Proton-irradiated Samples Research Articles

A study on initial formation stage of proton irradiation defects in reactor pressure vessel steel

The irradiation effect of a reactor pressure vessel (RPV) steel subjected to the proton irradiation with a dose of approximately 1 dpa and an energy of 240 keV at room temperature is investigated using the internal friction (IF) method. An evident IF relaxation peak at 357 °C has been detected in the proton-irradiated RPV sample but not in the as-received RPV sample. Based on theoretical analysis and experimental results in the references, this IF peak is believed to be associated with the formation of carbon-vacancy complexes (CmVn, specifically 4C2V-type). The gradual disappearance of the IF peak in the second and third IF heating spectra up to 400 °C indicates the dissolution of the proton-irradiation-induced CmVn complexes. Nanoindentation measurements and X-ray diffraction (XRD) strain analysis show the corresponding changes similar to the results of the IF measurement. The current study promotes an understanding of the influence of irradiation-induced CmVn complexes on the irradiation-induced hardening mechanism of the RPV steel, particularly during the initial formatiom stage of irradiation defects.

Towards a precise measurement of 157Tb nuclear decay data: Sample purification using resonance ionization mass spectrometry

In nuclear physics, 157Tb emerges as a prime candidate for experiments aimed at elucidating neutrino mass constraints and at searching for sterile neutrinos. Despite its importance, 157Tb exhibits highly uncertain values for its nuclear decay properties. A significant challenge in many efforts to measure such data lies in the simultaneous undesired presence of 158Tb in the samples, which hinders precise activity determination. Mass separation emerges as a crucial method for obtaining pure 157Tb specimens. This work outlines the production of an isotopically-pure 157Tb sample through mass separation and ion implantation, using the RISIKO facility at the University of Mainz. The initial material was obtained from proton-irradiated Ta samples through radiochemical separation at the Paul Scherrer Institute. In total, a sample containing 8.7(9) · 1012 atoms of 157Tb was obtained. The efficiency of the mass separation and ion implantation was 13(2) %. The purified material served as the basis for new research endeavors at the Physikalisch Technische Bundesanstalt Braunschweig aiming at the determination of nuclear data for 157Tb with significantly improved precision.

A spatially resolved analysis of dislocation loop and nanohardness evolution in proton irradiated Zircaloys

Proton irradiation is increasingly used as a surrogate for neutron irradiation, providing similar damage structures at significantly lower costs and less time compared to neutron irradiation. However, in contrast to neutrons, protons produce a depth dependent damage profile that incorporates a plateau region and a Bragg peak in the tens of microns region depending on the material and proton energy. Here we demonstrate that this depth dependent damage can be utilised to obtain new understanding about irradiation induced damage at different dose levels from a single sample by combining spatially resolved micro-beam synchrotron X-ray diffraction-based dislocation analysis and nanoindentation. For this purpose, and to study the damage evolution starting from very early stages, we have investigated microstructure evolution and hardening behaviour of Zircaloy-2 and Zircaloy-4 proton irradiated samples between 0.01 dpa and 17 dpa at 350 °C. The results highlight good agreements of SRIM-based damage depth predictions with irradiation-induced dislocation appearance and nanohardness. However, at even relatively low damage levels within the plateau region, dislocation line density and nanohardness profiles appear saturated across the entire irradiated region, even when the dpa levels differed significantly. When relating dislocation loop line densities to nanohardness, it was found that from a certain point hardness increased only very slightly with increasing line densities. This apparent discrepancy can be explained by a decreasing loop size for the highest line densities identified by from the diffraction line profile analysis and the application of a Dispersed Barrier Hardening model that relates obstacle strength to dislocation loop size.

