Effects Of Radiation-induced Defects Research Articles

Radiation-induced segregation at grain boundaries of alloy 800H: Experimentally-informed atomistic simulations

The irradiation of alloys can alter the spatial distribution of solute and impurity elements. The redistribution of alloying elements can cause local chemical changes at surfaces and interfaces, which may degrade the mechanical and chemical properties of alloys. In this paper, a combination of microscopic experiments and atomistic simulations are employed to study the effect of irradiation damage on radiation-induced segregation (RIS) at grain boundaries (GBs) of the alloy 800H. The grain boundary character distribution in alloy 800H was determined by electron backscatter diffraction, and proton-irradiation-induced defects were identified by transmission electron microscopy. The experimentally-observed GBs were recreated in atomistic simulations to further study their atomistic structure, grain boundary energies, and local element concentration. The effects of radiation-induced defects on the redistribution of alloying elements at various GBs were investigated. A mechanism is proposed to explain the local chemical changes at GBs after the interaction with radiation-induced dislocation loops, which is of importance to nuclear reactor performance.

Effects of Radiation-Induced Defects on Corrosion

The next generation of nuclear reactors will expose materials to conditions that, in some cases, are even more extreme than those in current fission reactors, inevitably leading to new materials science challenges. Radiation-induced damage and corrosion are two key phenomena that must be understood both independently and synergistically, but their interactions are often convoluted. In the light water reactor community, a tremendous amount of work has been done to illuminate irradiation-corrosion effects, and similar efforts are under way for heavy liquid metal and molten salt environments. While certain effects, such as radiolysis and irradiation-assisted stress corrosion cracking, are reasonably well established, the basic science of how irradiation-induced defects in the base material and the corrosion layer influence the corrosion process still presents many unanswered questions. In this review, we summarize the work that has been done to understand these coupled extremes, highlight the complex nature of this problem, and identify key knowledge gaps.

Effect of Radiation-Induced Defects Produced by Low-Energy Protons in a Heavily Doped Layer on the Characteristics of n+‒p‒p+ Si Structures

The irradiation of semiconductor structures with low-energy protons is used to control changes in their properties at a depth ranging from 0.1 to 1000 μm. Devices manufactured from such structures have high sensitivities to changes in the state of the surface region. The paper is dedicated to studying the effect of radiation-induced defects produced by low-energy protons in a heavily doped diffusion region on the properties of Si structures with an n+‒p junction. The structures are irradiated with a flux of protons with an energy of 40 keV and a dose of 1015 cm−2 at a sample temperature of 83 and 300 K. The distributions of the average number of interstitial Si, vacancies, and divacancies produced by one proton under these conditions per length unit of the projective range in the diffusion layer of an n+‒p junction are calculated. It is shown that the number of radiation-induced defects in the distribution maximum at a depth of 0.39 μm in a layer with n-type conductivity at a sample irradiation temperature of 83 K is significantly less than that at 300 K. This conclusion is confirmed by the results of studies of electrophysical and optical properties of irradiated n+‒p‒p+ structures.

Defect-induced change of temperature-dependent elastic constants in BCC iron

The effects of radiation-induced defects (randomly distributed vacancies, voids, and interstitial dislocation loops) on temperature-dependent elastic constants, C11, C12, and C44 in BCC iron, are studied with molecular dynamics method. The elastic constants are found to decrease with increasing temperatures for all cases containing different defects. The presence of vacancies, voids, or interstitial loops further decreases the elastic constants. For a given number of point defects, the randomly distributed vacancies show the strongest effect compared to voids or interstitial loops. All these results are expected to provide useful information to combine with experimental results for further understanding of radiation damage.

Effects of Channel Implant Variation on Radiation-Induced Edge Leakage Currents in n-Channel MOSFETs

The effects of radiation-induced defects and statistical variation in the dose and energy of MOSFET channel implants in a modern bulk CMOS technology are modeled using a process simulator in combination with analytical computations. The model integrates doping profiles obtained from process simulations and experimentally determined defect potentials into implicit surface potential equations. Solutions to these equations are used to model radiation-induced edge leakage currents in 90-nm bulk CMOS n-channel MOSFETs. The results indicate that slight variations in the channel implant parameters can have a significant impact on the doping profile along the shallow trench isolation sidewall and thus the radiation-induced edge leakage currents.

The separation effect of radiation-induced defects in nickel

Pure nickel, the model material for austenitic steels used in reactors, with an electrical resistivity ratio of ρ300 K/ρ4.2 K ~ 300 has been investigated under electron and neutron irradiation at TIRR ~ 320-340 K. Three of its states have been subjected to irradiation: a recrystallized state at 873 K, a deformed one to 90%, and an annealed one at 450 K after deformation to remove deformationinduced vacancies. It is has been experimentally shown that neutron and electron irradiation of the deformed nickel results in the sepa� ration of radiationinduced defects. This separation occurs because a significant portion of the radia� tioninduced interstitial atoms is captured by disloc ation sinks and does not participate in recombina� tion with vacancies. As a result, the concentration of accumulated vacancies in the deformed nickel can exceed their concentration in the annealed nickel and be almost twice as high. At higher doses of neutron irradiation, above 10 18 cm -2 , separation does not occur, since vacancy sinks in the form of clusters are more powerful than dislocation sinks.

