Neutron-irradiated Aluminum Research Articles

Recovery behavior of neutron-irradiated aluminum nitride with and without containing interstitial dislocation loops

Recovery behavior of the same AlN but neutron-irradiated with different conditions was studied by using XRD and dilatometry. Length recovery rates at each isothermal annealing step were analyzed by first to second-order kinetics. The specimen irradiated at lower neutron fluence at low irradiation temperature responded isotopic unit-cell expansion, which indicated random dispersion of point defects of vacancies and/or very small defect clusters. From irradiation temperature up to 523 K, the results of Arrhenius’ plot applied for second-order kinetics gives an activation energy value of 2.9 eV. An intermediate region, 573 to 1023 K, was represented by a slightly lower activation energy of 2.0 eV. For the first lower temperature range, migration of VN may be the mechanism and that of VAl for the second stage. At high-temperature region, 1073 to 1423 K, represents final constant recovery before the saturation of length recovery. In this region, the high activation energy of 5.8 eV was observed. It is supposed that dissociation of the vacancy-antisite cluster, interstitial nitrogen cluster, or formation of a complex containing vacancy and antisite can be candidate mechanisms. The specimen containing interstitial loops after the medium fluence at higher temperatures did not recover up to 723 K, indicating almost free of independent interstitials. Between 773 and 1123 K, recovery required a similar amount of energy to the high-temperature region of the lower fluence specimen (5.8 eV), and then the same mechanism could be applied. In the second region, 1173 to 1423 K, with a very high activation energy of ~18 eV, remarkable large and quick shrinkage was observed. Large volume shrinkage may be the result of diminishing anisotropic lattice swelling, i.e., unit-cell volume expansion by internal strain is relieved.

Physical property changes of neutron-irradiated aluminum nitride and their recovery behavior by annealing using a step-heating dilatometer

Aluminum nitride (AlN) is a candidate tritium permeation, electric insulation and corrosion barriers for several kinds of blankets such as molten salt–cooled (FLiBe) or liquid metal (Li-Pb or Li)-cooled blankets because of its desirably low dielectric constant and tritium diffusion. Commercially available AlN ceramic specimens were neutron-irradiated at two different fluences but the same irradiation temperature in the Japan Materials Testing Reactor. Specimen swelling was found to be slightly different for both conditions, with higher dose causing greater swelling. All irradiated specimens consisted from hexagonal AlN phase with α-Al2O3 phase occurring on the surface after long-time post-irradiation annealing in He atmosphere. The a- and c-axis experienced isotropic increase and degree of unit-cell volume change was almost the same with the macroscopic volume increase obtained from the length change. This result indicates uniform distribution of Frankel pairs. After step-wise thermal annealing by using a dilatometer up to 1673 K for 6 h at each step, the maximum recovery was found at 1573 K. Based on the recovery rates at each step by first-order analysis, macroscopic length recovery during annealing can be divided into three regions with different activation energies, low temperature (373–523 K) with ∼4.5 eV, intermediate temperature (523–873 K) with 0.5–1.0 eV, and high temperature (873–1273 K) with 2.0–2.5 eV. Over 1273 K, a slight increase of length was observed. It is thought that the expansion is due to oxidation.

Residual Radioisotopes Generated from Neutron Irradiated Aluminum Capsules

Aluminum (Al) is often used to house a molybdenum oxide (MoO3) target for neutron or proton-produced technetium-99m (99mTc) radioisotope. During neutron or proton bombardment of an Al body, residual radioisotopes could be generated following nuclear reactions between the incoming particles and the Al body. In this research, residual radioisotopes produced following nuclear reactor based-neutron irradiation of Al body were experimentally measured using a portable gamma ray spectroscopy system; whereas TALYS 2015 calculated data were used to evaluate various nuclear reactions for the by-product identification. As a comparison, Al body used in a cyclotron-based 99mTc production was also analyzed. Experimental data indicated that relatively long-lived radioisotopes such as 26Al, 22Na and 24Na were identified in the Al body following nuclear reactor-based 99mTc production, whereas the presence of 27Mg radioisotope was, for the first time, experimentally detected in both the Al bodies for nuclear reactor-based and cyclotron-based 99mTc production. A special safety attention should be paid to the radiation workers when producing 99mTc using a nuclear reactor since it generates 26Al (half life = 716,600 years).

