High-energy Heavy-ion Irradiation Research Articles

Irradiation resistance of vacuum arc chromium coatings for zirconium alloy fuel claddings

Effects of high-energy heavy ion irradiation on the structure of chromium coatings, which were deposited by the cathodic arc evaporation method on the Zr-based alloy (E110) substrate, have been studied. Within the framework of the accident-tolerant fuel claddings (ATFC) concept, chromium coatings seem to be promising for protection of zirconium alloys from oxidation. The radiation resistance of Cr deposited coatings was investigated through the study of void swelling after irradiation with 1.4 MeV argon ions at 400 °C to doses of 5, 15 and 25 dpa. The irradiation of chromium coatings causes the isotropic growth of grain size from initial 250 nm up to 295 nm, and also, the swelling up to 0.66% under irradiation dose of 25 dpa. It can be concluded that chromium coatings have a high resistance to irradiation and are a good candidate as a protection of zirconium alloys fuel claddings in the frame of the ATFC philosophy.

Nano-crystallization induced by high-energy heavy ion irradiation in UO2

Advanced microstructure investigations of the high-burnup structure (HBS) in UO2 produced by high-dose 84 MeV Xe ion irradiation are reported. Spark plasma sintered micro-grained UO2 was irradiated to 1357 dpa at 350 °C. The characteristic nano-grains and micro-pores of the HBS were formed. The grain size and grain boundary misorientation distributions of the HBS were measured using transmission electron microscopy based orientation imaging microscopy. Grain polygonization due to accumulation of radiation-induced dislocations was found to be the mechanism of nano-crystallization. The morphology of Xe bubbles was quantitatively investigated. This study provides crucial references for advanced fuel performance modeling of high-burnup UO2.

Anti-biofilm activity of Fe heavy ion irradiated polycarbonate

Polycarbonate (PC) polymers were investigated before and after high energy heavy ion irradiation for anti-bacterial properties. These PC films were irradiated by Fe heavy ions with two energies, viz, 60 and 120MeV, at different fluences in the range from 1×1011ions/cm2 to 1×1013ions/cm2. UV-Visible spectroscopic results showed optical band gap decreased with increase in ion fluences due to chain scission mainly at carbonyl group of PC which is also corroborated by Fourier transform infrared spectroscopic results. X-ray diffractogram results showed decrease in crystallinity of PC after irradiation which leads to decrease in molecular weight. This is confirmed by rheological studies and also by differential scanning calorimetric results. The irradiated PC samples showed modification in their surfaces prevents biofilm formation of human pathogen, Salmonella typhi.

Thermal spike effect in sputtering of porous germanium to form surface pattern by high energy heavy ions irradiation

Germanium exhibits a remarkable effect when subjected to high energy heavy ions irradiation. A synergic effect of high electronic energy loss (Se = 16.4 keV nm−1) and nuclear energy loss (Sn = 0.1 keV nm−1) of 100 MeV Ag ions irradiation in Ge is presented. The results show that crystalline Ge is insensitive to the ionizing part of energy loss whereas thermal spike generated in the damaged Ge leads to the formation of porous structure. Further, an unusual high sputtering of the porous structure opens up the sub-surface voids to show the surface pattern. We explore the role of electron and phonon confinement to explain this effect.

New application of NV centers in CVD diamonds as a fluorescent nuclear track detector

NV (nitrogen vacancy) center in a diamond is utilized for FNTD (fluorescent nuclear track detector) for the first time. We performed high energy heavy ion irradiation to single crystal type‐IIa diamonds with various nitrogen concentrations. After high temperature annealing, the nitrogen impurity combined with the vacancies created by a single ion strike. As a result the ion track is visualized as a train of fluorescent NV centers formed. We successfully observe the ion track in both HPHT (high pressure high temperature) and CVD (chemical vapor deposition) diamonds by using the laser scanning confocal microscope. We therefore conclude that a diamond containing nitrogen impurity is able to be used for FNTD.

Concurrent in situ ion irradiation transmission electron microscope

An in situ ion irradiation transmission electron microscope has been developed and is operational at Sandia National Laboratories. This facility permits high spatial resolution, real time observation of electron transparent samples under ion irradiation, implantation, mechanical loading, corrosive environments, and combinations thereof. This includes the simultaneous implantation of low-energy gas ions (0.8–30keV) during high-energy heavy ion irradiation (0.8–48MeV). Initial results in polycrystalline gold foils are provided to demonstrate the range of capabilities.