High precision half-life measurement of the extinct radio-lanthanide Dysprosium-154

Sixty years after the discovery of 154Dy, the half-life of this pure alpha-emitter was re-measured. 154Dy was radiochemically separated from proton-irradiated tantalum samples. Sector field- and multicollector-inductively coupled plasma mass spectrometry were used to determine the amount of 154Dy retrieved. The disintegration rate of the radio-lanthanide was measured by means of α-spectrometry. The half-life value was determined as (1.40 ± 0.08)∙106 y, with an uncertainty reduced by a factor of ~ 10 compared to the currently adopted value of (3.0 ± 1.5)∙106 y. This precise half-life value is useful for the the correct testing and evaluation of p-process nucleosynthetic models using 154Dy as a seed nucleus or as a reaction product, as well as for the safe disposal of irradiated target material from accelerator driven facilities. As a first application of the half-life value determined in this work, the excitation functions for the production of 154Dy in proton-irradiated Ta, Pb, and W targets were re-evaluated, which are now in agreement with theoretical calculations.

Simultaneous irradiation and thermal effects on 16 MeV proton irradiated tungsten samples

16 MeV protons have been used to irradiate 300 μm thick macroscopic W samples in a pilot experiment to 0.006 dpa damage dose under low and high temperature scenarios of ∼373 K and ∼1223 K, respectively. The linear pre-Bragg region has been used for damage where the electronic loss (heat) in the sample amounts to 1.5 MW · m−2. Post high-temperature irradiation, the W sample has been recrystallized as seen under the scanning electron microscope. Indentation measurements on the surface show a softening of 0.6 GPa post-recrystallization against an irradiation hardening of 0.8 GPa for the low-temperature irradiation scenario.

Critical phenomena of the layered ferrimagnet Mn3Si2Te6 following proton irradiation

The critical phenomena and magnetic entropy of the quasi-2D ferrimagnetic crystal, Mn3Si2Te6 (MST), is analyzed along the easy axis (H || ab) as a function of proton irradiance. The critical exponents β and γ do not fall into any particular universality class upon proton irradiation. However, for pristine and irradiated samples, the critical exponents lie closer to mean field-like interactions; therefore, long-range interactions are presumed to be sustained in MST. The effective spatial dimensionality reveals that MST remains at d=3 under proton irradiation, whereas spin dimensionality transitions from an initial n=1 to n=2 and n=3 for 1 × 1015 and 5 × 1015 H+/cm2, indicating XY and Heisenberg interactions, respectively. The spin correlation function reveals an increase in magnetic correlations at 5 × 1015 H+/cm2. Maximum change in magnetic entropy at 3 T is the largest for 5 × 1015 H+/cm2 at 2.45 J/kg K, in comparison to 1.60 J/kg K for pristine MST. These results intriguingly align with previous findings on MST where magnetization increased by ∼50% at 5 × 1015 H+/cm2, in comparison to its pristine counterpart [Martinez et al., Appl. Phys. Lett. 116, 172404 (2020)]. Magnetic entropy derived from heat capacity analysis shows no large deviations across the proton irradiated samples suggesting that the antiferromagnetic (AFM) coupling between the Mn sites is stable even after proton irradiation. This implies that magnetization is enhanced through a strengthening of the super-exchange interaction between Mn atoms mediated through Te rather than a weakening of the AFM component.

Growth and Characterizations of Iron-based Superconductor (Ba1-x Rb x ) Fe2As2 Single Crystals

Novel nematic states as well as remarkable superconducting properties were reported in iron-based superconductors. We synthesized high-quality single crystals of (Ba1-x Rb x )Fe2As2 close to the optimal composition of x ≈ 0.4, and have characterized normal state and superconducting properties for pristine and proton irradiated samples. The highest Tc was found to be ∼36.6 K for pristine samples. A maximum critical current density of 12 MA/cm2 was achieved in a proton irradiated sample, which is comparable to that in irradiated (Ba0.6K0.4) Fe2As2. Twin boundaries were observed optically in both non-doped and under-doped samples. We also attempted local magnetic field measurements induced by transport current in a sample with twin boundaries for future exploration of nematic states in different regions of doping.

