Kr Ions Research Articles

Ion Charge Influence on the Molecular Structure of Polyethylene Terephthalate Films after Irradiation with Swift Heavy Ions

We report here experimental results investigating the influence of the initial swift heavy ion charge on the structure of polyethylene terephthalate (PET) film after irradiation, using a structurally sensitive X-ray diffraction method. Kr ions with an energy of 100 MeV and charges of 13+, 14+, and 15+ were each used at irradiation fluences of 5 × 1010, 7.5 × 1010, 1 × 1011, 2.5 × 1011 and 5 × 1011 ions/cm2. At constant energy and irradiation fluence, the post-irradiation structural changes in PET film show a clear dependence on the initial ion charge. As either the fluence or ion charge increase, the latent tracks begin to overlap, leading to cross-linking of PET chain molecules to form rotational isomers (rotamers). We use the fluence corresponding to the onset of overlapping to estimate the size of latent tracks for different ion charges. At the highest fluences, the latent tracks become entirely overlapped, and the interchain cross-linking extends throughout the whole film. Since this cross-linking is due to the dipole–dipole interaction of subunits of repeat units of PET chain molecules, it is reversible, in contrast to the well-known chemical cross-linking of polymer chain molecules under irradiation.

An investigation on structures and strains of gas-ion-implanted and post-implantation-annealed SiC

Silicon carbide (SiC) single crystals were implanted by 5.3-MeV Kr ion, 2.3-MeV Ne ion, and 100-keV He ion with the fluence of 2.0 × 1014, 3.75 × 1015, 3.0 × 1016 ions/cm2, respectively. After ion implantation, SiC specimens were annealed at different temperatures in a high vacuum. The HRXRD measurements were used to characterize the structure damage, strain generation and their recovery processes. HRXRD results reveal that the full width at half maximum (FWHM) of the main diffraction peak broadens and new diffraction peaks appear at lower angles besides the main diffraction peak due to lattice expansions and strain occurrences caused by the implantation. Meanwhile, with increasing annealing temperature, the lattice recovery and strain relaxation occur gradually and several stages of the strain release are presented. Moreover, based on the Arrhenius model, the thermal relaxation activated energy of strains at different temperature ranges was estimated. The mechanisms on strain releases were discussed in detail.

Revealing the synergistic effects of sequential and simultaneous dual beam irradiations in tungsten via in-situ TEM

Elucidating the synergistic effects of different energetic beams on the radiation response of nuclear materials is critical for developing an improved methodology for their evaluation when exposed to extreme environments. This article describes in-situ sequential (He implantation followed by Kr irradiation and vice-versa) and simultaneous (heavy ion Kr irradiation and He implantation) dual beam irradiations performed on tungsten at 1223 K. Dislocation loop density, average area, and total loop damage as a function of irradiation history and dose/fluence are quantified. The loop Burgers vectors and cavity damage (cavity density, size and total change in volume) are also determined at the final maximum dose for each condition. The loop damage evolution was different in all cases, with the smallest loop damage observed in the simultaneous experiment. Annihilation of Kr generated dislocation loops during He implantation in the Kr + He experiment was an unanticipated observation that may be explained by the dynamic evolution of dislocation loop sink strengths and time-dependent defect fluxes. Dislocation loop raft formation, denuded zones near extended defects, and cavity damage are compared across the different conditions. The phenomena observed and discussed in this work will stimulate further experimental and computational modeling activities leading to improved fundamental understanding of the irradiation response of nuclear materials under reactor-similar environments.

Effects of Kr implanted O-polar ZnO thin films on structure and optical properties

Understanding of the structure and optical properties of films is important for their optoelectronic applications. In this paper, O-polar ZnO thin films were prepared by molecular beam epitaxy (MBE) on sapphire substrates, and Kr ions were doped into one of the films by ion implantation. Lattice structure and surface morphology of films were characterized by X-ray diffraction (XRD), Atomic force microscopy (AFM), respectively. The results show that compared with undoped O-polar ZnO film, the doped sample had granulated surface and enhanced absorption. Absorption Spectra, photoluminescence spectra (PL) and Spectroscopic Ellipsometry (SE) were used to characterize optical properties of films. The bandgap values obtained by absorption and SE method demonstrated that the bandgap decreases slightly as Kr ion implantation, and a new transition peak (3.56eV) appears from the SE result. This study provides information for controlling the band gap of ZnO materials by ion implantation and guidance for the application research of ZnO.

