Room Temperature Irradiation Research Articles

Effects of tensile stress on Cu clustering in irradiated Fe–Cu alloy

Effects of tensile stress on Cu clustering were explained using atom probe tomography (APT) results of Fe–0.6wt.%Cu alloy specimens irradiated with 6.4MeV Fe ions while applying a tensile stress of 60MPa at room temperature (less than 50°C) and 290°C. The hardening under the tensile-stressed irradiation was smaller than that under the stress-free irradiation at both room temperature and 290°C. APT results showed that well-defined Cu clusters were formed in all specimens even under the room temperature irradiation. The Cu clusters under the tensile-stressed condition were smaller and had higher densities than those under the stress-free condition. The lower Cu content in clusters and more diffuse Cu clustering were obtained for the specimens irradiated under the tensile-stressed condition. The hardening efficiency of Cu clusters was correlated with the Cu content in clusters and the coherency of interface between a cluster and the matrix. Application of tensile stress would control hardening by changing the nature of Cu clusters.

TEMPERATURE EFFECT OF Xe ION IRRADIATION TO 316 AUSTENITIC STAINLESS STEEL

Molten Salt Reactors (MSR) is one of the six most promising Generation IV fission reactors. In the ultimate goals, MSR should run at temperatures over 1000 K, and its neutron irradiation damage doses could reach 100 dpa or more for the core components. Hence, the evaluation of irradiation damage under high temperature for structural materials is of particular importance for ensuring the safe operation of MSR. It is generally accepted the structural materials used for MSR should be Ni-based alloys, especially the Hastelloy N alloy. Recently, the 316 austenitic stainless steel (316SS) was considered as a candidate structural material for MSR. In this study, bulk and TEM specimens of 316SS have been characterized by nanoindentation and TEM to determine the change of microhardness and microstructural evolution after 7 MeV Xe26+ and 1 MeV Xe20+ iron irradiation, respectively. The irradiation experiments were carried out at room temperature (about 22 degrees C) and 600 degrees C, and the ion fluences correspond to calculated peak damge dose of 0.62 and 3.7 dpa. The nanoindentation results for bulk specimens showed the irradiation induced hardening of 316SS irradiated at room temperature, and the hardenability increases with increasing ion damage dose. However, in the case of the irradiation at 600 degrees C, the hardness of 316SS keep the same level with that of the unirradiated specimen. The recovery of irradiation induced hardening occurred at 600 degrees C compared with the room temperature irradiation. The TEM results showed that the presence of high number density of nanoscale dislocation loops, with the diameter of 3 similar to 8 nm, in 316SS irradiated at room temperature. The number density of these dislocation loops increase with the increase of ion damage dose. As far as the irradiated 316SS under 600 degrees C, several solute clusters were observed with the size range from 4 to 12 nm, which a little larger than the dislocation loops. It should be noted that the number density is far smaller than that of the dislocation loops in former case. The radiation induced defects (dislocation loops, solute clusters) were believed to be responsible for the hardening in 316SS. The temperature effect of Xe ion irradiation to 316SS was discussed using the Orowan mechanism. The stronger diffusion of point defects caused by ion implantation at 600 degrees C was considered to be the main reason for the recovery of irradiation induced hardening, in which the vacancies and interstitials have greater probability for recombination and then disappear, resulting in the exiguous nucleation sites for the formation of solute clusters.

60 keV Ar+-ion induced modification of microstructural, compositional, and vibrational properties of InSb

Room temperature irradiation of InSb(111) by 60 keV Ar+-ions at normal (0°) and oblique (60°) angles of incidence led to the formation of nanoporous structure in the high fluence regime of 1 × 1017 to 3 × 1018 ions cm−2. While a porous layer comprising of a network of interconnected nanofibers was generated by normal ion incidence, evolution of plate-like structures was observed for obliquely incident ions. Systematic studies of composition and structure using energy dispersive x-ray spectroscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, Raman mapping, grazing incidence x-ray diffraction, and cross-sectional transmission electron microscopy revealed a high degree of oxidation of the ion-induced microstructures with the presence of In2O3 and Sb2O3 phases and presence of nanocrystallites within the nanoporous structures. The observed structural evolution was understood in terms of processes driven by ion-induced defect accumulation within InSb.

