In_(0.95)Ag_(0.045)Ga_(0.005)合金中的电四极相互作用

本文采用时间微分扰动角关联方法,测量了80—422K温度范围内~(111)Cd在In_(0.95)Ag_(0.043)Ga_(0.005)合金中的四极相互作用随温度的变化,进而导出晶格电场梯度的温度变化。在In_(0.95)Ag_(0.043)Ga_(0.005)合金中,晶格电场梯度的温度变化遵从T~(3/2)定律:V_(zz)(T)=V_(zz)(0)(1—BT~(3/2)),斜率B=7.48(47)·10~(-5)K~(-3/2)。在80、298和422K的电场梯度分布宽分别为0.1147(259)、0.0924(340)和1.344(175)。表明在液氮温度和室温时,合金的晶格结构特性较好,温度升高,晶格结构特性变坏。     

Lattice parameter variation of PuC,PuN, and Pu(C,N) between 50 and 300 K

The lattice parameters of PuC, PuN, and Pu(C, N) were measured between 50 and 300 K (PuC), or 50 and 345 K (PuN and Pu(C, N), resp. No phase transformations are observed in these temperature ranges. The expansion coefficients decrease with decreasing temperature. Below 273 K, PuC shows the same variation of the expansion coefficient as PuO₂, but PuN and Pu(C, N) have higher expansion coefficients than PuC and PuO₂. Below 170 K, the measured lattice contraction of PuC and PuN is lower than the sample contraction determined formerly with strain gauges. A ‘jump’ in the expansion curve of PuC at 80–100 K could not be confirmed.     

Ion implantation in TiO2: damage production and recovery,lattice site location and electrical conductivity

Ions with different oxidation states were implanted in TiO₂ (rutile). The lattice disorder as well as the lattice site location of the implanted ions were determined using Rutherford Backscattering and Channeling (RBS-C) spectrometry. The production of disorder as a function of dose and temperature, and its recovery was studied in detail. Important results are the observation of dynamic recovery at 293 K and above, and one isothermal at 77 K and two thermal recovery stages between 170 and 210 K and between 260 and 293 K. The recovery at 77 K is proportional to ln t, indicating that the activation energy increases with decreasing disorder density. The results concerning the lattice site location of 14 ion species reveal that 13 ions occupy Ti lattice site. With increasing netcharge, the maximum soluble concentration decreases by the formation of impurity–defect complexes probably enforced by charge compensation. Directed displacements from the substitutional lattice site provide some hints on the structures of these complexes. The electrical conductivity of the implanted samples increased by about 12 orders of magnitude irrespective of the oxidation state of the implanted species. From the temperature and dose dependence of the electrical conductivity as well as from its similar behaviour for noble-gas ions and other species it is concluded, that the carrier transport occurs by single energy states excitation at low doses and by variable range hopping between localized states at high doses.     

Annealing behavior of (Pu,Cm)O2 lattice and bulk expansion from self-irradiation damage

In order to investigate the effect of self-irradiation damage and accumulation of He on oxide fuel pellets containing minor actinides, the expansion and annealing behavior of (Pu_0.95Cm_0.05)O₂ lattice and bulk were examined comparatively. Since the lattice and bulk expansion at room temperature showed a similar dependence on the storage duration, the main factor of bulk expansion was found to be the lattice expansion due to the generation of point defects. The lattice parameter recovered to the undamaged value by annealing at 1429 K for 2 h, whereas the bulk expanded again by annealing at 1433 K and did not recover to the undamaged value. In the micrographs of the fracture surface of the annealed pellet, the formation of gas bubbles along grain boundaries was confirmed. The He gas bubble formation resulted in the pellet swelling, and it may affect the pellet thermal conduction.     

