Target Fabrication Research Articles

Fused Zinc Target for the Production of Gallium Radioisotopes

Gallium-68 is a popular radioisotope for positron emission tomography. To make gallium-68 more accessible, we developed a new solid target for medical cyclotrons. Fused zinc targets promise a new, efficient, and reliable technique without the downsides of other commonly used time-consuming methods for solid target fabrication, such as electroplating and sputtering. We manufactured targets by fusing small pressed zinc pellets into a recess in aluminum backings. Using a simple hotplate, the fusing could be accomplished in less than two minutes. Subsequently, the targets were cooled, polished, and used successfully for test irradiations at Ep = 12.8 MeV and up to 20 µA proton current.

Estimating Sample Heterogeneity and Expected Scatter Due to Cracking in Packed Powder Samples Using a Two-Phase Model

High-precision Hugoniot measurements of heterogeneous materials are a key tool in creating accurate equations of state, but such measurements are prone to larger uncertainties than their homogeneous counterparts. To efficiently reduce these uncertainties one must estimate the relative contributions of different error sources. Sample cracking is one likely source. Here we estimate its contribution through modeling, using computed tomography scans of powdered single crystal quartz samples to estimate typical packing variation within and between samples. Samples were prepared using the same materials and methods. Cracks were prominent in the samples. We describe a simple model to estimate shock transit time variation for a single shot due to cracking, and estimate that up to 3% variation can be attributed to these structures. This suggests that decreasing variation requires addressing such packing heterogeneities during target fabrication rather than experimental diagnostics.

Fabrication and characterization of targets of oxidizing materials for heavy ion nuclear reaction experiments

Fabrication of targets of materials which get readily oxidized poses lot of challenges in heavy ion nuclear reaction experiments. Targets of oxidizing elements, viz. Li, Ca, Pb, Nd, Gd, Sm, Ba, Ce, Pr, Bi, Er and Eu have been frequently fabricated in target development laboratory at Inter-University Accelerator Centre (IUAC) in the form of free standing films and foils with backing support. In some cases, foils of these elements are sandwiched between two protective foils to avoid oxidation while exposed to air. Role of sandwiching (encapsulation) in minimizing the oxidation of target surface and its effect in preservation of expensive isotopic targets for longer duration is reported in the present investigations. The level of contamination from parting agents in sandwiched targets is also reported in this paper.

Ultrafine Hydrogen Layer Formation in a Cryogenic Target under External Vibrational Influence

A considerable attention has recently been focused on the issue of large target fabrication for inertial confinement fusion (ICF) research on MJ-class laser facilities. The targets require a condensed uniform layer of hydrogen fuel on the inside of a spherical shell. The fusion fuel inside the targets must have such a structure, which supports the fuel layer survivability under target injection and transport through the reactor chamber. Over the last two decades, the Lebedev Physical Institute (LPI), has been devising the structuresensitive methods of forming high-quality hydrogen fuel with an isotropic structure (ultra-fine type of solid layers) to meet the requirements of implosion physics. A considerable anisotropy of HCP-phases of H2 and D2 (single crystal or coarse-grained crystalline layers) results in the layer degrading due to roughening of the layer surface before the target reaches the chamber center, or can result in the spherical-shock velocity dependence on the grain orientation. On the contrary, the ultra-fine solid layers have enhanced mechanical strength and thermal stability which is of critical importance for target fabrication, acceleration and injection. To meet the goal of ultra-fine solid layers formation, the LPI has constructed a piezo-vibration module, in which the couple “membrane & target” is driven by an input signal generated due to inverse piezoelectric effect during fuel cooling via the heat conductivity within vibrating targets. It allows one to modify the key experimental parameters (mechanical and thermal) for influencing the fuel microstructure and intensifying the creation of ultimate disordered structures with a large defect density, i.e., isotropic medium. In this report, the modeling results of the processes of cryogenic layer fabrication in the conditions of high-frequency mechanical influence are presented. The investigation is carried out to gain insight into the relation between the microstructure and bulk properties of the fusion fuel, and to fabricate this fuel with a given microstructure within ICF targets.

