Observation of light radiation induced by positrons in α-LiIO3 single crystals

Light radiation emitted by α-LiIO₃ single crystals under positron irradiation is detected. The radiation emergence model due to annihilation on two groups of electrons of the IO^-₃ quasimolecular complex is suggested to be in accordance with the annihilation data as well as with the electronic structure calculation results.     

Thermoluminescence of α-Al 2O 3 by neutron irradiation at low temperature

Thermoluminescence (TL) mechanisms of neutron-irradiated α-Al₂O₃ at 20 K is reported. The TL glow curves of neutron-irradiated and γ-ray-irradiated α-Al₂O₃ were observed. The TL emission bands near 340, 430, 530 and 694 nm were observed in the neutron-irradiated α-Al₂O₃. The γ-ray-irradiated α-Al₂O₃ only showed the TL emission line nearly at 694 nm, corresponding to the R lines of α-Al₂O₃:Cr³⁺. Therefore, the first three emission bands are related to the atomic displacement defects as F-type centers caused by neutron irradiation.     

Ionoluminescence and formation of color centers in α-Al2O3 single crystals under proton irradiation

This paper describes results of experimental studies on radiation defects in nominally pure single crystals of corundum in two initial states: α-Al₂O₃ with an unperturbed lattice and α-Al₂O₃:C with a high concentration of anion vacancies. Defects were identified from optical absorption spectra, ionoluminescence, pulsed cathodoluminescence and photoluminescence spectra. It is shown that mostly color centers of the F- and F⁺-types are formed in the α-Al₂O₃ lattice under irradiation with 5,7 MeV protons.     

Fabrication of α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> bi-functional composites with hierarchical and hollow structures and their application in water treatment

The α-Fe₂O₃/TiO₂ bi-functional composites with hierarchical and hollow structures are fabricated through a hydrothermal route. The adsorption performance and photocatalytic activity of the composites towards Pb²⁺ are investigated in this work. Different adsorption kinetics models and equilibrium models are used to explore the adsorption behavior of hierarchical α-Fe₂O₃/TiO₂ hollow spheres. Experimental data show that adsorption kinetics of the hierarchical α-Fe₂O₃/TiO₂ hollow spheres can be fitted well by the pseudo-second-order model, while the isothermal data can be perfectly described by the Langmuir adsorption model. The maximum adsorption capacity of the hierarchical α-Fe₂O₃/TiO₂ hollow spheres is 32.36 mg g^?1. Moreover, the hierarchical α-Fe₂O₃/TiO₂ hollow spheres possess photocatalytic oxidation character under simulated solar light irradiation. The results demonstrate that the hierarchical α-Fe₂O₃/TiO₂ hollow spheres, as effective and cheap materials, can be applied to the removal of heavy metal ions from wastewater.     

α-LiIO3晶体的电子辐照效应

用透射电子显微镜观察了电子辐照对α-LiIO₃晶体结构的影响。α-LiIO₃经100keV能量中等强度的电子束辐照后,最初转变为γ-LiIO₃继而转变为Li₂O和另一种新的、可能是非化学比的Li—O化合物,称之新产物X。若用强电子束进行辐照,则α-LiIO₃迅速熔化。此时减弱电子束或停止辐照,均能使熔融物质凝固成上述新产物X,新产物X在电子束辐照下逐渐转变为Li₂O和金属锂。从新产物X转变为Li₂O的相变有一定程度的可逆性。此外发现,在电子束辐照下,α-LiIO₃单晶的结构变化有明显的各向异性。 关键词：     

The stability of metallic glasses under ion irradiation

Abstract

Metallic glasses of Fe₈₀B₂₀ and Fe₈₀P₁₃C₇ prepared by rapid quenching have been implanted with 40 keV Ar⁺, P⁺ and B⁺ ions at doses up to 2.10¹⁶ ions cm^?2 at 273 K. The structure of the glasses was examined by X-ray diffraction. Crystallites of α-Fe and Fe₃B, present in F₈₀B₂₀ samples, either become highly defective or are amorphised. Implantation also produces structural changes in the amorphous Fe₈₀B₂₀ (a-Fe₈₀B₂₀) phase as revealed by changes in the width β of the principal diffraction halo. Both disordering and relaxation effects are observed, dependent on the initial degree of order within the a-Fe₈₀B₂₀ phase before irradiation. Implantation of F₈₀p₁₃C₇ results in an increase in the content of γ-Fe and Fe₃P crystallites, already present before irradiation, and in the nucleation of α-Fe.     

