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In the framework of the thermal-spike model the present paper deals with the effect of the electronic stopping power (Se) in metals irradiated by swift heavy ions. Using the strength of the electron-phonon coupling g(z) with the number of valence electrons z as the unique free parameter, the increment of lattice temperature induced by swift-heavy-ion irradiation is calculated. Choosing z=2, the calculated threshold of defect creation by Se for Ti, Zr, Co and Fe is about 11, 27.5, 28 and 41 keV nm-1, in good agreement with experiment. Taking the same z value, the calculation shows that Al, Cu, Nb and Ag are Se insensitive. Moreover, in Fe, the differences in the damage created by U ions of different energies but exhibiting the same value of Se may be interpreted by a velocity effect. Using z=2, other calculations suggest that Be (Se>or=11 keV nm-1), Ga (Se>or=5 keV nm-1) and Ni (Se>or=49 keV nm-1) should be sensitive to Se but Mg should not. These examples put the stress on the effect of the physical parameters governing the electron-phonon coupling constant apart from z determination: the sound velocity linked to the Debye temperature and the lattice thermal conductivity. Furthermore, a simple criterion is proposed in order to predict the Se sensitivity of metals.

Pure bismuth samples were irradiated at 20 K with swift heavy ions from 18O to 238U in the GeV range. The rate of the induced damage was deduced from in situ electrical resistance measurements. Above a threshold in the electronic stopping power Se equal to 24 keV nm-1, the damage is due to electronic slowing down. Above 30 keV nm-1, the electronic slowing down is efficient enough to induce latent tracks attributed to the appearance of a high-resistivity phase. The induced latent tracks radii can be up to 21.9 nm for Se=51 keV nm-1 which is the largest value reported so far for non-radiolytic materials. The evolution with Se of the latent tracks radii is calculated on the basis of the thermal spike model, assuming a realistic value for the electron-phonon coupling constant. A rather good agreement is obtained which supports the idea that the thermal spike could be operative in the observed radiation damage.

In the framework of swift heavy ion -matter interaction, the thermal spike has proved its worth since nearly two decades. This paper deals with the necessary refinement of the computation due to the kind of materials involved i.e. nanomaterials such as multilayered systems or composite films constitued of nanocylinders or nanospheres embedded in matrix. The three dimensional computation of the thermal spike model is applied for the first time in layers containing spherical nanoparticles embedded in a silica matrix. The temperature profile calculated at each point (x,y,z) of the target for times up to 10 −10 s allows a possible explanation of the particle shape change under irradiation with swift heavy ions having an energy of several MeV/u.m.a. The comparison made with the former 2D version of the code applied to cylindrical gold nanoparticles confirms the validity of the present 3D version.PACS numbers: 61.80.Jh, 68.60.Dv Submitted to: J. Phys. D: Appl. Phys. Ion radiation effects, swift heavy ion, thermal spike, nanoparticleThe 3D thermal spike model applied to nanoparticle irradiation with swift heavy ions 2

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