Radiation-induced Disordering Research Articles

Dose and dose rate effects on the microstructural and mechanical stability of long-range ordered precipitates in Inconel 718

Nickel-based alloys offer exceptional mechanical properties and corrosion resistance for various applications in extreme environments such as high neutron flux, temperature, and stress. Precipitates, resulting from thermal treatments, increase the strength and creep resistance of these alloys. In this study, heavy ion irradiation is shown to destabilize the γ′ and γ’’ precipitates in Inconel 718 nickel-based alloy by disordering and dissolution processes. Transmission electron microscopy and atom probe tomography reveal that the disordering and dissolution rates of the precipitates are proportional to both irradiation dose and dose rate. Irradiation induced disordering occurs at a higher rate than the dissolution. From analyzing the hardening contributions, microscale mechanical results suggest radiation-induced disordering is responsible for the majority of the softening response at low dose. In addition, low dose radiation-induced disordering results in strain localization and is believed to be the primary cause for the drastic degradation of uniform elongation and toughness in irradiated Inconel 718.

Radiation-Induced Changes in Single Crystal Calcite and Dolomite: Mineral Analogues of Light Water Reactor, Nuclear Power Plant Concrete Aggregates

Two analogues of aggregates (calcite and dolomite) found in nuclear power plant (NPP) concrete have been neutron irradiated to fluences up to 2 × 1020 n/cm2 at 52 °C and 4 × 1019 n/cm2 at 95 °C (E > 0.1 MeV). X-ray diffraction studies showed that these aging conditions affected crystallography of both calcite and dolomite, with both showing a growth in their unit cells compared to that of the unirradiated samples. Only dolomite samples showed a continuous increase of its lattice parameters with the increase in irradiation. In calcites, the lattice growth with irradiation dissipated after a fluence of 5 × 1018 n/cm2. Radiation-induced disordering of the crystal structure was observed in both materials, while a healing effect of irradiation temperature was mainly observed in calcites. Dislocation densities calculated by using XRD data also supported these observations. Insights made into the unit cells of both minerals by using Fourier synthesis showed that the Mg sites are more prone to the neutron irradiation than the Ca sites, resulting in larger radiation effects and higher disruption in the crystal structure of dolomite than that of calcite. Other than the polycrystalline characteristics observed by using TEM, these minerals did not show complete amorphization or significant structural decomposition at the studied irradiation fluences.

OH cleavage from tyrosine: debunking a myth.

During macromolecular X-ray crystallography experiments, protein crystals held at 100 K have been widely reported to exhibit reproducible bond scission events at doses on the order of several MGy. With the objective to mitigate the impact of radiation damage events on valid structure determination, it is essential to correctly understand the radiation chemistry mechanisms at play. OH-cleavage from tyrosine residues is regularly cited as amongst the most available damage pathways in protein crystals at 100 K, despite a lack of widespread reports of this phenomenon in protein crystal radiation damage studies. Furthermore, no clear mechanism for phenolic C-O bond cleavage in tyrosine has been reported, with the tyrosyl radical known to be relatively robust and long-lived in both aqueous solutions and the solid state. Here, the initial findings of Tyr -OH group damage in a myrosinase protein crystal have been reviewed. Consistent with that study, at increasing doses, clear electron density loss was detectable local to Tyr -OH groups. A systematic investigation performed on a range of protein crystal damage series deposited in the Protein Data Bank has established that Tyr -OH electron density loss is not generally a dominant damage pathway in protein crystals at 100 K. Full Tyr aromatic ring displacement is here proposed to account for instances of observable Tyr -OH electron density loss, with the original myrosinase data shown to be consistent with such a damage model. Systematic analysis of the effects of other environmental factors, including solvent accessibility and proximity to disulfide bonds or hydrogen bond interactions, is also presented. Residues in known active sites showed enhanced sensitivity to radiation-induced disordering, as has previously been reported.

Ion irradiation-induced crystal structure changes in inverse spinel MgIn2O4

400keV Ne and 200keV He ion irradiations were performed on fully inverse MgIn2O4 samples at cryogenic temperature (~77K), in order to examine the influence of radiation-induced cation disordering on crystal structure. In the case of MgIn2O4 samples irradiated with Ne ions to a peak displacement damage dose of 4 displacements per atom (dpa), a spinel-to-rocksalt phase transformation was observed. By contrast, for MgIn2O4 samples irradiated with He ions to a peak displacement damage dose of 5dpa, the only observed structural effect involved cation rearrangements from an inverse to a “random” spinel structure.