In-situ high temperature irradiation setup for temperature dependent structural studies of materials under swift heavy ion irradiation

An in-situ high temperature (1000K) setup is designed and installed in the materials science beam line of superconducting linear accelerator at the Inter-University Accelerator Centre (IUAC) for temperature dependent ion irradiation studies on the materials exposed with swift heavy ion (SHI) irradiation. The Gd2Ti2O7 pyrochlore is irradiated using 120MeV Au ion at 1000K using the high temperature irradiation facility and characterized by ex-situ X-ray diffraction (XRD). Another set of Gd2Ti2O7 samples are irradiated with the same ion beam parameter at 300K and simultaneously characterized using in-situ XRD available in same beam line. The XRD studies along with the Raman spectroscopic investigations reveal that the structural modification induced by the ion irradiation is strongly dependent on the temperature of the sample. The Gd2Ti2O7 is readily amorphized at an ion fluence 6×1012ions/cm2 on irradiation at 300K, whereas it is transformed to a radiation-resistant anion-deficient fluorite structure on high temperature irradiation, that amorphized at ion fluence higher than 1×1013ions/cm2. The temperature dependent ion irradiation studies showed that the ion fluence required to cause amorphization at 1000K irradiation is significantly higher than that required at room temperature irradiation. In addition to testing the efficiency of the in-situ high temperature irradiation facility, the present study establishes that the radiation stability of the pyrochlore is enhanced at higher temperatures.

Mechanical properties of acellular mouse lungs after sterilization by gamma irradiation

Lung bioengineering using decellularized organ scaffolds is a potential alternative for lung transplantation. Clinical application will require donor scaffold sterilization. As gamma-irradiation is a conventional method for sterilizing tissue preparations for clinical application, the aim of this study was to evaluate the effects of lung scaffold sterilization by gamma irradiation on the mechanical properties of the acellular lung when subjected to the artificial ventilation maneuvers typical within bioreactors. Twenty-six mouse lungs were decellularized by a sodium dodecyl sulfate detergent protocol. Eight lungs were used as controls and 18 of them were submitted to a 31kGy gamma irradiation sterilization process (9 kept frozen in dry ice and 9 at room temperature). Mechanical properties of acellular lungs were measured before and after irradiation. Lung resistance (RL) and elastance (EL) were computed by linear regression fitting of recorded signals during mechanical ventilation (tracheal pressure, flow and volume). Static (Est) and dynamic (Edyn) elastances were obtained by the end-inspiratory occlusion method. After irradiation lungs presented higher values of resistance and elastance than before irradiation: RL increased by 41.1% (room temperature irradiation) and 32.8% (frozen irradiation) and EL increased by 41.8% (room temperature irradiation) and 31.8% (frozen irradiation). Similar increases were induced by irradiation in Est and Edyn. Scanning electron microscopy showed slight structural changes after irradiation, particularly those kept frozen. Sterilization by gamma irradiation at a conventional dose to ensure sterilization modifies acellular lung mechanics, with potential implications for lung bioengineering.

Using Low Temperature Irradiation for ELDRS Estimation

The technique for low dose rate response prediction, based on the combination of low, room and elevated temperature irradiation was described. The possibility of using Test Method 1019.8 for space applications was considered.

Microstructure evolution in Xe-irradiated UO2 at room temperature

In situ Transmission Electron Microscopy was conducted for single crystal UO2 to understand the microstructure evolution during 300keVXe irradiation at room temperature. The dislocation microstructure evolution was shown to occur as nucleation and growth of dislocation loops at low irradiation doses, followed by transformation to extended dislocation segments and tangles at higher doses. Xe bubbles with dimensions of 1–2nm were observed after room-temperature irradiation. Electron Energy Loss Spectroscopy indicated that UO2 remained stoichiometric under room temperature Xe irradiation.

Microstructure and thermal desorption of deuterium in heavy-ion-irradiated pure tungsten

To understand the fundamental processes of deuterium retention and desorption of irradiated plasma facing materials, thermal desorption of deuterium in pure W with and without ion irradiation up to 2dpa by 2.4MeV Cu2+ have been investigated. After the ion irradiation at room temperature, high density of small interstitial typed dislocation loops and also nano-voids due to cascade collisions were detected by TEM observation. Thermal desorption of spectra of D showed that fine vacancy clusters are formed even at low fluence and at room temperature irradiation, these defects act as the strong trapping center of deuterium in the temperature range of 660–900K.