Properties of fluorine targets and their application on the astrophysically important 19F([formula omitted])16O reaction

We report on the production and testing of both evaporated and implanted fluorine targets to investigate their stability to irradiation by protons. We produced four targets by evaporating CaF2 and LiF powder on Ta backings and three targets by implanting 30 keV 19F ions into stainless steel backings; a 5μg/cm2 Cr protective layer was also evaporated on one of these implanted targets. We assessed each target’s stability by monitoring the γ-ray yields of the 19F(p,αγ)16O reaction. Our results indicate that the evaporated and implanted targets without Cr layer exhibited 30%∼75% and 13% deterioration after ∼2.5 Coulomb/cm2, 220–270 keV proton bombardment, respectively. The implanted target with protecting layer exhibited only about 2.5% deterioration, which can be regarded as stable. As we observed stability in one of the CaF2 evaporated targets up to 0.25 Coulomb/cm2 irradiation, this target was used to investigate the two resonances at Ep=225 and 237 keV of the 19F(p,αγ)16O reaction; the resonance parameters we extracted are consistent with the values found in the literature, giving us confidence in our analysis methods and our understanding of the target fabrication procedures described herein. In conclusion, the implantation technique provides a unique means to produce fluorine targets capable of withstanding high beam intensities, which is one of the necessary technical developments for the JUNA (Jinping Underground Nuclear Astrophysics) project in China.

Fabrication and characterization of (Ba, Sr)RuO3 ceramic targets and thin films for ferroelectric BaTiO3 thin-film capacitors

We report the preparation of (Ba, Sr)RuO3 ceramic targets in a conventional process in air at ambient pressure and their epitaxial thin-film growth on Ba0.7Sr0.3TiO3 buffered SrTiO3 substrates. We found that a simultaneous addition of CuO and SiO2 is effective in obtaining the relatively dense ceramics. The microstructural and chemical investigations show that the synergetic effect of a liquid-phase (Ba-Sr-O) assisted grain growth accelerated by Cu-derived Ru charge inhomogeneity along with a rearrangement of grains promoted by a liquid-phase silicate is the mechanism of the (Ba, Sr)RuO3 densification. We demonstrate that all epitaxial BaTiO3 thin-film capacitors with (Ba1−xSrx)RuO3 electrodes can be obtained up to x of 0.6.

A magnet-actuated biomimetic device for isolating biological entities in microwells

Microwell platforms show great promise in single-cell studies and protein measurements because of their low volume sampling, rapid analysis and high throughput screening ability. However, the existing actuation mechanisms to manipulate the target samples and fabrication procedures involved in the microwell-based microfluidic devices are complex, resource-intensive and require an external power source. In this work, we present proof of concept of a simple, power-free and low-cost closed magnet digital microfluidics device for isolating biological entities in femtoliter-sized microwells. The target biological entities were encapsulated in magnetic liquid marbles and shuttled back and forth between micropatterned top and bottom plates in the microdevice to obtain high loading efficiency and short processing time. The microdevice performance was studied through fluorescent detection of three different entities: microbeads, bovine serum albumin (BSA) and Escherichia coli, captured in the microwell array. Almost 80% of the microwells were loaded with single microbeads in five shuttling cycles, in less than a minute. Further, a low volume of BSA was compartmentalized in the microwell array over a two order range of concentration. The microdevice exhibits two unique features: lotus leaf stamps were used to fabricate micropatterns (microwells and micropillars) on top and bottom plates to impart functionality and cost-effectiveness, and the target samples were actuated by a permanent magnet to make the microdevice power-free and simple in operation. The developed biomimetic microdevice is therefore capable of capturing a multitude of biological entities in low-resource settings.

6th Target Fabrication Workshop, Greenwich, London, UK

6th Target Fabrication Workshop, Greenwich, London, UKThe 6th Target Fabrication Workshop was held at the University of Greenwich, London, 8 - 11 May 2017. Approximately 55 delegates took part from institutes in: UK, France, Germany, Spain, Hungary, Romania, US and Japan. Oral and poster presentations were given on a variety of Target Fabrication technologies used for manufacture of target for irradiation in high-energy laser experiments in institutes across the world. In depth discussions were held on collaborative opportunities between departments, with particular interest in creating an international delivery network to cater for all requirements, from any facility using the expertise from the wider Target Fabrication community.Conference Photograph available in this pdf.

6th Target Fabrication Workshop (TFW6) and the Targetry for High Repetition Rate Laser-Driven Sources (Targ3) Conference

Conference Proceedings, Editor’s Preface2017 was an exciting year for the Target Fabrication community with both the 6th Target Fabrication Workshop (TFW) held in Greenwich London, UK and the 3rd Targetry for High Repetition Rate Laser Driven Sources (Targ) workshop held Salamanca, Spain taking place.These well-established workshops, with their focus on different but complimentary areas of Target Fabrication, cover the main areas of research providing novel and high specification samples for the next generation of high power laser systems. The TFW series, has developed to cover high repetition rate solid targets, cryogenic targets and microfluidics and had exciting talks from many PhD students from around the world. The TargN workshop series brings together experts and key players involved in the latest trends on intense laser-plasma research, requiring the design of specific targets aimed at particular requirements to exploit unique opportunities presented by such extreme peak laser powers.

Wafer-scale fabrication of target arrays for stable generation of proton beams by laser-plasma interaction.

