Kr Ions Research Articles

Microstructural evolution in NF616 (P92) and Fe–9Cr–0.1C-model alloy under heavy ion irradiation

In this comparative study, in situ investigations of the microstructure evolution in a Fe–9Cr ferritic–martensitic steel, NF616, and a Fe–9Cr–0.1C-model alloy with a similar ferritic–martensitic microstructure have been performed. NF616 and Fe–9Cr–0.1C-model alloy were irradiated to high doses (up to ∼10 dpa) with 1 MeV Kr ions between 50 and 673 K. Defect cluster density increased with dose and saturated in both alloys. The average size of defect clusters in NF616 was constant between 50 and 573 K, on the other hand average defect size increased with dose in Fe–9Cr–0.1C-model alloy around ∼1 dpa. At low temperatures (50–298 K), alignment of small defect clusters resulted in the formation of extensive defects in Fe–9Cr–0.1C-model alloy around ∼2–3 dpa, while similar large defects in NF616 started to form at a high temperature of 673 K around ∼5 dpa. Interaction of defect clusters with the lath boundaries were found to be much more noticeable in Fe–9Cr–0.1C-model alloy. Differences in the microstructural evolution of NF616 and Fe–9Cr–0.1C-model alloy are explained by means of the defect cluster trapping by solute atoms which depends on the solute atom concentrations in the alloys.

Ultrasensitive resonance ionization mass spectrometer for evaluating krypton contamination in xenon dark matter detectors

An ultrasensitive resonance ionization mass spectrometer that can be applied to evaluate krypton (Kr) contamination in xenon (Xe) dark matter detectors has been developed for measuring Kr at the parts-per-trillion (ppt) or sub-ppt level in Xe. The gas sample is introduced without any condensation into a time-of-flight mass spectrometer through a pulsed supersonic valve. Using a nanosecond pulsed laser at 212.6nm, 84Kr atoms in the sample are resonantly ionized along with other Kr isotopes. 84Kr ions are then mass separated and detected by the mass spectrometer in order to measure the Kr impurity concentration. With our current setup, approximately 0.4ppt of Kr impurities contained in pure argon (Ar) gas are detectable with a measurement time of 1000s. Although Kr detection sensitivity in Xe is expected to be approximately half of that in Ar, our spectrometer can evaluate Kr contamination in Xe to the sub-ppt level.

THE ABUNDANCES OF LIGHT NEUTRON-CAPTURE ELEMENTS IN PLANETARY NEBULAE. III. THE IMPACT OF NEW ATOMIC DATA ON NEBULAR SELENIUM AND KRYPTON ABUNDANCE DETERMINATIONS

The detection of neutron(n)-capture elements in several planetary nebulae (PNe) has provided a new means of investigating s-process nucleosynthesis in low-mass stars. However, a lack of atomic data has inhibited accurate trans-iron element abundance determinations in astrophysical nebulae. Recently, photoionization and recombination data were determined for Se and Kr, the two most widely detected n-capture elements in nebular spectra. We have incorporated these new data into the photoionization code Cloudy. To test the atomic data, numerical models were computed for 15 PNe that exhibit emission lines from multiple Kr ions. We found systematic discrepancies between the predicted and observed emission lines that are most likely caused by inaccurate photoionization and recombination data. These discrepancies were removed by adjusting the Kr$^+$--Kr$^{3+}$ photoionization cross sections within their cited uncertainties and the dielectronic recombination rate coefficients by slightly larger amounts. From grids of models spanning the physical conditions encountered in PNe, we derive new, broadly applicable ionization correction factor (ICF) formulae for calculating Se and Kr elemental abundances. The ICFs were applied to our previous survey of near-infrared [Kr III] and [Se IV] emission lines in 120 PNe. The revised Se and Kr abundances are 0.1-0.3 dex lower than former estimates, with average values of [Se/(O, Ar)]=0.12$\pm$0.27 and [Kr/(O, Ar)]=0.82$\pm$0.29, but correlations previously found between their abundances and other nebular and stellar properties are unaffected. We also find a tendency for high-velocity PNe that can be associated with the Galactic thick disk to exhibit larger s-process enrichments than low-velocity PNe belonging to the thin disk population.

