Recovery of copper alloys after neutron irradiation at low temperatures

The effects of fast neutron irradiation near 4.2°K on dilute Cu, Cu₃Au, α-CuZn, β-CuZn and CuNi alloys were studied by electrical resistivity measurements. For Cu₃Au, the recovery stage at ～ 100°K becomes more distinct with increasing long-range order, and is attributed to migration of interstitials. The ratio of the number of replacements to the number of displacements (C _R /C _F ) is estimated to be about 50 for neutron irradiation, in contrast to the previously reported value of ～2 for electron irradiation. For α-CuZn, a large recovery stage at ～150°K is found and attributed to annihilation of interstitids whose migration produces ordering. For β-CuZn, migration of interstitials also produces ordering. It is also suggested that in β-CuZn, the ratio C _R /C _F is larger for neutron irradiation than for electron irradiation as in the case of Cu₃Au. The results on CuNi alloys are presented without explanation.     

Magnetoresistance measurements in Al-Ge alloys after neutron irradiation at 4.6 K

The influence of different structural defects, introduced by irradiation in a series of AlGe alloys is established by measuring the longitudinal magnetoresistance. The validity of Kohler's rule is absolute for both pure and alloyed samples that have been irradiated by neutrons at 4.6 K, while the rule breaks down after annealing at different temperatures.The origin of the breakdown of Kohler's rule appears to be the anisotropic scattering of the electrons on the clusters formed after annealing. This scattering depends on the size of the clusters which varies with the concentration of foreign atoms.     

Recovery of electrical resistivity in amorphous pdsi alloys after low temperature neutron irradiation

Measurements of electrical resistivity after low temperature fast neutron irradiation are made for amorphous Pd₈₀Si₂₀ and Pd₈₀Ni₂Sl₁₈ and then Pd₈₀Si₂₀ annealed at 230°C and 360°C, and the isochronal annealing curves are obtained. The resistivity increase of Pd₈₀Si₂₀ annealed at 360°C is about 10 times larger than that of amorphous alloys and no defined annealing stage is observed in amorphous alloys and Pd₈₀Si₂₀ annealed at 360°C. For amorphous Pd₈₀Si₂₀, about 60% of the resistivity increase by irradiation remains after annealing up to room temperature and these are discussed by the structural relaxation.     

Change of GeSx parameters after neutron irradiation

In the paper some experimental results on the dependence of thermal conductivity, temperature conductivity coefficient, heat capacity, dc conductivity and ac conductivity on integrated neutron flux within the range from 10¹⁶ n cm^–2 to 10¹⁹ n cm^–2 are described. At integrated neutron flux of 10¹⁷ n cm^–2 an extreme in all parameters was observed. This effect can be explained by means of compensation of unsaturated bonds in the glass due to defects caused by irradiation.     

Grain boundary impurity segregation and neutron irradiation effects in ferritic alloys

Segregation of alloying and impurity elements to grain boundaries in ferritic steels and alloys is known to modify the mechanical properties. This paper considers segregation of such elements, in particular phosphorus and carbon, that occur in ferritic nuclear pressure vessel steels subject to neutron irradiation and temperature typical of that encountered in service. Models are presented that allow the prediction of equilibrium and non-equilibrium segregation of phosphorus to grain boundaries and also take into account synergistic interaction with carbon under various combinations of neutron-irradiation temperature. These are related to a wide range of experimental observations compiled from data in the literature for mainly phosphorus and carbon measured at grain boundaries in neutron-irradiated ferritic vessel steels and alloys. The predictions from the segregation models are compared with these experimental data. The discussion provides a rationalization for the apparent variability in the measured grain boundary phosphorus compositions and thereby fracture susceptibility for various nuclear pressure vessel ferritic steels.     

Nanocrystalline magnetic PrFeCrB alloys

Ribbons of Pr₅Fe_77−xCr_xB₁₈ (x=0$x=0$, 1, 2, 2.5, 3, 4, 5) were produced by melt spinning and then annealed to develop an enhanced-remanence nanocrystalline magnetic material. These nanocomposites with Cr present a coercive field at least 50% higher than the Cr-free ones, which makes them promising materials for bonded magnets. Four different types of annealing were used in order to develop the nanocrystalline state and to optimize the magnetic properties of these alloys. The first was a conventional annealing, where the ribbons were wrapped in a tantalum foil and annealed in an argon atmosphere, but not encapsulated. The second was a flash annealing, where the ribbons were annealed by passing a current through them. The third was a conventional annealing in an external magnetic field. Finally, the fourth was a conventional annealing, where the ribbons were wrapped in a tantalum foil and encapsulated in quartz tubes with argon gas and then annealed. The annealed samples were studied by magnetic measurements, X-ray diffraction, scanning and transmission electron microscopy and atomic force microscopy. The best magnetic properties are found for Pr₅Fe₇₄Cr₃B₁₈, annealed by the fourth method, which resulted in the lowest oxygen content in the annealed nanocrystalline material as confirmed by scanning electron microscopy. The value for the coercive field for this composition is at least 50% higher than for the material without Cr (≈560 vs. ≈320 kA/m) and 40% higher than for the Nd₂Fe₁₄B/Fe₃B nanocomposite with Cr. Curie temperature measurements and X-ray diffraction data showed that the main phases present in all the samples are Pr₂Fe₁₄B, Fe₃B and α-Fe, Pr₂Fe₁₄B being the majoritary phase. From Curie temperature measurements it was also found that Cr atoms preferentially dissolve in the Fe₃B phase.     