양성자 조사가 316 스테인리스강의 미세조직과 표면산화 특성에 미치는 영향

Austenitic 316 stainless steel was irradiated with protons accelerated by an energy of 2 MeV at 360 ℃, the various defects induced by this proton irradiation were characterized with microscopic equipment. In our observations irradiation defects such as dislocations and micro-voids were clearly revealed. The typical irradiation defects observed differed according to depth, indicating the evolution of irradiation defects follows the characteristics of radiation damage profiles that depend on depth. Surface oxidation tests were conducted under the simulated primary water conditions of a pressurized water reactor (PWR) to understand the role irradiation defects play in surface oxidation behavior and also to investigate the resultant irradiation assisted stress corrosion cracking (IASCC) susceptibility that occurs after exposure to PWR primary water. We found that Cr and Fe became depleted while Ni was enriched at the grain boundary beneath the surface oxidation layer both in the non-irradiated and proton-irradiated specimens. However, the degree of Cr/Fe depletion and Ni enrichment was much higher in the proton-irradiated sample than in the non-irradiated one owing to radiation-induced segregation and the irradiation defects. The microstructural and microchemical changes induced by proton irradiation all appear to significantly increase the susceptibility of austenitic 316 stainless steel to IASCC.

Microstructural characterisation of 160 MeV oxygen irradiated niobium

ABSTRACT Microstructural changes due to 160 MeV oxygen ion irradiation on pure Nb have been characterised using X-ray Diffraction Line Profile Analyses. Microstructural parameters such as coherent domain size, microstrain within the domain and dislocation density are evaluated from the homogeneously damaged region. It is observed that the domain size decreases along with an increase in microstrain and dislocation density as a function of dose. The local changes in the microstructure have also been evaluated in terms of band contrast, mean angular deviation and local misorientation from electron backscattered diffraction data at the surface and an intermediate depth in the homogenously damaged region of selected irradiated samples and in the unirradiated sample. An increase in mean angular deviation and local misorientation is observed in the highest dose sample, which may be an indication of dislocation loop formation. Defect clusters and dislocation loops are observed using transmission electron microscopy in the highest dose sample. Microhardness measurement has also been carried out on the unirradiated and irradiated samples to correlate the microstructural changes with the mechanical property as a function of dose. It is observed that the hardness of the material increases as a function of dose due to the formation of defect clusters and dislocation loops that pin the movement of dislocations. Finally, a comparison of the microstructures in proton and heavy ion irradiated samples at approximately similar dpa-rate has been carried out to understand the effect of the ion species on the defect morphology.

On the nature of photosensitivity gain in Ga2O3 Schottky diode detectors: Effects of hole trapping by deep acceptors

Lightly n-type doped Ga2O3 layers grown by Halide Vapor Phase Epitaxy (HVPE) on bulk n+-Ga2O3 substrates were subjected to irradiation with fast reactor neutrons, 20 MeV protons, or treatment in high ion density Ar plasma. These treatments lead to a marked increase in the concentration of deep acceptors in the lower half of the bandgap. These acceptors have optical ionization thresholds near 2.3 eV and 3.1 eV. There is a simultaneous strong enhancement of the photocurrent of Schottky diodes fabricated on these layers in the UV spectral range, and a large increase in the Electron Beam Induced Current (EBIC) collection efficiency. The gain in photocurrent at −10 V reached 18 times for neutron and proton irradiated samples, and 104 times for the plasma treated samples. Similar increases in gain were observed in the EBIC current collection efficiency for beam energy 4 keV. With such beam energy, the electron–hole pairs are generated well within the space charge region. The results are explained by assuming that the capture of photoinduced or electron-beam-induced holes by the deep acceptors gives rise to a decrease in the effective Schottky barrier height and an increase of the electron current flow that is responsible for the observed high gain. The reported observation could form a basis for radical improvement of photosensitivity of Ga2O3-based solar-blind photodetectors. However, the photocurrent build-up and decay times in this mechanism are inherently long, on the order of some seconds.

