质子辐照空间级硅橡胶的正电子淹没寿命谱研究

 用正电子淹没寿命谱方法（PALS）研究了质子辐照对空间级硅橡胶KH-L-Y微观结构的影响。试验结果表明，PALS谱所揭示的最长寿命成分的t₃, I₃及自由体积分数Vf随辐照剂量的增加开始明显下降；而当辐照剂量大于10¹⁵cm^-2后，随剂量的增加平缓上升。辐照剂量小于10¹⁵cm^-2时，质子辐照使硅橡胶自由体积减小，分子链间堆砌紧密；辐照剂量大于10¹⁵cm^-2时，质子辐照使硅橡胶自由体积增大。交联密度及DMA测试结果同样表明，质子辐照在剂量较小时硅橡胶的交联密度及玻璃化转变温度增加，辐照以交联效应为主；而剂量较大时辐照降解占优势。     

铝纳米晶的正电子湮没研究

采用自悬浮定向流-真空热压法,在不同压强下制得铝纳米晶材料,并利用X射线衍射(XRD)和正电子湮没寿命谱(PALS)分析手段对铝纳米晶的结构和微观缺陷进行表征.XRD分析表明:所制备的铝纳米晶的晶粒度为48 nm.PALS分析表明:铝纳米晶的微观缺陷主要为类空位以及空位团,而微孔洞很少;短寿命τ1,中间寿命τ2以及其对应的强度I1,I2随压强变化而呈现阶段性变化;压制压强(P)低于0.39 GPa时制得的纳米晶空位团随压强的增加而逐渐转变为类空位;0.39 GPa P 0.72 GPa时,各类缺陷发生消除;P 0.72 GPa时,各类缺陷进一步发生消除.随压强的提高,铝纳米晶的密度增加,其显微硬度也明显增高.     

A compact positron annihilation lifetime spectrometer

Using LYSO scintillator coupled on HAMAMATSU R9800(a fast photomultiplier)to form the small size γ-ray detectors,a compact lifetime spectrometer has been built for the positron annihilation experiments.The system time resolution FWHM=193 ps and the coincidence counting rate -8 cps/μCi were achieved.A lifetime value of 219±1 ps of positron annihilation in well annealed Si was tested,which is in agreement with the typical values published in the previous lectures.     

Defect structure studies using positron annihilation spectroscopy

The positron annihilation method is a new addition to the range of sensitive complementary nuclear techniques available for materials’ research. The preferential sensitivity of positrons towards micro-defect domains which are not assessable by other techniques makes it an attractive tool for many materials science problems. The present paper is intended as a brief introduction on the principle of measurements and its potential is exemplified with the help of results on some metallic and ceramic systems.     

A compact positron annihilation lifetime spectrometer

Using LYSO scintillator coupled on HAMAMATSU R9800 (a fast photomultiplier) to form the small size γ-ray detectors, a compact lifetime spectrometer has been built for the positron annihilation experiments. The system time resolution FWHM=193 ps and the coincidence counting rate ～8 cps/μCi were achieved. A lifetime value of 219±1 ps of positron annihilation in well annealed Si was tested, which is in agreement with the typical values published in the previous lectures.     

多孔硅薄层的正电子湮灭寿命研究

用阳极氧化法按不同腐蚀条件制备的多孔硅，其薄层厚度仅为几十纳米，远小于^22Na源的正电子平均射程．文章提出了一种用控Na的正电子测量体寿命谱并扣除基片贡献的方法，来确定多孔硅薄层的平均孔径。     

Ionic conductivity of PVdF-co-HFP/LiClO4 in terms of free volume defects probed by positron annihilation lifetime spectroscopy

ABSTRACT

Polymers based on ionic conducting materials have important interest because of their potential applications in polymer electrolytes and membranes for fuel cell application. PVdF-co-HFP poly(viniliden-co-hexafluoropropylene) was chosen as a polymer matrix because of its high ionic conductivity and better mechanical properties. Polymer matrix composites were prepared with various amounts of LiClO₄ salt by a solution casting method. The sample-ionic conductivity measurements were recorded by AC impedance analyzer at different frequencies from 0.1?Hz to 20?MHz and at different temperatures from 273 to 373?K.

The changes of nanoscopic free volume and free volume fraction in these materials were investigated in terms of temperature from 273 to 373?K using Positron Annihilation Lifetime Spectroscopy (PALS) and Simha-Somcynsky (SS) Hole Theory. The free volume had a bump at about 3% in weight percentage of the salt and there is a slight increase after 10%. The effects of weight percentages of LiClO₄ and temperature were investigated. The mechanism of the ac ionic conductivity was presented in terms of the free volume models, however thermo-occupancy function justifies the best accurate representation of the data.     

