Function Of Irradiation Temperature Research Articles

Experimental study of total ionizing dose effect on SiC MOSFETs at temperature from −233 °C to 175 °C

The influence of temperature on the total ionizing dose response of silicon carbide (SiC) metal-oxide-semiconductor filed effect transistors (MOSFETs) was experimentally studied by γ-rays irradiation at temperatures ranging from −233 °C to 175 °C. Electrical parameters were investigated with Current-Voltage (I-V) measurements. Results showed that the threshold voltage shifted toward negative post-irradiation due to the radiation-induced oxide trapped charges. The shift of threshold voltage was a function of irradiation temperature. The shift of threshold voltage increased as temperature decreased. The reason was that there were less annealing for the radiation-induced oxide trapped charges at low temperatures.

Recent progress in experimental investigation of neutron irradiation response of tungsten

In order to facilitate its application as plasma facing material, neutron irradiation response of tungsten (W) has been extensively studied by employing fission reactors. In this article, the major findings of the microstructural evolution and thermo-mechanical property degradation of W following neutron irradiation in various reactors are summarized by reviewing the papers published in 2019–2021 from the US-Japan joint projects on fusion materials research and the EUROfusion program. Microstructural development of W following irradiation has been well documented as functions of irradiation temperature, dose, and neutron spectrum. Detailed characterization of the primary defect features, i.e., dislocations, voids, and precipitates, enables a better understanding of the interactions between displacement damage and solid transmutant elements. Irradiation hardening and embrittlement are the primary degradation phenomena of W exposed to neutrons, manifested by hardness and yield strength increase, ductility loss at high doses, and shift of the ductile to brittle transition temperature (DBTT). It is believed that the segregation and precipitation of the solid transmutant elements dominantly contributes to the property deterioration. Predicting W performance in real fusion neutron irradiation environments based on the current understanding of W response to fission neutrons remains an open question.

A Rate Theory Model of Radiation-Induced Swelling in an Austenitic Stainless Steel

Many rate theory models of cavity (void) swelling have been published over the past 50 years, all having the same, or similar, structures. A rigorous validation of the models has not been possible because of the dearth of information concerning the microstructures that correspond with the swelling data. Whereas the lack of microstructure information is still an issue for historical swelling data, in the past 10–20 years data have been published on the evolution of the microstructure (point defect yields from collision cascades, cavity number densities, and dislocation densities/yield strengths) allowing certain gaps in information to be filled when considering historic swelling data. With reasonable estimates of key microstructure parameters, a standard rate theory model can be applied, and the model parameter space explored, in connection with historical swelling data. By using published data on: (i) yield strength as a function of dose and temperature (to establish an empirical expression for dislocation density evolution); (ii) cavity number densities as a function of temperature; and (iii) freely migrating defect (FMD) production as a function of primary knock-on atom (PKA) spectrum, the necessary parameter and microstructure inputs that were previously unknown can be used in model development. This paper describes a rate-theory model for void swelling of 316 stainless steel irradiated in the EBR-2 reactor as a function of irradiation temperature and neutron dose.

Evolution of microstructure in neutron irradiated cold rolled tungsten and its correlation with hardness

The understanding of the neutron irradiation effects in tungsten is of significant importance for its use as a plasma facing material in future fusion devices. In this study, cold rolled tungsten is neutron irradiated at the Belgian BR2 fission reactor at the temperatures 600, 800, 900 and 1200 °C to a dose of 0.18 displacements per atom (dpa). The neutron induced changes in the microstructure are investigated as a function of irradiation temperature using transmission electron microscopy, positron annihilation spectroscopy and electrical resistivity measurements. The influence of the irradiation on the elastic properties and the hardness is examined using the impulse excitation techniques and depth-sensing indentation. Voids and dislocation loops are observed at all the irradiation temperatures. As the irradiation temperature increases the number density of both voids and loops decreases whereas their size increases. The total dislocation density increases after irradiation at 600 °C whereas it decreases for higher temperature irradiations. Furthermore, the formation of very small vacancy clusters in the temperature range of 800 - 900 °C is revealed by PAS measurements. A systematic decrease in the values of Young's and shear moduli is observed as the irradiation temperature increases and this decrease is of about 3.5% after irradiation at 1200 °C. A considerable hardening effect is observed at all irradiation temperatures. The hardness increases with irradiation temperature reaching a maximum at 800 °C and remains almost constant at higher irradiation temperatures.