In situ creep measurements on micropillar samples during heavy ion irradiation

We report on the development of an in situ micropillar compression apparatus capable of measuring creep under heavy ion beam irradiation. The apparatus has a force resolution of 1μN and a displacement resolution of 1nm. The experimental setup consists of a nanopositioner, a laser displacement sensor, and a microfabricated doubly clamped silicon-beam transducer. The system was tested by measuring the creep rate of amorphous Cu56Ti38Ag6 micropillars as a function of applied stress during room temperature irradiation with 2.1MeV Ne+. Measured values of the irradiation induced fluidity are in the range 0.5–3dpa−1GPa−1, and in good agreement with values obtained by stress relaxation experiments on other metallic glasses, and with predictions of molecular dynamics simulations. The in situ apparatus provides a practical approach for accelerated evaluation of irradiation induced creep in promising nuclear materials.

The role of helium implantation induced vacancy defect on hardening of tungsten

Vacancy-type defects created by helium implantation in tungsten and their impact on the nano-hardness characteristics were investigated by correlating the results from the positron annihilation spectroscopy and the nano-indentation technique. Helium implantation was performed at room temperature (RT) and at an elevated temperate of 600 °C. Also, the effect of post-annealing of the RT implanted sample was studied. The S parameter characterizing the open volume in the material was found to increase after helium irradiation and is significantly enhanced for the samples thermally treated at 600 °C either by irradiation at high temperature or by post-annealing. Two types of helium-vacancy defects were detected after helium irradiation; small defects with high helium-to-vacancy ratio (low S parameter) for RT irradiation and large defects with low helium-to-vacancy ratio (high S parameter) for thermally treated tungsten. The hardness of the heat treated tungsten coincides with the S parameter, and hence is controlled by the large helium-vacancy defects. The hardness of tungsten irradiated at RT without thermal treatment is dominated by manufacturing related defects such as dislocation loops and impurity clusters and additionally by trapped He atoms from irradiation effects, which enhance hardness. He-stabilized dislocation loops mainly cause the very high hardness values in RT irradiated samples without post-annealing.

Temporal evolution of nanoporous layer in off-normally ion irradiated GaSb

Room temperature irradiation of GaSb by 60 keV Ar+-ions at an oblique incidence of 60° leads to simultaneous formation of a nanoporous layer and undulations at the interface with the underlying substrate. Interestingly, with increasing ion fluence, a gradual embedding of the dense nanoporous layer takes place below ridge-like structures (up to the fluence of 1 × 1017 ions cm−2), which get extended to form a continuous layer (at fluences ≥4 × 1017 ions cm−2). Systematic compositional analyses reveal the co-existence of Ga2O3 and Sb2O3 in the surface layer. The results are discussed in terms of a competition between ion-induced defect accumulation and re-deposition of sputtered atoms on the surface.

Use of Ultrasound and Microwave Irradiation for Clean and Efficient Synthesis of 3,3’-(Arylmethylene)bis (2-hydroxynaphthalene-1,4-dione) Derivatives

Nine 3,3’-(arylmethylene)bis(2-hydroxynaphthalene-1,4-dione) derivatives were synthesized through the reaction between 2-hydroxy-1,4-naphthalen-1,4-dione and different aromatic alde-hydes in water applying ultrasonic irradiation for 5 min at room temperature and microwave irradiation for 15 min at 70°;C. Two of the nine derivatives, compounds 3-e and 3-i, obtained from 3-bromo-hydroxybenzaldehyde and 5-methylfuran-2-carbaldehyde, respectively, are previously unpublished. The structures of all compounds were established on the basis of their spectral data and mass analysis. The attractive features of this synthesis protocol include mild conditions, high atom-economy and excellent yields with the elimination of water as the only by-product.

Photochemical studies of (η5-C5H5)Ru(PPh3)2Cl and (η5-C5H5)Ru(PPh3)2Me: formation of Si–H and C–H bond activation products

Studies examining the photochemical reactivity of CpRu(PPh3)2Cl and CpRu(PPh3)2Me towards the two electron donor ligands PEt3, C2H4, DMSO, the CH bond activatable reagents tetrahydrofuran, toluene, and pyridine, and the SiH bond activatable reagents HSiEt3 and HSi(Me)2CH=CH2) are presented. Broadband UV irradiation of CpRu(PPh3)2Cl leads to the formation of mono-substitution products such as CpRu(PPh3)(PEt3)Cl which are inert to further photochemical reaction, although thermally bis-substituted products such as CpRu(PEt3)2Cl can be formed. Room temperature irradiation of the related complex CpRu(PPh3)2Me with L = PEt3, C2H4, and DMSO also produces CpRu(PPh3)(L)Me. However, when these reactions are followed by in situ laser irradiation (325 nm source) at low temperature, three solvent activated isomers (ortho, meta and para) of CpRu(PPh3)2(C6H4Me) are detected in toluene in addition to η(1)- and η(3)-coordinated benzyl species. Furthermore, photolysis in THF leads to both the C-D bond activation product CpRu(PPh3)2(OC4D7) and the labile coordination complex CpRu(PPh3)(THF)Me. Now CH4 rather than CH3D is liberated which suggests the involvement of an orthometallated species. The photochemically driven reaction of CpRu(PPh3)2Me with HSiEt3 at 198 K generates CpRu(κ(2)-2-C6H4PPh2)(SiEt3)H and thereby confirms a role for an orthometallated complex is this process. Irradiation in cyclohexane produces the known orthometallated complex, CpRu(κ(2)-2-C6H4PPh2)(PPh3), and CH4 in accordance with this reactivity.

