Swift heavy ions irradiation effects in polymers

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

Cuzco, Perú

Simposio; VII Latin American Symposium on Nuclear Physiscs and Applications; 2007

The swift heavy ions effects in polymeric materials depend strongly on the spatial distribution of deposited energy and therefore on ion species, energy and fluence. The sudden pass of the ions induces a very complex path of excited and ionised molecules. Those highly reactive molecules finally recombine and constitute the so call latent track. In this cylindrical region it can be found several physical–chemical effects such as bond breaking, free radicals, chain scissions, cross-linking effects, etc. In recent years there is a serious attempt to measure the intensity of each effect (the cross sections) and to study it as a function of the energy distribution around the ion path, stopping power, etc. The grafting process is a well known means to change the properties of a polymer. A maximum in the grafting yields at a certain fluence range was found for the first time in Betz review’s work [1]. A maximum in certain functional groups formation was also observed measuring the absorbance of infrared radiation (IR) [2, 3]. These experimental data of grafting yields and IR experiments were analysed and it was found a correlation between the characteristic fluence and stopping power [4] as shown in Fig. 1. In the present work we analysed the mathematical expression that was obtained assuming two different cross sections per ion: one to produce and another to destroy same particular chemical structure [5]. In this way it is possible to explain the linear relationship (Fig. 1) if we assume that these two cross sections are associated to some physical region of the latent track. The distance from the ion path, that limit these regions, correspond to certain electronic energy dose. The knowledge of this characteristic fluence became of great technological importance if, for instance, the induced physical-chemical change is related to some mechanical properties of the materials [6]. This indicate the optimum fluence value to maximize certain characteristic on the materials surface. The striking linear dependence over two orders of magnitude can be described assuming two different thresholds of electronic energy dose. Reference:                                                                                         [1] N. Betz. Nucl. Instr. and Meth. B 105 (1995 ) 55.  [2] V. C. Chappa et al. Nucl. Instr. and Meth. B 243 (2006 ) 58.  [3] M. F. del Grosso et al. Nucl. Instr. and Meth. B 245 (2006) 281.  [4] R. Mazzei et al. Nucl. Instr. and Meth. B 218 (2004) 313.  [5] G. García-Bermúdez et al., unpublished results.  [6] M. F. del Grosso et al., To be published.