Atomistic modeling of radiation-induced disordering and dissolution at a Ni/Ni3Al interface

Abstract

Rol' mekhanichnykh napruzhen' pry ionniy implantatsiyi tverdykh rozchyniv CdHgTe

The properties of n-CdxHg1 xTe/CdZnTe (x = 0.223) structures implanted with B+ and Ag+ ions with an energy of 100 keV to a dose of 3 x 10^13 cm^-2 are studied. The software package TRIM_2008 was applied to simulate the ion implantation process. The surface morphology of heterostructures and their optical, mechanical and electrical properties are studied. It is found that the ion irradiation of specimens gives rise to the formation of a characteristic relief on their surface, as well as a layer in the near-surface region, where the optical parameters differ from those in the matrix. The implantation of CdxHg1 xTe epitaxial layers with boron and silver ions with the same energy and to the same dose brings about the formation of a damaged layer, substantially non-uniform by the thickness and the damage character, with maximum mechanical stresses that differ by two orders of magnitude. The values of the crystal lattice contraction coefficient b and the mechanical stresses omax in the region of radiation-induced disordering in the solid solution are determined. The influence of mechanical stresses in the doped layer on the defect redistribution and the formation of properties of Cd0:223Hg0:777Te after the implantation is discussed.

The role of thermal spike compactness in radiation-induced disordering and Frenkel pair production in Ni3Al

We show that the shape of the kinetic energy distribution in radiation-induced thermal spikes may be described using a dimensionless number, proportional to (volume) 2/3 /(surface area), known as compactness. The disorder produced in thermal spikes in Ni 3 Al increases with compactness because the thermal spike cooling rate, which determines the time available for thermal disordering, decreases with compactness. On the other hand, Frenkel pair production is inversely correlated to compactness because longer thermal spike lifetimes enhance vacancy–interstitial recombination.

Radiation-induced disordering in crystalline actinide hosts

Radiation-induced disordering in crystalline actinide hosts

Superconductivity in iron silicideLu2Fe3Si5probed by radiation-induced disordering

Resistivity \ensuremath{\rho}($T$), Hall coefficient ${R}_{\mathrm{H}}$($T$), superconducting temperature ${T}_{c}$, and the slope of the upper critical field \ensuremath{-}d${H}_{c2}/$d$T$ were studied in poly- and single-crystalline samples of the Fe-based superconductor Lu${}_{2}$Fe${}_{3}$Si${}_{5}$ irradiated by fast neutrons. Atomic disordering induced by the neutron irradiation leads to a fast suppression of ${T}_{c}$ similarly to the case of doping of Lu${}_{2}$Fe${}_{3}$Si${}_{5}$ with magnetic (Dy) and nonmagnetic (Sc, Y) impurities. The same effect was observed in a novel FeAs-based superconductor La(O-F)FeAs after irradiation. Such behavior is accounted for by strong pair breaking that is traceable to scattering at nonmagnetic impurities or radiation defects in these unconventional superconductors. In such superconductors, the sign of the order parameter changes between the different Fermi sheets (s${}^{\ifmmode\pm\else\textpm\fi{}}$ model). Some relations that are specified for the properties of the normal and superconducting states in high-temperature superconductors are also observed in Lu${}_{2}$Fe${}_{3}$Si${}_{5}$. The first is the relationship \ensuremath{-}d${H}_{c}$${}_{2}/$d$T$ \ensuremath{\sim} ${T}_{c}$, which allows us to assign the compound Lu${}_{2}$Fe${}_{3}$Si${}_{5}$ to type II superconductors in the clean limit. The second is a correlation between the low-temperature linear coefficient $a$ in the resistivity \ensuremath{\rho} $=$ \ensuremath{\rho}${}_{0}$ $+$ ${a}_{1}T$, which appears presumably due to the scattering at magnetic fluctuations, and ${T}_{c}$, this correlation being an evidence of a tight relation between the superconductivity and magnetism. Data point to an unconventional (nonphononic) mechanism of superconductivity in Lu${}_{2}$Fe${}_{3}$Si${}_{5}$ and probably in some other Fe-based compounds, which can be fruitfully studied via the radiation-induced disordering.

Temperature effects in ion-electron emission of graphite quasicrystal

Analysis of the comparative influence of complete amorphization of a polycrystalline graphite surface layer and radiation-induced disordering of highly oriented pyrolytic graphite UPV-1T on the character of temperature dependences of the ion-electron emission yield under high-dose (1018–1019 ion/cm2) 30 keV Ar+ ion irradiation has been carried out.

