0000000000140373
AUTHOR
Christina Trautmann
Hardening and formation of dislocation structures in LiF crystals irradiated with MeV–GeV ions
Abstract Material modifications of LiF crystals irradiated with Au, Pb and Bi ions of MeV to GeV energy are studied by means of microindentation measurements and dislocation etching. Above a critical irradiation fluence of 10 9 ions/cm 2 , the microhardness can improve by a factor of 2 in the bulk and by more than 3 on the surface. Radiation-induced hardening follows the evolution of the energy loss along the ion path. Annealing experiments indicate that complex defect aggregates created in the tracks play a major role for the hardness change. Evidence for severe structural modifications is found when etching indentation impressions in highly irradiated crystals leading to similar pattern a…
Irradiation effects in CaF2probed by Raman scattering
The formation conditions and dynamics of Ca colloids and point defects that appear in irradiated single crystals of CaF2 were investigated by Raman spectroscopy. The intensity changes in the Raman spectra because of the presence of different concentrations of point defects and Ca colloids that emerged in CaF2 after irradiation with 2.2 GeV Au ions were used to study their distribution and stability under illumination with three laser wavelengths (473, 532 and 633 nm) at different output powers (2 to 200 mW). A damage saturation at a fluence of 6 × 1011 ion cm−2 was observed. The dependence of the spectral changes on the ion fluence can be described by a core/halo damage cross-section model.…
Hardening and long-range stress formation in lithium fluoride induced by energetic ions
Abstract LiF crystals were irradiated with Au, Pb, Bi and S ions in the energy range 400–2300 MeV and studied by means of Vickers microindentation. Remarkable hardening effects are observed which depend on the applied fluence and ion species, and correlate with the ion energy loss along the ion path. Structural investigations reveal irradiation-induced stress extending deep into the adjacent non-irradiated crystal and leading to the formation of dislocations. X-ray diffraction measurements of the irradiated crystals show a decrease of the lattice constant indicating the presence of internal stress.
Energy loss and fluence dependency of swift‐ion‐induced hardening in LiF
The depth profiles of the hardening effects of LiF irradiated with swift Au, Pb, Bi, Kr, Ni and S ions of MeV-GeV energy have been studied as a function of ion penetration depth. For all projectiles, the hardness increases scaling with the range of ions and depending on ion fluence and energy loss. Heavy ions (Au, Pb, Bi), for which the energy loss noticeably exceeds the threshold of about 10 keV/nm for severe track core damage, cause uniform increase of hardness in the entire irradiated layer. For irradiations with lighter S, Ni, Kr ions, the hardening displays strong depth dependence. Ion-induced hardening is related to pinning of dislocations by defect aggregates (possibly small Li collo…
Modeling of primary defect aggregation in tracks of swift heavy ions in LiF
To simulate aggregation of primary F centers created along the path of swift heavy ions in LiF, Monte Carlo simulations were developed. Parameters relevant for defect aggregation as a result of their random hopping, such as the migration energy, temperature in the track, initial defect concentration, and diffusion time, were estimated from available experimental data. It is estimated that in the electronically excited state and under temperature locally increased up to 1200 K F centers are mobile enough to make several tens of hops. Most of the F aggregates formed are extremely small and consist only of two or three F centers. The fraction of larger F clusters ~with more than 10 defects! is…
<title>Formation of dislocations and hardening of LiF crystals irradiated with energetic Au, Bi, Pb, and S ions</title>
The irradiation of LiF crystals with Au, Pb, Bi, and S ions in the range of 400 - 2200 MeV leads to a remarkable increase of the hardness. The effect appears for Bi and Pb ions at fluences above 109 ions/cm2 and for S ions above 1010 ions/cm2. The increase of hardness follows the energy loss and is related to the formation of defects along the ion path. Defect complexes, clusters and aggregates with nanoscale dimensions serve as strong obstacles for dislocations and cause dispersion strengthening. Structural investigations reveal the generation of long-range stress in the adjacent non-irradiated part of the crystal. Close to the implantation zone, the stress exceeds the yield strength, caus…
Anisotropic diffusion in etched particle tracks studied by field gradient NMR
Etched particle tracks produced after heavy ion irradiation of polymer foils are used as model systems to test the performance of NMR in a newly developed ultrahigh magnetic field gradient system. The stimulated NMR echo decay of molecules diffusing in the channels, formulated in terms of the self part of the intermediate scattering function, is anisotropic and yields the form factor of the channels.