Matias Rodriguez

Effect of the breakup on the fusion and elastic scattering of weakly bound projectiles on {sup 64}Zn

We study the behavior of the fusion, breakup, reaction, and elastic scattering of different projectiles on {sup 64}Zn, at near and above barrier energies. We present fusion and elastic scattering data with the tightly bound {sup 16}O and the stable weakly bound {sup 6}Li, {sup 7}Li, and {sup 9}Be projectiles. The data are analyzed by coupled channel calculations. The total fusion cross sections for these systems are not affected by the breakup process at energies above the barrier. The elastic (noncapture) breakup cross section is important at energies close to and above the Coulomb barrier and increases the reaction cross sections. In addition, we show that the breakup process at near and below barrier energies is responsible for the vanishing of the usual threshold anomaly of the optical potential and gives rise to a new type of anomaly.

SAXS investigations of the morphology of swift heavy ion tracks in α-quartz

The morphology of swift heavy ion tracks in crystalline α-quartz was investigated using small angle x-ray scattering (SAXS), molecular dynamics (MD) simulations and transmission electron microscopy. Tracks were generated by irradiation with heavy ions with energies between 27 MeV and 2.2 GeV. The analysis of the SAXS data indicates a density change of the tracks of ~2 ± 1% compared to the surrounding quartz matrix for all irradiation conditions. The track radii only show a weak dependence on the electronic energy loss at values above 17 keV nm(-1), in contrast to values previously reported from Rutherford backscattering spectrometry measurements and expectations from the inelastic thermal spike model. The MD simulations are in good agreement at low energy losses, yet predict larger radii than SAXS at high ion energies. The observed discrepancies are discussed with respect to the formation of a defective halo around an amorphous track core, the existence of high stresses and/or the possible presence of a boiling phase in quartz predicted by the inelastic thermal spike model.

Fusion, break-up and elastic scattering of weakly bound nuclei

We describe the behaviour of the fusion, break-up, reaction cross sections and elastic scattering of weakly bound nuclei, at near and above barrier energies. The total fusion cross sections are not affected by the break-up process at this energy regime. The elastic break-up cross sections are important at energies close and above the Coulomb barrier, even in systems with light targets, and increase the reaction cross sections. We also show that the break-up process at near and sub-barrier energies is responsible for the vanishing of the usual threshold anomaly of the optical potential and gives rise to a new type of anomaly, named by us as break-up threshold anomaly.

Effect of orientation on ion track formation in apatite and zircon

Abstract Fission track (FT) thermochornology is essentially based on empirical fits to annealing data of FTs revealed by chemical etching, because, until now, unetched, latent FTs could not be examined analytically at the atomic-scale. The major challenge to such an analysis has been the random orientation of FTs and their extremely small diameters. Here we use high-energy ions (2.2 GeV Au or 80 MeV Xe) to simulate FT formation along specific crystallographic orientations. By combining results from transmission electron microscopy (TEM) of single tracks and small-angle X-ray scattering (SAXS) for millions of tracks, a precise picture of track morphology as a function of orientation is obtained. High-resolution analysis reveals that orientation affects the shape of tracks in apatite and zircon through the preferential creation of damage along directions with highest atomic density. However, track radius does not depend on orientation, contradicting previous reports. Independent of track orientation, track radii, as measured at each point along the entire length of 80 MeV Xe ion tracks in apatite, can be understood using the thermal spike model of Szenes. Thus, the well-known track annealing anisotropy of apatite is not due to track radius anisotropy. The combination of ion-irradiations with TEM and SAXS analysis provides a unique opportunity to understand and model track formation and annealing under various geologic conditions.

Temperature dependence of ion track formation in quartz and apatite

Ion tracks were created in natural quartz and fluorapatite from Durango, Mexico, by irradiation with 2.2 GeV Au ions at elevated temperatures of up to 913 K. The track radii were analysed using small-angle X-ray scattering, revealing an increase in the ion track radius of approximately 0.1 nm per 100 K increase in irradiation temperature. Molecular dynamics simulations and thermal spike calculations are in good agreement with these values and indicate that the increase in track radii at elevated irradiation temperatures is due to a lower energy required to reach melting of the material. The post-irradiation annealing behaviour studied for apatite remained unchanged.

Nano-porosity in GaSb induced by swift heavy ion irradiation

Nano-porous structures form in GaSb after ion irradiation with 185 MeV Au ions. The porous layer formation is governed by the dominant electronic energy loss at this energy regime. The porous layer morphology differs significantly from that previously reported for low-energy, ion-irradiated GaSb. Prior to the onset of porosity, positron annihilation lifetime spectroscopy indicates the formation of small vacancy clusters in single ion impacts, while transmission electron microscopy reveals fragmentation of the GaSb into nanocrystallites embedded in an amorphous matrix. Following this fragmentation process, macroscopic porosity forms, presumably within the amorphous phase.

Orientation dependent annealing kinetics of ion tracks in c-SiO2

The structure and thermal response of amorphous ion tracks formed along the [112¯0], [101¯0], and [0001]-directions in crystalline quartz have been investigated using small angle x-ray scattering. The radii of the ion tracks vary by about 5% (0.3 nm) for tracks along different crystallographic directions. Molecular dynamics simulations reproduce this anisotropy along the [101¯0] and [0001] directions and suggest that differences in thermal conductivity along these directions are partly responsible for this observation. Using in situ annealing, tracks along the [101¯0] and [0001] directions were shown to recrystallize during thermal annealing around 960–1020 °C with activations energies around 6 eV, while those along the [112¯0]-direction already disappeared at 640 °C with a significantly lower activation energy around 3–4 eV.

Complete fusion of weakly bound nuclei applying the delayed X-ray technique: the 9Be + 144Sm system

The detection of delayed X-rays produced by the decay that follows electron capture in the residual nuclei has been used in the past for the determination of fusion cross sections of tightly bound nuclei. In this work we applied this technique to study the effect of the break-up of a weakly bound projectile, like in the case of the 9Be + 144Sm system. Preliminary results of the complete fusion in this system at near barrier energies are presented.

Fusion cross sections for the 6,7Li+27Al, 9Be+27Al systems

We present the results of total fusion cross sections measurements for the 6,7Li + 27Al, 9Be + 27Al, systems at energies above and below the Coulomb barrier (0.8Vb ⩽ E ⩽ 2.0Vb). The experimental evidence at the measured energy regime show that the total fusion cross sections of 6Li and 9Be with a light mass target are not affected by the break‐up process. The elastic break up cross sections for the 6Li + 27Al system were also measured and the results are being presented in this issue. The data for the 7Li + 27Al system are still being analyzed and therefore these results should be considered preliminary.

Measurement of Fusion Excitation Functions using a Novel Superconducting Solenoid

This work presents the essential features of a highly efficient detector system developed to make precise measurements of evaporation residues produced following heavy ion fusion reactions. The details of the measurements of fusion excitation function performed with this device for the system 58Ni + 60Ni are presented, and the results are compared with an existing set of data.