Gd2 SiO5:Eu3+ 的VUV-UV光谱特性

本文介绍了利用同步辐射光源对Gd2SiO5:Eu^3 的VUV－UV光谱特性进行的研究。重点讨论了在低温（10K）及室温下Gd2SiO5:Eu^3 中存在的各种能量传递过程，包括基质向Eu^3 ,Gd^3向Eu^3 的传递以及两种不同格位Eu^3 离子之间的能量传递。另一方面从探索新型量子剪裁材料的角度对比了186nm和276nm激发下的发射谱，指出Gd2SiO5:Eu^3 中可以发生有效的量子剪裁。     

Zr（Fe,Cr）2金属间化合物的氧化

用非自耗电弧炉熔炼了比值(重量比值)不同的Zr(Fe,Cr)_2,并在773K和973K的空气中氧化。经X射线衍射和电子衍射分析表明:当Fe/Cr≤4.5时,Zr(Fe,Cr)_2,是MgZn_2型(六方)的Laves相,它的晶格常数随Fe/Cr比增加而收缩。Zr(Fe,Cr)_2氧化后生成的稳定氧化物是单斜ZrO_2和六方(Fe,Cr)_2O_3。在形成稳定氧化物之前,还会出现亚稳定的立方ZrO_2。根据本实验结果讨论了Zr-4合金中Zr(Fe,Cr)_2第二相对腐蚀性能的影响。     

Self-radiation damage in plutonium and uranium mixed dioxide

In plutonium compounds, the lattice parameter increases due to self-radiation damage by α-decay of plutonium isotopes. The lattice parameter change and its thermal recovery in plutonium and uranium mixed dioxide (MOX) were studied. The lattice parameter for samples of MOX powders and pellets that had been left in the air for up to 32 years was measured. The lattice parameter increased and was saturated at about 0.29%. The change in lattice parameter was formulated as a function of self-radiation dose. Three stages in the thermal recovery of the damage were observed in temperature ranges of below 673 K, 673-1073 K and above 1073 K. The activation energies in each recovery stage were estimated to be 0.12, 0.73 and 1.2 eV, respectively, and the corresponding mechanism for each stage was considered to be the recovery of the anion Frenkel defect, the cation Frenkel defect and a defect connected with helium, respectively.     

Low-temperature relaxation processes in cold-worked zirconium

The internal friction and modulus relaxation spectrum of high-purity polycrystalline zirconium has been studied between 77 K and room temperature. Low (1 Hz) and high (50 kHz) frequency measurements are reported after room- and low-temperature tensile deformation. Three relaxation peaks appeared, called P₁, P₂ and P₃. The variation of these with the measuring frequency, amount of cold work and annealing of the specimen at temperatures above that of deformation was investigated. The peak P₁ appeared in the range 80 to 90 K at 1Hz after cold work at 80 K and dissappeared on heating the specimen above 200 K. P₂ appeared either after deformation at room temperature or at low temperature if followed by an annealing process above 200 K: this peak is a very wide one at low frequencies (1 Hz) with its maximum at about 150 K. P₃, generated by cold-working the specimen at 80 K, proved to be very unstable and recovered while being measured at 1 Hz: its physical origin is still uncertain. The recovery of the modulus defect after deformation at 80 K showed three stages, coincident with those of resistivity reported in the literature. The peak p₁ is considered to be due to the relaxation of dislocations against intrinsic lattice barriers, the peak P₂ to the interaction of point defects with dislocations.     

The thermal conductivity of hexagonal boron nitride parallel to the basal planes

Detailed measurements of the basal thermal conductivity and specific heat of boron nitride have recently been reported over the range 1.5–350 K. Boron nitride is a lattice conductor with a conductivity varying as T^2.4 below 10 K, while the lattice specific heat varies as T³ over the same range. This anomalous difference in the temperature dependence of lattice conductivity and specific heat is similar to that observed in graphite. The theory of the lattice conductivity of graphite parallel to the basal planes is applied to the explanation of this anomaly. It appears that the value of C₄₄ in this lattice must be smaller than that of graphite.     

Thermal spike model of defect production by electron excitation in Cu

The thermal spike model is investigated theoretically in order to clarify the mechanism of defect production by electron excitation in Cu [Iwase et al., J. Phys. Soc. Jpn 61 (1992) 3878]. The electron temperature and the lattice temperature are calculated numerically solving the heat-flow equation. It is clarified that the maximum lattice temperature is about 100 K when the electronic stopping power of the incident ion is 100 keV/nm and the initial lattice temperature is 10 K. This means that no defect is created by purely thermal processes induced by electron excitation in the case of Cu.     

