Pre-irradiation Heat Treatment Research Articles

Formation mechanisms of precursors of radiation-induced color centers during fabrication of silica optical fiber preform

Samples in the form of transverse slices of rods and optical fiber preforms made from the high-hydroxyl KU-1 and low-hydroxyl KS-4V silica by the plasma outside deposition (POD) method are γ-irradiated to a dose of ∼1 MGy (SiO2). Next, the radial dependences of the radiation-induced nonbridging oxygen hole center (NBOHC) and E′-center (three-coordinated silicon) in the samples are constructed by measuring the amplitudes of their 4.8 and 5.8 eV absorption bands, respectively. Based on the analysis of these radial dependences and considering the temperature and duration of the preirradiation heat treatment of the rods and preforms at the POD-installation, we determine the ratio of the oscillator strengths of the above bands and the microscopic thermoinduced processes occurring during preform fabrication and producing precursors of the radiation-induced NBOHC and E′-center. These processes are found to be associated with the escape of either H2 or H2O from neighboring hydroxyl groups, and, therefore, can occur in high-hydroxyl silica only. It is concluded that enhancement of the radiation resistance of high-hydroxyl silica optical fibers requires decreasing the temperature and duration of the preform fabrication process, in particular, changing from the POD-technology to the low-temperature plasmachemical vapor deposition (PCVD) or surface PCVD (SPCVD)-technology.

Determining irradiation damage and recovery by instrumented indentation in RAFM steel

The mechanical behavior of specific reduced-activation ferritic-martensitic steels (RAFM), designed for fusion applications, is investigated in the present study. Eurofer97 and F82H-mod specimens have been neutron-irradiated in the High Flux Reactor at Petten (HFR) up to a dose of 15dpa at 250–450°C. An indentation method [1], making use of a data post-analysis program based on neural networks, has been employed to identify tensile properties by multistage indents. The significant irradiation-induced hardening effect present at 15dpa in the range of 250–350°C could be observed in Vickers hardness and in the calculated material’s strength parameters, the influence of the pre-irradiation heat treatment could be identified. Post-irradiation annealing treatments have been realized at 500°C and 550°C and leads to a partial recovery of the irradiation damage.

The effects of pre-irradiation heat treatment and heating rate on the thermoluminescence glow peaks of natural CaF2

In this article, we have investigated the effects of pre-irradiation heat treatments on the thermoluminescence (TL) glow peaks of natural fluorite (CaF2) collected from the central Anatolia region of Turkey. A typical TL glow curve of phosphor consists of four clear glow peaks with maximum intensities occurring at temperatures around 100 °C, 120 °C, 190 °C and 290 °C for a sample irradiated to a dose of 48 Gy and readout at a heating rate of 1 °C/s. It was observed that the intensities of all the TL glow peaks are strongly sensitive to annealing temperatures and durations. Annealing at 450 °C for 15 min was found to be the best for reproducibility of experimental results. The dose–responses of individual TL peaks of this material were also examined after annealing at 450 °C for 15 min by β-irradiation to doses between 0.04 Gy and ≈10.4 kGy. It was observed that the total area and peak heights of all glow peaks showed similar trends with increasing radiation dose; first, they increased linearly up to ≈50 Gy and then saturation effects began above this dose value. The effect of heating rate on the TL glow peaks of the mineral was also studied and it was observed that the intensities of glow peaks are differently affected with variation in heating rate.

DLTS study of the oxygen dimer formation kinetics in silicon

The introduction rates of radiation defects, in particular the X- and M-centers for which the oxygen dimer is a precursor, are investigated as a function of duration of the pre-irradiation heat treatment at 480∘C in Czochralski-grown silicon both of n- and p-types. The characteristic annealing time to grow the X-center concentration in the n-type crystal is found to be about 1 h in accordance with the model which implies no significant barrier for the dimer formation. The M-center concentration in the p-type crystal is found to be nearly independent of duration of the pre-irradiation annealing after a few minutes transient period. This behavior is ascribed to the stabilization of dimer concentration due to an effective dimer trapping in these samples.