1005 照射欠陥の機械的特性への影響に関する原子論的検討(OS10. 電子・原子・マルチシミュレーションに基づく材料特性評価(1),オーガナイズドセッション講演)

原子炉における炉心シュラウドや圧力容器では,中性子照射によって照射損傷が導入され材料の硬化や脆化を引き起こす.本研究では,原子論的手法を用いて不純物原子の偏析,格子間原子・空孔型の凝集による照射欠陥ループ等の原子力材料特有の照射欠陥の機械的特性に与える影響について検討する.

Effects of radiation-induced defects on microstructural evolution of Fe–Cr model alloys

We investigate the role of radiation-induced defects in the microstructural evolution of Fe–Cr model alloys with two approaches; a positron annihilation measurement and computer simulations. We prepared Fe–Cr model alloys with different Cr contents which were irradiated with 2 MeV-electrons at the JAEA accelerator at Takasaki in Japan. The production of vacancy-type defects was verified by positron annihilation lifetime spectroscopy. The average positron lifetimes of the irradiated samples were increased by about 14% when compared to the unirradiated one. The ratio curves, derived from a Doppler broadening measurement, did not reveal a prominent change between the irradiated pure Fe and Fe–Cr alloys, which implies that there was no formation of a vacancy-Cr complex. We performed computer simulations by using the Metropolis Monte Carlo method to predict a possible microstructure composed of Cr and vacancies. As expected, the simulation also revealed that no vacancy-Cr complexes were formed. Both results support a small amount of radiation-induced swelling in the Fe–Cr alloys.

Effect of radiation-induced defects on the dielectric response of lead scandoniobate ferroelectric ceramics

The effect of ionizing gamma irradiation on the frequency and temperature dependences of the permittivity e’(T) for lead scandoniobate relaxor (disordered) ferroelectric ceramics before and after thermal annealing was investigated by low-and infralow-frequency dielectric spectroscopy. It was demonstrated that the irradiation leads to a shift in the temperatures of the maxima in the dependence e’(T) and the temperatures of the maxima in the dependence of the dispersion depth Δe’(T) toward the high-temperature range, as well as to the suppression of high-temperature (∼ 300–400°C) polarization relaxation. After annealing at a temperature T ∼ 600°C, the properties of the material were partially recovered.

Effects of radiation-induced defects on device performance in electron-irradiated SiC-MESFETs

The impact of radiation damage on the device performance of 4H-SiC metal semiconductor field effect transistors (MESFETs), which are irradiated at room temperature with 2-MeV electrons and 20-MeV protons, is studied. Different degradation behaviour with increasing fluence is observed for electron and proton irradiation. The degradation for low electron fluence is mainly attributed to the radiation-induced decrease of the Schottky barrier height at the gate contact. While no electron capture levels are observed before irradiation, three electron capture levels (E 1, E 2 and E 3) are induced after irradiation. The observed increase of the channel resistance is due to the induced lattice defects creating electron traps.

Test structures for analyzing proton radiation effects in bipolar technologies

Structures integrated onto BiCMOS test chips were specially designed to characterize the complex mechanisms related to radiation effects in bipolar technologies. Bipolar devices from two commercial processes were modified to include independent gate terminals. Through the use of gate control, the effects of radiation-induced defects on discrete bipolar devices and analog bipolar circuits can be analyzed independently, thereby facilitating a quantitative, experimentally verified, description of the non-linear relationship between the radiation defects and electrical response at both the device and circuit level.

Effect of radiation-induced defects on silicon solar cells

Recent experiments indicated an anomalous degradation of n+–p–p+ silicon space solar cells irradiated with high-energy protons or electrons. Several models have been proposed, which assumes that radiation-induced defects are responsible for the degradation. The effect of the radiation-induced deep defects with energy levels Ec−0.17, Ec−0.1, Ec−0.43, and Ev+0.36 eV on solar cells is studied in this article. It is shown that among these defects only the defect with energy level Ec−0.1 eV causes the anomalous degradation, when the base thickness W is approximately 250 μm.

The effects of radiation-induced defects on H + transport in SiO 2

The effects of radiation on H + transport in buried oxides have been studied. Mobile H + was introduced into the buried oxides in SIMOX and Unibond by hydrogen annealing. The position of the H + centroid was monitored by rapid point-contact transistor measurements. After irradiation, H + transit across the oxide is significantly slower. The concentration of mobile H + in the oxide remains nearly the same after irradiation. The significance of these findings to the contradictions between the radiation and hydrogen-annealing models are discussed.

X-ray irradiation as an improvement technique for oxygen ordering and enrichment of YBa2Cu3O7 − x single crystals

The effects of X-ray irradiation on as-grown YBa2Cu3O7 − x single crystals were investigated, in order to test the effects of radiation-induced defects during the subsequent annealing in O2, and to verify if short-circuits for diffusion could be provided that improve the oxygen enrichment of the specimens. X-ray irradiation was found to have a favourable effect on the homogeneity of the oxygen enrichment of the samples, as stated by the high reproducibility of resistance measurements carried out on specimens grown, irradiated and annealed under the same conditions. Even if X-ray irradiation seems unable to determine a significant reduction of the time needed for annealing, and it could not consequently be regarded as a totally resolutive step during the production of high-quality monocrystalline superconductors, the observed homogenization of lattice oxygen distribution seems to be exploitable.