Particle induced x ray cross section measurements and pixe analysis of forensic samples

Abstract

In the first chapter, basic aspects of ion atom collisions are discussed. Collisions of heavy ions with atoms define one of the most active areas of research within the vast field of atomic physics. In the last decades, the design and construction of accelerators needed for these experiments, as well as the theoretical description of ion-atom collisions has advanced considerably. Creations of vacancies in the inner most shells of the target atoms is one of the various processes associated with ion atom collision. The de-excitation of the vacant inner shells are characterised by emission of Auger electrons and/or characteristic x-rays. Many details of the atomic excitation accompanying the vacancy production by ion impact can be studied by examining the spectral distributions of the characteristic x-ray lines. Particle Induced X-ray Emission (PIXE) technique is based upon the ionisation of target inner shell electrons due to their Coulomb interaction with the incident projectile ion and subsequent emission of x-rays characteristic to the target atom. Accordingly in a multielemental specimen, each element can be traced and identified by referring to its characteristic x-ray lines. This technique proves to be a precise analytical technique featuring high sensitivity and non-destructiveness. Protons of energy 2-4 MeV are found to be the most suitable ionising agent to use as the ionising agent in PIXE principle. Forensic science may be defined as the application of various scientific disciplines to aid the criminal justice system. The primary tools in the investigation of forensic cases have been observation and interpretation of physical evidence. Elemental analysis of the evidences is one of the most commonly used methods to differentiate and associate them with one another. The analytical technique used for such analysis must be highly sensitive, quite precise and accurate in addition to being fast and non destructive.