Properties and identification of the oxygen-related radiation defects in silicon

Properties of the recently reported deep-level radiation defects in oxygen-rich silicon (the M-center in p-type Si with the DLTS levels at E v + 0.36 and E v + 0.12 eV , and the X-center in n-type Si with the level at E c - 0.11 eV , respectively) are investigated by means of DLTS and IR absorption. With a pre-irradiation heat treatment the linear correlation between the amount of oxygen dimers and the X- and M-center concentrations is established, indicating the oxygen dimer as the precursor of both radiation defects. The annihilation rates of the X- and M-centers in different charge states are measured in the temperature range of 295–350 K. The introduction rates and thermal stabilities of the M- and X-centers are found to be strongly different, which makes it difficult to correlate these levels with the same defect.

Thermoluminescent dosimetric characteristics of annealed quartz

In the given present study, the effect of pre-irradiation heat treatment at 500 and 600 °C on the glow peaks of synthetic quartz was examined as a function of annealing time to obtain an optimum annealing procedure. It was observed that the annealing time is not a strongly sensitive parameter to change the intensities of glow peaks. On the other hand, the intensities of glow peaks between room temperature (RT) and 200 °C were continuously increased during successive readings after heat treatments. Moreover, the intensities of glow peaks above 250 °C have good stabilities. The obtained repeatability of a glow peak at ∼320 °C over 10 cycles is within 5% after the application of annealing at 600 °C for 1 h. The general thermoluminescent dosimetric characteristics of synthetic quartz, such as the dose–response, signal fading as a function of storage time, and reusability were also tested using the annealing condition at 600 °C for 1 h. It was observed that dose-response behaviours of all glow peaks are similar to each other. They first follow linear part and then saturated at different dose levels. Peak 1 completely disappeared after 1 month storage in the dark room at RT. On the other hand, the intensity of peaks 2+3 was approximately reduced to 15% of its original value whereas the other peaks (P4–P5) were not sufficiently affected during this period.

Investigation of the stability of the radiation sensitivity of TL peaks of quartz extracted from tiles

One of the most important mineral in dosimetric investigation is quartz, which is found abundantly in archaeological and geological materials. Although there are many studies about its thermoluminescence (TL) properties in the literature, it may exhibit different properties for each quartz mineral extracted from the different region of the world. In the present work, the stabilities and dose responses of glow peaks of quartz obtained from the tiles of Kubad Abad Palace in central Turkey were investigated after annealing at 500 and 600 °C for 1 h. The variation of radiation sensitivity of TL peaks of the quartz grains extracted from tiles are found to be more stable after annealing at 600 °C than 500 °C for 1 h. The TL dose responses of glow peaks of annealed and unannealed quartz samples were also studied up to approximately 3 kGy. It was observed that the pre-irradiation heat treatments affect the dose response behaviors of glow peaks.

Thermoluminescence studies of rare earth doped Sr 2Mg(BO 3) 2 phosphor

The Sr 2Mg(BO 3) 2 phosphors doped respectively with Tm 3+, Tb 3+ and Dy 3+ as activator were prepared by high temperature solid-state reaction. All the thermoluminescence curves of the phosphors consisted of two isolated peaks and the Dy 3+ activated sample exhibited the strongest thermoluminescence intensity. The kinetic parameters of the thermoluminescence of Sr 2Mg(BO 3) 2 : 0.04 Dy were calculated employing the peak shape method and 3 dimensional thermoluminescent emission spectra were observed peaking at 480, 579, 662 and 755 nm due to the characteristic transition of Dy 3+. In addition, the pre-irradiation heat-treatment and the thermoluminescence dose response of Sr 2Mg(BO 3) 2 : 0.04 Dy were investigated.

Hydrogen blister formation and cracking behavior for various tungsten materials

In order to study hydrogen blistering and subsequent cracking behavior of pure W, K-doped W, and La2O3-doped W, 1keV H3+ (main ion components) ion beams were irradiated at 653K to fluences up to 1×1025H/m2. Two pre-irradiation heat treatments were done for stress relief (900°C) and recrystallization (1300°C for pure W and 1500°C for K-doped and La2O3-doped W). It was found that blister characteristics and cracking behavior strongly depended on microstructures and dopant materials. For W materials with layered microstructure, blister shapes were mostly spherical-like, while for W materials with recrystallized (or disordered) microstructures, blisters had complicated plateau-like shapes with many cracks. Addition of K or La2O3 dopants increased the number of blisters and exfoliations for both stress relieved and recrystallized W.