Superconductivity and transport properties in LaRu4Sb12 single crystals probed by radiation-induced disordering

Resistivity ρ(T) and Hall coefficient RH(T) in magnetic fields H up to 14T were studied in superconducting (Tc=3.3K) LaRu4Sb12 single crystals disordered by fast neutron irradiation. Atomic disordering leads to increase in residual resistivity ρ0, decrease of Hall number and suppression of superconductivity. The upper critical field slope −dHc2/dT increases approximately linear with ρ0. The irradiation effects are almost recovered after annealing at 500°C. The observed radiation-induced effects in LaRu4Sb12 are compared with those in PrOs4Sb12 in terms of unconventional mechanisms of superconductivity.

XANES measurements of the rate of radiation damage to selenomethionine side chains.

The radiation-induced disordering of selenomethionine (SeMet) side chains represents a significant impediment to protein structure solution. Not only does the increased B-factor of these sites result in a serious drop in phasing power, but some sites decay much faster than others in the same unit cell. These radio-labile SeMet side chains decay faster than high-order diffraction spots with dose, making it difficult to detect this kind of damage by inspection of the diffraction pattern. The selenium X-ray absorbance near-edge spectrum (XANES) from samples containing SeMet was found to change significantly after application of X-ray doses of 10-100 MGy. Most notably, the sharp ;white line' feature near the canonical Se edge disappears. The change was attributed to breakage of the Cgamma-Se bond in SeMet. This spectral change was used as a probe to measure the decay rate of SeMet with X-ray dose in cryo-cooled samples. Two protein crystal types and 15 solutions containing free SeMet amino acid were examined. The damage rate was influenced by the chemical and physical condition of the sample, and the half-decaying dose for the selenium XANES signal ranged from 5 to 43 MGy. These decay rates were 34- to 3.8-fold higher than the rate at which the Se atoms interacted directly with X-ray photons, so the damage mechanism must be a secondary effect. Samples that cooled to a more crystalline state generally decayed faster than samples that cooled to an amorphous solid. The single exception was a protein crystal where a nanocrystalline cryoprotectant had a protective effect. Lowering the pH, especially with ascorbic or nitric acids, had a protective effect, and SeMet lifetime increased monotonically with decreasing sample temperature (down to 93 K). The SeMet lifetime in one protein crystal was the same as that of the free amino acid, and the longest SeMet lifetime measured was found in the other protein crystal type. This protection was found to arise from the folded structure of the protein molecule. A mechanism to explain observed decay rates involving the damaging species following the electric field lines around protein molecules is proposed.

Reversible expansion of gallium-stabilized δ-plutonium

It is shown that the transient expansion of plutonium–gallium alloys observed both in the lattice parameter as well as in the dimension of a sample held at ambient temperature can be explained by assuming incipient precipitation of Pu 3Ga. However, this ordered ζ′-phase is also subject to radiation-induced disordering. As a result, the gallium-stabilized δ-phase, being metastable at ambient temperature, is driven towards thermodynamic equilibrium by radiation-enhanced diffusion of gallium and at the same time reverted back to its metastable state by radiation-induced disordering. A steady state is reached in which only a modest fraction of the gallium present is arranged in ordered ζ′-phase regions.

Influence of structural defects on magnetic properties of the submicrometer ceramic Mn3O4

A high-density single-phase submicrometer ceramic Mn{sub 3}O{sub 4} with a grain size d {>=} 0.06 {mu}m has been obtained by using spherically converging shock waves. The action of shock waves reduces the unit cell volume and increases the Curie temperature T{sub C}. The shape of the temperature dependences of reciprocal susceptibility x{sup -1} of a polycrystal and the submicrometer ceramic at T > T{sub C} is hyperbolic, which is typical of ferrimagnets. It is shown that the susceptibility of the ceramic in the region of short-range order at 78 K {<=} T {<=} 300 K is larger than that of the polycrystal, while the field dependences of the magnetization are nonlinear. The bombardment by electrons with a small dose of {phi} = 0.8 x 10{sup 18} cm{sup -2} increases the susceptibility of the submicrometer ceramic as well as that of the polycrystal. When the fluence increases to {phi} = 5 x 10{sup 18} cm{sup -2}, the susceptibility decreases, which can be explained by radiation-induced disordering and a change in the 'local' exchange interactions.

Transport properties in PrOs 4Sb 12 single crystals probed by radiation-induced disordering

Resistivity ρ ( T ) and Hall coefficient R H ( T ) in magnetic fields H up to 13.6 T were studied in superconducting ( T C = 1.8 K ) PrOs 4Sb 12 single crystals disordered by fast neutron irradiation. Disordering leads to very fast suppression of superconductivity and to large increase in low-temperature values of both ρ and R H . Kondo-like magnetic scattering is observed in disordered crystals. Positive magnetoresistance in the crystals with different values of disordering is observed only at T < 10 K . It is an evidence of magnetic field influence on the band of conduction electrons. It is shown that the electronic transport in a PrOs 4Sb 12 can be described by two-band model including heavy and light holes.

