New technique to estimate the track dimensions induced by heavy ions on UHMWPE

M. F. DEL GROSSO; V.C. CHAPPA; G. GARCÍA BERMÚDEZ; R.O. MAZZEI

Iguazú

Simposio; VI Latin American Symposium on Nuclear Physics and Applications; 2005

When a heavy ion penetrates a polymer film it induces a dense trail of excited and ionized molecules. The large amount of energy deposited in a very short time is mainly dissipated by electrons which are emitted essentially perpendicular to the ion direction, producing a damage zone around the ion path, the so-called latent tracks. This cylindrical region can be divided in two different areas, a inner core, in which considerable part of the ion energy loss is deposited, and a outer zone called penumbra, affected by elec- trons (delta rays) with enough energy to leave the core. The diameter of each zone depends on the ion type and its energy. In the present work we studied the physico-chemical modifications generated by the heavy ions as a function of the ion fluence. The medical grade UHMWPE, Ultra High Molecular Weight Polyethylene, (GUR 1050) used in this study was kindly supplied by Poly Hi Solidur (Germany). The polymeric material was cut in thin foils of approximately 20-30 mm thickness and then irradiated with different ions and energies, provided by the TANDAR accelerator. The analysis of the structural changes originated by the irradiation was performed by means of Fourier transform infrared (FTIR) spectroscopy in the transmission mode. To study the relationship between the irradiation fluence and the induced changes, Monte Carlo simulations were performed. It is assumed that the observed absorbance is proportional to the penumbra area without taken into account the carbonized central core area. The algorithm implemented as a Fortran program consists on randomly distribute, on a rectangular lattice, overlapping discs of radius R1, that represents the penumbra zone, filled with a second concentric disc of radius R2 < R1, that denotes the core zone. For each simulated fluence the total penumbra zone area was calculated. The simula- tion results reproduce the behavior of the experimental data The penumbra zone area reaches a maximum for a fluence that depends on the radii of both zones and the slope of the decreasing region of the curve is determined by the core radius. Finally, from the absorbance measurement as a function of the ion fluence, it is possible to obtain both the penumbra and core radii. The general characteristic of the present new technique is discussed, as well as the comparison with other methods, such as dechanneling, forward X-ray scattering and small-angle neutron scattering.