Thermoluminescence studies of LiF : Mg, Ti between 100 and 300 K

Thermoluminescence and phototransfer thermoluminescence glow curves, and the corresponding emission spectra of LiF (TLD-100) crystals were studied over the temperature range 100 to 300 K after pre-irradiation heat treatment at 373, 423 and 673 K for 1 h. The TL glow curve displays six glow peaks over this temperature range. The intensity and peak temperatures of glow peaks above 200 K are highly affected by the pre-irradiation heat treatment while the glow peaks below 200 K are not affected by this treatment. The various emission spectra include ‘ultraviolet’ bands at 5.42, 4.42 and 3.57 eV and ‘visible’ bands at 3.07, 2.65 and 2.22 eV. The first glow peak, seen at 138 K, emits in both the ultraviolet and visible with similar intensity. The next glow peak, seen at 156 K with reduced intensity, also emits in both regions but with relatively more in the ultraviolet than the visible. The peak intensity and energy of the individual visible emission bands are strongly affected by pre-irradiation heat treatment, while the ultraviolet bands are weakly affected. The data are explained with a band-gap model that extends Mayhugh–Christy's model for thermoluminescence above room temperature.

The effect of pre-irradiation heat treatment on TL glow curves of ZnS thin film deposited by spray pyrolysis method

In this work, the effect of pre-irradiation heat treatment on the TL glow curves (GCs) of ZnS thin films which were deposited onto glass substrate by spray pyrolysis method using mixed aqueous solutions of ZnCl 2 and thiourea was investigated. It was observed that in spite of significant effects of pre-irradition heat treatments on the number of trap states and intensity of TL GCs, there is no considerable effect of it on the trap parameters of glow peaks of developed ZnS thin film. The TL data obtained from the recorded GCs indicates an impurity influence on both the deep and shallow traps with heat treatment. TL results have been then discussed on the basis of a restructuring of the defect concentration resulting from alterations in the surface properties of the thin films and diffusion of impurities (chlorine and oxygen) induced by annealing.

Thermoluminescence properties of newly generated glow peak 3a in TLD-100 after pre-irradiation heat treatment at 150 °C

It is well known that the glow curve structure of TLD-100 highly depends on the pre-irradiation heat treatments. In this study, it was observed that a new glow peak at 175 °C (indicated as peak 3a) appears, located between peak 3 (160 °C) and peak 4 (190 °C) after pre-irradiation heat treatments at 150 °C for annealing times ta⩾30 min when recorded at a heating rate of 2 °C/s. Our investigations have shown that this peak has different thermoluminescence (TL) characteristics from its neighboring peaks 3 and 4. Deconvolution analysis of its TL emission spectra indicates that it has at least three prominent emission bands at near 396, 406, 563 nm and another major emission band at around 469 nm depending on the annealing time duration. Its dose-response was also studied between 25 mGy and 400 Gy by using computer glow curve deconvolution (CGCD) technique and it was observed that it has a linear dose response between 25 mGy and 20 Gy and then a supralinear behavior. In the first month following irradiation, the fading of this peak was reported that less than 12%. Finally, the effect of additional heat treatments at 150 °C on its trapping parameters has been studied in detail by using the CGCD method as a function of annealing time. The results showed that its kinetic order (b) remains nearly constant during the heat treatments but its activation energy (Ea) and frequency factor (s) extremely varies during the heat treatments.

Thermoluminescence properties of newly generated glow peak 3a in TLD-100 after pre-irradiation heat treatment at 150 °C