Current status of nanostructured tungsten-based materials development

Nanostructured tungsten (W)-based materials offer many advantages for use as plasma facing materials and components exposed to heavy thermal loads combined with irradiation with high-energy neutron and low-energy ion. This paper first presents the recent progress in nanostructured toughened, fine grained, recrystallized W materials. Thermal desorption spectrometry apparatus equipped with an ion gun has been installed in the radiation controlled area in our Center at Tohoku University to systematically investigate the effects of displacement damage due to high-energy neutron irradiation on hydrogen isotope retention in connection with the nano- or micro-structures in W-based materials. In this paper, the effects of high-energy heavy ion irradiation on deuterium retention in W with different microstructures are described as a preliminary work with the prospective view of neutron irradiation effects.

Evidence of anisotropic vortex pinning by intrinsic and irradiation-induced defects in Ba(Fe,Co)2 As2 studied by quantitative magneto-optical imaging

Here we present a study of the pinning properties of high-quality single crystals of Ba(Fe1−xCox)2As2 (x = 0.07) by means of the quantitative magneto-optical imaging (MOI). This technique allows us to measure the magnetic field and supercurrent distribution as a function of the applied magnetic field and temperature, thus extracting the local parameters such as the critical current density, without any model assumption. Since values of the local supercurrent are obtained on the micron scale, we are able to observe evidence of anisotropic pinning both of intrinsic defects and extrinsic defects induced by high-energy heavy-ion irradiation. In fact, we find that these crystals naturally show anisotropic pinning due to intrinsic planar defects (whose presence is confirmed by the structural measurements through electron microscopy), and with quantitative MOI analysis we are able to analyze the effects of anisotropy coming from irradiation-induced defects. We quantitatively evaluated the dependence of the critical current density on the magnetic field direction with respect to the lattice principal axes.

Amorphization and reduction of thermal conductivity in porous silicon by irradiation with swift heavy ions

In this article, we demonstrate that the thermal conductivity of nanostructured porous silicon is reduced by amorphization and also that this amorphous phase in porous silicon can be created by swift (high-energy) heavy ion irradiation. Porous silicon samples with 41%-75% porosity are irradiated with 110 MeV uranium ions at six different fluences. Structural characterisation by micro-Raman spectroscopy and SEM imaging show that swift heavy ion irradiation causes the creation of an amorphous phase in porous Si but without suppressing its porous structure. We demonstrate that the amorphization of porous silicon is caused by electronic-regime interactions, which is the first time such an effect is obtained in crystalline silicon with single-ion species. Furthermore, the impact on the thermal conductivity of porous silicon is studied by micro-Raman spectroscopy and scanning thermal microscopy. The creation of an amorphous phase in porous silicon leads to a reduction of its thermal conductivity, up to a factor of 3 compared to the non-irradiated sample. Therefore, this technique could be used to enhance the thermal insulation properties of porous Si. Finally, we show that this treatment can be combined with pre-oxidation at 300 °C, which is known to lower the thermal conductivity of porous Si, in order to obtain an even greater reduction.

Effects of high-energy heavy ion irradiation on the crystal structure in CeO2 thin films

We studied the change in crystal structure of 200MeV Xe and 10MeV I ion irradiated CeO2 thin films by means of X-ray diffraction (XRD). The experimental result showed that the average lattice parameter of CeO2 decreased and the full width at half maximum increased by the ion irradiation. Their changes are well correlated with the electronic stopping powers for I and Xe ions. The dependence of lattice parameter on the electronic energy loss was analyzed by using the Poisson’s law, and the radii of the regions affected by the irradiation were determined.