Residual Radioisotopes Generated from Neutron Irradiated Aluminum Capsules

Aluminum (Al) is often used to house a molybdenum oxide (MoO 3 ) target for neutron or proton-produced technetium-99m ( 99m Tc) radioisotope. During neutron or proton bombardment of an Al body, residual radioisotopes could be generated following nuclear reactions between the incoming particles and the Al body. In this research, residual radioisotopes produced following nuclear reactor based-neutron irradiation of Al body were experimentally measured using a portable gamma ray spectroscopy system; whereas TALYS 2015 calculated data were used to evaluate various nuclear reactions for the by-product identification. As a comparison, Al body used in a cyclotron-based 99m Tc production was also analyzed. Experimental data indicated that relatively long-lived radioisotopes such as 26 Al, 22 Na and 24 Na were identified in the Al body following nuclear reactor-based 99m Tc production, whereas the presence of 27 Mg radioisotope was, for the first time, experimentally detected in both the Al bodies for nuclear reactor-based and cyclotron-based 99m Tc production. A special safety attention should be paid to the radiation workers when producing 99m Tc using a nuclear reactor since it generates 26 Al (half life = 716,600 years).

Determination of radiogenic silicon and its isotopes in neutron irradiated aluminum alloys by ICP-MS

Aluminum alloy is frequently used as component material in research nuclear reactors.

Angular Distribution of Neutron Flux around the Tritium Target of 14 MeV Neutron Generator

The angular distribution of the 14 MeV neutrons emitted through D–T reaction was measured around the tritium target of a 14 MeV neutron generator using two different sample holders and also theoretically estimated. The samples were made out of 99.99% pure Aluminium foil and irradiated with the neutrons. In the neutron irradiated aluminum samples, the gamma-ray activity, induced through the nuclear reaction Al 27 (n,α)Na 24 was measured by a NaI(Tl) detector. Using one of the sample holders the axial distribution of neutron flux was also estimated. The discrepancy from the isotropic pattern was accounted for by reasons related to the in-between matrices and design of the tritium target mounting assembly.

Electric conductivity of neutron-irradiated aluminum alloys

The effect of ionizing radiation, temperature, and products of the radiolysis of water on the materials of fuel elements used in nuclear reactors during operation is examined. The effect of irradiation in a reactor on the electric conductivity and the change of the linear dimensions of the alloys SAV-1 and AMG-2 are investigated. It can be concluded on the basis of the relative elongation that the aluminum alloys studied can be used to fluence 10 20 cm −2 without appreciable loss of reliability.

Radiogenic silicon precipitates in neutron irradiated aluminum

A theory of precipitation of radiogenic Si in Al is developed. The aim of this study is to predict quantitatively the variation of microstructural parameters such as precipitates number and sizes dependently on irradiation parameters. Analogy with deposition of thin films and formation of silver halides is discussed. A model for the precipitation of radiogenic Si in Al is developed on the basis of the theory of Ostwald-ripening in precipitation processes with constant rate addition of monomers. The model predicts that after the precipitation process enters the ‘late’ stage, the number of precipitates depends only on the ratio between the thermal and fast neutron fluxes but not on the absolute values of flux and fluence. A quantitative interpretation of the spectral effect, suggested by Farrell [Mater. Res. Soc. Symp. Proc. 373 (1995) 165] is given. The predictions of the model are compared with experimental results.

Electron channelling contrast imaging of defect structures in neutron irradiated aluminium

Electron channelling contrast imaging of defect structures in neutron irradiated aluminium

A TEM study of radiogenic silicon precipitation in neutron irradiated aluminium

Following neutron irradiation of an aluminium component (1080 grade aluminium) from the high flux Australian reactor (HIFAR) to fluences of up to 2.6 × 10 26 thermal neutrons m −2, precipitation of up to 0.64 wt% radiogenic silicon has been observed using TEM. The onset of visible silicon precipitation occurred at 0.2 × 10 26 thermal neutrons m −2. At fluences ⩾1.8 × 10 26 thermal neutrons m −2 diffraction spots due to crystalline silicon were detectable using selected area electron diffraction. This technique showed that the silicon precipitate was predominantly in a cube//cube relationship with the matrix, with twinning observed on the {1 1 1} Si plane. This twinning influenced the shapes of the particles, which exhibited {1 0 0} and {1 1 1} type facets. A second minor orientation relationship (Kobayashi) was also observed.