Thermoluminescence response of various dosimeters as a function of irradiation temperature

The behavior of various TL dosimeters following two different thermal treatments with temperature ranging between 50 and 230 °C, was investigated in this particular study. The thermal treatment consists of two different protocols, including a simultaneous irradiation-heating and a post irradiation heating. The dosimeters that are the subject of the present study include two different families of lithium fluorides, namely the Harhsaw LiF family (TLD-600, TLD-700), LiF of the Krakow university (MTS-600, MTS-700), BeO and the commonly used CaSO4 samples with two different impurities (Dy and Tm). According to the analysis, it seems that the TLDs and MTS-600 are identical with regard to their characteristics, while MTS-700 is different. The treatment showed that the intensities of peak 5 of all LiF samples increases up to 20–30% at 110 °C which is followed by a decrease, while the high temperature peaks of LiF showed a high dependence on the treatment temperatures. As for the case of BeO, one peak has a minor increase of 10% at 80–90 °C and a decrease up to 230%, while the other is stable. CaSO4 samples show no increase and there is a decrease starting at 150 °C. Also, this work studied the kinetic parameters of all peaks for these samples via the computerized glow curve deconvolution method. In the end, there is a categorization of the LiF samples based on their properties and their glow curves. Lastly, the results indicate that the lack of strong increase of the TL response with increasing irradiation temperature for the majority of the TL peaks of these aforementioned phosphors does not support strong competition effects. A notable exception is observed for the high temperature TL peaks in all LiF samples regardless of whether these were purchased from Harshaw or from Poland.

Pair distribution function analysis of neutron-irradiated silicon carbide

We have employed x-ray total scattering to investigate the structure of polycrystalline 3C-silicon carbide following neutron irradiation. The structure as a function of irradiation temperature and dose was quantified by analyzing pair distribution functions. Although the SiC matrix retains its crystal structure after irradiation, a significant increase in the diffuse scattering component is observable indicating that neutron irradiation leads to changes in both the short- and medium-range order. These changes include both an irradiation dose- and temperature-dependent increase in the vacancy concentration leading to an increase in the Si and C atomic displacement parameters. A dose-dependent decrease in the size of defect free material is also quantified from the structural refinements due to an increase in the number of defects and defect clusters. Evidence of additional correlations in the short-range order (up to ∼4 Å) from differential pair distribution function analysis indicate that combinations of atomistic defects including anti-site defects, vacancies and defect clusters are present after these irradiation conditions. Such structural information will be valuable for direct comparison of experimental and simulated atomic structures of irradiated silicon carbide.

Thermoluminescence response of CaF2:Dy as a function of irradiation temperature between room temperature and 270 °C