A micromechanical analysis of intergranular stress corrosion cracking of an irradiated austenitic stainless steel

Irradiation Assisted Stress Corrosion Cracking (IASCC) is a material degradation phenomenon affecting austenitic stainless steels used in nuclear Pressurized Water Reactors (PWR), leading to the initiation and propagation of intergranular cracks. Such phenomenon belongs to the broader class of InterGranular Stress Corrosion Cracking (IGSCC). A micromechanical analysis of IGSCC of an irradiated austenitic stainless steel is performed in this study to assess local cracking conditions. A 304L proton irradiated sample tested in PWR environment and showing intergranular cracking is investigated. Serial sectioning, Electron BackScatter Diffraction (EBSD) and a two-step misalignment procedure are performed to reconstruct the 3D microstructure over an extended volume, to assess statistically cracking criteria. A methodology is also developed to compute Grain Boundary (GB) normal orientations based on the EBSD measurements. The statistical analysis shows that cracking occurs preferentially for GB normals aligned with the mechanical loading axis, but also for low values of the Luster-Morris slip transmission parameter. Micromechanical simulations based on the reconstructed 3D microstructure, FFT-based solver and crystal plasticity constitutive equations modified to account for slip transmission at grain boundaries are finally performed. These simulations rationalize the correlation obtained experimentally into a single stress-based criterion. The actual strengths and weaknesses of such micromechanical approach are discussed.

Applying a combination of laboratory X-Ray diffraction and digital image correlation for recording uniaxial stress-strain curves in thin surface layers

By combining laboratory-based x-ray diffraction stress analysis with optical digital image correlation recorded in-situ during tensile loading, a new methodology has been developed to obtain for surface specific stress-strain curves. This novel methodology has been validated by comparing the reconstructed stress-strain curves from the x-ray diffraction/optical digital image correlation approach with stress-strain curves recorded using standard methods. The validated methodology enables now the recording of standard mechanical test data of altered surface layers, such as shot peened and machined surfaces or from proton-irradiated samples where the irradiated layer is limited to a depth of 10 s of microns.

Carbon vacancy-related centers in 3C -silicon carbide: Negative- U properties and structural transformation

Combining electron paramagnetic resonance (EPR) spectroscopy and first-principles density functional theory calculations we have identified the carbon monovacancy center and a second carbon vacancy-related defect, the carbon vacancy--carbon antisite defect in $3C$-SiC. In close analogy to the vacancy in silicon, the carbon vacancy in $3C$-SiC with its four potentially equivalent silicon dangling bonds shows a strong Jahn-Teller effect, confirming previously predicted negative-$U$ properties. High-temperature annealing (above 700 \ifmmode^\circ\else\textdegree\fi{}C) of electron or proton irradiated samples anneals out the primary silicon monovacancies and generates a new defect, which we assign to the carbon vacancy--carbon antisite complex. As predicted by theory, this defect is the result of a structural instability of the silicon vacancy in the positive charge state, which transforms at high temperatures according to ${V}_{\mathrm{Si}}{\mathrm{C}}_{4}\ensuremath{\rightarrow}{V}_{\mathrm{C}}{\mathrm{C}}_{\mathrm{Si}}{\mathrm{C}}_{3}$. Both defects are deep donors and thus not suitable for achieving semi-insulating properties.