Lasing efficiency of krypton ions in the (8 – 14)-nm band upon pulsed laser excitation

The emission spectra of krypton plasma in the range of 8 – 14 nm upon excitation of a pulsed gas jet by 1.06-mm Nd : YAG laser radiation with a pulse energy of 0.85 J, pulse duration of 5.2 ns, and repetition rate of 10 Hz are investigated. The krypton emission spectrum is a wide (8 – 14 nm) band, peaking at 10.3 nm, which is formed by a series of much narrower lines. The observed lines are identified, and the fraction of laser pulse energy converted into the (8 – 14)-nm emission band and emitted into half-space (2π sr) is determined. The maximum conversion efficiency is found to be 21 %. The expected throughputs of lithographic systems with sources based on Sn, Xe, and Kr ions for different wavelengths, corresponding to the emission peaks of ions of these materials, are compared.

Efficiency and timing performance of time-of-flight detector utilizing thin foils and crossed static electric and magnetic fields for mass measurements with Rare-RI Ring facility

We developed a time-of-flight (TOF) detector for mass measurements of rare radioactive isotopes (RIs) with a storage ring, called the Rare-RI Ring, in RIKEN. For successful mass measurements, a time resolution of less than 100 ps and a detection efficiency close to 100% are required. Additionally, the change of ion velocity in the detector should be as small as possible (<10−4). To satisfy these requirements, the TOF detector utilizes ion-induced secondary electrons emitted from a thin foil and the crossed static electric and magnetic fields to transport the electrons isochronously to the microchannel plate detectors. The TOF detector was tested in both offline test with an alpha source and online test with heavy ions. In the online test with 84Kr ions of 200 MeV/nucleon, a time resolution of 38.6(2) ps in sigma and a position-averaged detection efficiency of 95.2(2)% were achieved in the entire area of 45-mm-diameter aluminum-coated Mylar foil. This good performance is attributed to the electromagnetic field achieved, which is the strongest thus far for a detector with this design.

Heavy Kr ion irradiation-induced amorphization on fluorapatite Ca10-2xLaxNax(PO4)6F2 (x=0.2 and 2)waste form with varying La loading

Polycrystal fluorapatite Ca10-2xLaxNax(PO4)6F2 (x = 0.2 and 2) were successfully synthesized by solid state reaction. The both samples were irradiated with 800 keV heavy Kr2+ ions at room temperature with fluences ranging from 5.0×1013 Kr2+/cm2 to 7.0×1014 Kr2+/cm2, corresponding to peak doses of 0.06–0.84 dpa. the irradiated samples were characterized by grazing incidence X-ray diffraction (GIXRD) and cross-sectional transmission electron microscopy (XTEM). A crystalline to amorphization phase transformation was observed as the irradiation fluence up to 1.0×1014 Kr2+/cm2, and the amorphization fraction became larger with the irradiation fluence increasing. However, the amorphization fraction of both samples are different at the same irradiation fluence, where the fluorapatite Ca10-2xLaxNax(PO4)6F2 with more La doping exhibited less amorphous fraction based on GIXRD measurements. Meanwhile, the nanocrystals existed in the irradiation damaged layer of Ca6La2Na2(PO4)6F2 with irradiation fluence of 7.0×1014 Kr2+/cm2, while a fully amorphous layer was observed in Ca9.6La0.2Na0.2(PO4)6F2 at the same fluence. The results suggest that more fraction of La3+ at AI site of apatite may enhance the irradiation tolerance, especially the amorphization resistance.

Comparative study of radiation defects in ion irradiated bulk and thin-foil tungsten

In this study, we employ transmission electron microscope (TEM) to analyze radiation defects in helium (He) and krypton (Kr) ions implanted bulk and thin-foil tungsten. For bulk tungsten, subgrains are formed near the surface region under both He+ and Kr+ irradiation. Dislocation loops are observed beyond ion implanted range. These observations are related to self-interstitial atoms (SIAs) diffusion and clustering. Ordered bubbles are formed in He+ implantation, while no cavities are detected in Kr+ irradiation. In thin-foil tungsten, line up of dislocation loops is found mainly aligns along {101} and {112} slip planes. Both 1/2<111> and 〈100〉 dislocation loops are identified. Compared to He+ irradiation, more 〈100〉 loops are detected in Kr+ irradiation due to higher energy collision cascade. Nanocavities are detected in irradiated thin-foil tungsten besides the formation of high density of interstitial loops. The number density of dislocation loops and the volume fractions of cavities are higher in He+ irradiation than in Kr+ irradiation. The differences in nature of radiation defects is attributed to the higher recombination rate of vacancies and interstitials in bulk sample, the significant surface sink effect in thin-foil irradiation and the chemical and physical effect of implanted ions.