Resilient ZnO nanowires in an irradiation environment: An in situ study

ZnO nanowires (NWs) have been extensively studied for various device applications. Although these nanowires are often suspected to be impractical and highly unstable under hostile radiation environments, to date little is known on their radiation tolerance. Here, we show outstanding resilience of ZnO NWs by using in situ Kr ion irradiation at room temperature inside a transmission electron microscope. Our studies show that ZnO nanowires with certain diameters become nearly immune to radiation damage due to the existence of dislocation loop denuded zones. A remarkable size effect also holds: the smaller the nanowire diameter, the lower the defect density. Rate theory modeling suggests that the size effect arises from fast interstitial migration and a limit in size to which interstitial loops can grow. In situ studies also revealed a surprising phenomenon: the pristine prismatic loops can prevail over the strongest known defect sinks, free surfaces, to trap radiation-induced defect clusters. This study comprises the first critical step toward in-depth understanding of radiation response of functional oxide nanowires for electronic device applications in extreme environments.

Charge distribution of Kr ions produced upon photoionization around the 2s edge

Charge state spectra of krypton ions generated after ionization (by a single photon) of the L shell have been measured by using the PEPICO technique. Relative abundances of Krq+ ions in charge state up to 8+ were obtained using monochromatized synchrotron radiation. A comparison with other experimental and theoretical data is presented.

Formation of ion tracks in amorphous silicon nitride films with MeV C60 ions

Amorphous silicon nitride (a-SiN) films (thickness 5–100nm) were irradiated with 0.12–5MeV C60, 100MeV Xe, 200MeV Kr, and 200 and 420MeV Au ions. Ion tracks were clearly observed using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) except for 100MeV Xe and 200MeV Kr. The observed HAADF-STEM images showed that the ion tracks consist of a low density core (0.5–2nm in radius) and a high density shell (several nm in radius). The observed core and shell radii are not simply correlated with the electronic energy loss indicating that the nuclear energy loss plays an important role in the both core and shell formations. The observed track radii were well reproduced by the unified thermal spike model with two thresholds for shell and core formations.

Structural damage in InGaN induced by MeV heavy ion irradiation

In0.18Ga0.82N films were irradiated with 4MeV 84Kr and 8.9MeV 209Bi ions to various fluences at room temperature. The irradiated films were analyzed by means of Rutherford backscattering/channeling (RBS/C) and high resolution X-ray diffraction (HRXRD). The RBS/C measurements show that under the irradiation conditions, the relative lattice disorder in the films, obtained from the normalized backscattering yield, exhibits a rapid increase in the range from ∼2% to 68%. There is also an increasing lattice expansion of the films with increasing ion fluence, as determined by the HRXRD measurements. At a comparable level of lattice disorder, the Kr irradiation leads to a more pronounced lattice expansion than the Bi irradiation. This may be attributed to a larger portion of the single interstitials in the films produced by the lighter Kr ion irradiation.

Erratum to: Raman Scattering in Natural Diamond Crystals Implanted with High-Energy Ions and Irradiated with Fast Neutrons

Raman scattering is studied in natural diamond crystals with radiation-induced defects produced by implantation of high energy Xe and Kr ions (ion kinetic energy >1 MeV/amu) and by irradiation with fast reactor neutrons (kinetic energy >100 keV). Confocal measurements of the Raman spectra along the surface of an oblique section of the ionimplanted diamonds are used to study the radiation damage profile. The evolution of the Raman scattering spectra with depth of the damaged layer in the ion-implanted diamonds, and as a function of annealing temperature of the neutron-irradiated diamond, is determined by spatial localization of phonons in the radiation disordered crystal lattice and by the formation of associations of intrinsic defects in the lattice.

In situ TEM study of G-phase precipitates under heavy ion irradiation in CF8 cast austenitic stainless steel

Thermally-aged cast austenitic stainless steels (CASS) CF8 was irradiated with 1MeV Kr ions at 300, 350 and 400°C to 1.88×1019ions/m2 (∼3dpa) at the IVEM-Tandem Facility at the Argonne National Laboratory. Before irradiation, the distribution of G-phase precipitates in the ferrite showed spatial variations, and both their size and density were affected by the ferrite–austenite phase boundary and presence of M23C6 carbides. Under 300°C irradiation, in situ TEM observation showed G-phase precipitates were relatively unchanged in the vicinity of the phase boundary M23C6 carbides, while the density of G-phase precipitates increased with increasing dose within the ferrite matrix. Coarsening of G-phase precipitates was observed in the vicinity of phase boundary M23C6 carbides at 350°C and 400°C.

Depth profiles of indentation hardness and dislocation mobility in MgO single crystals irradiated with swift 84Kr and 14N ions

The depth dependence of damage and modification of micromechanical properties in MgO single crystals irradiated with 150 MeV 84Kr and 24.5 MeV 14N ions (specific energy 1.75 MeV/u) at fluences up to 1015 ions/cm2 has been studied. The effects of ion-induced increase in hardness and reduction in dislocation mobility, magnitude of which varies along the ion range, were observed. These effects are related to ion-induced dislocations which were revealed by chemical etching. The results confirm a joint contribution of electronic excitations and atomic displacements by elastic collisions in the structural damage of MgO. The excitation mechanism in hardening dominates in the incoming part of ion range (up to the Bragg’s maximum), while the role of impact mechanism becomes dominant only at the end of ion range.

