PhD Alumni

Alberti Roberto

Present position: Technical Director at XGLab S.R.L. - Spinoff del Politecnico di Milano

Thesis title:  X-Ray Imaging Systems Based On Silicon Drift Detectors
Advisor:  Antonio Longoni
Research area:  Sensors and instrumentation
Thesis abstract:  
The purpose of this Ph.D research activity was the development of measurement systems for elemental analysis based on X-Rays Fluorescence (XRF) spectroscopy.
In particular, the author has cooperated to the development of electronics and instruments for “elemental mapping” applications (the identification of the chemical elements present in a sample and the determination of their spatial distribution) characterized by high spatial and energy resolution, high count rate, high gain stability and a low detection limit. Among the main experiments in which the developed instrumentation has been applied and the direct participation of the author has been involved it is worth noticing researches on molecular biology, on atomic and nuclear physics and on works of art analysis.
The developed systems are based on Silicon Drift Detectors (SDD) usually integrated in monolithic arrays of independent devices. The use of a new generation of this detectors leads to an energy resolution of the order of 130 eV FWHM on the Mn − Kα line with compact Peltier-cooling systems and high photons count rates (with the use of multi-element detectors up to 106 cps are reached). A spatial resolution of the order of 50 μm can be obtained by means of policapillary lenses coupled with compact X-ray generator used to focus the X-ray beam on the sample to be analyzed; moreover the use of zone plates optics coupled with monochromatic synchrotron light leads to a spatial resolution down to 10 nm.
The activity of the Ph.D. concerned a) the study of new monolithic arrays of SDD, b) the design of innovative front-end electronics for the readout and the elaboration of the detector signals c) the realization of complete measurement systems and d) the implementing of the developed systems in some application. The instrumentations guarantee optimum performances in terms of the energy resolution, of the stability at high count rates and of the low detection limit. Moreover, the elemental mapping is performed by means of automatic scanning with sub-micrometer resolution of the sample surface.
Chapter 1 after a brief overview on XRF phenomenon and technique presents an important class of solid state detectors (Silicon Drift Detector) that allow obtaining extremely good energy resolution almost at room temperature and very high photon count rates. This chapter also includes an essential background about radiation detectors read-out, concerning noise optimization and electronics chain requirements.
The author worked at the development of the front-end and processing electronics to be coupled to the SDDs. Both design and characterization of such circuits were carried out by the author. Chapter 2 presents the work done on electronic circuits studied to guarantee energy resolution and stability in a wide range of values of the revelation rates. Novel circuit solutions developed during the Ph.D work are here presented.
In the third chapter a complete spectrometer developed for elemental analysis of 2D areas (elemental mapping) with several examples of experimental results is presented. This spectrometer was carried out within the FELIX (Fast ELemental Imaging with X-ray) project, funded by INFN (the Italian institute for nuclear physics).
Chapter 4 describes two XRF imaging systems for biological application with sub-micro spatial resolution carried out in cooperation with synchrotron light source of ELETTRA Trieste, Italy and within the DRUIDNORMA (DRUgs delivery Image Detection with Non-Radioactive Markers) project of INFN.
Finally in chapter 5 is presented the innovative implementation of SDD and polycapillary optics in PIXE setup (Particle-Induced X-ray Emission) and a complete spectrometer developed in the framework of the INFN DANTE (Developments of Analytical Nuclear TEchniques) experiment.