Ion-irradiation-induced ferromagnetism in undoped ZnO thin films

We have introduced defects in ZnO epitaxial thin films by swift heavy 107Ag9+ ion irradiation and investigated systematically their magnetic, electrical and optical properties. Oxygen annealed ZnO films are epitaxial single crystals that exhibit no long-range magnetic order. However, in this paper it is shown that room-temperature ferromagnetism (RTFM) can be introduced in a controlled manner in these films using ion irradiation and that the magnetization increases with ion dose. This qualitatively agrees with earlier studies which showed that RTFM could be induced in ZnO films through either vacuum thermal annealing or pulsed laser annealing below energy densities that lead to melting. Raman studies of the ion irradiated samples revealed dramatic changes in the vibration modes that correlated with increases in the carrier concentration, indicative of lattice disorder and defect creation. We compare these results with those observed in laser irradiated and vacuum annealed samples, and then discuss these findings in the context of defects and defect complexes created during the high-energy heavy ion irradiation process. We propose a unified mechanism to explain RTFM and n-type conductivity enhancements during irradiation, and laser and vacuum annealing.

An in-situ TEM investigation of He bubble evolution in SiC

This paper presents work using the capabilities of two TEM with in-situ ion irradiation facilities: Microscope and Ion Accelerator for Materials Investigation (MIAMI) at the University of Huddersfield and Joint Accelerators for Nano-science and Nuclear Simulation JANNuS at Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse (CSNSM), Orsay, France, to study the nucleation and growth of He bubbles in silicon carbide (SiC) and to carry out an investigation into bubble behaviour at high temperatures and under displacing irradiation. Preliminary results on bubble nucleation and growth during He irradiation of SiC are presented together with results from a simultaneous anneal and high-energy heavy-ion irradiation of samples containing He bubbles. The displacing irradiation is observed to impede He bubble growth resulting in smaller bubbles than those obtained from an anneal alone. A tentative interpretation of these observations is presented.

Determination of the disorder profile in an ion‐implanted silicon carbide single crystal by Raman spectroscopy

Silicon carbide is an interesting material for GEN IV fission reactor projects because of its excellent properties. However, these properties will be altered under extreme conditions such as irradiation because of accumulation of damage. Mechanisms playing a role in defect formation require further studies in the case of high energy heavy ion irradiations. In this work a silicon carbide single crystal slice has been implanted with 20 MeV Au ions and probed by using Raman spectrometry. The resulting Raman spectra recorded as a function of depth clearly show a damaged zone, in which the width is in agreement with the projected range of the incident ions (Rp) calculated by using SRIM code. In this area, three damaged zones have been brought to light because of the high spatial resolution of the Raman spectrometry technique. The existence of these zones is discussed with regard to the different energy loss regimes of the implanted ions such as the electronic and nuclear ones. Copyright © 2012 John Wiley & Sons, Ltd.

Electronic excitation induced controlled modifications of semiconductor-to-metal transition in epitaxial VO2 thin films

Abstract

Raman scattering investigation of C-doped a-SiO2 after high energy heavy ion irradiations

Thermally grown amorphous SiO2 films were implanted at room temperature with 100 keV C-ions to 5.0×1017 or 1.2×1018 ions/cm2. These samples were irradiated at room temperature with 853 MeV Pb-ions to 5.0×1011, 1.0×1012, 5.0×1012 ions/cm2, or with 308 MeV Xe-ions to 1.0×1012, 1.0×1013, 1.0×1014 ions/cm2, respectively. Then the samples were investigated using micro-Raman spectroscopy. From the obtained Raman spectra, we deduced that Si—C bonds and sp2 carbon sites were created and nano-inclusions may also be produced in the heavy ion irradiated C-doped SiO2. Furthermore, some results show that Pb ion irradiations could produce larger size inclusions than Xe ions and the inclusion size decreased with increasing the irradiation fluence. The possible modification process of C-doped a-SiO2 under swift heavy ion irradiations was briefly discussed.

Gold nanoparticles resist deformation by swift heavy ion irradiation when embedded in a crystalline matrix

We have attempted to deform, by swift heavy ion irradiation, gold nanoparticles embedded in crystalline AlAs which resists amorphization. AlAs was first implanted with 1.3 MeV Au ions at room temperature to a fluence of 2 × 10 16 cm −2. Rapid thermal annealing (RTA) at 600 °C for 1 or 2 min was used to grow Au nanoparticles in the matrix. Deformation was attempted by 30 MeV Cu 5+ irradiation at liquid nitrogen temperature. Crystal damage of the matrix was studied using Rutherford backscattering spectrometry in channeling configuration and Raman spectrometry. The morphology of Au nanoparticles was investigated by Transmission Electron Microscopy. It was found that, in spite of some crystal damage, the AlAs remained crystalline throughout the experiment and spherical Au nanoparticles with size distribution between 2 and 12 nm were observed with no indication of elongation. Thus, high energy heavy ion irradiation does not deform spherical Au nanoparticles embedded in AlAs. This supports the suggestion that the deformation of the gold nanoparticles which has been observed for particles embedded in amorphous materials is a consequence of the hammering deformation of the matrix surrounding the nanoparticles.