Critical Power Characteristics in 37-rod Tight Lattice Bundles under Transient Conditions

Critical power characteristics in the postulated abnormal transient processes that may be possibly met in the operation of Innovative Water Reactor for Flexible Fuel Cycle (FLWR) were investigated for the design of the FLWR core. Transient Boiling Transition (BT) tests were carried out using two sets of 37-rod tight lattice rod bundles (rod diameter: 13 mm; rod clearance: 1.3 mm or 1.0 mm) at Japan Atomic Energy Agency (JAEA) under the conditions covering the FLWR operating condition (P_ex = 7:2 MPa, T_in = 556 K) for mass velocity G = 400-800 kg/(m² s). For the postulated power increase and flow decrease transients, no obvious change of the critical power against the steady one was observed. The traditional quasi-steady characteristic was confirmed to be working for the postulated power increase and flow decrease transients. The experiments were analyzed with TRAC-BF1 code, where the JAEA newest critical power correlation for the tight lattice rod bundles was implemented for the BT judgment. The TRAC-BF1 code showed good prediction for the occurrence or the non occurrence of the BT and for the exact BT starting time. The traditional quasi-steady state prediction of the BT in transient process was confirmed to be applicable for the postulated abnormal transient processes in the tight lattice rod bundles.     

聚变堆中第一壁材料钨的紧束缚理论研究

为研究辐照时处于电子激发态下第一壁材料钨（W）的结构演化规律和热力学性质,采用紧束缚方法对聚变堆中W的物理性质进行理论研究。结果表明,体系在高能粒子辐照下诱导的电子激发导致了体系中被辐照的区域自发出现微孔、晶格急剧膨胀、熔点下降等现象。具体地,在中等电子温度（~5 000 K）以下,W的晶格膨胀主要由晶格温度驱动,但在电子温度较高时电子温度导致被辐照区域的晶格膨胀效应不可被忽略。特别是当电子温度很高（>10 000 K）时,即便晶格温度不高,电子温度也会导致很大程度晶格膨胀。这对认识聚变堆中第一壁材料W在服役过程中的物理状态十分重要。     

Structural and optical properties of 6H-SiC helium-implanted at 600 K

Single crystals of 6H-SiC were implanted at 600 K with 100 keV He ions to three successively fluences and subsequently annealed at different temperatures ranging from 873 to 1473 K in vacuum. The recovery of lattice damage was investigated by different techniques including Rutherford backscattering spectrometry in channeling geometry, Raman spectroscopy and Fourier transform infrared spectroscopy. All three techniques showed that the damage induced by helium ion implantation in the lattice is closely related to the fluence. Rutherford backscattering spectrometry/channeling data on high temperature implantations suggest that for a fluence of 3 × 10¹⁶ He⁺/cm², extended defects are created by thermal annealing to 1473 K. Apart from a well-known intensity decrease of scattering peaks in Raman spectroscopy it was found that the absorbance peak in Fourier transform infrared spectroscopy due to the stretching vibration of Si-C bond shifted to smaller wave numbers with increasing fluence, shifting back to larger wave numbers with increasing annealing temperature. These phenomena are attributed to different lattice damage behavior induced by the hot implantation process, in which simultaneous recovery was prevailing.     

Sulfurization behavior of thorium dioxide with carbon disulfide

A novel reprocessing process based on sulfide chemistry has been proposed for the recovery of nuclear materials from spent fuel. To apply the sulfide process in the thorium fuel cycle, the sulfurization behavior of thorium dioxide (ThO₂) with CS₂ was examined as a basic study. When thorium dioxide powder reacted with a mixture gas of Ar and CS₂ at different temperatures in a quartz reaction tube, the phases after the reaction were identified by the X-ray diffraction method. At temperatures lower than 673 K, ThO₂ was found to be stable because the lattice parameter of the ThO₂ phases does not change with increasing sulfurization temperatures. However, the weight gradually increased, suggesting that a small amount of sulfur was trapped in the lattice from the sulfurization. The formation of the intermediate phase ThOS was observed at 973 K. At 1073 K, both the ThOS and ThS₂ phases were observed. Finally, a single phase of ThS₂ was obtained at temperatures higher than 1173 K. The obtained results were compared with the thermodynamic consideration by using the potential diagram of the Th-S₂-O₂ system and the experimental results were in good agreement with the thermodynamic considerations.     