Porous structure formation in ion irradiated germanium

The ion beam induced modification of amorphous germanium is characterised by the formation of voids close to the sample surface and the transformation into a sponge-like porous surface layer at high ion fluences. This extreme structural modification of the sample surface is independent of the (heavy) ion species used and accompanied by a strong volume expansion. Nevertheless, recently it was demonstrated that buried voids (and buried sponge-like layers) can be formed in the depth of the projected ion range, however, only for the irradiation with I-ions at high ion fluences. Thus, the ion species and their chemical properties seem to play an important role in the structural modification around the projected ion range. In this paper we investigate the influence of the ion species on the ion beam induced void formation in Ge for room temperature irradiation with 380keV I- and Au-ions as a function of the ion fluence. Independent of the ion species, a strong volume expansion is observed caused by void formation and the transformation into a sponge-like porous surface layer. For both ion species used, the final porous layers are structurally identical as established by cross section and plan view electron microscopy investigations. Further ion irradiation of the sponge-like porous structure, however, leads to significant differences in the ion beam induced structural evolution. For the Au-ion irradiation the porous layer remains nearly unchanged, whereas for the irradiation with I-ions a transformation from sponge-like to netlike porous layers occurs which is accompanied again by an extreme volume expansion. The underlying mechanism will be discussed based on chemical properties of the implanted ions.

Evaluation of Mechanical Properties Variations for Kr Ion‐Irradiated 6H‐SiC by Nanoindentation Methods

Nanoindentation experiments were performed to investigate the irradiation effects on the mechanical properties of 6H‐SiC irradiated by 4 MeV Kr ions at high fluences from room temperature (RT) to 550°C. The irradiation temperature is the primary factor that affects modifications of the comprehensive mechanical properties, while the effect of the fluence is less significant. Elastic modulus and hardness decrease drastically for RT‐irradiated samples, but they almost recover for elevated temperature samples, with hardness slightly higher than its original value. The hardness increases first and then decreases with increasing temperature, and the elastic modulus decreases linearly as the swelling increases. Meyer's index is related to the indentation size effect of hardness and the magnitude of the lattice damage. The ratio of irreversible work is associated with the degree of elastic recovery and the ratio of hardness to elastic modulus of SiC. Compared with the unirradiated value, fracture toughness changes slightly for RT irradiation, while increasing significantly for elevated temperature irradiation and has the same variation tendency of hardness. Results indicate that mechanical properties change with the variations of interatomic bond strength, dislocation mobility, and the behavior of crack propagation, which is strongly affected by the defects induced by heavy‐ion irradiation.

Irradiation-induced selective precipitation in Cu–Nb–W alloys: An approach towards coarsening resistance

A novel approach towards coarsening resistance in the precipitate-strengthened Cu-based alloys is proposed, taking advantage of selective precipitation during low-temperature ion irradiation. In the case of Cu–Nb–W, W precipitates during room temperature irradiation, forming highly ramified clusters. During subsequent thermal annealing of alloys with composition close to Cu90Nb9W1, the more mobile Nb atoms precipitate out on the W clusters, creating a core–shell structure and adopting the Bain orientation relationship within the Cu matrix. This structure is extremely resistant to coarsening. Annealing at 650°C for 1h results in a precipitates size <4nm in diameter, and annealing for an additional 9h causes no additional growth, even though Nb is highly mobile at this temperature and would coarsen in the absence of W. We attribute the remarkable stability of this precipitate structure to the strong immiscibility of W in Cu and to the highly ramified precipitate structure that W acquires during low-temperature irradiation.

