197Au Ions Research Articles

Multi-tile zinc-oxide-based radiation-hard fast scintillation counter for relativistic heavy-ion beam diagnostics: prototype design and test

This contribution summarizes the design and performance test of a prototype radiation-hard fast scintillation detector based on the indium-doped zinc oxide ceramic scintillator, ZnO(In). The prototype detector has been developed for use as a beam diagnostics tool for high-energy beam lines of the SIS18 synchrotron at the GSI Helmholtz Center for Heavy Ion Research GmbH. The new detector consists of multiple ZnO(In) scintillating ceramics tiles stacked on the front and back sides of a borosilicate light guide. The performance of the detector was tested in comparison to a standard plastic scintillation detector with 300 MeV/u energy 40Ar, 197Au, 208Pb, and 238U ion beams. The investigated prototype exhibits 100% counting efficiency and radiation hardness of a few orders of magnitude higher than the standard plastic scintillation counter. Therefore, it provides an improved beam diagnostics tool for relativistic heavy-ion beam measurements.

Thermal annealing of lattice defects in MgAl2O4 single crystals irradiated by swift heavy ions

The recovery of radiation damage induced by 156-МeV 132Хе and 2.25-GeV 197Au ions (fluences between 6.6 × 1010 and 2 × 1012 ions/cm2) in MgAl2O4 single crystals has been investigated via stepwise (isochronal) thermal annealing procedure. The integral of elementary bands of radiation-induced optical absorption (result of spectra decomposition into Gaussians) has been considered as a concentration measure of relevant structural defects. The general trends of the multistage annealing kinetics of the oxygen-vacancy-related F+ and F centers (430–850 K) as well as complex cation-related defects responsible for absorption bands peaked at 5.9, 6.6 and ∼7 eV (ends above 1000 K) have been considered. The features of the annealing kinetics of these defects induced by the xenon or gold ions with different values of mean energy loss along the ion trajectories (13.5 and 30.4 keV/nm, respectively) and fluences have been analyzed.

The annealing kinetics of the F-type defects in MgAl2O4 spinel single crystals irradiated by swift heavy ions

The annealing kinetics of the F and F+ color centers induced in MgAl2O4 single crystals under irradiation by 156-MeV 132Xe and 2.25-GeV 197Au ions are precisely measured via relevant optical absorption bands and analyzed in terms of the diffusion-controlled reactions between two pairs of anion Frenkel defects which determine thermal stability of irradiated material. It is demonstrated that two types of mobile oxygen interstitials (neutral and charged ones) are involved into recombination process with very different activation energies, which are practically independent on radiation fluencies.

Fabrication, swift heavy ion irradiation, and damage analysis of lanthanide targets

Abstract One limiting factor in progress in the discovery and study of new superheavy elements (SHE) is the maximum achievable thickness and irradiation stability of current generation actinide targets. The desired thickness of targets, using full excitation function widths, cannot be achieved with current target technology, especially the widely used molecular plating (MP). The aim of this study was to transfer progress in the electrochemistry of lanthanides and actinides to the production of targets. Here, we report on the production of lanthanide targets using anhydrous electrochemical routes. In a first irradiation series, thulium thin films with areal densities up to 1800 μg/cm2 were produced using anhydrous triflate compounds and subjected to irradiation tests, using 6.0 MeV/u 48Ca ions at a fluence of 3.9 × 1014 ions/cm2 and 8.6 MeV/u 197Au ions at fluences in the range of 3.0 × 1011 to 1.0 × 1013 ions/cm2. The thin films were characterised before and after the irradiations using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX).

Role of antioxidants in swift heavy ion tracks in polypropylene

Using synchrotron-based small angle X-ray scattering, ion tracks created in polypropylene foils with different antioxidant contents were investigated. Tracks were created by irradiation with 197Au, 209Bi, and 132Xe ions of energies 2.2 GeV, 710 MeV, and 160 MeV, respectively. The influence of antioxidant concentration in the polymer foils and aging of the samples on the structure of the ion tracks was explored. Polypropylene foils with high antioxidant content show a cylindrical track structure with a highly damaged core with significant mass loss and a gradual transition to the undamaged material. The size of the ion track can directly be correlated to the energy loss. On the other hand, ion tracks in low antioxidant content polypropylene foils exposed to Au/Bi ions reveal a cylindrical core shell structure with an over-dense shell area and a core region that is less dense than the pristine polymer. Oxygen uptake in the foils by the free radicals produced in the shell during the ion irradiation process was attributed to this structure due to prolonged exposure to ambient atmosphere. An overall mass increase was observed for these samples, consistent with the SAXS measurements and additional oxidation in a damaged halo produced by tracks.