Large-scale fabrication of targets for laser-driven acceleration of ion beams is a prerequisite to establish suitable applications, and to keep up with the challenge of increasing repetition rate of currently available high-power lasers. Here we present manufacturing and test results of large arrays of solid targets for TNSA laser-driven ion acceleration. By applying micro-electro-mechanical-system (MEMS) based methods allowing for parallel processing of thousands of targets on a single Si wafer, sub-micrometric, thin-layer metallic membranes were fabricated by combining photolithography, physical and chemical vapor deposition, selective etching, and Si micromachining. These structures were characterized by using optical and atomic force microscopy. Their performance for the production of laser-driven proton beams was tested on a purpose-made table-top Ti:Sapphire laser system running at 3 TW peak power with a contrast over ASE of 108. We have performed several test series achieving maximum proton energy values around 2 MeV.

A setup for micro-structured silicon targets by femtosecond laser irradiation

We present a process to fabricate micro-structured thin silicon foils with highly light absorbing properties over a broad wavelength region based on short-pulse laser treatment. We employ this fascinating technique to the fabrication of targets for high-intensity laser-plasma experiments. A polished silicon wafer is processed with high-intensity femtosecond laser pulses resulting in conical spikes within the irradiated region. Height, distance, and shape of these spikes depend primarily on the number, energy, central wavelength and duration of the incident laser pulses, as well as the ambient medium. This method is of great value for the future development of target fabrication. The broad parameter base offers a huge selection regarding shape and dimensions of the resulting structure. It can be included in existing laser operations within the manufacturing chain while offering a high degree of customisability. Within the reach of higher repetition rates of high-power laser systems and an increased number of requested targets, this manufacturing method can be scaled while being cost efficient and easily adaptable.

Characterisation of the oxide effects on aluminium opacity targets

900 nanometre thick aluminium strips were produced by the Target Fabrication Group for an experiment at the Central Laser Facility. They were specified to be supported horizontally at either end across an 800 micron void and to be 500 microns in height. The production method used a Parylene (C8H8) supporting layer which was removed by oxygen plasma etching. This process resulted in a problematic contaminant layer that caused substantial increase to the absorption of X-rays in the laser campaign. The contaminant layer was characterised by optical microscopy and Scanning Electron Microscopy. Energy Dispersive X-ray Spectroscopy was able to detect a high relative abundance of carbon and oxygen in the plastic etched strips when compared to control samples. It has been shown that partially etched Parylene can form carboxylic groups with a ratio of 4:1 carbon to oxygen atoms. This effect was observed and exacerbated by the sample geometry not in sufficient contact with the grounded chamber baseplate causing charging and therefore insufficient hydrogen abstraction in the plasma. An alternative production method produced strips that were not as flat over the open area as the previous method but had no significant contaminant layer. This process involved coating a release layer of sodium chloride before the aluminium strips. When lowered into water, the salt dissolves in water and the strips are suspended on the surface tension, allowing the strips to be picked onto the mount. Each target required measuring for form using a white light interferometer where around half were within specification.

Experimental Testing of Targets for a High Accuracy Microtarget Supply (HAMS) System on the Gemini Laser System

It is widely understood within the high-power laser community that recent developments in diode pumped and high repetition rate laser systems will give unprecedented access to laser shots. This will provide a challenge for target fabrication in making enough experimental samples. While in the past access to facilities and shot rates during access periods have been the limiting factor for high power laser experiments this will soon not be the case. There has already been a shift in development of the user base from fundamental science experiments to industrial applications using the laser experiment as a reliable source for secondary aims. The Astra Gemini laser system has been operating at a high repetition rate for high intensity (0.5PW) experiments for a number of years and the Central Laser Facility has developed a target methodology to deliver to the user community the maximum number of solid targets and to fully utilise the available time on the laser. Targets for the High Accuracy Microtarget Supply (HAMS) system have been tested and have been proven to survive in a manner to allow shot rates comparable with the available laser repetition rate (0.1Hz). Investigations into target geometry have been carried out and debris production has been studied by high frame rate camera imaging. The study of the relationship between target geometry and debris production has allowed the design of optimal target support infrastructure, such as aperture size and structure, for high rep rate experiments on the Gemini system.

Manufacture and Characterisation of Materials for High Power Laser Targets

The Target Fabrication group at the Central Laser Facility (CLF) works to develop and produce novel targets for the high-power laser community. Targets range from simple foils to more complex geometries and with many components and key part of the research is materials development. We describe the recent advances in the CLF in surface preparation for electroplating and the manufacture of thin films. Characterisation of these materials is carried out using Atomic Force Microscope and Scanning Electron Microscopy. These advances have been applied to target components that have been used experimentally on the Vulcan Laser system at the Rutherford Appleton Laboratory.

