Irradiation Of Metal Targets Research Articles

Studying the synthesis of metal nanoparticles during the laser irradiation of targets in liquid media

The results from experiments on the laser irradiation of metallic targets of the copper group immersed in liquid are reported. Comparative studies of the formation of colloids during the laser irradiation of targets with varying (from moderate to ultrahigh) radiation intensities are conducted. The dependence of the size of obtained particles on laser irradiation conditions (pulse duration and radiation intensity) is revealed.

Condensation of ablation plumes in the irradiation of metals by high-intensity nanosecond laser pulses at atmospheric pressure

The Anisimov – Luk'yanchuk model is adapted for describing the condensation of vapour-plasma plumes produced in the irradiation of metal targets by high-intensity nanosecond pulses at atmospheric pressure. The resultant data suggest that the initial stages of the development of metal ablation plumes correspond with a high degree of accuracy to the Zel'dovich – Raizer theory of dynamic condensation; however, at the stage of the ablation plume decay, the liquid-droplet phase is formed primarily by coalescence of ‘nuclei’.

Metal surface layers after pulsed electron beam treatment

Irradiation of metal targets with intense pulsed electron beams leads to rapid melting and solidification of the target surface layers. For beams generated by the GESA facility with 120kV acceleration voltage, 20–80J/cm2 beam energy density, and 20–50μs pulse duration, the induced changes in material properties are accompanied by the evolution of a topographical pattern on the target surface, typically tens of micrometers in height and hundreds of micrometers laterally. In this work, GESA-modified surface layers of stainless steel, copper, and aluminum alloy targets are characterized by a post-treatment study. Larger surface roughness is found for treatment with an electron beam of higher energy density. Similarly, the roughness amplitude increases for the repetitive application of high energy density pulses (60–80J/cm2, 40–50μs). Several shorter pulses with lower energy density (~30J/cm2, 25–30μs) lead to a coarsening of the surface features. The target material inhomogeneity and the aspect of the melt front are investigated by cross-sectional analysis. Material homogenization is observed in the melted surface layer. Straight melt fronts are found for stainless steel, whereas aluminum alloy shows non-uniform melting. Based on the experimental findings, different processes and their influence on the surface layer dynamics during the melted stage are discussed. These include intense evaporation and dissolution of inclusions into the surrounding melt material.

Possibility of applying a hydrodynamic model to describe the laser erosion of metals irradiated by high-intensity nanosecond pulses

We report the results of experimental investigations of the production and development of plasma-vapour plumes upon irradiation of metal targets by nanosecond pulses with a high power density under atmospheric conditions. The transition from a quasi-stationary thermal mechanism of metal erosion to an explosion hydrodynamic one takes place when the radiation power density increases from to . The resultant experimental information is extremely important for the laser deposition of metal nanostructures under atmospheric conditions, which is possible only for power densities of .

Long-term variation in nuclide activities under laser ablation of metallic targets in aqueous solutions of uranium salt

The long-term variation in the activities of nuclides belonging to the uranium series after laser irradiation of metallic targets (Au, Be, Al, Ti) in aqueous solutions of UO2Cl2 has been experimentally investigated. It is found that the activity of 234Th, in contrast to unirradiated solution, continues to increase for 50 to 60 days after laser irradiation and, having reached a stationary level, remains at it for a long time (about 1 yr). The activity dynamics is modeled theoretically on the assumption that a fraction of 238U in the irradiated solution is under peculiar conditions, so that its half-life ismuch shorter than that of spontaneous α decay of this nuclide under normal conditions. Possible mechanisms of variation in the shape of the potential barrier for α-particles in the presence of nanoparticles formed by laser ablation of targets are discussed.

