Damage and helium migration induced in fluorapatite sinters by swift heavy ion irradiations

We have studied the damage induced in fluorapatite (Ca10(PO4)6F2) sinters after 70-MeV Kr, 120 MeV I and 163-MeV Au ion irradiations at room temperature. On the basis of X-ray powder diffraction data we conclude that fluorapatite is not completely amorphized due to ion-induced recrystallization. This recrystallization of the amorphous phase is greatly enhanced for Au ions with a high electronic stopping power. We also have used the 3He(d, p) 4He nuclear reaction to study the migration of implanted 3-MeV 3He ions after swift heavy ion irradiations. The proton yield curves versus deuteron energy for irradiated samples exhibit two bumps for high fluences. These excitation curves are deconvoluted by using a computer code based on a two-diffusion equation model of helium atoms in two accumulation zones. Optimizations of the model parameters give access to the diffusion coefficients and helium depth profiles in the two zones. This yields two broad peaks in the helium depth profiles, the first one is near the end-of-range region and the second one is shifted at about half way between the surface and the first peak. This shift is interpreted as a Radiation-Enhanced Diffusion (RED) effect which is found to increase with fluence for Kr ions, and with electronic stopping power from Kr to Au ions.