Enhanced diffusion due to neutron irradiation in Cu-Ni alloys at different temperatures

The review of the existing data on the reverse annealing of boron implants in silicon is given. The idea of the exchange reaction of boron substitutionals with silicon selfinterstitials as being responsible for the phenomenon is critically considered. Instead, the possible involvement of oxygen and oxygen-related secondary defects is proposed.     

Short-range order of amorphous FeNiB alloy after neutron irradiation

Transmission Mössbauer spectroscopy was used to study irradiation-induced changes in the short-range order of an amorphous Fe_80-x Ni _x B₂₀ alloy. Neutron irradiation led to an increase of the width of a hyperfine field distribution implying atomic rearrangement towards disordering. Changes in a mean value of a HFD and Mössbauer line areas can be associated with a reorientation of spins due to radiation damage.     

Point defects in alkaline-earth fluorides after thermal neutron irradiation

Single crystals of MgF₂, CaF₂, SrF₂ and BaF₂ have been irradiated with polarized, thermal neutrons at temperatures between 10 K and 300 K. The neutron capture process creates polarized, -active²⁰F( =16s) probe nuclei, which are displaced by the recoil and thus produce some nearby point defects. These defects have been studied by their influence on²⁰F NMR signals being monitored via the asymmetric -decay radiation of the polarized²⁰F nuclei.From our results we conclude that in the fluorites CaF₂, SrF₂ and BaF₂ thermal neutron irradiation leads to the formation of anion Frenkel pairs, the predominant intrinsic defect in such crystals. Correlated recombination of these close Frenkel pairs with activation enthalpies of about 0.2 eV was observed at temperatures around 80 K. A second annealing stage occurs near 220 K corresponding to an activation enthalpy of about 0.6 eV. Possible annealing mechanisms responsible for this stage are discussed. In tetragonal MgF₂ two annealing stages were found at 13 K and 60 K corresponding to 0.037 eV and 0.17 eV, respectively. The stage at 60 K possibly reflects migration of the H entre whereas the interpretation of the 13 K stage remains an open question.     

Martensitic transformation in a copper-aluminum-nickel alloy single crystal after short-term neutron irradiation

The influence of neutron irradiation on the temperature kinetics of thermoelastic martensitic transformation in a Cu-Al(13.4%)-Ni(5%) alloy single crystal is investigated by measuring the electrical resistivity directly under irradiation of the sample in a nuclear reactor channel. It is revealed that, after irradiation of the crystal in a martensitic or two-phase state, the temperature of the phase transition upon heating becomes 25–30 K higher than that prior to irradiation. This shift in the transition temperature is observed only upon the first heating, and the kinetics of martensitic transformation is restored in subsequent thermocycles. The shift in the transformation temperatures after irradiation increases with an increase in the fluence. The experimental results are explained by a disturbance of coherence at the interfaces in the irradiated crystals.     

Analysis of multiple cell upset sensitivity in bulk CMOS SRAM after neutron irradiation

In our previous studies, we have proved that neutron irradiation can decrease the single event latch-up(SEL) sensitivity of CMOS SRAM. And one of the key contributions to the multiple cell upset(MCU) is the parasitic bipolar amplification,it bring us to study the impact of neutron irradiation on the SRAM's MCU sensitivity. After the neutron experiment, we test the devices' function and electrical parameters. Then, we use the heavy ion fluence to examine the changes on the devices' MCU sensitivity pre-and post-neutron-irradiation. Unfortunately, neutron irradiation makes the MCU phenomenon worse.Finally, we use the electric static discharge(ESD) testing technology to deduce the experimental results and find that the changes on the WPM region take the lead rather than the changes on the parasitic bipolar amplification for the 90 nm process.     

The effect of neutron irradiation on the Barkhausen noise in amorphous Fe40Ni40B40 alloys

Theoretical expression for the power spectra of Barkhausen noise was used to obtain information on the dynamical properties of domain walls from the experimental spectra. It was shown that after irradiation the domain wall mobility increases due to the change of the effective mass of domain wallsm _ef, damping constant and the spring constant.Dedicated to Dr. S. Krupika on the occasion of his 65th birthday.The authors wish to thank I. Gverdciteli, of the State Committee for Science and Technology of the Georgian SSR, Tbilisi (USSR), for supplying boron isotopes.     