Phase quantification in UAlx-Al dispersion targets for Mo-99 production

Uranium aluminide (UAlx) is a mixture of three distinct intermetallic compounds comprised of UAl2, UAl3 and UAl4, where the “x” is used to denote a mixture of those phases. Usually UAlx is formed during the target fabrication process by means of a solid state reaction between the uranium aluminide and aluminum. Quantitative techniques such as image analysis and X-ray diffraction using the Rietveld method were compared for their applicability in the determination of the UAl2, UAl3 and UAl4 concentrations, both in the UAl2 primary ingot and in the UAlx-Al dispersion. The UAlx composition was quantified in all stages of the target manufacturing. The image analysis method was shown to be useful for UAlx phase quantification in the primary UAl2 ingot, but was not applicable in the case of UAlx-Al dispersions. The X-ray diffraction method allowed the quantification of the existing UAlx phases in both the primary ingot and UAlx-Al dispersions. Possible sources of error are discussed. The method of quantification based on X-ray diffraction was shown to be appropriate to monitor the evolution of UAlx phases during the manufacturing process.

Progress of indirectly driven implosion experiments

Achieving ignition via inertial confinement approach is of strong application value and important science significance. It is also a project of large scale that depends on the national strength. Involving theory, target fabrication, diagnostics, and laser facilities, integrated implosion experiment plays an important role in the research of ICF. Since the first successful neutron production with directly driven implosion in the 80’s, the quasi one-dimensional implosion performance dominated by shock compression was demonstrated in the period of 1990–2010, and the quasi one-dimensional implosion performance dominated by inertial compression was achieved in recent years. All of these facts definitely show the progress on improving the performance of integrated implosion. With the completion of SG-III laser facility, and in the situation of facing frustration in the US ignition program, there is grand opportunity and challenge when we are exploring toward the ignition parameter space with higher convergence ratio and lower adiabat.

Recent progress in ICF target fabrication at RCLF

Target is one of the essential parts in inertial confinement fusion (ICF) experiments. To ensure the symmetry and hydrodynamic stability in the implosion, there are stringent specifications for the target. Driven by the need to fabricate the target required by ICF experiments, a series of target fabrication techniques, including capsule fabrication techniques and the techniques of target characterization and assembly, are developed by the Research Center of Laser Fusion (RCLF), China Academy of Engineering Physics (CAEP). The capsule fabrication techniques for preparing polymer shells, glow discharge polymer (GDP) shells and hollow glass micro-sphere (HGM) are studied, and the techniques of target characterization and assembly are also investigated in this paper. Fundamental research about the target fabrication is also done to improve the quality of the target. Based on the development of target fabrication techniques, some kinds of target have been prepared and applied in the ICF experiments.

Fabrication of 121Sb isotopic targets for the study of nuclear high spin features

Isotopic 121Sb targets with 197Au backing have been prepared by Physical Vapor Deposition (PVD) method using the diffusion pump based coating unit at target laboratory, Inter University Accelerator Centre (IUAC), New Delhi, India. The target thickness was measured by stylus profilo-meter and the purity of the targets was investigated by Energy Dispersive X-ray Analysis (EDXA). One of these targets has been used in an experiment which was performed at IUAC for nuclear structure study through fusion evaporation reaction. The excitation function of the 121Sb(12C,yxnγ) reaction has been performed for energies 58 to 70 MeV in steps of 4 MeV. The experimental results were compared with the calculations of statistical models : PACE4 and CASCADE. The methods adopted to achieve best quality foils and good deposition efficiency are reported in this paper.

A review of low-density porous target materials for laser plasma experiments

A new review article takes an in-depth look at different types of low-density porous materials for target fabrication in laser plasma experiments.

A review of low density porous materials used in laser plasma experiments

This review describes and categorizes the synthesis and properties of low density porous materials, which are commonly referred to as foams and are utilized for laser plasma experiments. By focusing a high-power laser on a small target composed of these materials, high energy and density states can be produced. In the past decade or so, various new target fabrication techniques have been developed by many laboratories that use high energy lasers and consequently, many publications and reviews followed these developments. However, the emphasis so far has been on targets that did not utilize low density porous materials. This review therefore, attempts to redress this balance and endeavors to review low density materials used in laser plasma experiments in recent years. The emphasis of this review will be on aspects of low density materials that are of relevance to high energy laser plasma experiments. Aspects of low density materials such as densities, elemental compositions, macroscopic structures, nanostructures, and characterization of these materials will be covered. Also, there will be a brief mention of how these aspects affect the results in laser plasma experiments and the constrictions that these requirements put on the fabrication of low density materials relevant to this field. This review is written from the chemists' point of view to aid physicists and the new comers to this field.