Accumulation of structural defects and modification of micromechanical properties of MgAl2O4 single crystals irradiated with swift heavy ions

Single crystals of MgAl2O4 have been irradiated by 156-МeV 132Хе and 2.25-GeV 197Au ions with fluences between 6.6 × 1010 and 2 × 1012 ions/cm2. After isodose ion-irradiation, the spectra of radiation-induced optical absorption (absorption of a pristine sample is subtracted) for the (100), (110) and (111) oriented crystals coincide. The fluence dependence of the concentration of several defects responsible for optical absorption at 4.5–7.1 eV have been analyzed. The integral of all five Gaussians, obtained via spectra decompositions and served as a measure of relevant defects, continuously increases with the fluence without any sign of saturation. Thus, similar to oxygen-vacancy-related F+ and F centers (Gaussians peaked at 4.8 and 5.3 eV, respectively), the defects responsible for elementary bands at 5.9, 6.6 and ∼7.1 eV are also of radiation-induced origin. The thermal stability of all defects has been determined via stepwise annealing of the irradiated samples. The tentative origin of the 5.9, 6.6 and ∼7.1 eV bands (their decay occurs by about 200 K higher than that for the F-type centers) is considered. Nanoindentation measurements show an ion-induced increase of the sample hardness up to 30%. The hardening effect follows the evolution of the energy loss of the Xe and Au ions as a function of sample depth.

Surface characterization of CaF2 crystals irradiated with MeV ions below charge state equilibrium

Single crystals of CaF2, cleaved along the (111) plane, were irradiated by 35Cl, 39K, 52Cr, 58Ni, 79Br and 197Au ions with energies from 2 to 48 MeV, charge states from 1+ to 11+ and ion fluences from 2 × 1010 to 1 × 1013 ions/cm2. The surface properties of the irradiated samples were studied using Atomic Force Microscopy in contact mode. Nanoscale surface structures were observed for some surfaces irradiated by Cl, K, Cr, Ni, Br and Au ions. Thresholds for nanostructure formation were found in terms of projectile ion velocity and electronic stopping power (Se). Clear surface modification was observed for projectiles with specific energies above approximately 0.04 MeV/u. The threshold in Se for the generation of distinct triangular structures was observed to be velocity-dependent. The average formation efficiency, referring to the ratio of the number of distinct nanostructures observed on the surface to the number of incident ions, as well as the average height of nanostructures increases with Se.

Radiation protection modelling for 2.5 Petawatt-laser production of ultrashort x-ray, proton and ion bunches: Monte Carlo model of the Munich CALA facility

The ‘Centre for Advanced Laser Applications’ (CALA) is a new research institute for laser-based acceleration of electron beams for brilliant x-ray generation, laser-driven sub-nanosecond bunches of protons and heavy ions for biomedical applications like imaging and tumour therapy as well as for nuclear and high-field physics.The radiation sources emerging from experiments using the up to 2.5 petawatt laser pulses with 25 femtosecond duration will be mixed particle-species of high intensity, high energy and pulsed, thus posing new challenges compared to conventional radiation protection. Such worldwide pioneering laser experiments result in source characteristics that require careful a-priori radiation safety simulations.The FLUKA Monte-Carlo code was used to model the five CALA experimental caves, including the corridors, halls and air spaces surrounding the caves. Beams of electrons (), protons (), 12C () and 197Au () ions were simulated using spectra, divergences and bunch-charges based on expectations from recent scientific progress.Simulated dose rates locally can exceed 1.5 kSv h−1 inside beam dumps. Vacuum pipes in the cave walls for laser transport and extraction channels for the generated x-rays result in small dose leakage to neighboring areas. Secondary neutrons contribute to most of the prompt dose rate outside caves into which the beam is delivered. This secondary radiation component causes non-negligible dose rates to occur behind walls to which large fluences of secondary particles are directed.By employing adequate beam dumps matched to beam-divergence, magnets, passive shielding and laser pulse repetition limits, average dose rates in- and outside the experimental building stay below design specifications () for unclassified areas, for supervised areas, maximum local dose rate) and regulatory limits ( for unclassified areas).