SU‐HH‐BRB‐04: Dosimetry of Low‐Energy Characteristic X‐Rays

Purpose: To measure dose rates in water and obtain percent depth dose (PDD) curves in phosphate‐buffered saline (PBS) solution for low‐energy (< 20 keV) characteristic x‐rays emitted from various metals. Dose‐rate data obtained here will be used to support measurements of RBE in human glioma and other cells. Method and Materials: Characteristic x‐rays were produced by irradiation of metal targets with a 55 kVp x‐ray spectrum from an Ag anode at constant mA. Dosimetry was performed using an extrapolation chamber. The chamber was oriented with its window parallel to the target surface at a distance of 65 mm from the target such that the charge produced in the chamber was due to the characteristic x‐ray emissions from the metal target. Dose rate to water at the position of the chamber window was determined using Burlin cavity theory, by varying the chamber electrode spacing and window thickness, while measuring the resulting change in the charge collected. Dose rates were used to create a calibration curve relating the optical density of Gafchromic EBT film to the dose to water. Percent depth dose was measured by sequentially irradiating pieces of film submerged in a PBS‐filled cell culture dish at a range of distances from the bottom of the dish. Results: Dose rates to water for this experimental arrangement were found to be approximately 4.17 cGy/min for Mo, 10.75 cGy/min for Ti, and 12.55 cGy/min for Zn. As expected, the slopes of the PDD curves were dependent on the characteristic x‐ray energies of each metal. Conclusion: The PDD curves may prove useful in assessing the trade‐off between RBE and depth of penetration in, for example, electronic brachytherapy devices that could make use of characteristic x‐rays produced by an apparatus similar to that in the present experiment.

Ion energy increase in laser-generated plasma expanding through axial magnetic field trap

Laser-generated plasma is obtained in high vacuum (10−7 mbar) by irradiation of metallic targets (Al, Cu, Ta) with laser beam with intensities of the order of 1010 W/cm2. An Nd:Yag laser operating at 1064 nm wavelength, 9 ns pulse width, and 500 mJ maximum pulse energy is used. Time of flight measurements of ion emission along the direction normal to the target surface were performed with an ion collector. Measurements with and without a 0.1 Tesla magnetic field, directed along the normal to the target surface, have been taken for different target-detector distances and for increasing laser pulse intensity. Results have demonstrated that the magnetic field configuration creates an electron trap in front of the target surface along the axial direction. Electric fields inside the trap induce ion acceleration; the presence of electron bundles not only focuses the ion beam but also increases its energy, mean charge state and current. The explanation of this phenomenon can be found in the electric field modification inside the non-equilibrium plasma because of an electron bunching that increases the number of electron-ion interactions. The magnetic field, in fact, modifies the electric field due to the charge separation between the clouds of fast electrons, many of which remain trapped in the magnetic hole, and slow ions, ejected from the ablated target; moreover it increases the number of electron-ion interactions producing higher charge states.

Modeling of breakdown of a gas by electrons of the boundary layer during irradiation of metal targets by picosecond laser pulses

Results are presented from a numerical simulation of the breakdown of a dense inert gas by boundary-layer electrons upon irradiation of a metal target by high-power picosecond laser pulses. It is shown that taking the electric field of the boundary layer into account leads to a substantial increase in the concentration of the seed electrons near the target surface, which accelerates the ionization process. The dependence of the breakdown time on the electric field intensity of the incident wave and the concentration of the gas atoms is derived.

Effect of pressure on the microstructure of an austenitic stainless steel shock-loaded by very short laser pulses

Irradiation of metallic targets by a high-energy pulsed laser can generate in materials shock waves with pressure amplitudes of the same order as with conventional shocks from explosives, flyer plate impact etc., but with much shorter pulse durations. Experiments were performed with a 0.6 ns pulsed laser on 304 austenitic stainless steel samples. The effects of induced pressure on the microstructure were investigated by transmission electron microscopy in addition to microhardness measurements and are compared with the conventional results. The twin density and the presence of α-phase are particularly studied. In spite of the very short pulses, twins were present in the observed areas whatever the pressure, while α-phase embryos were only present in the pressure range 15–25 GPa.

Irradiation of Metallic Targets with High-Energy Heavy Ions: High Electronic Excitation Induced Effects

Irradiation of Metallic Targets with High-Energy Heavy Ions: High Electronic Excitation Induced Effects