Implementation of PIXE for classification, discrimination, and identification of vehicle window glass samples: the way to database building (Metadata RADIATE TA Proposal 20002190-ST)

Proposal title "Implementation of PIXE for classification, discrimination, and identification of vehicle window glass samples: the way to database building". Measurements carried out at the external beam set-up for cultural heritage of the INFN LABEC accelerator laboratory), from 2 till 3 and from 9 till 11 December 2020 and on 20 September 2021. Hands-off mode.

Glass is a material frequently present at the scene of such events as car accidents, burglaries, assaults, and criminal offenses. Glass as physical evidence could provide valuable information to assist criminal investigations. One of the problems of forensic glass analysis is the comparison problem. The other task related to glass analysis, and frequently addressed, is a determination of the category of a glass fragment, for example, was the fragment from a window, or some glass container such as a bottle? This process is also called a classification problem and becomes especially important when there may be no control sample to compare with one found at the scene of a crime.

Characterization of glass fragments is normally accomplished by measuring the physical and optical properties of density and refractive index (RI).  However further discrimination, such as identification of a suspected source of origin, has become more difficult as the range of RI has narrowed within glass subtypes because of advances in glass manufacturing technology. Moreover, the main requirement for the chosen method should be non-destructive leaving the material available for re-use.

The motivation of the project is to develop the algorithm for glass fragments classification and discrimination using a combination of refractive index (RI) data and elemental analysis using ion beam analysis (IBA) methods and particularly, PIXE and PIGE

48 glass samples from 13 vehicles (different models, and production years) were analyzed by PIXE and PIGE techniques to determine minor and trace elements concentration for identifying unknown car glass fragments. The samples from car windows were provided by the Israeli police force. The measurements were carried out using an extracted proton beam of 3.0 MeV and two Silicon Drift Detectors for PIXE (one small area SDD for elements from Na to Ca, and one large area SDD for elements from Ti and above), one HPGe detector for PIGE and one SI PIN diode for RBS. The use of an external beam set-up has the advantage of allowing the easy positioning of the small irregular glass fragments, possibly avoiding errors in the analysis due to the positioning of the samples on fixed geometry sample holders in in-vacuum scattering chambers.

Every sample includes several small fragments (appr. 3 x 3 mm); a fragment from each sample has been selected randomly for each kind of sample. Three measurements were done for each fragment (on the two external smooth surfaces and one - on the rupture surface). Glass reference standards (NIST 1412, 620 and 610) were analysed frequently as well for quality assurance purposes.