Single-mode master-oscillator power amplifier at 647 nm with more than 500 mW output power.

Using an AlGaInP-based truncated tapered power amplifier, it was possible to boost the output power of a 647-nm distributed Bragg reflector laser from 50mW to more than 500mW. The light source has the potential to replace bulky Kr ion lasers still in use at this wavelength.

Two waveguide layers in lithium niobate crystal formed by swift heavy Kr ion irradiation**Project supported by the National Natural Science Foundation of China (Grant Nos. 11275117, U1432120, and 11274188) and the Heavy Ion Research Facility in Lanzhou (HIRFL), China.

We report the formation of two waveguide layers in a lithium niobate crystal by irradiation with swift heavy Kr ions with high (GeV) energies and ultralow fluences. The micro-Raman spectra are measured at different depths in the irradiated layer and show that the high electronic energy loss can cause lattice damage along the ion trajectory, while the nuclear energy loss causes damage at the end of the ion track. Two waveguide layers are formed by confinement with two barriers associated with decreases in the refractive index that are caused by electronic and nuclear energy losses, respectively.

Structure and band gap determination of irradiation-induced amorphous nano-channels in LiNbO3

The irradiation of lithium niobate with swift heavy ions results in the creation of amorphous nano-sized channels along the incident ion path. These nano-channels are on the order of a hundred microns in length and could be useful for photonic applications. However, there are two major challenges in these nano-channels characterization: (i) it is difficult to investigate the structural characteristics of these nano-channels due to their very long length and (ii) the analytical electron microscopic analysis of individual ion track is complicated due to electron beam sensitive nature of lithium niobate. Here, we report the first high resolution microscopic characterization of these amorphous nano-channels, widely known as ion-tracks, by direct imaging them at different depths in the material, and subsequently correlating the key characteristics with electronic energy loss of ions. Energetic Kr ions (84Kr22 with 1.98 GeV energy) are used to irradiate single crystal lithium niobate with a fluence of 2 × 1010 ions/cm2, which results in the formation of individual ion tracks with a penetration depth of ∼180 μm. Along the ion path, electron energy loss of the ions, which is responsible for creating the ion tracks, increases with depth under these conditions in LiNbO3, resulting in increases in track diameter of a factor of ∼2 with depth. This diameter increase with electronic energy loss is consistent with predictions of the inelastic thermal spike model. We also show a new method to measure the band gap in individual ion track by using electron energy-loss spectroscopy.

Phase stability in thermally-aged CASS CF8 under heavy ion irradiation

The stability of the microstructure of a cast austenitic stainless steel (CASS), before and after heavy ion irradiation, was investigated by atom probe tomography (APT). A CF8 ferrite–austenite duplex alloy was thermally aged at 400°C for 10,000h. After this treatment, APT revealed nanometer-sized G-phase precipitates and Fe-rich α and Cr-enriched α′ phase separated regions in the ferrite. The thermally-aged CF8 specimen was irradiated with 1MeV Kr ions to a fluence of 1.88×1019ions/m2 at 400°C. After irradiation, APT analysis revealed a strong spatial/dose dependence of the G-phase precipitates and the α–α′ spinodal decomposition in the ferrite. For the G-phase precipitates, the number density increased and the mean size decreased with increasing dose, and the particle size distribution changed considerably under irradiation. The inverse coarsening process can be described by recoil resolution. The amplitude of the α–α′ spinodal decomposition in the ferrite was apparently reduced after heavy ion irradiation.

Valence and Core-Valence Effects in N-Like Kr, Rb and Sr Ions

(Received December 17, 2013) Energy levels, wavelengths, transition rates and line strengths are reported for the 2s2p 2s2p transition array in Kr(XXX), Rb(XXXI) and Sr(XXXII). Wave functions were determined using the multicon guration Dirac Fock method with account for valence and core-valence correlation e ects. The present results are presented and compared with experimental data and with values from other calculations. The calculated values including corevalence correlation are in good agreement with other available theoretical and experimental values, and therefore can be used for the further astrophysical investigations.

Semiempirical calculation of radiative constants in the spectra of nickel-like ions Kr IX, Sr XI, Y XII, Ru XVII, Pd XIX, and Ag XX

The probabilities of the electric-dipole transitions 3d 94p, 3d 94f-3d 10, 3d 94s, and 3d 94d in the spectra of nickel-like ions Kr IX, Sr XI, Y XII, Ru XVII, Pd XIX, and Ag XX are calculated semiempirically with the use of published energy levels.