Microstructural examination of neutron, proton and self-ion irradiation damage in a model Fe9Cr alloy

Transmission electron microscopy (TEM) was used to compare the microstructural defects produced in an Fe9Cr model alloy during exposure to neutrons, protons, or self-ions. Samples from the same model alloy were irradiated using fission-neutrons, 2 MeV Fe+ ions or 1.2 MeV protons at similar temperatures (∼300 °C) and similar doses (∼2.0 dpa). The neutron-irradiated alloy contained visible interstitial dislocation loops with b = 111, and on average ∼5 nm in size. The density varied from 2±1 × 1020 m-3 (in the matrix far from dislocations and boundaries) to 1.2±0.3 ×1023 m-3 (close to helical dislocation lines). Chromium α′-phase precipitates were also identified at a density of 7.4±0.4 ×1023 m-3. Self-ion irradiation produced mostly homogeneously distributed dislocation loops (6–7 nm on average), and with a greater fraction of 100 loops (∼40%) than was seen in the neutron-irradiated alloy, and at a density of 6.8±0.8 ×1022 m-3. In contrast to the loops produced by neutron irradiation, the self-ion irradiated Fe9Cr contained only vacancy-type loops. Chromium also remained in solution. Proton-irradiated Fe9Cr contained interstitial dislocation loops close to helical-dislocation segments, similar to the neutron-irradiated sample. Chromium α′-phases were also identified in the proton-irradiated sample at a density of 2.5±0.3 ×1023 m-3, and large voids (up to 7 nm) were found at a density over 1022m−3. Like the neutron-irradiated sample, the density of dislocation loops was also heterogeneously distributed; far from grain boundaries and dislocation lines the density was 2.5±0.4 ×1022 m-3, while close to helical dislocation lines the density was 8.1±1.3 ×1022 m-3.

Ductilization of Nanoporous Ceramics by Crystallinity Control.

Synthesizing ceramic materials with a significant amount of deformability is one of the most important engineering pursuits. In this study, we demonstrate the emergence of metal-like plasticity through the crystallinity control in the monolithic zirconia with the vertically aligned honeycomb-like periodic nanopore structures fabricated using the anodizing technique. The crystalline orders of the nanoporous zirconia films vary between monoclinic, tetragonal, and amorphous phases after the heat treatment and/or proton irradiation, whereas the vertical pore structures are maintained. The micropillar compression tests on those samples reveal a large amount of plasticity, more than 20% of total stains, in the as-anodized and proton-irradiated samples, both of which contain the amorphous phase. In contrast, the fully crystallized zirconia that resulted from annealing at 500 °C shows the brittle failure, the typical characteristic of conventional ceramic foams. These results offer a new opportunity for the nanoporous ceramic materials to be used in various applications, benefited from the tunable structural stability.

The Study of Deep Level Traps and Their Influence on Current Characteristics of InP/InGaAs Heterostructures

The damage mechanism of proton irradiation in InP/InGaAs heterostructures was studied. The deep level traps were investigated in detail by deep level transient spectroscopy (DLTS), capacitance–voltage (C–V) measurements and SRIM (the stopping and range of ions in matter, Monte Carlo code) simulation for non-irradiated and 3 MeV proton-irradiated samples at a fluence of 5 × 1012 p/cm2. Compared with non-irradiated samples, a new electron trap at EC-0.37 eV was measured by DLTS in post-irradiated samples and was found to be closer to the center of the forbidden band. The trap concentration in bulk, the interface trap charge density and the electron capture cross-section were 4 × 1015 cm−3, 1.8 × 1012 cm−2, and 9.61 × 10−15 cm2, respectively. The deep level trap, acting as a recombination center, resulted in a large recombination current at a lower forward bias and made the forward current increase in InP/InGaAs heterostructures for post-irradiated samples. When the deep level trap parameters were added into the technology computer-aided design (TCAD) simulation tool, the simulation results matched the current–voltage measurements data well, which verifies the validity of the damage mechanism of proton irradiation.