It is well known that the glow curve structure of TLD-100 highly depends on the pre-irradiation heat treatments. In this study, it was observed that a new glow peak at 175 °C (indicated as peak 3a) appears, located between peak 3 (160 °C) and peak 4 (190 °C) after pre-irradiation heat treatments at 150 °C for annealing times t a⩾30 min when recorded at a heating rate of 2 °C/s. Our investigations have shown that this peak has different thermoluminescence (TL) characteristics from its neighboring peaks 3 and 4. Deconvolution analysis of its TL emission spectra indicates that it has at least three prominent emission bands at near 396, 406, 563 nm and another major emission band at around 469 nm depending on the annealing time duration. Its dose-response was also studied between 25 mGy and 400 Gy by using computer glow curve deconvolution (CGCD) technique and it was observed that it has a linear dose response between 25 mGy and 20 Gy and then a supralinear behavior. In the first month following irradiation, the fading of this peak was reported that less than 12%. Finally, the effect of additional heat treatments at 150 °C on its trapping parameters has been studied in detail by using the CGCD method as a function of annealing time. The results showed that its kinetic order ( b) remains nearly constant during the heat treatments but its activation energy ( E a) and frequency factor ( s) extremely varies during the heat treatments.

Microstructural examination of V–(3–6%)Cr–(3–5%)Ti irradiated in the ATR-A1 experiment

Microstructural examination results are reported for four heats of V–(3–6%)Cr–(3–5%)Ti irradiated in the ATR-A1 experiment to ∼4 dpa at 200°C and 300°C to provide an understanding of the microstructural evolution that may be associated with degradation of mechanical properties. Fine precipitates were observed in high density intermixed with small defect clusters for all conditions examined following the irradiation. The irradiation-induced precipitation does not appear to be affected by preirradiation heat treatment or composition.

Canopy Position and Heat Treatments Influence Gamma-irradiation-induced Changes in Phenylpropanoid Metabolism in Grapefruit

Irradiation is being evaluated as a quarantine treatment of grapefruit (Citrus paradisi Macf. `Marsh'), but it can cause damage to the fruit. Research was conducted to determine if preirradiation heat treatments would improve fruit tolerance to irradiation as they improve tolerance to low temperature injury and to determine if canopy position influenced fruit tolerance to irradiation. Initially, grapefruit were irradiated at 0 or 2.0 kGy at a dose rate of 0.14 kGy·min-1 and selected biochemical changes were monitored over time. There was a marked increase in phenylalanine ammonia-lyase (PAL) activity following irradiation. Maximum activity (≈18-fold increase) was attained 24 hours after irradiation. Subsequently, grapefruit were harvested from interior and exterior canopy positions and irradiated at 0 or 1.0 kGy at a dose rate of 0.15 kGy·min-1 before storage for 4 weeks at 10 °C. Following storage, pitting of flavedo was the most evident condition defect noted as a result of irradiation. Pitting was observed on 27% and 15% of irradiated exterior and interior canopy fruit, respectively, whereas there was no pitting on nonirradiated fruit. Heat treatment before irradiation decreased susceptibility of fruit to damage. Pitting was 26%, 19%, and 17% when fruit were held 2 hours at 20 (ambient), 38 or 42 °C, respectively. Irradiation-induced PAL activity was reduced by temperature conditioning at 38 or 42 °C. Exterior canopy fruit flavedo contained higher levels of total phenols, including flavanols and coumarins compared with interior canopy fruit. Deposition of lignin was not related to canopy position. Neither irradiation nor heat treatment had an effect on total phenols or lignin deposition. Generally, cholesterol, campesterol, stigmasterol, β-sitosterol, and isofucosterol were found to be higher in four steryl lipid fractions in exterior canopy fruit compared with interior canopy fruit. Irradiation increased campesterol in the free sterol and steryl glycoside fractions and decreased isofucosterol in the free sterol fraction. Heat treatments had no effect on individual sterol levels. It seems that irradiation causes a stress condition in the fruit, which leads to pitting of peel tissue. Heat treatment before irradiation reduced damaging effects of irradiation.

