Detecting Environmental, Industrial and Biomedical Signals

Preface

Contents

No abstract received.

The correct use of imaging equipment in radiological units is based on an appropriate knowledge of physical characteristics of the X-ray beam used. The aim of the FLUXEN project is the realization of a portable apparatus able of providing an exact spectral reconstruction of the radiation produced by a given X-ray tube. The apparatus is designed for quality controls in hospitals and for studying quality of new radiographic imaging systems, particularly for their comparison with older ones.

Technological developments occurred in the last ten years in several fields of applications also contributed to a remarkable improvement in medical radiological inspection. In particular, the use of high Z semiconductor detectors actually represents a concrete alternative to traditional equipments for radio-diagnosis applications. Solid state detectors (SSD) combine high stopping power, high sensitivity to X-ray radiation, excellent spectroscopic performances, good time response and also imaging capabilities while operating at room temperature. More specifically, the technical improvements in the fabrication process of CdTe and of CdZnTe detectors confirm the trend in continuously increasing of these tools in medical radio-diagnosis (many CdZnTe gamma cameras are presently operative at hospitals). However, the charge collection efficiency in a SSD strongly depends upon the point of interaction of an X-ray event in the detector, being also related to the energy of the primary photon. This prevents from a straightforward analysis of the signal from a SSD. Since both rise-time and charge collection efficiency are correlated with the depth of interaction, a measurement of the rise time of the collected charge can correct for the charge deficit in a SSD thus improving the spectroscopic performances. Bi-parametric technique is used as an indirect measurement of the collected charge rise-time and for the correction of the detected signal. The present work summarizes some basic features of the bi-parametric method, while describing the experimental laboratory set-up used to extract the information needed for the charge deficit correction procedure. Preliminary results are presented and future research plans are outlined.

In this work we present a new algorithm for searching massive opacities through intelligent detection (neural networks) of regions showing peculiar characteristics (Regions Of Interest). ROI protocol, by reducing the surface under study, is a viable strategy to minimize processing time without losing meaningful information. The related software was designed for a joint research project (PROGETTO CALMA) between physicists and radiologists from different Italian Universities and Hospitals.

In deep penetration laser welding the keyhole plays an important role in the energy transfer from the laser beam to the work-piece. Its dynamic behaviour influences the quality of the welded joint since fluctuations of process parameters may induce keyhole instabilities that result in weld defects and volume fluctuations of the thermal plasma filling it.

In this work we present an experimental study of the plasma optical emission in the UV-VIS range measured by means of photodiodes. We real-time investigated the intensity oscillations of the emission performing a FFT power spectrum of the acquired signal in the 0.4-20 kHz range. The influence of the variation of the main process parameters (incident power, welding speed, beam focus position and gas flow rate) on the joint quality and on the recorded FFT spectrum was analysed.

A comparison of these results with those predicted by a theoretical study of the dynamic behaviour of the keyhole has shown good agreement. The theoretical model is based on a pressure and energy balance between the different forces acting on the keyhole walls, which is assumed to be cylindrical. Any distortion of this balance induces radial, axial and azimuthal oscillations of the cavity and of the weld pool surrounding it, whose eigen-frequencies have been calculated.

These preliminary results can be used in order to assemble an innovative photodiode-based sensor for real-time welding process quality monitoring.

Laser-spectroscopic methods are attracting great interest in various areas, notably in the field of gas monitoring and analysis. Apart from high sensitivity and specificity they offer additional important features such as the lack of time-consuming sample preparation, on-line and remote sensing. The performance depends crucially on the availability of appropriate laser sources and detection schemes. Here we discuss various point-monitoring laser-based systems employing different lasers (near-infrared diode lasers, gas lasers, quantum cascade lasers and nonlinear optical devices) and different detection techniques (long-path absorption, photoacoustic and cavity ring-down). The performance of selected laser spectrometers is illustrated with examples including laboratory gas analyses and in situ measurements of traffic emissions.