碳纳米管束中的正电子理论

采用中性原子叠加模型和有限差分方法(SNA-FD)计算了大范围内不同管径的单壁碳纳米管束中的正电子情况，发现对于单壁碳纳米管束，正电子的主要湮没区域，湮没对象和正电子寿命随碳纳米管管径的不同而发生规律性变化.计算得到管径范围在0.8—1.6nm的碳纳米管束的正电子寿命范围为332—470ps，与实验测得的394ps符合较好.     

Studying the recovery of as-received industrial Al alloys by positron annihilation spectroscopy

Positron annihilation lifetime (PAL) spectroscopy, Doppler broadening of annihilation radiation (DBAR) spectroscopy and Vickers microhardness (Hv) measurements were performed to study the micro- and macro-structure variations during isochronal annealing from room temperature (RT) to 500 °C of commercial pure Al (1 1 0 0), Al-Mn-Mg (3 0 0 4) and Al-Mg-Si (6 2 0 1) alloys. Three annealing stages of microstructures have been identified as recovery, partial recrystallization and complete recrystallization followed by grain growth. A positive correlation between the macroscopic mechanical properties (Hv) and positron annihilation parameters has been achieved for the three samples under investigation.     

SmFeAsO材料的正电子寿命研究

首次用正电子湮灭寿命谱仪（PALS）测量SmFeAsO多晶样品常温下的寿命谱,得到两个寿命成分1516 ps和2903 ps,根据捕获模型得到正电子在SmFeAsO中湮灭的体寿命为1870 ps,与理论计算（广义梯度近似）得到的SmFeAsO单晶中的正电子体寿命173 ps符合较好.基于中性原子叠加模型-有限差分方法(SNA-FD)的理论计算得到正电子与单晶SmFeAsO中各个原子价电子的总湮灭率是其与各个原子核心内层电子总湮灭率的106倍,正电子与Fe,As,Sm,O原子的电子湮灭的概率之比是1∶13∶12∶1. 关键词： 高温超导 正电子寿命     

SmFeAsO材料的正电子寿命研究

首次用正电子湮灭寿命谱仪（PALS）测量SmFeAsO多晶样品常温下的寿命谱,得到两个寿命成分1516 ps和2903 ps,根据捕获模型得到正电子在SmFeAsO中湮灭的体寿命为1870 ps,与理论计算（广义梯度近似）得到的SmFeAsO单晶中的正电子体寿命173 ps符合较好.基于中性原子叠加模型-有限差分方法(SNA-FD)的理论计算得到正电子与单晶SmFeAsO中各个原子价电子的总湮灭率是其与各个原子核心内层电子总湮灭率的106倍,正电子与Fe,As,Sm,O原子的电子湮灭的概率之比是1∶13∶12∶1.     

Defect characterization of slow-cooled and quenched samples of calcium-copper-titanate through positron annihilation spectroscopy

Abstract

Positron annihilation lifetime and Doppler-broadened gamma-ray spectra have been analyzed for slow-cooled and thermally quenched polycrystalline samples of calcium-copper-titanate. Two positron lifetimes revealing the characteristic defects in the respective samples were carefully analyzed to compare and contrast the significance of their origin and implication. A third component arising from positronium formation at the powdered particle surfaces has been considered in the analysis although its significance is lost in its very small intensity (～ 1.1–1.2%). In the quenched sample, the defect-specific long positron lifetime (τ₂) is found to larger and the mean lifetime smaller while its intensity I₂ is found drastically smaller and the concentration of defects less by an order of magnitude as compared to the slow-cooled sample. The observed changes in electrical parameters of slow-cooled and quenched samples were found to have correlations with the positron annihilation lifetime and Doppler-broadened lineshape parameters.     

Positron annihilation studies of mesoporous silica films using a slow positron beam

Positron annihilation lifetime spectra were measured for mesoporous silica films, which were synthesized using triblock copolymer (EO₁₀₆PO₇₀EO₁₀₆) as a structure-directing agent. Different positron lifetime spectra for the deposited and calcined films indicated the formation of meso-structure after calcination, which was confirmed by Fourier transform infrared (FTIR) spectra and field emission-scanning electron microscopy (FE-SEM) observation. Open porosity or pore interconnectivity of a silica film might be evaluated by a two-dimensional positron annihilation lifetime spectrum of an uncapped film. Pore sizes and their distributions in the silica films were found to be affected by thermal treatments.     