EUV spectroscopy of Kr, Y and Mo ions using CoBITs

SynopsisCoBITs have been used to produce Kr, Y and Mo ions and EUV spectra have been recorded. The data indicate that the CoBIT spectra are significantly different to laser-produced plasma emission spectra for similar ion stages. This difference is attributed to the different number density of electrons in the two kinds of plasmas. The evolution of the line profiles with electron beam energy for a number of different ions has been studied.

Irradiation-Induced Segregation at Dislocation Loops in CoCrFeMnNi High Entropy Alloy

To understand the redistribution of alloying element in high entropy alloys (HEAs) under irradiation, a CoCrFeMnNi alloy was irradiated with 1 MeV Kr ions at room temperature and 500oC, and characterized with atom probe tomography (APT) and transmission electron microscopy. At 500oC, Co and Ni were enriched at interstitial dislocation loops resulted from the ion irradiation. In contrast, no segregation was observed at interstitial dislocation loops formed at room temperature. It is inferred that the inverse Kirkendall effect through vacancy flux, as opposed to interstitial binding, was the primary mechanism attributing to the observed segregation. In addition, APT concentration contour plots show a ring-shaped segregation pattern instead of a disk-shaped pattern at the faulted dislocation loops, indicating the non-equilibrium nature of the defect clustering and solute segregation process of the CoCrFeMnNi under irradiation at high temperature.

Effect of Sink Strength on Coherency Loss of Precipitates in Dilute Cu Base Alloys During in Situ Ion Irradiation

In situ irradiations with 1 MeV Kr ions at 50~613 K up to a fluence of 6.25 × 1014 ions/cm2 (~1.25 dpa) have been performed on pre-aged dilute Cu-0.9%Co, Cu-0.9%Fe and Cu-0.8%Cr alloys containing uniform matrix dispersions of coherent precipitates in order to study the effects of initial precipitate sink strength, damage dose and irradiation temperature on radiation-induced coherency loss of precipitates. Coherent precipitates with different sink strengths (2πNd , where N and d are the precipitate density and diameter) were used in this work to examine potential differences in atomic relaxation during absorption of point defects. At low sink strengths (~1013 m-2 ), loss of precipitate coherency could be induced for doses below ~0.1 dpa. There might be a preferential medium-range strain-induced bias for absorption of interstitial defects due to tensile strains at the undersized precipitates, which induces relatively rapid loss of coherency at low precipitate sink strengths. High sink strength (~1014 m-2 ) conditions were relatively resistant to the radiation-induced loss of coherency and this might be due to nearly equal numbers of interstitial and vacancy defects arriving at the precipitate interface for such high sink strength conditions. The precipitate coherency loss was observed to have a weak dependence on irradiation temperature. Molecular dynamics simulations confirm a strong effect of precipitate sink strength on the probability of interstitial absorption at precipitates.

A novel method to enhance the catalytic activity of PtRu on the support using CeO2 by high-energy ion-beam irradiation

As a novel method for the preparation of highly-active anode catalysts for direct methanol fuel cells (DMFCs), the effect of high-energy ion irradiation on the CeO2 embedded carbon nanofiber support (CECNF) of the PtRu/CECNF catalyst, that has been reported as a very active catalyst, on the methanol oxidation activity as well as the crystalline structure of the support materials were investigated. PtRu/CECNFs were prepared using the CECNFs that were irradiated by high-energy ion-beams under the different conditions, i.e., using 127 MeV Ar ions, 310 MeV Kr ions and 350 MeV Xe ions with different ion-fluences from 5 × 1011 ions cm−2 to 1 × 1013 ions cm−2. A change in the activity was observed at the low electrode potentials below 0.7 V vs RHE. An almost two times higher current density at 0.6 V vs RHE compared to that without irradiation was obtained by the Ar ion irradiation with the ion-fluence at around 5 × 1011 ions cm−2, while a higher ion-fluence reduced the activity. The reduction of the CeO2 crystalline size with the increase in the ion-fluence was observed by XRD measurements. The change in the catalytic activity roughly correlated with the increase in the lattice distance of CeO2 suggesting that the generated oxygen atom vacancies enhanced the activity.