Forecasting Radiation Environment around the NICA Booster

The results of using the FLUKA package to calculate the radiation environment around building no. 1 of the Laboratory of High Energy Physics, which contains the ion injection systems, booster, and Nuclotron of the NICA complex in operation for the collider and for experiments with fixed targets, are presented. The calculation has been performed for the mode of 197Au ion acceleration to an energy of 578 MeV/n The main dose-forming component of the radiation field around the building is neutrons of a wide energy range. Detailed models of an ion acceleration ring and the geometry of shields and building details are used in the calculation. The calculation results indicate that the adopted design decisions with the given rates of ion losses will ensure compliance with radiation-protection norms during the operation of the NICA booster.

Degradation of thermal transport properties in fine-grained isotropic graphite exposed to swift heavy ion beams

Isotropic polycrystalline graphite samples were irradiated with ~1 GeV 197Au and 238U ions of fluences up to 5 × 1013 ions/cm2. Beam-induced changes of thermophysical properties were characterized using frequency domain photothermal radiometry (PTR) and the underlying structural transformations were monitored by Raman spectroscopy. The ion range (~60 µm) was less than the sample thickness, therefore thermal diffusivity contributions of the irradiated as well as non-irradiated layer were considered when analyzing the PTR data. At the highest applied fluences, the thermal effusivity of the damaged layer degrades down to 20% of the pristine value and the corresponding calculated values of thermal conductivity decrease from 95 Wm−1K−1 for pristine material to 4 Wm−1K−1, a value characteristic for the glassy carbon allotrope. This technique provides quantitative data on thermal properties of ion-irradiated polycrystalline graphite and is very valuable for the prediction of lifetime expectancy in long-term applications in extreme radiation environments.

The Effect of Heavy Ion Irradiation on the Forward Dissolution Rate of Borosilicate Glasses Studied in Situ and Real Time by Fluid-Cell Raman Spectroscopy.

Borosilicate glasses are the favored material for immobilization of high-level nuclear waste (HLW) from the reprocessing of spent fuel used in nuclear power plants. To assess the long-term stability of nuclear waste glasses, it is crucial to understand how self-irradiation affects the structural state of the glass and influences its dissolution behavior. In this study, we focus on the effect of heavy ion irradiation on the forward dissolution rate of a non-radioactive ternary borosilicate glass. To create extended radiation defects, the glass was subjected to heavy ion irradiation using 197Au ions that penetrated ~50 µm deep into the glass. The structural damage was characterized by Raman spectroscopy, revealing a significant depolymerization of the silicate and borate network in the irradiated glass and a reduction of the average boron coordination number. Real time, in situ fluid-cell Raman spectroscopic corrosion experiments were performed with the irradiated glass in a silica-undersaturated, 0.5 M NaHCO3 solution at temperatures between 80 and 85 °C (initial pH = 7.1). The time- and space-resolved in situ Raman data revealed a 3.7 ± 0.5 times increased forward dissolution rate for the irradiated glass compared to the non-irradiated glass, demonstrating a significant impact of irradiation-induced structural damage on the dissolution kinetics.

Swift Heavy Ion induced interface mixing in a Te/Cd/Te trilayer thin film system

In the present study Swift Heavy Ion (SHI) induced mixing has been investigated at Te/Cd/Te interfaces using 100 MeV 58Ni, 107Ag and 197Au ion beams at a fluence of 5 × 1012 ions/cm2. The films were then characterized by using X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM) and UV-Vis spectroscopy. X-ray diffraction (XRD) study reveals the formation of CdTe phase in irradiated samples. The observed ion beam mixing is attributed to the inter-diffusion of atomic species across the interface during transient melt phase. The XRD results show that the average grain size is 28 nm, 20nm and 16nm for the films irradiated with 58Ni, 107Ag and 197Au ion beams at a fluence of 3×1012 ions cm−2.The crystallite size decreases with irradiation of heavier ions. Surface roughness as calculated by AFM is found to increase from 6.7 to 6.8 nm with heavier ions. The optical band gap Egis determined from UV-Vis spectroscopy. The band gap increases from 1.58 eV to 1.74 eV. The increase in band gap as a function of Se, is possibly because of the decreased grain-size.

Experimental Investigation of the Joint Influence of Reduced Supply Voltage and Charge Sharing on Single-Event Transient Waveforms in 65-nm Triple-Well CMOS

Full waveforms of single-event transients (SETs) in inverter chains were measured under focused heavy-ion microbeam irradiation. Inverter chains of varying spacings were irradiated with 48Ca and 197Au ions. The influence of changing the supply voltage from subthreshold to nominal level on SET forming and propagation was investigated, and the role of charge sharing is discussed. Key factors that influence SET widths and cross sections are identified across the applied range of supply voltages. A simple method is presented for estimating average SET widths at decreased supply voltages, and is based on the SET width measurements at nominal supply voltage, transistor-level simulations, and extracted circuit parameters. The proposed method matches well with the measured data.