Ion-irradiation enhancement of materials degradation in Fe–Cr single crystals detected by magnetic technique

Single crystalline Fe–20%Cr film was prepared using a molecular beam epitaxy technique, and 2.4MeV Cu2+ ion-irradiation was subsequently carried out at room temperature and at 748K. Magnetic hysteresis measurement and magnetic domain observation showed that room-temperature irradiation did not have a large effect on the magnetic properties of Fe–20%Cr films. However, irradiation at 748K caused a significant magnetic hardening and a drastic change in domain structures. It is assumed that the domain characteristics reflect the formation of chromium-rich precipitates due to the phase separation accelerated by irradiation. This study demonstrates the feasibility of nondestructive magnetic techniques for evaluating the materials degradation of Fe–Cr alloys under the irradiation environment.

Total Dose Effects on Bipolar Integrated Circuits at Low Temperature

Total dose damage in bipolar integrated circuits is investigated at low temperature, along with the temperature dependence of the electrical parameters of internal transistors. Bandgap narrowing causes the gain of npn transistors to decrease far more at low temperature compared to pnp transistors, due to the large difference in emitter doping concentration. When irradiations are done at temperatures of -138°C, no damage occurs until devices are warmed to temperatures above -50°C. After warm-up, subsequent cooling shows that damage is then present at low temperature, although it is much less than for room temperature irradiation. This can be explained by the temperature dependence of dispersive transport in the continuous-time-random-walk model, along with the reduction in charge yield at low temperature. For linear integrated circuits, low temperature operation is affected by the strong temperature dependence of npn transistors along with the higher sensitivity of lateral and substrate pnp transistors to radiation damage.

Long range lateral migration of intrinsic point defects in n-type 4H-SiC

The lateral distributions of intrinsic point defects in n-type (0001) 4H-SiC have been investigated following room temperature irradiation with a focused beam of 10 keV protons. Laterally resolved deep level transient spectroscopy measurements reveal that the well-known and prominent Z1/2 and S1/2 centers display lateral diffusion lenghts on the order of 1 mm with negligible (if any) motion parallel to the direction of the c-axis. The migration occurs only in the presence of excess charge carriers generated during the proton irradiation, and no further motion takes place even under subsequent optical excitation of high intensity. Assuming one-dimensional geometry, an effective defect diffusivity in excess of 10−6 cm2/s is deduced by numerical modelling of the experimental data, corresponding to an energy barrier for migration of ∼0.2 eV. Possible mechanisms for the rapid migration, invoking charge carrier recombination as a necessary condition, are discussed, and especially, an association with the glide of partial dislocations along the (0001) basal plane is scrutinized in some detail.

Effect of H and He irradiation on cavity formation and blistering in ceramics

Single- or poly-crystalline specimens of SiC, Si3N4, MgO, Al2O3 and MgAl2O4 were implanted with 0.4–1MeV H+ or He+ ion beams at room temperature and 650°C up to fluences of ∼1×1022/m2. This produced peak implanted gas and displacement damage levels as high as ∼50at.% and 34 displacements per atom (dpa). The specimens were subsequently examined optically, and in cross-section using transmission electron microscopy. Subsurface blistering occurred for specimens irradiated to H or He fluences greater than about 3×1021/m2 (∼15at.% peak implanted gas concentration), and surface exfoliation occurred for fluences above ∼1×1022/m2 (∼40at.% implanted gas). Both helium and hydrogen had comparable effectiveness for inducing blistering and exfoliation on an atomic basis. The threshold blistering and exfoliation fluences for both ions were weakly dependent on temperature between 25 and 650°C. Both H and He were found to be very effective in inducing matrix cavity formation, due to their low solubility in these ceramics. The implanted gas concentrations that resulted in visible cavity formation generally ranged from 1 to 5at.%. Visible cavity formation was readily induced during room temperature irradiation despite the limited vacancy mobility in these ceramics at room temperature. Three general types of cavity morphologies were observed: isolated cavities, clusters of small cavities (typically associated with dislocation loops), and two-dimensional platelets. Cavity formation was observed to initiate at the periphery of dislocation loops in some cases. During elevated temperature irradiation, cavity formation was often observed to be preferentially associated with certain low-index habit planes, particularly if the habit plane was oriented nearly parallel to the irradiated surface: (0001) and {11¯00} for Al2O3, (0001) for α–SiC, {001} and {110} for MgO, and {110} and {111} for MgAl2O4. The bubble formation and blistering behavior of the ceramics was similar to that observed in other studies of metals irradiated at comparable homologous temperatures. Ionization-induced diffusion effects associated with dual-beam light ion irradiation appeared to exert only a weak effect on cavity and dislocation loop growth compared to the single ion irradiation conditions.