Characterization of proton-irradiated Chinese A508-3-type reactor pressure vessel steel by slow positron beam, TEM, and nanoindentation

Evolution of matrix defects and hardening of Chinese A508-3-type reactor pressure vessel steel irradiated to the doses of 0.05 dpa, 0.1 dpa, and 0.2 dpa by 110-keV proton at room temperature were investigated by slow positron beam, TEM, and nanoindentation. Slow positron beam results showed that proton irradiation-induced vacancy-type defects were observed and only one type of vacancy-type defects was characterized. Size and concentration of vacancy-type defects increased with the dose. TEM images revealed that dislocation loops were produced in the proton-irradiated samples. The mean size of the dislocation loops was unchanged but the number density of the dislocation loops was increased with the dose. An obvious hardening phenomenon of proton irradiated samples was detected by nanoindentation test. The irradiation hardening was mainly attributed to irradiation-induced matrix defects such as vacancy clusters, H-vacancy complexes, and dislocation loops.

An approach in the analysis of microstructure of proton irradiated T91 through XRDLPA using synchrotron and laboratory source

The changes in the microstructure of 3.5 MeV proton irradiated T91 Ferritic-Martensitic steel samples with dose have been evaluated using detailed X-ray diffraction line profile analysis of the data collected using both laboratory and the synchrotron source. Different line profile analysis techniques like Williamson-Hall, modified Rietveld method and convolutional multiple whole profile fitting have been applied to evaluate the microstructural parameters such as domain size, microstrain, dislocation density and the character of the dislocation from both the data. The coherent domain size decreases and the corresponding microstrain increases at the first dose of irradiation. With further irradiation, these parameters show a slight recovery and eventually tend towards saturation with increasing dose. The dislocation density follows similar trend as the microstrain showing saturation at higher doses of irradiation in both the XRD data. However, a systematic change in the character of the dislocation from screw-type to edge-type could be ascertained only from the data obtained using synchrotron source. The Vickers microhardness of the samples is found to increase continuously with increasing irradiation dose supporting the observed change in the dislocation character from screw-type (glissile) to edge-type (sessile). Both EBSD and TEM analysis of the unirradiated and irradiated samples have supported the results obtained from the XRD analysis.

Effect of proton irradiation on the physical properties of PC/PBT blends

ABSTRACTSamples from polycarbonate/poly (butylene terephthalate) (PC/PBT) blends film have been irradiated using different fluences (1 × 1015– 5 × 1017 H+/cm2) of 1 MeV protons at the University of Surrey Ion Beam Center, UK. The structural modifications in the proton irradiated samples have been studied as a function of fluence using different characterization techniques such as X-ray diffraction and UV spectroscopy. The results indicate that the proton irradiation reduces the optical energy gap that could be attributed to the increase in structural disorder of the irradiated samples due to crosslinking. Furthermore, the color intensity ΔE, which is the color difference between the non-irradiated sample and those irradiated with different proton fluences, increased with increasing the proton fluence up to 5 × 1017 H+/cm2, convoyed by an increase in the red and yellow color components. In addition, the resultant effect of proton irradiation on the thermal properties of the PC/PBT samples has been investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). It is found that the PC/PBT decomposes in one weight loss stage. Also, the variation of transition temperatures with proton fluence has been determined using DSC. The PC/PBT thermograms were characterized by the appearance of two endothermic peaks due to the glass transition and melting temperatures. The melting temperature of the polymer, Tm, was investigated to probe the crystalline domains of the polymer, since the proton irradiation destroys the crystalline structure so reducing the melting temperature.

Proton irradiation studies on Al and Al5083 alloy

The change in the microstructural parameters and microhardness values in 6.5MeV proton irradiated pure Al and Al5083 alloy samples have been evaluated using different model based techniques of X-ray diffraction Line Profile Analysis (XRD) and microindendation techniques. The detailed line profile analysis of the XRD data showed that the domain size increases and saturates with irradiation dose both in the case of Al and Al5083 alloy. The corresponding microstrain values did not show any change with irradiation dose in the case of the pure Al but showed an increase at higher irradiation doses in the case of Al5083 alloy. The microindendation results showed that unirradiated Al5083 alloy has higher hardness value compared to that of unirradiated pure Al. The hardness increased marginally with irradiation dose in the case of Al5083, whereas for pure Al, there was no significant change with dose.