质子辐照ZnO白漆光学退化的慢正电子湮没分析

 采用慢正电子湮没光谱研究低能质子辐照下ZnO白漆的光学退化。研究结果表明,随质子辐照注量的增加, 多普勒展宽谱的S参数逐渐减小,W参数逐渐增大。质子辐照下S-W参数拟合曲线的斜率发生改变。S参数的减小可以归结为锌空位含量的减少以及准正电子素的形成。准正电子素{单电离氧空位（捕获一个电子）+正电子}的形成,能够降低正电子湮没的速率,导致S参数减小。S参数的减小证实了质子辐照导致ZnO白漆中单电离氧空位数量的增加。S-W参数拟合曲线斜率的变化可以归结于质子辐照下双电离氧空位向单电离氧空位的转变。     

不锈钢辐射损伤随温度和剂量的变化(英文)

用重离子辐照模拟和正电子湮没寿命技术研究了改进型316L不锈钢在21 和33 dpa辐照剂量下的辐照损伤在室温到802 °C温度范围随辐照温度变化和室温下0—100 dpa剂量范围随辐照剂量变化. 在580 °C左右实验观察到辐照肿胀峰， 在21 和33 dpa辐照剂量下相应的空位团分别由14和19个空位组成， 尺度分别为0.68 和0.82 nm. 空位团尺寸随辐照剂量增加， 在100 dpa时空位团由8个空位组成， 尺度为0.55 nm. 实验结果表明， 在改进型316L不锈钢中辐照损伤随辐照温度变化更灵敏.     

Irradiation behaviour of nuclear fuels

This paper gives a brief review of the important phenomena observed in metallic uranium and ceramic nuclear fuels during irradiation in reactors. The mechanism of irradiation growth, irradiation creep and swelling which are responsible for the dimensional instability of uranium has been described. Important phenomena observed in ceramic nuclear fuels,e.g. fuel densification, fuel restructuring, plutonium segregation, oxygen and fission product migration, irradiation creep, fission gas release and swelling have been discussed. A brief note is included on computer modelling for prediction of fuel element irradiation behaviour.     

The effect of gamma-ray irradiation on the electrical conductivity of CuO–PbO glasses

The effect of gamma-ray irradiation on the dc electrical conductivity of CuO–PbO glasses has been studied as a function of temperature. A 33% CuO–67% PbO glass composition has been prepared, using the melt-quenching technique. The samples have been irradiated to a dose of 0.5 MGy using a ⁶⁰Co γ-source. The electrical conductivity of this glass composition was investigated before and after gamma-ray irradiation. The values of the dc electrical conductivity have been measured from 303 to 373 K, and the activation energy of samples before and after gamma irradiation has been calculated. The observed data show that the electrical conductivity increases with temperature and following gamma irradiation. The electrical conductivity of CuO–PbO can be interpreted in terms of mixed ionic–electronic conduction.     

Porphyrin-sensitized laser swelling and ablation of polymer films

Laser-induced morphological changes of poly(methyl methacrylate), poly(N-vinylcarbazole), and gelatin films doped with porphyrins have been studied by etch depth measurement and scanning electron microscopy. An irreversible swelling of the irradiated surface was observed for all films in the case of low laser fluence. The swelling was replaced by ablation when the fluence was increased. The etch depth depends on the irradiation fluence and the dye concentration in the polymer. The observation of the irradiated surfaces suggests that the thermal effect is predominant both for swelling and ablation. The surface temperature at which swelling or ablation is initiated was estimated, assuming that these morphological changes take place at a certain temperature for any dye concentration in each polymer film.     

Molecular Dynamics as a tool to interpret macroscopic amorphization-induced swelling in silicon carbide

We present here an investigation of the irradiation-induced swelling of SiC using Classical Molecular Dynamics simulations. Heavy ion irradiation has been assumed to affect the material in two steps: (a) creation of local atomic disorder, modeled by the introduction of extended amorphous areas with various sizes and shapes in a crystalline SiC sample at constant volume (b) induced swelling, determined through relaxation using Molecular Dynamics at constant pressure. This swelling has been computed as a function of the amorphous fraction introduced. Two different definitions of the amorphous fraction were introduced to enable meaningful comparisons of our calculations with experiments and elastic modeling. One definition based on the displacements relative to the ideal lattice positions was used to compare the Molecular Dynamics results with data from experiments combining ion implantations and channeled Rutherford Backscattering analyses. A second definition based on atomic coordination was used to compare the Molecular Dynamics results to those yielded by a simplified elastic model. The simulation results using the lattice-based definition of the amorphous fraction compare very well with the experimental results. This proves that the modeling in two steps chosen for the creation of the amorphous regions is reasonable. Moreover, the results show very clearly that SiC swelling does not scale linearly with the amorphous fraction introduced. Two swelling regimes are observed relatively to the size of the amorphous area. Comparison of the elastic model with the Molecular Dynamics results using the coordination-based definition of the amorphous fraction has also enabled us to shed light on the swelling mechanisms and has shown that amorphization-induced swelling exhibits an elastic behavior. Furthermore, scalings for the swelling as a function of the two amorphous fractions considered, which can be used by larger scale models, have been determined. Finally, our study shows that classical Molecular Dynamics calculations enable one to connect the results of the available experiments with the elastic calculations and to get further insight into the swelling mechanisms.     