化合物半导体材料的正电子寿命计算

在局域密度理论（LDA）和广义梯度理论（GGA）的基础上计算了ZnO,GaN,GaAs,SiC和InP五种化合物半导体材料中的正电子湮没信息,包括化合物半导体材料中的自由态正电子的湮没寿命;还有不同类型空位（单空位,双空位）附近俘获的束缚态正电子密度分布和湮没率分布,以及束缚态正电子的湮没寿命. 关键词： 半导体 正电子寿命     

Detection of hydrogen in neutron-irradiated nickel using positron lifetime spectroscopy

Hydrogen in nano-voids in neutron-irradiated nickel has been detected using positron annihilation lifetime spectroscopy (PALS). As positron lifetime is greatly affected by nano-voids bound with hydrogen, special attention was paid to the analysis. The positron lifetime of neutron-irradiated nickel at higher irradiation doses increased with the dose, which is an indicator for vacancy cluster (nano-void) formation in the lattice. The introduction of hydrogen in well-annealed nickel by electrical charging also resulted in an increase in positron lifetime due to vacancy formation. In neutron-irradiated nickel specimens, hydrogen charging shortened the positron lifetime from 456 to 334 ps (irradiation dose: 3 × 10^?3 dpa). Isochronal annealing behaviour of hydrogen-charged nickel and neutron-irradiated nickel was also studied. Positron trapping rate was calculated using a simple trapping model. Thermal desorption spectroscopy was used for the investigation of hydrogen behaviour in non-irradiated hydrogen-charged nickel.     

SHI induced modification in CR-39 polycarbonate by positron annihilation lifetime studies

CR-39 is a polycarbonate widely used as SSNTD for recording nuclear charged particles and in other applications. Latent ion tracks produced in the polymers due to the damage produced by the passage of Swift Heavy Ions contain amorphous material with highest degree of disorder, changing the free volume properties which have strong correlation with the macroscopic properties of the material. Positron annihilation lifetime spectroscopy (PALS) provides direct information about the dimension, content and hole size distribution of free volume in polymers. The effect of irradiation of ⁴⁰Ar (14.9 MeV/n) ions on CR-39 polycarbonate by Positron Annihilation Lifetime Spectroscopy (PALS) is reported here. PALS provides a non-destructive and non-interfering probe, having high detection efficiency for free volume hole properties. From o-Ps lifetime mean free volume hole radius and average free volume of the micro-voids have been calculated. PAL measurement shows an increase in free volume on irradiation.     

正电子湮没谱和光致发光谱研究掺锌GaSb质子辐照缺陷

用正电子湮没谱和光致发光谱研究了质子辐照后掺锌GaSb中的缺陷.通过分析正电子的缺陷寿命τ₂及强度I₂的变化发现,在高能质子的辐照下产生了双空位缺陷V_GaV_Sb,可能同时产生了小的空位团.正电子平均寿命τ_av和S参数随着质子辐照剂量的变化也证明了这一结论.通过分析不同质子辐照剂量下掺锌GaS     

用正电子研究NaCl在NaY沸石上的固溶过程

用正电子湮没谱学研究NaCl与NaY沸石机械混合后, NaCl在NaY中的固溶扩散过程.分别测量不同质量比的NaCl/NaY［(1—20)%］经500℃烘烤1h，NaCl/NaY(15%)经不同温度烘烤1h,以及NaCl/NaY(15%)经500℃烘烤不同时间后的正电子寿命谱.所有寿命谱都出现了5个寿命分量, 其中第3，4，5寿命分别与β笼、超笼及沸石微粒界面空洞的大小和数量相关.实验表明正电子湮没谱学能敏感地表征NaCl在NaY中的固溶扩散过程. 关键词： 正电子湮没谱学 氯化钠 沸石     

利用正电子湮没技术研究钾掺杂钨合金中的缺陷

钨合金中钾的掺杂会引入大量的缺陷,如尺寸几十纳米的钾泡、高密度的位错以及微米量级的晶粒带来的晶界等,这些缺陷的浓度和分布直接影响合金的服役性能.本文运用正电子湮没谱学方法研究钾掺杂钨合金中的缺陷信息,首先模拟计算了合金中各种缺陷的正电子湮没寿命,发现钾的嵌入对空位团、位错、晶界等缺陷的寿命影响很小;然后测量了不同钾含量掺杂钨合金样品的正电子湮没寿命谱,建立三态捕获模型,发现样品中有高的位错密度和低的空位团簇浓度,验证了钾对位错的钉扎作用,阐述了在钾泡形成初期是钾元素与空位团簇结合并逐渐长大的过程;最后使用慢正电子多普勒展宽谱技术表征了样品中缺陷随深度的均匀分布和大量存在,通过扩散长度的比较肯定了钾泡、晶界等缺陷的存在.     

Effect of vacancy charge state on positron annihilation in silicon

The charge-state-dependent lattice relaxation of mono-vacancy in silicon is studied using the first-principles pseu- dopotential plane-wave method. We observe that the structural relaxation for the first-neighbor atoms of the mono-vacancy is strongly dependent on its charge state. The difference in total electron density between with and without charge states in mono-vacancy and its relevant change due to the localized positron are also examined by means of first-principles simu- lation, demonstrating the strong interplay between positron and electron. Our calculations reveal that the positron lifetime decreases with absolute charge value increasing.