Antonio De Sio

ON WATER FORMATION IN THE INTERSTELLAR MEDIUM: LABORATORY STUDY OF THE O+D REACTION ON SURFACES

In the interstellar medium (ISM), an important channel of water formation is the reaction of atoms on the surface of dust grains. Here, we report on a laboratory study of the formation of water via the O+D reaction network. While prior studies were done on ices, as appropriate to the formation of water in dense clouds, we explored how water formation occurs on bare surfaces, i.e., in conditions mimicking the transition from diffuse to dense clouds (Av ~ 1-5). Reaction products were detected during deposition and afterward when the sample is brought to a high temperature. We quantified the formation of water and intermediary products, such as D2O2, over a range of surface temperatures (15-25 K). The detection of OD on the surface signals the importance of this reactant in the overall scheme of water formation in the ISM.

Photochemical Synthesis of Citric Acid Cycle Intermediates Based on Titanium Dioxide

The emergence of the citric acid cycle is one of the most remarkable occurrences with regard to understanding the origin and evolution of metabolic pathways. Although the chemical steps of the cycle are preserved intact throughout nature, diverse organisms make wide use of its chemistry, and in some cases organisms use only a selected portion of the cycle. However, the origins of this cycle would have arisen in the more primitive anaerobic organism or even back in the proto-metabolism, which likely arose spontaneously under favorable prebiotic chemical conditions. In this context, we report that UV irradiation of formamide in the presence of titanium dioxide afforded 6 of the 11 carboxylic acid intermediates of the reductive version of the citric acid cycle. Since this cycle is the central metabolic pathway of contemporary biology, this report highlights the role of photochemical processes in the origin of the metabolic apparatus.

FORMATION OF MOLECULAR OXYGEN AND OZONE ON AMORPHOUS SILICATES

Oxygen in the interstellar medium is seen in the gas phase, in ices (incorporated in H{sub 2}O, CO, and CO{sub 2}), and in grains such as (Mg{sub x} Fe{sub 1-x} )SiO{sub 3} or (Mg{sub x} Fe{sub 1-x} ){sub 2}SiO{sub 4}, 0 < x < 1. In this investigation, we study the diffusion of oxygen atoms and the formation of oxygen molecules and ozone on the surface of an amorphous silicate film. We find that ozone is formed at low temperature (<30 K), and molecular oxygen forms when the diffusion of oxygen atoms becomes significant, at around 60 K. This experiment, besides being the first determination of the diffusion energy barrier (1785 {+-} 35 K) for oxygen atoms on a silicate surface, suggests bare silicates as a possible storage place for oxygen atoms in low-A{sub v} environments.

Alignment procedure for detector integration and characterization of the CaSSIS instrument onboard the TGO mission

The Colour and Stereo Surface Imaging System (CaSSIS) is a high-resolution camera for the ESA ExoMars Trace Gas Orbiter mission launched in March 2016. CaSSIS is capable of acquiring color stereo images of features on the surface of Mars to better understand the processes related to trace gas emission. The optical configuration of CaSSIS is based on a three-mirror anastigmatic off-axis imager with a relay mirror; to attain telecentric features and to maintain compact the design, the relay mirror has power. The University of Bern had the task of detector integration and characterization of CaSSIS focal plane. An OGSE (Optical Ground Support Equipment) characterization facility was set up for this purpose. A pinhole, imaged through an off-axis paraboloidal mirror, is used to produce a collimated beam. In this work, the procedures to align the OGSE and to link together the positions of each optical element will be presented. A global Reference System (RS) has been defined using an optical cube placed on the optical bench (OB) and linked to gravity through its X component; this global RS is used to correlate the alignment of the optical components. The main steps to characterize the position of the object to that of the CaSSIS focal plane have been repeated to guide and to verify the operations performed during the alignment procedures. A calculation system has been designed to work on the optical setup and on the detector simultaneously, and to compute online the new position of the focus plane with respect to the detector. Final results will be shown and discussed.

Graphitic Patterns on CVD Diamond Plate as Microheating/Thermometer Devices.

A simple compact temperature sensor and microheater in a wide temperature range has been developed, realizing a laser-patterned resistive structure on the surface of a synthetic polycrystalline diamond plate. Imaging and spectroscopy techniques used to investigate morphology, structure, and composition of the pattern showed that it incorporates different nondiamond carbon phases. Transport experiments revealed the semiconducting behavior of this microresistor. Thermal power measurements versus temperature are presented. A possible application of this device that may easily match compact experimental layouts avoiding both thermal anchoring offset and mechanical stress between sample and sensor is discussed. The patterned structure undergoes testing as a microthermometer, providing fast response and excellent stability versus time. It exhibits a good sensitivity that coupled to an easy calibration procedure minimizes errors and guarantees high accuracy. Plot of temperature versus input power of the resistive patterned line used as microheater shows a linear behavior in an extended temperature range.

Diamond dosimeters: applications to radiobiology and space environments

Biological experiments in space and ongoing human space missions devoted to the solar system exploration require significant advancements in the radiation environment monitoring systems. Radiation hazard has to be continuously monitored and the biological damage should be evaluated within short time. In this paper, we review the use of polycrystalline diamond films as dosimeters for space applications. The charge trapped into deep intra-gap defect levels during radiation exposure, and released during a high-temperature thermal scan to give thermally stimulated current (TSC), has been integrated as a function of time to evaluate the absorbed dose. TSC results have been proved to give correct evaluation of the dose absorbed during the space mission, assessing the capabilities of synthetic diamond and TSC read-out system as a proper dosimetry technique for space applications. The capability of diamond films to detect low doses has been demonstrated down to the mGys range. The results of the application of these dosimeters in low Earth orbit space missions are described.

PRESS-MAG-O: a unique instrument to probe materials and phenomena under extreme conditions at Frascati

PRESS-MAG-O is a new instrument under commission at the Laboratori Nazionali di Frascati of the Istituto Nazionale di Fisica Nucleare (INFN) designed to investigate materials under extreme conditions. The instrument, once completed, will allow combining high harmonic AC magnetic susceptibility measurements and magneto-optic experiments on samples under high pressures (HP), with a variable DC magnetic field in a wide temperature range. The system is designed to work at SINBAD, the IR synchrotron radiation beamline operational since 2001 at DAΦNE (Double AnnularΦ-factory for Nice Experiments), the storage ring of the Laboratori Nazionali di Frascati of the INFN. HP will be applied up to about 20 GPa to samples inside a Cu–Be diamond anvil cell designed to allow concurrent FTIR experiments and high harmonic AC susceptibility measurements in a DC magnetic field up to 8 T and in a wide temperature range.