Thermal expansion studies on Inconel-600 by high temperature X-ray diffraction

The lattice thermal expansion characteristics of Inconel-600^® have been studied by high temperature X-ray diffraction (HT-XRD) technique in the temperature range 298-1200 K. Altogether four experimental runs were conducted on thin foils of about 75-100 μm thickness. The diffraction profiles have been accurately calibrated to offset the shift in 2θ values introduced by sample buckling at elevated temperatures. The corrected lattice parameter data have been used to estimate the instantaneous and mean linear thermal expansion coefficients as a function of temperature. The thermal expansion values estimated in the present study show a fair degree of agreement with other existing dilatometer based bulk thermal expansion estimates. The lattice parameter for this alloy at 300 K is found to be 0.3549(1) nm. The mean linear thermal expansivity is found to be 11.4 × 10⁻⁶ K⁻¹.     

Calculations of thermodynamic properties of PuO2 by the first-principles and lattice vibration

Plutonium dioxide (PuO₂) is a key compound of mixed oxide fuel (MOX fuel). To predict the thermal properties of PuO₂ at high temperature, it is important to understand the properties of MOX fuel. In this study, thermodynamic properties of PuO₂ were evaluated by coupling of first-principles and lattice dynamics calculation. Cohesive energy was estimated from first-principles calculations, and the contribution of lattice vibration to total energy was evaluated by phonon calculations. Thermodynamic properties such as volume thermal expansion, bulk modulus and specific heat of PuO₂ were investigated up to 1500 K.     

Theory of He trapping, diffusion, and clustering in UO2

We have performed ab initio total energy calculations to investigate the behavior of helium and its diffusion properties in uranium dioxide (UO₂). Our investigations are based on the density functional theory within the generalized gradient approximation (GGA). The trapping behavior of He in UO₂ has been modeled with a supercell containing 96-atoms as well as uranium and oxygen vacancy trapping sites. The calculated incorporation energies show that for He a uranium vacancy is more stable than an oxygen vacancy or an octahedral interstitial site (OIS). Interstitial site hopping is found to be the rate-determining mechanism of the He diffusion process and the corresponding migration energy is computed as 2.79 eV at 0 K (with the spin-orbit coupling (SOC) included), and as 2.09 eV by using the thermally expanded lattice parameter of UO₂ at 1200 K, which is relatively close to the experimental value of 2.0 eV. The lattice expansion coefficient of He-induced swelling of UO₂ is calculated as 9 × 10⁻². For two He atoms, we have found that they form a dumbbell configuration if they are close enough to each other, and that the lattice expansion induced by a dumbbell is larger than by two distant interstitial He atoms. The clustering tendency of He has been studied for small clusters of up to six He atoms. We find that He strongly tends to cluster in the vicinity of an OIS, and that the collective action of the He atoms is sufficient to spontaneously create additional point defects around the He cluster in the UO₂ lattice.     

A classical molecular dynamics study of the correlation between the Bredig transition and thermal conductivity of stoichiometric uranium dioxide

Thermophysical properties of uranium dioxide are investigated by classical molecular dynamics for temperatures from 300 K to 3000 K. An increase of specific heat in the temperature range from 1300 K to 2500 K is noted. Comparison with a theoretical model shows that the origin of this behavior is only due to anharmonicity. Such characteristic features of the Bredig transition as the peak in specific heat and high ionic conductivity are investigated. We show that one more important feature was left unnoticed: the rise in the lattice contribution to thermal conductivity at high temperatures. An explanation is provided for this effect which is specific to superionic conductors. Reasonable agreement with experimental data up to 3000 K is obtained for thermal conductivity, even in the absence of electronic excitations.     

Chaleur specifique de 2 a 300 K du monocarbure de thorium

The specific heat of ThC has been measured in the range 1.5–300 K. From the results, we have calculated the thermodynamic functions at 298.15 K, the Debye and Einstein temperatures linked with the acoustic and optical branches, respec tively, of the lattice vibrations, and the coefficient (γ = 2.12 mJ/mol · K²) of electronic specific heat.