Temperature Interval of Radiation Swelling

The function describing the temperature dependence of radiation swelling in the context of the mechanism of diffusion-deformation instability of quasi-equilibrium excess vacancies in a metal under irradiation is suggested. The functions calculated for a number of metals are compared with the available experimental data. It is concluded that the mechanism of diffusion-deformation instability adequately describes the processes of forming radiation pores.     

Mechanisms of amorphization-induced swelling in silicon carbide: the molecular dynamics answer

We present here the continuation of an investigation of the irradiation-induced swelling of SiC using classical molecular dynamics (CMD) simulations. Heavy ion irradiation has been assumed to affect the material in two successive steps (a) creation of local atomic disorder, modeled by the introduction of extended amorphous areas with various sizes and shapes in a crystalline SiC sample at constant volume (b) induced swelling, determined through relaxation using Molecular Dynamics at constant pressure. This swelling has been computed as a function of the amorphous fraction introduced. Two different definitions of the amorphous fraction were introduced to enable meaningful comparisons of our calculations with experiments and elastic modeling. One definition based on the displacements relative to the ideal lattice positions was used to compare the CMD results with data from experiments combining ion implantations and channeled Rutherford Backscattering analyses. A second definition based on atomic coordination was used to compare the CMD results to those yielded by a simplified elastic model. The results obtained are as follows. On the one hand, comparison of the swelling obtained as a function of the lattice amorphous fraction with the experimental results shows that the melting-quench amorphization simulates the best the irradiation-induced amorphization observed experimentally. This is consistent with the thermal spike phenomenon taking place during ion implantation. On the other hand, disorder analysis at the atomic scale confirms the elastic behavior of the amorphization-induced swelling, in agreement with the comparison with the results of an elastic model. First, no major structural reconstruction occurs during relaxation or annealing. Second, the systems with the most disordered and constrained amorphous area undergo the largest swelling. This means that the disorder and the constraints of the bulk amorphous area are the driving forces for the swelling observed. On the contrary, the nature of the interface does not affect significantly the swelling observed.     

Pulsed nuclear magnetic resonance of gamma-irradiated lithium hydride

Some of the effects of ⁶⁰Co gamma irradiation on lithium hydride are described. Volume increase and nuclear magnetic resonance data are given for samples irradiated from 40 to 395°C. Maximum swelling occurs between 160 and 200°C; negligible swelling occurs above 300°C. Motionally narrowed proton and ⁷Li nuclear magnetic resonance signals appear on irradiation and increase with increasing swelling. These decomposition products, which are trapped inside the LiH, can amount to more than one-tenth the total sample at doses of 50 Grad. At this point, 25 volume per cent swelling has occurred and the growth rate has subsided. The hydrogen nuclear magnetic resonance signal has been shown to come from H₂ molecules by observation of the ortho-para conversion on cooling. Hydrogen densities derived independently from the longitudinal relaxation time and the swelling data are in reasonable agreement. The corresponding gas pressures range from 750 to 5000 atm. The H₂ is thought to be in bubbles which cause the volume growth, and recent electron microscopy results support this view. The ⁷Li signal has a Knight shift, and the lithium is present as metal particles. Above 200°C, the H₂ and Li back-react rapidly. Above 300°C this reaction takes place as fast as the decomposition, which was caused by the irradiation.     

Hot electrons and laser optoacoustics in metal nanoparticles

The theory of sound generation and heat transfer in matrix-embedded metal nanoparticles under ultra-short laser irradiation has been developed. The shape and time dependence of acoustic waves generated by a sharp change in the pressure of electrons have been investigated for a single nanoparticle and for the group of nanoparticles located on a 2-D flat matrix plane. The dependence of the electronic temperature and the temperature of the interface between the dielectric matrix and nanoparticle as a function of time has been derived.     

Radiation effects in crystalline SiO2: Infrared absorption from OH--related defects

Infrared absorption bands due to OH^- molecules have been investigated in unswept and hydrogen-swept crystals of synthetic quartz. The study included one series of bands introduced by electron irradiation, another series of bands present in the as-grown material, and two bands associated with the Al-OH^- center. They were studied first as a function of irradiation temperature and then as a function of radiation dose at 80 K. After irradiation at 80 K, the bands were monitored as a function of anneal temperature from 80 to 760 K.     

Neon ion irradiation studies on MgB2 superconductor

160 MeV of neon ion irradiation has been carried out on MgB₂ polycrystalline pellets at various doses. There has not been any significant change in T_c except at the highest dose of 1×10¹⁵ ions/cm². Increase in resistivity has been noticed. Resistivity data have been fitted with Bloch-Grüneisen function to extract the values of Debye temperature, residual resistivity and temperature coefficient of resistivity for irradiated as well as unirradiated samples. There has not been any significant effect on electron-phonon coupling due to irradiation as evident from Debye temperature and the electron-phonon coupling constant.     