The Themoluminescence (TL) response of CaF2:Dy (TLD-200) as a function of irradiation temperature was studied in the present work. The irradiation of a TL material at elevated temperatures has a twofold scope: (a) To provide knowledge and insight regarding the possibilities of radiation dosimetry at high temperature environments; (b) The fact that during irradiation at elevated temperatures trap filling and trap emptying take place simultaneously, makes this pre-conditioning the most promising for the reflection in the net glow-curve of competition effects between traps and centres. The irradiation temperature (Tirr) region was between room temperature (RT) and 270 °C in steps of 10 °C. Using the same conditions as far as dose and temperature are concerned, post irradiation annealing (PIA) measurements were also performed, which give only the results of trap emptying. Both experiments were performed using (a) one sample for all measurements (single-aliquot procedure) and (b) two samples for each temperature (multi-aliquot procedure). Deconvolution was also applied in all cases towards investigating the impact of the two protocols on the kinetic parameters of all peaks for this specific material. The results showed that there is not any dependence of the TL response in the case of multi-aliquot procedure. However, in the case of single-aliquot procedure, a very interesting dependence of the TL response on Tirr is observed only for the last TL peak of TLD-200. These results, although weaker, were also observed in the case of PIA procedure. Activation energies of the high-temperature, more stable peaks yield a dependence on both irradiation and PIA temperatures. The results are discussed in the framework of the trap competition models.

Effects of temperature during the irradiation of calcium carbonate

Calcium carbonate received gamma irradiation at different doses (0–309kGy) and temperature regimes (77–298K) to study the effects of irradiation temperature. The changes were followed by EPR spectroscopy. We observed the formation of a composite EPR spectrum, even at low radiation doses and temperature. There was a strong effect on the evaluation of the radicals formed as a function of irradiation temperature, probably due to the diffusion in the frozen powder and the recombination of some radicals at room temperature.

Quantitative comparison of sink efficiency of Cu–Nb, Cu–V and Cu–Ni interfaces for point defects

The efficacy of heterointerfaces as sinks for point defects in Cu was characterized using local measurements of tracer-impurity radiation-enhanced diffusion (RED). The measurements were performed as a function of irradiation temperature and Cu thickness in multilayer samples, with the results being compared to steady-state kinetic rate equations to determine sink strengths. Cu–Nb Kurdjumov–Sachs (KS) interfaces are found to be nearly ideal sinks for point defects, whereas Cu–Ni (111) heteroepitaxial interfaces are poor sinks; Cu–V KS interfaces are intermediate. Quantitative analysis of the RED data also yields the defect production efficiency for freely migrating defects in Cu, which is on the order of 1% for MeV Kr irradiation.

2 MeV e‐irradiation UHVEM study on the impact of O and Ge doping on {113}‐defect formation in Si

AbstractFirst results are presented of a study on the impact of O and Ge doping on {113}‐defect formation in Si using in situ 2 MeV e‐irradiation in a high voltage electron microscope. Comparison with undoped Si, reveals a suppression of {113}‐defect formation due to O and Ge. The observations are discussed in the frame of a theoretical model assuming quasi‐chemical reactions to describe the intrinsic point defect behaviour during irradiation as a function of irradiation temperature and specimen thickness. It is shown that for irradiations at high temperatures, intrinsic point defect diffusivity values derived from crystal growth and metal diffusion experiments can be used to explain the observations semi‐quantitatively.

Radiation induced electrical and microstructural degradation at high temperature for HP SiC

SiC based composites are candidates for possible use as structural materials, and flow channel inserts in Li–Pb tritium breeding blanket modules for DEMO and future fusion reactors. Previous studies showed noticeable changes in electrical conductivity and also amorphization after 1.8 MeV electron irradiation for irradiation temperatures between 290 and 650 °C. However this material is foreseen to be used at higher temperatures. In this work hot pressed (HP) SiC has been electron irradiated at temperatures up to 900 °C and the bulk electrical conductivity measured as a function of irradiation temperature and dose. Following irradiation modification of the microstructure was studied and the dependence on irradiation temperature addressed. It was found that the degradation of the material is lower for the higher irradiation temperature indicating that by about 900 °C the induced damage is efficiently annealed during irradiation.

