations agree very well with experimental data

Photodetector and scintillation crystals requirements for gamma-ray imaging

The diffusion of the PET and SPET techniques in different applications, like investigation on small organs and tissues or animal imaging, has induced in the past years the researchers to develop modular scintillation cameras to have compactness and versatility in order to obtain dimensions and configurations suitable to the particular application. To this purpose different photodetectors have been studied, as an alternative to the photomultiplier tubes (PMT) based on semiconductor technology. At the same time new scintillating crystals have been tested to match the requirements like high light yield or fast decay time, needed for SPET and PET application, respectively. In this paper we have investigated the photodetector and scintillation crystals requirements to optimize a gamma-ray imager based on scintillation crystals. To this aim we show results about the principal parameters characterizing a gamma-ray imaging, like energy and spatial resolution. The performances of a continuous LaBr3:Ce crystal (49×49×4mm3+3mm glass window) are compared to the ones from a pixellated and continuous NaI:Tl crystal, coupled to multi-anode photomultiplier tube (Hamamatsu H8500 MA-PMT). Furthermore the results are supported with Monte Carlo simulations. With the lanthanum detector, we obtain 1.1mm of intrinsic spatial resolution, comparable with that predicted by the MC simulations. We test also the new ultra bialkali PMT Hamamatsu R7600-200 with a QE = 42%, obtaining an improvement in terms of energy resolution of about 25%, respect to a standard PMT, with a LaBr3:Ce cylinder (1/2" ��φ × 1/2" thickness)

Comparison of the imaging performances for recently developed monolithic scintillators: CRY018 and CRY019 for dual isotope gamma ray imaging applications

The growing interest for new scintillation crystals with outstanding imaging performances (i.e. resolution and efficiency) has suggested the study of recently discovered scintillators named CRY018 and CRY019. The crystals under investigation are monolithic and have shown enhanced characteristics both for gamma ray spectrometry and for Nuclear Medicine imaging applications such as the dual isotope imaging. Moreover, the non-hygroscopic nature and the absence of afterglow make these scintillators even more attractive for the potential improvement in a wide range of applications. These scintillation crystals show a high energy resolution in the energy range involved in Nuclear Medicine, allowing the discrimination between very close energy values. Moreover, in order to prove their suitability of being powerful imaging systems, the imaging performances like the position linearity and the intrinsic spatial resolution have been evaluated obtaining satisfactory results thanks to the implementation of an optimized algorithm for the images reconstruction. © 2017 IOP Publishing Ltd and Sissa Medialab srl

Geochemistry of hydrothermal fluids from the eastern sector of the Sabatini Volcanic District (central Italy).

This study reports a complete geochemical dataset of 215 water and 9 gas samples collected in 2015 from thermal and cold discharges located in the eastern sector of the Sabatini Volcanic District (SVD), Italy. Based on these data, two main aquifers were recognized, as follows: 1) a cold Ca-HCO3 to Ca(Na)-HCO3 aquifer related to a shallow circuit within Pliocene-Pleistocene volcanic and sedimentary formations and 2) a deep CO2-pressurized aquifer hosted in Mesozoic carbonate-evaporitic rocks characterized by a Ca- HCO3(SO4) to Na(Ca)-HCO3(Cl) composition. A thick sequence of low-permeability formations represents a physical barrier between the two reservoirs. Interaction of the CO2-rich gas phase with the shallow aquifer, locally producing high-TDS and low-pH cold waters, is controlled by fractures and faults related to buried horst-graben structures. The d18O-H2O and dD-H2O values indicate meteoric water as the main source for both the shallow and deep reservoirs. Carbon dioxide, which is characterized by d13C-CO2 values ranging from 4.7 to þ1.0‰ V-PDB, is mostly produced by thermo-metamorphic decarbonation involving Mesozoic rock formations, masking possible CO2 contribution from mantle degassing. The relatively low R/Ra values (0.07e1.04) indicate dominant crustal He, with a minor mantle He contribution. The CO2/3He ratios, up to 6 1012, support a dominant crustal source for these two gases. The d34SH2S values (from þ9.3 to þ11.3‰ V-CDT) suggests that H2S is mainly related to thermogenic reduction of Triassic anhydrites. The d13C-CH4 and dD-CH4 values (from 33.4 to 24.9‰ V-PDB and from 168 to 140‰ V-SMOW, respectively) and the relatively low C1/C2þ ratios (<100) are indicative of a prevailing CH4 production through thermogenic degradation of organic matter. The low N2/Ar and high N2/ He ratios, as well as the 40Ar/36Ar ratios (<305) close to atmospheric ratio, suggest that both N2 and Ar mostly derive from air. Notwithstanding, the positive d15N-N2 values (from þ0.91 to þ3.7‰ NBS air) point to a significant extra-atmospheric N2 contribution. Gas geothermometry in the CH4-CO2-H2 and H2S-CO2-H2 systems indicate equilibrium temperatures <200 C, i.e. lower than those measured in deep geothermal wells (~300 C), due to either an incomplete attainment of the chemical equilibria or secondary processes (dilution and/or scrubbing) affecting the chemistry of the uprising fluids. Although the highly saline Na-Cl fluids discharged from the explorative geothermal wells in the study area support the occurrence of a well-developed hydrothermal reservoir suitable for direct exploitation, the chemistry of the fluid discharges highlights that the uprising hydrothermal fluids are efficiently cooled and diluted by the meteoric water recharge from the nearby Apennine sedimentary belt. This explains the different chemical and isotopic features shown by the fluids from the eastern and western sectors of SVD, respectively, the latter being influenced by this process at a lesser extent. Direct uses may be considered a valid alternative for the exploitation of this resource.Published187-2016A. Geochimica per l'ambiente2IT. Laboratori sperimentali e analitici1VV. AltroJCR Journa

Design and preliminary operation of a gasification plant for micro-CHP with internal combustion engine and SOFC

A gasification plant was designed and built to test syngas production from biomass for electricity generation on microscale. The plant is mainly composed by a downdraft reactor, a gas cleaning section with a cyclone and a wet scrubber, a blower for syngas extraction and an ICE (Internal Combustion Engine, Lombardini LGA 340), equipped with an alternator. A small quantity of producer was also eventually sent to a button cell SOFC (Solid Oxide Fuel Cell) for preliminary characterization. The plant was tested in a preliminary experimental campaign to evaluate mass and energy balances and process efficiency. Woody biomass was used and the producer gas firstly passed through impingers bottles, to condense and measure tar concentration (according to CEN/TS 15439), and then the remaining uncondensed gas was analyzed with a micro-GC (Gas Chromatograph). The paper presents and discusses the results of the preliminary tests carried out

In-flight performances of the BeppoSAX γ\gamma-Ray Burst Monitor

The Italian-Dutch satellite for X-ray Astronomy BeppoSAX is successfully operating on a 600 km equatorial orbit since May 1996. We present here the in-flight performances of the Gamma Ray Burst Monitor experiment during its first year of operation. The GRBM is the secondary function of the four CsI(Na) slabs primarily operating as an active anticoincidence of the PDS hard X-ray experiment.. It has a geometric area of about 4000 cm2 but, due to its location in the core of the satellite its effective area is dependent on the energy and direction of the impinging photons. A dedicated electronics allows to trigger on cosmic gamma-ray bursts. When the trigger condition is satisfied the light curve of the event is recorded from 8 s before to 98 s after the trigger time, with a maximum time resolution of 0.48 ms, in an energy band of 40-700 keV