A Spectral Effect on Phase Evolution in Neutron-Irradiated Aluminum?

AbstractIt is proposed that the spatial distribution of transmutation-produced silicon precipitates formed in aluminum by capture of thermal neutrons is systematically modified by the fast neutron portion of the spectrum, and the tensile strength is altered accordingly. The concept is used to rationalize some previously erratic tensile data.

Thermal and mechanical properties of neutron-irradiated aluminum nitride

High-purity translucent aluminum nitride was neutron-irradiated in the JMTR to fluences up to 5.2 × 10 24 n/ m 2 ( E > 1.0 MeV). Irradiation-induced linear swelling was less than that of SiC. Macroscopic volume swelling coincided fairly well with the volume swelling calculated from the axial length change, which showed an anisotropic expansion of the c-axis larger than the a-axis. Mechanical strength moderately degraded with increase in volume swelling. The Vickers hardness increased with increase in volume swelling. The thermal conductivity was markedly reduced by neutron irradiation, but maintained a value of 25–30 W/mK after irradiation. These changes in physical properties are discussed in terms of the irradiation induced microstructural change observed by TEM, where very small interstitial loops were formed on the (0001) plane, but no microcracking was observed.

Colour centres in neutron irradiated aluminium oxy-nitride

Aluminium oxy-nitride (9Al2O3.5AlN) has been neutron irradiated to fluences varying from 1018-1024 n m-2 (En>1 MeV) at 60 degrees C. The defect structures were studied by X-ray lattice parameter measurements and optical spectroscopy. The lowest neutron doses produced an anomalous volume expansion of 0.17% which was also reflected in a shift of the absorption edge to longer wavelengths. The exponential variation of the absorption edge with photon energy suggests that the 'edge' is the long wavelength side of an exciton band. The identification of two V bands with the intrinsic octahedral aluminium vacancy (2.225 eV) and the tetrahedral aluminium vacancy (3.15 eV), and their relative strengths after low neutron doses, suggested that the volume expansion may be associated with the octahedral aluminium vacancy centre. The oscillator strength of the two V bands was calculated to be 3*10-5. At higher neutron fluences the increase in lattice parameter and anion vacancy concentration showed good agreement with those found for equivalent doses in Al2O3. Comparison with the absorption spectrum of irradiated Al2O3 leads to the following assignment of anion vacancy centres to absorption bands in AlON:F-5.46 eV, F+-5.00 eV, FA-4.6 eV, F2-4.1 eV, F2+-3.68 eV.

Detection and analysis of microscopically invisible cascade defects in 14 MeV neutron irradiated aluminum and iron

Abstract Experiments to detect damage created by cascades in aluminum and iron, in which no defect structures have been observed by electron microscopy are designed by effectively combining 14 MeV neutron irradiation with electron irradiation damage by a high voltage electron microscope. The shrinkage and annihilation of interstitial loops formed by electron irradiation by subsequent neutron irradiation was most marked in aluminum and but occurred to some degree in iron. The result is explained by a simple model of diffusion of vacancies and interstitials based on the difference of the initial distribution profile between the two kinds of point defects in a cascade. The extent of the annihilation of neutron radiation induced defect clusters in iron formed at room temperature is detected by the variation of the interstitial cluster formation at 323 K by high energy electron irradiation. Two annealing stages of 523–573 K and 573–623 K are observed.