Void swelling in ion irradiated (15Ni–14Cr), Ti-modified stainless steel: A study using positron annihilation and step height measurements

The void swelling behaviour of (15Ni–14Cr) Ti-modified steels simulated by heavy ion irradiation, has been investigated using step height measurements and positron annihilation spectroscopy. 18% cold-worked samples were pre-implanted with helium at 170 keV and 275 keV energies so as to create a uniform helium concentration of 100 appm around the 588 nm depth region. This was followed by a 2.5 MeV Ni ion irradiation to create a peak damage of ~ 84 dpa (displacement per atom) at various irradiation temperatures between 700 and 970 K. The gross swelling which has occurred throughout the ion range is determined by step height measurements. Defect-sensitive positron annihilation lineshape S-parameter measurements show clear changes consequently to void formation as a function of sample depth. From the variation of the average S-parameter as a function of irradiation temperature, the peak swelling temperature has been deduced. The changes observed in step height measurements are compared with positron annihilation measurements and the results are discussed.

Effect of electronic energy loss and irradiation temperature on color-center creation in LiF and NaCl crystals irradiated with swift heavy ions

LiF and NaCl crystals were irradiated at 8 K and 300 K with various light and heavy ions (C, Ti, Ni, Kr, Sm, Au, Pb, and U) of kinetic energy between about 50 and 2600 MeV, providing electronic energy losses from 0.7 to 26.4 keV/nm. A cryostat installed at the beamline allowed in situ absorption spectroscopy and thermostimulated luminescence (TSL) measurements from 8 K upward. Creation of electron and hole color centers is analyzed as a function of irradiation temperature, fluence, and thermal and optical bleaching. Anion interstitials ($I$ and $H$ centers) were only observed in crystals irradiated at 8 K. These defects are unstable and disappear in the temperature range 10--100 K. For heavy ions (Au, U), the $F$-center accumulation efficiency at low fluences is larger at 8 K than at room temperature. The opposite effect is observed for light ions (C, Ti, Ni). The results are discussed within the frame of transient heating influencing separation or annealing of point defects.

Positron beam studies of void swelling in ion irradiated Ti-modified stainless steel

The void swelling behavior of heavy ion irradiated D9 steel has been investigated using variable low energy positron beam. The normalized defect-sensitive S-parameter shows up a large increase in the depth region corresponding to the maximum radiation damage as a function of irradiation temperature. From the variation of S-parameter as a function of irradiation temperature, the peak swelling temperature has been deduced and the results are discussed.

Variation of ion-irradiation induced strain as a function of ion fluence in Si

Strain in Si induced by ion irradiation at temperatures of 200–400°C has been measured at room temperature. Quantitative analysis of the strain distribution produced by 750-keV Si ion implantation in Si substrates was characterized by double-crystal X-ray diffraction (DCXRD). Strain in the Si surface layer was determined by modeling the DCXRD rocking curve using the program Rocking curve Analysis by Dynamic Simulation (RADS) where a generated strain profile is iteratively fitted to the measured rocking curve.The strain was tensile, resulting from a vacancy excess, and measured as a function of irradiation temperature and ion fluence. For a given temperature, strain increased as a function of ion fluence until a strain maximum was attained and then relaxed via dislocation formation. The maximum strain attainable decreased with an increase in irradiation temperature as consistent with thermally activated dislocation formation.

Microstructural development in cubic silicon carbide during irradiation at elevated temperatures

Microstructural development in chemically vapor-deposited (CVD) high-purity beta-SiC during neutron and self-ion irradiation at elevated temperatures was studied. The CVD SiC samples were examined by transmission electron microscopy following neutron irradiation to 4.5–7.7 × 10 25 n/m 2 ( E > 0.1 MeV) at 300 and 800 °C and 5.1 MeV Si 2+ ion irradiation up to ∼200 dpa at 600–1400 °C. The evolution of various irradiation-produced defects including black spot defects, dislocation loops, network dislocations, and cavities was characterized as a function of irradiation temperature and fluence. It was demonstrated that the black spot defects and small dislocation loops continue to dominate at relatively low temperatures (<∼800 °C), whereas they grow into Frank faulted loops and finally develop into dislocation networks at a higher temperature (1400 °C). Substantial cavity formation on grain boundaries and stacking faults was confirmed after ion irradiation at 1400 °C. These observations were discussed in relation with the known irradiation phenomena in SiC, such as low temperature swelling and cavity swelling.