Some general considerations about portable systems for Energy Dispersive X-Ray Fluorescence are discussed. Results are presented obtained for the analysis of Giotto’s frescoes in the chapel of the Scrovegni, of Michelangelo’s David and St. Nicola’s silver altar in Bari and of environmental samples.

Results about morphology, and structure of metal-fluoropolymer nanocomposites deposited by Ion Beam Sputtering are reported and related to their vapor-sensing properties based on swelling phenomena.

X-ray Photoelectron Spectroscopy and Brewster Angle Microscopy/Reflection Spectroscopy have been applied to characterisation of Langmuir Blodgett films of macrocycles deposited on quartz crystal microbalance as recognition elements of phenol sensors. Structure of phthalocyanines layers suggested by previous work has been confirmed. Interpretation of diffusion-controlled sensor response and reduced interference by fulvic/humic acids have been supported by spectroscopic and microscopic findings.

Functionalized conducting polymers are employed as active layers in sensors with a thin film transistor (TFT) device structure. Such devices can work as multi-parameter sensors with responses that are fast, repeatable and reversible at room temperature. In this work, a strategy is proposed to enhance the chemical selectivity of organic TFT sensors, by selecting active layers that are made of conducting polymers bearing chemically different substituents. A modulation of the devices sensitivity towards analytes such as alcohols and ketones is demonstrated.

No abstract received.

The research of the INFN Gruppo Collegato di Trento in the ambit of EXPLODET project for the humanitarian demining, is devoted to the development of a software procedure for the automatization of data analysis and decision taking about the presence of hidden explosive. Innovative algorithms of likely background calculation, a system based on neural networks for energy calibration and simple statistical methods for the qualitative consistency check of the signals are the main parts of the software performing the automatic data elaboration.

This paper reports the data analysis results for test performed at Geel Linear Accelerator (GELINA) in Belgium, on Resistive Plate Chambers modified with Gd₂O₃. The goal is studying their performance as thermal neutron detector.

The possibility of detecting thermal neutrons with single gap Resistive Plate Chambers has been investigated. The development of the detector has been performed in the framework of the DIAMINE European Project for Humanitarian De-mining. To convert neutrons the inner surface of one RPC electrode has been coated with a thin layer of ¹⁰B₄C. The RPC detects the charged particles generated by neutrons via the (n,α) reaction on Boron. Tests of converter samples have been performed with a thermalized ²⁵²Cf source in order to evaluate the conversion efficiency: a good agreement between experimental results and simulation has been achieved. Futhermore a detailed description of a first detector prototype together with the results of a test on low energy neutron beams are presented.

Resistive Plate Chambers (RPCs) are wide spread, cheap, easy-to-build and large size detectors, used mainly to reveal ionizing particles in high energy experiments.

Here a tecnique, consisting in coating the inner surface of the bakelite electrodes with a mixture of linseed oil and Gd₂O₃ will be reported; this allows to make RPCs sensitive also to thermal neutrons, making them suitable to be employed for industrial, medical or de-ming applications.

This new type, position sensitive gas detector can be operated at atmospheric pressure, is lightweighted, has low γ-ray sensitivity, and is easy to handle even when large areas are to be covered.

The inelastic scattering of neutrons is an efficient tool in several applications, the detection of hidden explosives [1] is achieved by determining the elemental ratio of C, N, O contained in common explosive materials employing well-known gamma-ray spectroscopy techniques. Moreover, this technique has been proposed to determine the content of unexploded ordnance (UXO) in which high explosive material has to be discriminated from chemical warfare agents or other fillings [2]. Several medical applications as well have been recently presented [3,4]. A peculiar feature of the present project is the use of tagged neutron beams: a linear array of alpha detectors is used to define 10 independent neutron beams that are exploring simultaneously 10 pixels, each of them having a surface of 10x10 cm². Each pixel is viewed by an independent gamma-ray detector operated in coincidence with the alpha particle array. The coincidence between alpha particles and gamma rays is known to be very effective for background reduction. Furthermore, the measure of the coincidence time opens the possibility to determine the position of the unknown object from the neutron time-of-flight and to subtract on-line the background.

List of Participants

Author Index