Evolution of cellular dislocation structures and defects in additively manufactured austenitic stainless steel under ion irradiation

The evolution of irradiation-induced defects in additively manufactured (AM) austenitic stainless steel was investigated in situ by 1 MeV Kr ion irradiation at 450 and 600 °C in a transmission electron microscope. Cellular dislocation structure in AM steel act as sink/trap sites for the irradiation-induced defects, resulting in the lower density and smaller dislocation loops in AM steel than conventional forged (CF) steel at 450 °C. The higher stacking fault energy and local stress concentration induced by cellular dislocation structure in AM steel promotes the unfaulting process and the formation of network dislocation at 600 °C.

Radiation damage in β-Ga2O3 induced by swift heavy ions

The amorphous latent tracks in β-Ga2O3 single crystal irradiated with ∼5–10 MeV u−1 181Ta and 86Kr ions were investigated by transmission electron microscopy (TEM). TEM images showed that the mean diameter of latent tracks increased from 2.2 to 8.8 nm with electronic energy loss (Se) values increasing from 18.3 to 41.5 keV nm−1. Moreover, the inelastic thermal spike model was used to predict the latent track size. The calculation results agreed well with the experimental results and the predicted Se threshold of latent track formation in β-Ga2O3 was about 17 keV nm−1 for 5–10 MeV u−1 heavy ions.

In-situ TEM characterization of the tensile deformation of ion-irradiated HT-UPS steel at RT and 400 °C

High-temperature ultra-fine precipitate strengthened (HT-UPS) steel samples were irradiated with 1 MeV Kr ions, and in-situ tensile deformed at room temperature (RT) and 400 °C. The dislocation flow in irradiated samples was significantly restricted by the irradiation defects, and the deformation took place in localized deformation bands. While in unirradiated specimens, the deformation happened evenly across the grains. As a result of the localized deformation, intricate deformation band structures were observed in the irradiated specimens, which are composed of a central band and two defect reduced zones on the two sides. The irradiation defects were in-situ observed to interact with deformation induced dislocations, and were removed by the latter. Despite of the differences, the irradiated samples reserved similar work hardening behaviors as the unirradiated samples. The deformation inside the defect reduced bands in irradiated samples showed similar characteristics as in the unirradiated sample. The last stage deformation also showed similar deformation characteristics, regardless of the irradiation history.

Diffusion of helium in radiation-damaged zircon

Diffusion of helium was characterized in natural zircon that had been implanted with Kr at a range of energies to simulate the effects of alpha recoil in natural radiation damage. Polished slabs of zircon, oriented either normal or parallel to c, were implanted with Kr+ ions at a series of energies to produce a damaged region ∼ 1μm in thickness, then implanted with 100keV 3He at a dose of 1×1015 3He/cm2, which placed the 3He within the region damaged by the Kr ion implantation. The implanted zircons were annealed isothermally in Pt capsules in 1-atm furnaces at temperatures ranging from 51 to 252°C and times ranging from 15min to 3 weeks. 3He distributions following experiments were measured with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. For diffusion in zircon normal to c, we obtain the following Arrhenius relation:D=1.7×10−8 exp(−71±2kJ mol−1/RT) m2sec−1.This activation energy for diffusion is about half of the value for He diffusion in zircon from the same sample locality but without Kr implantation, measured with an otherwise similar experimental and analytical approach (Cherniak et al., 2009). He diffusivities in the Kr-implanted material are also significantly faster. Further, He diffusivities normal and parallel to c in the Kr-implanted zircon are similar, in contrast to the marked diffusional anisotropy (with differences of two orders of magnitude for diffusion normal and parallel to c) observed for He diffusion in this zircon in samples not implanted with Kr.These data indicate that heavily damaged zircon will have very limited retentivity of helium. Only those zircons larger than a few hundred μm will have mean closure temperatures exceeding typical earth surface temperatures; mean closure temperatures for He in highly damaged zircon will be about ∼200°C lower than those for relatively undamaged zircon. At 200°C, equivalent amounts of He will be lost from severely damaged zircon at a rate about a million times faster than from relatively undamaged zircon. For retentivity of He comparable to that for low-damage zircon at 200°C, the severely damaged zircon would require residence temperatures of ∼ -10°C.