YBCO-Film Based FIR Detectors in Not Dissipative Regime: Local THz Response by Heavy-Ion Nanostructure Implantation

Broadband electromagnetic characterization of hot plasmas and electron beams requires real-time, direct detection of high flux of electromagnetic radiation. We report about a project aimed at creating robust THz detectors based on YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-x</sub> (YBCO) films, working around liquid nitrogen temperature and in a regime of low dissipation. The sensor layout mainly consists in two contiguous meanders that are integrated on the same substrate. One of them is nanostructured by local high-energy heavy-ion irradiation; the other one (as-grown YBCO) is used for thermo-electric signal reference. By measuring the voltage response to THz excitation of YBCO film, at a given bias current and temperature, on selected substrates (Yttria Stabilized Zirconia (YSZ) and MgO), it turns out that only the nanostructured part is brought in the dissipative state when exposed to THz radiation. We present estimated noise equivalent power and relaxation times for YBCO grown on YSZ and on MgO substrates. On the latter, we experimentally checked out the device response to time-varying Far-Infrared (FIR) signals up to 800 Hz. The proposed device turns out to fit the necessary requirements for measurement of electron cyclotron emission of hot plasmas or of electron beams in the FIR spectrum.

Radiation effects on film formation and nanostructural changes of iron disilicide thin film

Ion irradiation effects on the synthesis and modification of iron disilicide films have been investigated by cross-sectional transmission electron microscopy (TEM) observations in order to fabricate films with higher quality or unique properties. It has been observed that pre-treatment of the substrate surface by 0.8 keV Ne + irradiation affects the structure of the films and the interface. Highly oriented films with an atomically smooth interface with the substrate can be synthesized by optimizing the ion irradiation conditions. We also attempted to produce nanostructural changes by high-energy heavy-ion irradiation. In some cases, this led to the formation of columnar defects with an average diameter of a few nm, which appeared to be amorphous or heavily damaged. We found that the criterion determining whether such columnar defects were formed was the electronic stopping power.

Responses of Carbon Onions to High Energy Heavy Ion Irradiation

ABSTRACTWe report evidence for graphene layer rearrangements in heavy ion interactions with carbon onions at 140 MeV and 70 MeV per nucleon kinetic energies. Graphene layer rearrangements have been recently predicted in spherical and cylindrical multi-layer graphene systems. The implications of graphene layer rearrangement on the tribological performance of multi-layer nano-carbons in extreme environments are discussed.

Rugged superconducting detector for monitoring infrared energy sources in harshenvironments

Broadband electromagnetic characterization of hot plasmas, such as in nuclearfusion reactors and related experiments, requires detecting systems that mustwithstand high flux of particles and electromagnetic radiations. We propose arugged layout of a high temperature superconducting detector aimed at 3 THzcollective Thomson scattering (CTS) spectroscopy in hot fusion plasma. TheYBa2Cu3O7 − x superconducting film is patterned by standard photolithography and the sensing area of thedevice is created by means of high-energy heavy ion irradiation, in order to modify thecrystal structure both of the superconducting film and of the substrate. Thismethod diminishes process costs and resulting device fragility due to membrane orair-bridge structures that are commonly needed for MIR and FIR radiation detection.Moreover the sensing area of the device is wired by the same superconductingmaterial and thus excellent mechanical strength is exhibited by the whole device,due to the oxide substrate. Continuous wave operation of prototype devices isdemonstrated at liquid nitrogen temperature, for selected infrared spectra of broadbandthermal energy sources. Several solutions, which exploit the advantages comingfrom the robustness of this layout in terms of intrinsic radiation hardness of thesuperconducting material and of the needed optical components, are analysed withreference to applications of infrared electromagnetic detectors in a tokamak machineenvironment.