Radiation-induced disordering in magnesium aluminate spinel subjected to ionizing radiation

An analytical electron microscope study was carried out on single crystal specimens of magnesium aluminate spinel irradiated with 200 MeV Xe 14+ ions up to 5.0 × 10 15 and 2.0 × 10 16 ions/m 2 at ambient temperature. Bright-field images showed structurally disordered columns of about 4–5 nm in diameter along ion tracks. Tiny pits were observed on the incident surface of the columns. Quantitative HARECXS analysis of atomic configurations revealed that disordering proceeds in more extended regions over 10 nm in diameter. The configurations of Al 3+ ions are more disordered than that of Mg 2+ ions. The disordered areas are appeared to overlap each other in the specimen irradiated with 2.0 × 10 16 ions/m 2.

Transport properties in heavy fermion system PrOs 4Sb 12 probed by radiation-induced disordering

The influence of atomic disordering induced by fast neutron irradiation on resistivity ρ and Hall coefficient R H was studied in single crystal samples of heavy fermion system PrOs 4Sb 12. Both ρ( T) and R H( T) of the initial samples can be described by a two-band model with conductivities in the form of ( σ i ) −1= ρ i0 + A i T 2 (indexes i=1,2 correspond to heavy and light holes), where A 1≫ A 2. Disordering leads to the appearance of electronic-like band as well as Kondo-like term in the resistivity. In both cases the essential decrease in charge carrier concentration under influence of the magnetic field is observed.

Quasi-dynamic structural disorder induced by fast neutrons in Be3Al2Si6O18 crystals

The UV absorption spectra of beryl crystals exposed to fast neutrons with a fluence of 1014–1019 cm−2 are investigated. It is found that as the fluence of particles increases, a characteristic fan-shaped broadening of the long-wavelength edge is observed for the impurity adsorption band with a charge transfer. The experimental results are interpreted on the basis of the generalized Urbach rule in the approximation of an induced quasi-dynamic disorder. The effective cross section of radiation-induced lattice disordering in the crystals under investigation is estimated at a value (σ=2.58×10−18 cm2) close to the neutron amorphization cross sections for other crystalline silicates.

Spin susceptibility of neutron-irradiation-disordered YBa2Cu3O6.9 in the normal and superconducting states

The spin-spin relaxation rate 63T 2 −1 of 63Cu nuclei in CuO2 layers is measured in the normal and superconducting states of the compound YBa2Cu3O6.9 (T c onset =94 K) subjected to radiation-induced disordering by a fast-neutron flux Φ to T c onset =68 K (Φ=7×1018 cm−2) and T c onset <4 K (Φ=12×1018 cm−2). It is found that as the structural disorder increases, the contribution of the indirect spin-spin interaction 63T 2G −1 , which is related to the value of the spin susceptibility at the boundary of the Brillouin zone of the copper planes χs(q={π/a; π/a}), decreases slightly at the transition to the superconducting state for the initial sample and remains unchanged for the weakly disordered sample. This behavior of the short-wavelength contribution to the spin susceptibility attests to the stability of the x2−y2 symmetry of the energy gap against structural disorder, in accordance with proposed theoretical models of Cooper pairing for high-Tc cuprates.

Quantitative examination of radiation-induced disordering in precipitates with a cooled CCD camera attached to a TEM

A cooled CCD camera system attached to a TEM was successfully developed for the first time in order to detect electron diffraction intensity precisely for quantitative examination of radiation-induced disordering. Precipitation of γ' (Ni 3Ti) occurred after long time (3000–8000 h) aging at 600–700°C except near grain boundaries in an Fe-25Ni-15Cr-0.95Ti-0.02C alloy. After 150 keV proton irradiation to 30 dpa at 650°C, voids were formed preferentially in the γ'-depleted zone in the specimen aged at 650°C. In the coarse γ' precipitates of 600 nm in diameter formed after aging at 700°C for 8000 h, intensity ratio of superlattice [100] to fundamental [200] reflection decreased from 0.339 to 0.082 by the irradiation. In the specimens aged at temperatures lower than 650°C, fine γ' (Ni 3Ti) precipitates of less than 19 nm in diameter were formed, and small peaks were observed at the superlattice reflection position in the unirradiated specimens, but no peaks were observed in the irradiated specimens.