475 Heat Treatments Reduce Irradiation-induced Changes in Phenylpropanoid Metabolism in Grapefruit

Irradiation is being evaluated as a quarantine treatment of grapefruit (Citrus paradisi, Macf.), but it can cause damage to the fruit. We wanted to determine if pre-irradiation heat treatments would improve fruit tolerance to irradiation as they improve tolerance to low-temperature injury. `Marsh' grapefruit were harvested from interior and exterior canopy positions and irradiated at 0 or 1.0 kGy at a dose rate of 0.148 kGy·min-1 before storage for 4 weeks at 10 °C. Following storage, pitting of flavedo tissue was the most evident condition defect noted as a result of irradiation. Pitting was noted on 15% and 27% of irradiated interior and exterior canopy fruit, respectively, whereas there was no pitting on non-irradiated fruit. Temperature conditioning before irradiation decreased the susceptibility of fruit to damage. Pitting was 26%, 19%, and 17% when fruit were held 2 h at 20 (ambient), 38 or 42 °C, respectively. There was a marked increase in phenylalanine ammonia-lyase (PAL) activity following irradiation. Maximum activity (≈18-fold increase) was attained 24 h after irradiation. Irradiation-induced PAL activity was reduced significantly by temperature conditioning at 38 or 42 °C. Exterior canopy fruit flavedo contained higher levels of total phenols, including flavanols and coumarins, compared with interior canopy fruit. The deposition of lignin was not related to canopy position. Neither irradiation nor heat treatment had an effect on total phenols or lignin deposition. It seems that irradiation causes a stress condition in the fruit, which leads to pitting of peel tissue. Heat treatment before irradiation reduced the damaging effects of irradiation.

The Effect of Pre-Irradiation Heat Treatment on the Evaluated Trapping Parameters of LiF:Mg,Ti (TLD-100)

The effects of high ambient pre-irradiation heat treatment (125°C) on the trapping parameters of the various thermoluminescence peaks of LiF:Mg,Ti (TLD-100) crystals have been investigated in detail by using computerised glow curve deconvolution methods. Deconvolution of glow curves to their individual glow peaks demonstrates that the application of a pre-annealing stage changes the trapping parameters significantly. Computerised peak shape analysis showed that the order of kinetics of peak I increases from 1.0 to 2.5 whereas the order of kinetics of other peaks remained constant during the heat treatment. After approximately 7 h of heating, a new peak as a shoulder on the low temperature side of peak 3 and a new peak at the high temperature tail of peak 5 were observed. Shifts of peak temperature of peaks 3, 4 and 5 to the high temperature side were also noted. Significant changes to the activation energies and frequency factors of all peaks, especially peak 4, start immediately and continue throughout the annealing period. These results indicate that important defect structure modifications take place not only in the glow peaks 2 and 5 but also in peaks 1, 3 and 4.

Influence of composition, heat treatment and neutron irradiation on the electrical conductivity of copper alloys

The electrical conductivity of three different types of copper alloys, viz. CuNiBe, CuCrZr and Cu–Al 2O 3 as well as of pure copper are reported. The alloys have undergone different pre-irradiation heat treatments and have been fission-neutron irradiated up to 0.3 dpa. In some cases post-irradiation annealing has been carried out. The results are discussed with reference to equivalent Transmission Electron Microscopy results on the microstructure of the materials. The CuNiBe has the lowest conductivity (⩽55% of that of pure Cu), and Cu–Al 2O 3 the highest (75–90% of pure Cu).

Microstructural examination of irradiated V–(4–5%)Cr–(4–5%)Ti

Microstructural examination results are reported for two heats of V–(4–5%)Cr–(4–5%)Ti irradiated in the EBR-II X530 experiment to 4.5 dpa at ∼400°C to provide an understanding of the microstructural evolution that may be associated with degradation of mechanical properties. Fine precipitates were observed in high density intermixed with small defect clusters for all conditions examined following the irradiation. The irradiation-induced precipitation does not appear to be affected by preirradiation heat treatment at 950–1125°C. There was no evidence for a significant density of large (diameter > 10 nm) dislocation loops or network dislocations. Analytical investigations successfully demonstrated that the precipitates were enriched in titanium, depleted in vanadium and contained no nitrogen. These results are discussed in terms of future alloy development options.

Measurements of emission spectra during thermoluminescence (TL) from LiF(Mg, Cu, P) TL dosimeters

A detailed analysis of the spectrum of the light emitted during thermoluminescence (TL) from irradiated LiF(Mg, Cu, P) is presented. The data show how the emission characteristics vary as functions of the concentrations of the individual dopants (Mg, Cu and P) and of the pre-irradiation heat treatments. It is suggested that the data can be interpreted in terms of precipitated phases of Mg and P. It is speculated that the heat treatments cause the dissolution of these phases and this in turn alters the glow-curve structure and leads to a reduction of the TL sensitivity.