Damage induced in garnets by heavy ion irradiations: a study by optical spectroscopies

The damage induced by heavy-ion irradiation has been studied in yttrium iron garnet (Y3Fe5O12 or YIG) films, doped with Ca, Tb and Tm, grown by liquid-phase epitaxy on gadolinium gallium garnet (Gd3Ga5O12 or GGG) substrates. Irradiations of doped-YIG epitaxial films and GGG substrates with 36-MeV 183W and 12-MeV 197Au ions were applied for fluences between 1 × 1013 and 3 × 1015 cm–2 near room temperature. The radiation damage was monitored by micro-Raman spectroscopy and UV–visible optical absorption spectroscopy. Raman spectra revealed that amorphisation was achieved in YIG for both ions, whereas a high lattice disorder was induced in GGG without reaching amorphisation for the Au ion irradiation. Raman spectra also showed that a major damage of the tetrahedral sites was induced in GGG, as previously found for YIG. It is concluded that with such ions reaching the stopping power threshold of track formation in YIG and GGG the observed rate of amorphisation may result from a combination of electronic and nuclear energy losses as calculated using the unified thermal spike model.

Phase transformation and chemical decomposition of nanocrystalline SnO2 under heavy ion irradiation

A crystalline-to-crystalline phase transformation, including chemical decomposition, has been observed in SnO2 nanopowder irradiated by 2.2GeV 197Au ions. X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM) were used to characterize the transformation from tetragonal SnO2 (P42/mnm) to tetragonal SnO (P4/nmm), with trace quantities of β-Sn (I41/amd). At a fluence of approximately 2.0×1012ions/cm2, diffraction maxima corresponding to SnO became clearly evident and increased in intensity as fluence increased. The proportion of SnO, as determined by Rietveld refinement of XRD data, reached 23.1±0.8% at the maximum fluence investigated of 2.4×1013ions/cm2. Raman spectra show high photoluminescence (PL) intensity before and during initial SnO formation, indicating the importance of oxygen vacancies in the transformation process. Small-angle X-ray scattering (SAXS) analysis provided evidence of ion tracks, but no tracks were observed using high-resolution TEM (HRTEM). The transformation likely occurs through a multiple-impact mechanism, based on the accumulation of O vacancies, defect ordering, and partially localized Sn reduction.

Amorphization of Ta2O5 under swift heavy ion irradiation

Crystalline Ta2O5 powder is shown to amorphize under 2.2GeV 197Au ion irradiation. Synchrotron X-ray diffraction (XRD), Raman spectroscopy, small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) were used to characterize the structural transition from crystalline to fully-amorphous. Based on Rietveld refinement of XRD data, the initial structure is orthorhombic (P2mm) with a very large unit cell (a=6.20, b=40.29, c=3.89Å; V=971.7Å3), ideally containing 22Ta and 55 O atoms. At a fluence of approximately 3×1011ions/cm2, a diffuse amorphous background becomes evident, increasing in intensity relative to diffraction maxima until full amorphization is achieved at approximately 3×1012ions/cm2. An anisotropic distortion of the orthorhombic structure occurred during the amorphization process, with an approximately constant unit cell volume. The amorphous phase fraction as a function of fluence was determined, yielding a trend that is consistent with a direct-impact model for amorphization. SAXS and TEM data indicate that ion tracks exhibit a core-shell morphology. Raman data show that the amorphous phase is comprised of TaO6 and TaO5 coordination-polyhedra in contrast to the TaO6 and TaO7 units that exist in crystalline Ta2O5. Analysis of Raman data shows that oxygen-deficiency increases with fluence, indicating a loss of oxygen that leads to an estimated final stoichiometry of Ta2O4.2 at a fluence of 1×1013ions/cm2.

