Thermal neutron irradiation of Fe−Si−B glasses

Effect of thermal neutron irradiation of metallic glasses Fe₇₈Si₉B₁₃ and Fe₇₈Si₈B₁₄ has been studied using Mossbauer spectroscopy. The surfaces of the two specimens are found to behave very differently under irradiation. The difference may be attributed to the presence of a thin oxide layer at the surface of as-prepared Fe₇₈Si₉B₁₃.     

Stress relaxation in Fe/Si neutron supermirrors by He irradiation

Magnetic supermirrors are widely used in polarized neutron applications. A key issue in producing these multilayer structures is to avoid residual stress in the layers, which may cause the layers to peel off. In this work He⁺ ion irradiation of 500 keV energy was applied at fluences of 1, 24, 50, 100×10¹⁴ ions/cm² with the aim of reducing residual stress. Structural, magnetic and neutron-optical properties were investigated by grazing incidence high-angle X-ray diffraction, magneto-optical Kerr effect, conversion electron Mössbauer spectroscopy and polarized neutron reflectometry. We find a monotonous decrease of the tensile stress upon irradiation from 1.76 to 0.37 GPa with a coupled decrease of neutron reflectivity at the critical angle and decrease of the maximum polarizing efficiency from 23% to 4% at the highest fluence compared to the as-prepared reference supermirror. The supermirrors exhibit a superposition of uniaxial and fourfold in-plane magnetic anisotropy.     

磁控溅射方法制备直径120 mm高均匀性Mo/Si多层膜

为满足极紫外、软X射线和X射线大口径多层膜反射镜的需求,采用基板扫掠过矩形靶材表面的镀膜方法,在直径120 mm的平面基板上镀制了Mo/Si周期多层膜。通过调整基板扫掠过矩形靶材表面的速率修正了薄膜的沉积速率,极大地提高了薄膜厚度的均匀性。采用X射线衍射仪对反射镜不同位置多层膜周期厚度进行了测量,结果表明,在直径120 mm范围内,Mo/Si多层膜周期厚度的均匀性达到了0.26%。同步辐射测量多层膜样品不同位置处的反射率,结果表明,在直径120 mm范围内,多层膜的膜层厚度均匀,在入射角10°时13.75 nm波长处平均反射率为 66.82%。     

磁控溅射方法制备直径120 mm高均匀性Mo/Si多层膜

为满足极紫外、软X射线和X射线大口径多层膜反射镜的需求,采用基板扫掠过矩形靶材表面的镀膜方法,在直径120 mm的平面基板上镀制了Mo/Si周期多层膜。通过调整基板扫掠过矩形靶材表面的速率修正了薄膜的沉积速率,极大地提高了薄膜厚度的均匀性。采用X射线衍射仪对反射镜不同位置多层膜周期厚度进行了测量,结果表明,在直径120 mm范围内,Mo/Si多层膜周期厚度的均匀性达到了0.26%。同步辐射测量多层膜样品不同位置处的反射率,结果表明,在直径120 mm范围内,多层膜的膜层厚度均匀,在入射角10°时13.75 nm波长处平均反射率为66.82%。     

Displacement damage and transmutations in metals under neutron and proton irradiation

The knowledge of the defect and impurity generation rates, as well as the defect spatial distribution, is the corner stone for the understanding of the evolution of material properties under irradiation. This knowledge is also an essential element for comprehensive experimental simulations of the behavior of irradiated materials.In this article the interaction of neutron and proton irradiation with metals is discussed with respect to displacement damage production. Charged particle irradiation is also briefly illustrated. After discussion of the primary interaction of projectiles (neutrons, charged particles in general, and protons in particular) with target atoms/nuclei, we describe the interaction of a recoil atom with other target atoms resulting in the slowing down of the projectile, displacement damage, impurity atom production due to nuclear reactions, and the creation of atomic displacement cascades. Then the further evolution of defect structure is discussed. The next section, devoted to subcascade formation, is divided into two parts. The first experimental evidence of subcascade formation under neutron and charged particle irradiation is presented. Then the models of subcascade formation are described. Finally we review the models for the calculation of displacement damage and show how these models can be applied to displacement damage calculation under neutron irradiation with a demonstration of a real application of the methods discussed to several nuclear facilities. To cite this article: P. Vladimirov, S. Bouffard, C. R. Physique 9 (2008).     