Level structure of217Rn and221Ra investigated in the alpha-decay225Th →221Ra →217Rn

The nuclei²²¹Ra and²¹⁷Rn have been investigated in the α-decay chain²²⁵Th→²²¹Ra →²¹⁷Rn through γ-ray and conversion-electron studies. The short-lived²²⁵Th nuclei (T _1/2=8min) were produced in the²²⁶Ra(α, 5n) reaction, and γ-rays and conversion electrons were measured — between the irradiation periods — in coincidence with αparticles. In²²¹Ra the five lowest levels are interpreted as members of aK=5/2 paritydoublet with ΔE_π=104 keV. These levels, as well as a higher-lying K^π=3/2⁺ band, are consistent with an octupole deformation of²²¹Ra, as expected from theoretical considerations. In²¹⁷Rn only three excited levels are observed, with a favoured α-decay to a 5/2⁺ excited level thus establishing positive parity for the ground state of²²¹Ra.     

α-Al2O3:C晶体的热释光和光释光特性

以高纯α-Al₂O₃和石墨为原料,采用温梯法生长了α-Al₂O₃：C晶体,使用Ris TL/OSL-DA-15型热释光和光释光仪研究了其热释光和光释光特性.α-Al₂O₃：C晶体在462K附近有单一热释光峰,发射波长位于410nm.随着辐照剂量的增加,热释光强度逐渐增强,462K的热释光特征峰位置保持不变.α-Al₂O₃：C晶体的 关键词： 2O₃：C')" href="#">α-Al₂O₃：C 热释光 光释光     

Photocontrol of magnetization in Al-substituted Fe3O4 thin films

Thin films of (111)-oriented spinel ferrite Al_0.5Fe_2.5O₄ have been prepared by a pulsed-laser deposition (PLD) technique on α-Al₂O₃ (0001) substrates. The films exhibit cluster-glass behaviors with a spin-freezing temperature, T_g, near or above room temperature. The magnetization was found to increase following light irradiation below T_g, which indicates the photoinduced melting of cluster-glass states. An analysis comparing the dynamic behavior of magnetic response to light irradiation between zero-field-cooled (ZFC) states and field-cooled (FC) states at 10 K under various light intensities, I, revealed that the direct photoexcitation of spins occurs when I≤0.78 mW/mm², while the thermal heating effect following the light absorption of the samples also contributes to the enhancement of magnetization when I≥1.22 mW/mm². The magnetization of the films could be controlled by light irradiation even at room temperature. This suggests the possibility of utilizing these films in the development of novel magneto-optical memory devices.     

Scintillation and optical stimulated luminescence of Ce-doped CaF2

Scintillation and optical stimulated luminescence of Ce 0.1–20% doped CaF₂ crystals prepared by Tokuyama Corp. were investigated. In X-ray induced scintillation spectra, luminescence due to Ce³⁺ 5d–4f transition appeared around 320 nm with typically 40 ns decay time. By ²⁴¹Am 5.5 MeV α-ray irradiation, 0.1% doped one showed the highest scintillation light yield and the light yield monotonically decreased with Ce concentrations. Optically stimulated luminescence after X-ray irradiation was observed around 320 nm under 550 or 830 nm stimulation in all samples. As a result, intensities of optically stimulated luminescence were proportional to Ce concentrations. Consequently, scintillation and optically stimulated luminescence resulted to have a complementary relation in Ce-doped CaF₂ system.     

Reflection-absorption infrared spectrum of α-CO chemisorbed on polycrystalline tungsten

The infrared spectrum of chemisorbed α-CO on polycrystalline tungsten has been studied using ultrahigh vacuum techniques. The α-CO state has been spectroscopically resolved into two states, designated α₁-CO (wavenumber ～2128 cm^?1) and α₂-CO (wavenumber ～2090 cm^?1). α₂-CO adsorbs predominantly in the first stages of α-CO adsorption; α₁-CO forms primarily at high α-CO coverages at the partial expense of α₂-CO. α₁-CO is found to desorb at a slightly lower temperature than α₂-CO. Both α-CO states are postulated to involve sp-hybridized carbon which is bonded to the tungsten surface. These states have previously been detected in electron impact desorption measurements, where α₁-CO was shown to liberate CO⁺ and α₂-CO to liberate O⁺.     

UV cathodoluminescence of crystalline α-quartz at low temperatures

Two luminescence bands in the UV range were detected in crystalline α-quartz under electron beam excitation (6 kV, 3-5 μA). One band is situated at 5 eV and could be observed in pure samples. Its intensity increases with cooling below 100 K and undergoes saturation below 40 K alongside a slow growth with the time of irradiation at 9 K. The decay curve of the band at 5 eV contains two components, a fast (<10 ns) and a slow one in the range of 200 μs. The photoluminescence band at 5 eV with a similar temperature dependence was found in previously neutron-irradiated crystalline α-quartz. Therefore, the band at 5 eV was attributed to host material defects in both irradiation cases. The creation mechanism of such defects by electrons, the energy of which is lower than the threshold for a knock-out mechanism of defect creation, is discussed. Another band at 6 eV, containing subbands in different samples, appears in the samples containing aluminum, lithium and sodium ions. This luminescence is ascribed to a tunnel radiative transition in an association of (alkali atom)⁰-[AlO₄]⁺ that is formed after the trapping of an electron and a hole by Li⁺ (or Na⁺) and AlO₄.     

