DIRECT MASS MEASUREMENTS OF EXOTIC NUCLEI IN STORAGE RINGS

Mass measurements of exotic nuclei is a fast, developing field which is essential for basic nuclear physics and a wide range of applications. The method of storage ring mass spectrometry has many advantages: (1) a large amount of nuclides can be simultaneously measured; (2) very short-lived (T-1/2 greater than or similar to 50 mu s) and very rare species (yields down to single ions) can be accessed; (3) nuclides in several atomic charge states can be investigated, (4) half-life measurements can be performed with time-resolved mass spectrometry. In this contribution we concentrate on some recent achievements and future perspectives of the storage ring mass spectrometry.

双奇核~(142)Pm高自旋态能级纲图

利用能量为 75— 95MeV19F束流 ,通过反应12 8Te( 19F ,5nγ) 142 Pm研究了双奇核142 Pm的高自旋态能级结构 .实验中进行了γ射线的激发函数、γ射线单谱和γ γ符合测量 .建立了激发能达 70 3 0 .0keV的142 Pm的能级纲图 ,其中包括新发现的 2 5条γ射线和 1 3个新能级 .基于实验测量的γ跃迁各向异性度 ,建议了142 Pm能级的自旋值

质子滴线附近的β缓发质子衰变

简要回顾了我们小组在 1996~2004 年中发表的有关质子滴线附近β缓发质子衰变的实验结果, 即运用氦喷嘴快速带传输系统 +“p-γ”符合方法, 在稀土区质子滴线附近首次观测了 9种新核素的β缓发质子衰变, 在 A= 90 核区的 N = Z线附近获得了 5 种核素的β缓发质子衰变的新数据. 同时着重补充了一些重要的实验技术细节. 汇总了这 14 种核素的半衰期、自旋、宇称、形变以及生成反应截面的实验结果, 并与流行的核模型理论预言进行了系统的对比讨论. 从中看出:(ⅰ) Mo, Rh 以及“等待点”核 Ru 和 Pd 半衰期的实验值比近期 M?ller 等 85 92 89 93人的宏观-微观理论预言值长 5~10 倍, 因而明显地影响天体 rp-过程的核素丰度;(ⅱ) 实验指认的质子滴线核 Ho 和 Pm 的自旋和宇称, 与流行理论预言不符, 142 128但用 Woods-Saxon-Strutinsky 方法计算得到的位能面可以解释自旋和宇称的实验值; (ⅲ) 实验估计的 9 种稀土核的生成截面比通用的 Alice和 HIVAP 程序的计算值要小 1～2 个数量级.

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Matemàtiques al parc de la mar. 'Matemáticas en el Parque del Mar'.

En la Cub.: Materials didàctics

Suppression of cluster ions during particle formation events in the atmosphere

Cluster ions and charged and neutral nanoparticle concentrations were monitored using a neutral cluster and air ion spectrometer (NAIS) over a period of one year in Brisbane, Australia. The study yielded 242 complete days of usable data, of which particle formation events were observed on 101 days. Small, intermediate and large ion concentrations were evaluated in real time. In the diurnal cycle, small ion concentration was highest during the second half of the night while large ion concentrations were a maximum during the day. The small ion concentration showed a decrease when the large ion concentration increased. Particle formation was generally followed by a peak in the intermediate ion concentration. The rate of increase of intermediate ions was used as the criteria for identifying particle formation events. Such events were followed by a period of growth to larger sizes and usually occurred between 8 am and 2 pm. Particle formation events were found to be related to the wind direction. The gaseous precursors for the production of secondary particles in the urban environment of Brisbane have been shown to be ammonia and sulfuric acid. During these events, the nanoparticle number concentrations in the size range 1.6 to 42 nm, which were normally lower than 1x104 cm-3, often exceeded 5x104 cm-3 with occasional values over 1x105 cm-3. Cluster ions generally occurred in number concentrations between 300 and 600 cm-3 but decreased significantly to about 200 cm-3 during particle formation events. This was accompanied by an increase in the large ion concentration. We calculated the fraction of nanoparticles that were charged and investigated the occurrence of possible overcharging during particle formation events. Overcharging is defined as the condition where the charged fraction of particles is higher than in charge equilibrium. This can occur when cluster ions attach to neutral particles in the atmosphere, giving rise to larger concentrations of charged particles in the short term. Ion-induced nucleation is one of the mechanisms of particle formation in the atmosphere, and overcharging has previously been considered as an indicator of this process. The possible role of ions in particle formation was investigated.