Investigation of stability of ITER candidate Hall sensors under neutron irradiation

Hall sensors offer an attractive true non-inductive method of magnetic field measurements for fusion reactors. Their use for steady state magnetic diagnostics of ITER is presently limited by their questionable radiation and thermal stability. Issues of stable and reliable operation in ITER like radiation and thermal environment are addressed by the contribution. Recently, novel Hall sensors, compatible with temperatures up to 200°C, were developed and their radiation stability was tested at LVR-15 experimental fission reactor. Overview of the experimental set-up on LVR-15 reactor is given. Degradation of the sensor’s sensitivity by several tens of percents was observed after neutron irradiation by the total neutron fluence of 2 × 10¹⁷ n/cm² in LVR-15. This level of neutron fluence is comparable to that expected to occur over the whole ITER life time for a sensor location just outside the ITER vessel. The in-situ recalibration techniques are expected to handle the observed degree of Hall sensors performance degradation in ITER environment.     

Thermodynamic analysis of Si doping in GaN

Equilibrium calculations of Si-doping in GaN are investigated using the Gemini code. The method of the calculation is based on the minimisation of the Gibbs free energy. Experimental growth conditions are used for the calculation. The variables are the amount of the dopant and the temperature. The results show the formation of a solid Si₃N₄ compound with a certain quantity of the input SiH₄, that is the silicon precursor in our MOVPE system. Si₃N₄ formation can explain the limitation of Si incorporation and the surface roughening as revealed by MOVPE Si doped layers.     

Analysis of the relationship between neutron dose and Cerenkov photons under neutron irradiation through Monte Carlo method

To theoretically explore the feasibility of neutron dose characterized by Cerenkov photons, the relationship between Cerenkov photons and neutron dose in a water phantom was quantified using the Monte Carlo toolkit Geant4. Results showed that the ratio of the neutron dose deposited by secondary electrons above Cerenkov threshold energy to the total neutron dose is approximately a constant for monoenergetic neutrons from 0.01 eV to 100 eV. With the initial neutron beam energy from 0.01 eV to 100 eV, the number of Cerenkov photons has a good correlation with the total neutron dose along the central axis of the water phantom. The changes of neutron energy spectrum and mechanism analysis also explored at different depths. And the ratio of total neutron dose to the intensity of Cerenkov photons is independent of neutron energy for neutrons from 0.01 eV to 100 eV. These findings indicate that Cerenkov radiation also has potential in the application of neutron dose measurement in some specific fields.     

Metastability of Si1-yCy epilayers under 2 MeV alpha-particle irradiation

In this work we present some recent results concerning the alpha-particles irradiation of Si1-yCy alloy epitaxially grown on silicon. The study of the damage process is interesting because of the extensive use of backscattering technique as a tool of characterisation of this kind of materials and because of the possibility of adding information about the transformations that this metastable material undergoes. We point out that the irradiation damage process causes a change in the material structure different from that due to the thermal treatments. The irradiation damage occurs at a rate much higher than in Si, however it involves only a silicon atom fraction that appears to be proportional to the substitutional carbon content.     

Surface lifetime degradation in Si and Ge under low energy electron irradiation

The bombardment of n-type Ge and Si by 10–30 keV electron beams is shown to reduce the surface lifetime τ_P of minority carriers but not to affect mobility μ_P or diffusion constant D_P. For experiments, the electron beam in a scanning electron microscope is replaced a chopped light source to perform modified Haynes-Shockley experiment, and the measurements is used to calculate μ, D and τ. The reduction in τ is interpreted in terms of an increase in surface recombination velocity s. At a dose of approximately 10¹⁷ electrons cm^?2 for Ge and 10¹⁵ electrons cm^?2 for Si, a saturation value for s appears to be reached after which further bombardment has no effect. The values of τ obtained from both light and SEM Haynes-Shockley experiments performed in vacuum agree within approximately 5% both prior to and after bombardment. The initial values of lifetime can be restored by etching the samples.     

NMR study of magnetic moments arising in superconducting cuprates under electron/neutron irradiation

The measurements of direct-current magnetic susceptibility and nuclear magnetic resonance (NMR) were performed in the superconducting cuprates YBa₂Cu₃O_6.9 (⁸⁹Y,⁶³Cu), Tl₂Ba₂CaCu₂O₈ (¹⁷O,²⁰⁵Tl), irradiated by fast neutrons (E _n = 1 MeV) and electrons (E _e = 5 MeV). The influence of the radiation-induced structural disorder on the spin susceptibility and magnetic state of atoms in the CuO₂ layer is considered. The possible effect onT _c of the spin-exchange scattering of carriers by localized moments arising under irradiation was estimated following the Abrikosov-Gorkov approach and its contribution was found to be too small in comparison with the real suppression ofT _c under irradiation.     