光电耦合器的反应堆中子辐射效应

 选择3种典型光电耦合器开展了反应堆中子辐照实验,中子注量为3×10¹¹~5×10¹²cm^-2时,位移效应导致电流传输比下降,饱和压降提高。发光器件相同,探测器为Si PIN光电二极管的光电耦合器比探测器为Si NPN光敏晶体管的光电耦合器的初始电流传输比要小,但其抗位移损伤能力更强。探测器均为Si NPN光敏晶体管,发光器件为异质结LED要比硅两性掺杂LED的光电耦合器的电流传输比抗位移损伤能力提高2个量级;以光敏晶体管为探测器的光电耦合器,在较大的正向电流和输出负载电阻条件下工作可提高抗辐射水平。此外,光电耦合器的位移损伤存在加电退火效应。     

Interstitial-impurity reactions during stage I of platinum alloys after thermal and fast-neutron irradiation

Recovery spectra of pure platinum and selected dilute platinum alloys are compared to equivalent induced resistivities following either fast- or thermal-neutron irradiation at 4.4 K. Annealing during stage I (7–30 K) was significantly retarded due to the fast-neutron irradiation. Although a reduction in recovery due to alloying impurities was observed, it appears that due to the highly-localised defect concentration, interstitial-interstitial reactions were predominant during annealing of the fast-neutron defects, whilst in the case of the thermal neutrons, due to the generalised low defect concentration, interstitial-impurity reactions were more important.     

光电耦合器的反应堆中子辐射效应

选择3种典型光电耦合器开展了反应堆中子辐照实验,中子注量为3×1011~5×1012cm-2时,位移效应导致电流传输比下降,饱和压降提高。发光器件相同,探测器为Si PIN光电二极管的光电耦合器比探测器为Si NPN光敏晶体管的光电耦合器的初始电流传输比要小,但其抗位移损伤能力更强。探测器均为Si NPN光敏晶体管,发光器件为异质结LED要比硅两性掺杂LED的光电耦合器的电流传输比抗位移损伤能力提高2个量级;以光敏晶体管为探测器的光电耦合器,在较大的正向电流和输出负载电阻条件下工作可提高抗辐射水平。此外,光电耦合器的位移损伤存在加电退火效应。     

Nanocrystalline iron-based alloys investigated by Mössbauer spectrometry

Nanocrystalline alloys exhibit great fundamental and technological interests because of their microstructural properties, and their excellent soft magnetic properties. ⁵⁷Fe Mössbauer spectrometry is a well suitable technique to investigate Fe-based nanocrystalline alloys: its local probe behaviour permits to elucidate the nature of hyperfine interactions at different resonating iron nuclei and to distinguish their immediate atomic surroundings. We review on the recent Mössbauer developments performed on first FeCuMBSi and then FeCuBSi nanocrystalline alloys. From Mössbauer studies, one can estimate the crystalline (i.e., amorphous) fraction, the Si-content in Fe--Si nanocrystalline grains emerging from amorphous alloys of the first series, the temperature dependence of magnetic behaviours of both crystalline and amorphous phases; finally, we present a novel fitting procedure applied to FeCuBSi nanocrystalline alloys which result from bcc-Fe crystalline grains embedded in an amorphous matrix. In this case, the hyperfine structure is able to model the intergranular phase.     

Phase field modeling precipitation of β-phase and mechanical properties change in Zr–Nb alloys under neutron irradiation

ABSTRACT

We study microstructure transformation in Zr–Nb system under neutron irradiation and its mechanical properties change under mechanical loads in a form of shear deformation by using phase field methodology. The developed phase field approach takes into account defects dynamics based on reaction rate theory and elastic contribution to study mechanical properties change. A numerical modeling is provided in three stages: sample preparation, irradiation of the prepared sample and mechanical loading of the irradiated sample. A precipitation of β-Niobium particles of the size of several nanometers is discussed. Results of phase field modeling indicate that β-Niobium particles grow slowly during irradiation due to point defects rearrangement. Statistical analysis of dynamics of radiation-induced microstructure transformations is provided. Simulation results of shear deformation of pre-irradiated and post-irradiated alloys are discussed. Maps of local distribution of strain and stress and strain–stress curves are obtained. Results are verified with experimental data.     

Recovery of c-axis spacing in pyrolytic graphite after neutron irradiation at 5 K

Recovery of the c-axis spacing expansion in pyrolytic graphite after neutron irradiation at 5 K was measured in the range of 5 K ～ 900 K by the X-ray diffraction method. An unexpectedly large recovery of the spacing was found around 100 K.