Bremsstrahlung in low atomic number thick targets by proton incidence

PABLO PÉREZ; ANA BERTOL; TABATHA RODRIGUEZ; MARCOS VASCONCELLOS; JORGE TRINCAVELLI

Gramado - Rio Grande do Sul

Congreso; 13th International Conference on Particle-Induced X-ray Emission; 2013

Laboratório de Implantação Iónica, Instituo de Física, Universidade Federal do Rio Grande do Sul, Sociedade Brasileira de Física, International Atomic Energy Agency

The subtraction of the continuum from an x-ray spectrum emitted by proton bombardment is usually carried out by means of a mathematical fitting. Thus, the emission lines corresponding to the atoms present in the sample are separated from the background generated in it. The purpose of the present work is to develop an analytical function to model the continuous spectrum generated in a PIXE experiment for different incident beam energies and atomic numbers in thick targets of light elements. PIXE spectra were measured at the 3 MeV ion accelerator (High Voltage Engineering, Tandetron 3MV) in the Laboratório de Implantação Iônica, IF-UFRGS, Brazil, in thick samples of low atomic number: Be, B, C and BN. The results obtained can be applied to the more general case of thin targets deposited on light substrates like carbon or polymeric materials. The proton beam energies were varied between 700 and 2000 keV. The spectra analysis was performed taking into account the main four effects underlying the production of the continuous spectrum: Secondary Electron Bremsstrahlung (SEB), Quasi Free Electron Bremsstrahlung (QFEB), Nuclear Bremsstrahlung (NB) and Atomic Bremsstrahlung (AB) [1]. Nevertheless, it was found that for the cases considered, AB is the most important one and the other contributions can be neglected in a first rough approximation. The experimental spectra from carbon thick targets corrected by self-absorption and detector efficiency are shown in the figure. These spectra generated within the sample were parameterized as a function of the photon energy using an exponential polynomial [2]. Finally, the behavior with atomic number was studied for the light element range. [1] S. Johansson, J. Campbell, K. Malmqvist, Particle-Induced X-Ray Emission Spectrometry (PIXE), first ed., John Wiley & Sons, New York, 1995. [2] K. Murozono, K. Ishii, H. Yamazaki, S. Matsuyama, S. Iwasaki, Nucl. Instrum. Methods Phys. Res., Sect. B 150 (1999) 76-82.