The loss of boron in ultra-shallow boron implanted Si under heavy ion irradiation

Heavy ion impact has been known to cause a loss of light elements from the near-surface region of the irradiated sample. One of the possible approaches to a better understanding of the processes responsible for the release of specific elements is to irradiate shallow-implanted samples, which exhibit a well-known depth distribution of the implanted species. In this work, the samples studied were produced by implantation of Si<1 0 0>wafers with ¹¹B at implantation energies of 250 and 500 eV and fluence of 1.0×10¹⁵ atoms/cm ². Elastic Recoil Detection Analysis was applied to monitor the remnant boron fluence in the sample. Irradiation of the samples by a 14.2 MeV ¹⁹F ⁴⁺ beam resulted in a slow decrease of boron remnant fluence with initial loss rates of the order of 0.05 B atom per impact ion. Under irradiation with 12 MeV ³²S ³⁺ ions, the remnant boron fluence in Si decreased exponentially with a much faster loss rate of boron and became constant after a certain heavy ion irradiation dose. A simple model, which assumes a finite desorption range and corresponding depletion of the near-surface region, was used to describe the observations. The depletion depths under the given irradiation conditions were calculated from the measured data.     

Investigation of doping in Si crystals by means of electroreflectance

Summary In this work the importance of electroreflectance is evidenced in two specific applications concerning studies of semiconductor surfaces: i) determination of junction depths and carrier profiles, ii) mapping of inhomogeneity curves of the carrier distribution on Si surfaces. New information in both cases is obtained and briefly discussed. Work partially supported by Progetto Finalizzato Energetica (Sottoprogetto Energia Solare) of consiglio Nazionale delle Ricerche.     

Study of Fe−Ni−Cr−Mo−Si−B metallic glasses after neutron irradiation

Chromium containing metallic glasses are studied by transmission⁵⁷Fe Mössbauer spectroscopy after neutron irradiation. Increasing number of nonmagnetic chromium atoms causes a compositional dependence of Curie temperature. The unirradiated samples are fully paramagnetic forx≥10 at. % Cr at room temperature. Radiation induced changes in the magnetic structure imply a decrease of the Curie temperature. Ferromagnetic-to-paramagnetic transition is observed at room temperature for 8 at. % Cr after the exposure with 10¹⁹ n/cm². Using low temperature measurements, the Curie temperature for the sample containing 10 at. % Cr is estimated to be about 270 K.     

Procedure for rapid spectroscopic control of the distribution of oxygen and of doping impurities in silicon ingots

Spectral dependences of the coefficients of absorption by free carriers and of multiphoton absorption by a silicon lattice in the region of the interstitial oxygen band at 5.8 μm are established. A procedure for measurement of the distribution of oxygen and alloying impurities in silicon ingots is given. The effectiveness of the spectrometers developed for controlling the segregation of impurities and nonstationary convection of the silicon melt in growing ingots by the Czochralski method is shown. Belarusian State University, 4, F. Skorina Ave., Minsk, 220080, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 655–659, September–October, 1997.     

Elastic neutron transfer in the scattering of Si isotopes

Angular distributions of the elastic scattering of ²⁸Si on ²⁹Si and ³⁰Si have been measured for incident beam energies at E = 65 and 70 MeV with a time-of-flight spectrometer for heavy ions. At 70 MeV the neutron transfer ³⁰Si(²⁸Si, ²⁹Si)²⁹Si was observed in addition to the elastic channel. The pronounced oscillations in the elastic scattering distributions are interpreted as being due to an elastic transfer of neutrons between the colliding nuclei during the scattering process. This assumption is in accordance with some general features of the data and allows for the extraction of spectroscopic factors of the transferred neutrons.     

Surface doping of semiconductors by pulsed-laser irradiation in reactive atmosphere

Intense pulsed-laser irradiation in a suitable chemical atmosphere can produce a significant incorporation of chemical species from the environment to the surface molten layer. This process has been used to produce p-n junctions in silicon and GaAs irradiated, respectively, in PCl₃ and SiH₄ atmospheres. A modelling of the incorporation process, taking into account the solid-liquid-solid transition of the surface layer, has been developed following both a numerical and a semi-analytical approach. The modelling of the doping process gives results in a reasonably good agreement with the experimental doping profiles, obtained by irradiating Si samples in PCl₃ atmosphere.