钠米材料Fe2O3微结构的正电子寿命谱学研究

用Ｘ射线衍射确定了纳米材料Fe₂O₃的平均粒径。测量了正电子的寿命。给出了平均粒径随退火温度的变化和短寿命成分τ₁、中等寿命成分τ₂以及它们的强度比Ｉ₂／Ｉ₁随平均粒径的变化。讨论了纳米材料Fe₂O₃的界面结构、平均正电子寿命τ与多普勒展宽谱Ｓ参效间的对应关系。 关键词：     

Energy deposition effects on amorphous selenium,by low temperature neutron irradiation

We have observed recently that neutron irradiation at low temperature can induce very strong changes in configurational disorder of glasses. This conclusion has been drawn from enthalpy change diagrams performed near Tg, by differential scanning calorimetry, on amorphous selenium. A progressive change was observed from a stabilized relaxation state to a highly quenched state as a function of the neutron dose. We explain these effects by a local heating process.

The irradiation was done at low temperature (30 K) and fission and capture effects were shielded by enclosing samples in NB cells.     

聚丙烯酰胺水凝胶的核磁共振微成象

用核磁共振微成象中的自旋回波成象方法研究了γ辐射交联聚丙烯酰胺水凝胶体系,得到PAMG样品中交联网络的质子自旋密度分布之直观图象.对4个不同溶胀度的PAMG样品进行了实验测量,其实验结果清晰而直观地显示出样品中的交联网络随样品溶胀度的不同而变化的情况.     

High voltage electron microscopy observations of the growth of interstitial loops in an iron-nitrogen alloy

Precipitation of interstitial loops and iron nitride in an iron nitrogen alloy, has been examined in the temperature range 30 °C to 300 °C using a High Voltage Electron Microscope. The use of thick foils has enabled the direct observation of iron nitride precipitation. Observations confirm both theoretical and indirect experimental studies of the hardening behaviour of α-iron alloys following neutron irradiation.

Many of the interstitial loops are of {100} type. In certain cases, the unfaulted ½{110} type are observed. The precipitation of iron nitride at the edge of the loop, effectively prevents further growth thus inhibiting void swelling.     

Registration temperature effect on sensitivity of CR-39(DOP) and SR-90 polymer track detectors

The samples of CR-39(DOP) and SR-90 polymer track detectors have been exposed to -particles from ²⁴¹Am source in an exposure unit. The temperature of the detectors during irradiation has been varied from −30°C to 70°C. These exposed samples have been etched in 6.25 N NaOH solution at 60°C for various etching times. The variation of sensitivity of these detectors as a function of registration temperature has been studied. It has been observed that at the fixed registration temperature, the sensitivity of SR-90 is more than CR-39(DOP) polymer track detector. However, the enhancement in sensitivity with the decrease in registration temperature is more pronounced in case of CR-39(DOP) than SR-90.     

Dependence of thermoluminescence response of calcium sulphate activated by dysprosium on the temperature irradiation

Radiation dosimetry is a very important issue in space research and in experiments that try to simulate chemical processes that may occur in cometary nucleus, interstellar grains, and other extraterrestrial environments, due to their irradiation by cosmic rays. The temperature effect is an important factor that has not been considered in many of these experiments. In this work, this effect was studied in TLD dosimeters exposed to gamma rays. The irradiations were done from 77 to 298 K in a Gamma cell unit with a dose rate of 1.0 Gy/s. Results obtained for CaSO₄:Dy show that there is a considerable effect in the evaluation of the dose as function of the irradiation temperature.     

Changes in the electrical properties of pure and doped polymers under the influence of small doses of X-rays

Abstract

A study has been made of the temperature dependence of the d.c. conductivity of pure and borated low density polyethylene LDPE (4% and 8% borax). The above calculations were carried out before and after X-ray irradiation. The irradiation dose was varied from 0 to 1000 rad.

The d.c. electrical conductivity of Polyvinyl chloride (PVC) and perspex was measured as a function of temperature ranging from 20°C to 100°C. These samples were irradiated with X-rays of dose 200 rad. The variation of the d.c. conductivity of the treated samples versus temperature was investigated.

The results reveal that the d.c. conductivity of LDPE is highly affected by radiation and/or dopant. In addition, the sensitivity of the explored polymers to X-ray irradiation is strongly dependent on its chemical nature.     

Ion beam mixing of AG on glass

A series of Ag-glass samples have been studied. They were irradiated as a function of bombarding ion species, dose, temperature, and energy. The results by RBS indicate that ion beam mixing of Ag-glass takes place not only at higher energy irradiation (I. OMeV Xe+), but also at lower energy irradiation (120KeV Ar+ and Kr+). The effective diffusion lengths squared, Dt, were introduced for comparison. It is found that Dt is dependent on the nuclear stopping power, dose and irradiation temperature.