S. Valentini

Characterization of a Silicon Strip Detector and a YAG:Ce Calorimeter for a Proton Computed Radiography Apparatus

Today, there is a steadily growing interest in the use of proton beams for tumor therapy, as they permit to tightly shape the dose delivered to the target reducing the exposure of the surrounding healthy tissues. Nonetheless, accuracy in the determination of the dose distribution in proton-therapy is up to now limited by the uncertainty in stopping powers, which are presently calculated from the photon attenuation coefficients measured by X-ray tomography. Proton computed tomography apparatus (pCT) has been proposed to directly measure the stopping power and reduce this uncertainty. Main problem with proton imaging is the blurring effect introduced by multiple Coulomb scattering: single proton tracking is a promising technique to face this difficulty. As a first step towards a pCT system, we designed a proton radiography (pCR) prototype based on a silicon microstrip tracker (to characterize particle trajectories) and a segmented YAG:Ce calorimeter (to measure their residual energy). Aim of the system is to detect protons with a ~1 MHz particle rate of and with kinetic energy in the range 250-270 MeV, high enough to pass through human body. Design and development of the pCR prototype, as well as the characterization of its single components, are described in this paper.

Silicon micromachined accelerometers for the detection of compliant anti-personnel landmines

Acoustic methods have been recently investigated for the detection of shallow landmines. Some plastic landmines have a compliant case which can made to vibrate by an airborne excitation like a loudspeaker. Our study is based on the possibility to detect landmines by contact or non-contact sensors like accelerometers or phonometers. Phonometers can provide sufficient seismic sensitivity but their response is influenced by direct acoustic wave coupling from the driving source. On the contrary accelerometers are much less influenced by the direct acoustic wave coupling and they have high sensitivity to acquire soil surface vibrations. In our experiments we can measure typical accelerations in order of 2 m/s2 with sensitivity of 800 mV/g. The acceleration signal elaboration and visualization developed in this work demonstrates the suitability of these sensors for acoustic landmine detection study and allows a fast analysis to evaluate the presence of a buried landmine.

Theoretical and experimental analysis of an equivalent circuit model for the investigation of shallow landmines with acoustic methods

Acoustic methods have been recently investigated for the detection of shallow landmines. Some plastic landmines have a flexible case which can made to vibrate by an airborne excitation like a loudspeaker. The soil-mine system shows a resonant behavior which is used as a signature to discriminate from other rigid objects. The mechanical resonance can be detected at the soil surface by a remote sensing systems like a laser interferometer. An equivalent physical model of the mine-soil system has been investigated having the known physical characteristics of mine simulants. The authors designed and built a test-object with known mechanical characteristics (mass, elasticity, damping factor). The model has been characterized in laboratory and the results compared with the classic mass-spring loss oscillator described by Voigt. The vibrations at the soil surface have been measured in various positions with a micro machined accelerometer. The results of the simulations for the acceleration of the soil-mine system agree well with the experiment. The calibrated mine model is useful to investigate the variation of the resonance frequency for various buried depths and to compare the results for different soils in different environmental conditions.

A Single Display for RASCAN 5-frequency 2-polarisation Holographic Radar Scans

The RASCAN holographic radar system has been developed by the Remote Sensing Laboratory of Bauman Moscow Technical University. The present design uses flve frequencies and two polarisations to give 10 distinct images of scan from buried objects. Because of the sinusoidal phase variation of the interference signals, all displays show a complex picture of dark and light phases which vary in a complicated way between difierent frequencies and polarizations. This is a preliminary investigation into the optimal presentation of the 10 images as a single composite image. The objective is to display as much as possible of the information present in the original image. The solution presented here is to sum the absolute values of the background-corrected amplitude over both the flve frequencies and the two polarizations. The method is justifled using an experiment in which nine US pennies, and 9 metal washers, were buried in sand at increasing depths in the range 0 to 56mm. The method is illustrated by example images from the flelds of civil engineering and mine detection.

Development of a proton computed radiography apparatus

There is today a growing up interest in proton therapy for tumor treatment, because these particles permit to tightly shape the dose to the target. Anyway, the accuracy in the determination of dose distribution for proton therapy is presently limited by the uncertainty in stopping power distribution, which is calculated from the photon attenuation coefficients measured by X-ray tomography. A proton computed tomography apparatus (pCT) could be used to directly measure stopping power and reduce this uncertainty. The main problem with proton imaging is the blurring effect introduced by multiple Coulomb scattering, but single proton tracking is a promising technique to face this difficulty. As a first step toward a pCT system, we designed a proton radiography (pCR) prototype based on a silicon microstrip tracker to characterize particle trajectories and on a segmented YAG:Ce calorimeter to measure their residual energy. The target is to detect protons with initial kinetic energy in the range 250-270 MeV and with a particle rate of ∼1MHz. Design and development of the pCR prototype, as well as the characterization of its single components, are described in this article. Status of development of reconstruction algorithms capable to account for Coulomb scattering is reported too.

A study of acoustic methods for compliant landmines detection by using the surface acceleration parameter

This paper presents the experimental results for an acousto-seismic buried landmine detection method. The excitation source used was a woofer loudspeaker and lightweight silicon MEMS accelerometers were adopted to measure the ground surface acceleration. The experiments were performed in an outdoor unconsohdated sand test-bed with several kinds of compliant and rigid test-objects, all buried at depth of 4cm and placed at distances ranging from 10cm to 50cm. The different responses of the compliant and rigid objects was processed in both time and frequency domains. A novel audio representation of the acquired signals was developed for exploiting the human-hearing capabilities for the identification of buried objects.