Production of biosurfactant “Biosur-Pm” by Pseudomonas maltophila CSV89: characterization and role in hydrocarbon uptake

Pseudomonas maltophilia CSV89, a soil bacterium, produces an extracellular biosurfactant, ''Biosur-Pm''. The partially purified product is nondialyzable and chemically composed of 50% protein and 12-15% sugar, which indicates the complex nature of Biosur-Pm. It reduces the surface tension of water from 73 to 53 x 10(-3) N m(-1) and has a critical micellar concentration of 80 mg/l. Compared to aliphatic hydrocarbons, Biosur-Pm shows good activity against aromatic hydrocarbons. The emulsion formed is stable and does not require any metal ions for emulsification. The kinetics of Biosur-Pm production suggest that its synthesis isa growth-associated and pH-dependent process. At pH 7.0, cells produced more Biosur-Pm with less cell surface hydrophobicity. At pH 8.0, however, the cells produced less Biosur-Pm with more cell surface hydrophobicity and showed a twofold higher affinity for aromatic hydrocarbons compared to the cells grown at pH 7.0. The Biosur-Pm showed a pH-dependent release, stimulated growth of the producer strain on mineral salts medium with 1-naphthoic acid when added externally, and facilitated the conversion of salicylate to catechol. All these results suggest that Biosur-Pm is probably a cell-wall component and helps in hydrocarbon assimilation/uptake.

Kinetics of Sulphation of Nickel and Cobalt Ferrites with Na$O, Melt Containing F'e3+ Ions

It has been experimentally established that nickel and cobalt can be extracted from their ferrites with sodium sulphate melt containing femc ions. The kinetics of extraction from synthetic ferrites using a melt of sodium and ferric sulphates of eutectic composition has been studied as a function of the particle size of the ferrite and temperature in the range 900 to 1073 K. The divalent ions in the ferrite exchange with the ferric ion in the melt, leaving a residue of hematite.The rate of reaction conforms to the Crank-Ginstling-Brounshtein diffusion model. The reaction rate is governed by the counter-diffusion of ~ e an~d ~+i ' +(or co2+) ions in the hematite lattice. Analytical expressions for the rate constants have been derived from the experimental data as a function of particle size and temperature. The activation energy for the extraction of nickel from nickel ferrite is 154(+10) kJ mol-' and the corresponding value for cobalt is 142(+10)kJ mol;'. In sulphation roasting of minerals containing nickel, the yield of nickel is generally limited to 75% due to the formation of insoluble ferrites. The use of melts based on sodium sulphate provides a possible route for enhancing the recovery of nickel to approximately 98%.

Effect of F- ions on emission cross-section and fluorescence lifetime of Yb3+-doped tellurite glasses

The effects of F- ions in Yb3+-doped tellurite glass systems on the emission cross-section and measured fluorescence lifetime are investigated. The results show that both the emission cross-section and the fluorescence lifetime of Yb3+ ions increase from 1.32 to 1.39 pm(2) and from 0.93 to 1.12 ms respectively with the increase of F- ions from 0 to 10 mol% and that such oxyfluoride tellurite glass system is a promising laser host matrix for high power generation. FT-IR spectra were used to analyze the effect of F- ions on the structure of tellurite glasses and the change of OH- groups in this glass system. Analysis demonstrates that the addition of fluoride decreases the symmetry of the structure of tellurite glasses resulting in increasing of the emission cross-section and removes the OH- groups resulting in increasing of the measured fluorescence lifetime of Yb3+ ions. (c) 2005 Elsevier B.V. All rights reserved.

Self-assembled gold nanoparticle chains in presence of silver ions

A simple method has been developed to assemble gold nanoparticles to generate 1D assemblies by the assistance of silver ions. The lengths of nanoparticle chains can be controlled by adjusting the content of silver ions in the system. The assembly procedure of gold nanoparticles chains requires no template. The gold nanoparticle chains were characterized using TEM and XPS techniques.