Radiation effects in Zr and Hf containing garnets

Garnets have been considered as host phases for the safe immobilisation of high-level nuclear waste, as they have been shown to accommodate a wide range of elements across three different cation sites, such as Ca, Y, Mn on the a-site, Fe, Al, U, Zr, and Ti on the b-site, and Si, Fe, Al on the c-site. Garnets, due to their ability to have variable composition, make ideal model materials for the examination of radiation damage and recovery in nuclear materials, including as potential waste forms. Kimzeyite, Ca3Zr2FeAlSiO12, has been shown naturally to contain up to 30wt% Zr, and has previously been examined to elucidate both the structure and ordering within the lattice. This study examines the effects of radiation damage and recovery using in-situ ion beam irradiation with 1MeV Kr ions at the IVEM-TANDEM facility, Argonne National Laboratory. The complementary Hf containing system Ca3Hf2FeAlSiO12 was also examined, and found to have a different response to irradiation damage. A sample of irradiated Ca3Zr2FeAlSiO12, at 1000K, was characterised using aberration corrected (S)TEM and found to contain discreet, nano-sized, crystalline Fe rich particles, indicating a competing process during recovery is occurring.

Strong irradiation tolerance to amorphization in delta-Sc4Ti3O12

Polycrystalline delta-phase Sc4Ti3O12 was irradiated under two separate conditions, with 200keV Ne+ or 600keV Kr3+ at cryogenic temperature (∼77K) to examine its radiation tolerance to amorphization. Irradiated samples were characterized using grazing incidence X-ray diffraction and cross-sectional transmission electron microscopy. An order-to-disorder (O–D) structural transformation was observed under both ion beam irradiation conditions, but the threshold irradiation doses to produce the O–D transformation differ significantly. The order to disorder phase transformation was completed by a fluence of 2×1019Ne/m2 (or a peak dose of ∼0.7dpa) with Ne irradiation, while it was not accomplished until a fluence of 5×1020Kr/m2 (or a peak dose of ∼93dpa) with Kr irradiation. This observation was interpreted in terms of greater probability of defect survivability in dilute Ne versus dense Kr ion cascades. More interesting aspect in this study, in the basis of so-called “chemical effects”, Ti-bearing oxide Sc4Ti3O12 should be readily amorphous when exposed to ion irradiation, but no amorphization was observed even after 93 displacements per atom in Kr irradiation. These observations exhibit that the temperature–composition (T–C) phase diagram is a good indicator for radiation tolerance, especially for amorphization.

Radiative lifetime of the1S0metastable state in doubly charged Kr ions

The radiative lifetime of the $4{s}^{2}4{p}^{4}{\phantom{\rule{0.16em}{0ex}}}^{1}{S}_{0}$ metastable state in $\mathrm{K}{\mathrm{r}}^{2+}$ ions has been experimentally determined using an electrostatic ion trap of the ion-beam storage type. The radiative lifetime was obtained by measuring the number of 350-nm photons emitted during the ${}^{1}{S}_{0}{\ensuremath{\rightarrow}}^{3}{P}_{1}$ magnetic dipole transition of $\mathrm{K}{\mathrm{r}}^{2+}$ as a function of the storage time. The storage lifetime of the $\mathrm{K}{\mathrm{r}}^{2+}$ beam in the trap, which is a correction term in the determination of the radiative lifetime, was measured by detecting Kr neutrals produced by electron capture collisions with residual gases in the trap. We have obtained a lifetime value of $17.4\ifmmode\pm\else\textpm\fi{}0.4\phantom{\rule{0.16em}{0ex}}\mathrm{ms}$, which is larger than the previous experimental results, but consistent with theoretical predictions.

Raman Scattering in Natural Diamond Crystals Implanted with High-Energy Ions and Irradiated with Fast Neutrons

Raman scattering is studied in natural diamond crystals with radiation-induced defects produced by implantation of high energy Xe and Kr ions (ion kinetic energy >1 MeV/amu) and by irradiation with fast reactor neutrons (kinetic energy >100 keV). Confocal measurements of the Raman spectra along the surface of an oblique section of the ionimplanted diamonds are used to study the radiation damage profile. The evolution of the Raman scattering spectra with depth of the damaged layer in the ion-implanted diamonds, and as a function of annealing temperature of the neutron-irradiated diamond, is determined by spatial localization of phonons in the radiation disordered crystal lattice and by the formation of associations of intrinsic defects in the lattice.