Basic phenomena induced by swift heavy ions in polymers

The modifications induced by the high energy ions in materials may be understood only if the particularities of the energy transfer from the ion to the target are considered. This is true in particular for polymers. Indeed the ion irradiations are characterised by their large value of the linear energy transfer and certainly by their spatial distribution of the primary events and of the damages. The primary events are strongly correlated to each other: they are mainly located in a small cylinder centred on the ion path. The density of ionisation and the radius of this cylinder (the core region) depend on the projectile and on its velocity. Roughly, the higher the ion energy, the larger the radius is and the lower the ionisation density is. So the dose (the amount of energy absorbed by unit mass of the target) is not sufficient to characterise a high energy ion irradiation. In this paper we describe the physical aspects of the ion irradiation and we shall demonstrate that three parameters are needed to have a non-ambiguous description of these irradiations. They should be, for example, the atomic number, the velocity and the fluence.