Effects of Helium Production and Heat Treatment on Neutron Irradiation Hardening of F82H Steels Irradiated with Neutrons

The inftucence of addition of 1 0 B and 1 1 B on radiation hardening as a function of irradiation temperature was examined in reduced-activation martensitic F82H+B steels (8Cr-2W-0.2V-0.04Ta-0.1C-0.006B). Specimens used were 1 0 B doped, 1 0 B+ 1 1 B doped and 1 1 B doped F82H steels. Helium concentration produced in the specimens through 1 0 B(n, α) 7 Li reaction was measured from about 15 to about 330appm. Radiation hardening of the specimens irradiated at 300°C to 2.3 dpa and 150°C to 1.9 dpa was observed. Increment of radiation hardening possibly due to helium in the specimen irradiated at 300°C tended to increase slightly with increasing helium production in tensile test at 20°C, but it was not observed for 150°C irradiation. Therefore, it can be mentioned that the enhancement of radiation hardening in the 1 0 B( 1 1 B) doped steels depends on irradiation temperature, The dependence of radiation hardening on tempering time was also examined for F82H-std irradiated at 150'C to 1.9 dpa. Increment of yield strength of F82H-std tended to increase with increasing tempering time. The relation between the shift of DBTT and the increment of yield strength due to irradiation suggest that the extension of tempering time or the increase of tempering temperature would be beneficial for mechanical properties of F82H-std.

Defect structure and evolution in silicon carbide irradiated to 1 dpa-SiC at 1100 °C

Transmission electron microscopy (TEM), swelling measurements, isochronal annealing, and thermal diffusivity testing were used to characterize the effects of radiation damage in SiC. Together, these techniques provided a comprehensive set of tools for observing and characterizing the structure and evolution of radiation-induced defects in SiC as a function of irradiation temperature and dose. In this study, two types of dense, crystalline, monolithic SiC were subjected to irradiation doses up to 1 dpa-SiC at a temperature of 1100 °C, as well as post-irradiation annealing up to 1500 °C. The microscopic defect structures observed by TEM were correlated to changes in the macroscopic dimensions, thermal diffusivity and thermal conductivity. The results demonstrated the value of using ultrapure β-SiC as an effective reference material to characterize the nature of expected radiation damage in other, more complex, SiC-based materials such as SiC/SiC composites.

Recent results for the ferritics isotopic tailoring (FIST) experiment

An alloy of F82H prepared using the isotope 54Fe in order to encourage H and He production in a fission reactor has been irradiated in the HFIR JP20 experiment at three temperatures to 7 dpa as TEM disks. Irradiated disks were shear punch tested, examined by TEM, analyzed for He and H content, and compared with previous results in order to quantify irradiation hardening due to transmutation-induced H and He. Hardening due to irradiation is found following irradiation at 300 and 400 °C, that is intermediate between that at lower and higher dose, but hardening is negligible following irradiation at 500 °C. Microstructural examinations show typical behavior of irradiation as a function of irradiation temperature, with moderate swelling after 400 °C irradiation but few bubbles after irradiation at 300 °C. Correlations of change in hardening with He and H content show little indication of transmutation-induced hardening, but measured H levels do not agree with predictions and therefore H production and analysis requires further study.

Electron-trapping probability in natural dosemeters as a function of irradiation temperature.

The electron-trapping probability in OSL traps as a function of irradiation temperature is investigated for sedimentary quartz and feldspar. A dependency was found for both minerals; this phenomenon could give rise to errors in dose estimation when the irradiation temperature used in laboratory procedures is different from that in the natural environment. No evidence was found for the existence of shallow trap saturation effects that could give rise to a dose-rate dependency of electron trapping.