Magnetic and Structural Properties of ZnO Implanted with Co, Kr, and Ar Ions

Magnetic and Structural Properties of ZnO Implanted with Co, Kr, and Ar Ions

Vibrational modes in La2Zr2O7 pyrochlore irradiated with disparate electrical energy losses**Project supported by the National Natural Science Foundation of China (Grant Nos. 11705246, 11675233, and 11690041) and the Natural Science Foundation of Gansu Province, China (Grant No. 17JR5RA316).

Polycrystalline samples of La2Zr2O7 pyrochlore are irradiated by different energetic heavy ions to investigate the dependence of the vibrational mode variations on the irradiation parameters. The applied electronic energy loss (dE/dx)e increases from about 5.2 keV/nm to 39.6 keV/nm. The ion fluence ranges from 1 × 1011 ions/cm2 to 6 × 1015 ions/cm2. Vibrational modes of irradiated pyrochlore are analyzed by using Raman spectrum. Infrared active modes F1u at 192, 308, and 651 cm−1 appear in Raman spectra, and the F2g band at 265 cm−1 rises up due to the irradiation by 200-MeV Kr ions with (dE/dx)e of 16.0 keV/nm. Differently, for the pyrochlore irradiated by 1750-MeV Bi ions with (dE/dx)e of 39.6 keV/nm, in spite of the appearance of infrared active mode F1u 651 cm−1, the amorphous structure occurs according to the vibrational mode variations of pyrochlore irradiated at higher ion fluences. Amorphous tracks are observed in the samples, which confirm the occurrence of pyrochlore–amorphous transition in pyrochlore irradiated with (dE/dx)e of 39.6 keV/nm.

Phase transformation and modifications in high-k ZrO2 nanocrystalline thin films by low energy Kr5+ ion beam irradiation

In present communication, zirconium oxide (ZrO2) thin films of thickness (155 nm) were grown by using RF sputtering technique. To address and systematically understand the effects of low energy (800 keV) irradiation, high-k ZrO2 thin films were irradiated at room temperature by Kr ions with a range of fluence 1E15 to 1E17 ions. cm−2. The polymorphous zirconia pristine and irradiated thin films were characterized through X-ray diffraction (XRD) technique which confirms the coexistence of monoclinic and tetragonal phases. Monoclinic to tetragonal structural phase transformation was observed for Kr5+ ions irradiated samples at a fluence of 5E15, 1E16, 1E17 ions. cm−2. All samples were characterized by UV–Vis spectroscopy to study the mechanism of variation in optical energy band gap (4.42–4.52 eV), Urbach energy (402–449 meV) and refractive index (1.518–1.523) with increasing ion fluence. Photoluminescence (PL) spectroscopy was done at room temperature to record the significant PL broad prominent emission peaks at 350 nm and 430 nm and the peak intensity of these peaks significantly varies due to the annihilation of primary defects or generation of new defects centres by the influence of Kr ion irradiation. To determine the significant variation in grain size (50–85 nm) and RMS surface roughness (0.54–1.04 nm), pristine and irradiated sample were characterized by atomic force microscopy (AFM). A complete mechanism of the evolution of surface roughness was analyzed by determining the power spectral density (PSD). Further surface roughness component in the range of 0.4–1.7 was calculated using the slope of the tail of PSD. The FTIR spectra of pristine and low energy ion irradiated ZrO2 thin films were recorded in the range of 1250–3200 cm−1. The Rutherford backscattering spectrometry (RBS) was carried out in channeling condition and the experimental results were simulated to evaluate the elemental composition of Zr and O (⁓1:2) and film thickness (155 nm) of the samples. The changes of the chemical binding energy of ZrO2 thin films of Zr 3d and O 1s region before and after ion irradiation were investigated by x-ray photoelectron spectroscopy (XPS).

Cascade size and dose rate effects on α′ precipitation in ion-irradiated Fe14Cr alloy

Dose rate and cascade size effects on α′ formation in Fe14Cr have been studied under ion irradiation using analytical scanning transmission electron microscopy. Samples were irradiated with 100 keV He, 350 keV Ne or 1 MeV Kr ions at 300 °C to a dose of 2.5 DPA at dose rates of 10−4 and 10−3 displacements per atom (DPA)/s. Higher dose rates commensurately accelerate α′ precipitation under He ion irradiation, resulting in similar precipitate sizes and density. Number densities of α′ precipitates decreased with increasing ion mass and energy attributed to ballistic mixing from high-energy-density cascade formation and sub-cascade overlap.