The α-efficiency of corals and its importance for ESR-dating

The uncertainty in an ESR age results almost completely from the error in the evaluation of the annual dose. In the case of corals, α-efficiency has a high influence on D_E (Paleodose). The published k_α-values vary from 0.05 to 0.2, so the correct determination of k_α is crucial. In this experiment, based on direct irradiation with an ²⁴¹Am-source, we used seven samples (20 aliquots for each sample) with different ages. The first aim was to improve the measurement conditions to reach a reliable data base for the α-efficiency calculation and the second was the question of age dependency of k_α. With respect to the results of our experiments we propose an α-efficiency value for corals of 0.06–0.07 which leads to younger ages of about 7–10% less than with the k_α factor of 0.05 we used in previous studies.     

Effect of γ irradiation on the structural and thermal properties of [N(C2H5)4]2ZnBr4 in the vicinity of a first-order phase transition

The unit cell parameters a and c of nonirradiated [N(C₂H₅)₄]₂ZnBr₄ crystals in the temperature region 90–300 K and of samples irradiated with γ rays to doses of 10⁶ and 5 × 10⁶ R in the 270-to 300-K interval were measured using x-ray diffraction. The data obtained were used to derive the thermal expansion coefficients α_a and α_c. It is shown that the parameter a increases and the parameter c decreases with increasing temperature. In the vicinity of the phase transition (PT) at T = 285 K, the temperature dependences of a(T) and c(T) reveal anomalies in the form of jumps and the α_a(T) and α_c(T) curves have a maximum and a minimum, respectively. The heat capacity of nonirradiated and irradiated [N(C₂H₅)₄]₂ZnBr₄ samples was measured by adiabatic calorimetry. A maximum was found in the C _p(T) curve at T = 285 K. Both x-ray diffraction and heat capacity measurements showed that the PT temperature decreased after γ irradiation.     

Investigation of the 19F(n, α)16N reaction excitation function in neutron energy range of 4–7.35 MeV

New method based on ionization chamber with Frisch grid and digital signal processing was developed for experimental investigation of ¹⁹F(n, α)¹⁶N reaction. The chamber filling gas with CF₄ additive was used as the fluorine-containing target. The experimental investigation of ¹⁹F(n, α)¹⁶N reaction cross-section in 4–7.35 MeV energy range is represented in this work. The total cross section of ¹⁹F(n, α)¹⁶N reaction was measured as well as partial cross-section for sum of α₀-α₃ and sum of α₄ and α₅ reaction channels.     

Die Konversion des86mRb

^86mRb was produced by irradiation of natural Rb and Rb enriched in⁸⁷Rb (99.2%) with fast neutrons. The half-life ofT _1/2=(61.2±1.0) sec and the energy ofE _ρ=(556.03±0.25) keV were remeasured. The experimental conversion coefficients α_tot=0.0184±0.0015 andα _K =0.0158±0.0015 yield the multipolarity of E4 for the isomeric transition. The spin of 6^? was assigned to the isomeric state. It is proposed that the spin 6^? is formed by coupling ap _3/2-proton and ag _9/2-neutron according to Nordheim's “weak” rule.     

Die Konversion des Hg199m

Hg^199m was produced from natural HgO by fastn irradiation. The cascade decay was investigated with scintillation spectrometers by application of the summing technique. The following results were obtained: half-lifeT _1/2=(43±0,5) min; energy of the isomeric transitionE _γ1=(375±3)keV; conversion coefficients α _K375=3,05±0,25; α_total=5,45±0,25; yielding the multipole order of the isomeric transition to beM4+(25±15)%E5; energy of the second transitionE _γ2=(159±2)keV; conversion coefficients α _K159=0,30±0,03; α_total=0,9±0,1, confirming the multipolarityE2 of this transition.     

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.     

The decay of the isotopes176Ir and177Ir

^176,177Ir were produced by irradiation of¹⁴¹Pr with⁴⁰Ar. β-delayed γ-rays of^176,177Ir were observed for the first time. From γγ-coincidence data decay schemes could be constructed. A new half-life of¹⁷⁷Ir was obtained yielding t_1/2=30 (2) s. α-branching ratios of 3.1(6) % for¹⁷⁶Ir and 0.06(1)% for¹⁷⁷Ir were measured.     

Die Konversion des79m Br

⁷⁹ mBr was produced by irradiation of natural Br with fast neutrons. The half-lifeT _1/2=(4.87±0.15) sec and the energyE _γ=(208±1) keV were remeasured. For the first time the conversion coefficients were determined to beα _K=0.25±0.02 and α_total=0.28±0.05, yielding the multipolarityE3 for the isomeric transition.