The role of helium in the development of damage structure and swelling in neutron-irradiated aluminium

Abstract Helium and its state of agglomeration in pure aluminium prior to neutron irradiation are investigated with respect to its influence on the microstructural features developed during irradiation to doses of 0·005 to 2·6d.p.a. at about 328 K (0·35 Tm). A level of 4 a.p.p.m. helium, in either submicroscopic form or as small bubbles at the resolvable limit of 2 nm diameter, induces large increases in both the cavity and dislocation components of the damage structure. It also causes swelling to begin much earlier in the neutron dose and to exhibit two different stages of evolution, one early in the dose where the dose exponent of swelling is high, the other at later stages with lower exponent. When the helium is coarsened into 7-nm bubbles by annealing at 0·96 Tm before irradiation it has relatively small effects on damage structure and swelling. The increases in concentrations of cavities and dislocation loops in the presence of helium are attributed to trapping of radiation-produced vacancits by the ...

Study of the trapping of positive muons by extended defects in aluminum

PulsedμSR spectra were measured with surfaceμ + in neutron irradiated aluminum as a function of specimen temperature above room temperature. It was found that the depolarization rate ofμ + increases and the precession frequency decreases as the specimen temperature is raised. This fact was attributed to the trapping ofμ + by radiation induced voids and suggests the importance ofμ +-surface interactions in the case of voids.

Positron annihilation study of fast neutron irradiated aluminium

Doppler broadening of the positron annihilation line was measured in annealed aluminium and neutron irradiated ( T irr = 90°C ) aluminium, as a function of temperature, below the irrradiation temperature. Positron lifetime spectra were also measured as a function of temperature in the same temperature interval. From these measurements it is concluded that a high concentration of very small voids has to be present in our samples. An annealing experiment showed that the irradiation induced defects are all annealed out at 600 K.

Solute Effects in Neutron Irradiated Aluminum

The effects that trace impurities have on the radiation damage characteristics of aluminum has been studied by Farrell and Houston, (1979). A large number of aluminum alloys containing 100 ppma of various elements were neutron irradiated to several fluences and studied by TEM. The results of this study indicated that copper is a strong suppressor of void swelling in aluminum. Because of this, the A1 + 100 ppma Cu alloy was chosen for further analysis of its defect microstructure by the use of the dislocation loop catalog compiled by the authors (1979). Neutron irradiated pure aluminum (99.9999%) and A1 + 100 ppma Si were also examined so a standard for comparison could be achieved (the A1-Si alloy was chosen because of the transmutation of A1 to Si during neutron irradiation).

The kinetics of void annealing in neutron irradiated aluminum

The kinetics of void annealing in neutron-irradiated, high purity aluminum containing 0.006 void volume fraction was studied by means of dilatometry. Over the temperature range 358–573 K, the isothermal recovery of void volume fraction exhibited a logarithmic kinetic behavior. The data were analyzed in terms of a recovery rate equation of the form df dt = −fK 1 exp−[ Q 0−βf RT ] A theory for void annealing in irradiated aluminum is described based on the premise that voids shrinking under the action of interfacial forces emit single vacancies which migrate by diffusion to internal sinks where they are annihilated. In the theory, Q 0 is equal to the self diffusion activation energy. For the parameters Q 0 and K 1, satisfactory agreement between theory and experiment was achieved. The theory as presented cannot account for the parameter β. Its influence on recovery was speculated to be related to the damage state of the material. The ratio-of-slopes method was used to analyze recovery rate data from isochronal experiments. In common with the isothermal results, the measured activation energy for void annealing was found to be a function of how much void volume fraction remained to be annealed. An approximate void size distribution function was derived which agreed satisfactorily with experiment.

A quenching and annealing study of neutron-irradiated aluminium by positron annihilation

Abstract The Doppler broadening of the positron annihilation line has been measured on polycrystal samples of quenched aluminium, neutron-irradiated aluminium, and quenched, neutron-irradiated aluminium, as a function of temperature over the range 130 K to ∼600 K. A peak in the lineshape (S) parameter is observed in both quenched samples, and is attributed to vacancy clustering. This peak is enhanced in the irradiated sample, probably b ecause of the presence of transmutation-produced silicon in this sample. The S parameter for the unquenched, irradiated sample also shows an interesting temperature dependence, some of which is produced by the temperature dependence of positron trapping into voids.