Effect of annealing high-dose heavy-ion irradiated high-temperature superconductor wires

Heavy-ion irradiation of high-temperature superconducting thin films has long been known to generate damage tracks of amorphized material that are of close-to-ideal dimension to effectively contribute to pinning of magnetic flux lines and thereby enhance the in-field critical current. At the same time, though, the presence of these tracks reduces the superconducting volume fraction available to transport current while the irradiation process itself generates oxygen depletion and disorder in the remaining superconducting material. We have irradiated commercially available superconducting coated conductors consisting of a thick film of (Y,Dy)Ba2Cu3O7 deposited on a buffered metal tape substrate in a continuous reel-to-reel process. Irradiation was by 185MeV 197Au ions. A high fluence of 3×1011ions/cm2 was chosen to emphasize the detrimental effects. The critical current was reduced following this irradiation, but annealing at relatively low temperatures of 200°C and 400°C substantially restore the critical current of the irradiated material. At high fields and high temperatures there is a net benefit of critical current compared to the untreated material.

Swift heavy ion irradiation induced nanograin formation in CdTe thin films

Swift Heavy Ion (SHI) irradiation is a unique technique for nanograin formation through grain fragmentation. Contrary to the generally reported SHI irradiation induced grain growth on CdTe thin films, we report fragmentation leading to nanograin formation. Thermally evaporated polycrystalline CdTe thin films were irradiated with 100MeV 197Au, 107Ag and 58Ni ions beams up to a fluence of 5×1012ions/cm2. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) were carried out for surface analysis before and after irradiation. SEM micrographs indicate that the larger grains in the as-deposited films were fragmented into smaller grains due to irradiation. The extent of fragmentation was found to increase with increasing electronic energy loss (Se). AFM pictures also supported the irradiation induced fragmentation. Structural characterization was done using X-ray Diffraction (XRD) technique. The ion induced strain and dislocation density were calculated from the XRD data. Both the strain and dislocation density were found to increase with increasing Se. The observed grain fragmentation is explained on the basis of a combined effect of strain induced disintegration of grains after the Coulomb explosion, and an ‘incomplete’ re-crystallization of the molten thermal spikes. Moreover, the optical band gap Eg (1.5eV for as-deposited film), determined from UV–vis spectroscopy, increased with Se, and possibly because of ion induced strain and defect annealing.

Structural response of titanate pyrochlores to swift heavy ion irradiation

The structure, size, and morphology of ion tracks resulting from irradiation of five different pyrochlore compositions (A2Ti2O7, A = Yb, Er, Y, Gd, Sm) with 2.2 GeV 197Au ions were investigated by means of synchrotron X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Radiation-induced amorphization occurred in all five materials analyzed following an exponential rate as a function of ion fluence. XRD patterns showed a general trend of increasing susceptibility of amorphization with increasing ratio of A- to B-site cation ionic radii (rA/rB) with the exception of Y2Ti2O7 and Sm2Ti2O7. This indicates that the track size does not necessarily increase with rA/rB, in contrast with results from previous swift heavy ion studies on Gd2Zr2-xTixO7 pyrochlore materials. For Y2Ti2O7, this effect is attributed to the significantly lower electron density of this material relative to the lanthanide-bearing pyrochlores, thus lowering the electronic energy loss (dE/dx) of the high-energy ions in this composition. An energy loss normalization procedure was performed which reveals an initial increase of amorphous track size with rA/rB that saturates above a cation radius ratio larger than Gd2Ti2O7. This is in agreement with previous low-energy ion irradiation experiments and first principles calculations of the disordering energy of titanate pyrochlores indicating that the same trends in disordering energy apply to radiation damage induced in both the nuclear and electronic energy loss regimes. HRTEM images indicate that single ion tracks in Yb2Ti2O7 and Er2Ti2O7, which have small A-site cations and low rA/rB, exhibit a core-shell structure with a small amorphous core surrounded by a larger disordered shell. In contrast, single tracks in Gd2Ti2O7 and Sm2Ti2O7, have a larger amorphous core with minimal disordered shells.

Shape manipulation of ion irradiated Ag nanoparticles embedded in lithium niobate

Spherical silver nanoparticles were prepared by means of ion beam synthesis in lithium niobate. The embedded nanoparticles were then irradiated with energetic 84Kr and 197Au ions, resulting in different electronic energy losses between 8.1 and 27.5 keV nm−1 in the top layer of the samples. Due to the high electronic energy losses of the irradiating ions, molten ion tracks are formed inside the lithium niobate in which the elongated Ag nanoparticles are formed. This process is strongly dependent on the initial particle size and leads to a broad aspect ratio distribution. Extinction spectra of the samples feature the extinction maximum with shoulders on either side. While the maximum is caused by numerous remaining spherical nanoparticles, the shoulders can be attributed to elongated particles. The latter could be verified by COMSOL simulations. The extinction spectra are thus a superposition of the spectra of all individual particles.